D AMAGE A NALYSIS OF L OW SPEED IMPACT ON C … involved in the impact of targets, ... speed impact...

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 5, May 2017, pp. 717–727, Article ID: IJCIET_08_05_080 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=5 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed

DAMAGE ANALYSIS OF LOW SPEED IMPACT ON COMPOSITE MATERIALS

K Veeranjaneyulu

Department of Aeronautical Engineering MLR Institute of Technology, Hyderabad, India

M S N Gupta


Dhana Jayan Department of Aeronautical Engineering

MLR Institute of Technology, Hyderabad, India

Vamsi V


ABSTRACT Composite materials are widely used in aeronautical and aerospace applications.

Composite materials used in aircraft components may suffer from impact damage. The component is subjected to low velocity impact, medium velocity impact and high velocity impact. The damage analysis of very important in the characterization of the composite materials.

For a low velocity impact, invisible cracks often occur, but they cannot be seen using the naked eye. It is important to understand the deformation and damage mechanisms involved in the impact of targets, for the effective design of composite structures. The Glass fiber composite laminate has been fabricated and tested for low velocity impact. The specimen for the test is prepared as per the ASTM standards. An Ultrasonic testing method is used to detect the invisible cracks in the specimen. The test is performed on the specimen before and after the low speed impact. The low speed impact on the specimen is performed by the charpy Test, Izod test and weight drop test. The failure modes of composite Charpyand Izode impact tests depend on the specimen orientation. Often, specimens exhibit fiber fracture and fiber pull-out, while other times delamination failure is the primary failure mode. Key words: Composite materials; ASTM; delamination; low velocity impact.

K Veeranjaneyulu, M S N Gupta, Dhana Jayan and Vamsi V


Cite this Article: K Veeranjaneyulu, M S N Gupta, Dhana Jayan and Vamsi V, Damage Analysis of Low Speed Impact on Composite Materials. International Journal of Civil Engineering and Technology, 8(5), 2017, pp. 717–727. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=5

1. INTRODUCTION As we are in the advanced era the technology had increased in everything and everywhere the use of composite materials has become much more prevalent in many different areas. As manufacturing costs have decreased, composite materials have seen greater use in aerospace, automotive, and high-end sporting equipment applications. For example, the Boeing 787 Dreamliner airplane, shown in in recent decades, composite materials have become much more prevalent in many different areas. As manufacturing costs have decreased, composite materials have seen greater use in aerospace, automotive, and high-end sporting equipment applications. For example, the Boeing 787 Dreamliner airplane is comprised of 50 % composite materials, which is an increased use from the Boeing 777 (Boeing 2014). Boeing chose to make increased use of composite materials as they can be made lighter than aluminum components without decreasing the load-bearing capacity and also high resistance to heat. While this does increase the cost of components, the fuel savings that accompany decreased weight made composites a cost-competitive material choice. As these materials become more widespread, it is particularly important that engineers understand the physical properties and behaviors of advanced composite materials.

Composite materials are created by combining two or more constituent materials on a macroscopic level. A composite material can be designed and manufactured to improve specific properties over the base materials. This includes properties such as strength, stiffness, corrosion resistance, fatigue life, and weight. Because their properties can be tailored to specific applications and the weight savings composite materials have over traditional materials (such as metals), composites can be desirable as modern structural materials. Common types of composite reinforcement include fibrous, laminated, and particulate composites, or combinations of the three. The role of the reinforcement is to bear the majority of the load. Fiber reinforcement is often used, and may be implemented as long continuous fibers or short chopped fibers. Continuous fibers can also be woven into fabrics or textile geometries, which can have more advantageous stiffness and damage tolerance properties over simple aligned fibers. Other types of reinforcements include particulate and flake reinforcement, and they are often used for specialized applications Composite matrices are often composed of polymers/epoxies, and they can also be made from metals or ceramics. The main role of the matrix is to transfer load to and maintain the structure of the reinforcement material. The matrix material is chosen to give the desired structural characteristics and should be compatible with the reinforcement material. Individual layers of unidirectional fibers or woven sheets, called lamina, can be combined into laminated composites. An expanded view of an angle-ply laminated composite. Laminated composites can have improved in-plane properties compared to unidirectional composites, since the load-bearing fibers run in multiple directions. While composites have advantages over traditional structural materials, they do have some distinct drawbacks. Foremost amongst these is damage tolerance. In a metal structure, a low-velocity impact might leave a visible indent on the surface. This deformation would be a visible indication of damage and, depending on the structure, loads, and severity, would not likely lead to catastrophic failure as metals tend to be ductile. Further, the stresses, strains, and failure modes for metals and other traditional structural materials are fairly well understood. Composite materials, on the other hand, tend to be less resistant to damage and have much more complicated failure modes. An impact on

Damage Analysis of Low Speed Impact on Composite Materials


a composite structure might leave no visible surface damage, but damage could develop on the rear face or even internally. Because of this, while a visual inspection of a metal structure may be sufficient to identify damage and determine safe use, the same procedure might not be adequate for a composite structure. A visual inspection could underreport the amount of damage present which may result in the use of an unsafe composite structure. Since damage to a composite structure decreases its strength and stiffness, an accurate assessment of damage is necessary to determine if the structure is capable of bearing the operational loads. A simple visual inspection will not suffice, and so more advanced detection methods must be implemented. Traditionally, internal damage to laminated composite structures is measured using destructive techniques. While these methods do provide accurate measurements of internal damage, they are not useful for functional components; it would not be practical to cut apart an airplane wing just to check for damage. This has motivated research and development of non-destructive imaging techniques, as discussed in a later section. In the present work, the behavior of carbon fiber reinforced polymer matrix composites subject to low-velocity impact and non-destructive damage assessment techniques are considered. The literature review in the following section focuses on studies analyzing both low-velocity impact damage and the state of the art for nondestructive damage evaluation of laminated composites

2. FABRICATION

2.1. Fabrication Techniques There are numerous methods for fabricating composite components. Some methods have been borrowed (injection molding, for example), but many were developed to meet specific design or manufacturing challenges. Selection of a method for a particular part, therefore, will depend on the materials, the part design and end-use or application.

2.2. Wet/Hand Lay-Up Resins are impregnated by hand into fibers which are in the form of woven fabrics. This is usually accomplished by rollers or brushes, with an increasing use of roller type impregnators for forcing resin into the fabrics by means of rotating rollers. It is recommended for small and medium volumes requiring minimal investment in molds and equipment. The contact molding consists of applying these elements successively onto mold surface :

A release agent

A gel coat

A layer of liquid thermosetting resin of viscosity

between 0.3 and 0.4pas and medium reactivity

Figure 1 Wet - Hand Lay up



2.3. E-Glass Fabric E-Glass or electrical grade glass was originally developed for standoff insulators for electrical wiring. It was later found to have excellent fiber forming capabilities and is now used almost exclusively as the reinforcing phase in the material commonly known as fiberglass.

The use of E-Glass as the reinforcement material in polymer matrix composites is extremely common. Optimal strength properties are gained when straight, continuous fibers are aligned parallel in a single direction. To promote strength in other directions, laminate structures can be constructed, with continuous fibers aligned in other directions. Such structures are used in storage tanks and the like.

Technical Specifications Nomenclature : 13mil E-GLASS FABRIC

Thickness, mm : 0.36

Width, inch : 40"

Weave : 4 Harness Satin Construction Warp, Threads/inch : 48 Weft, Threads/inch : 36

Weight per Sq.mtr : 455.400 gms

Breaking Strength per 50 mm: Warp : 383.000 Kgs Weft : 258.000 Kgs

Resin and Hardener Resin and hardener used in this project are Lapox L-12(Resin) and K-6 (Hardener). Lapox L-12 is a liquid, unmodified epoxyresin of medium viscosity which can be used with various hardeners for making glassfiber reinforced composites

Technical Specifications Lapox L-12

Epoxide equivalent 182-192 gm/eq

Epoxy value 5.2-5.5 eq/kg

Hardener K-6

Visual appearance Pale yellow liquid

Refractive index at 25°c 1.4940-1.5000

2.4. Fabrication of Rectangular Plate The fabric is laid on work bench covered with polythene sheet Marking is taken up with

mold dimensions 200*800 mm and the sequence of vertical strip is increased by 0.1 for every layup

Matrix is weighed as per specification of fabric that is 76gms for 10 plies, pigment of 5% for color surface typically white and harden is added in the ration of 1:10



Appling matrix to create bonding layers. This is usually accomplished by brushes with an increasing using brushes by impregnating

Figure 2 Control panel

forcing resin into fabrics

The surface of the mold is cleaned with 0-grade Emery paper, the clearance holes are cleaned with acetone and a release agent (waxpol) is applied. If the surface is not clean, then the release agent will not function properly

An optional sacrificial layer (Surface mat) is laid up on the mold surface. This layer is usually a fiberglass fabric made with the same resin system as the composite laminate. The sacrificial layer protects the laminate from surface abrasion and surface irregularities during manufacturing.

Inner mold is fitted and one by one plies are Layered to the mold

Removing the polythene sheet from the ply

Folding all the ply to inner side to form the half flange

Assembling and fixing of die

Folding the ply to form other half of flange and cutting respectively

Finally mold is closed and kept in Hydraulic press

Figure 3 Fabrication process

Fig2.2 control



The process of polymerization is called "curing", and can be controlled through temperature and choice of resin and hardener compounds; the process can take minutes to hours. Some formulations benefit from heating externally supplied during the cure period, whereas others simply require time, and cure on account of mild increase in internal temperatures on account of chemical reaction

Figure 4 Fabrication process

In the first stage of cure cycle temperature up to 60 °C and dwelling at this temperature for nearly 60 minutes. At the end of the temperature dwell, the oven temperature is increased to the actual curing temperature for the resin that is 80°C. After setting the oven temperature to 80°C the part temperature slightly increases to 120°C, and later 160°C The temperature is maintained for 4 hours or more, until a pre-determined level of cure has occurred.

Table 1 Curing cycle data

Time

Elapsed time from starting

(min)

Temp setting in

thermoset(˚c)

Actual temp of part(˚c)

Oven temp

Corrected part temp

9:15 0 200 26 26 25 9:30 15 200 32 170 31 9:45 30 200 41 189 40

10:00 45 200 47 195 46 10:15 60 200 54 192 53 10:30 75 200 61 193 60 10:45 90 200 67 193 66 11:00 105 200 73 193 71 11:15 120 200 78 193 76 11:30 135 200 77 148 75 11:45 150 200 85 192 83 12:00 165 200 88 195 86 12:15 180 200 93 193 91 12:30 195 200 97 194 95 12:45 210 200 100 193 97 13:00 215 200 104 196 101 13:15 230 200 107 192 104



Figure 5 0-0 Laminate Curing Temperature Graph

Figure 6 0-90 Laminate Curing Temperature Graph

Figure 7 Ultrasonic test

After curing,the laminated plate is taken from the autoclave/owven and tested for internal defects using ultrasonic testing machine.The laminate is found to be free fron internal defects and external damages.

3. SPECIMEN FOR TESTING Specimens for the testing is made as per the ASTM D 5628 standards

Figure 8 Specimen for Impact Test



L = 126 ± 1 mm, D = 12.7 ± 0.15 mm, and 3.00 mm < w < 12.7 mm

Figure 9 Specimens for Impact Test

Figure 10 Impact testing machine

Impact energy=mg(hf-hi)

Figure 11 Specimens after test

Impact strength = 450kJ/m2

Energy absorbed = 4.48J



3.1. Drop Weight Test Drop Weight Impact testing machine was used for carrying out for the required project. A schematic diagram of the test is shown below. Energy vs time and Velocity vs. Time data is acquired by the data acquisition system. The initiation and propagation energy are calculated using this data.

Impact energy corresponding to the maximum impact force is defined as initiation energy. Propagation energy is defined as the difference between the maximum impact energy and the initiation energy. Three different velocities and a tool weights were used for doing the impact testing. Specimens were tested at velocities of 2m/s to 4m/s using tool weights of 315 grams. Each group was tested at three different locations namely from different hight that surrounded the center of the specimen and the response was acquired

Figure 12 Tool Drop Test Apparatus

400 mm height

Figure 13 Energy Vs Time Figure 14 Velocity Vs Time

Fig 13 show the resuls of a tool drop test when the tool is dropped from the height of 400mm.

Damage after impact

Figure 15 Specimen after drop test



500 mm height

Figure 16 Energy Vs Time Figure 17 Velocity Vs Time

Damage after Impact

Figure 18 Specimen after drop test

4. CONCLUSIONS The low speed impact damage analysis of the Glass fiber composite laminated plate has been performed in this work. Based on the results obtained, the following conclusions are derived.

The failure types for composite Charpy impact tests depend on the specimen orientation. Often, specimens exhibit fiber fracture and fiber pull-out, while other times delamination failure is the primary failure mode. Some specimens failed by the combination of fiber pull-out and fiber-matrix separation and failed at the fiber-matrix interface. The failure type is important when characterizing composites.

The level of damage in weight drop test depends on the shape and the geometry of the drop tool. The specimen deforms in all three directions and the deformation in Z-direction is maximum.

The energy absorbed by the specimen during impact test is very close to the experimental values.

REFERENCES [1] R. Mantena, P. (Dept. of Mechanical Engineering, The University of Mississippi); Mann,

R.; Nori, C. Low-velocity impact response and dynamic characteristics of glass-resin composites; Journal of Reinforced Plastics and Composites, 20, p 513-533, 2001.

[2] ASTM D 3763, High Speed Puncture Properties of Plastics Using Load and Displacement Sensors, 1997.

[3] W.R. Hoover, Effect of Test System Response Time on Instrumented Charpy Impact Data; Instrumented Impact Testing, ASTM STP 563, p203-214, 1974.

[4] ASTM D 6110, Determining the Charpy Impact Resistance of Notched Specimens of Plastics; 2002.

[5] D.F. Adams, L.A. Carlsson, R.B. Pipes, Experimental Characterization of Advanced Composite Materials, CRC Press, 3 rd ed. 2003.



[6] Tomita, Yoshiyuki (Osaka Prefecture Univ); Tamaki, Toru; Morioka, Kojiro,Effect of fiber strength on notch bending fracture of unidirectional long carbon fiber-reinforced epoxy composites; Materials Characterization, 41, p 123-135, Oct, 1998.

[7] C.B. Bucknall (Cranfield Inst of Technology), Relevance of impact testing in the materials science of polymers; Plastics, Rubber and Composites Processing and Applications, 17, p 141-145, 1992.

[8] R.H. Toland, Impact Testing of Carbon-Epoxy Composite Materials; Instrumented Impact Testing, ASTM STP 563, p 133-145, 1974.

[9] M. Nagai and H. Miyairi, The Study on Charpy impact testing method of CFRP; Advanced Composite Materials: The Official Journal of the Japan Society of Composite Materials, 3, p 177-190, 1994.

[10] ASTM D 5628 Standard Test Method for Impact Resistance of Flat, Rigid Plastic Specimens by Means of a Falling Dart (Tup or Falling Mass), 1996.

[11] S. Ujihashi, (Tokyo Inst of Technology); Intelligent method to determine the mechanical properties of composites under impact loading; Composite Structures, 23, p 149-163, 1993

[12] Taylor, R.P.Fibre Composite Aircraft - Capability and Safety. Australia: Australian Transport Safety Bureau, 2008.

[13] M. Nayeem Ahmed, Dr. P. Vijaya Kumar, Dr. H.K. Shivanand and Syed Basith Muzammil. A Study on Flexural Strength of Hybrid Polymer Composite Materials (E Glass Fibre-Carbon Fibre-Graphite) on Different Matrix Material By Varying its Thickness. International Journal of Mechanical Engineering and Technology, 4(4), 2013, pp. 274–286

D AMAGE A NALYSIS OF L OW SPEED IMPACT ON C … involved in the impact of targets, ... speed impact...

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