Assessing Hazard Degree of Crack-Like Defects Based on Acoustic Emission Testing under Local Low-Temperature Loading

Abstract—

The scientific foundations for the development of a method for assessing the degree of danger of single crack-like defects found in thin-sheet metal structural elements are being investigated using AE testing using the low-temperature loading method. As a criterion, it is proposed to use the “critical activity” of the AE source, calculated using the equations of fracture mechanics and thermal conductivity. Loading is carried out via cooling the local ring-shaped zone by placing the carbon dioxide with a temperature of –78°C. At the same time, as a result of thermal contraction, tensile stresses arise that load the defect area during AE testing. The resulting temperature field and mechanical stresses are calculated by known theoretical methods using the heat and fracture mechanics equations. The annular appearance of the cooling zone determines the invariance of loading relative to the angle of the crack plane. Fracture mechanics criteria are employed that use the known power-law dependence of the number of acoustic emission acts on the stress intensity factor. Thus, the possibility of using the fracture mechanics criteria to assess the danger of crack-like defects by AE testing using the known power-law dependence of the number of acoustic emission acts on the stress intensity factor is shown.