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 ultrasonic 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 structure,and represents the nonlinearity of the rocks.By the advanced instruments and harmonic reinforcement techniques,ultrasonic 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.
