Caracterização de defeitos de soldagem por análise fractal utilizando emissão acústica em ensaios de tração

Abstract

The present work aims at characterizing and correlating waveforms of acoustic emission signals from welded test samples, with defects, of ASTM 516 - Grade 60 steel used in pressure vessels, pipes, storage spheres, etc., by us-ing fractal analysis and spectral analysis, in order to evaluate their structural integrity. The signals were generated by submitting the samples to tensile tests, and were analyzed in the time domain by using the box counting method, which gives the fractal dimension, and the rescaled range Hurst technique, and, in the frequency domain, the spectral method of Fourier. From the relations predicted by the scaling laws, it can be concluded that the exponents obtained from the spectral analysis and rescaled range Hurst analysis are correlated between themselves and to the fractal dimension obtained by the box counting method. It was also shown that there are two distinct regions which characterize the transi-tion between the elastic and plastic regimes for the samples submitted to the tensile loading. It has also been verified that this behaviour was characteristic of the welded materials as well as of the base metal.