Time of flight diffraction for rough planar defects
Time of flight diffraction for rough planar defects
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DOI：
10.1016/j.ndteint.2021.102521
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发表时间：
2021-08-24
影响因子：
4.2
通讯作者：
Shi, Fan
中科院分区：
文献类型：
--
作者：
Haslinger, Stewart G.;Lowe, Michael J. S.;Shi, Fan
超声波无损评估技术，例如飞行时间衍射 (ToFD)，通过分析从裂纹尖端衍射的波的到达时间来定位缺陷并确定缺陷尺寸，对于光滑缺陷来说是众所周知的。在温度和压力发生极端变化的环境中，可能出现的损坏通常是不均匀的，并且在设计和鉴定检查时更难以表征。本文研究了使用纯理论方法来确定粗糙缺陷尺寸的 ToFD 方法的实现。高保真有限元建模和随机蒙特卡罗方法用于提供物理和统计见解，以了解平面缺陷情况下入射光束角度和粗糙度的依赖性。超声波 ToFD 技术的最佳入射角是在 20 世纪 80 年代确定的，但主要基于对光滑缺陷的理论和实验研究。然而，粗糙缺陷产生的尖端衍射特征比光滑缺陷更复杂，这主要是由于与模式转换和表面波沿粗糙表面传播相关的多重散射效应。结果表明，粗糙度可能会在不同角度导致更大的衍射振幅值，从而导致尺寸确定时的不确定性增加，并提供了说明性示例和物理解释。还演示了相同尺寸的光滑和粗糙缺陷的振幅比较。采用包络峰值检测和自相关方法的 ToFD 方法来估计粗糙裂纹的尺寸，并通过统计分析研究粗糙度对该尺寸精度的影响。
Ultrasonic non-destructive evaluation techniques, such as time-of-flight diffraction (ToFD) for which the arrival times of waves diffracted from crack tips are analysed to locate and size defects, are well understood for smooth defects. In environments where extreme changes in temperature and pressure occur, the damage that may arise is often non-uniform and more difficult to characterise when designing and qualifying an inspection. This article investigates the implementation of ToFD methods for sizing rough defects using a purely theoretical approach. High-fidelity finite element modelling and stochastic Monte Carlo methods are used to provide physical and statistical insights for the dependence on both incident beam angle and degree of roughness for the case of planar defects. Optimal incident angles for ultrasonic ToFD techniques were determined in the 1980s but largely based on theoretical and experimental investigations for smooth defects. However, rough defects produce tip-diffracted signatures that are more complicated than for their smooth counterparts, largely due to multiple scattering effects related to mode conversion and propagation of surface waves along the rough surface. It is shown that roughness may cause larger diffraction amplitude values at different angles, which leads to increased uncertainty when sizing, with illustrative examples and physical interpretations provided. Comparisons of amplitudes for smooth and rough defects of the same size are also demonstrated. The ToFD method, using envelope peak detection and autocorrelation approaches, is implemented to estimate the size of rough cracks, and the effects of roughness on the accuracy of this sizing are investigated with statistical analysis.