ANALYSIS ON BICYCLE CRANK ARM USING TENSILE TEST

SHAIFATUL SHIMA BINTI SHAARI

This report is submitted in partial fulfillment of the requirement for the

Degree of Bachelor of Mechanical Engineering

(Design & Innovation)

Faculty of Mechanical Engineering

Universiti Teknikal Malaysia Melaka

APRIL 2010

“I hereby declared that I have read through this report and found that is has comply the

partial fulfillment for awarding the degree of Bachelor of Mechanical Engineering

(Design & Innovation)

Signature : ……………………………………….

Supervisor’s I Name : ……………………………………….

Date : ………………………………………..

i

ACKNOWLEDGEMENT

Assalamualaikum, firstly I would like to thanks God because on his mercy I

finally able to complete my final year project of Analysis on Bicycle Crank Arm

Using Tensile Test. I would like to express my deepest appreciation to my supervisor

Mr Asri Bin Yusuff, and also for his invaluable support, guidance, encouragement,

criticism, and insight throughout the research. It was a great pleasure for me to work

with him. And also to Miss Siti Nor Baya Binti Sahadan as my mentor for helped me

to finished up this project.

For many valuable encouragements and discussions on my project, I am

indebted to my colleagues at Universiti Teknikal Malaysia Melaka (UTeM), who has

also involved during the project. I am also grateful to all technicians from structure

department especially to Mr Rashdan Bin Seman who has been an indefatigable

advisor; teach the procedure for my experiment which include to handling the

machine and all the equipment in the laboratories for helping me in my final year

project.

I would like thanks to UTeM for its facilities and resources mainly in the

library, laboratory and their up-to-date equipment. It has indeed been a great help for

me in reducing my expenses and obtaining precise reading and measurement for my

research.

ii

ABSTRACT

The mechanical properties of a material are directly related to the response of

the material when it's subjected to mechanical stresses. The results of tensile tests are

used in selecting materials for engineering applications. Tensile properties frequently

are included in material specifications to ensure quality. Tensile properties often are

measured during development of new materials and processes, so that different

materials and processes can be compared. Since characteristic phenomena or

behavior occur at discrete engineering stress and strain levels, the basic mechanical

properties of a material are found by determining the stresses and corresponding

strains for various critical occurrences. A wealth of information about a material's

mechanical behavior can be determined by conducting a simple tensile test for

bicycle crank arm of uniform cross-section is pulled until it ruptures or fractures into

separate pieces. Finally, tensile properties often are used to predict the behavior of a

material under forms of loading other than uniaxial tension. This mechanical testing

was done by using Instron 8802 Dynamic Machine. Based on the initial geometry of

the sample, the engineering stress-strain behavior (stress-strain curve) can be easily

generated from which numerous mechanical properties, such as yield strength and

elastic modulus, can be determined. The major parameters that describe the stress-

strain curve obtained during the tension test are the tensile strength (UTS), yield

strength or yield point (σy), and elastic modulus (E). By using the X-Ray

Diffractormeter, it can determine the types of material which include in the bicycle

crank arm.

.

iii

ABSTRAK

Sifat-sifat mekanikal sesuatu bahan adalah berkaitan dengan terus untuk

tindak balas bahan tersebut apabila ia di bawah beban mekanikal. Keputusan-

keputusan ujian tegangan adalah digunakan sebagai pemilihan bahan-bahan untuk

aplikasi kejuruteraan. Ciri-ciri tegangan sering didapati dalam setiap bahan yang

terkandung bagi menentukan kualiti bahan tersebut. Ia juga kerap diukur semasa

membuat sesuatu bahan baru dan proses supaya bahan dan proses yang berbeza dapat

dibandingkan. Sejak fenomena tekanan kejuruteraan ini berlaku pada peringkat

terikan, sifat-sifat mekanikal asas sesuatu bahan di temui bagi menentukan beban dan

tegangan yang sesuai untuk pelbagai keadaan kritikal. Banyak maklumat tentang

sifat-sifat mekanikal bahan boleh ditentukan dengan menjalankan satu ujian tegangan

mudah terhadap lengan engkol basikal. Keratan rentas seragam di tarik sehingga ia

pecah atau retak kepada keping-keping berasingan. Akhir nya, ciri-ciri tegangan di

gunakan untuk meramalkan sifat sesuatu bahan. Ujian mekanik ini di lakukan

dengan menggunakan Mesin Instron 8802 Dynamic. Berdasarkan geometri awal

sampel tersebut, sifat mekanikal ketegangan tekanan (lengkung tegasan-terikan)

boleh dibina dengan mudah di mana banyak sifat-sifat mekanikal boleh di perolehi ,

seperti kekuatan alah dan modulus kenyal boleh ditentukan. Parameter utama yang

dapat di huraikan adalah lengkung tegasan-terikan yang diperolehi semasa ujian

tegangan kekuatan tegangan (UTS), kekuatan alah atau takat alah (σy),dan modulus

kenyal (E). Dengan menggunakan X-Ray Diffractormeter, ia dapat menentukan jenis

bahan yang terkandung dalam lengan engkol basikal.

iv

LIST OF CONTENTS

CHAPTER TITLE PAGES

ACKNOWLEDGEMENT i

ABSTRACT ii

LIST OF CONTENTS iv

LIST OF TABLES vi

LIST OF FIGURES vii

LIST OF SYMBOLS xi

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.2 Objectives 5

1.3 Problem Statement 5

1.4 Scope of the Research 6

CHAPTER 2 LITERATURE REVIEW

2.1 An Overview of Metal Structure 8

2.2 Introduction to Material Testing and Mechanical

Properties of Metal Structure 14

2.3 Fatigues in Metal Structure. 14

2.4 Bicycle Crank Arm 19

v

CHAPTER 3 METHODOLOGY

3.1 Introduction 22

3.2 Material and Specimen Preparation 24

3.3 Method of Mechanical Testing 26

3.4 Method of Calculation 40

3.5 Material Analysis via X-Ray Diffractormeter 44

(XRD)

CHAPTER 4 RESULT AND DISCUSSION

4.1 Introduction 48

4.2 Result of Tensile Test 48

4.3 Result of X-Ray Diffractormeter (XRD) 59

CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Conclusion 60

5.2 Recommendation 62

REFERENCES 63

BIBLOGRAPHY 64

APPENDICES 67

vi

LIST OF TABLE

BIL TITLE PAGES

1.1 Gantt chart PSM 2 7

3.1 INSTRON 8802 Machine Specification 27

(Source: UTeM Laboratory)

4.1 Experimental Data for bicycle crank arm under Tensile Test 51

vii

LIST OF FIGURE

BIL TITLE PAGES

2.1 Flow for different types of material 9

(Source: Mortimer, 1975)

2.2 Typical fatigue-failure surfaces. 16

(Source: Chalmers, B. 1986)

2.3 Intrusion-extrusion model of fatigue crack initiation. 17

(Source: Roylance, D. 2001)

2. 4 Part of Bicycle 19

(www.wikipedia.com)

2.5 Flow of Mechanical Properties of Composite Material 21

(Source: Minak, (2008))

viii

3.1 Process Flow Chart of Research 23

3.2 Flow of Material Preparation 24

3.3 Part of Bicycle Crank Arm 25

(Source: www.wikipedia org)

3.4 Instron 8802 Machine 26

(Source: UTeM Laboratory)

3.5 Extensometer 28

(Source: www.tensiletest.com)

3.6 Schematic illustration showing how the sample is tested using

extensometer 29

(Source: www.composite.tensile.com )

3.7. Bicycle Crank Arm 32

(Source: UTeM Laboratory)

3.8 Measurement and marked the specimen 32

3.9 Bicycle crank arm with the pin insertion 33

ix

3.10 Position of bicycle crank arm during tensile test 33

3.11 Side view of bicycle crank arm 34

3.12 A close up view of bicycle crank 34

3.13 BLUEHILL Software 35

3.14 Example of graph to show the point of yield point,

Maximum load and load at break 42

3.15 X-Ray Diffractormeter Machine (XRD) 44

3.16 Specimen on the stage 47

3.17 Machine in operation 47

4.1 Bicycle Crank Arm before Tensile Testing 50

4.2 Bicycle Crank Arm after Tensile Testing 50

4.3 A close up view of the bicycle crank arm before and after

tensile test 50

4.4 Graph of Load, kN versus extension, mm under tensile test for

bicycle crank arm 52

x

4.5 Graph of Stress, MPa versus Strain, % under tensile test for

bicycle crank arm. 53

4.6 Graph Stress, MPa versus Strain, % under tensile test for

bicycle crank arm with other value 54

4.7 The region of stress-strain curve for bicycle crank arm under

tensile test 57

xi

LIST OF SYMBOLS

є = True Strain

σ = True Stress, Pa

S = Engineering Stress, Pa

e = Engineering Strain

P = Load, N

A = Area, m2

L = Length, m

l0 = Original Gage Length, m

lf = Final Gage Length, m

tf = Final Thickness, m

E = Modulus Elasticity

σ UTS = Ultimate Tensile Strength

1

CHAPTER 1

INTRODUCTION

1.1 Introduction

Failure of material means the progressive or sudden deterioration of their

mechanical strength because of loadings or thermal or chemical effect.All materials have

different properties that result in advantages and disadvantages. Study and understanding

of these properties is critical to the design of a mechanical system and the selection of

the correct materials for a given part. One crucial failure mode is fatigue. Fatigue is the

weakening or failure of a material resulting from prolonged stress. The strength of a

material is its ability to withstand an applied stress without failure. Yield strength refers

to the point on the engineering stress-strain curve (as opposed to true stress-strain curve)

beyond which the material begins deformation that cannot be reversed upon removal of

the loading. Ultimate strength refers to the point on the engineering stress-strain curve

corresponding to the maximum stress. The applied stress may be tensile, compressive, or

shear.

2

The selected material was choosing is crank arm for paddle bicycle.

This material is structural material which consists of combining two or more

constituents. Normally, cranks are constructed of an aluminum alloy, titanium, carbon

fiber, chromoly steel, or some less expensive steel.This crank arm is the component of

the bicycle that transfers the force exerted on the pedals to the crank set. Crank arms can

crack in a number of places. Sometimes a crack will develop between the pedal

mounting hole and the end of the arm. A crack also will develop at the crotch of the

chaining-mounting arms (spider arms) and the crank arm.

The effects of dynamic loading are probably the most important practical part of

the strength of bicycle crank arm, especially the problem of fatigue. Repeated loading

often initiates brittle cracks, which grow slowly until failure occurs. However, the term

strength of materials most often refers to various methods of calculating stresses in

structural members. The methods that can be employed to predict the response of a

structure under loading and its susceptibility to various failure modes may take into

account various properties of the materials other than material (yield or ultimate)

strength.

In basic, tensile stress is the stress state caused by an applied load that tends to

elongate the material which is bicycle crank arm in the axis of the applied load,

in other words the stress caused by pulling the material. The strength of structures

of equal cross sectional area loaded in tension is independent of cross section geometry.

Materials loaded in tension are susceptible to stress concentrations such as

material defects or abrupt changes in geometry. However, materials exhibiting

ductile behavior (metals for example) can tolerate some defects while brittle

materials (such as ceramics) can fail well below their ultimate stress.

3

Most crucial structures subjected to fatigue failures in metallic structure are a

well-known technical problem. It is of great importance for engineers the time a fatigue

crack will take to grow from initial size to the critical value in designing structures and

determining inspection intervals. Failures apparently occurred without any previous

warning.

Fatigue of materials is a well known situation whereby rupture can be caused by

a large number of stress variations at a point even though the maximum stress is less

than the proof or yield stress. The fracture is initiated by tensile stress at a macro or

microscopic flaw. Once started the edge of the crack acts as a stress raiser and thus

assists in propagation of the crack until the reduced section can no longer carry the

imposed load. While it appears that fatigue failure may occur in all materials, there are

marked differences in the incidence of fatigue.

The total fatigue life of a component can be divided into three phases which is

crack initiation, crack propagation and fracture.After a certain number of fluctuations,

the accumulated damage cause the initiation and subsequent propagation of crack in the

plastically damage regions. This process can many cases does cause the fracture of

components. The more severe the stress concentration, the shorter the time to initiate the

fatigue crack.

4

By using the INSTRON machine it is to determine the mechanical properties of

bicycle crank arm by mechanical testing which is tensile test. From this method to

measure the strength of crank arm. This is to obtain the yield strength of each specimen.

The data will be collected using software BLUEHILL. From the graph, it also can

determine the yield point, % elongation, maximum load, strength of the material, and

also can develop the stress and strain graph. In this research, the tensile test with

constant load is utilized use to discuss the affect of the structure and the strength of the

bicycle crank arm.

5

1.2 Objectives

The objectives of this research are:

a) Learn to conduct an experiment related with tensile test.

b) To analyze the effect of constant load to the bicycle crank arm structure.

c) To study and analyze the material properties of the bicycle crank arms.

1.3 Problem Statement

This research has been carried out due to the strength of material for the selected

material which is bicycle crank arm. The bicycle crank arm is one of the bicycle parts

which received high load. Analysis need to be done to figure out the maximum load

capacity that the crank arm could stand. The tensile test was conducted to measure the

strength of this material under constant load. Due to the matters set out above, this study

will analyze the strength of bicycle crank arm structure under constant loading.

6

1.4 Scope of the Research

This research comprises of the following scope:-

a) To do literature study on metal structure.

b) To carry out tensile test on bicycle crank arm.

c) To anaylize affect to the structure

d) To carry out analyze the experiment data analysis after tensile test.

e) Conclusion and suggestion for future study.

7

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8

CHAPTER 2

LITERATURE REVIEW

2.1 An Overview of Metal Structure.

Material can be anything a finished product in its own right or an unprocessed

raw material. Raw materials are first extracted or harvested from the earth and

divided into a form that can be easily transported and stored, then processed to

produce semi-finished materials. These can be input into a new cycle of production

and finishing processes to create finished materials, ready for distribution,

construction, and consumption. In chemistry materials can be divided into two which

is metals and non metals. [1]

All elements of the world, based on their physical and chemical properties,

are divided into solids, liquids, and gases. Solids can be of two types which is metals

and non metals. This grouping is done mainly on the basis of their physical

properties. Metals are usually elements in solid form that have a shiny body surface.

They are tough, and some are malleable while others are ductile. Most metals are

good conductors of heat. Most of them are also good conductors of electricity. [1]

9

2.1.1 Types of Metal

This is one of the three groups of elements in materials. Some metals and

metal alloys possess high structural strength per unit mass, making them useful

materials for carrying large loads or resisting impact damage. Metal be divided into

three which is ferrous, non ferrous and alloys. [2]

In this research the main objective is

to analyze the metal structure.

Figure 2.1: Flow for different types of material

(Source: Mortimer (1975))

Thermoplastic

Polystyrene

Acrylic

Thermo sets

Melamine

Epoxy Resin

Ferrous

Mild steel

Tool steel

Stainless steel

Cast iron

Non-Ferrous

Aluminum

Brass

Copper

lead

Alloys

Aluminium alloys

Brass

Steel

Solder

Materials

Metal Ceramic Polymer

Crystalline

ceramics Non-Crystalline

ceramics

10

2.1.1.1 Ferrous

Ferrous metals are those metals which contain iron. They may have small

amounts of other metals or other elements added, to give the required properties. All

ferrous metals are magnetic and give little resistance to corrosion. Most commonly

used ferrous metals are mild steel, high speed steel, stainless steel, high tensile steel

and cast iron. [1]

2.1.1.2 Non-Ferrous

Non ferrous metals are those metals which does not contain iron. They are

not magnetic and are usually more resistant to corrosion than ferrous metals. Most

commonly used non ferrous metals are aluminium, copper, brass, lead, tin, gilding

metal and zinc. [1]

2.1.1.3 Alloys

An alloy is a mixture of two or more metals. When a material is needed

which requires certain properties and this does not exist in a pure metal we combine

metals. Pure white aluminium is very soft and ductile. Other elements can be added

to create an aluminium alloy. This can produce a metal which is stronger than mild

steel has improved hardness and is resistant to corrosion while still remaining light in

weight. By changing the properties to form alloys, metals can be easily bent, twisted,

welded and also stretched. [1]

11

2.1.2 Metallic Properties.

Metals are usually shiny solids with high melting points and are very good

conductors of heat and electricity. They are malleable, so they can be beaten into

sheets, and ductile, which means they can be drawn into wires. Most are strong and

cannot be broken easily. Mercury, for example, is a metal that has a low boiling point

and is liquid at room temperature. [1]

In general metal have:

1. Density

2. Ductility

3. Thermal Conductivity

4. High electric

2.1.2.1 Density

The high density of most metals is due to the tightly-packed crystal lattice of

the metallic structure. The strength of metallic bonds for different metals reaches a

maximum around the centre of the transition series, as those elements have large

amounts of delocalized electrons in a metallic bond. [1]