Lecture_3.pdf - Science and Engineering of Materials CEP...

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Science and Engineering of Materials CEP 319 Lecture 3
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Toughness and Impact test Toughness is the amount of energy a material can absorb before fracturing. Toughness is of engineering importance because it indicates the ability of a material to withstand an impact load without fracturing. One of the simplest methods of measuring toughness is to use an impact-testing apparatus. Ref: William F. Smith. Foundations of Materials Science and Engineering pg - 246
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Impact Test The Charpy test is commonly used as impact test. The test specimen may either be notched or unnotched; the V-notched specimens better measure the resistance of the material to crack propagation. Procedure: In the test, a heavy pendulum which starts at an elevation h o swings through its arc, strikes and breaks the specimen, and reaches a lower final elevation h f . By knowing the initial and final elevations of the pendulum, the difference in potential energy can be calculated. This difference is the impact energy absorbed by the specimen during failure. The ability of a material to withstand an impact blow is often referred to as the toughness of the material. Ref: Askeland. D. The Science and Engineering of Materials pg : 110-111
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Ref: William F. Smith. Foundations of Materials Science and Engineering pg - 246 Watch the video: https://www.youtube. com/watch?v=tpGhq QvftAo
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Results of the Impact Test The results of a series of impact tests performed at various temperatures are shown below: 1. At high temperatures, a large absorbed energy is required to cause the specimen to fail, whereas at low temperatures the material fails with little absorbed energy. 2. At high temperatures the material behaves in a ductile manner, with extensive deformation and stretching of the specimen prior to failure. 3. At low temperatures, the material is brittle and little deformation at the point of fracture is observed. The transition temperature is the temperature at which the material changes from ductile to brittle failure. Ref: Askeland. D. The Science and Engineering of Materials pg : 111
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Results of the Impact Test Therefore, a material that may be subjected to an impact blow during service must have a transition temperature below the temperature of the material’s surroundings.
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