中文摘要：

岩石具有较强的非均质性和强衰减特性，谐波测量的难度较大。建立超声谐波测试实验系统，采用单频脉冲串（toneburst）激发、门控放大、脉冲反转和叠加等增强二次及高次谐波，研究岩石超声谐波的发育与振幅特征，定义名义非线性系数，分析单轴应力下岩石超声谐波及名义非线性系数随应力的变化。结果表明，超声谐波包含了丰富的岩石内部结构信息，表征了岩石的非线性特性，利用先进的仪器系统，采用谐波强化技术，可有效地获得岩石的超声谐波及其振幅，进行岩石非线性特性、微结构变化与损伤演化的监测。

英文摘要：

The strong heterogeneity and strong attenuation in rocks make ultrasonic harmonic measurement more difficult. An experimental system for observing the ultrasonic harmonic was established. The measurement resolution of high harmonic waves was improved through the tone burst excitation, high power gated amplifier, pulse inversion technique and stacks of many repeated measurements. The growth and intensity of uhrasonic harmonic waves were discussed, the nominal nonlinear coefficient was defined, and the variations of harmonic characteristics and the nominal nonlinear coefficient with stress in rocks were investigated. The results show that ultrasonic harmonic includes the abundant information on rock internal struc- ture, and represents the nonlinearity of the rocks. By the advanced instruments and harmonic reinforcement techniques, ul- trasonic harmonic and its amplititude can be effectively measured, and the damage evolution and the variations of nonlinearity and microstructure in loaded rocks can be monitored.