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采用Lemaitre韧性断裂准则与有限元模拟相结合来预测材料在塑性成形过程中的开裂是广泛应用的一种方法,其中的Lemaitre准则是以损伤值与塑性应变呈线性关系为基础的,而实际一些材料的损伤值与塑性应变间却是非线性的。为此,本文将原Lemaitre准则中反映损伤值与塑性应变间的线性关系修正为非线性关系,得到了改进的Le-maitre准则。对比采用改进前后的Lemaitre准则对锥形件旋压和分形旋压开裂的预测结果表明,改进后的Lemaitre准则的预测结果更符合实际。采用改进后的Lemaitre准则在旋压成形中进行应用,获得了偏离率和芯模转速对锥形件旋压过程中损伤值分布和变化的影响。结果表明:零偏离时的损伤值较小,分布也较均匀;大的负、正偏离率下工件的损伤发生的区域不同,在大的负偏离率下,损伤主要发生在工件的顶部大拉应力作用区和旋轮作用下的变形区,在大的正偏离率下,旋轮和起皱后凸缘的干涉作用导致损伤主要分布在凸缘处;当进给比一定时,芯模转速越小,损伤发展越缓慢,越有利于工件的成形。
Using Lemaitre ductile fracture criterion and finite element simulation to predict the cracking of materials during plastic forming is a widely used method. The Lemaitre criterion is based on the linear relationship between damage and plastic strain. However, some actual The damage value of the material and the plastic strain are nonlinear. Therefore, in this paper, the linear relationship between the damage value and the plastic strain in the original Lemaitre criterion is corrected to a non-linear relationship, and an improved Le-maitre criterion is obtained. The results of the prediction of the spinning and fractal spin-fractures using the Lemaitre criterion before and after the comparison show that the improved Lemaitre criterion is more realistic. The modified Lemaitre criterion was applied to the spinning process to obtain the effect of the deflection rate and the speed of the mandrel on the damage distribution and the variation during the spinning process of conical parts. The results show that the damage value is smaller and the distribution is more uniform when the zero deviation occurs; the damage occurs in the workpiece with large negative and positive deviations, and the damage occurs mainly at the top of the workpiece under the large negative deviation rate Under the large positive deviating rate, the interference zone between the wheel and the crepe flange led to the damage mainly distributed in the flange. When the feed ratio was constant, the rotation speed of the mandrel The smaller, the slower the damage development, the more conducive to the formation of the workpiece.