MSE_250_LAB-4 - MSE 250 LAB # 4 Mechanical Properties of...

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MSE 250 LAB # 4 Mechanical Properties of Materials–Impact Test Introcution: Another interesting mechanical performance of materials is the impact performance at different temperatures. In metals, plastic deformation at room temperature may occur by the dislocation motion. The stress required to move a dislocation depends on the atomic bonding, crystal structure, and obstacles such as solute atoms, grain boundaries, precipitate particles and other dislocations. If the stress needed to move dislocations is too high, the metal will fail by the propagation of cracks and the failure will be brittle. Thus, fracture of metals occurs by either plastic flow or crack propagation, depending on which process requires the smaller applied stress. For BCC metals, the flow stress reduced with decreasing temperature, whereas the crack propagation stress is relatively independent of temperature. Thus, the mode of failure changes from plastic flow (ductile) at high temperatures to brittle fracture at low temperatures. For FCC
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MSE_250_LAB-4 - MSE 250 LAB # 4 Mechanical Properties of...

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