Modification, Design And Construct A Laboratory Scale Fatique Testing Machine

ABSTRACT

This work is on modification, design and fabrication of a fatigue testing machine. Many engineering machines and mechanical components are subjected to fluctuating stresses, taking place at relatively high frequencies and under these conditions failure is found to occur. This is called fatigue failure. And this led to the invention of a fatigue testing machine. In view of effective design that will not fail accidentally, this research is conceived. This testing machine will determine the strength of materials under the action of fatigue load. Specimens are subjected to repeated varying forces or fluctuating loading of specific magnitude while the no. of cycles are counted till the breakage of specimen and results are plotted.

TABLE OF CONTENTS

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

1.0      INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

1.2      PROBLEM STATEMENT

1.3      AIM AND OBJECTIVES OF THE PROJECT

1.4      SCOPE OF THE STUDY

CHAPTER TWO

2.0     LITERATURE REVIEW

2.1      OVERVIEW OF THE STUDY

2.2      CHARACTERISTICS OF FATIGUE

2.3      REVIEW OF FATIGUE TEST

2.4      TYPES OF FATIGUE TEST

2.5      CLASSIFICATION OF FATIGUE TESTING MACHINE

2.6      REVIEW OF RELATED STUDIES

CHAPTER THREE

3.0     METHODOLOGY

3.1      DESIGN FLOW CHART

3.2     MATERIAL SELECTION

3.3      CONSTRUCTION FOR THE CHOICE OF MATERIALS CAST

3.4      WORKING PRINCIPLE

3.5      COMPONENTS OF FATIGUE TESTING MACHINE

3.6      DESIGN AND CALCULATIONS OF MACHINE COMPONENTS

CHAPTER FOUR

4.0      RESULT ANALYSIS

4.1     RESULTS AND DISCUSSION

4.2      RESULTS

CHAPTER FIVE

5.0      CONCLUSION

5.1      RECOMMENDATION

5.2      REFERENCES

CHAPTER ONE

1.0                                                      INTRODUCTION

1.1                                        BACKGROUND OF THE STUDY

Isaac Newton wrote to Robert Hooke “If I have seen further, it is because I have stood on the shoulders of giants. Since, the first research on metal fatigue began in the 18 th century, a very large number of researchers from all over the world have contributed to the knowledge base that has been amassed. Some workers have contributed to the characterization of fatigue failures, the discovery of the mechanisms of fatigue, and the testing of materials. Other researchers have contributed by adding to the theoretical and mathematical models that allow us to make predictions about how components will behave in the future when subjected to periodic loading under different conditions. Preliminary understanding about fatigue failure of metals developed in 19th century during industrial revolution in Europe when heavy duty locomotives, boilers, etc. failed under cyclic loads. It was William Albert who in 1837 first published an article on fatigue that established a correlation between cyclic load and durability of the metal. Two years later in 1839, Jean-Victor Poncelet, designer of cast iron axles for mill wheels, officially used the term fatigue for the first time in a book on mechanics. Some pioneering work followed from

August Wöhler during 1860-1870, when he investigated failure mechanism of locomotive axles by applying controlled load cycles. He introduced the concept of rotating-bending fatigue test that subsequently led to the development of stress-Number of cycles (S-N) diagram for estimating fatigue life and endurance or fatigue limit of metal, the fatigue limit representing the stress level below which the component would have infinite or very high fatigue life. By the end of 19th century, Gerber and Goodman investigated the influence of mean stress on fatigue parameters and proposed simplified theories for fatigue life. Based on these theories, designers and engineers started to implement fatigue analysis in product development and were able to predict product life better than ever before. At the beginning of the 20th century, J. A. Ewing demonstrated the origin of fatigue failure in microscopic cracks. In 1910, O.H. Baskin defined the shape of a typical S-N curve by using Wöhler's test data and proposed a log-log relationship.

Birth of fracture mechanics took place with the work of Alan A. Griffith in 1920 who investigated cracks in brittle glass. This promoted understanding of fatigue since concepts of fracture mechanics are essentially involved in fatigue crack characteristics. However, despite these developments, fatigue and fracture analysis was still not regularly practiced or implemented by the designers. Importance of the subject was finally realized when serious accidents took place around World War II in 20th century that spurred full-fledged research work on the subject. Fatigue research is truly a multidisciplinary field that incorporates:

Mechanical engineering expertise to understand the stresses and strains to components are subjected;

Materials science expertise to understand how the stresses and strains affect, and are affected by, the microstructure of the components; and statistical expertise to recognize and mathematically describe the microstructures, loads, and geometries of the components that are all inherently variable, and how these variability will affect the fatigue behaviour of an individual component, or a fleet of components.

The first person to observe and report what we now know as metal fatigue was a German mining administrator named Wilhelm Albert. He investigated the failure of mine hoist chains. He then built a machine which subjected lengths of chain to repeated loads of up to 100,000 cycles. He authored the first paper on metal fatigue in 1838.

The importance of fatique in transportation was well established by the 1850’s. The failure of axles of both horse drawn and railroad carriages were investigated by Arthur Morin in France, and William Rankine and J.O. York in Great Britain. The actual usage of the term “fatigue” has been attributed to most often to Jean-Victor Poncelet, but also to Morin, Frederick Braithwaite, and his colleague Mr. Field. Whoever coined the term, the historical record is clear that by the mid-19 th century, it was already well-established that fatigue was a significant problem in allmodes of transportation, and in many industries as well.

Unfortunately, it is often catastrophic accidents that provide the impulse and direction of fatique testing and research. One of the first accidents that spurred the growth and direction of fatique research was the famous railroad mishap that occurred in 1842, on the railroad from Versailles to Paris, France. While transporting revelers back to Paris from King Louis Phillipe I’s birthday celebration at Versailles, a locomotive suffered an axle failure, which caused a derailment. The trailing carriages ran into the engine, and they all caught fire. The crash killed over 60 people, and was the one of the worst railroad accidents that occurred during the 19th century. A failure analysis investigation was conducted by Rankine, who found brittle cracking of the shaft. Railroad mishaps, many caused by fatigue failures, were so commonplace that newspapers in Great Britain were reporting “the most serious railway accidents of the week” even into the late 1880’s. By the mid 1800’s, several engineers in the British railroad industry had conducted tests of axles and members used in railroad bridges, and had already determined that even a load of half the ultimate strength of iron and steel components was sufficient to cause failure of metal components. They had also created a predecessor to what engineers now call the endurance limit or “safe life” of components used in the railroad industry.

1.2                                               PROBLEM STATEMENT

Basically, the problem of fatique of materials has led to the break-down of machines or other mechanical produced equipment because the strength or durability of the individual materials are not tested before being put to work. The idea behind this research is not to provide answers to the unanswered questions but to solve the difficulty in answering them from different perspective.

This involves defining the unpredictable nature of fatique failure by conducting tests on various specimens and explains the known techniques of fatique testing.

1.3                                 AIM AND OBJECTIVES OF THE STUDY.

The aim of this study is to modify, design and construct a laboratory scale fatigue testing machine. The specific objectives of the laboratory scale fatique testing machine are:

1. To determine the strength of materials under the action of fatique load.
2. To build the low cycle fatique testing machine with low cost.

• To get the fatique strength of the material for research people or student laboratory work.

1.4                                                SCOPE OF THE STUDY

The scope of this study is to efficiently and effectively develop a means of testing the fatique of a material (metal) in a laboratory by means of a scale. This study is bounded to bringing about the use of switch to on/off the machine with the use of an A.C/electric motor in powering speed of the machine. The required load is set on the spring load by adjusting the nuts below with the springs load mechanism and the supply is turned ON. With help of the digital counter to count and reset its value when a material fails and a reload is done in a repetitive manner for different load specimen.

1.5                                        SIGNIFICANCE OF THE STUDY.

This study will be of great significant endeavour in promoting good work in the laboratory, small enterprise and in the industries. Provision of this study will maximize the efficient use of time in the laboratories for academic work.

The fatigue testing machine helps to determine a material ability to withstand cyclic fatique loading condition. By the design, a material is selected to meet or exceed service loads that are anticipated to fatique testing application. This study provides a great aid to students in carrying out their experiments in the laboratory providing them with a portable, easy and well learnt machine principles of carrying out research on the strength of materials for their course work.

More so, it is easily constructed, saves cost (low cost of production) and finally every engineering laboratory can have one because of its suitability for tensile, compression and alternating load test. Thus, this study is aimed also to provide easy maintenance and repair, easy handling and movement of machine and finally yield an improved output for the laboratory.