Controlling plasticity in the contour method of residual stress measurement
Controlling plasticity in the contour method of residual stress measurement
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残余应力测量轮廓法中控制塑性
DOI：
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发表时间：
2013
期刊：
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通讯作者：
Y. Traoré
中科院分区：
文献类型：
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作者：
Y. Traoré
轮廓法已成为一种很有前途的技术，用于测量相对较大，较厚和复杂的工程构件的残余应力。该方法包括在感兴趣的样品中进行切割，测量切割表面的随后的松弛变形轮廓，并使用该轮廓通过有限元建模来反算原始平面外残余应力场。该方法是基于弹性理论，在测试样本切割过程中的应力松弛被假定为完全弹性的。然而，当测量接近材料屈服强度的残余应力时，可能发生塑性，这在测量的应力分布中引入误差。
本论文的主要目的是开发方法，以减轻和估计塑性引起的误差轮廓法残余应力测量。
根据断裂力学原理，将应力松弛过程类比为裂纹板，探讨了围道法中塑性的起源。结果表明，切尖应力强度因子（KT）和相应的塑性区参数是表征轮廓法中塑性引起的误差的最重要参数。为了提高该方法的精度和可靠性，进行了大量的有限元分析，以了解和控制与塑性相关的误差。
这项研究的结果提供了一个有价值的洞察如何积累的塑性不同的约束条件影响的轮廓法的性能。提出了一种新的切削策略，通过控制切削过程中切削尖端应力集中（即应力强度因子）的严重程度来减轻塑性引起的误差。此外，程序（相关性）开发，以估计塑性引起的误差的轮廓法的结果。最后，提出了指导方针，并应用于一个案例研究，以减轻与塑性的轮廓法残余应力测量的错误。
The contour method has emerged as a promising technique for residual stress measurement in relatively large, thick and complex engineering components. The method involves making a cut in the sample of interest, measuring the subsequent relaxed deformation profile of the cut surface and using this profile to back-calculate the original out-of-plane residual stress field by finite element modelling. The method is based on the theory of elasticity in that the stress relaxation during test specimen cutting is assumed to be entirely elastic. However, when measuring residual stresses of magnitude approaching the material yield strength, plasticity can occur which introduces errors in the measured stress profile.
The main aim of this thesis was to develop methods of mitigating and estimating plasticity induced errors in contour method residual stress measurements.
Based on the principles of fracture mechanics, an analogy was made between the stress relaxation process and a cracked plate to investigate the origin of plasticity in the contour method. It was demonstrated that that the cut tip stress intensity factor (KT) and the corresponding plastic zone parameters are the most important parameters for characterising plasticity-induced errors in the contour method. Extensive finite element analyses were carried out to understand and control the errors associated with plasticity with a view of improving the accuracy and reliability of the method.
The outcomes of this research provide a valuable insight into how accumulation of plasticity for different restraining conditions affects the performance of the contour method. A novel cutting strategy that aims at mitigating plasticity-induced error by controlling the severity of the cut tip stress concentration (i.e. stress intensity factor) during the cutting process has been developed. Furthermore, procedures (correlations) are developed to estimate the plasticity-induced errors in the results of the contour method. Finally guidelines are proposed and applied to a case study for mitigating the errors associated with plasticity in a contour method residual stress measurement.