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【正文】 eometry. TEAR STRENGTH AND HARDNESS OF POLYMERS Polymers are softer than metals and ceramics, and most hardness tests are conducted by peration techniques similar to those described for metals in the previous section. Rockwell tests are frequently used for polymers. 2022/3/13 Chapter 7 Mechanical Properties 37 PROPERTY VARIABI LITY AND DESIGN / SAFETY FACTORS 金屬材料性能的可變性 (數(shù)據(jù)分散性 ) Scatter and Variability of materials properties are inevitable and must be dealt with appropriately. VARIABILITY OF MATERIAL PROPERTIES Question 1: ‘‘What is the fracture strength of this alloy?’’ Question 2: ‘‘What is the probability of failure of this alloy under these given circumstances?’’ COMPUTATION OF AVERAGE AND STANDARD DEVIATION VALUES (CDROM) 2022/3/13 Chapter 7 Mechanical Properties 38 PROPERTY VARIABI LITY AND DESIGN / SAFETY FACTORS 設(shè)計參數(shù) /安全系數(shù) Design stress (?d): Product of the calculated stress level (on the basis of estimated maximum load) and a design factor (which has a value greater than unity). Used to protect against unanticipated failure. DESIGN/SAFETY FACTORS cd N ??39。?Safe stress (?w): A stress used for design purposes。 for ductile metals, it is the yield strength divided by a factor of safety. Nyw?? ?2022/3/13 Chapter 7 Mechanical Properties 39 PROPERTY VARIABI LITY AND DESIGN / SAFETY FACTORS 設(shè)計參數(shù) /安全系數(shù) Design stress (?d): Product of the calculated stress level (on the basis of estimated maximum load) and a design factor (which has a value greater than unity). Used to protect against unanticipated failure. DESIGN/SAFETY FACTORS HBp s iTSHBM P aTS????5 0 0)()(2022/3/13 Chapter 7 Mechanical Properties 40 Home works ? P190, ? P192, ? P196, 2022/3/13 Chapter 7 Mechanical Properties 41 The end of chapter 7
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