Thermal, Magnetic, and Mechanical Modulations of Ultrasonic Diffuse Fields

摘要：本项目通过研究超声弥散信号对温度、磁场和应力参数变化的依赖性，探索超声无损评价和材料表征的新模式。常规（非弥漫性）超声对多种具有工程意义的材料特性敏感。它对外部应用的参数也很敏感。其中值得注意的是温度和（在钢中）磁场。热变系数和磁变系数取决于应力。这意味着，温度和磁场变化的超声波测量应该允许推断应力。最近的证明表明，超声波漫射场更敏感（因为传播时间比传统的超声波场长得多）和更稳健（因为对仪器的要求更少），波速变化的指标表明，这些变化可以非常精确地测量出来。漫射场在这个项目中被用来测量超声波的速度，因为它取决于温度和磁场。在各种静态载荷下测量试样的变化，并评估相关性（变异系数与应力）。超声波也受到低频振动和相关微裂纹的打开和关闭的影响。在这个项目中，扩散场的变化作为试样受到低频准静态应变（如振动）也被测量，并与疲劳裂纹的打开和关闭的存在相关。该研究将为现场检测分布损伤、单个疲劳裂纹、残余应力和外加应力提供新的方法。无损评估的相应改进将加强对剩余结构寿命的评估，这对老化的航空机队和民用基础设施至关重要。

Richard L. WeaverUniversity of Illinois at Urbana-ChampaignProposal # 9988645Thermal, Magnetic, and Mechanical Modulations of Ultrasonic Diffuse FieldsAbstract:This project explores novel modalities for ultrasonic NonDestructive Evaluation and Materials Characterization by investigating the dependence of diffuse ultrasonic signals on parametric variations of temperature, magnetic field, and stress. Conventional (non-diffuse) ultrasound is sensitive to a variety of material properties of engineering significance. It is also sensitive to externally applied parameters. Notable amongst these are temperature, and (in steels) magnetic field. The coefficients of thermal and magnetic variation depend on stress. This implies that ultrasonic measurements of temperature and magnetic field variations should allow inference of stress.Recent demonstrations that ultrasonic diffuse fields are more sensitive (because travel times are much longer than those of conventional ultrasonic fields) and more robust (because demands on apparatus are less) indicators of wave speed change suggest that these variations can be measured with great precision. Diffuse fields are used in this project to measure ultrasonic wave speed as it depends on temperature and magnetic field. The variations are measured with specimens under a variety of static loads, and the correlation (coefficient-of-variation versus stress) assessed. Ultrasound is also affected by low-frequency vibrations and the associated opening and closing of microcracks. In this project the variations of diffuse fields as a specimen is subjected to low-frequency quasi-static strains (e.g. vibrations) are also measured, and correlated with the presence of opening and closing fatigue cracks.The research will lead to new methods for field detection of distributed damage, of individual fatigue cracks, and of residual and applied stress. The corresponding improvements in nondestructive evaluation will tighten assessments of remaining structural life, critical for aging air fleets and civil infrastructure.