ABSTRACT
The process involved in the design and fabrication of a creep material testing equipment ranges from carrying out the feasibility studies of the project to the designed and especially of ensuring its functionality. Since it is used in the testing of failure of material under loading, different engineering principles employed in the design and fabrication includes bending moments and deflection of beam etc. the main objective of this project is to design a mechanical structure that can test the failure of substance hence creep s defined as the failure of substance under continuous loading. It also involves the cutting of the specimen that will be used to conducting the test. After the completion of the different components of the machine, it is assembled and a test turn conducted. As a result, it was finally observed that creep material testing equipment is used in determining the failure of material under continual loading.
TABLE OF CONTENTS
CHAPTER ONE
1.0 INTRODCUTION
CHAPTER TWO
2.0 DESCRIPTION OF APARATUS AND DESIGN THEORY
CHAPTER THREE
CHAPTER FOUR
4.0 FABRICATION
4.10 EXPERIMENTAL PROCEDURE AND RESULT
4.11 LEAD SPECIMEN AT OTHER TEMPERATURES
4.12 METHOD OF ASSEMBLY
4.13 PRINCIPAL OF OPERATION
CHAPTER FIVE
5.0 BILL OF QUANTITIES
CHAPTER ONE
INTRODUCTION
When a material like steel is plastically deformed at ambient temperature, its strength is increased due to work hardening. This work hardening effectively prevents any further deformation from taking place if the stress remains approximately constant. Annealing the deformed steel at an elevated temperature removes the work hardening and restores the steel to its original condition. However, if the steel is plastically deformed at an elevated temperature, then both work hardening and annealing takes place simultaneously. A consequence of this is that steel under a constant stress at an elevated temperature will continuously deform with time that is it is said to “Creep”.
Creep in steel is important only at elevated temperatures. In general creep becomes significant at temperatures about 0.HTM, where TM is the absolute melting temperature. However, materials having low melting temperature will exhibit creep at ambient temperature, lead and various types of plastic are good examples for example, lead has a melting point at 3260C (5990K), and at 200C (2930K, or about 0.5 TM) it exhibits similar creep characteristics to those of iron at 6500C.
The creep material measuring apparatus is in simple unit designed for demonstrating and investigating the creep characteristics of lead and polyurethane specimen at room temperature. A temperature module is provided to enable investigation of the effects of temperature on creep rate.
1.10 THE CREEP CONCEPT
materials when subjected to stress will deform with time. Creeps occurs at all temperatures, even at stresses as low as few mentor’s per square millimeter. When considering low temperatures creep become negligible at stress below the yield strength and may require many life time to be detectable. At high temperature creep is important and will often determine the design stress that should not be exceeded in the structural component.
Creep can take place and lead to fracture at static stresses much smaller than those which will break the specimen when loaded quickly in the temperature range 0.5 – 0.7 of the melting point (1MK) the variation with time of extension of a metal under different stresses is shown below.
Three conditions can be recognized:
a. The primary stage: When relatively rapid extension takes place on but at a decreasing rate (because gradient is negative). This is of interest to a designer since it forms part of the extension reached in a given time and may affect clearances. Two alternative equation are used to describe the primary creep.
1st aE = log t, Where = a constant t = time
(Not applicable to Aluminum, Rubber and glass) 2nd E = Bt 1/3, where B = constant applicable for higher temperature.
b. The secondary stage: The secondary stage is the period at which creep occurs at more or less constant rates sometimes referred to as minimum creep rate. This is important part of the cure for most applications.
Equation is a straight line;
E = Kt
Creep rate K = DE
Dt
DE = AQn E x P (Q/RT)
Dt
Where n and A = constant
N = 3 – 7 (for metals)
N = 1 – 2 (for polymers)
Q = Activation energy for creep I
approximately activating for diffusion.
c. The tertiary stage: The tertiary stage is when the rate of extension accelerates and finally leads to rupture. The use of alloys at the stage should be avoided but the change from secondary to the tertiary stage is not always easy to determine from creep curve from more materials.
1.11 CREEP TESTING MACHINES
mechanical testing of materials are conducted in commercial, academic and research laboratories using state of the art equipment designed for specific mechanical properties evaluations.
Creep testing in machine requires a means of loading the specimen and recording the response for evaluating the results. The creep testing are generally performed by unaxial loading through 10 to 15 – 1 lever arm system typical suing a back of say 10 – 20 units. Very high temperature tests of low strength materials can be used more economical direct loading systems of simple design. Beam configuration with appropriate loading fixtures are generally used for brittle materials. In contrast to tension compression tester which are usually obtained from commercial sources, creep testing machines are generally of – in – house design.
The design being considered in this work uses a simple lever to apply a steady load to the specimen. The specimen is attached at one end to the lever mechanism by steel pin and fixed at the other and to the bearing block by another steel pin. Loads are applied to the lever arm which is pinned to the lever arm. The weight hanger has two (2) pinning position while the other is used to pin the hanger I the loaded position.
1.12 THE PURPOSE OF THE PROJECT
To the best of our knowledge, available data has shown that there is no company in Nigeria, which specializes in the manufacturing of creep measuring machines. In view of the manufacturing of creep, it become necessary for us to go into the design and fabrication of the machine. It is our intention that this will go a long way to making this product available to schools, industries and even to research institutes.
The project will also help manufacturers to know the simpler methods involved in the design and manufacturing of this machine. The creep machine designed and produced in this project works with higher efficiency compared to the model obtainable elsewhere. Similarly with the availability of this machine the analysis of creep rates of different engineering materials will become much easier in the institute of management and technology, Enugu. The choice of materials by designers for different working conditions becomes more accurate and precise.
1.13 DEMAND FOR THE EQUIPMENT
The demand for the equipment is very high because of the simplified methods of production employed, the equipment is highly competitive. Unlike other versions of the equipment, which employed processes like casting, the carefully avoided any process, which will increase cost unnecessarily.
Another special feature is the high maximum loading specified by this equipment. This makes it very competitive as it can test materials like nylon, lead, and polypropylene etc. As a matter of fact, the equipment’s high demand cannot be over emphasized.
1.14 LITERATURE REVIEW
The only existing model of this machine available else where during the course of the research was the “SM106 MK11 creep measurement apparatus. It was manufactured by TEC equipment”. This model of the equipment is small and has a specification of about 5N/M2 most of the parts were cast making it very costly. In our version of the machine, we refused to employ the casting process but combined other engineering processes to manufacture various parts of the machine.
Almost all materials consulted even manufacturers of the existing model agreed on some basic design consideration.
The design consideration include:
1.15 KINDS OF PHENOMENA
Some of the different kinds of creep phenomena that can be exhibited by materials are shown in the diagram below.
The strain E = DL /LO, in which Lo is the initial length of a body and L is its increase in length, is plotted against the time t for which it is subjected to an applied stress. The most common kind of creep response is represented by the curve a following the loading strain E0, the creep rate, as indicated by the slope of the curve, is high but decreases as the material deforms during the primary creep stage. At sufficiently large strains the materials creeps at a constant rate. This is called the secondary or steady state creep stage. Ordinarily this is the most important stage of creep since the time to failure it is determined primarily by the secondary creep rate Es. In the case of tension creep, the secondary creep stage is eventually interrupted by the on set of tertiary creep, which is characterized by internal fracturing of the material, creep acceleration and finally failure. At low temperatures or applied stresses the time scale can be thousands of years or longer while under different conditions the entire creep process can occur in a matter of seconds. Another kinds of creep response is shown by curve B, this is the sort of strain time behaviour observed when the applied stress is partially or completely removed in the course of creep. This result in this dependent or inel
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