Tensile Testing of Metallic Materials - Assignment Example

Name Tutor Course Date Introduction Tensile 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. Case Study application of tensile testing The establishment of the mechanical properties for engineering materials can be analyzed through tensile testing. Specimen of grey cast iron3.5%, normalized carbon steel 0.1%, normalized carbon steel 0.8% , brass in the form of annealed 70/30 and drawn brass 70/30, can be examined in order to understand mechanical properties of metals and the material behavior that is associated to such properties. Background The background of the experiment can be practically applied in materials such as bridges, automobiles, ships and pressure vehicles. Metallic tensile properties form the basis for the criteria for development of safe designs. This is due to the fact that designers attain more awareness about the property differences of metals, therefore identifying the suitable metal for a particular design (Krutasova 34). Aim of the Experiment The key intent of the laboratory experiment is to ascertain the mechanical parameters of varied metals used in of engineering using a tensile machine that is standard, and in relations to British standards that are relevant. Secondly the experiment aims at creating an understanding of the association between the said parameter and material behavior (Askeland, 150). Objectives To collect test results, construct the required stress-strain curves and make an analysis and for the held mechanical parameters. The second objective is to the production of a report which entails an example of application of the particular technique in industry. Thirdly is to conduct a tensile test that is standard and applicable to British standards. Lab Set-Up and Method 1. Record the length and the original diameter of the specimens to be tested using a Vernier calliper. The parallel length of the dog-bone” sample should only be taken only. 2.One of the each specimen is provides which includes grey cast iron3.5%, normalized carbon steel 0.1%, normalized carbon steel 0.8% , brass in the form of annealed 70/30 and drawn brass 70/30 3. The specimen should be loaded each at a time into the Hounsfield extensometer, jaws. It is essential to reset parameters that are measurable (distance traveled and the load) to zero prior to the start of the test. 4. The specimen should then be tested to failure. The load requires to be slowly applied, the relevant deformation speed is soft metals-6 mm/s while hard metals 3 mm/s. The Hounsfield extensometer is supposed to maintain a pulling speed that is constant for the whole duration. 5. After the specimen fails, the extensometer has to be stopped. Prior to sending the results of the test to the computer of data acquisition, it is necessary to load the software used for data gathering on the PC so as save and display the results of the test in a format that is graphical as indicated by figure (3). The speed of recording the acquisition system of data is a indicated by 5 data points per second as indicated above. 6. The broken specimen is removed from the jaws and the final approximate diameter of the specimen is measured at the neck region (Callister, 67). Test Results and Discussion 1. The gathered data for each of the samples will read be read in terms of force applied against the elongation measurement of the specimen in (mm).The values should be converted into engineering stress values which are ( in N/m2 or Pa)and the engine strain(). The calculation of engineering stress is done by dividing the applied force over the area of the initial cross-section, while engineering strain is calculated as elongation over the over the initial length. 2. The curves of engineering  -  should be plotted in a format that is graphical in excel and identification of the corresponding out come and stress for each material. 3. Ductility, the capacity of a material to go through plastic deformation under tension, is calculated for each of the specimen using elongation differences. As highlighted ; 4. The change in cross-sectional area is also calculated by 5. The comparison of the various materials is done and most particular the impact of increasing the content of carbon in steel and the impacts of working on brass in cold conditions. 6. It is essential to compare the empirical findings in the lab with those published and then a comparison should be made out of this analysis. The effects of alloying (Effect of increasing the carbon content in steel) The strength exhibited by of carburized steel is grounded on the straight yielded by the residual and core stresses .By increasing the concentration or amount of carbon in steel the strength yielded at the core increases while the comprehensive stress reduces. There is usually carbon concentration that is optimum that mainly depends on the size of the material and alloying of the steel. For instance in carbonized steel with a small diameter of 8-12mm, the strength of bending and fatigue may limit high carbon concentration which is at .19–0.24%. Increasing the amount of carbon in steel increases both hardness and strength, up to a particular amount that is 1.5-2%. Various tests to measure hardness are available .All the methods involve the use of a loading condition that is known in order to put indentation on the material. Indentation produces the capacity of hardness found within a material. The implication of the experiment is that the bigger the indent form the softer the material (Callister, 67). In the figure (3).The load increased slowly and the specimen will elongate or stretch in the fraction of the tensile load. The specimen elongates in the direction of the load without increasing the load capacity. This is referred to as the yield point of steel and marks the stop of the proportion of elasticity. If the load is eliminated at point A the specimen returned back to the original position. Yielding appears from point A to B this forms the elastic deformation .If the load was to be removed at point B the specimen would not return to its original dimension but rather it would take a permanent set. The interpretation of the curve above is the application of stress on steel leads to development of cracks which results to an increase stretching, therefore the more the carbon the stronger steel becomes. Escalating the amount of carbon in steel also increases ductility however above the standard amount ductility reduces this therefore makes steel very brittle. Cold working on the mechanical properties of metallic elements (Effect of cold-working on brass.) When measuring tensile strength at room temperature, it has been discovered that in certain cases, the strength yielded plays a significant part in the resolving of the 3R, repair, run and replacement for a particular component. The strength found on ductile materials depends on several factors such as temperature either hot or cold and the strain rate. When examining the effects of cold working on brass if worked at L62 at 200–250° C there will be a rise in the elastic limit and when the temperatures are reduced reversibility is increased.  Opposite to the conduct of the elastic limit and elastic effect afterwards, tensile strength, elongation when at a fracture, furthermore hardness characteristics of profoundly cold worked brass (up to 58%) L62, which do not posses significant excessive values that are impacted by reheating temperature. Conclusion Tensile testing can be used in the analysis of various metallic properties .The examination of various features that metals exhibit requires analysis of the available data, Marjory basing on the principals of stress and strain. Works Cited Avner, Sidney H. Introduction to Physical Metallurgy, New York: McGraw-Hill, inc. Askeland, D.R.. The Science & Engineering of Materials, 3rd Edition. Chapman & Hall. 1996,pgs 140 – 149. Callister, W.D. Materials Science & Engineering – An Introduction, London; John Wiley & Sons, 1995. Krutasova, A. Reliability of Power Equipment Metal. Energoatomizdat; Moscow, Energoatomizdat, 1981. http://www.me.ust.hk/~mejswu/MECH141/MECH141F.pdf Read More