重庆大学：《金属材料的力学行为 mechanical behavior of metallic materials》PPT教学课件（2/2，彭晓东，附听课备注）

Mechanical Behavior of Metallic Materials(2) PENG Xiaodong Ph.D. Professor School of materials science and Engineering Chongqing University Chongqing 400044 P.R. China

Mechanical Behavior of Metallic Materials(2) PENG Xiaodong Ph.D., Professor School of Materials Science and Engineering Chongqing University Chongqing 400044 P.R. China

Mechanical Behavior of metallic Materials Fracture of metals failed in 1941

Mechanical Behavior of Metallic Materials Fracture of Metals failed in 1941

Mechanical Behavior of metallic Materials Theoretic Cohesive Strength 入 2 ③千大

Mechanical Behavior of Metallic Materials Theoretic Cohesive Strength

Mechanical Behavior of metallic Materials 兀X 2x 0=0 SIn C do2丌oe O Hooke's law E do E d CHONGQING UNIVENTTY

Mechanical Behavior of Metallic Materials 2 sin 2 2 c c c x x d dx           =  = 0 E x a  = 0 d E dx a  = Hooke’s law

Mechanical Behavior of metallic Materials do 2O E 法显示该图片。 E c 2nt ao E O≈ 元 ③大季

Mechanical Behavior of Metallic Materials 0 0 2 2 c c d E dx a E a       = = = 0 2 a   c E   

Mechanical Behavior of metallic Materials Maximum Strengths of solids Material f, GPa EGPa E Silica fiber 24.1 971 4 Iron whisker 13.1 295.2 23 Silicon whisker 647 1657 26 Alum ina whisker 15.2 4962 33 Ausformed steel 3.14 200.1 64 Piano wire 2.75 200.1 73 CHONGQING UNIVENTTY

Mechanical Behavior of Metallic Materials Material , GPa E, GPa Silica fiber 24.1 97.1 4 Iron whisker 13.1 295.2 23 Silicon whisker 6.47 165.7 26 Alumina whisker 15.2 496.2 33 Ausformed steel 3.14 200.1 64 Piano wire 2.75 200.1 73  f E  f Maximum Strengths of Solids

Mechanical Behavior of metallic Materials Deformation and accumulation of irreversible damage Defects such as porosity, shrin kage cavities, quench cracks, grinding and stamping marks, seams, and weld-related cracks nclusions, brittle second-phase particles, and grain boundary films-lead to crack formation stress growth defect C今 crack fracture ③大季

Mechanical Behavior of Metallic Materials Deformation and accumulation of irreversible damage Defects such as porosity, shrinkage cavities, quench cracks, grinding and stamping marks, seams, and weld-related cracks. Inclusions, brittle second-phase particles, and grain boundary films—lead to crack formation defect crack fracture growth stress

Mechanical Behavior of metallic Materials The Stress-Concentration Factor 2a max 1+ b 2 b O max a(1+2/p) ≈2o√a ③大季

Mechanical Behavior of Metallic Materials The Stress-Concentration Factor max 2 1 a a b   = + 2 b a  = max (1 2 ) 2 a a a a      = + 

Mechanical Behavior of metallic Materials is defined as the stress-concentration k,=2√a factor and describes the effect of crack geometry on the local crack- tip stress level The stress-concentration factor increase with increasing crack length and decreasing crack tip radius Plastic deformation in the highly stressed The crack tip blunts. crack-tip region ③大季

Mechanical Behavior of Metallic Materials 2 t k a =  is defined as the stress-concentration factor and describes the effect of crack geometry on the local crack￾tip stress level. The stress-concentration factor increase with increasing crack length and decreasing crack tip radius. Plastic deformation in the highly stressed crack-tip region. The crack tip blunts

Mechanical Behavior of metallic Materials 30 3.0 28 28 26 26 22 2.2 k 2.0 20上 Dd=1.5 1.8 18 D/d=1.3 1.6 1.6 D/d=5 D/d= 2 14 D/d=1.5 ED/d=3 D/d=2 1.2 1.2 10 101 0.1234 rld (b)

Mechanical Behavior of Metallic Materials