4-1-2应力和应变( (stress and strain) 应力:单位面积上的内力,其值与外加的力相等 名义应力:面积为材料受力前的初始面积的应力 真实应力:面积为受力后的真实面积的应力 应变:受到外力不惯性移动时,几何形状和尺寸的变化 1.材料的应变方式 各向同性材料,三种基本类型: 简单拉伸 tension 简单剪切 shear 均匀压缩 compression 还有扭转和弯曲形变
4-1-2 应力和应变 (stress and strain) 1. 材料的应变方式 各向同性材料，三种基本类型： 简单拉伸 tension 简单剪切 shear 均匀压缩 compression 还有扭转和弯曲形变。 应力：单位面积上的内力，其值与外加的力相等。 名义应力：面积为材料受力前的初始面积的应力。 真实应力：面积为受力后的真实面积的应力。 应变：受到外力不惯性移动时，几何形状和尺寸的变化
(1)简单拉伸( tensile) 8=(L-LO/L0=4Lllo σ=F/S0 F F F垂直于截面、大小相等、方向相反并作用于同一直线上
（1）简单拉伸(tensile) = ( l – l 0 ) / l 0 = l / l 0 =F / S 0 F垂直于截面、大小相等、方向相反并作用于同一直线上
Tension is one of the most common mechanical stress-strain test the tension test can be used to ascertain several mechanical properties of materials that is very important in design Reduced section 0.505" Diameter 大 Diameter 2 Gauge length Radius A standard tensile specimen
A standard tensile specimen Tension is one of the most common mechanical stress-strain test. the tension test can be used to ascertain several mechanical properties of materials that is very important in design
(2)简单剪切( shear) y= tan d 切应变y=l/ 剪切力σ=F/S ￥+平 F与截面平行、大小相等,方向相反且不在同一直线上的两个力
（2）简单剪切(shear) 切应变 = l / l 剪切力 s= F / S 0 F与截面平行、大小相等，方向相反且不在同一直线上的两个力
(3)均匀压缩( compress Compression stress-stain tests may be conducted when in-service 0 forces are of this type. A com pression test Is conducted in a manner similar to the tension test. except that the force is compressive and the specimen contrasts along the direction of the stress F:周围压力p 压缩应变Yy γy=(Vo-V)/V0=AV/0
（3）均匀压缩(compress) F：周围压力p V = ( V0 压缩应变 - V ) / V0 = V/ V0 V Compression stress-stain tests may be conducted when in-service forces are of this type. A com- -pression test is conducted in a manner similar to the tension test, except that the force is compressive and the specimen contrasts along the direction of the stress