Acoustic Emission Monitoring Research Articles

Influence of gravel content and cement on conglomerate fracture

Tight reservoirs are typically developed by horizontal wells and multi-stage hydraulic fracturing. The conglomerate reservoir is one type of tight reservoirs, which is different from homogeneous rock, such as tight sandstone. This is because that the existence of gravels makes conglomerate have strong heterogeneity. Thus, it is difficult to grasp the fracture mechanism and the law of fracture propagation of conglomerate, which limits the efficient development of the conglomerate reservoir. In this paper, the fracture characteristics and factors influencing the fracturing of Mahu conglomerate were studied by uniaxial compression, acoustic emission monitoring and X-ray computed tomography (CT) scanning experiments. The results show that the fracture characteristics of conglomerates are influenced by the gravel content and cement. The conglomerate in the study area is mainly divided into carbonate cemented conglomerate and clay cemented conglomerate. The fracture complexity of carbonate cemented conglomerate first increases and then decreases with increasing gravel content. However, for clay cemented conglomerates, the fracture complexity increases over the gravel content. The crack development stress is a significant parameter in the crack assessment of conglomerates. This study is useful to understand the influence of meso-fabric characteristics of conglomerates on their fracturing and crack evolution and guides the design of hydraulic fracturing.

Theoretical and experimental exploration on the combined mode I + III fracture toughness of shale using the edge-notched disk bending method with acoustic emission monitoring

The combined mode I + III fracture toughness of shale plays a significant role in the exploitation of shale gas. To investigate the combined mode I + III fracture characteristics of shale, the ENDB (edge-notched disk bending) fracture experiments with AE (acoustic emission) monitoring are implemented to accomplish the full range of fractures from pure mode I (tension) to pure mode III (tearing). By considering the contribution of the mean strain energy to the onset of fracturing, this work develops the 3D-MSED (mean strain energy density) criterion. The measured results indicate that the fracturing energy of the ENDB shale increases linearly with the move from pure tension to pure tearing, while the effective fracture toughness for the ENDB shale decreases linearly. In comparison with the published 3D fracture criteria, the developed 3D-MSED criterion can predict an excellent combined mode I + III fracture toughness envelope for the ENDB shale. Interestingly, the Gaussian function can adequately describe the distribution of AE amplitudes, and the distribution discrepancy in AE amplitudes is insignificant for the ENDB shale specimens under different loading types. However, the percentage of the AE high dominant frequency for the tearing-dominated loading case is relatively greater than that of the tension-dominated loading case, and the tearing-dominated fracturing response is characterized by the nonplanar shear deformation.

Investigations of fracture behavior and pore structure change in pulse fracturing for cement block

Pulse fracturing can reduce fracture initiation pressure and increase stimulation effectiveness. To investigate the effect of frequency and amplitude on fracture propagation behavior in pulse fracturing, tri-axial experiments with acoustic emission (AE) monitoring are applied. The results demonstrate that pulse fracturing can generate mixed mode fractures, and the distinct deviation of the fracture propagation near-wellbore can be seen for pulse fracturing. Both pulse frequency and amplitude are critical parameters for the propagation path, measured AE accounts, accumulative energy and pore connectivity. The increase in amplitude is beneficial for large fracturing energy, but the increase in frequency is not necessarily helpful for fracture effectiveness. The harmony between the rock and pump frequency can yield the largest acoustic events and pore connectivity. The pore structure and microfracture change of rock before and after pulse fracturing at different distances are measured with nuclear magnetic resonance (NMR) and CT scans, indicating that pulse fracturing has a strong capability to create a larger stimulated area than the monotonic fracturing model. In addition, obvious microfracture generation and pore space expansion can be seen near the injection port. However, the pore structure comparison indicates that the pulse fracturing mode mainly improves the scale of macropores, which is primarily because of the relatively small pulse fracturing parameters used in these experiments. Thus, this study provides an understanding of pulse frequency and amplitude effects for stimulation effectiveness related to pulse fracturing of tight reservoirs.

Acoustic Emission Characterization Analysis of Quasi-Static and Fatigue Compression Properties of Aluminum Foam

In order to explore the evolution of physical and mechanical properties and acoustic emission (AE) characteristics of aluminum foam under fatigue and quasi-static compression from a microscopic point of view, the AE monitoring technology was used to analyze the deformation, hardening, and energy absorption characteristics of open-cell aluminum foam under quasi-static compression at different rates (2, 10 and 50 mm/min) and fatigue loading tests with different peak stress ratios k (k = maximum stress/yield stress) by means of MTS fatigue testing machine and CCD camera. The results indicated that under different compression rates, the AE ring down count had the same trend as the engineering stress–strain response of the specimens, the AE ring down count rate at the plastic deformation stage showed the same performance as the work hardening rate, and the AE energy absorption efficiency corresponded well to the experimental results. The specimen entered the densification stage with the stability of AE count and the decrease in energy absorption efficiency. During the fatigue tests of different k values, the change trend of strain was consistent with the response of acoustic emission characteristic parameters, and the fatigue compression damage caused by the deformation process of the specimen can be monitored by the change in AE characteristics. The AE characteristics can dynamically monitor the compression process and provide a new research method and idea for the study of mechanical properties of aluminum foam.

An experimental study of fault slips under unloading condition in coal mines

To investigate the mechanism of fault slips in coal mines, a biaxial shear experiment was carried out under unloading condition based on the fault F16 in Yima city, China. Two rock samples were used in the experiment and each sample was composed of two triangular sandstone blocks which were put together to simulate the fault. One rock sample was used to do fault slip tests and it was called slip-test sample. The other sample for comparison with the slip-test one was untested, and it was named non-slip-test sample. During the biaxial shear experiment of the slip-test sample, normal and shear strains near the fault, acoustic emission (AE) signals, and the sliding displacement were measured. After the experiment, microscopic profiles of fault surfaces of both rock samples were examined by scanning electron microscope (SEM). In addition, a numerical simulation was conducted to model the slip of the fault F16. The results indicate that: (1) three fault slips occurred during the biaxial shear experiment, and the shear stress, normal and shear strains in the first slip showed the maximum variation among three slips; (2) Shear strains near the two ends of the fault had a more significate variation than that in the middle part, and the typical trend of shear strains was first dropping, then increasing rapidly, and then falling slowly to a specific value during the first slip; (3) The first slip had the largest sliding displacement of 29.89 mu m, and in the first slip three phases including slow slip, main shock and aftershock occurred based on AE monitoring results. (4) On the fault surface of non-slip-test sample, microstructures such as bulges, voids and veins were ubiquitous and notable, making the fault surface much rough, while similar microstructures were few and the fault surface of the slip-test sample was flattened after fault slips; (5) The slipping direction in the shallow part and deep part of the fault F16 were opposite during mining.

Characteristic analysis of cement grouted asphalt mixture cracking based on acoustic emission

Cracking is one of the main diseases of cement grouted asphalt mixture (CGAM). This paper aims to disclose the whole process failure characteristics of CGAM under different loads. Three types of tests under acoustic emission monitoring were designed to observe the performance of CGAM under indirect tension, bending tension and compression. Stone matrix asphalt (SMA) was used as the control group. The results show that the failure process of CGAM can be divided into three stages. Large damage will be produced in one or more short periods. The cracking of cement mesh is one of the main factors to form cracks in CGAM, and its brittleness leads to the proportion of macro cracks of CGAM in each stage being greater than that of SMA. The proportion of shear failure of CGAM is higher than that of SMA, so more attention should be paid to its shear resistance in material design.

Investigation of compression after impact failure in carbon fiber reinforced polymers using acoustic emission

Although several studies have been performed, the compression after impact (CAI) failure of CFRP is still not entirely understood. It is still unclear what sequence of events determines the onset of failure in CAI tests and how the different damage modes are involved in this process. To experimentally investigate this matter, the present work relies on acoustic emission (AE) monitoring and advanced acoustic signal analysis. A series of preliminary tests was conducted to correlate damage modes with recorded acoustic waveforms. Four types of waveforms were separated and associated to different damage modes. Following the preliminary tests, AE was monitored in actual CAI tests. A damage accumulation study was conducted combining three indicators, namely wavelet packet components, sentry function and energy b-value. The results evidence different phases in the damage accumulation process that were not shown in previous literature. In all specimens, the onset of the unstable damage accumulation appeared to be triggered by an intermediate frequency acoustic event associated to a combination of matrix cracking and fiber-matrix debonding, occurring at 80% of failure displacement.

Study on Staged Damage Behaviors of Rock-like Materials with Different Brittleness Degrees Based on Multiple Parameters

Understanding the brittle fracture behavior of rock is crucial for engineering and Earth science. In this paper, based on acoustic emission (AE) and laser Doppler vibration (LDV) monitoring technology, the staged damage behaviors of rock-like materials with different brittleness degrees under uniaxial compression are studied via multiple parameters. The results show that the brittleness degree determines the fracture mode. As the specimen's brittleness degree increases, the tensile failure increases and shear failure decreases. AE activity is enhanced at the crack damage point. With an increasing specimen brittleness degree, different instability precursor information is shown during the unstable crack growth stage: the AE b value changes from the fluctuating to continuously decreasing state, and the natural frequency changes from the stable fluctuation to upward fluctuation state. The AE b value near the stress drop is the smallest, and it decreases with an increasing brittleness degree. The natural frequency reduction indicates the rock-like fracture. The natural frequency is a symbolic index that reflects staged damage characteristics and predicts the amount of energy released by brittle failure. These findings provide guidelines for rock stability monitoring and provide support for better responses to stability evaluations of rock slopes, rock collapses, and tunnel surrounding rock in engineering.

Experimental Study on Uniaxial Compression Mechanics and Failure Characteristics of Non-Through Fractured Rock

The stability of damaged rock mass is a critical problem in the control of surrounding rock in underground engineering. As the main macroscopic defect of rock surrounding engineering, it is of great significance to study its propagation mechanism and the experimental characteristics of rock mechanics. Surface-fractured rock mass is a typical representative of three-dimensional fracture. To reveal the failure mechanism of surface-fractured rock mass, a three-dimensional mechanical failure model of a surface-fractured rock specimen was established, including the initiation, crack propagation, and cooperative deformation of the rock micro-element. Taking the depth of the surface horizontal fissure as a variable, standard rock specimens with surface horizontal fissures of different depths were prepared, and an experimental study of surface-fractured rock specimens was carried out. The RMT rock mechanics test system was used to perform uniaxial compression tests on standard specimens containing fractured rock specimens of different depths. The complete stress–strain curves of samples with different fracture depths were obtained, and the influence of different fracture depths on rock strength and deformation characteristics was analyzed. The crack initiation, propagation, and failure modes of the specimens under uniaxial compression were analyzed based on high-speed camera technology. Through the combination of 3D image processing and acoustic emission monitoring, differences between failure before and after the peak in both asymmetrically damaged rock specimens and symmetrically damaged rock specimens were found. The mechanism of weak strength and weak stability of asymmetrically damaged rock specimens after the peak was explained theoretically. The research results showed that the existence of the horizontal joint plane directly led to a significant reduction in the strength of the jointed rock sample, and the fracture depth played an important role in controlling the failure mode of the jointed rock specimens. The uniaxial compression of rock specimens with horizontal non-penetrating surface fissures produced three-dimensional failure modes, and the depth of surface fissures changed the failure mode of the specimens under uniaxial compression. As the crack depth increased, the failure mode of the specimen changed from tensile failure to shear failure. The surface crack sample showed regional asymmetric failure and poor structural stability.

Experimental study on hydraulic fracture propagation in heterogeneous glutenite rock

To understand the fracture behavior and discuss the possibility of the reservoir-stimulated volume concept on glutenite rock, true triaxial hydraulic fracturing experiments were performed on glutenite rocks with acoustic emission monitoring. Experimental results indicate that a curved hydraulic fracture (HF) can be created. In addition, in situ stress plays the greatest role in HF propagation direction regardless of gravel characteristics; however, the gravel with high mechanical strength could affect hydraulic fracture path locally. Intense fluctuate extension pressure and discrete surged acoustic emission (AE) events not only occur during the breakdown stage but also during the shut-in stage, indicating embedded gravels tend to influence HF process. The breakdown pressure is the highest for sample with low horizontal stress difference, while breakdown pressure for large-size sample with small gravel numbers is the lowest. The highest AE amplitude can be observed for sample where fracture positions on gravels are at the initial stage, while continuous high AE amplitude is observed for samples with high pump rates during the entire process, indicating intense fracture and gravel interactions. Moreover, four possible interaction behaviors between HF and gravels, namely, fracture penetration, deflection, diversion and arrest, can be identified near wellbore and far-field failure zones. In general, fracture penetration behavior is exclusively observed within the near wellbore failure zone. Additionally, the fracture width for a penetration fracture is the largest due to high fracturing energy, while fracture diversion and arrest exhibit the smallest fracture width. Given the existence of gravels, branch fractures are difficult to merge with residual fracturing energy. An extremely coarse HF surface and tortuous HF path can be found for all samples; thus, the selection of a suitable pump rate and fracturing fluid is necessary to migrate near wellbore tortuosity.

Evaluation of the Behaviour of Steel Bar in the Concrete under Cyclic Loading Using Magnetic Flux Leakage and Acoustic Emission Techniques

The behaviour of the steel bar in concrete under cyclic loading has been evaluated using magnetic flux leakage associated with acoustic emission monitoring technique. Visual observation was used to observe the deformation of the beam under cyclic loading. The sensors of metal magnetic memory were scanned in the middle of the beam at a distance of 320 mm at the bottom part. Twenty-two cyclic ranges were performed for cyclic loading of 100 or 200 cycles for each range, with a frequency of 1 Hz and a sinusoidal wave mode. The magnetic flux leakage signal, acoustic emission characteristics and crack width were measured and analysed to evaluate the behaviour of the steel bar in the concrete beam. The magnetic flux leakage signal and acoustic emission energy results were well matched with the occurrence of cracks at the centre of the beam. It was found that the relationship between the magnetic leakage flux signal and crack opening showed a strong correlation with R2 of 0.969. A high acoustic emission energy of 1300 nVs is observed at the centre of the beam. Based on the results, the behaviour of the steel in the concrete beam can be determined by the integrity assessment of a structure.

Experimental study on cracking process and fracture properties of granite under mode I loading by acoustic emission and digital image correlation

AbstractTo explore mode‐I fracture process of hard brittle rocks, semi‐circular bending (SCB) experiments were performed with the concurrent monitoring of acoustic emission (AE) and digital image correlation (DIC). Experimental results revealed that all specimens exhibited ductile fracture characteristic and the fracture planes deviated from the ligament plane to different degrees due to interference from mineral crystals or pre‐existing weak surfaces within the intergranular boundaries. The whole cracking process can be divided into four stages: Microcrack initiation preparation, microcrack initiation and stable propagation, macrocrack formation and unstable propagation, and macrocrack coalescence. The onset of the microcrack initiation occurred at about pre‐80% load. The fracture process zone (FPZ) maintained a constant length as the crack propagated and the length of the traction free zone (TFZ) increased. The identified crack lengths based on the AE locations and energy statistical analysis consisted well with the crack lengths obtained from the DIC.

Acoustic Emission Monitoring as a Non-invasive Tool to Assist the Conservator in the Reactivation and Maintenance of Historical Vehicle Engines

ABSTRACT Historical cars are an important part of the cultural heritage of the last 150 years. Their preservation in technical museums raises the question of how to preserve their primary functionality, namely their mobility. This implies being able to reactivate and to maintain their thermal engines, which are the source of their motion. However, the diversity and complexity of these engines generally require the presence of highly qualified personnel as well as detailed condition reports to assist the conservators. This study proposes to use acoustic emission techniques to facilitate these conservation procedures by objectifying the evaluation of the state of the engines and by providing systematic quantitative indicators for their health monitoring. To illustrate the implementation and the potentialities of this approach, different tests have been carried out at the National Automobile Museum of Mulhouse, on a Renault Type AG1. A dedicated experimental setup and the associated measurement protocol are presented in this paper. The derived results show the ability of this method to detect specific types of engine malfunctions, both during bench test and in situ measurement conditions. A critical discussion is finally proposed to highlight the feasibility and the possibilities of such laboratory techniques in the context of conservation assistance.

Experimental study on the evolutionary characteristics of acoustic signals produced by granite damage under uniaxial compression

Acoustic signals emitted during rock fracture constitute an important tool for rock damage evaluation. To investigate the evolutionary characteristics of acoustic emission (AE), microseismic (MS), and sound signals produced by hard rock fracture, uniaxial compression tests on granite specimens observed by AE, MS and sound monitoring were carried out. The evolution characteristics of the acoustic signal index, including its waveform, fractal dimension, b value, main frequency, energy proportion of signal frequency bands, and signal activeness, were analysed. The results indicate that there are significant differences in some characteristics of the AE, MS, and sound on the eve of granite failures, such as the waveform amplitude density, the average decline rate of the b value, the distribution of the main frequency, and the evolution of the energy proportion of the advantage frequency band. The three types of acoustic signals can characterize different scales of rock fracture under uniaxial compression. AE is sensitive to small-scale rock fractures, and MS and sound are sensitive to large-scale rock fractures. In addition, a unified damage evolution equation established by acoustic signals is proposed to quantitatively describe the damage process of granite specimens during uniaxial compression tests.

Passive acoustic mapping within the cranial vault during microbubble-mediated ultrasound brain therapy

Over the past 15 years, the use of passive sensor arrays combined with established beamforming algorithms to image acoustic activity during ultrasound therapies, so-called passive acoustic mapping (PAM), has been increasingly investigated for cavitation-based treatment monitoring and control purposes. Our group is interested in applications of microbubble-mediated ultrasound therapy in the brain, during which the skull bone presents unique challenges for both treatment delivery and acoustic emissions monitoring. We have demonstrated that skull-specific transcranial aberration correction methods can be applied during receive beamforming to augment PAM image quality through the skull bone, borrowing techniques developed originally for transmit beam focusing. Using custom clinical-prototype transmit/receive phased arrays, we have performed 3D microbubble imaging in vivo through ex vivo human skullcaps, and have exploited the resulting spatiotemporal cavitation information for real-time exposure level calibration and offline bioeffect distribution prediction. Ultrafast processing of acoustic emissions data can uncover cavitation dynamics hidden by conventional whole-burst temporal averaging, as well as inform temporal under-sampling strategies when millisecond-long tone bursts are applied. This talk will provide a historical overview of PAM for ultrasound therapy monitoring throughout the body, followed by a summary of recent progress made in mapping cavitation activity within the cranial vault during brain applications.

Spatio-temporal evolution and precursory indicators of rock failure processes using acoustic emission tomography

The characterization of stress and crack development plays important part in monitoring disasters. To capture the instability enlightenment from the spatio-temporal evolution of rock damage, this paper constructs the velocity field of key nodes in the rock failure process with the active and passive collaborative acoustic emission (AE) tomography method. It realizes the exploration of the micro-crack propagation law and its potential connection with the stress environment, combining the velocity field, the AE density field, and the energy field. Furthermore, from the spatial integrity and directional evolution of the velocity field, the mutation trend coefficient (MTC) and deformation coefficient (DC) of the velocity field are proposed as precursor indicators of rock instability, respectively. Results show that the anisotropy of the velocity field increases with the aggravation of rock damage, and the stress environment controls the spatial heterogeneity of the velocity field. The most important feature of spatial heterogeneity is that there are the continuous decrease and extension of low-velocity regions and the transformation from the high velocity to the low velocity. Real-time acoustic emission monitoring of the velocity field with MTC and DC can early identify rock instability precursors and principal stress direction, which provides vital pre-alarm information for geotechnical engineering.

Improving the Performance of Convolutional GAN Using History-State Ensemble for Unsupervised Early Fault Detection with Acoustic Emission Signals

Early fault detection (EFD) in run-to-failure processes plays a crucial role in the condition monitoring of modern industrial rotating facilities, which entail increasing demands for safety, energy and ecological savings and efficiency. To enable effective protection measures, the evolving faults have to be recognized and identified as early as possible. The major challenge is to distil discriminative features on the basis of only the ‘health’ signal, which is uniquely available from various possible sensors before damage sets in and before the signatures of incipient damage become obvious and well-understood in the signal. Acoustic emission (AE) signals have been frequently reported to be able to deliver early diagnostic information due to their inherently high sensitivity to the incipient fault activities, highlighting the great potential of the AE technique for EFD, which may outperform the traditional vibration-based analysis in many situations. To date, the ‘feature-based’ multivariate analysis dominates the interpretation of AE waveforms. In this way, the decision-making relies heavily on experts’ knowledge and experience, which is often a weak link in the entire EFD chain. With the advent of artificial intelligence, practitioners seek an intelligent method capable of tackling this challenge. In the present paper, we introduce a versatile approach towards intelligent data analysis adapted to AE signals streaming from the sensors used for the continuous monitoring of rotating machinery. A new architecture with a convolutional generative adversarial network (GAN) is designed to extract the deep information embedded in the AE waveforms. In order to improve the robustness of the proposed EFD framework, a novel ensemble technique referred to as ‘history-state ensemble’ (HSE) is introduced and paired with GAN. The primary merits of HSE are twofold: (1) it does not require extra computing time to obtain the base models, and (2) it does not require a special design of the network architecture and can be applied to different networks. To evaluate the proposed method, a durability rolling contact fatigue test was performed with the use of AE monitoring. The experimental results have demonstrated that the proposed ensemble method largely improves the robustness of GAN.

A transfer learning approach for acoustic emission zonal localization on steel plate-like structure using numerical simulation and unsupervised domain adaptation

The detection and localization of damage in metallic structures using acoustic emission (AE) monitoring and artificial intelligence technology such as deep learning has been widely studied. However, a current challenge of this approach is the difficulty of obtaining sufficient labeled historical AE signals for the training process of deep learning models. This problem can be approached through the implementation of transfer learning. The innovation of this paper lies in the development of a transfer learning approach for AE source localization on a stainless-steel structure when no historical labeled AE signals are available for training. A finite element model is developed to generate numerical AE signals for the training. Unsupervised domain adaptation (UDA) technology is utilized to reduce the distribution difference between the numerical and the realistic AE signals and to derive the localization results of the unlabeled realistic AE signals. The results suggest that the proposed approach is capable of localizing AE signals with high accuracy in the absence of labeled training data.

Influence of industrial graphene oxide on tensile behavior of cemented waste rock backfill

Cemented waste rock backfill (CWRB) is an important supporting technology for underground engineering safety and waste recycling. However, the brittle nature of cementitious materials, particularly weak tensile behavior, always compromises the performance of the CWRB. In this study, the industrial graphene oxide (IGO) was adopted to reinforce the tensile behavior of the CWRB specimens and be mixed with fly ash to fabricate environmentally friendly, cost-effective, high-performance backfilling materials. The results showed that the tensile strength of the CWRB specimens was significantly improved up to approximately 230%, by only mixing 0.007 wt% IGO. The low water-to-cement (W/C) ratio benefited from the enhancing effects of the IGO on CWRB’s tensile performance. Molecular dynamics simulations further revealed the underlying nanoscale reinforcing mechanisms of IGO, indicating that the tensile strength enhancement is mainly due to GO nanosheets effectively improving the ductility of the nanocomposites and delaying the failure of cementitious materials. The microstructure characterization proved that IGO could generate nucleation effects and pore infilling effects to optimize the microstructure in the interfacial transition zone (ITZ) of CWRB. Acoustic emission monitoring and digital photography characterization technologies implied that incorporating IGO could effectively reduce the micro-damage degree of the CWRB specimens during the failure process. This phenomenon ensures the integrity of the specimen during the destabilization failure process and reinforces resistance to the compressive load. This research not only broadens our understanding of GO in enhancing cementitious composites but also inspires the potential application of the IGO for strengthening the performance of cemented rockfill and the sustainability of waste rock recycling.

On the effect of coatings on the tensile and fatigue properties of 7075-T6 aluminum alloy monitored with acoustic Emission (AE): Towards lifetime estimation

Acoustic Emission (AE) is used to monitor the fatigue behaviour of specimens made of aluminium alloy 7075-T6 and covered with different coating combinations: anodic oxidation (alumina) - primer layer (organic coating) - topcoat layer (organic coating)). AE monitoring allows to understand and differentiate the processes and damage mechanisms in action during fatigue for all types of specimens. The type of coating applied has a significant influence on the damage process and the fatigue lifetime of the material. AE-based indicators are defined to assess the overall damage state of the specimens during fatigue testing. Some indicators are based on the distinction of the acoustic activity acquired during the loading and unloading phases of the cycles. As an example, the joint analysis of these indicators on anodized samples allows to highlight characteristic times ranging from 15% to 70% of the specimen’s lifetime. The early time at 15% is related to the saturation of cracking of the oxide layer during the first cycles of fatigue tests. By 70% of failure life, the AE activity correlates with the propagation of the main crack in the substrate, assisted by brittle fracture of the surrounding oxide layer. These specific times provide information on the Remaining Useful Lifetime (RUL) of the material and could be used to anticipate future failure.