Diagnostics of deformational and fracture stages based on integral parameters of the flow of acoustic-emission acts

Abstract

The relationships between the sequence of deformational and fracture stages in solids and the integral parameters of an accompanying acoustic emission (AE) are analyzed. A method for reconstruction of the true (radiated) intensity of flow, the spectrum, and the duration and energy of an AE-act is described and the results obtained are presented. The S-shape of the curve of AE-act flow is physically interpreted. The possibility of identifying the fracture stages and, based on the positions of the break points in this curve, estimating the concentration of defects and their multiplication constants is shown. It is found that the lower break point in the curve corresponds to the transition point from the stage of plastic deformation to the stage of scattered accumulation of flaws. It is suggested that the appearance of this break point be used for the early detection of a material's destruction point. The upper break point is interpreted as the point of a change in the multiplication constant caused by the beginning of the localization of the defect generation process.The diagnostics and modeling of the early stages of a solid's fracture encounter considerable difficulties. Classic methods of continuum mechanics and fracture mechanics can be applied if the characteristic size of a single defect (crack) is at least 1 mm. This means that the presence of a single crack has a considerable effect on the strain-stress state (SSS) in the vicinity of a crack. In view of this, a new approach based on the study of the relationship between acoustic emission (AE) parameters and the kinetics of flaw accumulation in solids has actively been developed for over 30 years, along with conventional approaches.So far, the AE methods of diagnostics which find the widest practical use are based on such integral (in the general meaning of this term) parameters of the AE flow as intensity (activity), total number, and energy of detected AE signals. The high informativeness of these parameters follows directly from the nature of the AE phenomenon that involves radiation of elastic waves formed directly in the process of internal local restructuring (or damage) of a solid's structure.The relationship between AE and the stages of the defect generation processes, as well as the possibility of diagnosing the early fracture stages based on integral AE parameters, is studied in the present work.Each collective act of damaging (or restructuring) a structure (dislocation avalanche, merging of microcracks, merging of microcracks with a macrocrack, etc.) is accompanied by generation of an initial elastic pulse; the process of its radiation is known as an acoustic-emission act. Therefore, measurements of either flow intensity (flow rate) of AE acts or their total number N a makes it possible in principle to quantitatively study the kinetics of flaw accumulation and to diagnose the early fracture stages.From the formal point of view, it does not make any difference which parameter to detect, because it is easy to calculate ( t ) using the measured funct...