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 2 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.
The mechanisms of nanoscale fatigue of functionally graded TiN/TiNi films have been studied using multiple-loading cycle nanoindentation and nano-impact tests. The functionally graded films were sputter deposited onto silicon substrates, in which the TiNi film provides pseudo-elasticity and shape memory behaviour, while a top TiN surface layer provides tribological and anti-corrosion properties. Nanomechanical tests were performed to investigate the localised film performance and failure modes of the functionally graded film using both Berkovich and conical indenters with loads between 100 lN and 500 mN. The loading history was critical to define film failure modes (i.e. backward depth deviation) and the pseudo-elastic/shape memory effect of the functionally graded layer. The results were sensitive to the applied load, loading mode (e.g. semi-static, dynamic) and probe geometry. Based on indentation force-depth profiles, depth-time data and post-test surface observations of films, it was concluded that the shape of the indenter is critical to induce localised indentation stress and film failure, and generation of pseudo-elasticity at a lower load range. Finite-element simulation of the elastic loading process indicated that the location of subsurface maximum stress near the interface influences the backward depth deviation type of film failure.
The estimation of energy dissipation during particle impact is a key aspect in evaluating the abrasive potential of impact process. Whereas numerous numerical and analytical approaches exist, aimed at explaining observed wear phenomena, few researchers have attempted to measure the energy dissipation during impact. This article reports the results of systematic acoustic emission (AE) energy measurements aimed at detecting the amount of energy dissipated in a carbon steel target during airborne particle impact. Three experimental arrangements were used to investigate three impact regimes; low velocitylow mass (impact speeds of 12.5 m/s and masses of 4.9 Â 10 À6 to 2.3 Â 10 À4 g), low velocityhigh mass (sphere masses of 0.0012 g), and high velocitylow mass (impact speeds of 416 m/s). Within each of these regimes, both single-particle and multiple-particle impacts were studied in order to investigate the effect of overlapping events. Two parameters, particle diameter and particle impact speed, both of which affect the energy dissipated into the material were investigated and correlated with AE energy. The results show that AE increases with the third power of particle diameter, i.e. the mass, and with the second power of the velocity, as would be expected. The diameter exponent was only valid up to particle sizes of around 1.5 mm, an observation which was attributed to different energy dissipation mechanisms with the higher associated momentum. The velocity exponent, and the general level of the energy were lower for multiple impacts than for single impacts, and this was attributed to particle interactions in the guide tube and/or near the surface leading to an underestimate of the actual impact velocity in magnitude and direction.
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