Avaliação da falha em corpos de prova submetidos a compressão por meio do monitoramento de emissões acústicas

Abstract

Structures subjected to loading experience damage processes in the materials that compose them throughout the load history, even without external cracking. Microscopic failure processes occur within the structure material, this generation and growth of microcracks gives rise to acoustic emissions (EAs). By using sensors glued to the surface of the material, it is possible to capture these AEs that travel in the form of elastic waves. And so process the data provided by the waves to study and monitor the internal behavior of the material. The present work aims to analyze and characterize the cracking processes that occur in specimens subjected to axial compression, studying the parameters provided by the elastic waves produced by the deformation energy released at the origin and propagation of cracks. Using accelerometers located on the surface of the specimens, the conversion of elastic waves into electrical signals was performed, which are amplified for the analysis process. These signals were obtained in compression tests performed with three different boundary conditions. One is an anti-friction medium: brush plate, another boundary condition is the reference: traditional standardized test.Finally, a maximum friction configuration is studied: metallic sheets with a thickness of 3 mm glued to the contact faces of the specimens. It was possible to classify the cracks into type I (tensile cracking) and type II (shear cracking). Thus, it was observed that the maximum friction configuration presents characteristic shear cracks (type II) at the extremes close to the machine plates. In the reference test, the influence of friction between the plates of the test machine and the contact faces of the specimen decreases considerably. Finally, using the antifriction medium, the cracking before and after the maximum loading is tensile (type I) being the closest behavior to the test we are performing. As a way of predicting failure in specimens, three approaches are considered. (I) analysis of the value b, (II) analysis of long-range correlations with the exponents “α and h” and (III) analysis of the domain of natural time (NT). These methodologies are applied to data collected from accelerometers placed on 3 specimens of each boundary condition. It is important to take these results into account in the academic context and in engineering practice, as it is a test carried out to verify the compressive strength of the concrete used on site.