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Development of non-contact NDE method by high performance laser AE system

利用高性能激光AE系统开发非接触式NDE方法

基本信息

批准号：
11555180
负责人：
ENOKI Manabu
金额：
$ 8.38万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

In this, research the method using laser interferometer, which can measure the absolute velocity of surface of materials in non-contact, was developed for acoustic emission (AE) transducer. We have demonstrated that this method could detect acoustic emission signals without contact and also applied it to the evaluation of fracture behavior of coating materials at elevated temperature. One of the problems of this method is to have less sensitivity compared with the conventional AE transducer using piezo elastic elements. The purpose of the research is to improve the system for AE measurement and increase the sensitivity for detection... The improvements were done in two ways. (1) The demodulator has been originally designed for laser Doppler vibrator. The frequency' characteristics of demodulator were focused for AE frequency and the noise components of systems were reduced by redesign of internal circuit. (2) Each channel of interferometer is affected by electromagnetic noise, mechanic … More al noise and so on. These noises can not be eliminated basically because AE signal is essentially transient phenomenon. We tried to reduce the noise components by the multi-channel detection of AE signals at the same point and numerical averaging of signals after recording. The method is possible to reduce the only noise component without loss of the characteristics of rising point and peak amplitude of AE wave form. These techniques of laser AE were applied to the thermal cycle tests of coating materials. Location of AE source was analyzed from multi-channel AE measurement and fracture mode was evaluated based on the simulation of elastic wave propagation by finite element method. Finally fracture mechanisms of coating materials were investigated. As the strength of coatings is affected by the initial defects due to plasma spray process, AE behavior was monitored during cooling process after plasma spray using laser AE method and the effect of process conditions on generation of defects was considered. Less

为此，研究了声发射换能器中利用激光干涉仪非接触测量材料表面绝对速度的方法。我们已经证明，该方法可以非接触地检测声发射信号，并将其应用于涂层材料高温断裂行为的评估。这种方法的一个问题是与传统的压电式弹性元件声发射换能器相比，灵敏度较低。研究目的是改进声发射测量系统，提高声发射检测的灵敏度。这些改进是通过两种方式完成的。(1)本解调器是为激光多普勒振荡器而设计的。重点研究了解调器的频率特性对声发射频率的影响，通过对内部电路的重新设计，降低了系统的噪声分量。(2)干涉仪的各个通道都受到电磁噪声、机械…的影响更多的Al噪音等等。由于声发射信号本质上是一种暂态现象，这些噪声基本上不能消除。通过对同一时间点的声发射信号进行多通道检测，并对记录后的信号进行数值平均，以降低噪声分量。该方法可以在不损失声发射波形的上升点和峰值幅度特性的情况下，降低唯一的噪声分量。将这些激光声发射技术应用于涂层材料的热循环试验。通过多通道声发射测量分析了声发射源的位置，并在有限元模拟弹性波传播的基础上对断裂模式进行了评价。最后对涂层材料的断裂机理进行了探讨。针对等离子喷涂过程中初始缺陷对涂层强度的影响，采用激光声发射技术对等离子喷涂后冷却过程中的声发射行为进行了监测，并考虑了工艺条件对缺陷产生的影响。较少