STUDY OF AE WAVE GENERATION BY STRESS WAVE VISUALIZATION METHOD

利用应力波可视化技术模拟了声发射的产生、传播及其与接收信号的关系。为了模拟声发射波的产生，在玻璃模型试件中引入一条缝隙来模拟裂纹，并在缝隙尖端放置一个压电换能器，使其在施加电脉冲的情况下发生类似于裂纹尖端断裂的变形，用两种矩形的PZT换能器来模拟实际的裂纹尖端断裂，其中一种作为I型断裂，另一种作为II型断裂，沿厚度方向变形。应用应力波可视化技术，我使用了声速与钢相似的玻璃模型试件。采用正方形和杆状两种试件，研究了试件形状对声发射波产生的影响。本研究中使用的应力波可视化系统最初是为了在固体中进行超声波可视化而开发的。两种类型的宽带声发射传感器和Re…更多的声波类型被用来接收声发射波，以表征这些声发射传感器。在这种模拟方法中，可以重复产生相同的声发射波，从而能够通过接收相同的声发射波来进行准确的比较来评估声发射传感器的接收特性。1.尽管在缝隙尖端放置了不同类型的PZT，但纵波和横波都是以声发射波的形式从缝隙尖端发出的。然而，由厚度变形模式PZT产生的主波是纵波，由剪切变形模式PZT产生的波是横波，并且每个波具有不同的方向性。2.不同形状的试件在声发射波的产生和传播上存在差异。在杆型试件中，沿试件表面传播的部分纵波由节点型转变为横波。3.声发射传感器接收到的声发射信号与实际的爆发式声发射信号相似。当接收到相同的由放置在缝隙尖端的PZT产生的声发射波时，从每个声发射传感器观察到不同的信号。较少

I simulated AE generation, propagation and its relation to received signal by means of stress wave visualization techniques. In order to simulate the AE wave generation, I introduced a slit into a glass model specimen as a simulation of a crack and put a piezoelectric transducer in the slit tip to deform like crack tip fracture by applying an electric pulse.Two types of PZT transducers, having rectangular shape, were used to simulate the actual crack tip fracture; one was deformed to thickness direction as mode I fracture and the other made shear deformation as mode II fracture. Applying the stress wave visualization technique, I used glass model specimens which have similar sound velocities to that of steel. Square shape and bar type specimens were used to study the effects of specimen shape to the AE wave generation.The system for stress wave visualization used in this study was originally developed for ultrasonic wave visualization in a solid.Two types of wide band AE sensors and re … More sonant type one were used to receive the AE wave for characterizing these AE sensors. In this simulation method, the same AE wave can be generated repeatedly so that exact comparison is enable to evaluate receiving characteristics of the AE sensors by receiving the same AE wave.Results obtained in this study are as follows. 1. In spite of the different types of PZT put in the slit tip, both longitudinal and shear wave were emitted as an AE wave from the slit tip. However, a main wave generated by the thickness deformation mode PZT was a longitudinal wave and the wave generated by the shear deformation mode PZT was a shear wave, and each wave has different directivity. 2. There are differences in the AE wave generation and propagation between the specimen shapes. In the bar type specimen, part of longitudinal waves propagating along the specimen surface were inode-coriverted to shear waves. 3. Received AE signals by the AE sensors were similar to actual burst type AE signal. When receiving the same AE wave generated by the PZT put at the slit tip, different signal were observed from each AE sensor. Less