Tensile failure analysis of structural materials using acoustic emission.

Materials testing is an extremely important process in the modern world with new colossal structures being built in every corner of the earth, with the ever increasing size of structures making safety of vital importance. This project examines the mechanical behaviour of three commonly used structural metals when subjected to a tensile loading; Steel, Aluminium and Brass. The tensile load was applied to the metallic specimens at different loading rates. Acoustic Emission (AE) was the main monitoring tool implemented into the procedure to record in real time the elastic waves produced from the three individual materials, as they were applied with the load until failure. Fractography was also implemented into the analysis to compare the AE signals with microscopic deformation characteristics of the materials. The discussion of AE activity was divided up into individual regions on the loading graphs. Although displaying unique graph shapes, the same regions were still available for all materials. The results showed that for the three materials, steel produced the most amount of AE activity for all loading rates tested. It was also concluded that the elastic region of loading graph produced highest accumulation of AE activity for all the materials. The AE signals were also seen to be amplified when increasing the loading rate of tensile load applied to specimens. Each material displayed unique characteristics in relation to the AE activity with defining features when monitoring until failure. Fractography was an effective method for determining the type of fracture of the material, however interpretation of AE source from photographs was highly dependent on investigator- further research into the field would be required. The AE technique proved effective at distinguishing between the three materials, when applied with a tensile load until failure. Through further investigation into specific field, the AE technique could be implemented into any structure to ensure integrity monitoring

Acoustic emission method for defect detection and identification in carbon steel welded joints.

Detecting welding defects in industrial equipment (welded joints and built-up structures) is a key aspect in evaluating the probability of failure in different situations. Acoustic emission (AE) is an effective non-destructive detecting technique, and can be a promising application for welding defect detection. This work presents a systematic experimental investigation on using AE technique for detecting and classifying different weld defects in carbon steel joint material. Four certified carbon steel samples were used in this study. A defect free control sample was used as the reference and three samples with induced defects, namely slag, porosity and crack. A pencil lead break (PLB) test was used to generate simulated AE sources on one side of the joint whereas the AE sensor was mounted on the other side to capture AE signals. A total of four experimental arrangements were used to investigate the effect of propagating distance (sensor to source distance) on the ability of AE to detect and identify defects in welds. For each of these arrangements, AE features such as peak amplitude, rise time, decay time, duration, and count numbers along with statistical features such as AE energy, root mean square (RMS) were extracted and analysed. Also, frequency analysis using FFT and wavelet transform were investigated for each weld test specimen for all arrangements. The results show that AE energy, peak amplitude and RMS value can be used to automatically detect and identify the presence of a defect in carbon steel welds. It is concluded that AE has a considerable potential in use in welding inspection to assess the overall structural health and identify defects that can significantly reduce the strength and reliability of welded material and consequently reduce the risk of component's failure