190> 入安 Figure 6.4 Schematic representation showing normal ('and shear ('stresses that act on a plane oriented at an angle 6 relative to the plane taken perpendicular to the direction along which a pure tensile stress (is applied. 。-s0-+22） 入 -sn0cs0-(2） SINO-ITALIAN CAMPUS
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190> NGJI UNIVERS、 On an atomic scale,macroscopic elastic strain is manifested as small changes in the interatomic spacing and the stretching of interatomic bonds. The magnitude of the modulus of elasticity is a measure of the resistance to separation of adjacent atoms,that is,the interatomic bonding forces. This modulus is proportional to the slope of the interatomic force-separation curve at the equilibrium spacing: Attractive force FA 0 Interatomic separation r Repulsive force FR r0 Net force FN SINO-ITALIAN CAMPUS
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190 E dr NGJ Figure 6.7 Force versus interatomic separation for weakly and strongly Strongly bonded bonded atoms.The magnitude of the (dF modulus of elasticity ro is proportional to 0 Separation r the slope of each curve at the equilibrium interatomic Weakly separation ro. bonded Covalent-ionic Metallic E 人S Secondary SINO-ITALIAN CAMPUS
SINO-ITALIAN CAMPUS Covalent-ionic Metallic Secondary E Tm
190 CONGJI UNIVERSTT Elastic modulus for different materials Metals E(GPa) Ceramics E(GPa) Plastics E(GPa) W 400 Diamond 1000 Melammidic 6-7 Mo alloys 320-365 WC 450-650 Polimmidic 3-5 Mg alloys 45 SiC 450 PMMA 3,4 Ni alloys 214-234 Al2O3 370-390 Polystyrene 3-3.4 Co alloys 200-248 BeO 380 Epossydic 3 Steels 190-200 Tic 379 Polycarbonate 2.6 Cast iron 170-190 SigNa 290 Polyesther 1-5 Cu alloys 124-150 MgO 250 Polyethilene 0,2-08 Al alloys 69-79 ZrO2 160-240 Rubber 0,01-0,1 Ti alloys 105-120 SiO2 72-94 SINO-ITALIAN CAMPUS
SINO-ITALIAN CAMPUS Elastic modulus for different materials
8 190 G Figure 6.8 Plot of Temperature ("F) modulus of elasticity -400 0 400 800 1200 1600 versus temperature 70 for tungsten,steel, and aluminum. 60 400 (Adapted from Tungsten K.M.Ralls,T.H. 50 Courtney,and (ed0) J.Wulff,Introduction 300 40 to Materials Science and Engineering. Copyright©1976 200 Steel 30 by John Wiley Sons,New York. 20 Reprinted by 100 permission of John Aluminum 10 Wiley Sons.Inc.) 0 0 -200 200 400 600 800 Temperature(C) SINO-ITALIAN CAMPUS
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