E45 Uniaxial Tensile Test Lab Report

E45 Uniaxial Tensile Test Lab Report - E45 Lab Report 2:...

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e 2: Stress-strain curve showing 0.02% yield strength. Figure 1: Stress-strain curve example. E45 Lab Report Norbert Wang Uniaxial Tensile Test Abstract This lab explored a very important property of metallic alloys, strength and toughness. The uniaxial tensile test provided the standard to judge this property for two kinds of steel (AISI 1020 and AISI 4340) and 2024-T3 aluminum-copper alloy. A stress-strain curve was calculated from the machine’s results for each material. The ultimate tensile strength, fracture strength, and toughness approximations were all generated from the stress-strain curves. It was found that hardness and temperature of the material were clear factors in strength and toughness. AISI 4340 steel was the hardest of the three materials so it toughest material by far. AISI 1020 steel followed and 2024-T3 aluminum was the softest and weakest. The Charpy impact test judged two temperatures of AISI 1020 steel, one at liquid nitrogen temperature and the other at room temperature. The colder steel fracture much more easily than the warmer steel. Therefore warm materials are more ductile than cold materials. Introduction How a material deforms is a very important in engineering applications. Many of the metallic alloys used today have both an elastic and plastic region of deformation. The engineering stress-strain curve shows this concept well. An example of this is shown in Figure 1. The elastic region of the curve is the initial linear trend portion. Here the Young’s modulus (E) can be calculated from the slope of the line. The curve will resemble a line until the upper yield strength (UYS) is reached which is the onset of plastic deformation. In carbon steels, this is immediately followed by lower yield strength (LYS). Following this region is a bit of oscillations in the curve. This exists because carbon atoms tend to sit next to dislocations in the
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plastically deformed iron lattice. The carbon will oppose the movement of the dislocation until the carbon gains too much vibrational energy from the process and releases. The dislocation will move a little until it encounters another carbon atom and so on. These oscillations are called serrated yield. For aluminum- copper alloys this is not seen in the stress-strain curve mainly because copper does not behave the same way as carbon. Once the yield stress has been surpassed, the region is now known as the plastic region. Stresses applied here will deform the material to the point where it cannot revert back to its original shape. An example of plastic deformation is bending a copper wire and noticing that it will not bend back when the stress has been released. When the stress peaks, this point is called the ultimate tensile stress (UTS). After reaching the UTS, the curve will decrease stopping at the fracture stress. The region from the point of UTS to the point of fracture is also known as the “necking” region. It was named this way because the material undergoes rapid reduction of cross-section area during this region and eventually snaps. Some materials, little aluminum alloys, don’t show obvious yield points. A method known as the “0.2%
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This note was uploaded on 01/21/2010 for the course ENGIN 45 taught by Professor Devine during the Fall '07 term at University of California, Berkeley.

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E45 Uniaxial Tensile Test Lab Report - E45 Lab Report 2:...

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