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目前,小孔松弛法测定焊接残余应力在推广使用中的主要问题是如何提高其测量精度。标定试件一般是在拉应力σ≤1/3σ_s时确定常数,然后进行实测。我们认为,当残余应力较大时,按弹性范围的标定常数测取残余应力必然产生误差。残余应力越大,误差越大,当σ接近σ_s时,在本文标定中确定的测量误差为19％。文章对如何进一步提高测量精度进行了新的探索,着重对由于孔边应力集中引起的孔边塑性变形而产生的测量误差作了研究。发现当σ>1/2σ_s时测得的释放应变ε是由纯弹性释放应变ε_e和孔边塑性变形的影响ε_p所组成。计算时应在ε中减去ε_p,即用ε_e算得的残余应力才是真值。本文采用修正方法用ε_e代替ε,在σ接近σ_s时,其测量误差已降至2％以下,从而提高了小孔松弛法测定焊接残余应力的精度。
At present, the main problem in the determination of welding residual stress by small hole relaxation method is how to improve its measurement accuracy. The calibration test specimen is generally determined at a tensile stress σ ≤ 1/3σ_s and then measured. We believe that when the residual stress is large, measuring the residual stress by the calibration constant of the elastic range will inevitably produce errors. The larger the residual stress, the greater the error. When σ is close to σ_s, the measurement error determined in this paper’s calibration is 19%. This article has made a new exploration on how to further improve the measurement accuracy, and focuses on the measurement error caused by the plastic deformation of the hole caused by the hole stress concentration. It is found that the release strain ε measured when σ>1/2σ_s is composed of the pure elastic release strain ε_e and the plastic deformation effect of the edge ε_p. In the calculation, ε_p should be subtracted from ε, that is, the residual stress calculated by ε_e is the true value. In this paper, the correction method is used to replace ε with ε_e. When σ is close to σ_s, the measurement error has dropped to less than 2%, which improves the accuracy of the small hole relaxation method to determine the welding residual stress.