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AE波的产生，我在玻璃模型试样中引入一条狭缝作为裂纹的模拟，并在狭缝尖端放置一个压电换能器，通过施加电脉冲使其像裂纹尖端断裂一样变形。采用两种矩形PZT换能器模拟实际裂纹尖端断裂；一个向厚度方向变形为I型断裂，另一个剪切变形为II型断裂。应用应力波可视化技术，我使用了与钢具有相似声速的玻璃模型试样。采用方形和条形试样研究了试样形状对声发射波形产生的影响。本研究中使用的应力波显示系统最初是为固体中的超声波显示而开发的。采用两种宽频带声发射传感器和高频型声发射传感器接收声发射波形，对两种声发射传感器进行表征。在这种仿真方法中，可以重复产生相同的声发射波，以便通过接收相同的声发射波来准确地比较评价声发射传感器的接收特性。本研究的结果如下：1. 在狭缝尖端放置不同类型的压电陶瓷，纵波和横波都以声发射的形式从狭缝尖端发射。而厚度变形模式PZT产生的主波为纵波，剪切变形模式PZT产生的波为横波，且各波具有不同的指向性。2. 不同形状的试样在声发射波的产生和传播方面存在差异。在杆型试件中，沿试件表面传播的部分纵波发生了向纵波的倾变。3. 声发射传感器接收到的声发射信号与实际突发型声发射信号相似。当接收到放置在狭缝尖端的压电陶瓷产生的相同声发射波时，每个声发射传感器发出的信号不同。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