基于小波变换的混凝土压缩损伤模式识别

为了实时获取混凝土中微裂纹扩展演化的物理信息，对实验采集的每一个声发射信号作小波变换，识别出3种典型模式的声发射信号；根据声发射信号的事件密度变化规律和脆性材料断裂理论，将混凝土压缩破坏过程分为微孔洞压缩闭合、裂纹萌生、裂纹生长和裂纹汇合4个阶段。根据混凝土材料中声发射信号频率与裂纹源尺寸呈反比例关系以及声发射信号在4个破坏阶段中的分布特征，将3种模式的声发射信号分别对应于裂纹萌生、裂纹生长和微孔洞压缩闭合、裂纹汇合。实验结果表明，裂纹萌生、裂纹生长和微孔洞压缩闭合、裂纹汇合对应的声发射信号的上升时间依次增长、频率逐渐降低，与应变能释放理论相符合。

Identification of Damage Modes of Concrete under Compressive Loading Based on Wavelet Transform

In order to acquire the physical information about the evolution of microcraks in concrete in real time,three typical types of acoustic emission (AE) signals are identified by the wavelet transform of experimentally collected AE signals.The whole compressive fracture process of concrete is divided into four stages,i.e.,microvoid compressive closure,crack initiation,crack growth and crack coalescence,on the basis of the event density fluctuation of AE signals andthe fracture theory of brittle materials.Based on the inverse proportional relationship between the frequency of AE signal and crack size,and the distribution characteristics of the three types of AE signals at four fracture stages,the AE signals are associated with crack initiation,crack growth (or microvoid compressive closure) and crack coalescence,respectively.The experimental results show that the rise times and frequencies of AE signals caused by crack initiation,crack growth (or microvoid compressive closure) and crack coalescence increase in turns and decrease gradually,respectively,which conform to the strain energy release theory.