Thermal, Magnetic, and Mechanical Modulations of Ultrasonic Diffuse Fields

理查德·L·韦弗伊利诺伊大学香槟分校#9988645#9988645超声漫射场的热、磁和机械调制摘要：该项目通过研究扩散超声信号与温度、磁场和应力参数变化的相关性，探索了超声无损评估和材料表征的新模式。常规(非扩散)超声对具有工程意义的各种材料特性敏感。它对外部施加的参数也很敏感。其中值得注意的是温度和(钢材)磁场。热变化系数和磁变化系数取决于应力。这意味着超声波对温度和磁场变化的测量应该允许推断应力。最近的证据表明，超声波漫射场更敏感(因为走时比传统超声场要长得多)和更稳健(因为对仪器的要求更低)的波速变化指示器表明，这些变化可以非常精确地测量。由于超声波传播速度依赖于温度和磁场，因此本课题采用漫射场来测量超声波传播速度。用不同静载下的试件测量了变化，并评估了相关性(变化系数与应力)。超声波还受到低频振动以及相关微裂纹的开启和闭合的影响。在本项目中，还测量了试件在低频准静态应变(如振动)作用下扩散场的变化，并将其与张开和闭合疲劳裂纹的存在进行了关联。该研究将为现场检测分布损伤、单个疲劳裂纹以及残余应力和外加应力提供新的方法。无损评估方面的相应改进将加强对剩余结构寿命的评估，这对老化的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.