Increase In Acoustic Emission Research Articles

Prediction of Coal Dilatancy Point Using Acoustic Emission Characteristics: Insight Experimental and Artificial Intelligence Approaches

This research offers a combination of experimental and artificial approaches to estimate the dilatancy point under different coal conditions and develop an early warning system. The effect of water content on dilatancy point was investigated under uniaxial loading in three distinct states of coal: dry, natural, and water-saturated. Results showed that the stiffness-stress curve of coal in different states was affected differently at various stages of the process. Crack closure stages and the propagation of unstable cracks were accelerated by water. However, the water slowed the elastic deformation and the propagation of stable cracks. The peak strength, dilatancy stress, elastic modulus, and peak stress of natural and water-saturated coal were less than those of dry. An index that determines the dilatancy point was derived from the absolute strain energy rate. It was discovered that the crack initiation point and dilatancy point decreased with the increase in acoustic emission (AE) count. AE counts were utilized in artificial neural networks, random forest, and k-nearest neighbor approaches for predicting the dilatancy point. A comparison of the evaluation index revealed that artificial neural networks prediction was superior to others. The findings of this study may be valuable for predicting early failures in rock engineering.

Acoustic emission monitoring for necking in sheet metal forming

There is extensive evidence in the literature that plastic deformation of metals is associated with an increase in Acoustic Emission (AE) activity. Thus, AE measurement techniques have the potential to monitor a forming process in real time and provide a signal for feedback control, to exploit optimum formability. In this work, custom-made AE sensors employing piezoelectric crystals are implemented to measure the emitted acoustic signal during uniaxial tension and cup drawing tests of an AA6013-T4 aluminum sheet (1.5 mm thick). The uniaxial tension tests are conducted with two AE sensors clamped to each end of the specimen gage section, along with full-field surface strain measurement using Digital Image Correlation (DIC) techniques. The AE signals along with the interrogation of the DIC images reveal that the maximum AE amplitude corresponds to the onset of diffuse necking, i.e., when the strain field starts to become spatially inhomogeneous. Interestingly, this onset occurs before the maximum force is attained. Comparing these observations to a model of dislocation activity supports the notion that dislocation is the main driver of AE activity. With these findings, AE measurements are performed in a cup drawing process where a custom-made Marciniak-type punch incorporates three AE sensors. These sensors are used to triangulate and determine the location of necking and eminent fracture based on the time difference of arriving signals to each sensor. The results from the cup drawing tests show that AE signals can identify the onset of necking and accurately predict the location of necking and fracture.

Comparative analysis of acoustic and electromagnetic emissions of rocks

Comparative analysis of acoustic and electromagnetic emissions recorded during the intact rock samples deformation and dynamic rupture of simulated crustal fault is presented. Specialized machines for uniaxial compression and shear tests of rock samples with identical data acquisition systems for both test cases were employed. Increase of acoustic emission was observed accompanied by significant rise of intensity and amplitude of electromagnetic signals at high stress of the rock samples under the uniaxial compression or dynamic failure in the spring-block model. Such correlation is consistent with the previous conclusions that an increase of electromagnetic emission may be considered as a rock failure precursor. Any specific characteristics of the detected electromagnetic signals to be used for prediction of impending rock failure or the earthquake fault rupture were not found. The similarity of electromagnetic signals and their spectra obtained at the press equipment and the spring-block model suggests that in both cases, the signals observed are generated by the crack formations and shear. The electromagnetic emission appeared only in dry samples. The samples saturated by water with the salinity of over 0.1% demonstrated no electromagnetic emission.

Evaluation of the surface properties of hair with acoustic emission analysis.

ObjectiveThe tactile sensation of hair is an important consumer‐perceivable attribute. There are limited instrumental options to measure the haptic properties of hair. In this study, we introduce a novel technique using the acoustic emissions produced when skin comes in contact with dry hair in a stroking motion.MethodsUsing a free‐field microphone with a frequency response of 8–12,500 Hz, we recorded acoustic emission data of the interaction of skin with hair. Data were captured with Electroacoustics Toolbox software and analysed with Matlab. Acoustic emission profiles were generated allowing us to monitor the acoustic response at distinct frequencies.ResultsVarious experiments were conducted to develop this novel technique as a suitable measure to monitor the surface properties of hair. Increasing the normal force and velocity of the interaction led to an increase in acoustic emissions. We also examined the acoustic profile of hair that underwent chemical treatment. For example, bleached hair produced a much higher magnitude acoustic response than the corresponding virgin hair. On the other hand, hair conditioner systems mitigated the acoustic response. Finally, investigations of textured hair revealed that the three‐dimensional structure of the hair fibre assembly and its ability to return to its original state when perturbed produce the most dominant acoustic response for this type of hair.ConclusionWe introduce a cutting‐edge method to reproducibly evaluate the surface properties of hair. Different types of hair geometry produce unique acoustic profiles as do hair types that experience harsh damaging treatments. This is also a very practical and efficient way to evaluate the degree of protection or conditioning of the fibre.

On the effect of spray parameters on CO and NOx emissions in a liquid fuel fired flameless combustor

In this paper, numerical and experimental investigations have been carried out to delineate the effect of various spray parameters on CO and NOx emissions in a combustor operating in flameless combustion mode with kerosene fuel. Thermal input was varied in the range of 20–41kW (Heat release density ∼5–10MW/m3) with different fuel injectors and various fuel injection pressures. Spray parameters were varied by employing two separate conditions (i) same fuel flow rate with different solid cone pressure swirl spray nozzles (N1 – N4) and injection pressures (2.5–14bar) to achieve varying spray parameters at same thermal input (ii) same fuel injection nozzle at different fuel flow rates and injection pressures (5–13bar) to understand their effect on combustion and emissions. In both the cases, Sauter Mean Diameter (SMD) varied in the range of 34–58μm with spray cone angle varying from 42° to 56° using different nozzles and fuel injection pressures. Tangential air injection helped achieve higher recirculation of hot combustion products in the primary zone of the combustor for all thermal inputs. The finer sprays obtained at higher injection pressures helped achieve improved recirculation and better mixing, resulting in uniform temperature and hence reduced CO and NOx emissions. The measured CO and NOx emissions were in the range of 28–70ppm and 2–10ppm for all heat inputs with global equivalence ratio varying from ϕ=0.6 to 1, respectively. Measured acoustic emission levels were in the range of 98–101dB and 104–107dB for the flameless and transition mode respectively. The measured CO, NOx and acoustic emissions are an order of magnitude smaller those corresponding to conventional combustion mode. It was observed that coarser sprays led to a significant increase in acoustic emissions, relatively non-uniform temperature distribution and higher CO, NOx emissions during flameless combustion mode.

Experimental Studies on the Effects of Nozzle Structures on Characteristics of Submerged Gas Jet Noise

The structures of nozzle outlet have great effects on jet noise generated by submerged gas jet. Five nozzles with different cross-sections were designed to study the influences of nozzle structures on sound levels by experimental methods. The flow characteristics and sound pressure levels were measured and the gas-liquid flows formed by submerged gas jets under different Weber numbers were also observed. The results show that the gas-liquid flows transformed from bubbling regime to jetting regime with the increase of Weber numbers. With respect to bubbling flow, no significant differences in sound levels for different nozzles were found. However, a remarkable increase of acoustic emission was caused by the transformation of flow patterns over the frequency bands of 0.6-4 kHz for all nozzles. In addition, sound pressure levels for elliptical nozzle were much lower than those of other nozzles over the frequency bands of 0.6-4 kHz. Therefore, it would be a reasonable strategy to adopt several elliptical orifices instead of round nozzle to reduce the gas jet noise in the design of underwater exhaust muffler.

Application of acoustic emission to detect damage mechanisms of particulate filled thermoset polymeric coatings in four point bend tests

In this study, particulate filled thermoset polymeric coatings with two different coating thicknesses were subjected to four point bend loading while being monitored by acoustic emission in order to establish the failure modes of the filled polymeric coatings. The polymeric coatings were approximately 260 μm and 350 μm in thickness on a steel substrate, and filled with 9% by volume of calcium silicate. After testing the thinner coating was found to exhibit more microcracks on the surface of the coating while the thicker coating showed more extensive delamination between the coating layer and the steel substrate. A noticeable load relaxation was observed during the plastic deformation of the coating samples which was coincident with an increase in acoustic emission. This was linked to the development of macrocracks and their propagation through the coating thickness. The number and amplitude of the acoustic emission events were investigated and correlated with the failure mechanisms present during the four point bend test, such as debonding of the embedded fillers, delamination of the coating layer from the substrate and the initiation and propagation of cracks. This then allows the failure modes of particulate filled thermoset coatings and their location to be identified from the acoustic emission detected during the four point bend test.

Verification of moisture-induced delayed failure of thermal barrier coatings

Thermal barrier coatings prepared by physical vapor deposition were isothermally pre-oxidized at 1050 °C. Application of a few drops of distilled water leads to a significant increase in acoustic emission. Specimens that were pre-oxidized near to failure underwent delamination of the thermal barrier coating within 15 s to 15 min after the water was added, thereby verifying the results of Smialek et al. A failure mechanism based on hydrogen embrittlement is supported by acoustic emission measurements.

Yield of nuclear reaction products from deuterium-saturated composite materials and layered structures

We have studied the nuclear reaction products emitted from layered structures and composite materials saturated with deuterium. As a rule, the neutron output from our samples was at the background level. The γ-ray output from the Ti+Si, Ti+Pd, and Ti+ceramic samples was 1.5–2 times the background level. The excess output of γ-rays is accompanied by an increase in acoustic emissions (AE). We measured the energy spectrum of the γ-rays for the Ti+ceramic sample, and found that near-3.0 MeV γ-rays were emitted with the highest probability.

Scratch adhesion test of reactively sputtered TiN coatings on a soft substrate

Reactively sputtered TiN coatings on the relatively soft substrate, Crofer 1700 (Vickers' hardness about 176 HV), were subjected to a scratch test for adhesion. The critical load of the coating/substrate combination is defined as the load at the onset of coating failure as cracking or loss of the coating that causes an increase in acoustic emission. For example, at the critical load of a thicker coating (approximately 1.5 μm), not only cracking but also loss of the coating were observed with an increase in acoustic emission. However, at the critical loads of thinner coatings (1.2 μm or less), coating loss was not observed in spite of an increase in the emission but coating cracking did occur. A failure model is suggested for the given coating plus soft substrate system. Using this model, the maximum observed in a typical acoustic emission curve is explained.

Evaluation of conventional and microfilled composite resins using an acoustic emission technique.

Load-load line displacement diagrams and acoustic emission characteristics were measured in the transverse test of conventional and microfilled composite resins in order to develop a method for the evaluation of strength of dental restorative materials and the non-destructive inspection of restorations in oral cavity. Both conventional and microfilled composite resins exhibited burst type acoustic emission. Conventional composite resins generated the abrupt acoustic emission, but microfilled composite resins did not showed an appreciable increase in acoustic emission before fracture for a low acoustic emission activity.