第第12 12章章动载荷与疲劳强度概述动载荷与疲劳强度概述 summarize summarize about about mobile mobile load and load and Fatigue strength Fatigue strength ??工程结构中还有一些构件或零部件中的应力这些应力的大小或方向却工程结构中还有一些构件或零部件中的应力这些应力的大小或方向却随着时间而变化,这种应力称为交变应力。在交变应力作用下发生的随着时间而变化,这种应力称为交变应力。在交变应力作用下发生的失效,称为疲劳失效,简称为疲劳。。失效,称为疲劳失效,简称为疲劳。。?? In engineering structure, value or direction of ponent stress is In engineering structure, value or direction of ponent stress is variational variational along with time, this kind of stress be called variety along with time, this kind of stress be called variety is is called Fatigue invalidation on this condition of variety stress. Fatigue for called Fatigue invalidation on this condition of variety stress. Fatigue for short. short. 等加速度直线运动时构件上的惯性力与动应力等加速度直线运动时构件上的惯性力与动应力 inertial force inertial force and and dynamic stress above dynamic stress above constant acceleration constant acceleration component component ??以图以图 12-1 12-1 中的起重机吊重物为例,作用在钢丝绳中的起重机吊重物为例,作用在钢丝绳??的总载荷是动载荷与静载荷之和: 的总载荷是动载荷与静载荷之和: for for example,crane example,crane suspend clog as diagram 12- suspend clog as diagram 12- 1, total load effecting steel wire rope is sum of dynamic load and static load 1, total load effecting steel wire rope is sum of dynamic load and static load ???? (12-3) (12-3) T I st W F F F ma W a W g ? ?????式中, FT 为总载荷 total load total load ; Fst 与 FI分别为静载荷 static load static load 与惯性力 inertial force inertial force 引起 evocable 的动载荷 dynamic load dynamic load 。图图 12-1 12-1 NT T st I FF A A ? ??? ???, st I W W a A Ag ? ?? ? 1 T st I st I st aKg ? ????? ?? ????? ?? ? 1 IaKg ? ?按照单向拉伸时杆件的应力公式,钢丝绳横截面上的总正应力 According one-way pulled stretch pole of stress formula, Total positive stress above above the steel wire rope cross section steel wire rope c
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