Measuring stress levels in loaded structures is crucial to assess and monitor structure health and to predict the length of remaining structural life. Many ultrasonic methods are able to accurately predict in-plane stresses inside a controlled laboratory environment but struggle to be robust outside, in a real-world setting. That is because these methods rely either on knowing beforehand the material constants (which are difficult to acquire) or require significant calibration for each specimen. This paper presents an ultrasonic method to evaluate the in-plane stress in situ directly, without knowing any material constants. The method is simple in principle, as it only requires measuring the speed of two angled shear waves. It is based on a formula that is exact for incompressible solids, such as soft gels or tissues, and is approximately true for compressible “hard” solids, such as steel and other metals. The formula is validated by finite element simulations, showing that it displays excellent accuracy, with a small error on the order of 1%.

中文翻译：

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一种无需校准即可测量应力的超声方法：角向剪切波方法

测量负载结构中的应力水平对于评估和监视结构健康状况以及预测剩余结构寿命的长度至关重要。许多超声方法能够在受控的实验室环境中准确预测平面应力，但在实际环境中却难以在外部保持坚固。这是因为这些方法要么依赖于事先了解材料常数（很难获取），要么需要对每个样本进行大量校准。本文提出了一种超声方法来原位评估平面应力直接，而不知道任何材料常数。该方法原理上很简单，因为它只需要测量两个成角度的剪切波的速度即可。它基于适用于不可压缩固体（例如软凝胶或薄纸）的公式，适用于可压缩“硬”固体（例如钢和其他金属）的公式。该公式已通过有限元模拟进行了验证，表明该公式显示出极佳的准确性，且误差很小，约为1％。