DESIGN OF A 60 KN CAPACITY ELECTROMECHANICALLY POWERED TENSILE TESTING MACHINE
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CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Tensile testing, which is also known as tension testing (Horst et al, 2006), is a fundamental material test, where a standard sample is subjected to controlled tensional loading until the material fails and fractures. The test results are generally used in materials selection in design applications, prediction of material behaviour under different types of loading other than uniaxial tension, and for quality control. Tensile properties of materials are often measured during the development of new materials and processes so that different materials and processes of manufacture can be compared (Davis, 2004).
Tensile testing directly records the load/elongation profile of the test specimen. In particular, tensile testing measures properties such as the yield point, maximum load, and load at fracture. It also measures uniform and maximum elongation, as indices of ductility. Using these data, both the engineering and the true stress-strain curves can be plotted from which the material’s fundamental properties such as Young’s Modulus, Yield Strength, Ultimate Tensile Strength, Poisson ratio and strain-hardening characteristics can be computed using appropriate algorithms.
For isotropic materials, the most commonly used test for obtaining mechanical properties is the uniaxial tensile test, while for anisotropic materials such as composites and textile materials, multi-directional tensile testing serves to enable the parameterization of the extent of anisotropy.
1.2 Statement of the Problem
The dearth of necessary and needed infrastructure in the nation’s institutions of learning is glaring to all concerned. The need for students in general, and engineering students in particular, to have a firm and practical grasp of the all-important tensile test cannot be over-emphasized.
Hence, the need to develop an instructional model of the tensile testing machine using, as much as possible, locally sourced materials, in order to bridge the gap between theoretical lectures on tensile testing and the much needed practical aspect of it.
1.3 Objectives
The objectives of this project include the main and specific objectives which are outlined below: 1.3.1 Main Objective
The main objective of the project is the design of a 60 kN capacity electromechanically powered tensile testing machine. 1.3.2 Specific Objectives
The specific objectives of this project include:
- Specification of the various parts of the machine.
- Specifying optimal engineering materials, from which the various parts can be made, based on a compromise of factors such as cost, availability of materials and amenability to locally available fabrication process.
- Production of the detailed design drawings of the machine parts as well as the assembly drawing of the machine as a whole using AutoCAD design and modeling software.
- Contribute to the process of bridging the gap between theory and practical in the teaching of materials testing.
1.4 Significance of the Project
The significance of the project includes the qualitative impartation of the knowledge of materials testing to students practically, as opposed to mere theory and the attendant difficulty of comprehension.
1.4 Scope of Work In this project, the dual column type of a 60 kN capacity tensile testing machine, including the various parts, will be designed. The specimen-holding cross-heads, based on ASTM E8/E8M Standards, will also be specified. Accommodation will be made in the design for the critical components such as the load cell and extensometer to be purchased and fitted on the machine. These are, however, expected to be fully integrated into the machine on subsequent and further work by students. The present model design will be for uniaxial loading only, complete with compression and bending capabilities. Finally, detailed design drawings of the machine and its various parts will be produced using AutoCAD design and modeling software.