Thermal, Magnetic, and Mechanical Modulations of Ultrasonic Diffuse Fields

Richard L.韦弗伊利诺伊大学厄巴纳-香槟分校提案#9988645热，磁，和机械调制的超声波扩散fieldsAbstract：该项目探讨了新的超声无损评价和材料表征的方式，通过调查扩散的超声波信号的温度，磁场和应力的参数变化的依赖。 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（在钢中）磁场。 热变系数和磁变系数取决于应力。 这意味着超声波测量温度和磁场的变化应该允许推断stress.Recent示威，超声波扩散场更敏感（因为旅行时间比传统的超声波场长得多）和更强大（因为对设备的要求是少）的波速变化的指标表明，这些变化可以测量精度很高。 由于超声波的传播速度受温度和磁场的影响，本课题采用扩散场法测量超声波的传播速度。 在各种静态载荷下测量样本的变化，并评估相关性（变异系数与应力）。 超声波还受到低频振动和相关的微裂纹打开和关闭的影响。 在这个项目中，扩散场的变化作为一个试样受到低频准静态应变（如振动）也进行了测量，并与开放和闭合疲劳裂纹的存在相关。该研究将导致新的方法，现场检测的分布损伤，单个疲劳裂纹，和残余应力和外加应力。 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.