Abstract Acoustic Emission Activity Research Articles

Acoustic emission generated by glass beads in compression and shearing

Acoustic emission (AE) monitoring offers the potential to sense particle-scale interactions that lead to macro-scale responses of granular materials. This paper presents results from a programme of drained triaxial tests performed on densely packed glass beads to establish quantitative interpretation of AE during isotropic compression, shearing and associated stick–slip events. Relationships have been quantified between: AE and boundary work (i.e. AE generated per Joule) for a unit volume of glass beads under isotropic compression and shear; AE and shear displacement rate; and the amplitude of deviator stress cycles and AE activity during stick–slip events. In shear, AE generation increased with shear strain and reached peak values that were maintained from volume minimum (i.e. the transition from contractive to dilative behaviour) to peak dilatancy, whereupon AE generation gradually reduced and then remained around a constant mean value with further increments of shear strain. In each stick–slip event, AE activity increased during shear strength mobilisation, particle climbing and dilation, and then reduced with the subsequent deviator stress drop during particle sliding and contraction. The amplitude of these cycles in AE activity were governed by the amplitude of deviator stress cycles during stick–slip events, which were also proportional to the imposed stress level and inversely proportional to particle size.

ASSESSMENT OF CRACK INITIATION AND PROPAGATION IN BONE USING ACOUSTIC EMISSION (AE) TECHNIQUES

Acoustic emission (AE) is a nondestructive testing (NDT) technique used for detecting damages, cracks, and leaks in different structures such as metals, composites, wood, fiberglass, ceramics, plastics, etc. In recent years, AE has gained popularity within the field of biomedical applications. The structure of bone is similar to composite materials, therefore, it is advantageous to use NDT technique. Thus, it can be used for monitoring the fracture behavior, crack initiation/propagation, and fatigue detection in bones. The goal of this study was to determine the usefulness of AE techniques in fracture detection phase of bones and to develop an NDT methodology for the monitoring of crack initiation and propagation in bones. This study describes AE activity during fracture of bone tissue under tensile loads. The experiments were carried out in vitro techniques using intact and fracture-simulated bovine tibias. The specimens were loaded to failure in tension using a mechanical testing machine. During the mechanical tests, AE signals were measured and recorded by using AE system processor equipped with two wideband piezoelectric sensors fixed to the surfaces of both ends of the test specimens. By superposing the load–time curve and the cumulative AE event–time curve, AE activities of crack initiation and propagation were identified. In all experiments, the cumulative AE number for each period of time rose up exponentially with the incremental tensile load. Load for AE initiation demonstrated a convincing linear interaction with AE event generation.

Spatial scanning for anomaly detection in acoustic emission testing of an aerospace structure

Acoustic emission (AE) monitoring of engineering structures potentially provides a convenient, cost-effective means of performing structural health monitoring. Networks of AE sensors can be easily and unobtrusively installed upon structures, giving the ability to detect and locate damage-related strain releases (‘events’) in the structure. Use of the technique is not widespread due to the lack of a simple and effective method for detecting abnormal activity levels: the sensitivity of AE sensor networks is such that events unrelated to damage are prevalent in most applications. In this publication, we propose to monitor AE activity in a structure using a spatial scanning statistic, developed and used effectively in the field of epidemiology. The technique is demonstrated on an aerospace structure – an Airbus A320 main landing gear fitting – undergoing fatigue loading, and the method is compared to existing techniques. Despite its simplicity, the scanning statistic proves to be an extremely effective tool in detecting the onset of damage in the structure: it requires little to no user intervention or expertise, is inexpensive to compute and has an easily interpretable output. Furthermore, the generic nature of the method allows the technique to be used in a variety of monitoring scenarios, to detect damage in a wide range of structures.

ACOUSTIC EMISSION FROM PZT-5A AND PZT-8 CERAMICS DURING THE APPLICATION OF AC FIELD AT DIFFERENT FREQUENCIES

Acoustic Emission (AE) and hysteresis parameters were studied from PZT-5A (soft) and PZT-8 (hard) ceramics during the application of ac fields in the frequency range of 0.2 Hz to 5 Hz. AE was found to occur mainly due to domain switching in these ceramics during the application of ac fields. In PZT-5A, a threshold field was observed for the AE activity to begin in both the direction of the applied field and in general, it was found to decrease with increasing frequency. Apart from this, AE activity was found to decrease with increasing number of applied ac cycles, and is attributed to domain pinning. In the case of PZT-8, AE was found to occur even at zero field at higher frequencies and AE activity was found to increase with increasing number of field cycles. These are explained on the basis of the defect dipole — domain interaction in these ceramics.

Assessment of Tensile and Fatigue Damage in 316L Stainless Steel by Acoustic Emission Technique

Acoustic emission (AE) technique was applied to evaluate both tensile deformation of 316L stainless steel and bending-fatigue damage of socket-welded pipe. AE activity was monitored during tensile deformation of plate-type specimens subjected to various heat treatments. Variation in RMS voltage of AE signal was correlated with the amount of strain-induced martensite phase. Secondly, actual size of socket-welded pipe specimen was bending-fatigued under various stresses. Crack initiation was determined by observing an abrupt increase in AE count, and confirmed by radiographic examination before and after the crack initiation cycle. Potentials of AE technique for monitoring fatigue crack initiation were discussed.

Damage Assessment of Reinforced Concrete Beams Qualified by Acoustic Emission

Acoustic emission (AE) techniques have been widely studied in concrete engineering and are presently being applied to monitoring concrete structures in service. In order to assess the damage levels of the structures, a criterion based on the Kaiser effect of AE is proposed in the recommended practice recently published by the Japanese Society for Non-Destructive Inspection. New AE parameters of load and calm ratio are defined for qualification of the damages. Accordingly, the feasibility of the damage qualification is experimentally examined using reinforced concrete (RC) beams damaged under incremental cyclic loading. It was found that the damages qualified by the 2 ratios were in good agreement with actual damages of the beams. This suggests that the damages of such RC structures in service as bridges, docks, and buildings are quantitatively assessed by simply applying cyclic loading and monitoring AE activity.

Thermally induced acoustic emission from polycrystalline buckminsterfullerene

Acoustic emission activity has been detected in C60 polycrystals at 260 K and at 190–200 K by heating and cooling the C60 crystals in the 180–300 K interval; the main acoustic activity is attributed to the fcc–sc phase transition in the polycrystalline materials.

Effect of transient stress on acoustic emission behaviour during firing of dental porcelain

Acoustic emission activity was measured in the glass transition range of dental porcelain during firing. Transient and residual stresses in porcelain during cooling from a temperature higher than porcelain sag point and during re-heating of the tempered porcelain were calculated by computer simulation using a viscoelastic stress analysis. The detected acoustic emission event was discussed with the relative rules of the simulated transient stresses. High acoustic emission activity was detected at the temperature where the internal stress faded away for heating and build up for cooling. The low-level acoustic emission pulses were only detected in the following conditions: (1) in the temperature range where porcelain behaved like an elastic solid; (2) at temperatures higher than the deformation point of porcelain; (3) with a re-heating process of the porcelain without tempered stress. From these results, it was concluded that elastic energy is released related to transient stress in porcelain during viscoelastic deformation and can be detected by the acoustic emission method. The acoustic emission method is considered to be helpful in non-destructive testing in order to understand transient stress due to viscoelastic deformation of glassy materials in heat treatment.

MONITORING CORROSION BY ACOUSTIC EMISSION

Abstract Acoustic emission activity had been noted previously on corroding steel structures. This work identified the acoustic outputs from the various potential oxides formed and from paint fracture. By an algebraic prcoess it proved possible to determine when corrosion commenced and what oxide species were involved. High correlation co-efficients were determined throughout the whole work and it was finally shown that corrosion films as thin as 10 μm or as light as 3.5mg could be detected.

Nondestructive Evaluation of Bond Quality of Bimetallic Strips Using Acoustic Emission

Abstract Acoustic emission (AE) appears to hold good promise for nondestructive evaluation of bond strength of bimetallic strips in two ways: (1) as a quality control tool in batch sampling and (2) as a 100% inspection method. A program has been initiated at the Aerospace Engineering Department of the Indian Institute of Science to explore the feasibility of utilizing the acoustic emission technique for evaluation of bond strength of bimetallic strips. As a first step, acoustic emission was monitored during tensile testing of copper-lead bimetallic strips. The results obtained during these tests indicate differences in AE activity between specimens with poor and good bonding at very small loads which can be utilized for inspecting the bond quality.

Acoustic Emission/Rupture Load Characterizations of Double-Braided Nylon Rope

Acoustic emission (AE) nondestructive evaluation characterizations have been obtained from new Samson double-braided 2-in-1, 0.635-cm-diameter (¼ in.) nylon rope in the dry condition at room temperature. A parameter called the "AE load delay" has been defined as the tensile load required to produce a specified low baseline level of AE activity. It has been observed that the AE load delay can be correlated with the ultimate rupture load of the rope with cut core yarns and with a variety of stress-concentrating knots.

Acoustic emission induced by hydride formation in tantalum

Acoustic emission activity during hydride formation in tantalum at CH=7.2 at.% was detected as a function of temperature by measuring the ringdown count rate, the total number of events, and their amplitude distributions. Elastic modulus and internal friction measurements were also conducted in the same specimen to provide evidence of H precipitation. There are indications that, as in niobium, the acoustic emission phenomenon is caused by cracking at the precipitate particles.

Acoustic Emission Produced During Heating of Tin and Zinc Single Crystals

AbstractAcoustic emission activity has been detected during heating of tin (Sn) and zinc (Zn) single crystals from 0 to 130°C. The emission of Sn occurs copiously only if the heating starts below a temperature of about 18°C, and lasts up to a higher temperature between 60 and 80°C. The results may be interpreted by relating acoustic emission to processes in the α ↔ β phase transformation. Although still qualitative, such a hypothesis permits us to have useful information on the nucleation time of the α-phase and on the temperature hysteresis of the transformation.