利用间隙元的方法计算和分析疲劳寿命

提出了一个利用结构有限元方法中间隙元的原理来计算和分析疲劳寿命的新的累积损伤模型和方法。该方法利用间隙来模拟裂纹的形成和扩展 ,并提出新的累积损伤理论。不仅可以得到构件的疲劳总寿命 ,而且还可以用于计算裂纹的生成寿命、扩展寿命。同时又描述了裂纹的开裂过程 ,即裂纹的开裂尺寸和开裂方向。这为进行各种疲劳强度设计提供了一个新的思路和方法     

Comparison and analysis of two Coulomb friction models on the dynamic behavior of slider-crank mechanism with a revolute clearance joint

The objective of this study is to investigate the effects of the Coulomb dry friction model versus the modified Coulomb friction model on the dynamic behavior of the slider-crank mechanism with a revolute clearance joint. The normal and tangential forces acting on the contact points between the journal and the bearing are described by using a Hertzian-based contact force model and the Coulomb friction models, respectively. The dynamic equations of the mechanism are derived based on the Lagrange equations of the first kind and the Baumgarte stabilization method. The frictional force is solved via the linear complementarity problem (LCP) algorithm and the trial-and-error algorithm. Finally, three numerical examples are given to show the influence of the two Coulomb friction models on the dynamic behavior of the mechanism. Numerical results show that due to the stick friction, the slider-crank mechanism may exhibit stick-slip motion and can balance at some special positions, while the mechanism with ideal joints cannot.