材料性能 Ch_1.2_Fracture课件.ppt

Fracture of Materials;Ductile fracture brittle fracture/金属的韧性断裂与脆性断裂;１） Micro-mechanism of ductile fracture /韧断机制;Dimples/韧窝;Brittle fracture/脆性断裂：;虞闯带逊苗屯续绝凡贞壤烧序颗艺炊钎丙兢给绸宋哆爵吻贿败烧罢糠扑诀材料性能 Ch_1.2_Fracture课件材料性能 Ch_1.2_Fracture课件;Transgranular intergranular fracture/穿晶与沿晶断裂(裂纹发生途径);Cleavage /解理断裂: cleavage fracture happens along with or alongside of a crystalline plane , called cleavage plane，for example (100)plane of BCC metals。。;Fracture Toughness/断裂韧性 ;Why did Titanic sink and what is the reason? ;This approach uses the flaw size and features, component geometry, loading conditions and the material property called fracture toughness to evaluate the ability of a component containing a flaw to resist fracture. ;Three types ;The stress intensity factor is a function of loading, crack size, and structural geometry. The stress intensity factor may be represented by the following equation: ;Role of Material Thickness ;The relationship between stress intensity, KI, and fracture toughness, KIC, is similar to the relationship between stress and tensile stress. The stress intensity, KI, represents the level of “stress” at the tip of the crack and the fracture toughness, KIC, is the highest value of stress intensity that a material under very specific (plane-strain) conditions that a material can withstand without fracture. ;Plane-Strain and Plane-Stress ;1. Material within the crack tip stress field, situated close to a free surface, can deform laterally (in the z-direction of the image) because there can be no stresses normal to the free surface. The state of stress tends to biaxial and the material fractures in a characteristic ductile manner, with a 45o shear lip being formed at each free surface. This condition is called “plane-stress and it occurs in relatively thin bodies where the stress through the thickness cannot vary appreciably due to the thin section. ;Plane-Strain Fracture Toughness Testing ;理论断裂强度： a : 原子间距; 　　裂纹尖端前沿有应力集中产生，形成一个裂纹尖端应力场。表示应力场强度的参数——“应力场强度因子”