材料力学第五版刘鸿文主编第十一章交变应力pptPMB.pdf

Mechanics of Materials Chapter 11 Alternating Stress (Alternating Stress) 第十一章 交变应力 （Alternating stress ） §11–1 交变应力与疲劳失效(Alternating stress and fatigue failure) §11–2 交变应力的循环特征、应力幅和平 均应力(The cycle symbol,stress amplitude and mean stress for alternating stress） §11–3 持久极限(Endurance limit) §11–4 影响持久极限的因素 (The effective factors of endurance limit ) (Alternating Stress) §11–5 对称循环下构件的疲劳强度计算 (Calculation of the fatigue strength of the member under symmetric cycles) §11–6 持久极限曲线 (Enduring limit curve) §11–7 不对称循环下构件的疲劳强度计算 (Calculation of the fatigue strength of the member under unsymmetric cycles) §11–8 弯扭组合交变应力的强度计算 (Calculation of the strength of composit (Alternating Stress) §11–1 交变应力与疲劳失效 (Alternating stress and fatigue failure) 一、交变应力(Alternating stress ) 构件内一点处的应力随时间作周期性变化,这种应力称为交变应力. P A σ t (Alternating Stress) 二、产生的原因(Reasons) 1、载荷做周期性变化 (Load changes periodically with time) 2、载荷不变,构件点的位置随时间做周期性的变化 (The point changes his location periodically with time under an unchangeable load) 例题1 一简支梁在梁中间部分固接一电动机, 由于电动机的 重力作用产生静弯曲变形,当电动机工作时, 由于转子的偏心 而引起离心惯性力. 由于离心惯性力的垂直分量随时间作 周期性的变化,梁产生交变应力. (Alternating Stress) ωt  静平衡位置 x a m  t s  n i m 