镍基单晶合金CT试样裂纹尖端应力结构及晶体滑移特性

 针对3种不同晶体取向（［001］,［011］,［111］）的镍基单晶合金DD3紧凑拉伸（CT）试样，利用考虑有限变形和晶格转动效应的率相关晶体滑移有限元程序对其裂纹尖端三维应力场进行了弹塑性模拟计算分析，深入考察了裂尖等效应力和滑移系分切应力分布以及滑移系激活规律，并对裂纹扩展路径进行了理论预测和试验研究。结果表明，裂纹尖端应力结构有较大的变化，呈现复杂的变化规律，对此试样的晶体取向有较大的影响；裂纹尖端自由表面形成具有特定矢量方向的滑移带，裂纹启裂和扩张途径与该滑移带有关，晶体学结构分析表明其特征敏感于晶体取向。裂纹尖端的等效应力、最大分切应力沿厚度方向分布均为在试样心部较为均匀，而在外表面处则下降较快，有限元计算和实验测定结果证实这两部分分别与试样断口上的纤维区和剪切唇区相对应。

Characteristics of Crack-tip Stress Structure and Crystal Slipping in Nickel-base Single Supperalloy CT Specimens

Using compact tension(CT)specimens made of nickel-base single supperalloy DD3 in three crystallographic orientations(001],011],111]),the three dimensional elastic-plastic stress fields at the crack-tip have been analyzed by a crystallographic finite element program,which takes the effects of lattice rotation and finite deformation into consideration.The special attention is paid on the resolved shear stress and activating of slip system.The growth path of the crack is predicted by the crystallographic slip theory,which agrees with experiment exactly.The results show that the stress structure is dependent on the crystallographic orientation of specimen.The slip bands take place in specific sectors near crack tip in free surface,on which the initiation and growth of the crack are dependent.The crystallographic structure shows that the number and feature of slip bands are related to the crack orientation.The equivalent Mises stress and resolved shear stress along the thickness direction are nearly constant in the midsections and tend to decrease sharply near the free surfaces,which are experimentally confirmed to correspond to the smooth region and the shear lip on the fracture face respectively.