材料性能 Ch1_Uniaxial Mechanical Properties课件.ppt

机械设计中应首先考虑材料的力学性能。通俗地讲力学性能决定了在多大和怎样形式的载荷条件下而不致于改变零件几何形状和尺寸的能力。;The mechanical properties of a material are those properties that involve a reaction to an applied load. mechanical properties of a material are not constants and often change as a function of temperature, rate of loading, and other conditions. 材料在外加载荷（外力或能量）作用下或载荷与环境因素（温度、介质和加载速率）联合作用下表现出来的行为。 The mechanical properties of metals determine the range of usefulness of a material and establish the service life (without failures like deformation or fracture) that can be expected. －－主要是指材料在力的作用下抵抗变形和开裂的性能。 　　;;Stress-Strain Curve Note: Engineering stress and strain;Usually, four stages/segments;Four stages/segments/四阶段： 1．Seg.I（oab）―Elastic deformation(弹性变形阶段) a: Pp? b: Elastic Limit Pe the greatest stress that can be applied to a material without causing permanent deformation（不产生永久变形的最大抗力） oa段：△L∝ P?? Linear 直线阶段 ab段：极微量塑性变形（0.001--0.005%) 2．Seg. II（bcd）―Yielding(屈服变形) c: Yield Limit: 屈服点 ? Ps;第一章 绪论; Varying but characteristic types of curves shown by different materials 　　　　;2. Stiffness and Elasticity/刚度和弹性 ;比例极限：σp=Pp/Fo?? 应力――应变保持线性关系的极限应力值 弹性极限：σe=Pe/Fo ???? 不产永久变形的最大抗力。 工程上，σp、σe视为同一值，通常也可用σ0.01 ;Ductility/塑性;Lk:试样拉断后最终标距长度 延伸率与试样尺寸有关， d5 ,?? d10 (Lo=5do, 10do); ψ =△F/Fo=(Fo-Fk)/Fo x 100% ψ越大，塑性愈好 ψ 5%, 脆性材料;――材料所能承受的极限应力. ;Yield strengthσs /屈服强度;Yield strength is a very important value for use in engineering structural design. ;Yield point criteria /屈服标准;Yield strength σs offset yield strength σ0.02 /屈服强度和条件屈服强度 ???????? ; （中高碳钢、无屈服点，以产生一定的微量塑性变形的抗力的极限应力值来表示。）;Factors influencing yield strength ;There are several ways in which crystalline and amorphous materials can be engineered to increase their yield strength, ;Strain hardening/形变硬化;Mechanism of strain hardening;Most non-brittle metals with a reasonably high melting point as well as several polymers can be strengthened in this fashion ;Tensile strength Necking/抗拉强度与颈缩条件 ;Prerequisite for necking /颈缩条件;1. True fra