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TENSILE TESTING OF METALS Aim: The aim of the experiment is to determine the behaviour in tension of metallic materials. Depending on the material and the production method used to produce the test piece various kinds of responses are possible in extension to the applied load. Introduction: The tensile test provides an estimate of the strength and ductility of metal materials. The test is carried out on a small sample of material according to BS 18 Methods for tensile testing of metals. It should be noted that the results obtained can only be used as a guide to the performance of the material as a whole. The following experiment was designed to determine some of the mechanical characteristics of various materials. These included the stress strain characteristics, such as Young's Modulus, yield strength and tensile strength. I will use the theory of material science to help explain the properties of our samples, and predict the outcome of the results and then compare this to what actually happened once the test is complete. I will take into account how carbon has affected the properties of steel and as has alloying to Aluminum. A lot can be learnt about a substance from tensile testing. By pulling on something, it is possible to determine (very quickly) how the material will react to forces being applied in tension. As the material is being pulled, it is easy to find out its strength along with how much it elongates.


A; 8,400N divided by 20mm2 = 420 F; 10,450N divided by 10mm2 = 1,045 Sample Yield Strength* A 420 F 1045 * All results are in N/mm2 Samples After the Test Analysis of Results In the calculation of breaking or tensile strength, the original cross section area was used (this is known as the nominal stress or the engineering stress). My initial assumption of samples Y and U being based on the same metal aluminum and A, F both based on steel, have resulted in 2 very different results. I would have initially thought that the pair of metals would have acted quiet similar to one another however it wasn't the case. U results varied widely to that of Y and so is the case with metals A and F. - Metal samples A and F Now as established earlier two materials contain carbon, the steel with carbon content, samples A and F. Most steel contains less than 0.35 percent carbon. Plain carbon steels can be grouped into 3 categories; - Mild steel = 0.10 to 0.25% Carbon - Medium carbon steel = 0.25 to 0.5% Carbon - High Carbon steel = 0.50 to 1.5% Carbon * Thus sample A is mild steel and F is a high carbon content steel Carbon is very special because it can form so many compounds. The explanation lies inside the carbon atom. Carbon atoms can form strong links with four other atoms.


Sample U has 4% copper alloy, and because of this it has increased strength, however has lost some durability. The result graph show that sample U is a very strong material that will not break easily which means it can withstand large forces, this due to copper added. Aluminium-copper alloys containing 2 to 10% Cu, generally with other additions, form important families of alloys. Copper is the principal alloying element in this sample. These alloys normally require solution heat-treatment to obtain optimum properties. Also artificial aging can be used to further increase the mechanical properties. This treatment materially increases yield strength, with attendant loss in elongation. 10 Conclusion In this experiment, we determined the mechanical characteristics of four unknown samples. Based on collected data we were able to describe such characteristics as relative hardness and stress-strain characteristics. Combining these mechanical properties with the theory of material science, we were able to explain some of the characteristics of our materials and assume their compositions. In conclusion it was evident that the inclusion and alloying metals could alter how ductile they were and their strength. Samples Y and A were the most ductile materials and the Young modulus of Steel (sample F) revealed that it is the stiffest material. Sample F was found to be the strongest material because of its high tensile and breaking strength, however it wasn't very malleable until carbon was added. I feel that the accuracy of the results were satisfactory but they could have been improved by repeating the tensile test several times and taking an average.

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