Reliability Evaluation of small Specimen by Laser AE System

本研究的目的是从理论上改进基于激光的声发射技术及其应用，并论证该方法在可靠性评估中的有效性。通过分析常规无损评价方法和声发射技术的优缺点，明确了研究对象。虽然传统的PZT元件声发射方法存在传感器粘着问题，但激光干涉仪声发射测量技术具有表面速度绝对测量、恶劣环境下无损检测等优点。将该技术应用于薄介质薄膜介电击穿过程的评价，结果表明，断裂形态按产生电场大小和频率进行分类，前驱体电流不是由相变和微断裂引起的。成功地检测到了作为声发射信号…的微小局部放电更多的是通过这种方法直接在液体中进行。对活性复合材料的热变形过程进行了研究，结果表明，热应力引起的微断裂是导致材料工作特性非线性的原因。此外，还对引入损伤的温度范围进行了评估。用声发射的小波分析来了解这些复合材料的断裂过程。将该方法应用于几十微米厚的金属薄膜，成功地检测到了这些样品由于变形和损伤而产生的声发射信号。将该激光声发射技术应用于材料加工，并通过在线监测对材料的可靠性进行了评价。利用激光声发射技术对陶瓷的烧结过程进行了监测，并测量到了超过1500℃的微裂纹。这些结果是通过这种独特的激光声发射技术获得的，这表明该技术对于了解材料的断裂行为和材料加工设计是非常有用的。较少

The objective of this research project is to improve the laser based AE (acoustic emission) technique by theoretical consideration and its application and demonstrate the effectiveness of this method for reliability evaluation. Research target was clearly focused by analyzing the advantages and weak points of conventional nondestructive evaluation (NDE) method and AE technique. Although here are some problems in the conventional AE method using PZT elements concerning adhesion of sensor, AE measuring technique using laser interferometer has some advantages such as absolute measurement of surface velocity, NDE in severe environment and so on. This technique was applied to the evaluation of dielectric breakdown process of thin dielectric film, and it was demonstrated that fracture morphology was classified by generation electric field value and frequency and precursor current was not due to phase transition and microfracture. Small partial discharge was successfully detected as AE signal … More by this method directly in liquid. Thermal deformation process in active composite materials was investigated and it was clearly shown that the cause of non-linearity of operating characteristics was due to microfracture induced by thermal stress. Also temperature range where damage was introduced was evaluated. Wavelet analysis of AE was used to understand the fracture process these composites. This method was also applied to thin metallic films with thickness of several tens micron and AE signals of these samples due to deformation and damage were successfully detected. This laser AE technique was applied to materials processing and reliability of materials was evaluated by in-process monitoring. Sintering of ceramics was monitored by laser AE technique and microcracks generated over 1500℃ were measured. These results were obtained by this unique laser AE technique and it was demonstrated that this technique was very useful for understanding of the fracture behavior and design of materials processing. Less