A NEW CRITERION OF COMBINED TYPE CRACK—THE CRITERION OF MINIMUM DISTANCE(r_(min))IN PLASTIC REGION

The existence of the plastic area around the crack tip is an important factor against thecracking.In this plastic region.the cracking most likely develops in such a direction alongwhich the distance from the existant crack tip to the plastic region edge is the shortest one.Substituting the stress components at the crack tip for a combined cracking into R.Von.Mises equation of yielding condition,the boundary equation of the plastic regionaround the crack tip can be expressed as:where r is the distance from the crack tip to the boundary of plastic region.The direction inwhich the cracking develops can be determined by following conditions:One form of the material failures is the slipping under the action of shear stress.Underthe conditions of complex stress,the octahedral shear stress on a point around the crack tipis here.B devotes the.factor of the octahedral shear stress,which relates to the size. pattern ofcrack and the exerted stress.Its magnitude reflects the strength of the stress field aroundthe c     

探讨一种新的复合型断裂判据——塑性区最短距离r_(min)判据

裂纹尖端塑性区的存在是抗裂的重要因素,在同一个塑性区上,哪个方向上塑性区距离最短(指裂纹尖端到塑性区边缘的距离),裂纹就最容易从哪个方向上扩展.将复合型裂纹尖端应力分量代入R.von Mises屈服条件,得到裂纹尖端塑性区的边界方程:r表示从裂纹尖端到塑性区边缘的距离,裂纹沿rmin方向扩展,即由条件确定裂纹扩展方向.材料破坏的形式之一是在剪应力作用下产生滑动,在复杂受力下,八面体剪应力就是促使这种破坏的作用力.裂纹尖端附近某一点的八面体剪应力为:可令上式中B是一个和裂纹大小、形状以及外加应力有关的量.它的大小反映了裂纹尖端附近应力场的强弱.显然它可作为裂纹临界扩展的判据.当B达到临界值BC时,裂纹开始扩展,即B=BC,用本判据理论研究Ⅰ型裂纹问题,得到本判据理论是根据弹性力学八面体剪应力和R.von Mises屈服条件建立起来的,它把断裂力学和传统的力学理论联系了起来,概念清楚、计算简便.从电算结果来看,它比S判据、(σθ)_max判据,G判据更合理、更准确些.     

用宏观和微观相结合方法研究断裂力学

目前流行的断裂力学,包括线弹性断裂力学(Griffith-Lrwin理论)和弹塑性断裂力学(HRR奇异性理论)可称为宏观断裂力学。它不计及构件内部晶体间的变化及其引起的力学效应,只是从整体上研究宏观缺陷产生的力学效应,从而导出裂纹扩展的规律,以企对断裂问题做出宏观的定量分析。目前力学界和工程界研究的主要内容就是这种宏观断裂力学。它既与强度理论有着...     

应用修正的虚裂纹模型研究混凝土结构的三维裂缝扩展

本文在虚裂纹模型中引入初裂强度因子的概念以研究混凝土结构的三维裂缝扩展。虚裂纹的扩展由裂纹尖端的初裂强度因子和虚裂纹所传递的软化应力共同控制。将软化应力分析曲线分段线性化进行模拟,这使问题得到很大程度的简化,同时又保证了解的必要精度。对所建立的有限元基本方程组建议了一次性的求解方法,可以不进行迭代,这既保持了解的稳定,又减轻了计算工作量。