INVESTIGATE BLADE FAILURE

IN AXIAL COMPRESSOR

MOHAMMAD ASYRAF B OMAR

This Report Is Submitted In

Partial Fullfillment of Requirements For the

Barchelor Degree of Mechanical Engineering (Structural & Material)

Fakulti Kejuruteraan Mekanikal

Universiti Teknikal Malaysia Melaka

APRIL 2009

ii

DECLARATION

I hereby declare that this project report entitled

INVESTIGATE BLADE FAILURE IN AXIAL COMPRESSOR

is written by me and is my own effort except the ideas and summaries which I have

clarified their sources.

Signature :…………………………………

Author :…………………………………

Date : ………………………………...

i

VERIFICATION

“I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in

terms of scope and quality for the award of degree of Bachelor Mechanical Engineering

(Structure & Material)”

Signature :…………………………………

Supervisor’s Name :…………………………………

Date : ………………………………...

iii

ACKNOWLEGEMENT

Thanks to Allah, for giving me permission to complete this project. In here I

would like to record my graceful thank to all the support, encouragement and

inspirations that I have received during completing this project.

I also would like to express greatest thankfulness and appreciation to my

supervising lecturer, Mr. Nazri b. Md Daud of which we had a good working

relationship, and who had offered me a wonderful help and encouragement. He also

gives me full of support and advice.

Special thanks to Mr. Razmi b. A. Razak who has given me information about

the blade of axial compressor for this project.

All the Lecturers and Technicians of Faculty of Mechanical Engineering, I would

like to acknowledge and express my gratitude for giving me their cooperation and help

in order to complete this project.

Last but not least to my family and all my fellow friends, for their concern,

encouragement and understanding.

iv

ABSTRACT

This project presents the analysis blade of the axial compressor by using the

Finite Element Method (FEM). The axial compressor is one of the important devices

that always use in industry. The maintenance for the compressor and its parts is

necessary in order to ensure that the compressor perform well. This need to be done for

certain period that had been set. Sometimes, the compressor will have a problem or fail

to perform well. There are many factors that cause the failure of this compressor. The

one of the factor that may cause the failure is the damage of the component of the

compressor. The problem for compressor to perform well will disturb the flow of the

production in industry, thus will make the cost increase. To avoid this situation, the

compressor and its components need to be service for every period that has been set.

Since blade is the one of the main parts to generate the compressor this project will deal

with analysis for the blade of axial compressor. Hope that this study will help to reduce

failure of the blade which is one of the components of the axial compressor. The blade

will be designed base on the actual dimension by using the Solidwork software, and then

it will be exported in the MSC Nastran Patran software. The blade had been simulated in

different of mesh or global length. The best result which has the lowest percentages of

error was selected to undergo for further analysis. After undergo the simulation analysis

with MSC Nastran Patran, the maximum stress was found to be 66MPa while the

maximum displacement is 42.91 10 m−

× . The approximation theoretical value for

maximum stress which is 78.66MPa shows the 16% of percentage of error for the

simulation with the Nastran Patran software. Lastly the factor of the safety for the blade

was calculated and the value is 3.65.

v

ABSTRAK

Projek ini mempersembahkan analisis bilah pemampat paksi dengan

menggunakan Kaedah Unsur Terhingga . Pemampat paksi adalah salah satu peranti

penting yang selalu digunakan dalam industri. Penyelenggaraan untuk pemampat paksi

dan komponen-komponenya adalah perlu untuk memastikan ianya sentiasa berfungsi

dengan baik. Ini hendaklah dilakukan untuk jangka masa tertentu yang telah ditetapkan.

Kadang kala, pemampat akan menghadapi masalah atau gagal berfungsi dengan baik.

Terdapat banyak faktor yang menyebabkan kegagalan pemampat ini. Salah satu faktor

yang menyebabkan kegagalan ini adalah kerosakan pada komponen pemampat. Masalah

kepada pemampat untuk berfungsi dengan baik akan mengganggu aliran pengeluaran

dalam industri, seterusnya akan membuat kos meningkat. Untuk mengelakkan situasi ini,

pemampat dan komponennya perlu diservis untuk setiap jangka masa yang telah

ditetapkan. Memandangkan bilah adalah salah satu bahagian utama untuk menggerakkan

pemampat, projek ini akan berurusan dengan analisis untuk bilah pemampat paksi.

Diharap agar kajian ini akan membantu untuk mengurangkan kegagalan pada bilah

dimana ia adalah salah satu komponen pemampat paksi. Bilah ini telah disimulasikan

dalam berbeza sirat atau panjang global. Keputusan terbaik yang telah mendapat

peratusan terendah ralat telah dipilih untuk menjalani analisis seterusnya. Selepas

menjalani analisis simulasi dengan MSC Nastran Patran, tekanan maksimum yang

diperolehi adalah 66MPa manakala sesaran maksimum adalah 42.91 10 m−

× .

Penghampiran nilai teori untuk tekanan maksimum yang mana adalah 78.66 MPa

menunjukkan 16% peratusan ralat untuk simulasi dengan menggunakan perisian Nastran

Patran. Akhir sekali, faktor keselamatan untuk bilah telah dikira dan nilainya adalah

3.65.

vi

TABLE OF CONTENT

CHAPTER TITLE PAGE

VERIFICATION i

DECLARATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENT vi

LIST OF TABLE ix

LIST OF FIGURE x

LIST OF SYMBOL xiii

LIST OF APPENDICES xiv

CHAPTER 1 INTRODUCTION 1

1.1 Background 1

1.2 Objective 2

1.3 Scope 3

1.4 Problem statement 3

CHAPTER 2 LITERATURE REVIEW 4

2.1 Introduction 4

2.2 Investigate blade failure 4

2.3 Performance losses in axial compressor 6

vii

2.4 Analysis using Finite Element

Method (FEM) 8

CHAPTER 3 FINITE ELEMENT METHOD 10

3.1 Finite Element Method Theory 11

3.2 MSC Nastran 14

3.2.1 MSC Nastran benefits 16

3.2.2 MSC Nastran applications 16

3.3 MSC Patran 17

3.3.1 Using Patran with MSC and 18

Third-party solvers

3.4 Results 19

CHAPTER 4 METHODOLOGY 20

4.1 Overview 20

4.2 Flowchart 20

4.3 Model Design using Solidwork 22

4.3.1 Step in Drawing using Solidwork 23

4.4 Analysis Model in MSC Nastran/Patran 39

4.4.1 Import the model 39

4.4.2 Elements 40

4.4.3 Load and Boundary Conditions 41

4.4.4 Material and Properties 43

4.4.5 Simulation 45

4.4.6 Result 47

4.4.7 Different Mesh 48

4.5 Theoretical Calculation 49

viii

CHAPTER 5 RESULT AND DISCUSSION 50

5.1 Expected result 50

5.2 Result 51

5.3 Comparison with Theoretical

Calculation 58

5.4 The Effect of Mesh 63

5.4.1 The Comparison of Mesh 65

5.5 Analysis of the Blade 67

CHAPTER 6 CONCLUSION 70

6.1 Overall Conclusion 70

6.2 Recommendations 71

REFERENCES 72

APPENDIX A 74

APPENDIX B 75

APPENDIX C 76

APPENDIX D 77

APPENDIX E 78

APPENDIX F 79

APPENDIX G 80

ix

LIST OF TABLE

NO TITLE PAGE

3.1 Type of element 12

5.1 Properties of AISI 316 Stainless Steel 51

5.2 The Numbers of Nodes and Elements 63

5.3 Comparison Between Mesh 65

x

LIST OF FIGURE

NO. TITLE PAGE

3.1 Sample Finite Element Model 11

3.2 Flow of MSC Nastran Patran software 18

3.3 Example of analysis results 19

4.1 Flowchart of the process 22

4.2 Figure of the blade design in Solidwork 23

4.3 The sketch of the blade 24

4.4 Sketch 2 in plane 1 25

4.5 Loft the sketch 26

4.6 The sketch in the first plane 27

4.7 Extrude of the sketch 28

4.8 The sketch and extrude of the part 29

4.9 The sketch and extrude 30

4.10 The sketch and cut extrude 31

4.11 The sketch and cut extrude 32

4.12 The circular pattern 33

4.13 The new plane on part 34

4.14 The sketch on plane 4 35

4.15 The sketch on plane 1 36

4.16 The loft of the sketch 37

xi

NO. TITLE PAGE

4.17 The sketch on top plane 38

4.18 The cut extrude of the part 38

4.19 The complete model 39

4.20 The import model 40

4.21 Mesh on the solid model 41

4.22 The fix at the model 42

4.23 The pressure applied 43

4.24 Input properties of the material 44

4.25 The input properties 45

4.26 The analyzed model in Nastran 46

4.27 Access result 47

4.28 Result of the simulation 48

4.29 The input value of global edge length 49

5.1 The area that will have a maximum stress 51

5.2 Simulation 1 52

5.3 Simulation 1 53

5.4 Simulation 2 54

5.5 Simulation 2 55

5.6 Simulation 3 56

5.7 Simulation 3 57

5.8 Graph of Number of Nodes and Elements vs Global 64

Edge Length

5.9 Graph of Maximum Stress vs Number of Elements 66

xii

NO. TITLE PAGE

5.10 The critical area 67

5.11 The maximum displacement 68

xiii

LIST OF SYMBOLS

M - mass

b - width

k - stiffness

d - distance

F - force

Y - distance from the neutral axis

I - moment inersia

�m - maximum stress

{u}e - the displacement vector

{f}e - forces acting on the element.

[ ]k - stiffness matrix

totq - theoretical total head

dfq - loss from disc friction

thq - head available

impη - efficiency of impeller

stageη - stage efficiency

osfq - frictional forces encountered in the stator

oaq - the overall actual adiabatic head

xiv

LIST OF APPENDICES

Appendix Title Page

A GANTT CHART FOR PSM I & II

74

B Axial Flow Compressor

75

C Full Blade Drawing

76

D Full command for the drawing of the blade

77

E Drawing of the blade

78

F Assembly Blade Drawing

79

G Dimension of the blade

80

1

CHAPTER 1

INTRODUCTION

1.1 Background

The axial-flow compressor often use in turbine gas especially over 5MW

units. An axial-flow compressor is one in which the flow enters the compressor in an

axial direction (parallel with the axis of rotation), and exits from the gas turbine also

in an axial direction.The axial-flow compressor compresses its working fluid by first

accelerating the fluid and then diffusing it to obtain a pressure increase. The fluid is

accelerated by a row of rotating airfoils (blades) called the rotor, and then diffused in

a row of stationary blades (the stator). All angles that describe the blade and its

orientation are measured with respect to the shaft (z axis) of the compressor.

2

Blades in axial compressor were designed by arranging thickness distribution

around a camber line. Recent research in the axial flow compressor blade, based on

understanding the flow behaviors in the blades, where stacking lines of the airfoils

are curvilinear, has generated favorable results in terms of loss reduction and thereby

efficiency. The blade also can have some defect or fail to operate successful after a

few year operations. The damage could happen due to many factors. High

temperature and vibration may cause the power loss and damage to the blade in the

axial compressor. This project will investigate and analysis the failure using the

Nasran Patran software. The model of the blade will be designed according to the

real dimension using the Solidwork. The complete model from Solidwork will be

eksported to Nasran Patran software to analysis and calculate the stress on the blade.

1.2 Objectives

This project carried out the study and analyze problem those related to the

failure of blade in axial compressor. The other objectives that contain in this project

are:

1. To model the blade of the axial compressor based on the actual

dimensions by using Solidwork software.

2. To simulate the blade and investigate the failure of axial compressor

blade using MSC Nasran/Patran software.

3

1.3 Scopes

The scopes of this study are:

1. Modeling the blade in axial compressor based on the actual dimension with

Solidwork software.

2. Simulate the blade with different mesh using Nasran Patran and comparison

with theoretical value need to be done.

1.4 Problem Statement

After a long time usage of a blade in axial compressor, it may have some

defect or failed to give a better performance. If this things occur in industry, it will

disturb the flow of production thus will make the cost increase. This thing should not

be happen and must be avoided to ensure that the low cost of the production in order

to make a profit for an industry. So, this study will deal with an analysis using the

MSC Nastran Patran software to simulate the blade.

4

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

The literature review consists of various aspects regarding the investigate

blade failure, performance loses in axial compressor, and analysis using the finite

element method.

2.2 Investigate blade failure

Xiaolei Xu and Zhiwei Yu (2006) have conducted a failure investigation on

the turbine blades used in a locomotive turbochanger, which are made from K418

Ni-base superalloy. Fractography investigation on the troubled blade indicates that

cracks initiated from the surface of the concave side close to the trailing edge and

propagated towards to the leading edge. The multi-origin fatigue fracture is the

dominant failure mechanism of the blade. Metallographic morphology typical of

over-heat damage features, such as re-dissolution of the eutectic � + �’ melting of the

local region of the grain boundary appears in the microstructure of the airfoil part of

the failed blades. Appearance of over-heat damage structure in the serviced blades

makes the strength of the blade material decrease intensely to initiate fatigue cracks

and make one of the blades fracture first. Fragments from the blade fractured first

would crash the other blades to make the blades break or bending deformation.

5

From the investigations that have been done, the blades used in a locomotive

turbocharger were damaged to different extent in servicing. The accumulated service

time of the blades is about 6 years. It was reported that a mayor repair had been

conducted on the turbine once. The blade material is specified as K418 superalloy

(C: 0.08–0.16; Al: 5.50–6.40; Si 6 0.50; Nb: 1.80–2.50; Mo: 3.80–4.80; Ti: 0.50–

1.00; Cr: 11.50–13.50; balance: Ni). The observation and analysis of failure of a few

representative failed blades to assess the possible failure reasons.

The method of investigation that uses to determine the chemical composition

of the blade material is spectroscopy chemical analysis method. The micro-

composition in various zones of the fracture surfaces was determined by energy

dispersive X-ray spectrometer (EDX). The microstructure of the sectional specimens

near the fracture was observed by scanning electron microscopy (SEM) on a Philips

XL-30 scanning electron microscope. The fracture surfaces were analyzed by visual

and SEM observation to study the failure mechanism.

N. Vardar and A. Ekerim (2006) had done a case study of failure analysis of a

40 MW gas turbine blade made of Udimet 500. The cause of failure is found to be

intergranular cracks which started during exposure to high temperature. The cracks

initiated from the grain boundaries and propagated to the critical length to result in

catastrophic fracture. In many locations 6M C type secondary carbides were found

agglomerated on grain boundaries. Also micro-cavities were found on fracture

surfaces which served as an origin of creeping failure mechanism. The investigation

of the failure was carried out by using several experimental tests, including optical

microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy

(EDS), X-Ray diffraction (XRD) and X-Ray fluorescence (XRF). The

microstructural investigation of the blade airfoil revealed the presence of continuous

film of carbides in grain boundaries of the base material as a result of transformation

of carbides of MC type to carbides of 6M C type due to high temperature operation

of the blades.

6

2.3 Performance losses in axial compressor

In axial-flow compressor journal written by Meherwan P. Boyce (2006)

stated that the calculation of the performance of an axial-flow compressor at both

design and off-design conditions requires the knowledge of the various types of

losses encountered in an axial-flow compressor. The accurate calculation and proper

evaluation of the losses within the axial-flow compressor are as important as the

calculation of the blade-loading parameter, since unless the proper parameters are

controlled, the efficiency drops. The evaluation of the various losses is a combination

of experimental results and theory. The losses are divided into two groups: (1) losses

encountered in the rotor, and (2) losses encountered in the stator. The losses usually

are expressed as a loss of heat and enthalpy. A convenient way to express the losses

is in a no dimensional manner with reference to the blade speed. The theoretical total

head available (totq ) is equal to the head available from the energy equation

( )th totq q− plus the head, which is loss from disc friction.

tot tot dfq q q= + (1)

The adiabatic head that is actually available at the rotor discharge is equal to

the theoretical head minus the heat losses from the shock in the rotor, the incidence

loss, the blade loadings and profile losses, the clearance between the rotor and the

shroud, and the secondary losses encountered in the flow passage

ia th in sh bl c sfq q q q q q q= − − − − − (2)

7

Therefore, the adiabatic efficiency in the impeller is

ia

tot

qimp

qη =

(3)

The calculation of the overall stage efficiency must also include the losses

encountered in the stator. Thus, the overall actual adiabatic head attained would be

the actual adiabatic head of the impeller minus the head losses encountered in the

stator from wake caused by the impeller blade, the loss of part of the kinetic head at

the exit of the stator, and the loss of head from the frictional forces encountered in

the stator

oa ia w ex osfq q q q q= − − − (4)

Therefore, the adiabatic efficiency in the stage

oa

tot

qstage

qη =

(5)

There are many losses that may occur in the axial compressor system. For the

example is disc friction loss. This loss is from skin friction on the discs that house the

blades of the compressors. This loss varies with different types of discs. The other

loss is incidence loss. This loss is caused by the angle of the air and the blade angle

not being coincident. The loss is at a minimum to about an angle of ± 4°, after which

the loss increases rapidly. Blade loading and profile loss. This loss is due to the

negative velocity gradients in the boundary layer, which gives rise to flow

separation. The loss is from skin friction on the blade surfaces and on the annular

walls and this is called a skin friction loss. Clearance loss. This loss is due to the

8

clearance between the blade tips and the casing. Wake loss. This loss is from the

wake produced at the exit of the rotary. Stator profile and skin friction loss. This loss

is from skin friction and the attack angle of the flow entering the stator. For the exit

loss the loss is due to the kinetic energy head leaving the stator.

2.4 Analysis using Finite Element Method (FEM)

The finite element method (FEM) is a numerical technique to find

approximate solutions of partial differential equations (PDE) as well as of integral

equations. This method also called finite element analysis. The solution approach is

based either on eliminating the differential equation completely (steady state

problems), or rendering the PDE into an approximating system of ordinary

differential equations, which are then solved using standard techniques such as

Euler's method, Runge-Kutta, etc.

There are many study cases and analysis had been carried out by using this

method. For the example, Wang Wei, Li Junfeng and Wang Tianshu (2008) had done

a modal analysis of liquid sloshing with different contact line boundary conditions

using finite element method. A finite element method (FEM) for liquid sloshing

modal analysis is established. Surface tension and three kinds of contact line

boundary conditions, namely, free-end, pin-end and wetting boundary conditions, are

taken into account.

Sloshing damping caused by energy dissipation at the wall, in the interior

fluid and at the contact line is calculated. Numerical results are compared with the

analytical values and measurements. For the pin-end and free-end boundary

conditions the differences between numerical value and analytical value are small,

and for the wetting boundary condition,because approximation is used, the

differences are more significant.

9

This finite element also has software to carry out the certain analysis. For

the example is MSC Nastran Patran. M. E. Stavroulaki, G. E. Stavroulakis and B.

Leftheris (1995) had conducted a structural analysis and optimization techniques

within the MSC/NASTRAN software for the analysis of optimal prestress restoration

of buildings. This analysis is done to alleviate admissible stress violations a

minimum prestress reinforcement is sought along with the position of the prestressed

elements. Prestressing is modelled by fictitious thermal loading on the linear (rod)

elements which model the prestressing cables (tendons). A quadratic cost function

for the prestressing cost with a penalty term that counts for stress violations is

assumed for the optimal prestressing problem. Certain aspects of the computer

implementation, including the use of mathematical programming and structural

optimization tools for large-scale structures, are included. The theory is illustrated by

numerical examples concerning the prestress restoration of a masonry wall subjected

to static loading.