轴向拉伸与压缩 概念：作用在直杆上的外力或外合外力的作用 材料力学 A 学习总结 截面法求解内力的步骤： 1 、截开， 2 、代替， 3 、 平衡 F m m FF=Fn m m

应力：内力分布的集度 拉压杆横截面计算公式： σ=F/A 拉压杆斜截面计算公式： σ=Fcosa^2/A ( 正应力） τ=Fsin2a/2A （切应力） 平面假定：原为平面的横截面在变形后仍为平面

拉压杆胡克定律及拉压杆内的应变能 线应变：杆沿轴向的单位长度变形量 计算公式：纵向： ε=ΔL/L 横向： ε ‘ =ΔL ’ /L 泊松比： ν=|ε ’ /ε| 胡克定律： ΔL=FL/EA 应力状态的胡克定律 :ε=σ/E

应变能 ：变形固体因变形而储存的能量 计算公式： V=FΔL/2=F^2L/2EA=EAΔL^2/2L 应变能密度：单位体积储存的能量 材料在拉压时的力学性能 试样要求

低碳钢拉伸实验 四个阶段：弹性阶段 屈服阶段 强化阶段 局部变形阶段 在铸铁拉伸实验中：强度极限 是衡量强度的唯一标准，为塑性材料

低碳钢拉伸实验 铸铁拉伸实验

这章需掌握：应力与应变 轴力图 材料的力学性能 拉压强度计算 熟悉概念，牢记公式，贯通使用

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