Acoustic Emission Event Count Research Articles

Experimental study of the effects of fracture number on the creep and acoustic emission characteristics of sandstone

Creep and acoustic emission tests were conducted under uniaxial compression on sandstone samples with no (i.e. intact), one and two prefabricated fractures collected from the Xiaolangdi Reservoir area using a RLJW-2000 rock microcomputer-controlled rheology servotest system and PCI-2 acoustic emission testing equipment, respectively. The change laws of the acoustic emission amplitudes, peak frequencies, acoustic emission events and b values of samples with different fracture numbers (i.e. number of fractures) were systematically analysed. The differences between the prediction made by acoustic emission b values and cumulative ringing count for the precursor time of creep failure in a rock mass were studied comparatively, thereby identifying the effects of fracture number on the creep and acoustic emission characteristics of sandstone. According to the study results: (1) With an increase in the prefabricated fracture number, the acoustic emission signal counts of samples increased within the amplitude intervals of 60–80 and 80–100 dB. The signal counts were especially high in the high-amplitude interval of 80–100 dB but they decreased within the low-amplitude interval of 45–60 dB. (2) Under each stress level, the total acoustic emission event counts generated by the single- and double-fracture samples were 1.90 and 2.36 times that generated by the intact sample, respectively. Under the last stress level, the event counts generated by the single- and double-fracture samples were 4.64 and 6.19 times the event count generated by the intact sample, respectively. A higher prefabricated fracture number implied higher total acoustic emission event counts generated by samples and higher acoustic emission event counts generated under the last stress level. (3) Under the same stress level, the frequency band concentration of acoustic emission signals of samples became more pronounced as the prefabricated fracture number increased. Under the last stress level, as the prefabricated fracture number increased, the peak frequencies of the acoustic emission signals of samples were concentrated in a greater number of frequency ranges (four, seven and eight frequency ranges, respectively). (4) With an increase in the prefabricated fracture number, the average acoustic emission b values of samples presented an overall declining trend, with an increased Δ b range. (5) The plunge rates of acoustic emission b values of the single- and double-fracture samples before accelerated creep failure increased by 8.0 and 11.2%, respectively, compared with the intact sample. (6) The acoustic emission b value curves and cumulative ringing count curves for samples with different fracture numbers predicted creep failure in the rock mass earlier than the strain curves. For all samples, the precursor time points of creep failure in the rock mass predicted by acoustic emission b value curves were all earlier than those predicted by corresponding cumulative ringing count curves. As the prefabricated fracture number increased, the precursor time points of creep failure in the rock mass predicted by acoustic emission b value curves occurred even earlier. Thematic collection: This article is part of the Engineering Geology and Hydrogeology of the Anthropocene collection available at: https://www.lyellcollection.org/topic/collections/engineering-geology-and-hydrogeology-of-the-anthropocene

Experimental study on the effect of anchors on the creep mechanical properties and acoustic emission characteristics of fractured sandstone under uniaxial compression

This study conducts laboratory tests to investigate the creep and acoustic emission (AE) of unanchored and anchored fractured sandstone samples under uniaxial compression by taking the Triassic fine sandstone collected from the Xiaolangdi Reservoir area as the research object and ensuring the same testing conditions using an RLJW-2000 rock rheometer and a PCI-Ⅱ AE instrument. Moreover, this study identified the effects of anchors on the creep mechanics and AE characteristics of fractured sandstone samples by analyzing the strain, long-term strength, AE event count, AE rate, AE energy rate, and rising angle – average frequency (RA-AF) characteristics of each sample before and after anchoring. According to the study results: (1) Under the same stress level, the anchored sample's instantaneous strain, creep strain, and total strain are smaller than those of the unanchored sample. Anchors exerted the largest inhibitory effect on creep strain, followed by the total strain, while anchors inhibited instantaneous strain to the smallest extent. (2) Compared to the unanchored sample, the anchored sample experienced a significant increase (as high as 50%) in long-term strength. Anchor reinforcement significantly improves the long-term strength of samples. (3) Under the same stress level, the AE event count and cumulative AE event count of the anchored sample are smaller than those of the unanchored sample. Anchors significantly inhibited microcracks initiation, propagation, overlapping, and penetration in samples. (4) The maximum AE rate of the anchored sample is only 69.30% of that of the unanchored sample, whereas the peak AE energy rate of the anchored sample is only 23.21% of that of the unanchored sample. Anchors reduce the AE event count generated and the AE energy released by samples per unit of time, exerting a significant crack-arrest effect on them. (5) The presence of anchors changes the type and number of microcracks in the samples' creep process. Anchors greatly inhibit the generation of high-RA and low-AF AE signals and generate low-RA and high-AF ones. As a result, more tensile microcracks occur in samples under stress levels close to the failure stress level (especially the last stress level), which inhibit the formation of shear microcracks in samples and causes samples to be more prone to macroscopic tensile-shear failure. (6) The microcrack characteristics of samples characterized by RA-AF values are consistent with the macrocrack characteristics of samples. Therefore, RA-AF values can satisfactorily characterize the microcracks' variation characteristics in the sandstone samples' creep process before and after anchoring.

Performance of acoustic emission and digital image correlation for fracture analysis in cementitious mortars under fatigue loading

Fatigue loading in brittle materials introduces damage at a micro-scale. These micro-fractures can accumulate and cause a significant reduction in material stiffness or even lead to structural failure. Deformation-based monitoring techniques can be inadequate when detecting damage at a micro-level. Hence, here is where advanced nondestructive testing (NDT) methods such as acoustic emission (AE) and digital image correlation (DIC) can play a great role. The paper aims to combine AE and DIC for advanced fatigue damage analysis on a cylindrical sample subjected to a fatigue Brazilian splitting test. The damage progress quantified from cumulative AE event count, and horizontal displacement measured with DIC showed a very good correlation. The damaged region was identified with an AE localization plot and with a DIC displacement field plot, the damaged area was well represented by both techniques. When a material goes through an irreversible change, part of the released energy will generate an elastic wave. The wave will propagate through the material and the whole phenomenon is termed an acoustic emission. By using AE sensors on the surface of the sample, these waves are captured and analyzed to better understand the source of the emission. Its high sensitivity to micro-changes makes it an ideal technique to use for fatigue damage investigation. Digital image correlation relates sequentially taken images to determine displacement and strain measurements. While DIC analyzes material evolution using surface deformation measurements, AE on the other hand is capable of monitoring damage inside the volume of material. Hence, their combination provides an efficient test setup for monitoring fatigue micro-fracture. The paper aims to combine AE and DIC for advanced fatigue damage analysis on cylindrical samples that are subjected to monotonic and fatigue Brazilian splitting tests. The analysis will use damage progress under monotonic loading as a reference to further understand fatigue fracture. Methods of AE data filtering and AE source localization are discussed and evaluated for their use in fracture analysis. The utilization of DIC to track the material stiffness evolution is investigated. In addition, the paper compares fracture process zones quantified by AE and DIC. From the experimental analysis, it was found that both methods captured the fatigue damage patterns, yet provided complementary information for damage evaluation.

Energy Evolution and Acoustic Emission Characteristics of Uniaxial Compression Failure of Anchored Layered Sandstone

To study the energy evolution and acoustic emission characteristics of layered sandstone under anchorage in the process of deformation and failure, the sandstone samples from Chuxiong Yi Autonomous Prefecture, Yunnan Province were selected for uniaxial compression testing. The energy evolution in the process of sandstone failure and the spatial fractal characteristics of acoustic emission events in the process of deformation and failure were investigated. Research results show that anchoring can make layered sandstone store more energy, the stored energy first increases, then decreases with the increase of bedding angle; the B value of sandstone under anchorage is generally higher than that of unanchored sandstone in the whole deformation and failure process, and the continuous decline in B value can be used to indicate a precursor to instability and failure; under the action of anchoring, the D value of sandstone (its fractal dimension) also increases, then decreases with the increase of bedding angle. The D value changes within [2, 3]. At a given bedding angle, the D value of anchored sandstone is greater than that of unanchored sandstone, the D value of 30° anchored sandstone increased the most (by 12.33%); the maximum D value occurred in 45° anchored sandstone (reaching 2.72) and the spatial distribution of acoustic emission events and damage of sandstone under anchorage is also more uniform; under increasing stress, the number of acoustic emission events is less widely distributed in the early stage and more densely distributed in the later stage. The growth rate of the D value varies across different peak stress ranges, which is more significant under the action of anchorage. The acoustic emission event counts grow evenly and slowly in the space, and the toughness of sandstone is improved to a certain extent under the action of anchorage.

Acoustic Emission b Value Characteristics of Granite under True Triaxial Stress

The acoustic emission b value is an important and widely used parameter for the early prediction of rock fractures. In this study, five groups of true triaxial compression tests were conducted on granite specimens to analyze changes in b value during the process of rock failure, and to investigate the b value characteristics of acoustic emission events. First, the acoustic emission events that simultaneously triggered at least four sensors were located using P-wave arrivals and sensor coordinates. Then, considering various intervals of acoustic emission event counts, stress magnitude, and stress proportion, b values were calculated using the values of the maximum amplitude, average amplitude, maximum absolute energy, and average absolute energy of the acoustic emission events. In addition, the goodness of the fitting curves was used to evaluate the fitting reliability of the b values. The results indicated higher accuracy of b value when calculated using the average amplitude setting for intervals of acoustic emission event counts of 200 or greater, stress magnitude of 20 MPa or greater, and stress proportion of 10% or greater. Moreover, the interval of event counts of 200 is suggested as a window parameter for b value calculations, and the b values are observed to exhibit a decreasing trend before fracture for more than 80% of the specimens. Furthermore, the b value tends to decrease with an increase in confining pressure. Thus, the b value can be used as an indicator for validating the stress concentration area, including magnitudes and accumulative probability density distribution of events, which is a beneficial complement to clarifying precursor information of rock mass instability.

Experimental Investigation of Early-Warning Critical Energy for Strainbursts

This research aimed to establish an early-warning critical energy for coal instability based on the energy theory and acoustic emission characteristics of coal under triaxial compression. To obtain an early-warning critical strain energy indicating the increase in the risk of coal instability, conventional triaxial compression and acoustic emission (AE) tests were carried out on coal specimens taken from a 980-m-deep mine with initial confining pressures of 10, 15, 20, 25, 30 and 35 MPa. Stress–strain relations, AE features, and energy evolution characteristics during triaxial compression were analyzed. It was found that the energy evolution and AE event count changes across different loading stages. With increasing axial stress, most of the input energy stored in the coal specimens was in the form of elastic strain energy and the AE event count was close to zero, indicating that the coal grains reach a state of balance. After the elastic deformation stage, a portion of the input energy was consumed by inelastic deformation. Once the stress level exceeded the volumetric compressibility–dilatancy transition stress, the AE event entered a period of relative quiet, and the rate of energy dissipation abruptly accelerated, indicating that the coal grains achieved another state of balance before THE instability or failure. The balance of the rock grains is broken again (AE event count and the rate of energy dissipation both increased dramatically), coal achieved the peak strength and instability soon. The point at which the dissipated energy ratio α increased rapidly or the starting point of a quiet period, indicates an increase in the risk of coal instability. The corresponding elastic strain energy accumulated within the coal can be regarded as a precursor to instability or strainburst. Accordingly, a fitting formula is presented to predict the early-warning critical energy for brittle coal subject to different minimum principal stress. The analysis results in this paper can be helpful in the assessment of coal instability risk.

Uniaxial compression creep and acoustic emission characteristics of sandstone under loading-unloading paths

Specimens of red sandstone are subjected to creep and acoustic emission (AE) tests under only multi-level loading and multi-level loading-unloading. Creep deformation characteristics and AE parameters of the red sandstone specimens under these two loading paths are compared and analyzed, and a creep AE damage-variable model is used for the damage evolution of the micro-cracked structures inside the rock during the creep process. The research results reveal the following: (1) During the creep process involving multi-level loading-unloading, the temporal variation of the AE amplitude is similar to that observed during the creep process involving only multi-level loading. (2) The variations of the cumulative AE event and cumulative AE ring-down count in the creep process involving multi-level loading-unloading are similar to those in the creep process involving only multi-level loading, while the actual values are higher in the former process. (3) The creep AE damage-variable model performs well on characterizing the damage evolution of the internal micro-crack structure of the rock in both creep processes.

Mechanical and Failure Characteristics of Rock-coal-rock Combined Body under Different Strain Rates: A Numerical Study from Micro Perspective

Strain rate has critical influence on rock and coal strength. Understanding and controlling rock failure is critical in many geological projects, such as mining, tunneling and other underground engineering project. The mechanical and failure characteristics of rock-coal-rock sandwich structures under different strain rates of uniaxial compression were numerically investigated. And detailed analysis of uniaxial compressive strength (UCS), elastic modulus, full scale stress-strain curves and acoustic emission (AE) characteristics of roof rock-coal-floor rock combined body is presented. The results show that with the increase of strain rate, the peak strain, peak strength and crack number all show an increasing trend. However, elastic modulus decreases with increasing strain rate. And with the increase of strain rate, the AE event count of rock-coal-rock combined body increases accordingly. The failure of rock-coal-rock combined body extends from the rock on both sides of coal to the whole rock on both sides, and the failure is more serious. This study provides an explanation for the strength and deformation of the rock-coal-rock combined sample in engineering from a micro perspective.

Acoustic Emission Generation Behavior in A7075-T651 and A6061-T6 Aluminum Alloys With and Without Cathodic Hydrogen Charging Under Cyclic Loading

Acoustic emission (AE) signals from non-charged and cathodic hydrogen charged A7075-T651 and A6061-T6 samples under tension–tension cyclic loading conditions at various stress intensity factor ranges were monitored. Although the AE event counts per cyclic load (AE count rates) were proportional to the crack growth rates in all kind of the sample, the rates were less than unity. Many cracked inclusions were observed on the crack surfaces and were identified as AE sources. Large inclusions in both Al alloys were prone to be fractured. The AE count rate in the A7075 sample was 10 times higher than that in A6061. However, no significant difference in the AE count rates and fatigue crack growth between the non-charged and charged samples were observed.

An Experimental Investigation on the Relationship between MS Frequency Response and Coal and Gas Outburst

Microseismic (MS) frequency response is an important part of high-efficiency data mining to achieve the aim of coal and gas outburst (CGOB) early warning. Based on the variation pattern of acoustic emission (AE) signal in the coal failure process, the experimental characteristics of MS activity and typical signals CGOB were obtained in this study. First, the AE behavior of coal failure experiment was studied, and an explanation of laws was provided as follows: the fracture behavior of coal sample exhibits certain characteristics of AE response in terms of AE event count, signal amplitude, and frequency; each stage has its own physical meaning during the process of loading test. Based on these laws, CGOB experiments were carried out using a large CGOB physical simulation system with a MS monitoring system. Notching filter and wavelet packet transform technique were used in the denoising and feature extraction of six typical MS events (signals). The features of each stage, including the time-frequency domain, were extracted and quantitatively expressed. We finally arrive at the following conclusions: (1) CGOB exhibits significantly periodic characteristics, and each CGOB stage corresponds to the significant response characteristics of MS. CGOB presents varying characteristics, such as “valley-peaks-valley”. (2) From the incubation stage to happen stage of outburst, the spectrum significantly moved from extremely low frequency (100-200 Hz) to high-frequency band (approach to 1600 Hz). During the residual stage, MS frequency manifested the concentration distribution (50 Hz) and offered the advantage of energy concentration. (3) The phenomenon of signal energy also shows the trend of energy transform low to high and to low modes along with the process. Signals total energy distribution (42.81%, 1,437.5-1,812.5 Hz) in the happen stage are markedly larger than those of events in incubation stage (7.01%) and residual stage (1.44%). The methodology presented in this paper for CGOB signal analysis provides a new method to obtain MS response precursor and predict CGOB disaster. This approach can be useful for rockburst anticipation and control during mining in gas and highly stressed coal mines.

Failure Behavior of Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings Under Three-Point Bending Test via Acoustic Emission Technique

In this paper, the failure behavior of plasma-sprayed yttria-stabilized zirconia thermal barrier coatings fabricated by atmospheric plasma spraying (APS-TBCs) under three-point bending (3PB) test has been characterized via acoustic emission (AE) technique. Linear positioning method has been adopted to monitor dynamic failure process of the APS-TBCs under 3PB test. The investigation results indicate that the variation of AE parameters (AE event counts, amplitudes and AE energy) corresponds well with the change of stress–strain curve of the loading processes. The failure mechanism was analyzed based on the characteristics of AE parameters. The distribution of frequency of crack propagation has been obtained. The AE signals came from two aspects: i.e., plastic deformation of substrates, initiation and propagation of the cracks in the coatings. The AE analysis combined with cross-sectional observation has indicated that many critical cracks initiate at the surface of the top-coat. And some main cracks tend to propagate toward the substrate/bond-coat interface. The actual failure mechanism of the APS-TBCs under 3PB test is attributed to the debonding of metallic coating from the substrates and the propagation of the horizontal crack along the substrate/bond-coat interface under the action of flexural moment.

AE Monitoring of Hydrogen Embrittlement Crack in Maraging Steel

AE (Acoustic Emission) result from initiation and propagation of cracks in materials. Then AE monitoring can detect the micro cracks. Maraging steels witch have superior strength are used as structural materials. However, these have hydrogen embrittlement problem under humid air. Hydrogen embrittlement resistance of maraging steels is usually estimated by visual testing (VT) which checks whether rupture or not in laboratory. However the testing method is batch style testing. Then it is difficult to estimate the exact rupture time through VT. Then the AE monitoring applied to detect hydrogen embrittlement of maraging steel. Hydrogen embrittlement crack accelerated by a droplet of NaCl solution that was set on the center of the maraging steel thin plate. In this case, the droplet was too small to determine the hydrogen embrittlement crack through the electrochemistry method.AE sensor also set on the plate and detected AE signals.AE signals were classified as to amplitude, frequency, and wave form. AE event rate was also focused. The surface crack propagation was also recorded by digital camera. Crack growth was confirmed from the pictures. AE event counts separate 3 regions. At first region, AE event counts detect before surface cracks were able to be observed. In this region, cracks may initiate under the droplet. At Second region, AE event counts were constantly increased. In this region it was observed that increment by crack growth was constant by digital camera. It shows that means the second region was the crack growth stage. At third region, AE event rate was increased twice. The second crack growth was observed in digital camera images. Then AE event rate reflected the number of cracks. There was good relation between crack propagation and AE event rate. AE event rates were difference between types of steels. The other steel which has high hydrogen embrittlement resistance tend to have low AE events rate.

Acoustic emission response of magnesium alloy during cyclic and creep tests

We studied the acoustic emission (AE) response to AZ31B alloy during cyclic and creep tests. The peak total AE event count appeared at the 400th cycle before material fracture during the compressive–tensile (C–T) cyclic test at a strain amplitude of 0.4%. In the case of 0.75% strain amplitude, the peak AE event count during compressive unloading occurred at approximately the 100th cycle before fracture. In creep tests at 423 and 523K, the AE event count in the tertiary creep stage involved increased activations of slips and cracks. The AE responses indicated the transition of the deformation mechanism. The results suggest that the fracture of magnesium alloys can be predicted on the basis of in situ AE measurements.

Regularities of Acoustic Emission in the Freight Car Solebar Materials

Acoustic emission results which were obtained during tests of the samples, which were made from foundry solebars with the developing fatigue crack, are presented. The dependences of the acoustic emission event count, the force critical value during the stationary acoustic emission process, and the growth rate of the event count from the cycles number are determined. The amplitude signal distributions relating to the crack growth were received. It is offered to use the force critical value and the amplitude threshold in the rejection criteria.

A novel active prevention technology for borehole instability under the influence of mining activities

Coal bed methane (CBM) drainage is an efficient method used to control gas hazards. Nevertheless, borehole instability is prone to occur under repeated disturbances by external stress from mining activities. Consequently, the collapsed coal blocks the gas-flow channel to further induce several gas drainage problems, including low gas concentration and flow, poor drainage result, etc. Due to these problems, screen pipes were installed in this work to provide active support in order to prevent borehole instability. Initially, the effect of mining activities on borehole stability was analysed. Subsequently, we explored the instability characteristics and corresponding acoustic emission (AE) properties of a non-supported borehole and a borehole stabilized by internal active support. These boreholes were drilled in the lab sample instead of the real coal sample. Moreover, the abilities of the holes to resist disturbances due to external stresses were compared. When the stress reached 10 MPa, the non-supported borehole was completely destroyed, whereas the actively supported borehole only slightly deformed. As the stress continuously increased to 14 MPa, a deformation of 15 mm was detected along the radial direction of the actively supported borehole. Additionally, an analysis of the dynamic changes in the strain on the screen pipe surface, the AE time–sequence parameter and location information indicated that the maximum AE event count and energy dissipation rate of the supported borehole at 14 MPa were 44% and 23% lower, respectively, than the corresponding values for the non-supported borehole at 10 MPa. Thus, the support increases the ability of the borehole to resist disturbance by at least 40%. Furthermore, the locating points and energy rate appeared to temporally cluster at coal-yielding or failure stage. Hence, the supporting effect of the screen pipe on the coal around boreholes at the crushing stage is significant. The internal support to the borehole provides a positive confining pressure for the coal in the fracture zone to improve the coal's residual strength. Depending on the support from the screen pipe, the coal can mesh to remain in place and thus prevent collapse, which improves the stability of the borehole.

G0300206 マグネシウム合金AZ31Bのクリープ変形時のAE測定

A tensile test of a magnesium alloy (AZ31B) was performed in various temperature environments, and the change of the mechanical characteristics of the magnesium alloy with temperature was examined. A creep test of the magnesium alloy was performed, and the relation between creep damage and the acoustic emission (AE) occurrence behavior under high temperature conditions was investigated. In the tensile test, when temperature rise in more than 150℃, the 0.2% proof stress and tensile strength of the magnesium alloy (AZ31B) became small, and the elongation of it increased. In the creep test, although AE event count increased in the transient creep stage just after loading, it decreased in the stationary creep stage and increased again in the accelerating creep stage. Since the relation between AE occurrence and each stage of the creep deformation was observed clearly, it was confirmed that the acoustic emission method was available in creep damage evaluation of the magnesium alloy.

Failure Mechanism of Rock Bridge Based on Acoustic Emission Technique

Acoustic emission (AE) technique is widely used in various fields as a reliable nondestructive examination technology. Two experimental tests were carried out in a rock mechanics laboratory, which include (1) small scale direct shear tests of rock bridge with different lengths and (2) large scale landslide model with locked section. The relationship of AE event count and record time was analyzed during the tests. The AE source location technology and comparative analysis with its actual failure model were done. It can be found that whether it is small scale test or large scale landslide model test, AE technique accurately located the AE source point, which reflected the failure generation and expansion of internal cracks in rock samples. Large scale landslide model with locked section test showed that rock bridge in rocky slope has typical brittle failure behavior. The two tests based on AE technique well revealed the rock failure mechanism in rocky slope and clarified the cause of high speed and long distance sliding of rocky slope.

Compaction creep of sands due to time‐dependent grain failure: Effects of chemical environment, applied stress, and grain size

AbstractTime‐dependent brittle creep plays a role in controlling compaction of sands and sandstones under upper crustal conditions, influencing phenomena such as production‐induced reservoir compaction, surface subsidence, and induced seismicity. Brittle creep also plays a role in determining the mechanical behavior of gouge‐rich faults. We performed uniaxial creep experiments on sand to investigate the effects of chemical environment (dry versus solution flooded), grain size (d = 196–378 µm), and applied effective stress (σa up to 30 MPa), at room temperature conditions favoring grain‐scale brittle processes. Creep measurements were complemented with acoustic emission (AE) detection and microstructural analysis to characterize the main creep mechanism. Wet samples showed much higher creep strains than dry‐tested samples. AE event counts showed a direct relation between grain failure and creep strain, with higher AE rates occurring in the wet samples. Therefore, we inferred that time‐dependent deformation was dominated by subcritical crack growth, resulting in grain failure accompanied by intergranular sliding rearrangements, and that crack growth in the presence of chemically active fluids was controlled by stress corrosion. The sensitivity of the compaction rate of the sands to d and σa can be expressed as where i ≈ 6 and j ≈ 21 under dry conditions and i ≈ 9 and j ≈ 15 under wet conditions. Our results were compared to a simple model based on Hertzian contact theory, linear elastic fracture mechanics, and subcritical crack growth. This model showed agreement between the observed stress and grain size sensitivities of creep, within a factor of 2.

Monitoring of compression-after-impact testing of CFRP laminates subjected to simulated lightning damage by acoustic emission

The progress of damage during compression-after-impact (CAI) tests of carbon-fibre reinforced plastics (CFRP) laminates made of nanoparticles-coated carbon fibres and subjected to a simulated lightning strike was monitored by acoustic emission (AE). The effects of nanoparticles coating and the degree of damage induced by the simulated lightning strikes on AE activities were examined, with the relationship between the compressive residual strength and AE behaviour being evaluated in terms of AE event counts and the onset of AE activities during the compressive loading. AE monitoring appeared to be useful to assess the degree of impact-damage hence the structural integrity of laminated CFRP structures damaged by lightning strikes.

Investigation of Compressive Damage Mechanisms in 3D Braided Composites by the Acoustic Emission Events Energy and Amplitude

The deformation behavior and damage mechanism of 3-D carbon/epoxy braided composites with different braiding angles under the monotonic compressive loading are investigated by the acoustic emission (AE) technique. The damage process is divided into several different regions based on the change of the accumulative AE event counts. Correlations between the damage mechanisms and the AE results are established in terms of the events energy and amplitude. These correlations can be used to monitor the fracture growth process in the braided composites. Experimental results reveal that the AE technique is an effective tool for identifying damage mechanisms.