IntroductionTensile testing of metallic materials is used to analyze metallic properties that are present at ambient temperature. Tensile testing procedures offer engineers data that is quantitative for design work. Tensile testing is a common procedure for determining the mechanical properties of materials in order to provide engineers with quantitative data required for instance in design work. The test entails the straining of the metallic test piece in an environment of tension in order to produce a fracture, for the key intention of determining various mechanical properties that exist in metals.
The metallic samples are gripped in order to align the specimen in an axially direction for the purpose of minimizing bending. The testing procedures are usually carried out using two methods, foremost is the controlling of the strain rate for the purpose of minimizing the strain rate variation, the second method involves the determination of the stress rate. The choice of the experimental method should properly be organized in order to proper estimations that can portray metallic properties. The engineering strain-stress curve is created by the calculation of the applied force and the specimens cross sectional area in N/m2.The area of the original cross section and the calculated strain are divided by the elongation over the original the length of the original specimen, which has features of being dimensionless (Callister, 2007). A distinctive stress-strain curve is revealed in the figure below; (a)(b)Fig 1 (a) – 1, Callister, 2007, page 145 on engineering stress-strain curve, M and F indicate the ultimate fracture and tensile stress respectively. In the figure illustrated above, the proportion of the straight line signifies the limit of elastic deformation which is usually reversible when load that is applied is removed.
The elasticity limit is described by the Yield stress level (y) which found at the connection between the strain and stress curve, where a channel is drawn parallel to the curves linear proportion with a strain off set of 0.002, which matches up a change in length of 0.2%. The highest stress that can be supported by a sample is defined as the Ultimate tensile stress (UTS). Further pulling or deformation will result to the “necking” of the sample, which may cause repeated reduction in the area of the cross-section, thus reducing the stress/force needed and eventually resulting to failure. The Universal extensometer indicated in figure.
(2) has a tensile test machine which is used to control the pulling speed. The Hounsfield extensometer is however used in the British context. Figure. (2)The specimen being tested is held using grips that are found on the piston and the cross- head. The oil is found in the cylinder is put under control by the unloaded and the loaded waves. Proper grip alignment removes the bending of loads and ensures the specimen being tested is only put through the axial load.
If loads are enlarged on the specimen being tested this result to the stress not being uniform across the thickness. During this particular testing, the Load cell (a device which mounted on the Winston bridge) and the Extensometer transfer electronic signal that are analogue to the control tower of the Instron. The measured out put is based on the deflation rate. The measurement of the area of the final cross section and the specimens length will additional give information about the ductility of the sample.