用弹塑性有限元法求解脉动循环载荷有超载时裂尖前方的应力、应变分布及塑性区的大小

 本文用弹塑性有限元法求解了理想塑性材料在三个脉动循环载荷下有超载时裂尖前方的应力、应变分布及塑性区的大小。文中用平均刚度法、一阶自校正法进行了计算,讨论了这两种方法的优缺点。结果表明,当有超载时裂尖引起很大的残余压应力,使固有塑性区尺寸大大缩小,从而在一定的条件下,可使裂纹扩展延缓。计算结果与H.Miyamoto~1]的结果作了比较,得到相当满意的吻合。

CALCULATION OF STRESS, STRAIN AND PLASTIC ZONE AHEAD OF CRACK TIP UNDER PEAK OVERLOAD WITH PULSATING LOADS BY ELASTOPLASTIC FEM

The calculation deals with a rectangular plate with central crack under tensile pulsating loads in y-direction. The stress and strain distributions and the size of plastic zone ahead of the crack tip are determined by means of elastoplastic FEM. The material of the plate is assumed to be perfectly elastoplastic. Average rigidity method and first order self-correction method are used respectively in the calculation. The strong and weak points of both the methods are discussed.The calculation demonstrates that there is a high compressive residual stress ahead of the crack tip when a peak of overload is followed by pulsating loads. The size of the intrinsic plastic region becomes smaller. This would cause retardation of the fatigue crack propagation rate. Moreover, The COD increases with the peak overload. This may accelerate the growth of the crack. It is shown wrong that the peak overload should be as large as possible. There must be a limit on it.The results of the calculation agree well with data of H. Miyamo-to, but the machine time is lessened.