Precursor Of Failure Research Articles

Experimental Investigation on Influence Factors of Acoustic Emission Activity in Coal Failure Process

Stress-dominated coal and gas outburst disaster has become one of the main safety problems in deep coal mines. Acoustic emission (AE) or microseismic technology has been viewed as a promising method that can effectively reflect the stress and stability status of rock mass. The AE activity precursor of coal failure is the theoretical basis of this technology. In this study, AE experiments in failure process of coal specimens with different properties and under different stress conditions were performed in laboratory to explore influence factors and their effect of AE activity, and AE activity pattern classification was proposed based on the failure type of coal. The results indicate that the AE activity of different coals under loading are associated with the failure phase, and the evolution pattern of AE activity depends on the failure type of stressed coal. Both the mechanical property and the external stress condition have an important influential effect on the failure type and AE activity pattern in coal failure process. The internal mechanical property decides the inherent tendency of stressed coals to perform brittle or ductile behavior, and the responded AE activity pattern. The contrast of fissure distribution of specimens suggested that fissure structure in coal significantly affects the fracturing mode of coal in uniaxial compression and the AE activity pattern. The external stress condition has a transition effect on AE event energy distribution and AE activity pattern. Under the effect of external stress condition, the energy distribution of AE events was transforming between relative disperse and relative concentration, the failure type and AE activity evolution pattern of coal could appear the brittle-ductile transition. Based on the view of failure type, the pattern of AE activity of coal failure can be classified into three types, i.e., ductile, brittle, and semi-brittle pattern. It is suggested that the high-level AE activity can be viewed as the precursor of brittle instability of coal, and relative quiet phenomenon of AE activity as the precursor of ductile or semi-brittle instability. The research achievement can provide a theoretical base for the prewarning criteria establishment of coal and rock dynamic disasters at depth and improve the insight of AE activity in the coal failure process.

Acoustic emission and kinetic fracture theory for time-dependent breakage of granite

Earthquakes, mine failures, and initiation of hydraulic fractures have all been associated with time-delayed breakage of rocks subjected to loads insufficient to incur instantaneous failure. To better model and identify failure precursors for rocks under these so-called static fatigue conditions, Acoustic Emission (AE) was monitored in beams of Coldspring Charcoal Granite subjected to constant three point loading. As a result of varying the magnitude of the loading, the times to failure range from O(101)toO(105) seconds. The experiments show a number of consistencies in the AE data. In all cases the event rate exponentially declines for a period that is about 0.4–0.6 of the total time to failure. This period is followed by a period in which the event rate exponentially increases. The total number of events generated during these two periods is also consistent among the experiments. Motivated by these observations, we propose a modified kinetic fracture theory that captures both the period of event rate decline and the period of event rate increase. It does this by firstly accounting for early time depletion of available bonds for breakage, similar to previous models. The model also accounts for generation of critically stressed bonds in the vicinity of previous bond breakages due to stress redistribution, thereby also predicting the event rate increase and further providing consistency with the observed tendency of the events to become increasingly concentrated around the eventual plane of failure as time progresses.

Prognostic Health Monitoring Method for Fatigue Failure of Solder Joints on Printed Circuit Boards Based on a Canary Circuit

Devices mounted on printed circuit boards (PCBs) are subject to temperature variations resulting from power switching and ambient temperature changes, and may be subject to random dynamic load histories from sources such as vibration. Since solder material is mechanically the most ductile part, fatigue failure may occur in solder joints. Health monitoring for fatigue life under field conditions is a key issue for improving availability and serviceability for maintenance. We have developed a failure precursor detection technology and a fatigue life estimation method for ball grid array (BGA) solder joints, based on a canary circuit. This method estimates fatigue failure life of an actual circuit by detecting failure connections in a canary circuit (a dummy circuit of daisy-chained solder joints). The canary circuit is designed to fail before the actual circuit under the same failure mode by using accelerated reliability testing and inelastic stress simulation. A feasibility study of the failure probability estimation method is conducted by applying the method to a PCB on which a BGA component is mounted. It is confirmed that the fatigue life under a thermal cyclic load can be estimated from a canary circuit, that estimation of fatigue life under a random dynamic load is feasible, and that the estimation results are consistent with results from actual random vibration tests. The proposed method is found to be useful for prognostic health monitoring of solder joint fatigue failure.

Microscopic dynamics and failure precursors of a gel under mechanical load

Material failure is ubiquitous, with implications from geology to everyday life and material science. It often involves sudden, unpredictable events, with little or no macroscopically detectable precursors. A deeper understanding of the microscopic mechanisms eventually leading to failure is clearly required, but experiments remain scarce. Here, we show that the microscopic dynamics of a colloidal gel, a model network-forming system, exhibit dramatic changes that precede its macroscopic failure by thousands of seconds. Using an original setup coupling light scattering and rheology, we simultaneously measure the macroscopic deformation and the microscopic dynamics of the gel, while applying a constant shear stress. We show that the network failure is preceded by qualitative and quantitative changes of the dynamics, from reversible particle displacements to a burst of irreversible plastic rearrangements.

Experimental modelling of cardiac pressure overload hypertrophy: Modified technique for precise, reproducible, safe and easy aortic arch banding-debanding in mice

Pressure overload left ventricular hypertrophy is a known precursor of heart failure with ominous prognosis. The development of experimental models that reproduce this phenomenon is instrumental for the advancement in our understanding of its pathophysiology. The gold standard of these models is the controlled constriction of the mid aortic arch in mice according to Rockman’s technique (RT). We developed a modified technique that allows individualized and fully controlled constriction of the aorta, improves efficiency and generates a reproducible stenosis that is technically easy to perform and release. An algorithm calculates, based on the echocardiographic arch diameter, the intended perimeter at the constriction, and a suture is prepared with two knots separated accordingly. The aorta is encircled twice with the suture and the loop is closed with a microclip under both knots. We performed controlled aortic constriction with Rockman’s and the double loop-clip (DLC) techniques in mice. DLC proved superiority in efficiency (mortality and invalid experiments) and more homogeneity of the results (transcoarctational gradients, LV mass, cardiomyocyte hypertrophy, gene expression) than RT. DLC technique optimizes animal use and generates a consistent and customized aortic constriction with homogeneous LV pressure overload morphofunctional, structural, and molecular features.

Failure analyses of unconfined CCWBM body in uniaxial compression based on central pressure variation.

Cemented coal waste backfill material (CCWBM) is made of coal gangue, fly ash and cementitious materials. It has been widely used in the field of backfill mining to control surface subsidence and protect the environment. A large number of unconfined backfill bodies without lateral support are formed in partial backfill mining. To study the failure characteristics of unconfined CCWBM body in partial backfill, the stress-strain curves of the CCWBM were obtained by uniaxial compression tests at different ages (1-28 d). The central pressure was measured by the embedded pressure sensors. The failure characteristics of the specimen were monitored by acoustic emission (AE) positioning technique. Three observations can be made. 1. The central pressure variation curves lag behind the mean stress change curves. The central pressure curve can be divided into three stages: slow increase stage, rapid growth stage and decline stage. It has two pressure manifestations: early appearance and peak appearance. They can be as the failure precursor and instability critical, respectively. 2. The specimen forms a central elastic bearing area in the process of compression. The plastic area develops to the inner side with the increase of pressure, and an upper and lower compound cone-shaped residual area is finally formed. 3. The embedded pressure sensor can be used to monitor the instability of the unconfined backfill body. The research results can provide guidance for the in-situ stability monitoring and reinforcement of unconfined CCWBM body in partial backfill.

New prognostic neural method by discrete wavelet transforms for electromechanical flight controls affected by progressive faults

Progressive failures affecting onboard electromechanical actuators (EMA), especially if related to primary flight commands, could be a critical issue for the aircraft reliability and, in the worst cases, could compromise its safety. In the last years strong interest is expected by the development of prognostic algorithms able to provide an early identification of the precursors of EMA progressive failures. In this work authors proposes a new prognostic method based on two artificial neural networks (ANN), a basic and an enhanced feedforward neural network, performing the fault detection and identification of two critical progressive faults often affecting the EMA brushless motor (i.e. turn-to-turn short circuit of a stator coil and rotor static eccentricity); in order to identify a suitable data set able to guarantee an affordable ANN classification, the said failures precursors are properly pre-processed by a Discrete Wavelet Transform, extracting several features used as input of the proposed prognostic algorithm.

Dynamic failure of viscoplastic structures under ASB and micro-voiding

Adiabatic shear bands are known to cause premature structural failure in high strength metals and alloys. The observation of adiabatic shear bands inside partially fractured specimens evidences the presence of micro-voids as the precursor of the ultimate failure. An enriched model containing the effects of adiabatic shear banding and micro-voiding mechanisms was developed and it is here taken through a calibration procedure. The aim of the present work is to evaluate the performances of the enriched model considering an initial-boundary value problem. To that purpose, the model has been implemented as user material in the engineering finite element computation code LS-DYNA. Numerical simulation of the dynamic shearing of hat shaped structures is conducted and the interest of accounting for the pre-failure stage consisting of micro-voiding in the ASB wake is emphasized.

Energy dissipation rate: An indicator of coal deformation and failure under static and dynamic compressive loads

Dynamic disasters in Chinese coal mines pose a significant threat to coal productivity. Thus, a thorough understanding of the deformation and failure processes of coal is necessary. In this study, the energy dissipation rate is proposed as a novel indicator of coal deformation and failure under static and dynamic compressive loads. The relationship between stress-strain, uniaxial compressive strength, displacement rate, loading rate, fractal dimension, and energy dissipation rate was investigated through experiments conducted using the MTS C60 tests (static loads) and split Hopkinson pressure bar system (dynamic loads). The results show that the energy dissipation rate peaks are associated with stress drop during coal deformation, and also positively related to the uniaxial compressive strength. A higher displacement rate of quasi-static loads leads to an initial increase and then a decrease in energy dissipation rate, whereas a higher loading rate of dynamic loads results in larger energy dissipation rate. Theoretical analysis indicates that a sudden increase in energy dissipation rate suggests partial fracture occurring within coal under both quasi-static and dynamic loads. Hence, the energy dissipation rate is an essential indicator of partial fracture and final failure within coal, as well as a prospective precursor for catastrophic failure in coal mine.

The Maoxian landslide as seen from space: detecting precursors of failure with Sentinel-1 data

Post-event Interferometric Synthetic Aperture Radar (InSAR) analysis on a stack of 45 C-band SAR images acquired by the ESA Sentinel-1 satellites from 9 October 2014 to 19 June 2017 allowed the identification of a clear precursory deformation signal for the Maoxian landslide (Mao County, Sichuan Province, China). The landslide occurred in the early morning of 24 June 2017 and killed more than 100 people in the village of Xinmo. Sentinel-1 images have been processed through an advanced multi-interferogram analysis capable of maximising the density of measurement points, generating ground deformation maps and displacement time series for an area of 460 km2 straddling the Minjiang River and the Songping Gully. InSAR data clearly show the precursors of the slope failure in the source area of the Maoxian landslide, with a maximum displacement rate detected of 27 mm/year along the line of sight of the satellite. Deformation time series of measurement points identified within the main scarp of the landslide exhibit an acceleration starting from April 2017. A detailed time series analysis leads to the classification of different deformation behaviours. The Fukuzono method for forecasting the time of failure appear to be applicable to the displacement data exhibiting progressive acceleration. Results suggest that satellite radar data, systematically acquired over large areas with short revisiting time, could be used not only as a tool for mapping unstable areas, but also for landslide monitoring, at least for some typologies of sliding phenomena.

Mechanisms contributing to cardiac remodelling.

Cardiac remodelling is classified as physiological (in response to growth, exercise and pregnancy) or pathological (in response to inflammation, ischaemia, ischaemia/reperfusion (I/R) injury, biomechanical stress, excess neurohormonal activation and excess afterload). Physiological remodelling of the heart is characterized by a fine-tuned and orchestrated process of beneficial adaptations. Pathological cardiac remodelling is the process of structural and functional changes in the left ventricle (LV) in response to internal or external cardiovascular damage or influence by pathogenic risk factors, and is a precursor of clinical heart failure (HF). Pathological remodelling is associated with fibrosis, inflammation and cellular dysfunction (e.g. abnormal cardiomyocyte/non-cardiomyocyte interactions, oxidative stress, endoplasmic reticulum (ER) stress, autophagy alterations, impairment of metabolism and signalling pathways), leading to HF. This review describes the key molecular and cellular responses involved in pathological cardiac remodelling.

Fractal analysis of acoustic emission parameter series of coal with different properties under uniaxial loading

In order to study acoustic emission (AE) evolution characteristics of coal with different mechanical properties in failure process, uniaxial compression experiments of coals from 4 mines were carried out to analyse fractal feature of AE time series by G-P algorithm. The results indicate that AE parameter series of all 4 different coals have fractal feature, and the fractal dimension value of coal with different properties go through a process of “first rise, then fall”. The change of AE fractal dimension value can reflect the cracking evolution in coal failure process, which is closely related with the failure phase. The continuous decline of AE fractal dimension can be viewed as a precursor of impending failure of coal, which could provide theoretical basis for the AE pre-warning model establishment of coal dynamic disaster.

Myocarditis in auto-immune or auto-inflammatory diseases.

Myocarditis is a major cause of heart disease in young patients and a common precursor of heart failure due to dilated cardiomyopathy. Some auto-immune and/or auto-inflammatory diseases may be accompanied by myocarditis, such as sarcoidosis, Behçet's disease, eosinophilic granulomatosis with polyangiitis, myositis, and systemic lupus erythematosus. However, data concerning myocarditis in such auto-immune and/or auto-inflammatory diseases are sparse. New therapeutic strategies should better target the modulation of the immune system, depending on the phase of the disease and the type of underlying auto-immune and/or auto-inflammatory disease.

Adiabatic shear banding assisted dynamic failure: Some modeling issues

Adiabatic shear banding (ASB) is a precursor of failure of high strength metals and alloys when submitted to impact and other high strain rate loading. As a mechanism of plastic flow localization triggered by a thermo-mechanical instability in the context of dynamic plasticity, ASB causes a discontinuity of the strain/strain rate field. In the present paper, some models available in literature are assessed regarding their ability to reproduce ASB features and further consequences. Some tracks for further developments in the field are also given.

Simultaneous On-State Voltage and Bond-Wire Resistance Monitoring of Silicon Carbide MOSFETs

In fast switching power semiconductors, the use of a fourth terminal to provide the reference potential for the gate signal—known as a kelvin-source terminal—is becoming common. The introduction of this terminal presents opportunities for condition monitoring systems. This article demonstrates how the voltage between the kelvin-source and power-source can be used to specifically monitor bond-wire degradation. Meanwhile, the drain to kelvin-source voltage can be monitored to track defects in the semiconductor die or gate driver. Through an accelerated aging test on 20 A Silicon Carbide Metal-Oxide-Semiconductor-Field-Effect Transistors (MOSFETs), it is shown that there are opposing trends in the evolution of the on-state resistances of both the bond-wires and the MOSFET die. In summary, after 50,000 temperature cycles, the resistance of the bond-wires increased by up to 2 mΩ, while the on-state resistance of the MOSFET dies decreased by approximately 1 mΩ. The conventional failure precursor (monitoring a single forward voltage) cannot distinguish between semiconductor die or bond-wire degradation. Therefore, the ability to monitor both these parameters due to the presence of an auxiliary-source terminal can provide more detailed information regarding the aging process of a device.

3D Remote survey of a rock wall hosting a multi-sensor monitoring system in a test-site (Acuto, Italy)

A multi-sensor monitoring system was installed in an abandoned quarry at Acuto (Frosinone - Central Italy) to test multi-sensing and multi-parametric remote techniques for early warning incase of rock failures threating strategic infrastructures. The multisensory monitoring system consist in: i) a meteo-climatic system, including a conventional weather stations and an innovative TSA-BOXone; ii) a geotechnical system, including thermometer for the rock mass temperature, strain-gauges for micro-fractures of rock mass, extensometers on open joints for detecting stress-strain conditions; iii) a nanoseismic monitoring system was also temporary installed to detect low magnitude vibrations to be regarded as precursors of rock failures. To correctly design the multi-parametric monitoring system, the rock wall was scanned to identify the main joint sets.Three GPS monographs were preliminary obtained in order to spatially geocoding the rock wall. From November 2015 to May 2016 remote scanning surveys were carried out on the quarry face by two different approaches: i) topographic 3D survey by Leica Total Station; ii) optical survey by 3D photos technique analyzed by Structure from Motion technique. The topographic survey provided high definition geocoded point clouds. These outputs were compared with the ones obtained by the SFM technique on 3D photos to test their reliability. At this aim, a Gaussian bi-modal distribution of the surveyed distances was obtained from each measurement; the comparison among the so derived distributions demonstrates that the computed errors are negligible and the main differences result at the boundaries of the sampled 3D domain. This comparison encourages the use of the photography technology by SfM technique to obtain multi-temporal geocoded point clouds for change detection analyses to point out evidences of scar zones due to slope failures. Thisapproach guarantees a very quick and accurate practice with easy management hardware and low software costs.

Background thermal noise correction methodology for average infrared radiation temperature of coal under uniaxial loading

This paper proposes a new background thermal noise correction (BTNC) Methodology for better utilization of average infrared radiation temperature (AIRT) as a precursor for rock fracturing and failure under uniaxial loading. The key innovative concept in the proposed Methodology is the introduction of control samples in the thermal infrared experimental setup. A strong linear correlation was observed between the background thermal noise (BTN) of the test samples and that of control samples, which was used to develop the AIRT-BTNC model. By utilizing the AIRT-BTNC model, the signal-to-noise ratio (SNR) of AIRT can be improved by two orders of magnitude from a mean value of 0.40–70.69. The variation in the AIRT after BTNC on the surface of the uniaxial loading coal samples can be categorized into two types instead of the three reported by previous researchers. The above achievements will be useful in monitoring and forecasting the natural and engineering hazards related to rock/coal structural failures during mining activities.

Investigating Rock Mass Failure Precursors Using a Multi-sensor Monitoring System: Preliminary Results From a Test-Site (Acuto, Italy)

In the last few years, several approaches and methods have been proposed to improve early warning systems for managing risks due to rapid slope failures where important infrastructures are the main exposed elements. To this aim, a multi-sensor monitoring system has been installed in an abandoned quarry at Acuto (central Italy) to realise a natural-scale test site for detecting rock-falls from a cliff slope. The installed multi-sensor monitoring system consists of: i) two weather stations; ii) optical cam (Smart Camera) connected to an Artificial Intelligence (AI) system; iii) stress- strain geotechnical system; iv) seismic monitoring device and nano-seismic array for detecting microseismic events on the cliff slope. The main objective of the experiment at this test site is to investigate precursors of rock mass failures by coupling remote and local sensors. The integrated monitoring system is devoted to record strain rates of rock mass joints, capturing their variations as an effect of forcing actions, which are the temperature, the rainfalls and the wind velocity and direction. The preliminary tests demonstrate that the data analysis methods allowed the identification of external destabilizing actions responsible for strain effects on rock joints. More in particular, it was observed that the temperature variations play a significant role for detectable strains of rock mass joints. The preliminary results obtained so far encourage further experiments.

Complex Method of Detection Reliable Precursors of Stressed Rock Samples Failure

Studies of brittle rock samples failure were carried out in Laboratory of Geodynamics of Far-Eastern University, Vladivostok, Russia. It was assisted by servocontrol loading machine MTS-816, acoustic emission (AE) complex, and multi-channel complex. The regularities of formation and development of dissipative mesocracks structures in rock samples under uniaxial compression were determined as a result of complex deformation and acoustic experiments at final stage of loading. Anomalous deformations of high stressed rock samples were associated with acoustic characteristics. The system of reliable precursors of failure involving long-term and middle-term was established. This system of precursors reflects the stages of formation and development of dissipative mesodefects structures in high stressed rock samples.

Acoustic Emission Monitoring and Failure Precursors of Sandstone Samples under Various Loading and Unloading Paths

To explore the failure precursors of hard rock, a series of triaxial loading and unloading experiments were carried out on sandstone sample using the acoustic emission systems. The extreme-point symmetric mode decomposition method (ESMD method) was used to denoise and reconstruct the AE data. The AE quiet period in Scheme I becomes much more obvious with the confining pressure increasing, which can be regarded as the precursor information of the sample failure under conventional triaxial compression. Unlike Scheme I, there are no obvious precursory characteristics before failure in Schemes II and III, and the count rate reaches the maximum at the peak point. When the stress ratio ranges from 0.8 to 1.0, the fractal values of acoustic emission can be used to investigate the failure precursors of samples at a lower confining pressure. When the time ratio is greater than 0.8 under higher confining pressures, the fractal values of sandstone samples under unloading paths are rapidly reduced, which can be used to predict rock failure at higher confining pressures.