To gain an insight into the evolution of micro-cracks in concrete materials, a quantitative acoustic emission investigation on the damage process of concrete prisms subjected to three-point bending loading was performed. Each of the monitored acoustic emission signals was processed by a two-level wavelet packet decomposition into four different frequency bands (AA₂, DA₂, AD₂, and DD₂), and the energy coefficients R₁, R₂, R₃, and R₄ that parameterize their characteristic frequency bands were calculated. By analyzing variations in energy coefficients of the lowest frequency band (AA₂), R₁, and the energy coefficients of the highest frequency band (DD₂), R₄, the whole damage process was divided into three stages: crack initiation, crack growth, and crack coalescence. An inverse relationship between the frequency of the acoustic emission signal emitted by the propagating crack and the crack size in concrete materials was acquired based on the damage theory of brittle materials and the strain energy release theory. The statistical analysis results of the experimental data indicated that the average of R₁ increased in turn, and the average of R₄ correspondingly decreased in turn from Stage 1 to Stage 3. It revealed that the frequencies of acoustic emission signals decreased gradually with the evolution of the damage of concrete prisms, which is in a good agreement with the theoretical analysis result.

为了深入了解混凝土材料中微裂纹的演变，对混凝土棱柱体在三点弯曲载荷作用下的损伤过程进行了定量声发射研究。每个监测到的声发射信号经过两级小波包分解处理成四个不同的频段（AA ₂、DA ₂、AD ₂和DD ₂），能量系数R ₁、R ₂、R ₃、和R ₄参数化他们的特征频带被计算。通过分析最低频段 (AA ₂ )能量系数的变化，R ₁，以及最高频段（DD ₂）的能量系数R ₄，整个损伤过程分为裂纹萌生、裂纹扩展和裂纹合并三个阶段。基于脆性材料损伤理论和应变能释放理论，得到了裂纹扩展声发射信号频率与混凝土材料裂纹尺寸的反比关系。实验数据的统计分析结果表明，R ₁的平均值依次增加，R ₄的平均值依次增加。 相应地从第 1 阶段到第 3 阶段依次降低。结果表明，随着混凝土棱柱体损伤的演变，声发射信号的频率逐渐降低，与理论分析结果吻合较好。