AE Techniques Research Articles

Characterizing damage patterns and evolution in Multi-Hole GLARE laminates under tensile load via integrated AE and DIC techniques

In this study, a combined numerical simulation and experimental approach was employed to investigate the mechanical behavior and damage mechanisms of multi-hole GLARE laminates with varying off-axis angles under static tensile loading. Digital image correlation techniques were used to monitor changes in the strain field near the open hole region. The acoustic emission parameters were used to recognize damage patterns and evolution. The progressive damage evolution processes of various GLARE components were investigated using a 3D finite element model (FEM) based on the Hashin strain criterion and cohesive zone modeling. The results indicate that GLARE experiences damage modes such as aluminum alloy breakage, matrix cracking, fiber/matrix debonding, delamination, and fiber breakage. The frequency ranges associated with the five damage modes are as follows: [0–50 kHz], [100–175 kHz], [175–220 kHz], [220–300 kHz], and [300–400 kHz]. The dominant damage mode throughout the tensile phase is matrix cracking, but the ultimate failure of the specimen is determined by aluminum alloy breakage and fiber breakage. In addition, increasing the off-axis angle of the multi-hole leads to a shift in the final failure mode from tensile-dominated to tensile shear-dominated, while also slightly reducing the overall initial stiffness of the specimen.

Assessment of tensile damage mechanism of open‐hole GLARE laminates based on acoustic emission and digital image correlation techniques

AbstractGLARE laminates have emerged as a favored option for the construction of fuselage and wing skins in large airliners, owing to their exceptional mechanical characteristics. Nevertheless, the incorporation of open‐hole designs poses a challenge as it disrupts the continuity of the laminates, resulting in stress concentration and subsequent damage. To investigate the impact of various layup orientations and hole sizes on the tensile properties of open‐hole GLARE laminates, this study conducted axial tensile tests. Additionally, the tensile damage process was monitored using DIC and AE techniques, enabling the identification of damage patterns and the analysis of their evolution. The results demonstrate a noteworthy decline in the ultimate strength and failure strain as the size of the opening increases. Moreover, the retention rate of failure strain displays a marked sensitivity to the layup orientation. In conjunction with observations made through DIC and SEM, the k‐means++ algorithm successfully clustered peak frequencies, thereby revealing distinct damage patterns and their corresponding frequency ranges as aluminum alloy damage [0–90 kHz], matrix cracking [104–174 kHz], fiber/matrix debonding [175–224 kHz], interlaminar delamination [234–300 kHz], and fiber fracture [304–469 kHz]. AE cumulative counts were utilized to evaluate the progression of individual damage modes. The results emphasize that matrix cracking demonstrates the most substantial cumulative counts, whereas damage to the fibers and aluminum alloy noticeably affects the load‐carrying capability of the laminate. Furthermore, the fibers/matrix debonding and interlaminar delamination, exhibit heightened susceptibility to layup orientation and hole size.Highlights The tensile performance evaluation of GLARE laminates with open‐hole varying layup orientations and hole sizes was investigated. A combination of DIC and AE techniques was used to monitor the tensile damage process. Damage pattern was identified based on the observations of DIC and SEM. An approach based on Pearson's correlation coefficient and k‐means++ clustering algorithm was used for damage pattern recognition in GLARE laminates. AE cumulative counts were employed to assess the evolution of each damage mode.

Damage pattern recognition for corroded beams strengthened by CFRP anchorage system based on acoustic emission techniques

This study presents a damage pattern recognition approach for corroded steel beams strengthened by CFRP anchorage system based on acoustic emission clustering analysis. The proposed method includes four steps: acoustic emission signal acquisition, feature extraction, clustering analysis, and damage pattern recognition. Four corroded beams with different corrosion levels and strengthening schemes were tested under four-point bending loading. The acoustic emission signals were collected during the loading process and analyzed using Gaussian mixture model clustering method. The results showed that the collected AE data were analyzed using clustering analysis, successfully distinguishing the distinct damage patterns associated with each mode. The AE signals exhibited distinct characteristics for different damage modes: concrete matrix damage had high-frequency and low-energy characteristics, CFRP-matrix debonding showed intermediate values for all parameters, and CFRP tearing had longer durations, lower peak frequencies, and high-energy characteristics. Besides, the study identified three stages of the damage process: an initial stage with fewer low-intensity AE signals, a damage development stage characterized by an increase in concrete-matrix damage and CFRP – matrix debonding signals, and a continuous damage growth stage with significant AE signals associated with three damage modes. Furthermore, the degree of corrosion significantly influenced the cumulative AE energy of damage modes. Lower degrees of corrosion led to higher cumulative energy from concrete matrix damage and CFRP-matrix debonding. These findings provide valuable insights for understanding the damage evolution and failure mechanisms of CFRP-strengthened corroded beams. The use of AE techniques for damage pattern recognition can enhance the evaluation and design of CFRP anchorage systems, leading to more effective rehabilitation strategies for corroded structures.

Brazilian splitting testing of the restorative properties of eco-friendly epoxy resin on cracked granite samples with various widths

Tensile strength is a crucial mechanical property of rock. Various mass ratios kCE curing agent to eco-friendly epoxy resin are used to repair fractured rock masses by considering kSCA(mass concentrations of SCA) for rock surface treatment. To address the issue of asymmetry in bi-material samples, a novel stress-balanced sample (SRSBD) is proposed for conducting Brazilian splitting tests to evaluate the tensile behavior of repaired granite. The initiation and propagation characteristics of cracks in intact and repaired samples with different repair material thicknesses are investigated using AE and digital DIC techniques. At the minimum bonding thickness, the tensile strength (at 28 d and 42 d) is approximately 11.45 MPa with a strength recovery rate of 83.58%; however, the energy absorption is 1.28 times that of the intact rock, indicating improved ductility characteristics. For UPC, the repair effect is only 4.25 MPa at 42 d. As the epoxy thickness increases, the tensile strain proportionally increases. The tensile strength initially rises and then declines, reaching a maximum of 12.78 MPa with a 1 mm-repair. Moreover, DIC indicates that the tensile strain of the epoxy-repaired sample surpasses that of the intact specimen; while AE displays a postponed ringing onset and a reduction in early-stage frequency. Changes in kCE and the kSCA have minimal impact on the tensile repair effect, with damage primarily originating from the rock side rather than the repair material. This finding demonstrates that the eco-friendly epoxy-repaired material has a clear advantage over UPC, providing a favorable repair effect for establishing sufficient bond strength and ensuring stability in underground engineering projects.

Influence of heterogeneity on size effect models and fracture characteristics of plain concrete

Material heterogeneity strongly influences the fracture process zone in concrete, which is responsible for the exhibition of size effect in the nominal strength. The fundamental aspect in deriving the size effect law lies with the non-negligible process zone, which strongly correlates with the material heterogeneity size. Therefore, it is essential to establish the correlation between the size effect parameters and the heterogeneity size to predict fracture behaviour. In this work, detailed experimental investigations have been performed under the centre point loading of beams to evaluate the influence of heterogeneity on the fracture performance of plain concrete members through the DIC and AE techniques. A new definition of fully developed FPZ under monotonic loading has been proposed to occur between 95%–75% of the post-peak load. The effects of aggregate size on the fracture characteristics of concrete have been observed with reference to the work of fracture method (WFM), size effect law (SEL), and boundary effect method (BEM) and found in agreement with the existing literature. The existing size effect models, such as the size effect law and boundary effect model, have been modified by establishing the correlations between the model material parameters, namely, D0 and a∞ and the material heterogeneity. Finally, regression-based equations have been developed to establish the correlation between Lch, predicted through WFM, the effective lengths of fracture process zone, Cf of SEL, and Lch and a∞ of BEM. The applicability of the developed equations has been verified with the available experimental data from the literature.

Contribution of elastic wave approaches to civil engineering digital transformation

As for DX for civil infrastructures, digital twin of point-clouds of spillway of a rock fill dam is demonstrated. Reproduction of existing structures with point-clouds from still or movie images are shown. Necessary information in addition to the point-clouds such as surface and internal condition of the structure are depicted. As for the diagnosis methods for internal condition, brief history with elastic wave approaches is reviewed. Information such as surface deterioration condition as well as internal condition composed of elastic wave velocities, which will be crucially important to realize life-cycle-oriented design, construction, and maintenance, is incorporated into the digital twin. Through the suggested model, overall damage of the spillway is discussed in combination with the pin-point excavations for the verification. Through the life cycle of the civil engineering structures roles of elastic wave approaches including AE techniques will be suggestively indicated.

Experimental study on cracking behavior of concrete containing hole defects

Cavity often exists in the mass concrete when insufficient vibration occurs. These defects play an important role in the failure mechanism of concrete. Cracking behavior of surface flaws in concrete is widely investigated, while research on failure mechanism of internal flaws is limited because it is difficult to cut internal flaws in specimens and cannot capture the cracking processes of internal flaws through direct observations. In this study, a novel method for preparing concrete samples with embedded flaws is first proposed by volatilization of camphor. AE and CT techniques are adopted to investigate the internal damage failure behavior of hollowed concrete. Experimental results demonstrate that internal hole defects result in a reduction of strength and deformation properties of concrete materials. The peak strength, crack initiation stress, and deformation properties of hollowed concrete specimen decrease with the cavity diameters. Since hole defects induce high stress concentration which exacerbates crack initiation, AE events of specimen with an internal cavity occurred much earlier than the case of intact specimen. The ultimate failure modes of concretes are dominated by tension failure. For intact specimens, tension cracks mainly happen near to the boundaries of specimens. While for hollowed specimens, tension cracks initiated at the cavity perimeter, which then propagated to the boundaries of specimens.

Failure Characterization of Flax/Epoxy Composite Materials with Filler Under Acoustic Wave

Researches on bio-composites are increased due to their environment friendly. Some research shows a good improvement in their mechanical property with the polymer/synthetic composites. In this paper, the damage characterization of flax epoxy composite with alumina powder as filler under acoustic emission at various stages are studied. For this work, the alumina powder with various percentages such as 3% and 5% are chosen. In this project, tensile and flexural tests are performed. From the tensile test peak load and strain functions are calculated. Acoustic emission is non-destructive technique used to find the damage mode. AE has the advantage over other method due to its high sensitivity. The three-point bending is performed on the filler infused flax/epoxy composite to evaluate the flexural damage at various percentage of filler composition. The damage characterization is studied based on the frequency obtained over the time. These failure modes such as delamination, matrix cracking fibre damage are associated with frequencies are evaluated using standard mode of damage. Duration (μs) vs. amplitude (dB) and force (N) vs. position (mm) curves are plotted to evaluate the damage. The real time various damage levels occurs during flexural loading and it was evaluated using AE techniques.

Anterior Cruciate Ligament Reconstruction in Skeletally Immature Athletes Using All-Epiphyseal Techniques.

All-epiphyseal anterior cruciate ligament reconstruction (AE ACLR) has become an alternative technique for skeletally immature patients with a significant amount of growth remaining. This technique involves graft fixation within the epiphysis without crossing the physis. Either quadriceps tendon or hamstring autograft can be used when performing this procedure. Previous studies have shown that the complication rate is not higher in AE techniques versus previously developed techniques. Additionally, in our hands, the revision rate was found to be significantly lower in an AE ACLR compared with patients who had a transphyseal ACLR.

Characterization of anisotropic mode II fracture behaviors of a typical layered rock combining AE and DIC techniques

Shear-sliding mode fracture, i.e., mode II fracture, is a very common rupture mode of layered rocks. To achieve a better understanding of the anisotropy in the real mode II fracture, which propagates in a self-similar manner, a series of direct shear tests were conducted on single-notched specimens made of shale with three bedding angles, i.e., β = 0°, 45° and 90°. The ranking of the anisotropic mode II fracture toughness (KIIc) with different bedding angles is KIIc,45° >KIIc,90° >KIIc,0°, which is different from that of the anisotropic mode II fracture energy release rate (GIIc), i.e., GIIc,90° >GIIc,45° >GIIc,0°, suggesting that, unlike isotropic rocks, the crack propagation resistance of a layered rock cannot be completely characterized by its fracture toughness. From the acoustic emission monitoring results, it is found that the fracture process initiates and accelerates from the notch front once the applied mode II stress intensity factor (SIF) reaches its first and second thresholds, KII, FPI (approximately 50%∼70% of the fracture toughness) and KII, FPA (approximately 85%∼95% of the fracture toughness), respectively; generally, both KII, FPI and KII, FPA show noticeable anisotropies. The results of the b value indicate that more small-scale events occur in the specimen with β = 0°, and large-scale events account for a greater proportion in the specimen with β = 45°. A dominant high strain zone along the prefabricated crack direction and a secondary high strain zone along the bedding planes were discovered. Combining the acoustic emission and digital image correlation results, three typical fracture mechanisms were observed: (1) shear fracture along bedding planes when shearing along beddings; (2) shear fracture in matrix and along bedding planes for β = 45°; and (3) shear fracture in matrix and tensile fracture of bedding planes when shearing perpendicular to the beddings.

Coupling Influence of Inclination Angle and Moisture Content on Mechanical Properties and Microcrack Fracture of Coal Specimens

Abstract Waterproof coal pillar in the underground reservoir is affected significantly by inclination loads and water erosion. Comprehensive understanding of the influence of moisture content and inclination angle on the mechanics properties and microfracture behavior of coal specimens plays an important role for revealing the instability mechanism of waterproof coal pillar. In this paper, a new modified combined compression and shear test (MC-CAST) system was firstly developed for achieving the specimen inclined loading and then used to carry out the inclined uniaxial compression test of water-bearing coal specimens at the inclination angle of 0°, 5°, 10°, and 15° and the moisture content of 0%, 2.42%, 5.53%, 7.55%, and 10.08%. The mechanical and microfracture behaviors of water-bearing coal specimens were analyzed and discussed by AE techniques and SEM. Research results indicate that ① the peak shear stress, peak strength, and elastic modulus of coals showed obvious moisture content weakening effect, and the weakening effect was more significant at larger inclination angle; ② the peak strength and elastic modulus decreased nonlinearly as inclination angle increased, of which decreasing amplitude was greater at high moisture content than that at low moisture content; ③ the peak shear stress gradually increased with the increasing inclination angle for 0%-7.55% moisture content, while it increased first and then decreased, and reached the maximum value at 10° inclination angle for 10.08% moisture content; ④ the stress thresholds of crack closure, initiation, and damage of coal specimens decreased gradually with the increase of moisture content and inclination angle, but the ratio of above three thresholds to their corresponding peak strength was basically unchanged; and ⑤ the erosion-stripping effect of bound water and pore pressure effect of free water, respectively, caused initial damage and secondary superposition damage of coal specimens before and after inclination loading test. Combining with the promotion effect of additional shear stress on crack initiation, propagation, and coalescence, the coupling effect of the above three factors was the fundamental reason for the strength deterioration of water-bearing coals under inclined loading. The research results can provide an important basis for the strength and stability evaluation of waterproof coal pillars of underground reservoirs in ecologically fragile areas.

A novel in-situ stress measurement method incorporating non-oriented core ground re-orientation and acoustic emission: A case study of a deep borehole

The measurement of in-situ stress is a critical prerequisite for the mining design and the stability analysis of surrounding rock in deep mining engineering. In this study, a novel re-oriented core acoustic emission (RCAE) method incorporating the non-oriented core ground re-orientation and AE techniques was proposed for in-situ stress measurement. First, the principle of non-oriented core ground re-orientation is established according to the spatial coupling relationship between the drilling trajectory and the core surface characteristics. Then, an innovative apparatus was designed for recovering the original spatial orientation of non-oriented cores. Furthermore, the measurement procedures of RCAE method are described in detail, involving suitability analysis, outdoor operations, core re-orientation, specimen preparation, AE test and stress calculation. Using this method, a case study for in-situ stress measurement was performed in an ultra-deep borehole (2360 m) of the Sanshandao gold mine, China. Meanwhile, the verifications of measurement accuracy were conducted based on the tectonic stress inversion and the underground overcoring method. The results show that the measurement accuracy of RCAE method is acceptable, especially the horizontal maximum principal stress and its azimuth measured are well matched with those measured by other methods. In addition, the field applications indicate that the in-borehole procedure of RCAE method only requires drilling trajectory measurement without excessive complex operations, and the adequate measuring depth of this method in the case area is up to 3841 ± 521 m according to the damage stress threshold analysis. Therefore, the RCAE method could break through the challenges caused by the restricted measuring space and large measuring depth when no deep underground access exists. Moreover, the non-oriented cores can be rapidly re-oriented on the ground, which could expand the application value of ordinary geological boreholes in the field of deep geostress and tectonic measurement.

The rate effect on fracture mechanics of dam concrete based on DIC and AE techniques

In order to study the effect of loading rate on fracture behavior of dam concrete, wedge splitting tests of various loading rates (0.1, 0.01, and 0.001 mm/s) are carried out on two kinds of full-graded dam concrete notched cubes with side lengths of 300 and 450 mm, respectively. Digital image correlation and acoustic emission technique are used to measure the deformation and acoustic emission parameters of the dam concrete. Test results show that: the peak load and fracture energy of dam concrete specimens increases with the increase of loading rate. And the higher the loading rate is, the fracture of concrete shows more obvious brittleness. Influenced by the boundary effect, the CTOD increases with the increasing of loading rate, however, the length of crack decreases as loading rate increases. With the loading rate increases, the energy mutation area is more obvious, while the accumulated acoustic emission energy is affected by both the loading rate and the maximum aggregate size. The number of acoustic emission three-dimensional locating points and the shear signal decrease with the increase of loading rate, which is attributed to that the faster the loading rate is, the less sufficient the development of micro cracks in concrete is. The test results can supply experimental data to the fracture mechanics of dam concrete.

Experimental Study on Post-peak Cyclic Characteristics of Self-compacting Concrete Combined with AE and DIC Techniques

Experimental Study on Post-peak Cyclic Characteristics of Self-compacting Concrete Combined with AE and DIC Techniques

Experimental investigation of progressive cracking processes in granite under uniaxial loading using digital imaging and AE techniques

For a full understanding of the cracking processes in granite, uniaxial compression tests are conducted on prismatic specimens with pre-existing flaws, and digital imaging and AE techniques are applied to monitor real-time rupture behaviors. The digital image correlation (DIC) method is used to detect the process zone nucleation characteristics in granite. A novel approach for representing AE data in terms of the inter-event time (IET) function F(τ) is employed to analyze fracture-related AE event rate characteristics. Based on the coupled analyses of the acousto-optic-mechanical characteristics, the complete cracking processes of granite are classified into six levels, which are distinguishable by five characteristic stresses. Process zone nucleation, which represents the clustering of micro-cracks, is incorporated into the classification for the first time. Process zone nucleation is visualized as a white patch and is either linear or diffuse. By DIC analysis, the maximum principal strain field reliably predicts a linear white patch, and the maximum shear strain field implies a diffuse white patch. The evolutionary rules of the IET function F(τ) strongly support the new classification of cracking levels in granite. For the identification of stress thresholds and cracking levels, a combined acousto-optic-mechanical methodology is established, in which the role of the IET function F(τ) is highlighted.

Augmented Endoscopy for Surveillance of Colonic Inflammatory Bowel Disease: Systematic Review With Network Meta-analysis.

Considering the high risk of dysplasia and cancer in inflammatory bowel disease [IBD], surveillance is advocated. However, international guidelines do not reach a uniform recommendation on the way to perform surveillance. We performed a systematic review with a meta-analysis to assess the best endoscopic surveillance strategy in colonic IBD. The systematic review was performed in PubMed/MEDLINE, EMBASE, SCOPUS, and Cochrane databases to identify studies comparing white light endoscopy [WLE] and augmented endoscopy [AE] in the detection of dysplasia/neoplasia in colonic IBD. A sub-analysis between dye-spray chromoendoscopy [DCE], narrow-band imaging [NBI], I-SCAN, full-spectrum endoscopy [FUSE], and auto-fluorescence imaging [AFI] was also performed. Furthermore, a meta-regression and a network meta-analysis were also performed. A total of 27 studies [6167 IBD patients with 2024 dysplastic lesions] met the inclusion criteria. There was no publication bias. AE showed a higher likelihood of detecting dysplasia than WLE (19.3% vs 8.5%, odds ratio [OR] = 2.036), with an incremental yield [IY] of 10.8%. DCE [OR = 2.605] and AFI [OR = 3.055] had higher likelihood of detecting dysplasia than WLE; otherwise, I-SCAN [OR = 1.096], NBI [OR = 0.650], and FUSE [OR = 1.118] were not superior to WLE. Dysplasia was found in 1256/7267 targeted biopsies [17.3%] and in 363/110 040 random biopsies [0.33%] [OR = 66.559, IY = 16.9%]. Meta-regression found no variable impacting on the efficacy of AE techniques. Network meta-analysis identified a significant superiority of DCE to WLE in detecting dysplasia [OR 2.12], but no other single technique was found to be superior to all others in dysplasia detection. DCE was associated with higher likelihood of discovering dysplastic lesions than WLE. Chromoendoscopy is the best supported endoscopic technique for IBD surveillance.

Acoustic emissions and electric signal recordings, when cement mortar beams are subjected to three-point bending under various loading protocols

Two experimental techniques are used study the response of cement mortar beams subjected to three-point bending under various loading protocols. The techniques used are the detection of weak electric current emissions known as Pressure Stimulated Currents and the Acoustic Emissions (in particular, the cumulative AE energy and the b-value analysis). Patterns are detected that can be used to predict upcoming fracture, regardless of the adopted loading protocol in each experiment. The experimental results of the AE and PSC techniques lead to the conclusion that when the calculated Ib values decrease, the PSC starts increasing strongly.

The role of flaws on crack growth in rock-like material assessed by AE technique

Experiments for the rectangular rock-like samples (made of high-strength gypsum and water–cement ratio is 1) with two parallel pre-existing flaws subjected to uniaxial compression were carried out to further investigate the influence of varying flaw geometries on mechanical properties and crack coalescence behaviors. According to the tests results, eight crack types were characterized on a basis of the mechanisms of crack nucleation, formation and propagation, and seven coalescence modes occurred through the ligament, including S-mode, M1-mode, M2-mode, M3-mode, T1-mode, T2-mode and T3-mode. The AE and photographic monitoring techniques were adopted to further clarify the procedure of the crack coalescence and failure during uniaxial compression tests and in consequence the whole process of crack emergence, growth, coalescence and failure was recorded in real time. The results of AE technique revealed that the characteristics of acoustic emission energy associate with crack coalescence modes, and AE location method can emphasize the moments of crack occurrences and follow the crack growth until final failure. This study put forward better understanding of the fracture and failure mechanism of underground rock engineering, like rock burst.

Damage and Fracture Investigation of Three-Point Bending Notched Sandstone Beams by DIC and AE Techniques

Damage and Fracture Investigation of Three-Point Bending Notched Sandstone Beams by DIC and AE Techniques

A study on using acoustic emission in rock slope with difficult ground — focused on rainfall

This study attempted to predict slope failures by applying AE techniques to a rock slope with a history of collapse. Damage levels were assessed on the basis of the AE characteristics estimated by conducting laboratory tests on simulated slope failures. The test results showed that the specimen showed a very high degree of failure at the initial stage of loading, which was analyzed using the AE characteristics to assess the damage levels. The variation in the measured number of AE hits and AE events in field tests may indicate minute variations in the slope. The measured values appeared to be insignificant as they were less than the minimum criterion for damage. An analysis of rainfall, which is an important factor in slope behavior, showed that as rainfall increased, the number of AE hits and AE events also increased. In particular, when the cumulative rainfall was constant, the cumulative number of AE hits and AE events appeared to converge, indicating that the cumulative rainfall and the number of AE hits are closely connected. When applying AE techniques to a slope that has a high probability of failure, the failure prediction of the specific location and the early prediction of failure behavior on rock slopes became possible.