Электромагнитные методы контроля изменений напряженно-деформированного состояния диэлектрических материалов

Mechanical-electrical and acoustic-electrical complex methods of testing cracking while changing the stress-strain state in dielectrics are discussed on the example of rock samples. The paper discusses the results of numerical and experimental studies of changes in the electromagnetic responses parameters under the pulse deterministic acoustic excitation of rock samples with different composition and texture. Also the results of mathematical calculations of the stress concentration on cracks located along the sample axis are presented, perpendicular to which deterministic acoustic pulses were introduced. The experimental studies results of sample electromagnetic emission with containing calcite and magnetite under uniaxial compression to fracture are shown. Regularities in the electromagnetic signals amplitudes changes during acoustic sounding in the process of «stepwise» uniaxial loading by compression to destruction are given.

Acoustic-electrical testing of defects in the cement-sand and cement-glass model samples

A complex method of acoustic-electrical testing of defects in dielectric samples made from cement-sand and cement-glass mixtures is discussed. The paper reports the results of studies of changes in the parameters of electromagnetic responses and their spectra under pulsed deterministic acoustic excitation of model samples with defects in the form of solid-state inclusions. The results of mathematical calculations of the time variation in the stress-strain state induced in a defective dielectric model sample by deterministic acoustic pulse are presented. The relationship is shown between the parameters of the acoustic excitation and the electromagnetic response to the impact in a magnetic field. The study revealed that the specific electrical resistance of the cement-sand and cement-glass mixtures differs significantly. Excitation of electrical double layers by acoustic pulses causes an electromagnetic signal, parameters of which depend on the parameters of the acoustic impact and acoustic and electrical properties of the material. As a result, a reduced specific electrical resistance of the mixture increases its conductivity. The numerical calculation of the propagation of the deterministic acoustic pulse showed that its parameters change when it passes through a defect with acoustic impedance different from that of the mixture used.