Experimental Study On The Vibration Effect Of Rock Under Ultrasonic Excitation

Ultrasound has many advantages,such as high frequency,short wavelength,high energy,good direction,strong penetration ability and high power.The application of ultrasonic technology to rock breaking is an important direction for exploring high efficiency rock breaking in the future.Therefore,taking the common hard rock red sandstone in coal measures strata as an example,the vibration and damage characteristics of rocks under ultrasonic excitation are studied by combining theoretical analysis,laboratory experiments and numerical simulation,which can provide reference for the mechanism of ultrasonic rock breaking in the future.The main research results are as follows:(1)According to the basic characteristics of rock,rock is regarded as an elastic-plastic body,and rock vibration mechanics model under ultrasonic excitation is established,rock particle vibration equation under ultrasonic excitation is obtained;rock damage accumulation and fracture failure characteristics under ultrasonic excitation are analyzed,and rock stress wave energy density under ultrasonic excitation and effective stress wave damage energy under ultrasonic excitation are obtained.The expression of the magnitude can grasp the characteristics of the effective damage energy of rock and the energy density of loading stress wave under the excitation of ultrasonic wave.(2)Based on the vibration experiment under ultrasonic excitation,the frequency,acceleration and strain characteristics of three size specimens(Class A: 50 mm *100mm,Class B: 100 mm *100mm,Class C: 200 mm *200mm *100mm)under ultrasonic excitation were studied.The vibration frequencies of specimens with different sizes under ultrasonic excitation are consistent with the excitation frequencies;the smaller the size of specimens is,the larger the acceleration is.The acceleration of specimens with the same size has attenuation at different spatial positions,and the transverse attenuation is smaller than the longitudinal attenuation;the smaller the size of specimens,the larger the strain value.(3)Based on the response characteristics and damage analysis of rock under ultrasonic excitation,the displacement variation characteristics of specimens with different sizes under ultrasonic excitation are mastered.The displacement fluctuation amplitude of specimens with class C is the smallest.When loading synchronization is the same,the internal damage of type A specimens is the largest,and the cracks are more developed.The spatial characteristics,maximum depth of action and longitudinal position of different depths of specimens with the same size under ultrasonic excitation are analyzed.The magnitude of displacement attenuation is large,and the change of lateral displacement is symmetrical with the excitation center as the axis,and the closer the excitation point is,the smaller the lateral displacement is.The damage characteristics of rock interior caused by increasing the area of ultrasonic excitation are clearly defined.When the diameter of excitation area increases from 20 mm to 30 mm,the number of internal cracks in type B specimen increases by 107%.(4)The wave velocities of specimens of different sizes before and after ultrasonic excitation are tested and analyzed.It is concluded that the damage amount of type A specimens is about 0.4075 when the excitation time is 60 s.When the volume of specimens increases by 5 times,the damage amount inside the rock decreases by 48%,and when the volume increases by 20 times,the damage amount inside the rock decreases by 77%.A preliminary method to increase the damage amount of rock is proposed.