振动声无基线无损检测
Vibro-acoustic baseline-free nondestructive testing
摘要：
在过去的二十年里，用于检测和表征各种结构和材料缺陷的振动声调制方法一直在积极研究。大多数研究集中在宏观裂纹的检测和监测上，需要调制指数的良好建立的基线（无损伤）值。基线值是特定于特定结构、测量设置和其他因素的，并且在许多实际情况下，如果没有长期监测以寻找调制指数的相对变化，则无法建立基线值。在这项工作中，我们提出并研究了一种无基线的声振调制方法，它不需要监测相对调制指数的变化，不像传统的方法。有人假设，非线性机制（和相应的非线性响应）的结构是不同的未损坏和损坏的材料。举例来说：没有损伤或处于疲劳早期阶段的材料具有经典的弹性或滞后/耗散非线性，而损伤（破裂）材料可能表现出接触双线性或赫兹非线性机制。这些机制产生调制指数（MI）作为所施加的振动频率输入振幅的函数的不同幂律依赖性，B：MI ~ B^b。因此，二次非线性产生线性依赖性，b =1，并且赫兹非线性导致b<1。其他非线性机制产生不同的幂律。因此，测量功率损伤系数b代替MI可以提供没有既定参考值的测试。对损伤演化过程中的非线性机制转换也有一定的认识。该方法进行了实验研究和验证。
英文摘要：
Vibro-Acoustic Modulation method for detection and characterization of various structural and material flaws has been actively researched for the last two decades. Most of the studies focused on detection and monitoring of macro-cracks requiring well established baseline (no-damage) value of the modulation index. The baseline value is specific for a particular structure, measuring setup, and other factors and can't be established in many practical situations without a long term monitoring looking for a relative change in the Modulation Index. In this work, we propose and investigate a baseline-free Vibro-Acoustic Modulation method, which does not require monitoring of relative Modulation Index change, unlike conventional approach. It was hypothesized that the nonlinear mechanisms (and respective nonlinear response) of a structure are different for undamaged and damaged material. For example: material without damage or at early stages of fatigue have classic elastic or hysteretic/dissipative nonlinearity while damaged (cracked) material may exhibit contact bi-linear or Hertzian nonlinear mechanisms. These mechanisms yield different power law dependencies of Modulation Index (MI) as function of applied vibration frequency input amplitude, B: MI ~ B^b Thus, quadratic nonlinearity yields linear dependence, b =1, and Hertzian nonlinearity results in b<1. Other nonlinear mechanisms yield different power laws. Therefore, measuring power damage coefficient b instead of MI may offer testing without established reference value. It is also offer some insights into the nonlinear mechanisms transformation during damage evolution. This approach was experimentally investigated and validated.
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