Italian Air Force, Flight Test Centre, Airport De Bernardi, Pratica di Mare, Rome, Italy.
J Acoust Soc Am. 2011 Oct;130(4):1829-37. doi: 10.1121/1.3621714.
Prediction of crack growth and fatigue life estimation of metals using linear/nonlinear acousto-ultrasound methods is an ongoing issue. It is known that by measuring nonlinear parameters, the relative accumulated fatigue damage can be evaluated. However, there is still a need to measure two crack propagation states to assess the absolute residual fatigue life. A procedure based on the measurement of a third-order acoustic nonlinear parameter is presented to assess the residual fatigue life of a metallic component without the need of a baseline. The analytical evaluation of how the cubic nonlinear-parameter evolves during crack propagation is presented by combining the Paris law to the Nazarov-Sutin crack equation. Unlike other developed models, the proposed model assumes a crack surface topology with variable geometrical parameters. Measurements of the cubic nonlinearity parameter on AA2024-T351 specimens demonstrated high sensitivity to crack propagation and excellent agreement with the predicted theoretical behavior. The advantages of using the cubic nonlinearity parameter for fatigue cracks on metals are discussed by comparing the relevant results of a quadratic nonlinear parameter. Then the methodology to estimate crack size and residual fatigue life without the need of a baseline is presented, and advantages and limitations are discussed.
使用线性/非线性超声方法预测金属的裂纹扩展和疲劳寿命估计是一个持续存在的问题。已知通过测量非线性参数，可以评估相对累积的疲劳损伤。然而，仍然需要测量两个裂纹扩展状态来评估绝对剩余疲劳寿命。提出了一种基于测量三阶声非线性参数的方法，无需基线即可评估金属部件的剩余疲劳寿命。通过将巴黎定律与纳扎罗夫-苏廷裂纹方程相结合，提出了分析评估裂纹扩展过程中立方非线性参数如何演变的方法。与其他已开发的模型不同，所提出的模型假设裂纹表面拓扑具有可变的几何参数。对 AA2024-T351 试样的三阶非线性参数测量表现出对裂纹扩展的高灵敏度，并且与预测的理论行为非常吻合。通过比较二次非线性参数的相关结果，讨论了在金属疲劳裂纹中使用三阶非线性参数的优点。然后提出了一种无需基线即可估计裂纹尺寸和剩余疲劳寿命的方法，并讨论了其优点和局限性。
