FINAL TECHNICAL REPORT · Aluminium alloys are now in widespread use in Europe and elsewhere for...

FINAL TECHNICAL REPORT

CONTRACT N° : G3RD-CT-2002-00829 PROJECT N° : GRD2-2001-50065 ACRONYM : ALJOIN TITLE : CRASHWORTHINESS OF JOINTS IN ALUMINIUM RAIL VEHICLES PROJECT CO-ORDINATOR: D’APPOLONIA S.P.A. PARTNERS : D’APPOLONIA S.P.A. ADVANCED RAILWAY RESEARCH CENTRE (ARRC) – The University of Sheffield (before 1

March 2004) NEWRAIL – The University of Newcastle (from 1 March 2004 onwards) ALCAN BOMBARDIER TRANSPORTATION DANSTIR THE WELDING INSTITUTE (TWI) REPORTING PERIOD : FROM 1 AUGUST 2002 TO 31 JULY 2005 PROJECT START DATE : 1 AUGUST 2002 DURATION : 36 MONTHS Date of issue of this report : October 2005

Project funded by the European Community under the ‘Competitive and Sustainable Growth’ Programme (1998-2002)

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ1. TABLE OF CONTENTS

Page

1. TABLE OF CONTENTS ...................................................................................... 2

2. EXECUTIVE PUBLISHABLE SUMMARY .......................................................... 3

3. OBJECTIVES ...................................................................................................... 5

4. SCIENTIFIC AND TECHNICAL DESCRIPTION OF THE RESULTS ................. 6 4.1 Work Package 2: Performance Criteria ........................................................ 6 4.2 WORK PACKAGE 3: EXISTING JOINT ASSESSMENT ................................ 8 4.3 WORK PACKAGE 4A: STATIC MODELING OF JOINTS ............................ 11 4.4 WORK PACKAGE 4B: DYNAMIC MODELING OF COMPONENTS AND STRUCTURES ...................................................................................................... 17 4.5 WORK PACKAGE 5: NEW JOINING TECHNIQUES AND JOINTS ............ 24 4.6 WORK PACKAGE 6: EXPLOITATION PRODUCTS AND STANDARDS .... 27 4.7 WORK PACKAGE 7: METHOD FOR ASSESSING CRASHWORTHINESS 29 4.8 WORK PACKAGE 8: DEMONSTRATORS ................................................... 30 4.9 WORK PACKAGE 9: VALIDATION .............................................................. 33

5. LIST OF DELIVERABLES ................................................................................ 38

6. COMPARISON OF INITIALLY PLANNED ACTIVITIES AND WORK ACTUALLY ACCOMPLISHED ..................................................................................................... 40

7. MANAGEMENT AND CO-ORDINATION ASPECTS ........................................ 42 7.1 Project co-ordination ................................................................................... 42 7.2 Man Power and Progress Follow-up Table ................................................ 43 7.3 Work Plan ...................................................................................................... 48 7.4 Updated contact details for the consortium .............................................. 49

8. RESULTS AND CONCLUSIONS ...................................................................... 51

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ2. EXECUTIVE PUBLISHABLE SUMMARY

Aluminium alloys are now in widespread use in Europe and elsewhere for rail vehicle construction from commuter to express trains. The main contributor to the success of aluminium alloys as structural materials in rail transport, is the development of closed cell aluminium extrusions that can easily be welded together to form lightweight rail vehicles with high inherent rigidity that could not be achieved with older designs.

As rail transport is becoming more popular throughout Europe, there is an increased need to improve passenger safety by improving the crashworthiness of rail vehicles to minimise fatalities and injuries if an accident does occur.

The strength, integrity and performance of aluminium welds in rail vehicles contribute greatly to the overall body shell strength and crashworthiness. In recent collisions involving seam welded aluminium rail coaches, some of the longitudinal seam welds fractured for some meters beyond the zone of severe damage, the panels themselves generally being intact without significant distortion.

The experts on crashworthiness agree (in Cullen report recommendation 57) that consideration should be given, in the case of new vehicles constructed of aluminium, to the following:

• use of alternatives to fusion welding;

• use of improved grades of aluminium less susceptible to fusion weld weakening;

• further development of analytical techniques to increase confidence in the crashworthiness of rail vehicle structures, particularly those constructed of aluminium.

The strategy that ALJOIN used to approach the problem can be described as follows:

• creation of performance criteria for the properties of aluminium welds in the new generation of rail vehicles in terms of their stress/strain performance;

• assessing the existing methods of joining techniques and joints;

• static and dynamic modelling of joints and structures;

• formulating new joining techniques and joints;

• definition of a method for assessing crashworthiness;

• demonstration and validation of the innovative technologies developed against the performance criteria.

Real improvements in the safety of rail vehicles, introduction of innovative techniques for aluminium welding and improvements in the crashworthiness of the new generation of rail vehicles are among the main ALJOIN outputs.

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJThe expected impact is a real improvement in the safety of the new generations of rail vehicles, contributing to the safety of European citizens as well as to the EC policies in safety issues and standardisation of the materials and aluminium welding methods used in the rail industry.

The duration of the ALJOIN project was three years. In the first year ALJOIN was dedicated to the research phase where a thorough investigation of existing joint designs and joining techniques was carried out. This has revealed shortcomings in existing joint designs.

First is the adverse effect of using partial penetration welds, which act as crack initiators facilitating the process of dynamic tear of welds under impact loading and second, the use of Al-Si filler wire (allowed by current manufacturing standards) which produces welds with lower strength, ductility and fracture toughness compared to welds produced with Al-Mg filler wires.

The second year of the work concentrated on the understanding of the fundamental properties of aluminium weldments and an investigation of the performance of alternative joining techniques such as adhesive bonding, bolted joints, laser welding and friction stir welding. With the exception of adhesive bonding, which from an early stage proved unsuitable for rail vehicle construction, the determined joint properties were used for the development of analytical failure models and validated with component tests. The modelling efforts have produced a very close agreement between experiment and prediction. The modelling procedure was then used to examine solutions for improved joint performance.

The final year of the project has concentrated on modelling efforts to simulate rail vehicle impact with and without the implementation of the recommendations for improved joint, as they arose from the previous work.

Furthermore an experimental methodology for assessing the dynamic loading performance of joints was developed which can be used as a method of "ranking" the impact performance of various joint designs. The experimental results were also used to further validate model predictions.

The major outputs from this work can be summarised as follows:

• The stress levels at the weld region should be brought close to those of the parent plate, through thickening of the aluminium plate at the weld region. The precise amount of thickening would depend on alloy grade and welding procedure.

• Friction stir welding (FSW) and MIG welding with Al-Mg filler wire are the best performing joining methods in terms of crashworthiness as long as the above recommendation is implemented.

• Aluminium alloys other than the 6005 alloy in the T6 temper have not provided any appreciable improvement in joint strength.

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ3. OBJECTIVES

The aim of the project can be summarised to provide sufficient knowledge to design cost effective aluminium rail vehicle bodies that will not fail by catastrophic joint failure under extreme loading. To achieve such overall goal several specific objectives were addressed:

• To determine the performance specifications required by critical aluminium joints in rail vehicle cars to ensure the structural integrity;

• To provide physical evidence of the energy absorption capability of aluminium alloy welds by testing;

• To investigate performance and failure criteria for aluminium welded and bolted joints;

• To explain test results assessing the adequacy or inadequacy of current design and construction practices of aluminium alloy welds in the context of crashworthiness;

• Implementation and validation of material failure models for welds of aluminium alloys;

• Definition of the main material and structural parameters which can influence the mechanical behaviour of the joints;

• Development of the material constitutive modelling for the parent material and the material in the welded volume;

• Numerical modelling of simple joints subjected to axial and transversal forces;

• Numerical analysis of components and structures subjected to quasi-static and impact (dynamic) loading conditions in order to evaluate the structural response in terms of mean axial crushing force, total energy absorption, load efficiency and uniformity, deformation mechanism.

• To investigate alternative welding techniques and/or joint designs for improved joints of aluminium alloys.

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ4. SCIENTIFIC AND TECHNICAL DESCRIPTION OF THE RESULTS

4.1 Work Package 2: Performance Criteria

Introduction

The future of aluminium in rail vehicles will depend on the performance of aluminium joints. The objective of this Work Package was to determine the performance specifications required by critical aluminium joints in rail vehicle cars to ensure the structural integrity and the crashworthiness of the vehicles and to determine the improved future performance required of the new crashworthy aluminium rail vehicles.

Aluminium is currently one of the preferred materials for rail vehicle manufacture. Aluminium railway carbodies are manufactured from longitudinal extrusions which are traditionally joined by automated metal inert gas (MIG) welding or bolting. The advantages of using aluminium extrusions in the manufacture of rail vehicles are the highly efficient assembly methods and the significant weight savings, whereas a disadvantage is the potential crashworthy performance. There have been cases where aluminium rail vehicles have been involved in accidents where, the energy absorption devices appeared to have failed to operate effectively. The failure of these devices is thought to be due to the breakdown of the supporting carbodies structural integrity.

Energy absorption devices can only operate effectively if the structural integrity of the bodyshell is maintained. With current aluminium rail vehicles manufactured from full length extruded sections, the structural integrity of the bodyshell is dependant on the crashworthiness performance of the joints between the extrusions. There is an increased effort to improve the crashworthy performance of aluminium rail vehicles and the research is being concentrated to improve the joints and refine the analytical modelling of these joints in crash scenarios.

Description of Results

The requirements for aluminium joints are directly related to the crashworthiness performance of the vehicle, since they contribute to the structural integrity of the bodyshell. In current designs of aluminium railway vehicles, the typical longitudinal joints are either welded or bolted. Various techniques are available for welding and bolting carbody structures to form a shell. Currently the most widely used welding techniques are MIG, Twin Wire MIG and Friction Stir Welding (FSW). Typical bolted joints use Huck Bolt connections. Figure 1 shows a typical bodyside/floor Huck Bolt connection being assembled.

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ

Figure 1: Current vehicle floor structure (left) and bodyside/floor Huck Bolted (Bombardier)

The European standards that target the design of rail vehicles and the welding procedure for metallic materials do not detail the performance criteria of the joints in aluminium rail vehicles. The standards and requirements of reference to be taken into account comprise the following:

• BS 8118: Part 1 (1991) “Structural use of Aluminium”;

• BS 288-4 (1992) “Welding procedures for metallic materials”;

• Euronorm CEN 256 / BS-EN 12663 (2000) “Structural requirements of railway vehicle bodies”

• TSI 96/48 – ST05 part 2 “Passive Safety Crashworthiness”

• Railtrack Safety & Standard GM/RT 2100: part 3 (October 2000), “Structural requirements for railway vehicles”.

When a new weld is first designed it has to satisfy British/EN standard 288-4. One of the major concerns about the current situation is that the mechanical properties and crash performance of the weld and heat affected zones are not understood. Improvements in knowledge of these properties would give numerical modellers more confidence in the results from analytical models. From the standards examined there is no specific requirement to generate detailed performance criteria for the joints in rail vehicles, but there is a need to understand the properties of the joints to improve the crashworthiness. To achieve this a comprehensive testing plan of current MIG welds is proposed which involves static, quasi-static and dynamic testing, all will give valuable information and will go towards addressing the lack of understanding of current joints. The results from testing should characterise the parent metal, the weld and the heat affected zones and this information will be used in two areas. Primarily the data will be used to establish a benchmark for future work, where the use of new joining techniques and different aluminium alloys will be investigated. Secondly the results will be used to refine the current analysis techniques, so the elements representing the weld region in crash scenarios are fully validated with experimental work. Once confidence has been established in relating test results to element properties, similar procedures can be used when changes are made to the joining process or the material.

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJIn an ideal situation the joint should not be the ‘weakest link’ in the bodyshell, put simply ‘Joint performance should be equal to that of the parent metal’.

4.2 WORK PACKAGE 3: EXISTING JOINT ASSESSMENT

Introduction

Carbodies of rail passenger vehicles have been manufactured using welded 6000 series aluminium alloy extrusions for many years in the UK and Europe. Although welded joints designed to conventional codes have performed satisfactorily under the normal operational loads, it is less certain how welded joints would behave under extreme loading conditions. In recent accidents involving welded aluminium rail vehicles, observations showed that some of the longitudinal welds had fractured for some metres beyond the zone of severe damage. There is a lack of knowledge in the design of welded joints for high rate loading situations. The objective of this work package are therefore:

• To provide physical evidence of energy absorption capability, or incapability, of aluminium alloy welds by joint tests.

• To establish failure criteria of aluminium welded joints.

• To investigate performance and failure criteria of aluminium bolted joints.

• To explain structural performance observed in joint tests.

• To asses the adequacy on inadequacy of current design and construction practices of aluminium alloy welds in the context of crashworthiness.

The MIG process is the main welding process employed by the industry today in the UK and Europe. Either silicon or magnesium alloyed fillers are recommended for the welding of 6000 series aluminium alloys, but this does not mean that the welds will perform as well as the parent material. There is a need to investigate the effects of the filler material on the structural behaviour of the welds.

Description of results

Materials and weld production

The aluminium alloy used in the present work was EN AW 6005A-T6. Extrusions of this alloy are widely used for the construction of the carbody of rail passenger vehicles. Some ten meters of welds were produced with the MIG process using either aluminium-silicon or aluminium-magnesium filler. These were butt welds in either 6mm thickness extruded plates or rail vehicle floor extrusions.

Material characterisation testing

Material characterisation tests were conducted to investigate material behaviour in the parent material, the weld metal and the HAZ of the MIG welds. These included hardness surveys, tensile testing, Charpy impact testing and fracture resistance testing.

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJThe hardness of the parent material was about 100HV5. The reduction in hardness values of the weld metal and the HAZ was confirmed in the hardness tests. The lowest hardness value in the welds made using aluminium-silicon filler was about 45HV at the weld centre line. The lowest hardness value in the welds made using aluminium-magnesium filler was about 60HV at a distance of 5 to 10mm from the weld centre line in the HAZ. The width of the zone of reduced hardness was about 30-40mm.

The parent material tensile properties as tested in transverse specimens were slightly different from those in the longitudinal specimens, which suggested that the parent material extrusion was slightly anisotropic. The specimen-to-specimen variation of the tensile properties of the HAZ was relatively large. The lowest average 0.2% proof strength, ultimate strength and area reduction were from the weld metal of weld made using the aluminium-silicon filler. Although the weld metal 0.2% proof strength of the weld made using aluminium-magnesium filler was about 55% of that of the parent material, its ultimate strength was slightly higher than that of the parent material. The elongation of the HAZ at the maximum load was relatively low, only 4 to 5%, and the weld metals elongated a relatively small amount after the maximum load.

Tensile testing of notched cylindrical specimens was carried out for weldments made using aluminium-silicon or aluminium-magnesium filler. Figure 2 shows the tensile testing set-up at NEWRAIL. Fracture strains as a function of stress triaxiality were obtained for the different zones in the welded joints.

Figure 2: Tensile testing set-up (NEWRAIL)

The average Charpy value of the base material was about 6 Joules. The lowest Charpy energy, 5Joules, was from the aluminium-silicon filler weld metal. The highest average, 18Joules, was from the weld metal of the aluminium-magnesium filler weld. The variation of the Charpy energy of the HAZ was relatively large, while the Charpy energy values of the weld metals and the parent material varied little.

Some seventy single edge notch bend specimens were tested under either quasi-static or dynamic loading. Different effects were found in the J R-curves of the three material zones, i.e. the parent material, the weld metal and the fusion boundary. For the parent material, the magnitudes of J under dynamic loading were higher than those under quasi-static loading for the same amount of crack extension, but the slopes of the trend lines of the J R-curves were quite similar. For the aluminium-silicon filler weld metal and the associated fusion boundary, the J values under dynamic loading were generally

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJhigher than those under quasi-static loading for crack extensions of less than 1.5mm. They tended to be lower when the crack extension was greater than 1.5mm, and the trend lines of the J values under the dynamic loading were flatter. For the aluminium-magnesium filler weld metal and the associated fusion boundary, the J values under dynamic loading were generally lower than those under quasi-static loading for crack extensions of less than 1mm. They tended to be higher, when the crack extension was greater than 1.5mm, and the trend lines of the J values under the dynamic loading were steeper.

Joint and component testing

Cross weld tensile specimens were extracted from welded rail vehicle floor extrusion and tested under quasi-static tensile loading. Plastic strain changes were monitored continuously during the testing and fracture locations were recorded.

Welded joint components were extracted from the welded rail vehicle floor extrusions. Component behaviour was investigated under axial quasi-static crush and drop weight impact loading. The loading mode in these tests was predominately axial compression. The welds in the rail vehicle floor extrusions did not fail catastrophically by fracture, although severe plastic deformation occurred in the parent material. Local buckling developed at the attainment of the maximum load. This was followed by tearing damage in the local buckling area, particularly in the parent material at corners where the internal web met the external skin.

Testing of bolted joints were developed with the aim of providing test data for finite element simulation of failure in bolted joints. Tests have comprised testing of bolted tubes subjected to axial impact (Figure 3 shows the example of damage joints after testing done at TWI) and bolted joint tearing tests (Figure 4 shows the results of testing and some details of the failure mode.

Figure 3: example of damage joints after testing (TWI)

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Figure 4: Result of test and detail of bolt 1 failure (NEWRAIL)

Main Conclusions

Damage and final fracture will most likely be confined to the weld metal, the HAZ and /or the interface between the two in MIG welded joints, which are designed for normal operation loads, in a event of crash generating sufficient load normal to the weld, mainly because strength undermatch. Al-Si weld metal is shown to have poor strength and poor fracture toughness relative to the base material, the HAZ and the Al-Mg weld metal. The present results have provided some explanation for the material aspect in real life weld failures such as those in the Ladbroke Grove accident.

It is clear from the test results that the mechanical properties of the MIG welds made with aluminium-magnesium filler metal in 6005A-T6 aluminium alloy extrusions were superior in terms of strength, ductility and fracture toughness to those made with aluminium-silicon filler metal. But there is limited scope for improvement of the mechanical properties of the HAZ, particularly strength, as long as a fusion welding process is employed.

4.3 WORK PACKAGE 4A: STATIC MODELING OF JOINTS

Introduction

The failure process of aluminium alloys involves void nucleation, growth and coalescence. Failure mechanisms are investigated in WP3 by metallurgical and microstructural examinations. Potential failure criteria are studied for implementation and validation. The prediction of the fracture mechanism occurring in the welded regions is

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJused to evaluate the progressive failure of the whole component that can occur without significant yielding in the base material and in some cases under elastic stresses.

This work package aims to deliver:

• material failure models for aluminium alloy welds;

• constitutive model of the different welded joints;

• numerical results of simple joints subjected to axial and transverse forces.

Description of results

Material Failure Models

Dimpled rupture is a failure mode of aluminium alloys. It is strongly influenced by stress triaxiality and by the volume fraction of inclusions and second phase particles.

There are two material failure models used widely for modelling of dimpled rupture, namely the Hancook and Johnson & Cook model and the Gurson-Tvergaard model. In the former, the fracture strain is expressed by the following equation:

)D(EXPDDvM

mf

σσ

+=ε 321

where σm is the mean stress and σvM is the von Mises equivalent stress. σm/σvM is term stress triaxiality in the literature. D1, D2 and D3 are material constants.

This model predicts the fracture strain decreases exponentially with increasing stress triaxiality, but the material damage before the final fracture is not modelled. The damage is a result of the nucleation and growth of voids at inclusions and second phase particles. Fracture is the final stage of this progressive damage process.

The Gurson-Tvergaard model provides a means of modelling the progressive damage. The essence of the Gurson-Tvergaard model is contained in the yielding function below:

)fq(qcoshfqFy

m

y

e 23

21

2

1232 +−⎟

⎟⎠

⎞⎜⎜⎝

⎛

σσ

−+⎟⎟⎠

⎞⎜⎜⎝

⎛

σσ

=

This yield function contains both the stress triaxiality and void volume fraction, which are the two major factors in the dimpled rupture. Details of the two models will be discussed in a final report for work package 4. Some of the numerical results using these two failure models for fracture modelling are given below.

Numerical Simulation of Notched cylindrical specimen under tension

Fracture characterisation was carried out using a series of notched cylindrical specimens. Results of load versus displacement were used to determine values of the parameters in the Gurson-Tvergaard model through a calibration.

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJThere were three specimens in a series. The diameter at the minimum section was 3mm and the three notch radii are 2, 6 and 10mm, respectively. Finite element meshes for the three notched cylindrical specimens are shown in Figure 5. Each of the finite element models with axi-symmetrical elements represents one half of the corresponding cylindrical specimen. The plane at the minimum diameter is a symmetrical plane, where displacements in the vertical direction were set zero in the finite element analyses.

(a) (a) (a)

Figure 5: Finite element mesh for notched cylindrical specimen with minimum neck radius a=1.5mm: (a) R=2mm; (b) R=6mm; and (c) R=10mm

Values of Young’s modulus and Poisson’s ratio used in the analyses for the parent material 6005A-T6 were equal to 60GPa and 0.3, respectively. The true stress versus true plastic strain was described by the following equation:

βεαε+σ=σ )/( .. 2020 1

where σ0.2=262MPa, ε0.2=σ0.2/E, α=0.15 and ß=0.135.

Best estimate values for the parameters in Gurson-Tvergaard model for the parent material 6005A-T6 are summarised in Table 1.

Table 1 Best estimate values for the parameters in Gurson-Tvergaard model

q1 q2 q3 εN SN fN fc fN

1.5 1.0 2.25 0.10 0.01 0.04 0.08 0.2

The measured and computed results of load versus axial displacement in a gauge length of 12.5mm are compared in Figure 6. The agreement between the measured and computed curves is not excellent and needs to be improved. Nevertheless, the calibrated Gurson-Tvergaard model provides a basis for modelling fracture of the parent material 6005A-T6.

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0.0

1.0

2.0

3.0

4.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Axial displacement (12.5mm gauge length), mm

Axi

al lo

ad, k

N

a1.5R2 - Test data (M11-39)

a1.5R6 - Test data (M11-40)

a1.5R10 - Test data (M11-41)

a1.5R2 FEA GT 19

a1.5R6 FEA GT19

a1.5R10 FEA GT 19

Figure 6: Comparison of measured and computed load versus displacement curves for notch cylindrical specimen under tension

Numerical Simulation of single edge notched specimen under bending

Finite element analyses were carried out to predict crack propagation using the above calibrated Gurson-Tvergaard model in a single edge notch bend (SENB) specimen of the parent material 6005A-T6 under three point bending. Dimensions of the SENB specimen are 5mm thickness, 15mm width and 60mm span. The ratio of initial crack depth to specimen width is 0.35.

A three-dimensional finite element model for the SENB specimen is shown in Figure 7. It is only necessary to model one quarter of the specimen geometry because of the double symmetry. The linear strain brick elements are used.

Load Line

Support

Figure 7: Finite element mesh for a quarter of a SENB specimen (B=5mm, W=15mm,

a/W=0.35, S=4W)

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJThe shape and position of the crack front are illustrated in Figure 8 for different amounts of load line displacement. The initial crack advanced about 0.15mm at the mid-thickness when the load line displacement was 0.86 ΔPmax, where ΔPmax is the load line displacement at the maximum load sustained in the specimen. The crack continued to advance as the load line displacement increased. The initially straight crack front became a curved line with much smaller amounts of crack extension near the outside surface than in the mid-thickness.

Current crack front

Initial crack front

Mid-Thickness plane

(a) (c)(b)

Figure 8: Shape and position of current crack front: (a) D=0.87DPmax; (b) D=DPmax; (c) D=1.4DPmax

Rail vehicle floor component under quasi-static crush

Quasi-static testing of the rail vehicle floor extrusion component is described in detail in the report for work package 3. The testing was simulated using the general purpose finite element ABAQUS. A deformed shape of the rail vehicle floor component at the maximum applied load is shown in Figure 9. This is very similar to the deformed shape of the tested specimens. A comparison of the measured and computed load versus displacement curves is also given in Figure 9.

0

200

400

600

800

1000

1200

0 1 2 3 4 5 6 7 8 9displacement (mm)

load

(kN

)

fine mesh - modes 1 to 10 imperfections

experimental data after machine stiffness and non-linearity correction

Figure 9: Deformed shape of rail vehicle floor component and Comparison of measured and computed load versus displacement curve

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJRail vehicle floor component under drop weight impact

Drop weight impact testing of the rail vehicle floor extrusion component was simulated using the general purpose finite element ABAQUS. A finite element model for the simulation and a comparison of the measured and computed load versus time curves is given in Figure 10.

Ground concrete support

anvil

Drop mass

Specimen

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8Time, ms

Load

, kN

10

FEA

Test (W05-05)

Figure 10: Finite element model for drop weight impact testing (left) and Comparison of measured and computed load versus time curves

Single bolt lap joint under tension

Finite element analyses were carried out for a single bolt lap joint of the parent material 6005A-T6 under tension. A finite element model is shown in Figure 11. The bolt pre-tension was simulated with a temperature field. The friction forces between the mating parts were modelled using contact modelling capability. Progressive damage in the joint as loading increases was modelled using the Gurson-Tvergaard model. The fractured joint is shown in Figure 11.

Figure 11: Finite element model for single bolt lap joint and fracture simulation

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4.4 WORK PACKAGE 4B: DYNAMIC MODELING OF COMPONENTS AND STRUCTURES

Introduction

Dynamic modelling of small- and full-scale structures and analysis of correlation between design parameters and crashworthiness. The modelling work reflects the performance criteria defined in WP2. Structures to be modelled comprise thin-walled members and sandwich members with various types of cross sections in which the influence of the welding is studied.

Objective of this work package is to design and model crashworthy structures which deform under a controlled force and preserve sufficient survival space around the occupants to limit body injury during an accident. To perform numerical analysis of components and structures subjected to quasi-static and impact loading conditions in order to evaluate the structural response in terms of mean axial crushing force, total energy absorption, deformation mechanism. To review of load conditions, rates of strain and modes of deformation of aluminium alloy welds of the rail vehicle under crash and derailment scenarios.

The activities performed included:

• Plain and Notched Tensile Tests

• CTOA tearing tests

• Tearing tests of bolted joints

• Bolted Tubes subjected to axial impact

• Cleavage tests


Plain and Notched Tensile Tests

Simulations of plain and notched tensile tests have been carried out to analyse mesh sensitivity and to verify the possibility of the Gurson model implemented in LS-DYNA to take into account different mesh sizes. The procedure used for the determination of the Gurson parameters was to start fixing most of the parameters (q1=1.5, q2=1, fN=0.01, En=0.3, Sn=0.1) and using the experimental results of load vs. axial displacement to determine the values of the remaining parameters (F0 and Fc) by best fit. An element size dependent function for Ff (failure void volume fraction) was defined based on finite element simulation of the tensile test results with 4 or 5 meshes of different sizes (see Figure 12). Figure 13 shows the simulation of the failure of a notched specimen (notch radius 2 millimetres) subjected to tensile loading.

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Figure 12: Meshes of 2 mm notched specimen

Figure 13: Simulation of failure of notched specimen subjected to tensile loading

CTOA tearing tests

Numerical analyses considered the Crack Tip Opening Angle (CTOA) tearing tests carried out by ARRC. Testing was performed on 250 kN Mayes testing machine with a strain rate of 0.02mm/second. Figure 14 shows testing equipment and the detail of the crack growth along the weld and at the interface between the weld and the HAZ. Figure

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ15 shows the specimen geometry. Specimens were taken from the railway vehicle double skinned extrusions so that a crack initiator could be centred in one of the relevant zones: parent metal, HAZ and weld. The gauge section was machined to 2mm thick to remove any evidence of variation in the extrusion process and ensure flatness. Samples had a crack initiator machined in the centre of the gauge section to start the initial crack in different zones: the parent metal, the weld and the HAZ.

Figure 14: CTOA testing set-up (left) and details of crack growth along the weld (up) and at the interface between HAZ and weld

Figure 15 Crack Tip Opening Angle (CTOA) tearing tests (ARRC)

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Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJThe numerical analyses were carried out using the both the LS-DYNA explicit code and the FRANC2D code. Figure 16 shows the results of the analysis, in terms of distribution of the Von Mises equivalent stress, demonstrating the crack propagation along the centreline of the specimen. Figure 17 shows the results of the simulations done using the FRANC2D code1 which allows to explicitly model the crack propagation in the mesh. As the cracks propagate, automatic remeshing algorithms delete the mesh local to the crack tip, extend the crack, and build a new mesh around the new tip. The constant critical crack tip opening angle (CTOA) fracture criterion was used in the simulations. The CTOD fracture criterion assumes that the crack growth will occur when the angle made by the upper crack surface, the crack tip, and the lower crack surface reaches a critical value. In a two-dimensional analysis, the displacement δ, perpendicular to the crack, at a fixed distance d behind the crack tip are monitored during the analytical loading of the model. When the displacements are such that the critical angle CTOA (ψC) is attained (see equation 1), the crack is advanced by releasing the crack tip nodes until a total distance d of crack growth is achieved.

⎟⎠⎞

⎜⎝⎛= −

dtan2 1

Cδψ (1)

Then, the applied displacements are held constant while the internal forces are returned to equilibrium. At each load increment, the CTOA was calculated and compared to a critical value. When the CTOA exceeded this critical value, the crack-tip node was released and the crack advanced.

t = 0.6 s

t = 2.0 s

Figure 16 Numerical Analysis of Crack Tip Opening (CTOA) tearing tests (Von Mises Equivalent Stress)

1 Swenson D., James M., “FRANC2D/L: A Crack Propagation Simulator for Plane Layered Structures Version 1.4 User's Guide”, Kansas State University •Manhattan, Kansas

20


Figure 17 Numerical Analysis of CTOA tearing tests showing crack running along the weld (left) and crack deviating towards the weld/HAZ interface

Tearing tests of bolted joints

The aim of these numerical analyses was to assess the existing criteria for the simulation of bolted joints in dynamic loading conditions and validate the approach which has been selected to model the bolted joints.

The activities performed include:

• numerical simulations of the tearing tests;

• validation of the material model;

• critical review and analysis of the results.

Several simulations have been performed, considering both shell and solid elements to mesh the specimen. The bolts have been modelled using solid elements. The numerical results are in good agreement with the experimental results. In particular Figure 18 shows the results of the simulation in terms of global deformation and failure mode, which correspond to the real behaviour (see Figure 4). Figure 19 reports the comparison of the diagram of force versus displacements corresponding to three tests and the numerical prediction. The numerical model is able to predict with a good accuracy the peak force corresponding to the failure of the bolts. The difference in terms of displacements is due to the pre-load in the bolts, not considered in the model.

21


Figure 18 Results of the simulation of tearing tests of bolted joints – deformed structure

Figure 19: Tearing tests of bolted joints - comparison of measured and computed load versus displacement curves

Bolted tubes subjected to axial impact

The work performed consisted mainly in:

• Selection of standard aluminium extrusions to be provided by ALCAN for the preparation of the samples;

• Definition of small-scale sample geometry to obtain tubular bolted structures for dynamic impact testing (see Figure 20);

• Design of the experiments: a fractional-factorial design of experiments using orthogonal arrays was selected. The factors comprise: the material and temper condition (AA 6005-T6 and 6008-T6), the number of bolts, and the impact velocity

• Numerical analysis of the configurations selected.

22


∅ = 6 mm bolt diameter

e = 28 mm edge distance

d = 24 mm

t = 2.4 - 6 mm thickness thinnest outside ply

d

e

d

e

Figure 20 Definition of small-scale bolted samples

Figure 21 Numerical analysis of bolted joints subjected to axial impact – deformed structure (above) and comparison of measured and computed load versus time curves

23

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJWP4B Overall comments

• An extensive modelling work has been developed aiming at the definition of proper material models and simulation approaches for structures and joints under different loading conditions;

• Simulations of tensile tests have been carried out to analyse mesh sensitivity and to verify the possibility of the Gurson model implemented in LS-DYNA to take into account different mesh sizes

• Simulations of CTOA tearing tests, tearing tests of bolted samples, impact tests of bolted structures are in good agreement with test results.

4.5 WORK PACKAGE 5: NEW JOINING TECHNIQUES AND JOINTS

Introduction

Conventional MIG welding processes and joint designs have been shown to be inadequate for the increasing demand of crashworthiness performance of rail vehicles. This has been highlighted by recent rail vehicle accidents. The need for alternative joining techniques and joint designs is reinforced by the findings in the work package 3 (WP3) (existing joint assessment). The objectives of this work package (WP5) are:

• investigate alternative welding techniques and/or joint designs for improved joints.

• compare adhesive bonding and fraction stir welding with traditional methods.

A review of all the emerging joining techniques was carried out and the results were discussed. Mechanical tests were carried out on the joints made using friction stir welding and adhesive bonding techniques. A new design for butt welded joints was proposed and is presented in the report, along with the use of finite element analyses to assist joint design.


New joining techniques

A review of MIG welding as well as laser and hybrid laser-arc processes for the fabrication of rail vehicle carbodies was carried out at TWI. For fusion welding processes it will not be possible to eliminate entirely the HAZ associated with Al alloy weldments. Hybrid laser-arc processes offer advantages over and above those of laser and arc processes individually, including: higher welding speeds leading to increased productivity and reduced distortion, improved weld quality (e.g. a reduced incidence of welding defects such as pores and cracks), increased penetration, and increased tolerance to fit-up, which is crucial in a production environment. For hybrid laser-arc processes, an appropriate selection of process parameters and filler wire is anticipated

24

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJto lead to as-welded ultimate tensile strengths above those reported for laser welds (~60-80% of parent), with tensile failure occurring in the HAZ.

Extruded plates (6mm thick) of 6005A-T6, 6008-T6 and 6008-T7 have been welded by friction stir welding (FSW) at DanStir (see Figure 22). The parent materials were supplied by ALCAN. The samples were welded in a butt-joint configuration with a backing bar to simulate the more common joint configuration in double-skin rail car structures.

Figure 22 Welded extruded 6mm thick plate by friction stir welding at DanStir - overall view (left) and close-up showing backing bar

Mechanical tests were performed to characterise material and joint mechanical behaviour. These included hardness survey, Charpy impact, fracture mechanics and cross weld tensile tests. Test results of FSW welds showed that:

• Strength and elongation of the FSW welded joints were similar to those of the Al-Mg welded joints.

• Fracture toughness of the FSW weld nugget was much better than that of the MIG weld metals.

Adhesive bonded full-scale rail vehicle carbody components were manufactured. Preliminary tests were carried out under drop weight impact loading conditions. Peak loads sustained by the specimens ranged from 16 to 28kN, which were much lower than those sustained by the welded joints.

New joint design

The behaviour of partial penetration welds made by the MIG process was studied in the “cleavage” tests by Bombardier. These tests demonstrated that the most likely failure mode is weld fracture. Because of low fracture toughness of Al-Si weld metal as clearly shown in the small scale fracture mechanics tests, partial penetration welds made using Al-Si filler should not be used in safety critical components and structures. If there are no other options, but partial penetration weld, Al-Mg filler metal is preferred. The size of the weld should be such that the stresses in the weld metal should be similar to those in the other zones immediately adjacent to the weld metal. This can be achieved by joint geometry optimisation. An example of such a joint design is illustrated in Fig.11. Basically, the local weld zone area is “over sized”.

25


Figure 23 An example of new joint design showing local thickened area circled

Finite element analysis was employed to investigate the effect of weld over sizing on joint behaviour. The stress-strain data and failure models established in work package 3 and 4 were used in the finite element analyses. It was shown that the minimum weld over sizing factor was 1.4, corresponding to a situation where the critical section is not in the joint (see Figure 24).

No weld oversizing: failure in the HAZ

Weld oversizing factor = 1.2: failure in the HAZ

Weld oversizing factor = 1.4: critical section not in

the joint

Weld oversizing factor = 1.6: critical section not in

the joint

Figure 24 Finite element analysis of effect of joint geometry on fracture failure (D’Appolonia)

Main Conclusions

Many different joining/welding techniques, as an alternative to the conventional MIG process, were investigated for rail vehicle carbody construction. This work included reviews of AC-pulsed MIG, Tandem MIG, Low Stress No Distortion (LSND), Laser, and Hybrid laser-arc process, mechanical tests of welds made using Tandem MIG, FSW,

26

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJLaser, and Hybrid laser-arc process, and drop weight impact tests of adhesive bonded joints.

The review of various fusion welding techniques has suggested that the hybrid laser arc technique has potential in improving productivity and joint performance. Test results of FSW welds showed that: strength and elongation of the FSW welded joints were similar to those of the Al-Mg welded joints and that fracture toughness of the FSW weld nugget was much better than that of the MIG weld metals.

For rupture due to over load transverse to the weld, localised failure will still occur in FSW joints, and therefore energy absorption will still be limited by the joint failure. Strength of the weld zone can be improved by increasing thickness in the weld zone area. A new joint has been designed for the MIG process. Finite element analyses conformed the improvement in strength of the new joints.

4.6 WORK PACKAGE 6: EXPLOITATION PRODUCTS AND STANDARDS

Introduction

It is envisaged that new joining technologies and materials will be used for further development and, eventually, commercial exploitation in rail vehicle construction. Additionally exploitation will be undertaken to develop other solutions in other transport sectors and in different industries.


Exploitation Products

Current codes and standards allow an option to use Magnesium or Silicon based aluminium alloy welding wire based on structural performance although this has not been based on ‘Crashworthiness’ considerations. The comparison of partial penetration welds with silicon and magnesium alloy filler wire subject to dynamic loading clearly demonstrated the higher performance of magnesium welding in impact conditions (see . This result clarifies the most suitable option for Rail applications with regard to crash performance and also clarifies future design requirements for weld areas as being based on the parent material properties for the rail industry and has potential benefits for other transportation industries e.g. Automotive, Maritime.

27


Figure 25 Silicon vs. Magnesium – partial penetration welds (Bombardier)

Current improvements within Bombardier as a direct exploitation of the available results comprise:

• change to magnesium based filler wire;

• Friction Stir Welding of bodysides;

• increase in material thickness around HAZ;

• bolt together structures.

Figure 26 reports an example of the current improvements in Bombardier, corresponding to new overmatched design of welded joints on the Electrostar Bodysides.

Figure 26 New Over-matched MIG Butt weld and FSW joint on Electrostar Bodysides (Bombardier)

Standards

The two most relevant CEN standards are prEN 15085 “Railway applications – Welding of railway vehicles and components” and prEN 15227, the draft standard for Crashworthiness of Rail Vehicle Bodies. Comments have been sent for both standards to include (amongst other text) the following or similar statements to the effect that:

• “Magnesium aluminium alloy (5000 series) weld fillers should be used for welding of 6000 series aluminium alloys.”,

28


• “It is recommended that in the main structural welds along the carbody length, the geometry of the extrusion should ensure that weld and HAZ strength is matched to the parent material strength. This will generally require the weld and HAZ to be between 1.4 and 1.6 times thicker than the adjacent parent material.”

Therefore Aljoin has produced results that will be made available for the review of the future revisions of the relevant standards in the field of aluminium joint crashworthiness and for the construction of the future aluminium railway carbodies. Moreover Aljoin provided a significant contribution in relation to the report to the Cullen Enquiry, related to the Ladbroke Grove crash (1999), that was prepared by Bombardier.

4.7 WORK PACKAGE 7: METHOD FOR ASSESSING CRASHWORTHINESS

Introduction

The behaviour of aluminium joints under highly dynamic conditions was largely unknown before ALJOIN and also no reference testing of representative (railway) structures existed. In order to address such issues the work has been addressed in a direction to design a new method for assessing the crashworthiness of aluminium joints to be able to represent the real critical loading conditions. In particular the problem of weld unzipping needed to be studied and tested in more detail.


A demonstrator representative of full-scale rail vehicle sub-structure was designed by Bombardier. The test pieces are constructed from a pair of extrusions joined using a number of different welding processes. The extrusions contain representative weld construction features and a robust ‘C’ slot for mounting in the test rig. A typical cross-section is shown in Figure 27. The welded pairs will be in the order of 500mm long, the ‘C’ slot on the upper extrusion is used to support the test piece in the rig and the ‘C’ slot in the lower extrusion is used to load the test piece.

Figure 27: Demonstrator Design for FSW (above) and MIG joints (Bombardier)

29

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJThe test piece is to be loaded dynamically and this has been done at Bombardier's test facility in Crespin, France using an Air Cannon (see Figure 28). The test rig is shown in Figure 29. One load cell each was installed in each of the four legs of the test rig for obtaining transient forces. Transient displacements at the vicinity of the impact point were measured with a Laser sensor.

Figure 28: Air gun facility at Bombardier Crespin

Figure 29: Test-Rig for the testing of demonstrators (Bombardier)

4.8 WORK PACKAGE 8: DEMONSTRATORS

Introduction

30

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJThe objective of this work package is the manufacturing and testing of the demonstrators, in agreement of the findings of WP 7 where the methodology for the assessment of their performance was defined. The challenge of this WP was mainly related to the set up of the manufacturing processes for the manufacturing of demonstrators characterised by constant and repetitive characteristics and the Design of the testing Experiments. More in detail the objectives of the WP were:

• to apply the developed methods to the assessment of crashworthiness of large-scale components.

• to demonstrate structural performance of welded joints of aluminium alloys made by new technique and design.

• to perform large-scale tests of components of body shells under controlled laboratory loading conditions reflecting those in vehicle collision scenarios.


It is worth mention that more than 150 demonstrators were manufactured and tested. There were two extrusion designs produced: one for MIG or hybrid Laser-MIG welds and the other for friction stir welds. Double skin extrusions similar to those used for rail vehicle floors were produced at Alcan, Switzerland, according to the sketch shown in Figure 27. One of the FSW demonstrators being manufactured, and one MIG demonstrator are shown in Figure 30.

Figure 30: FSW demonstrator (left) (Danstir) and MIG demonstrator (TWI)

The different configurations tested comprise a combination of the following parameters:

• 2 material grades:

o 6005 o 6008

• 2 material conditions:

o T6 o T7

• 3 weld thicknesses (weld oversizing) :

31


o 3mm (no oversizing of the weld – normal skin thickness used on the Ladbroke Grove vehicles)

o 4.2mm (oversizing factor 1.4) o 4.8mm (oversizing factor 1.6)

• 3 Welding Processes

o MIG welded demonstrators with 5356 welding wire o LASER welded demonstrators o FSW demonstrators

• Initiator location:

o 1: no initiator o 4: initiator located in correspondence of the parent material and

the HAZ

For the final test programme, three specimens each with or without initiator were prepared for each combination of conditions. For each combination of aluminium grade and welding process, test would stop when all six samples (3 each with or without initiator) fractured in the parent material.

Test results show that fracture occurs mostly in the weld zone of the joint without weld oversizing. The fracture runs through the entire length of the weld without arrest. There is hardly global plasticity deformation in the specimen. An example of welded specimens after being tested are shown in Figure 31.

Figure 31: example of welded specimens after testing.

The performance of the three parent materials in the impact tests is assessed in terms of force and energy. Comparison of the performance of the three materials in terms of absorbed energy in shown in Figure 32, from which it could be observed that 6005AT6 is considered to be stronger and more crashworthy than 6008T6 or 6008T7.

32


Figure 32: comparison of performance of the three materials with respect to the absorbed energy.

Some tentative conclusions from the analysis of the test results are reported below:

• In the impact tests, 6005AT6 sustained higher fracture force and absorbed more energy than 6008T6. With the initially available kinetic energy of about 6.4kJ, 6005AT6 did not fracture completely through the entire length of the specimen, while 6008T6 did. 6005AT6 was, therefore, a more crashworthy material than 6008T6 under the loading conditions similar to those prevailing in the tests.

• the weld zone stress levels can be reduced enough for fracture to occur in the parent material by the increase of the weld zone thickness. The minimum ratio of the thickness of the weld zone to that of the parent material has been found to be between 1.4 to 1.6 for 3mm extrusion skins. The precise ratio would depend on welding process and aluminium grade. Increases in thickness above the optimum although they increase the static failure load they have an adverse effect on the dynamic response.

• from a crashworthiness viewpoint, fracture in the parent material appears to be the best option. With this in mind, all the welding processes considered in the present work can be used to produce good quality butt welded joints, which should lead to fracture in the parent material when the thickness of the weld zone is increased to the above mentioned values.

4.9 WORK PACKAGE 9: VALIDATION

Introduction

The objectives of WP9 are to validate project results by testing and by modelling. Validation by testing has comprised the detailed analysis of the tests results of the demonstrators with the aim of understanding the effects of the main parameters (parent

33

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJmaterial, filler material, welding technology, joint design) on the performance of the joints in terms of crashworthiness (adsorbed energy, and resistance to crack growth) and then to transfer such findings to the design of the new joints of the full vehicle. Validation by modelling has comprised the simulation of the testing of the demonstrators with the aim of setting up the material models and the related parameters. Finally the validated models have been used to the prediction of the performance of the joints of a full vehicle under various collision scenarios.


Simulation of the demonstrator tests has been carried out with the aim of validating the material models. Two materials models have been considered at this purpose: the Gurson model and a model based on the maximum strain at failure. The two models are able to simulate the crack initiation and growth in the material, as demonstrated in Figure 33. Figure on the left of Figure 33 shows a case (material 6005 T6, weld thickness 4.2 millimetres, magnesium filler wire, no crack initiator) in which failure was located in the parent material and the material failure model was based on the maximum plastic strain. Figure on the right of Figure 33 shows a case (material 6005 T6, weld thickness 3.0 millimetres, magnesium filler wire, no crack initiator) in which failure was located at the interface between the HAZ and the weld, and the material model was the Gurson model. The results shows the ability of the code and of the material model to represent the crack growth in the structure. Different mesh densities have been considered in order to assess the mesh sensitivity.

Figure 33: Results of the simulation of the demonstrators in case of failure located in the parent material (left) and in the joint area

Simulations have been extended to the analysis of a full vehicle. Bombardier Vehicle Class 165 was selected, being the type of vehicle involved in the Ladbroke Grove disaster which originated ALJOIN. The computer model of the vehicle is shown in Figure 34. The goal was to demonstrate the progress made within ALJOIN with respect to the state of the art concerning the ability to design crashworthy joints in aluminium rail structures and to model their behaviour under impact conditions. The benchmark for such analysis is represented by the vehicle which was involved in the Ladbroke Grove

34

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJaccident, shown in Figure 35. The pictures clearly show the catastrophic failure of the longitudinal joints (partial penetration welds) without any plastic deformation.

Various impact scenarios have been investigated (different obstacle shapes) with the aim of study the effect on the joints and their failure. Figure 36 shows the result of the simulations considering an impact at 20 kilometres per hour against a flat obstacle and with standard welded joints. The weld lines are highlighted in red. In the figure it is clearly visible the simulation is able to predict the catastrophic failure of the longitudinal joints ahead of the area of impact, a mechanism which is analogue to what occurred in the Ladbroke Grove impact. The way forward to the current situation is represented by the results of the simulations shown in Figure 37 and Figure 38. Figure 37 shows the results of the simulations using the validated material model and considering a joint oversising factor of 1.4. In this case we do not observe a dramatic failure of the joints ahead of the area of impact and the entire section of the vehicle remain connected, providing an improved protection to the passengers.

The analyses have been further extended to consider different shapes of the obstacles with the aim of putting the joints in different loading conditions. Figure 38 shows the results of the simulations obtained considering the Gurson material model, and oversizing factor of 1.4 for the joints, and an obstacle of cylindrical and prismatic shape. Also in this case the joints do not fail catastrophically, and the structure can exploit a certain plastic deformation as a mechanism to increase impact energy absorption.

Figure 34: FEM model of Bombardier Vehicle Class 165 (Bombadier)

35


Figure 35: vehicle involved in the Ladbroke Grove accident (Bombadier)

Figure 36: Simulation of full-vehicle impact at speed of 20 km/h with standard welded

joints

Figure 37: Simulation of full-vehicle impact with improved joint design

36


Figure 38: Simulation of full-vehicle impact with improved joint design and different obstacle shape

37

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ5. LIST OF DELIVERABLES The list of deliverables, according to the Work Programme, is presented in the table below.

Table 2 Deliverables produced in the first 18 Month period

TASK DELIVERABLE Date Partner TYPE & CONTENT

WP 2 Performance Criteria Report February 2003 ARRC,

Bombardier

Report Formulation of performance criteria Future requirements for crashworthy

aluminium rail vehicles.

WP 3

Progress Report on ALJOIN WP3 – material and structural behaviour

of MIG butt welds in 6005A-T6 aluminium alloy extrusions under quasi-static and impact

loading

October 2003 TWI

Report containing the findings on testing of 6005A-T6 aluminium alloy

extrusions under different test conditions

WP 3

WP3 Testing

September 2003

ARRC Report containing ARRC results on hardness tests, notched tensile, and Crack Tip Opening Angle (CTOA)

tearing tests. FEA of tests was also performed.

WP 3

Material and structural behaviour of MIG butt

welds in 6005A-T6 aluminium alloy

extrusions under quasi-static and impact loading

February 2004 TWI

Report containing the findings on testing of 6005A-T6 aluminium alloy

extrusions under different test conditions

WP 3

Plain and notched tensile tests and analysis on

welded 6005A-T6 specimens for ALJOIN

WP 3

January 2002 ARRC

Report containing results of a set of plain and notched tensile tests for the evaluation of the tri-axiality and true

strain values required by the selected failure model.

WP 3

Laser and hybrid laser-arc welding of aluminium alloys – Principles and

potential for application to rail vehicle body

structures

January 2004 TWI

Report containing a review of current application of laser and hybrid laser-

arc welding of aluminium alloys in transportation and feasibility for application to rail vehicle body

structures

WP3

Mechanical and Material Analysis of Welded

Aluminium 6005A-T6 Specimens for ALJOIN

Work Package 3

May 2004 NEWRAIL

Report detailing the development and the results of uniaxial tests, TOA tests,

hardness tests developed by NEWRAIL. Also microscopy images

of the materials are reported and commented.

WP3 Bolted Tearing Tests November

2004 NEWRAIL Description of results of bolted tearing tests performed by NEWRAIL

WP3 Adhesive and Silicon Welded Tensile test

November 2004 NEWRAIL

Report describing tensile tests on adhesive and silicon welded joints

performed by NEWRAIL

WP 4A Static Modelling of Joints March 2004 TWI Report delivering: material failure models for aluminium alloy welds, constitutive model of the different

welded joints, and numerical results of

38


TASK DELIVERABLE Date Partner TYPE & CONTENT

simple joints subjected to axial and transverse forces

WP4B WP4B-Dynamic

Modelling of Components and Structures

March 2004 D’Appolonia

Report detailing the results of the simulations of CTOA tearing tests, tearing tests of bolted joints, bolted

Tubes subjected to axial impact, and cleavage tests

WP5 WP5 Report - New

Joining Techniques and Joints

March 2004 TWI Report providing the results of WP5 concerning new joining techniques

and joints

WP6 Technological Implementation Plan

March 2004 Bombardier + all

Draft of TIP for the mid term of project containing the plans for the

exploitation of the project results by all partners

WP7 Design of Cleavage test and test specifications

May 2004 Bombardier Drawings of the MIG and FSW

demonstrators to be tested dynamically and test specifications

WP8

Analysis of large scale impact tests of welded rail

vehicle components of aluminium alloys

July 2005 TWI

Report describing the methodology used for the testing of the ALJOIN

demonstrators and the analysis of the results

WP8 Demonstrator Test Results

July 2005 Bombardier

Test results of demonstrators, containing the values of the forces

and impact energy measured/calculated from the tests

and the pictures of the tested samples

WP9

Validation of the modelling activities and

new joints design performance evaluation

September 2005 D’Appolonia

Presentation of the validation activities at the Final ALJOIN Workshop held in

York

The list of milestones, according to the Work Programme, is presented in the table below.

Table 3 Overview of Milestones OO VV EE RR VV II EE WW OO FF MM II LL EE SS TT OO NN EE SS

Milestone No.

Due date M

Brief description of milestone objectives

Decision criteria for assessment

M1.1 6 Consortium agreement. Approved and signed by all the partners.

M2.1 6 Completion of WP2 Performance Criteria report

Criteria assessed, future performance investigated

M3.1 12 Completion of WP3 report Method of assessing Joints in Aluminum created.

M1.2 18 MID-TERM REVIEW Successful evaluation of the innovative solutions

39


6. COMPARISON OF INITIALLY PLANNED ACTIVITIES AND WORK ACTUALLY ACCOMPLISHED

The work has been carried out according to the original Work Programme. The table below summarises the status of each project task with respect to the planned progress.

Table 1: Status of Project Tasks

WORK PACKAGE ACTUAL vs. PLANNED PROGRESS STATUS

WP 2 – Performance

Criteria

Performance criteria for critical aluminium joints in railway vehicles have been defined.

No deviation from the planning. Completed

WP 3 – Existing Joint Assessment

An extensive testing activity has been carried out on different materials.

An extension of this WP was required to perform tests originally not planned.

Completed

WP 4A – Static Modelling of Joints

Material failure models suitable for the simulation of the aluminium extrusions and the ALJOIN materials have

been analysed. Numerical results on simple joints have been carried

out using such material models. No deviation from the planning.

Completed

WP 4B - Dynamic Modeling of

Components and Structures

Numerical analysis of bolted structures, Crack Tip Opening Angle (CTOA) tearing tests, numerical

analysis of “cleavage” test, tearing tests of bolted joints. No deviation from the planning.

Completed

WP 5: New Joining

Techniques and Joints

New Joining techniques and Joints have been analysed, comprising Hybrid laser-arc process, adhesive bonded joints, and friction stir joints.

No deviation from the planning.

Completed

WP 6: Exploitation Products and

Standards

The innovations produced within ALJOIN, in particular concerning the new joining techniques, have been

already used by Bombardier in their production. Comments to the main standards relevant to ALJOIN

have been issued. No deviation from the planning.

Completed

WP 7: Method for Assessing

Crashworthiness

Test planning completed for the tests to be developed on small specimens and full-scale components.

No deviation from the planning. Completed

WP 8: Demonstrators

A prototype dynamic cleavage demonstrator component test methodology has been developed and

Completed

40


WORK PACKAGE ACTUAL vs. PLANNED PROGRESS STATUS

prototype demonstrators have been tested. The test has the potential to become a new standard for the evaluation of resistance to crack growth of welded

structures. No deviation from the planning.

WP 9: Validation Validation by modelling of rail vehicle in crash

scenarios and of full-scale cleavage tests Completed

41

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1 AL OINJ7. MANAGEMENT AND CO-ORDINATION ASPECTS

7.1 Project co-ordination A number of technical meetings were held during the project development to address the main technical aspects of the work. The list of the main project meetings is shown in the following Table.

Table 4 List of Main Meetings

Description

Location

Date

ALJOIN kick-off meeting D’appolonia

Genova 06-09-02

A general Kick-off meeting, with introduction presentations and discussions about the ALJOIN project

WP2 Meeting Bombardier Transport, Derby 17-10-02 Discussed design standards. Different joining techniques. Alternative materials

and WP3 kick-off meeting FSW workshop TWI – Cambridge 06-11-02

A Friction Stir Welding workshop, Chaired by Torben Lorentzen (DANSTIR) presentations on technical benefits, current and potential applications and

demonstrations WP2 Review Meeting TWI – Cambridge 13-11-02

Discuss the work needed to complete WP2 WP2 Review Meeting ARRC – University of

Sheffield 20-11-02

ARRC and D’Appolonia discussed the work needed to complete WP2 WP3 Kick off meeting ARRC – University of

Sheffield 28-11-02

WP3 kick-off meeting, presentations from all represented parties, development of a matrix for the testing to be carried out in WP3

WP2 Report Preparation Discussion Meeting

Bombardier Transport, Derby 14-01-03

To discuss the performance criteria report for WP2 and further work necessary for WP2 deliverables

WP2 Report Preparation Discussion Meeting

ARRC – University of Sheffield

05-02-03

ARRC and D’Appolonia to discuss the current version of the report for WP2 6 Month Management

Meeting D’Appolonia S.p.A., Genova 24-02-03

Six Month Meeting to discuss the accomplished activities 12 Month Management

Meeting TWI The Welding Institute 30-07-03

12 Month Meeting to discuss the accomplished activities WP5 Kick Off Meeting TWI The Welding Institute 27-08-03

To discuss the work needed on WP5 WP3 Tear Test

Discussion Meeting ARRC – University of

Sheffield September 03

Discussed results from WP3 testing

42

Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1

43

AL OINJ

Description

Location

Date

Pre-18 Month Review Meeting

Bombardier Transport, Derby January 04

Review of project development in preparation to the Mid Term Review and discussion on RSSB participation and demonstrator testing

18 Month Review Meeting NEWRAIL, Newcastle University, UK

March 04

Mid Term Assessment Meeting 21 Month Meeting TWI, Cambridge April 04 Technical Meeting to review the progress of work and discuss the testing

activities 24 Month Review Meeting D’Appolonia S.p.A., Genova August 04

24 Month Review Meeting 30 Month Meeting Bombardier Transport,

Bruxelles February 05

30 Month Meeting Demonstrator Testing Bombardier Transport,

Crespin (France) April 05

Attendance to the demonstrator testing Technical Meeting Newrail, Newcastle (UK) June 05

Discussion on overall project development in preparation to the Final Review Final Meeting D’Appolonia S.p.A., Rome July 05

Final Review Meeting

7.2 Man Power and Progress Follow-up Table The Man Power and Progress Follow-up Table is reported in the next pages. The effort globally spent by the partners in the project shows no major deviation from what planned.

Table 5 Man Power and Progress Follow-up Table Contract N

umber G

3RD

-CT-2002-00829

Final Technical R

eport – draft 1

44

AL

OIN

JDevia-

tion (MM)

Devia-tion (%)

Month 1-18

Month 18-24 Year 3 Total Month 1-

18Month 18-24 Year 3 Total Totals Month 1-

18Month 18-24 Year 3 Month 1-

18Month 18-24 Year 3 Month 36

a b c d a1 b1 c1 d1 d1-d a/d (a+b)/d (a+b+c)/d a1/d1 (a1+b1)/

d1

(a1+b1+c1)

/d1(d1-d)/d

DAPP 6 2 3 11 7,1 3,75 2,4 13,25 2,25 55% 73% 100% 54% 82% 100% 20%NEWR 4,5 1,5 3 9 3,75 1,5 4,5 9,75 0,75 50% 67% 100% 38% 54% 100% 8%ALCAN 0 0 0 0% 0% 0% 0% 0% 0% 0%BOM 0 0 0 0% 0% 0% 0% 0% 0% 0%DAN 0 0 0 0% 0% 0% 0% 0% 0% 0%TWI 0 0 0 0% 0% 0% 0% 0% 0% 0%

Total 10,5 3,5 6 20 10,85 5,25 6,9 23 3 53% 70% 100% 47% 70% 100% 15%

DAPP 0 0 0 0% 0% 0% 0% 0% 0% 0%NEWR 3 3 3 3 0 100% 100% 100% 100% 100% 100% 0%ALCAN 0 0 0 0% 0% 0% 0% 0% 0% 0%BOM 2 2 2,5 2,5 0,5 100% 100% 100% 100% 100% 100% 25%DAN 0 0 0 0% 0% 0% 0% 0% 0% 0%TWI 0 0 0 0% 0% 0% 0% 0% 0% 0%

Total 5 0 0 5 5,5 0 0 5,5 0,5 100% 100% 100% 100% 100% 100% 10%

DAPP 0 0 0 0% 0% 0% 0% 0% 0% 0%NEWR 5 1 6 5 1 6 0 83% 100% 100% 83% 100% 100% 0%ALCAN 1 1 1 1 0 100% 100% 100% 100% 100% 100% 0%BOM 5 5 5 5 0 100% 100% 100% 100% 100% 100% 0%DAN 0 0 0 0% 0% 0% 0% 0% 0% 0%TWI 6 6 6 6 0 100% 100% 100% 100% 100% 100% 0%

Total 17 1 0 18 17 1 0 18 0 94% 100% 100% 94% 100% 100% 0%

Comments on major deviations and/or

modifications of planned efforts.

Task/Subtask

(N°/title)

Partner

(Name/ abbrev.)

Planned efforts - at start of period (MM)

Planned (%)

Assessed* (%)

Actual effort (MM)

WP1 Project Management and

Dissemination

WP2 Performance Criteria

WP3 Existing Joint Assessment

Table 5 Man Power and Progress Follow-up Table (continue from previous page) Contract N

umber G

3RD

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Final Technical R

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45

AL

OIN

JDevia-

tion (MM)

Devia-tion (%)

Month 1-18






d1

(a1+b1+c1)

/d1(d1-d)/d

DAPP 19 19 0 38 21,6 24 0 45,6 7,6 50% 100% 100% 47% 100% 100% 20%NEWR 6 6 12 0 12 12 0 50% 100% 100% 0% 100% 100% 0%ALCAN 0 0 0 0% 0% 0% 0% 0% 0% 0%BOM 0 0,5 0,5 0,5 0% 0% 0% 0% 0% 0% 0%DAN 0 0 0 0% 0% 0% 0% 0% 0% 0%TWI 8,5 6,5 15 8,8 6,2 2,5 17,5 2,5 57% 100% 100% 50% 86% 100% 17%

Total 33,5 31,5 0 65 30,9 42,2 2,5 75,6 10,6 52% 100% 100% 41% 97% 100% 16%

DAPP 0 0 0 0% 0% 0% 0% 0% 0% 0%NEWR 0 0 0 0% 0% 0% 0% 0% 0% 0%ALCAN 1,9 1,1 3 1,9 1,1 3 0 63% 100% 100% 63% 100% 100% 0%BOM 0 0,5 0,5 1 1 0% 0% 0% 0% 0% 0% 0%DAN 0,7 0,3 1 0,7 0,3 1 0 70% 100% 100% 70% 100% 100% 0%TWI 2,5 2,5 5 2,5 2,5 2,5 7,5 2,5 50% 100% 100% 33% 67% 100% 50%

Total 5,1 3,9 0 9 5,6 4,4 2,5 12,5 3,5 57% 100% 100% 45% 80% 100% 39%

DAPP 0 0 0 0% 0% 0% 0% 0% 0% 0%NEWR 3 3 6 0,5 5,5 6 0 0% 50% 100% 0% 8% 100% 0%ALCAN 0 0 0 0% 0% 0% 0% 0% 0% 0%BOM 1,5 1,5 3 6 1,5 1 3,5 6 0 25% 50% 100% 25% 42% 100% 0%DAN 0 0 0 0% 0% 0% 0% 0% 0% 0%TWI 0,5 0,5 1 2 0,5 0,5 2,5 3,5 1,5 25% 50% 100% 14% 29% 100% 75%

Total 2 5 7 14 2 2 11,5 15,5 1,5 14% 50% 100% 13% 26% 100% 11%


Assessed* (%)

Partner

(Name/ abbrev.)

WP4 Dynamic Modelling of

Components and Structures

WP6 Exploitation Products and

Standards

WP5 New Joining Techniques and

Joints

Task/Subtask

(N°/title)



Planned (%)

Actual effort (MM)

Table 5 Man Power and Progress Follow-up Table (continue from previous page) Contract N

umber G

3RD

-CT-2002-00829

Final Technical R

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46

AL

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JDevia-

tion (MM)

Devia-tion (%)

Month 1-18






d1

(a1+b1+c1)

/d1(d1-d)/d

DAPP 0 0 0 0% 0% 0% 0% 0% 0% 0%NEWR 3 3 6 0,5 5,5 6 0 0% 50% 100% 0% 8% 100% 0%ALCAN 0 0 0 0% 0% 0% 0% 0% 0% 0%BOM 3 3 6 4 3 7 1 0% 50% 100% 0% 57% 100% 17%DAN 0 0 0 0% 0% 0% 0% 0% 0% 0%TWI 0 0 0 0% 0% 0% 0% 0% 0% 0%

Total 0 6 6 12 0 4,5 8,5 13 1 0% 50% 100% 0% 35% 100% 8%

DAPP 0 0 0 0% 0% 0% 0% 0% 0% 0%NEWR 0 0 0 0% 0% 0% 0% 0% 0% 0%ALCAN 3,3 3 6,3 1,8 4,5 6,3 0 0% 52% 100% 0% 29% 100% 0%BOM 10 10 20 2 4 14 20 0 0% 50% 100% 10% 30% 100% 0%DAN 1 2 3 0,5 3,9 4,4 1,4 0% 33% 100% 0% 11% 100% 47%TWI 1 1 2 1 2 3 1 0% 50% 100% 0% 33% 100% 50%

Total 0 15,3 16 31,3 2 7,3 24,4 33,7 2,4 0% 49% 100% 6% 28% 100% 8%

DAPP 6 6 1 6 7 1 0% 0% 100% 0% 14% 100% 17%NEWR 6 6 6 6 0 0% 0% 100% 0% 0% 100% 0%ALCAN 0 0 0 0% 0% 0% 0% 0% 0% 0%BOM 3 3 3 3 0 0% 0% 100% 0% 0% 100% 0%DAN 0 0 0 0% 0% 0% 0% 0% 0% 0%TWI 0 0 0 0% 0% 0% 0% 0% 0% 0%

Total 0 0 15 15 0 1 15 16 1 0% 0% 100% 0% 6% 100% 7%

WP7 Method for assessing

crashworthiness

WP8 Demonstrators

WP9 Validation

Task/Subtask

(N°/title)

Partner

(Name/ abbrev.)


Planned (%)

Assessed* (%)



Actual effort (MM)

47

Contract N

umber G

3RD

-CT-2002-00829

Final Technical R

eport – draft 1 A

LO

INJ

Table 5 Man Power and Progress Follow-up Table (continue from previous page)

Devia-tion (MM)

Devia-tion (%)

Month 1-18






d1

(a1+b1+c1)

/d1(d1-d)/d

DAPP 25 21 9 55 28,7 28,75 8,4 65,85 10,85 45% 84% 100% 44% 87% 100% 20%NEWR 18,5 14,5 15 48 11,75 15,5 21,5 48,75 0,75 39% 69% 100% 24% 56% 100% 2%ALCAN 2,9 4,4 3 10,3 2,9 2,9 4,5 10,3 0 28% 71% 100% 28% 56% 100% 0%BOM 8,5 14,5 19 42 12 9,5 23,5 45 3 20% 55% 100% 27% 48% 100% 7%DAN 0,7 1,3 2 4 0,7 0,8 3,9 5,4 1,4 18% 50% 100% 13% 28% 100% 35%TWI 17,5 10,5 2 30 17,8 10,2 9,5 37,5 7,5 58% 93% 100% 47% 75% 100% 25%

TOTAL 73,1 66,2 50 189,3 73,85 67,65 71,3 212,8 23,5 39% 74% 100% 35% 66% 100% 12%

*) Please note that the actual technical progress percentage and the updated remaining efforts must reflect the physically assessed status of the work.

TOTALS

Task/Subtask

(N°/title)

Assessed* (%)



Partner

(Name/ abbrev.)


Planned (%)

Actual effort (MM)

GROWTH PROJECT ALJOIN Contract N° G3RD-CT-2002-00829 Final Technical Report – draft 1

AL OINJ

48

7.3 Work Plan The Work Plan diagram is reported on next page. The only modification agreed with the partners was the extension of WP3, in order to complete the testing plan.


49

AL OINJ7.4 Updated contact details for the consortium

CONTACT PERSON

PARTNER NAME

ADDRESS TEL./FAX/E-MAIL

COORDINATOR Andrea Barbagelata Maura Primavori Donato Zangani

D'Appolonia S.p.A. Via S. Nazaro 19 16145 Genova Italy

tel. +39-010-3628148 fax +39-010-3621078 [email protected] [email protected] [email protected]

CONTRACTORS Mark Robinson George Kotsikos

NEWRAIL

University of Newcastle Department of Mechanical & Systems Engineering Stephenson Building Newcastle upon Tyne NE1 7RU

Tel: +44 (0)191 222 5889 Fax: +44 (0)191 2227679 [email protected] [email protected]

Denis Hofmann Christian Leppin

ALCAN Fabrication Europe

Alcan Technology & Management Ltd. Badische Bahnhofstrasse 16 CH-8212 Neuhausen Switzerland

tel. +41-(0)-52 674 9523 fax +41-(0)-52 674 9216 mobile: +41 (0) 79 432 4841 [email protected] tel. +41-(0)-52 674 9527 [email protected]

Mick Roe Martin Wilson Mick Wood

Bombardier Transportation

Litchurch Lane Derby, DE24 8AD United Kingdom

tel. +44 (0)1332 266056 fax +44 (0)1332 251840 mobile +44 (0)7789 08779 [email protected] [email protected] [email protected]

Torben Lorentzen DanStir ApS Danish Stir Welding Technology

Park Allé 345 Box 124 DK-2605 Brondby Denmark

tel: +45 4326 7035 fax: +45 4326 7040 mobile: +45 2330 3383 [email protected]

John Davenport Weiguang Xu

TWI Limited Granta Park, Great Abington Cambridge CB1 6AL United Kingdom

tel. +44-(0)-1223 891162 fax +44-(0)-1223 892588 [email protected] fax +44-(0)-1223 890689 [email protected]

OTHER MEMBERS Aqeel Janjua Rail Safety &

Standards Board

Floor 1 Evergreen House 160 Euston Road London NW1 2DX United Kingdom

tel. +44 (0) 20 7904 7966 [email protected]

EUROPEAN COMMISSION Dennis Schut European

Commission Officer European Commission DG RTD H2, Office-B7 02/111, B-1049 Rue Belliard 7,

Tel. +32 2 295 09 27 fax: +32 2 296 33 07 [email protected]

mailto:[email protected]















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AL OINJBrussels Belgium

Sandro Maluta Project External Assessor

Via M. Lutero, 8 20126 Milano, Italy

Tel. +30-333 9076104 [email protected]



51

AL OINJ8. RESULTS AND CONCLUSIONS The introduction of double skinned construction, through the use of aluminium closed cell extrusions, has greatly improved the crash resistance of rail vehicles. On the other hand, the impact resistance of fusion welds that have traditionally been the joining technique of the extruded sections, had not received adequate consideration, in terms of the contribution of they make on the crash resistance of a rail vehicle. The ALJOIN project arose from the need to improve the crashworthiness design of aluminium rail vehicles and establish guidelines for the future build of such vehicles. Aluminium alloys derive their physical properties (i.e. strength, stress corrosion cracking resistance etc) through a range of elaborate heat treatments. The additional heat input introduced by the fusion welding process alters the microstructure at the weld region resulting in a reduction of strength there of up to 50% of that of the parent plate. This can have detrimental effects in the behaviour of such joints in high velocity impact situations. This effect has been demonstrated by the failure of the rail coaches in the Ladbroke Grove accident in the UK. ALJOIN has carried out a detailed investigation of the joining of components in rail vehicles by initially reviewing the current state of the art and assessing alternative joining techniques. It has been found that the use of Al-Mg filler wires in MIG welding results in superior performance welds in terms of strength, ductility and fracture toughness compared to Al-Si filler wires. Other joining techniques such as Laser Welding (LW) and Friction Stir Welding (FSW) have also been investigated with the former technique appearing attractive in terms of increased productivity and the latter in terms of a moderate increase in fracture toughness and improved surface finish, when they were compared to the traditional automated MIG welding process. ALJOIN has shown that the use of MIG welding with Al-Mg filler and FSW are both good candidates for future built of train vehicles. It has also been demonstrated that the design of the joint is equally important in the impact performance of the joint. Under-matching in an aluminium weldment is unavoidable due to the reduction in strength at that region even after moderate heat inputs (as in the case of FSW). After extensive testing both on small specimens and large demonstrators a significant output of the ALJOIN project has been the recommendation for the


52

AL OINJaluminium sheet thickness at the weld region to be increased, so that the resultant stress levels there are equivalent to those of the parent plate. The amount of thickening of the plate is a factor of the aluminium grade and welding process. Another joint design improvement realised by this project is the avoidance of partial penetration welds through appropriate shaping of the extrusions at the joint region. The validity of the design recommendations described above has been proved through large scale demonstrator tests which have shown that dynamic failure always takes place in the parent plate (that inherently possesses much higher toughness) rather than the weldments. Adhesive bonding of aluminium sections has also been investigated but has not proved attractive neither in terms of productivity nor strength or impact resistance. Furthermore, other issues such as the ease of carrying out NDE inspections for both quality control or to establish levels of damage and need for repair after minor impacts have proved impractical. A methodology to assess experimentally the performance of welded aluminium extruded sections was also developed during the ALJOIN project. The methodology measures the energy absorbed by the specimen and the displacement of the free end as it "tears away" from the clamped part of the specimen and provide a measure of the tearing resistance of the material when subjected to high loading rates. The term "tearing resistance" in this test is not to be confused with the fracture mechanics derived term. Since there is no sharp crack to initiate the failure the test can be considered as dynamic tensile test where the peak load describes the energy required to yield the cross-section and tear the material. The subsequent rate of load drop is a measure of how easily the tear propagates through the material. The results of this work have shown that the parent material (6005-T6) possesses substantial tearing resistance and have also demonstrated the benefits of increasing the cross-section thickness at the weld region in diverting failure (i.e. crack initiation and propagation) away from the weld and into the parent material. The tests also demonstrated that increasing this increase in the section thickness is a function of alloy grade and welding process. It is important here to note that there is an optimum increase in the section thickness at the weld region. Any further increase, although it improved the static strength of the joint, it reduced the dynamic loading response, resulting in a lower initiation load and tearing


53

AL OINJresistance. This was attributed to the increased thickness moving the failure mode from plain stress to plain strain failure. The ability to accurately model the collision behaviour of a rail vehicle has also been a major output of the ALJOIN project. The modelling efforts have been aided by detailed static and quasi-static mechanical property tests in order to derive the material parameters that can best describe failure. In addition to mechanical property and fracture mechanics tests, component tests were carried out to validate the resultant models. The Gurson-Tvergaard model used within the LS-DYNA finite element analysis code has provided very good predictions of failure under static, quasi-static and dynamic loading conditions. A model of a rail vehicle (class 165 by Bombardier, involved in the Ladbroke Grove accident) was constructed and subjected to a number of head on collision scenarios. The modelling exercise has demonstrated a notable improvement in the failure mode when the joint design recommendations developed through this project were implemented, (use of Al-Mg filler wire, increase of the sheet thickness at the weld region and full penetration welds throughout). ALJOIN has provided a number of results that have demonstrably improved the structural integrity of rail vehicles and their crashworthiness. It is important to note though that a collision between two rail vehicles or derailment cannot be accurately modelled as there is an infinite number of loading configurations that a rail vehicle and its individual structural components could be subjected to. Off-axis loads as well as extreme loading rates are possible and it is clear that there could still be a risk of fast fracture of weldments. The pipeline industry that for many years has encountered fast fractures that can run for kilometres understand the limitation in predicting this material behaviour. This project is nevertheless a major step forward in understanding the role of weldments in the crashwothiness of rail vehicles and produced recommendations to improve the performance of weldments subjected to dynamic loading.

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