Total Acoustic Emission Energy Research Articles

Influence of loading rate on failure property of concrete twin fibers pull-out test

Under the premise of considering the mesoscopic heterogeneity of each phase material, we use the dynamic finite element analysis software RFPA^3D-dynamics to establish a three-dimensional dynamic numerical model of concrete twin fibers pull-out test and study the effect of different loading rates on fracture performance of concrete twin fibers pull-out specimens. Based on the elastic damage constitutive relation of mesoscopic elements, the failure diagram of the whole process, distribution curve of interfacial shear stress, acoustic emission (AE) histogram, accumulative AE curves and AE energy analysis of each specimen have been obtained. The results show that the fracture process of concrete twin fibers pull-out specimens under different loading rates goes through the following stages: elastic stage, elastic-plastic damage stage, interface debonding stage and steel fiber pull-out stage. The higher the loading rate, the faster the crack propagation and the interfacial shear stress transmission, and the higher the cumulative acoustic emission counts and the total acoustic emission energy.

Imaging opening-mode fracture in sandstone under three-point bending: A direct identification of the fracture process zone and traction-free crack based on cohesive zone model

Influence of the fracture process zone (FPZ) poses a challenge to accurately determine the FPZ and traction-free crack during the fracture process in a rock structure. In this study, an engineering approach based on concepts of the cohesive zone model, is proposed to identify them in a sandstone beam under three-point bending. Two types of specimens were tested, including center notch and smooth boundary beams. Acoustic emission (AE) and digital image correlation (DIC) were used to monitor the local material behaviors, which involves two crucial parameters: AE energy and DIC opening displacement pattern. (i) Three levels of AE energy have been classified to “filter” the FPZ from AE events cluster. Based on AE energy levels, three groups of AE events can be obtained. For Level 1, AE events involves AE energy that is 1 or 2 order larger than that within Level 2 and 3, such that they occupy about 95% of total AE energy release. Thus, Level 1 is considered to represent the group of large AE energy. For Level 2 and 3, although many AE events are detected, these events have little influence on the fracture process. The FPZ consists of only AE events within Level 1. (ii) Four types of DIC opening displacement patterns have been observed on the specimen surface to identify the FPZ. Every displacement pattern represents a feature that is related to specific loadings in the cohesive zone model. Depending on the distribution of opening displacements and displacement gradients, displacement pattern can be decided and the individual pattern has its own special physical correlation: pattern (I) is related to elastic tension of the material; pattern (II) suggests the possible existence of the FPZ; pattern (III) indicates the possible onset of a traction-free crack; pattern (IV) confirms material softening within the FPZ and material unloading outside the FPZ. These patterns together with different reference loads are used to identify the FPZ and traction-free crack. With the help of two parameters, the precise kinematics of the FPZ and traction-free crack in the specimen are determined, and the fracture properties such as the FPZ length and critical opening displacement are also reported. Finally, experimental results provide insights to understand opening-mode fracture and related structural response, i.e., possible formation of the traction-free crack at peak under three-point bending, reasonable assumption of elastic material behavior before the softening, and the dynamic effect of fracture propagation on laboratory determination of fracture properties.

Using acoustic emission technique to monitor damage progress around joints in brittle materials

A vast amount of experimental research is available on crack initiation and propagation studies in brittle samples containing joints and rock bridges between them. One of the developed experimental methods is Acoustic Emission (AE) technique which is widely used in different studies as a non-destructive method in order to monitor failure mechanisms. A significant correlation exists between the AE signal characteristics and fracturing of a loaded material. In the present research, in order to monitor failure and damage process of large-scale pre-jointed samples with different geometries, uniaxial compression tests were performed while both AE technique and online photographic monitoring were utilized concurrently to visualize the failure progress around joints and their associated rock bridges. Results showed that by combining stress-time diagram with AE parameters (such as energy and count), failure stages can be identified from onset of loading until complete failure. These include sample compression, wing crack growth, crack coalescence, silence mode (stick-slip phenomenon) and final rupture. Inclination of the joints and their relative alignment with respect to the loading direction control the AE characteristics. Maximum amount of wing crack initiation stress, total AE energy and released energy during coalescence stage were attributed to samples that have shear or mixed failure mode. Furthermore, a two dimensional AE source location method alongside with a simple new algorithm were used to locate crack initiation and follow its growing path and make a comparison with the actual cracks in the loaded sample. Good correlation between AE recordings and actual observed damages showed accurate predictions of AE method is possible for recognizing damage location and its mechanism.

Flow noise identification using acoustic emission (AE) energy decomposition for sand monitoring in flow pipeline

In pipelines used for petroleum production and transportation, sand particles may be present in the multi-phase flow of oil and gas and water. The Acoustic Emission (AE) measurement technique is used in the field of sand monitoring and detection in the oil and gas industry. However, as the AE signals recorded are strongly influenced by flow conditions in the pipe, identification of sand particle related signals or events remain a significant challenge in interpretation of AE signals. Therefore, a systematic investigation of sand particle impact AE energy measurements, using a sensor mounted on the outer surface of a sharp bend in a carbon steel pipe, was carried out in the laboratory to characterise flow signals using a slurry impingement flow loop test rig. A range of silica sand particles fractions of mean particle size (212–710 μm) were used in the flow with particle nominal concentration between (1 and 5 wt.%) while the free stream velocity was changed between (4.2 and 14 ms−1).A signal processing technique was developed in which the total AE energy associated with particle-free water impingement was divided into static and oscillated parts and a demodulated frequency analysis was carried out on the oscillated part to identify major spectral components and hence the sources of AE signals. A simple theoretical model for water impingement AE signals was then developed to show the dependence of AE energy components on different flow speeds. A similar decomposition of AE energy into static and oscillatory components was used to analyse AE signals for particle-laden flows. The effect of flow speed on the spectral AE energy for different sand concentrations and particle size fractions was investigated and the results show that the 100 Hz band is attributed to mechanical noise, the 42 Hz band is due to fluid turbulence and the dominant band is broad oscillated component.The AE energy decomposition method together with the water impingement model and coupled with spectral peaks filtering enable isolation of AE energy associated with particle impact from other AE sources and noise and, hence, the proposed decomposition approach can enhance the interpretation of AE data in pipeline flows.

Size effects on granite behavior under unloading rockburst test

Based on previous studies of rock behavior versus rock sample size and various research on rockburst simulation tests, a modified true-triaxial unloading testing machine was utilized to perform rockburst tests on granite specimens with changing heights for size effect investigation. The parameter of the height-to-thickness ratio (H/T) is proposed to characterize the rock scale, and it varies from 5 to 2 with a fixed thickness of 30 mm and changing heights from 150 to 60 mm. In this study, several testing methods were adopted to study the influence of H/T including non-destructive acoustic emission (AE) technology and high-speed camera recording systems as well as fragment kinetic energy analysis. The experimental results indicated that a size effect does exist during the rockburst simulation process and affects the rock failure strength and fracture mode. It can be seen that rock failure strength has an increasing trend with the decreasing of H/T. And at the higher H/T, extensile and splitting failures are dominant, and then the mixed failure mode including tensile and shear appears with decreasing H/T, until the single-plane shear becomes the main failure mode at the lowest H/T. AE energy release and kinetic energy of ejected fragments are not quite sensitive to sample size for H/T lower than 3. When the ratio of height and width is not lower than 3, the total AE energy during rock failure and kinetic energy of ejected fragments increased with the decreasing of sample size. With a further decrease of the ratio to 2, the total AE energy and kinetic energy of ejected fragments began to decrease.

Detection of segmentation cracks in top coat of thermal barrier coatings during plasma spraying by non-contact acoustic emission method

Numerous cracks can be observed in the top coat of thermal barrier coatings (TBCs) deposited by the atmospheric plasma spraying (APS) method. These cracks can be classified into vertical and horizontal ones and they have opposite impact on the properties of TBCs. Vertical cracks reduce the residual stress in the top coat and provide strain tolerance. On the contrary, horizontal cracks trigger delamination of the top coat. However, monitoring methods of cracks generation during APS are rare even though they are strongly desired. Therefore, an in situ, non-contact and non-destructive evaluation method for this objective was developed in this study with the laser acoustic emission (AE) technique by using laser interferometers as a sensor. More AE events could be detected by introducing an improved noise reduction filter and AE event detection procedures with multiple thresholds. Generation of vertical cracks was successfully separated from horizontal cracks by a newly introduced scanning pattern of a plasma torch. Thus, generation of vertical cracks was detected with certainty by this monitoring method because AE events were detected only during spraying and a positive correlation was observed between the development degree of vertical cracks and the total AE energy in one experiment.

Acoustic emission monitoring of an eighteenth-century wardrobe to support a strategy for indoor climate management

The on-site monitoring of acoustic emission (AE) has allowed the direct tracing of climate-induced crack propagation in an eighteenth-century wardrobe displayed in the Gallery of Decorative Art in the National Museum in Krakow, Poland. The anti-correlation measuring scheme and frequency filtering allowed very low levels of physical damage to the wardrobe to be detected in spite of the high background noise typical of the museum environment. The total AE energy recorded during two years of monitoring corresponded to a fractured area of 12 mm2 or a total crack propagation of 1.2 mm for two10-mm-thick panels. Although the total damage recorded was minute, correlation between the events of fracturing and falls in indoor relative humidity (RH) in winter due to insufficient humidification was evident. The risk of damage, expressed in terms of crack propagation, was quantified as a function of the magnitude of the RH falls of the duration compatible with the response time of the object. The data allow acceptable RH falls to be identified if a conservation professional or a curator selects a ‘tolerable’ yearly propagation of the fracture, in other words the progress of damage considered insignificant.

Investigation of Low Temperature Cracking in Asphalt Mixtures by Acoustic Emission

ABSTRACT This paper investigates the use of acoustic emission (AE) to characterize microstructural phenomena and the corresponding macroscopic behavior during the low temperature fracture of asphalt mixtures. An acoustic emission system with eight channels of recording was used to monitor the failure process during testing at low temperature using the semi circular bend (SCB) configuration in three Superpave mixtures used at MnROAD facility. Algorithms to automatically detect the relative arrival time of the AE signal and to locate the AE source were developed. The analysis of the accumulated AE events illustrated the relationship between the micro damage and macroscopic behavior at different loading levels. The damage level under certain loading conditions was evaluated and preliminary results showed that the load level corresponding to the localization played a critical role in the damage process of the material. As a first step, the fracture energy of asphalt concrete specimen was related to the accumulated AE energy. By observing the distribution of microcracks with different energy levels, it was reasonably assumed that 95% of the total AE energy before peak load corresponded to the process zone and this zone was determined to be around 3–6 mm in width and 20–30 mm in length for the materials tested in this research effort.

Crack propagation and acoustic emission behavior of silver-added Dy123 bulk superconductor

The relationship between the crack propagation process and acoustic emission (AE) signals was investigated in 3-point bending tests in which stress loading was applied parallel to the c-axis of U-notched specimens cut from Dy123 bulk superconductors with and without the addition of silver (Ag). The average bending stress of the specimens containing 10 mass% of Ag was approximately 20% higher than that of the specimens without the addition of Ag; the total AE energy of the former specimens was approximately fourfold greater than that of the latter specimens. However, cracks initiated in all of the specimens at a bending stress level of around 25MPa, regardless of the presence or absence of Ag. An analysis of the amplitude distribution revealed that the failure mode was matrix failure in both types of specimens. Cracks in the low-strength specimens without Ag propagated between gas holes or along cleavage planes, and the AE event count and total AE energy were low. By contrast, the high-strength Ag-added specimens had fewer gas holes and cleavage cracks on account of their improved microstructure. In these samples, crack propagation orthogonal to the cleavage planes caused Ag particles to separate from the matrix and induced cleavage cracks. The addition of Ag presumably had the effect of inhibiting crack propagation, with the result that the AE event count and AE energy increased.The results of this study indicate that failure phenomena can be interpreted by evaluating the amplitude distribution, AE event count and total AE energy. This suggests that the AE method is also applicable to evaluations of bulk superconductors.

Investigation of Low Temperature Cracking in Asphalt Mixtures by Acoustic Emission

ABSTRACT This paper investigates the use of acoustic emission (AE) to characterize microstructural phenomena and the corresponding macroscopic behavior during the low temperature fracture of asphalt mixtures. An acoustic emission system with eight channels of recording was used to monitor the failure process during testing at low temperature using the semi circular bend (SCB) configuration in three Superpave mixtures used at MnROAD facility. Algorithms to automatically detect the relative arrival time of the AE signal and to locate the AE source were developed. The analysis of the accumulated AE events illustrated the relationship between the micro damage and macroscopic behavior at different loading levels. The damage level under certain loading conditions was evaluated and preliminary results showed that the load level corresponding to the localization played a critical role in the damage process of the material. As a first step, the fracture energy of asphalt concrete specimen was related to the accumulated AE energy. By observing the distribution of microcracks with different energy levels, it was reasonably assumed that 95% of the total AE energy before peak load corresponded to the process zone and this zone was determined to be around 3–6 mm in width and 20–30 mm in length for the materials tested in this research effort.

Acoustic emission behavior under bending deformation of YBCO bulk superconductor

Bending tests were conducted on U-notched specimens cut from a YBCO bulk superconductor. Acoustic emission (AE) signals obtained under loading parallel or perpendicular to the c-axis were analyzed to investigate the correlation between crack growth behavior and the AE signals. As a result of analyzing log–log plots of strength ( σ B) versus total AE energy ( ΣE AE), a linear relationship was found between ΣE AE and σ B n . Cracks could be broadly divided into two types based on the value of n as an index of crack growth behavior. One type consisted of microcracks originating from cleavage planes and gas holes; these crack propagated parallel to the c-axis and had an n index value of approximately 0.7. The other type was a main crack that originated from the U-notch and had an n index value of approximately 6.5. A sample (A) loaded parallel to the c-axis showed mean bending strength of 74.8 MPa. Cracks displaying two different growth patterns of n = 0.7 and 6.5 were presented in this sample. Microcracks parallel to the c-axis occurred in the vicinity of 5–10 MPa. This sample was characterized by mixed crack growth of a main crack and microcracks. A sample (B) loaded perpendicular to the c-axis displayed mean bending strength of 43 MPa. A main crack occurred in the vicinity of 20 MPa and displayed a single growth pattern of n = 6.5. By analyzing AE signals in this way in the process of conducting a strength evaluation, it was possible to evaluate the failure process of the bulk superconductor in relation to the strength level induced by the applied load.

Effect of tetragonality ratio on photo-induced domain switching in poled (Pb1-xLax)TiO3 ferroelectric ceramics

The effect of the tetragonality (c/a) ratio on photo-induced domain switching in (Pb1−xLax)TiO3 ferroelectric ceramics preliminarily poled at 1.5kVmm−1 was investigated by measuring photovoltaic current and acoustic emission (AE) signals. Results of total increment of photovoltaic current (Jpv), total AE event count and AE energy distribution showed that non-steady state behavior of Jpv was dominantly dependent on the activity of 90° domain switching during illumination. The activity of photo-induced domain switching was explained in terms of the coercive field and the space charge field. It was confirmed that the magnitudes of the space charge field and coercive field were found to be optimal for the photo-induced 90° domain switching at a c/a of 1.021.

Acoustic Emission Analysis of Fracture Events in Cu Films with W Overlayers

AbstractIndentation-induced delamination of thin films provides the basis for adhesion calculations. In the case of ductile Cu films plastic deformation usually prevents a film from debonding from the substrate. Deadhesion is facilitated by the use of a hard W superlayer, which promotes indenter-induced Cu film failure, increasing the delamination area by an order of magnitude. Radial as well as annular cracking acts like a secondary mechanism in the strain energy release, and can be resolved from excursions on the load-displacement curves. For the thicker Cu films no excursions were observed, though radial cracking took place. It is important to identify fracture events as they occur in order to understand the system behavior and accurately apply the analysis. An acoustic emission signal is used to detect the magnitude of fracture events in thin Cu films. For the films of different thickness from 40 nm to 3 microns the corresponding interfacial fracture energy ranged from 0.2 to over 100 J/m2. Limits of plastic energy dissipation are determined with the lower limit, the true work of adhesion, being associated with a dislocation emission criterion. Crack arrest marks were found upon the blister removal, and are proposed to represent the shape of the crack tip. Total acoustic emission energy was found to be inversely proportional to the strain energy release rate.

Study of Fracture Mechanisms of FRPP by Acoustic Emission Technique. Effects of Screw Design and Number of Screw Rotations.

Effects of screw design and number of screw rotations on fracture mechanisms of fiber-reinforced polypropylene (FRPP) are studied by means of acoustic emission (AE) technique. The fiber length, the fiber orientation angle and the AE characteristics are explained in terms of the apparent shearing stresses on the various number of rotations for B and C screws with shallow groove and deep one. It is clear from specimen molded by a screw with shallow groove that the maximum load is high, the maximum cumulative AE event count and the maximum total AE energy are low on the smaller fiber orientation angle, but the load is low and the AE characteristics are high on the larger orientation angle. It is found from the AE frequency analysis that the fiber breakings dominate the damage modes of specimens molded by B screw, but the fiber debonding and the breaking appear on the specimens molded by C screw.

Fracture Mechanisms of Short-Fiber-Reinforced PETby Acoustic Emission Method. (Effects of Fiber Content and Loading Direction).

The fracture mechanisms of short-fiber-reinforced PET (FRPET) are studied by the acoustic emission (AE) method to examine the effects of fiber content and loading direction. The maximum loads of test specimens increase with increase in the fiber content, and the loads decrease with increase in the angle between the directions of injection and loading. The cumulative AE event count and the total AE energy are affected by the fiber content and the loading direction. The effects of the fiber content and the loading direction on the total AE energy can be explained by AE amplitude distribution. The loads of Pb and Pc determined by the stress intensity factor method are in agreement with the loads determined by the AE energy gradient method. Damage is generated by the debonding between fiber and resin at the load point of Pb and by the fiber breaking at the load point of Pc in materials with fiber content of 15 and 30% by weight.

A study of Fracture Mechanisms of Short Fiber Reinforced PET by Acoustic Emission Method. Effects of Notch Length and Fiber Content.

Effects of notch length and fiber content on the tensile fracture behavior of short fiber reinforced polyethylene terephthalate (FRPET) are studied using the acoustic emission (AE) method. The cumulative AE event count and the total AE energy increase with increases in the notch length. The total AE energy decreases with increases in the fiber content, but the cumulative AE event count has a maximum value at a fiber content by volume of 17.3%. The log-log plot of the relationship between the total AE energy and the stress intensity factor has two broken points at Kb and KC which correspond to the changes in failure mode, respectively. The ratios of Pb/Pmax are varied, and Pc/P<max> values are roughly constant at the various notch lengths and fiber contents, where the Pb and Pc are loads determined by Kb and Kc, and Pmax is the maximum load. The relationship between the damage state at the notch tip and the AE frequency spectrum determines the fracture mechanisms of FRPET at the applied loads of Pb/Pmax and Pc/Pmax.

ＡＥ法による平織ＣＦＲＰの破壊機構に関する研究 繊維と樹脂の界面および経糸と緯糸間のはく離の推定

Acoustic emission (AE) characteristics of smoothed and notched specimens were investigated for a plain woven carbon fabric composite. The failure behavior of the smoothed specimen under tensile loading was estimated by the failure modes, AE parameters, and the load-elongation curve of the notched specimen. The results obtained are as follows:(1) The AE cumulative event count and the total AE energy of the smoothed specimen were larger than those of the notched specimen due to the difference in load level.(2) The AE amplitude distribution showed that the debonding of fiber/matrix and transverse/longitudinal fibers was the dominant failure mode before final fracture and generated much more AE than the fiber breakage. The AE activity of the smoothed specimen was larger than that of the notched specimen.(3) The load at the broken point of log-log plot for the total AE energy and stress intensity factor corresponded to the initiation of fiber/matrix debonding. It also agreed with the occurrence of AE.(4) The load-elongation curves of the smoothed and notched specimens could be divided into three parts. It was found that the initiation of the above debonding in the smoothed specimen can be estimated by the ratio of the load at the broken point to the maximum load of the notched specimen.

Prediction for split initiation in notched unidirectional carbon/epoxy laminate under tensile loading.

The notched strength of unidirectional carbon/epoxy laminate, Toray T800H/#3631, was evaluated under tensile loading using center-notched specimens having various fiber orientations relative to the loading axis. On the basis of acoustic emission (AE) monitoring and fractography, failure mechanisms can be classified into two modes: tensile failure and shear failure. For the case of tensile failure, no AE signal was detected before the split initiation; the fracture surface was covered with epoxy resin. On the other hand, for the case of shear failure, a gradual increase in total AE energy was observed before the split initiation; the fracture surface was characterized by many hackles and fiber/matrix interfacial debonding. The measured strength for the split initiation from notches showed good agreement with the predictions from the modified average stress model combined with the maximum stress criterion proposed by the authors. No interaction was observed between tensile failure and shear failure for split initiation.

Acoustic emission during deformation of dual-phase steels

The study of acoustic emission (AE) during deformation of dual-phase steels consisting of ferrite (F) and pearlite (P)/martensite (M) indicates that the AE peak in the yielding region always appears at the beginning of the macroplastic deformation. After macroyielding starts, the AE decreases because the dislocation velocity, νd, decreases. The total AE energy, ∑Elp, emitted during Luders band propagation is related to the Luders strain, el and ∑Elp/ el, decreases as el increases because of the increase in e, resulting from the decrease in dislocation velocity, νd. After quenching from the two-phase region at cooling rates larger than a certain critical value, a second AE peak, which is produced by the cracking mainly at the interfaces between M and F and secondly in martensitic particles, appears in a certain plastic strain range in addition to the one in the yielding region. As the cooling rate becomes too fast, the AE peak in the yielding region disappears, and the second AE peak cannot be completed due to the brittle fracture.

ＡＥ法によるクラスＡ‐ＳＭＣの疲労破壊機構の一考察

The fatigue fracture mechanism of class A-SMC which has been developed for the outer panel in automobiles was studied by determining the parameters of acoustic emission (AE) detected during its fatigue fracture process. The results obtained are as follows:(1) The macroscopic fatigue fracture behavior is accurately reflected by the AE event count rate and the total AE energy, which are the most proper AE parameters to represent the macroscopic fracture pattern of composite materials.(2) It is confirmed that the fatigue fracture mechanism can not be explained by the AE amplitude, even if by using the results of the macroscopic and microscopic observations of fatigue fracture surface.(3) The microscopic fracture mechanism during the fatigue test can be clarified by observing the fracture surface microscopically and applying the relation among the AE frequency, the load and the power spectrum obtained on the static tensile test to the relation among the AE frequency, the number of cycle and the power spectrum obtained in the tensile fatigue test. It is found that the most proper AE parameter to represent the fatigue fracture behavior of constituent elements in the composite materials is the AE frequency spectrum.