金属箔厚向为一个或几个晶粒时微塑性成形的本构模型(英文)

Constitutive model for thin sheet metal with one or several grains across thickness in micro-forming

为了描述4个因素(晶粒尺寸d、材料厚度t、厚度方向的晶粒数目(t/d)以及表面特性)对金属箔流动应力的影响,将表面层模型和位错密度结合,定量分析厚度方向晶粒数目对纯铜箔流动应力的影响,提出临界晶粒数目的判断准则。预测结果表明,当t/d大于某一临界值时,厚度方向晶粒数目对流动应力的影响可以忽略;而由于临界晶粒数目的影响,晶粒尺寸和厚度分别与流动应力的变化曲线也都出现了明显的转折点。基于以上分析,建立了一个综合的材料本构模型。该模型同时考虑了以上4个因素对金属箔流动应力的影响。将模型的计算结果与已有文献中高纯度镍的实验数据进行对比。结果表明,预测结果与实验数据相吻合且具有相同的变化趋势。特别是随着t/d比值的减小,Hall-Petch关系以及真实应力的变化曲线都具有2个明显的转折点。

Effects of four factors on thin sheet metal flow stress were considered, including grain size d, thickness t, grain number across thickness （t/d ratio） and surface property. Surface model was adopted to quantitatively describe the effect of t/d ratio on flow stress for pure copper. It is predicted that when t/d ratio is larger than a critical value, effect of t/d ratio on flow stress can be neglected. Existence of critical t/d ratio changes the Hall-Petch relationship and evolution of flow stress with thickness. A criterion was proposed to determine critical t/d ratio. Then a comprehensive constitutive model was developed to consider all the four factors, with parameters determined by fitting experimental data of high purity Ni. The predicted results show the same tendencies with experiment results. Particularly when t/d ratio decreases, Hall-Petch relationship and evolution of true stress show varied slopes with two transition points.