Nondestructive Testing of Local Microcracking in Laboratory Mineral Samples Using an Acoustic Method with a Laser Source of Ultrasound and Its Verification with X-ray Computed Tomography

An acoustic technique for nondestructive testing of the degree of local microcracking in laboratory mineral samples based on laser generation of ultrasound is proposed. The spectral power of broadband signals of longitudinal ultrasonic waves is measured. The waves were generated by absorption of pulsed laser radiation in a special material that served as a laser source of ultrasound and further scattered by microcracks in samples (the so-called structural noise power). For two types of feldspars with a nonuniform volumetric distribution of microcracks, a direct relationship was obtained between an increase in microcracks and an increase in the power of structural noise in the sounded sections of the samples. For the first time, an independent method of X-ray computed tomography of complex-shaped samples confirmed the reliability of the results of acoustic measurements. The established relationship between the local microcracking and structural noise power can be used in the monitoring systems for observing the crack formation in rocks and minerals under various external loadings.