受载混凝土破坏全过程声发射信号频带能量特征

摘要

Acoustic emission (AE)tests of a concrete specimen's damage process under uniaxial compression were conducted in order to find more effective concrete failure precursor criteria.The AE signal waveform data in damage process were acquired directly with a SAEU2S digital AE acquisition system.Then these signals at the different damage stages were processed by using FFT and wavelet packet transformation respectively,to find out the frequency distribution rule and the frequency band energy varying rule of the AE signals at the different damage stages.The concrete failure mechanism was explained from the perspective of the relationship between AE signal frequency change and crack propagation.The frequency band energy distribution histograms of the acoustic emission signal at different damage stages were computed and drawn by using the energy calculation method of wavelet packet transformation with Matlab,the energy percentage of the low-frequency band in the range of 0~26 kHz and it versus time change rule were analyzed especially. Accordingly,an important criterion indicator that the low-frequency energy percentage above a certain threshold is the damage critical point was proposed.This index could be used as the failure precursor criterion for stability monitoring and early warning of concretes,and it provided a theoretical guidance for evaluating internal damage of concretes.%为寻找更有效的混凝土工程破坏前兆判据，开展混凝土单轴加载破坏全过程声发射试验。通过SAEU2S型数字声发射采集系统直接采集破坏全过程声发射信号波形，分别用FFT变换及小波包变换对不同破坏阶段声发射信号分析处理，发现不同破坏阶段声发射信号频率分布、频带能量变化规律，并从声发射信号频率变迁与裂纹扩展关系角度阐释混凝土破坏机理。采用小波包变换频带能量计算方法在Matlab中计算并绘制不同破坏阶段声发射信号频带能量分布直方图，重点分析0～26 kHz低频带能量占比及随加载时间变化规律，提出低频能量占比达某门限值即为破坏临界点的重要判据指标。此规律可作为混凝土工程稳定性监测预警前兆判据，对评估混凝土内部损伤具有理论指导意义。