材料性能 Ch1 Uniaxial Mechanical Properties.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。
Mechanical Properties
材料的力学性能
Usually, materials’ mechanical properties are the first consideration in structural objects design, such as architectures, vehicles, machinery, utensils, tools, to name just a few, which always withstand loading/forces in service as prerequisite.
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。
1. Definitions of Mechanical properties /力学性能
The mon properties considered are strength, ductility, hardness, impact resistance, and fracture toughness.
tensile test:
Steady-state Mechanical Properties Under Uniaxial Tension
Uniaxial Mechanical Response
静载单向静拉伸
Stress-Strain Curve
Note: Engineering stress and strain
应力――应变曲线
Usually, four stages/segments
Four stages/segments/四阶段:
(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(--%)
. II(bcd)―Yielding(屈服变形)
c: Yield Limit: 屈服点  Ps
拉伸机上,低碳钢缓慢加载单向静拉伸曲线
Yielding屈服现象:金属材料开始产生明显塑性变形的标志。
Yielding( or the yield strength or yield point) of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically.
第一章绪论
. III(dB)― Uniform plastic deformation (均匀塑性变形阶段)
B:  Ultimate Tensile Strength Pb 材料所能承受的最大载荷
(BK) ― non-uniform/localized plastic deformation, concentration of plastic deformation 局部集中塑性变形
拉伸机上,低碳钢缓慢加载单向静拉