Measuring internal residual stress in Al-Cu alloy forgings by crack compliance method with optimized parameters

Abstract

Measuring the internal stress of Al alloy forgings accurately is critical for controlling the deformation during the subsequent machine process. In this work, the crack compliance method was used to calculate the internal residual stress of Al-Cu high strength alloys, and the effect of various model parameters of crack compliance method on the calculated precision was studied by combining the numerical simulation and experimental method. The results show that the precision first increased and then decreased with increasing the crack range. The decreased precision when using a high crack range was due to the strain fluctuation during the machining process, and the optimized crack range was 71% of the thickness of forgings. Low orders of Legendre polynomial can result in residual stress curve more smooth, while high orders led to the occurrence of distortion. The Tikhonov regularization method effectively suppressed the distortion of residual stress caused by the fluctuation of strain data, which significantly improved the precision. In addition, the crack compliance method with optimized parameters was used to measure the residual stress of Al-Cu alloy with different quenching methods. The calculated results demonstrated that the distribution of residual stress was obtained accurately.

摘要

准确测量铝合金锻件内部残余应力对于控制合金后续机加工变形具有重要作用。本文采用裂纹 柔度法计算了铝铜合金锻件内部残余应力, 结合实验和仿真的方法研究了裂纹柔度法模型参数对残余 应力计算精度的影响。结果表明, 随着引入裂纹深度的增加, 计算精度先逐渐增加再逐渐降低。机加 工过程中的应变数据波动导致残余应力计算精度降低, 最优的裂纹深度范围为锻件厚度的71%。采用 低阶插值阶数会导致残余应力曲线过于平滑, 而高阶插值阶数会使残余应力曲线出现扭曲。吉洪诺夫 正则法可有效抑制应变数据波动导致残余应力曲线计算失真, 从而大幅提高计算精度。采用优化的裂 纹柔度法测量了不同淬火方式铝铜合金锻件内部残余应力, 计算结果表明使用该方法可以准确地测量 合金内部残余应力。