Predicting acoustic emission attenuation in solids using ray-tracing within a 3D solid model

Acoustic Emission (AE), is a non-destructive testing and monitoring technique that can be applied to a wide range of situations for condition monitoring and fault diagnosis in mechanical systems and components. Acoustic emission technology involves the propagation of elastic (stress) waves generated by such events as particle impingement, cracking or fluid flow. These waves are recorded at one or more surface-mounted sensor placed at some distance from the generating site(s) and it is necessary to have a means of coping with the implications of the propagation path. It is generally not practicable to solve the wave equation for all possible modes of AE propagation in a solid and this project is based on simulating such propagation using ray tracing applied within a computer-generated solid model representing the structure being monitored. As the attenuation of AE waves is affected not only by the material properties but also by the geometry of the object and the type of surrounding media, knowledge of attenuation is essential to ensure that sensors can be placed appropriately on large or complex structures. The aim of the current work was to establish the capability of predicting the attenuation of AE using a computer-graphical ray tracing technique incorporated in a 3D solid model. The investigative approach involved simulating AE propagation in a range of simple objects of various shapes and sizes and also measuring propagation in these objects using a point source. By comparing simulated and measured attenuation, it was possible to determine appropriate values for the parameters of the simulation, such as the reflection coefficients and the degree of internal friction as well as the proportion of energy carried in surface and bulk waves, respectively. It is concluded that the ray tracing technique has the capability to predict AE attenuation in different shapes and with different environments and materials using a simple division of wave modes into bulk and surface waves. Refinements are suggested in the further work for cases where a more precise representation of the propagation modes is needed

Monitoring of Deep Groove Ball Bearing Defects Using the Acoustic Emission Technology

One of the essential components in rotating machinery are Rolling element bearings and their failure proved to be one of the most common reasons behind machine breakdown. Acoustic Emission (AE), a passive listening technique, has evolved as a significant opportunity to diagnose and monitor the mechanical integrity of rolling element bearings. The investigation reported in this paper mainly focuses on the application of the AE technology for detecting the defect on a radially loaded bearing. In order to undertake this task, a special purpose test-rig was designed so that defect could be seeded onto the outer race of a test bearing using an electrical engraver. By applying varying rotating speed and radial load, twenty tests were carried out. The structure mechanism allows locating an AE sensor directly on the bearing outer race. The AE wave signal has been analyzed in time and frequency domain. It was concluded that the AE can provide good indications of bearing defects. Moreover, it has been noted that the amplitude, absolute energy, and RMS provided indications of bearing condition

Comparative analysis of different wave turbine designs based on conditions relevant to northern coast of Egypt

Wave energy has a great potential to solve the unrelenting energy deficiency in Egypt. The present work recommends Wells turbine as a suitable choice for the Egyptian coasts due to its simple and efficient operation under low input air flow. In addition, the possibility of extracting the wave energy from the Egyptian coasts was investigated using the oscillating water system based on real data from the site. To achieve this purpose, two-dimensional numerical models for Wells turbine airfoils, functioning under sinusoidal wave flow conditions, were built. Moreover, the running and starting characteristics under sinusoidal-flow conditions were investigated using a mathematical code. The results were discussed using the first law analysis, in addition to the second law analysis by using the entropy generation minimization method. It was found that the NACA0015 airfoil always gives a global entropy generation rate that is less than other airfoils by approximately -14%, -10.3% and -14.7% for the sinusoidal wave with time periods equal to 4, 6 and 8 seconds respectively. Moreover, the effects of blade profile, time period and solidity on the output power (kW) value were discussed

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

Acoustic emission testing of composite-to-metal and metal-to-metal adhesive bond strengths.

Composite sandwich structures consisting of two layers with an adhesive contacting interface are of importance in a number of industrial applications such as aerospace, marine and automotive. This research therefore aims to characterise the failure behaviour of adhesively bonded specimen (e.g. carbon fibre reinforced composite-tometal adhesive bonded substrates) and failure modes namely Mode I: double cantilever beam (DCB) and Mode II: threepoint end notch flexures (3-ENF) using the acoustic emission (AE) monitoring technique. AE may aid in the understanding of the mechanics behind the specified failure modes of adhesively joined composite structures. In order to control the adhesively bonded area, a dry anti-stick film was applied to the mating surfaces, which can simulate a bonding quality. Twelve adhesively bonded specimens, for each failure mode, were prepared using two types of adhesive bond materials (acrylic-based ductile bond and cyanoacrylate-based brittle bond) with three variations of adhesive bond quality. Prior to mechanical testing, the adhesive bonded specimens were examined using AE to obtain understanding of signal transmission within the structure. It was possible for the maximum AE amplitude method to select the AE events of mechanical significance (e.g. adhesive failure, substrate deformation) for further identification through thorough analysis. From this maximum AE amplitude method, it was possible to distinguish between the different AE sources of mechanical significance. However, it was proved difficult to propose a definitive AE trait for the mechanical phenomena occurring within specific AE event signals, for all adhesive types, bond qualities, and substrate configurations; therefore all specimen combinations. There was a notable shift in spectral energy proportion as the AE source of mechanical significance varied along the specimen length for particular specimen combinations. However, it was difficult to confirm this distinctive trait for all specimen combinations due to difficulty in confirming the location and exact mechanical source. However, the proposed measurement technique can be useful to assess the overall structural health of a bonded system (e.g. pipe-in-pipe) and may allow identification of defects that can significantly reduce the strength and reliability of material, consequently increasing the risk of component failure