creep testing on material

CREEP TESTING ONMATERlAL

L yruana Binti Johnny Yakop

Bachelor of Enginee ring with Honours

TA

(Mechanical Engineering and Manuf acturing Syst ems)

418.22 2004

L983

2004

Universiti Malaysia Sarawak

BORANG PENYERAHAN LAPORAN PROJEK TAHUN AKB1R

Judul: CREEP TESTING ON MATERIAL

SESI PENGA.IIAN: 200312004

LYDIANA BINT! JOHNNY YAKOP Saya

(HURUF BESAR)

mengaku membenarkan tesis ini disimpan di Pusat Khidmat Maklumat Akademik. Universiti Malaysia Sarawak dengan syarat-syarat kegtlOaan seperti berikut:

l. Hakmilik lapomn adalah milik penutis dan UNIMAS.

2. Naskhah salinan di dalam bentuk kertas atau mikro hanya boleh dibuat dengan kebenarnn bertulis daripada UNlMAS atau penulis.

3. Pusat Khidmat Maklumat Akaderuik, UNIMAS dibenarkan membuat salman uotuk pengajiao mereka.

4. Laporao hanya holeb diterbitkan dengan kebenaran penulis atau UNlMAS. Bayaran royaiti adalall mengikut kadar yang dipersetujui ketak.

5. ^>10 Saya memhenarlcanllidak ruembenarkan Pusat Khidmat Maklumat Akademik membuat salinan laporan ini

sebagai hahan pertukaran <Ii antara institusi pengajian tinggi.

6. ..'" SiJa tandakan ( v ) dj mana kotak yang berkenaan

D

^SULIT (Mengandungi maklumat yang berdaljab keselamatan atau kepentingan Malaysia seper1i yang termaktub di daJam AKTA RAHSlA RASMl 1972).

D

^TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan olell organisasil Badan <Ii mana penyelidikan dijaLankan).

~ TlOAK TERHAD

Disahkan oleb

~~

(T~AJlG~1\I^PENULIS)

Alamat tetap: NO 69, BATU 9,

JALAN MATANG, 93050,

PROF. MADYA DR SININ HAMDAN Nama Penyel..ia

APPROVAL SHEET

This project entitled 'Creep Testing On Mater/af' prepared by Lydiana bt Johnny Yakop as a partial fulfillment of the requirement for the Degree of Bachelor Mechanical Engineering and Manufacturing System is hereby read and approved by:

ASSOC ~RDR

SININ HAMDAN FIRST SUPERVISOR

MSl~

DR MOHD OSMAN SECOND SUPERVISOR

... ^~ ... , .. ... """Ii-JY.d _~iI~"""'1L tt. d\n::~11J

UNIVERSm MALAYSIA SARAWAJo 94~O(1 KOla Samarahan

CREEP TESTING ON MATERIAL

P.K HIDMATMAKLUMATAKADEMIK UIIMAS

1111111111111111111111111

1000125801

LYDIANA BT JOHNNY YAKOP

This project is submitted in partial fulfillment of

the requirements for the degree of Bachelor of Mechanical Engineering and Manufacturing Systems

Faculty of Engineering UNIVERSITI MALAYSIA SARAWAK

2004

Dedicated to my beloved family ,

11

ACKNOWLEDGEMENT

First and foremost, ALHAMDULLILLAH, I would like to express my grateful to ALLAH s.w.t , as I had manage to complete my fmal year project successfully. I would like to take this opportunity to thank numbers of people that have contributed direct or indirectly to my thesis project.

Million thanks to my supervisors, Associate Professor Dr. Sinin Hamdan and Dr. Mohd Shahril Osman who initiated the project and provide excellent guidance and support, and also valuable discussion during my work.

I also would like to thank the technicians at mechanical laboratory especially, Mr. Masri, Mr. Zaidi, Mr.Sabariman and the rest for the best cooperation and guidance when I was using the mechanical laboratory.

Last but not least, thank you to all my supportive friends and mechanical lecturers for creating a stimulating atmosphere at University Malaysia Sarawak.

Finally, I would like to thank my beloved family for the strong moral support given.

Once again, THANK YOU.

ABSTRACT

The works present the phenomenon of creep in wood where compression was studied experimentally at constant load. The testing model of wood berun with its apparatus was described. Research based on the investigation ofload levels used in creep testing response at elevated temperature and the moist condition were included as well. This investigation of different load levels was determined upon two experimentations that were conducted in two different environments. Thus, it was found that moisture content and high load on the specimen will runplifies creep more compared to specimen at elevated temperature. The in situ performance of a creep phenomenon was measured by frequent monitoring, which includes collecting data from the pressure effect towards specimen (which cause slow deformation), static load testing and inspection of the specimen. The results of the experimental were used herein to develop an analytical model for time-dependant response. The result analysis showed that a simple creep measurement can be created in situ.

IV

ABSTRAK

Kerja ini menunjukkan fenomena creep dalam kayu di mana eksperimen creep dijalankan secara pemampatan dengan daya beban yang tetap. Ujikaji model ialah bongkah kayu dengan alat radas seperti yang telah diterangkan. Kajian ini dijalankan untuk menyelidik ten tang daya beban berlainan yang digunakan dalam ujian creep terhadap persekitaran biasa dan keadaan yang lembap. Dua eksperimen telah dilaksanakan dalam dua keadaan yang berbeza. Keputusan menunjukkan bahawa keadaan yang lembap dan daya beban yang tinggi terhadap spesimen meningkatkan keputusan creep berbanding dengan spesimen dalam suhu persekitaran biasa. Analisa ujian creep dijalankan dengan kaedah pemerhatian melalui pengambilan data hasil dari tekanan ke atas spesimen ( menyebabkan kecacatan dalaman kayu yang perlahan ), daya statik ke atas beban dan penyeliaan ke atas spesimen. Keputusan eksperimen digunakan untuk membentuk sebuah model analitikal yang bergantung kepada reaksi masa. Hasil keputusan analisis menunjukkan bahawa penentukuran creep dapat dibuat dan dapat diaplikasikan di mana-mana.

· ,

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CONTENTS

Contents Pages

Borang Penyerahan Laporan Appoval Sheet

Thesis Title

Dedication ii

Contents V1

List of Figures V1l1

Acknowledgement III

Abstract iv

Abstrak v

List of Tables x

Chapter 1: Introduction

1.0 Introduction 1

1.1 Deformation in material 2

1.2 The occurance of creep 5

Chapter 2: Literature Review

2.0 Definition of creep 8

2.1 Stress-strain-time-temperature relationship 9

2.2 Creep test 11

2.3 Material aspect of creep design 13

2.4 Creep of non metal 16

2.4. 1 Creep in wood 16

Chapter 3 : Experimental Work

3.0 Introduction 19

3. 1 Experimental set up 19

vi

3.1.1 Creep experimentation in normal environment 19 3.1.2 Creep experimentation in moisture condition 27

Chapter 4: Experimental Results and Discussion

4.0 Introduction 29

4.1 Results of experimentation in normal condition 29

4.1.1 First experiment (3 kN- 4 kN) 30

4.1.2 Second experiment (4 kN-5 kN) 33

4.1.3 Third experiment (5 kN-6 kN) 35

4.2 Results of experimentation in moisture condition 37 4.2.1 First experiment (3 kN- 4 kN) 37 4.2.2 Second experiment (4 kN- 5 kN) 39 4.2.3 Third experiment (5 kN-6 kN) 41

4.3 Results Discussion 43

Chapter 5: Conclusion and Recommendation

5.0 Conclusion 47

5.1 Recommendation 48

References 49

Appendices

Appendix A: Graph results 51

Appendix B : Load cell test sheet 57

LIST OF FIGURES

List of Figures Pages

1.0 Types of fracture; i)brittle, ii) ductile 4 1.1 The stages of fatigue failure. The ultimate fracture 5

is crystalline

1.2 A tungsten lightbulb filament sagging under its own 6

and can lead to touching of adjacent coils, which causes bulb failure.

weight. The deflection increases with time due to creep

2.0 Accumulation of creep strain with time under constant 10 stress, and partial recovery after removal of the stress

2. 1 Typical creep curve showing the three stages of creep during 11 a long time, high temperature creep test

2.2 Creep test setup 12

2.3 Mechanism of creep by diffusion of vacancies within a 15 crystal grain

2.4 Adjustment of working stresses for various durations 17 of load application.

3.0 The Jelutong wood specimen 20

3. 1 The specimen is compressed in radial direction 21 3.2 Example of graph result from Testometric machine 21

where it stops compressing at 579.20 kgf

3.3 Schematic diagram of creep experimentation in normal 23 environment

3.4 The load cell with its connector 23

3.5 Pico Technology 24

3.6 Example of graph result from Pico Oscilloscope 24

Vlll

3.7 Example of graph force versus time 25

3.8 Example of creep graph 25

3.9 The plate steel to cover the upper area of specimen 26 3.10 The load cell gives even distributed load 26 3.11 Schematic diagram of creep experimentation in 27

moisture environment

3.12 The specimen is immersed in the water but the load 28 cell is not immersed in the water

4.0 Results for load imposed 3 kN- 4 kN in Normal Environment 32 4.1 Results for load imposed 4 kN- 5 kN in Normal Environment 34 4.2 Results for load imposed 5 kN- 6 kN in Normal Environment 36 4.3 Results for load imposed 3 kN- 4 kN in Moisture Environment 38 4.4 Results for load imposed 4 kN- 5 kN in Moisture Environment 40 4.5 Results for load imposed 5 kN- 6 kN in Moisture Environment 42

4.6 Compression perpendicular to grain 44

4.7 Comparison in creep graph between Normal and 46 Moisture environment

LIST OF TABLES

List of tables Pages

4.0 The initial value of first experiment in normal condition 30 for calibration purpose

4.1 The initial value of second experiment in normal condition 33 for calibration purpose

4.2 The initial value of third experiment in normal condition 35 for calibration purpose

4.3 The initial value of first experiment in moisture condition 37 for calibration purpose

4.4 The initial value of second experiment in moisture condition 39 for calibration purpose

4.5 The initial value of third experiment in moisture condition 41 for calibration purpose

x

CHAPTER 1

INTRODUCT ION

CHAPTER 1

INTRODUCTION

1.0lNTRODUCTION

Broadly, in engineering components, failure occurs either mechanically or by some form of corrosive attack. The study of deformation and cracking in materials is called mechanical behaviour of materials. Knowledge of this area provides the basis for avoiding these types of failure in engineering application.

In the identification of failure, it is necessary to recognize the failure mechanism and any relationship with the structure, compositional characteristic or design of the material component which may be revealed. The possible failure mechanisms of failure are brittle and ductile fracture, fatigue (high or low cycle).

creep, buckling or other forms of instability. In the recognition of these mechanisms, investigation techniques are carried out to examine the region of deformation, the fracture surface, the composition and mechanical properties of associated material. On the other hand, failure in components must be avoided entirely, or strictly limited, so that it does not progress to the point of complete failure.

1

Creep is a defonnation that occurs over a period of time. Under certain condition it will, if allowed to do so, culminate into fracture. Creep is the result of an externally applied load but can also occur as the result of self weight. Creep behaviour can be summarise as; the higher the temperature and the stress, the creep rate is greater.

In this thesis, works will be carried out to investigate creep behaviour in material which involved mechanical testing and building a system for creep measurement.

1.1 DEFORMATION IN MATERIAL

In reference [ I ], deformation in material occur for a number of reasons, such as external loads, change in temperature, tightening of bolts, irradiation effects, etc. Bending, twisting, compression torsion and shear or combination or these are common modes of defonnation.

However, in manufacturing operations, many parts are fonned into various shapes by applying external forces to the workpiece by means of tools and dies.

Hence, an understanding of the behavior of materials in response to externally applied forces is important.

values of forces, it may result in material permanent deformation without fracture and, for low enough forces, the material may deform only in an elastic way.

When load is subjected to a structural member, its response depends not only on the type of material from which it is made but also on the environments condition and the manner of the loading. Depending on how the member is loaded, it may fail by excessive deflection, which results in the member being unable to perform its design function. Reference [3], also demonstrate the more important potential causes of failure which can be examined quantitatively such as brittleness, creep, fatigue and chemical influence of the environment in which the component is operating.

Fracture can be classified as either 'brittle ' or 'ductile' and the mode of fracture produced is governed by the stress at which it occurs in relation to the elastic/plastic properties of the material. Brittle material failure occur before any appreciable plastic deformation can take place by shear. Ductile fracture takes place at some stress above the shear strength of the material so that some plastic flow precedes fracture. Figure 1.0 shows the above mentioned behavior.

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Figure 1.0: Types of fracture; i) brittle , ii) ductile

Fatigue refers to the failure of material under changing stress or under repeated fluctuating stresses. Fatigue failure develop in three stages, nucleation, crack growth and ultimate failure. Figure 1.1 shows the three stages. The crack propagation is sudden and catastrophic which lead to ultimate fracture when the unbroken portion is no longer able to sustain the load.

At high temperature, material can flow plastically and eventually fracture under conditions of a constant applied stress. Creep is defined as the continuing permanent deformation with time at a fixed stress. Creep deformation and fracture are both related to thermally assisted deformation processes that provide for and

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Figure 1.1 : The stages of fatigue failure. The ultimate fracture is crystalline

This projects will dealt on creep behaviour of material. Creep behaviour in material are often neglected in design process. This is due to the behaviour which depends on prolonged period of time to occur. In subsequent chapter, the detail of the experiment performed and the results will be presented.

1.2 THE OCCURANCE OF CREEP

Creep is a concern for engineers in the design of bridges, buildings, and other permanent structures in which the structural members have relatively large dead or static loads. Creep is also a function of temperature. The higher the temperature, the faster the materials will creep under the same loads. These facts lead to several methods of determining the amount of creep a beam or other part will undergo over a period of time [4).

Creep is often an important problem when high temperature is encountered, such as in gas-turbine aircraft engines. An example of creep failure is buckling which can occur in a time - dependent manner.

5

Another example of an application involving creep deformation is the design

,

of tungsten lightbulb filaments. Sagging of the filament coil between its support increases with time due to creep deformation caused by the weight of the filament itself. If too much deformation occurs, the adjacent turns of the coil touch one another, causing an electrical short and local overheating, which quickly leads to failure of the filament. The coil geometry and supports are therefore designed to limit the stresses caused by the weight of the filament, and a special tungsten alloy that creeps less than pure tungsten is used [5[.

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Figure l.2: A tungsten lightbulb filament sagging under its own weight. The deflection increases with time due to creep and can lead to touching of adjacent coils, which causes bulb failure

Another evidence of creep are windows in old churches in Europe are thinner at the top than at the bottom has been attributed to the creep of the glass under the effect of gravity. Today, engineers and scientists confront creep in energy -producing systems such as power-generating plants (coal, gas and nuclear plants).

Creep also occurs in energy conversion systems, such as thermionic converters, and in modem day applications of electronic packaging that involve the heat transfer and cooling of microcircuit (microelectronic chips, electronic circuit boards, solder joints ,etc) [6].

Some materials such as plastics and rubber exhibit creep at room temperatures but most structural materials require high temperature or long duration loading at moderate temperatures. In some 'soft' metals, such as zinc and lead, creeps occurs over a relatively short period of time whereas materials such as concrete may be subject to creep over a period of years. Creep occurs in steel to a slight extent at normal temperatures but becomes very important at temperature above 316'C [7] .

Creep is especially important in high - temperature applications, such as gas turbine blades and similar components in jet engines and rocket motors. High pressure steam lines and nuclear -fuel elements are also subject to creep. Creep deformation can also occur in tools and dies that are subjected to high stresses at elevated temperatures during hot working operations, such as forging and extrusion [8].

7

There is circumstances in which the possibility of creep rupture may safely be neglected in which the service condition involves stress relaxation. The simplest example is a screwed fastener. When two articles are clamped together by a bolt and nu t, the clamping force is provided by the elastic extension of the shank of the bolt as the nut is tightened down. The stress is progressively relaxed and as it does so the danger of fracture recedes. Of course, the clamping force simultaneously decreases and bolts on equipment such as pressure vessels which operate under creep conditions must regularly be retightened, and if this is done often enough, rupture again becomes a hazard 191.

CHAPTER 2

LITERATURE R EVIEW

CHAPTER 2

LITERATURE REVIEW

2.0 DEFINITION OF CREEP

Creep in nonmetal is a topic of major

imp

ortance in the engineering design of advanced technology, such as chemical p

lant,

gas turbine

, and power

generation plant.

As mentioned before, creep is the occurrence of time - dependent strain in a

loaded

structural

me

mber, normally at elevated temperatures. Creep deform ation

continues until the part

fails

because of e

ither

excessive deformation or creep

rupture. Besides that, creep is an inelastic

action. If

the mechanism of creep is

operating, the strain or elongation continues as

long

as the

load

is present

.

The

strain continues to increase even though the stress has become constant which

result

in a great number of stru

ctural

materials continue to deform slowly and

progressively under load over a period of time.

To

be precise, creep

is the

permanent elongation of a component under a static load maintained for a period of