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This paper addresses two incipient subjects with potential impact in the composites industry: 3D-printing of fiber-reinforced plastics and ultrasound testing of lay-ups with curved fiber. First, the advances made hitherto in the field of ultrasound propagation through solid media are reviewed, highlighting the attributes of the main typologies of wave. Then, results of a pulsed sine wave test performed on a 3D-printed CFRP specimen with curved fibers are obtained and studied. The data registered correspond to the measurement of the signal amplitude—wave energy—over a meshed region of the specimen under different configurations of the emitting/receiving transducers. In such a way it can be eventually demonstrated a moderate dependence between the curvature of the fibers and the trajectory followed by the ultrasound waves. These results open the doors towards further development that may enable the control of ultrasound propagation with such potential applications as the addressing of vibrations in sensitive components or the simulation of the operating principle of the electronic SAW devices.

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.

A gear system is a power and motion transmission device that is applied most extensively in various kinds of industrial equipment. Great damage to the whole production is always a risk caused by faults and failures of gears. Therefore, the diagnosis of gear faults is of significant importance. Acoustic Emission (AE) is one of the best technologies for health monitoring and diagnosis of rotating machineries, such as gearboxes. The aim of this work is to detect defects on seeded spur gears at an early stage. The typical AE signals have been analyzed in time (i.e. absolute energy and root mean square “r.m.s”) and frequency domains for different speed and load conditions. It is concluded that the seeded defect can be detected using AE. A numerical relationship between speed, load and AE is also presented.

As it is well known, AE signal amplitude is the key parameter for the calculation of the b-value (GutenbergRichter index), used as an efficient index to evaluate damage in materials and structures. However, several physical aspects clearly influence on the signal amplitude, i.e. wave attenuation, propagation mode type and geometry of the specimen. In composite materials as reinforced concrete (RC), attenuation is quantitatively important, which leads to work to low frequencies sensors for which attenuation decreases significantly and larger distances between sensors can be used. In this context, the influence of attenuation of the acoustic emission (AE) waves on the behaviour of b-value used for damage evaluation is examined in this work. For that, the AE signals coming from pencil lead breaks and generated during three-points bending tests carried out on notched RC beams were used to make this study. The influence of the source-sensor distance, the detection threshold and the frequency range of the sensors and filter used were analysed along the different tests, clearly showing that all of them have a very significant effect on the b-value. In particular, low frequency sensors (20100 kHz) commonly used for RC structures, as expected, provided better results due to the lower attenuation of the elastic waves, even when the source-sensor distance becomes larger. The importance of the detection threshold is also a relevant contribution of this paper.

Acoustic emission testing is a quasi-non-destructive testing method to detect and record the ignition and propagation of irreversible damage in materials under load. In tensile testing of fiber reinforced plastics, first micro cracks occur as soon as a critical strain is exceeded. They emit a characteristic sound, which can be detected via acoustic emission analysis. By increasing the load, the amount of acoustic emissions rises. Even, if the plastic´s matrix causesa high damping rate, a sudden change in amplitude is indicating the critical strain. Further, the analysis shows signals of the whole frequency range which can be distinguished into three different damage mechanisms (matrix cracking, interfacial failure and fiber breakage) by using pattern recognition techniques. It can be shown that the appearance of micro cracks can be correlated with a specific strain value which is interpreted as the critical strain.