盲孔法测曲面残余应力时释放系数的数值模拟

Numerical Simulation for Hole-drilling Strain Gage Method Applied on Curved Surface

盲孔法是一种测试表层残余应力的高精度机械方法,但现行盲孔法标准的分析和研究都是基于大平板试样,对于待测部位像角焊缝或管表面等非平面的情况,表面形状会对残余应力测试造成多大的影响是文中研究的重点.在材料参数固定的情况下,形状因素直接影响应变释放系数a、b的变化.文中首先基于弹性力学,对比分析平面、凹凸球面模型的几何钻孔截面,发现三者的应力释放差异是由于应变片至孔边的距离D_h不同造成;随后通过ANSYS有限元模拟不同曲率的凹、凸球面模型的钻孔过程,以量化应力释放差异,该模拟结果与D_h随孔深变化的规律一致.另外,基于球面的a、b系数变化结果,提出了适用于包括柱面等所有曲面的a、b系数计算方案.

Hole-drilling method is a mechanical way with high accuracy to measure residual stress on surface.The existing analyses and studies on hole-drilling standard are wholly based on large plane surface,while there is little research on surfaces with curvature,such as the surface of fillet weld or tubes.Thus the objective of this study is to clarify the influence of surface shape on the residual stress level.When the material parameters are fixed,the surface shape have direct influence on the calibration constants a and b.Based on the mechanics elasticity,the comparative analysis of borehole cross-section of the plane surface and spherical surface were carried out.The result shows that stress relief difference is caused by factor D_h,which is the distance from the strain gauge to the edge of the hole.Then the drilling process of concave and convex spherical models with different curvatures were simulated by finite element model ANSYS to quantify the stress relief of different models.The simulation results are consistent with the changing regularity of D_h and hole depth.In addition,based on the results of spherical coefficients,a calculation scheme for general revolution surface was presented,which may be applied to all kinds of surfaces includes cylinders.