Pressure stimulated current in progressive failure process of combined coal-rock under uniaxial compression:Response and mechanism

Effective monitoring of the structural health of combined coal-rock under complex geological conditions by pressure stimulated currents(PSCs)has great potential for the understanding of dynamic disasters in underground engineering.To reveal the effect of this way,the uniaxial compression experiments with PSC monitoring were conducted on three types of coal-rock combination samples with different strength combinations.The mechanism explanation of PSCs are investigated by resistivity test,atomic force microscopy(AFM)and computed tomography(CT)methods,and a PSC flow model based on progressive failure process is proposed.The influence of strength combinations on PSCs in the progressive failure process are emphasized.The results show the PSC responses between rock part,coal part and the two components are different,which are affected by multi-scale fracture characteristics and electrical properties.As the rock strength decreases,the progressive failure process changes obviously with the influence range of interface constraint effect decreasing,resulting in the different responses of PSC strength and direction in different parts to fracture behaviors.The PSC flow model is initially validated by the relationship between the accumulated charges of different parts.The results are expected to provide a new reference and method for mining design and roadway quality assessment.

Numerical Simulation on Failure Process in Brittle and Heterogeneous Matrix Filled with Randomly Distributed Particles

Based on an essential assumption of meso-heterogeneity of material, the macro characteristic of composite reinfiorced with particles, the crack initiation, propagation and the failure process in composite were studied by using a numerical code. The composite is subjected to a uniaxial tension, aact stiff or soft particles are distributed at random manner but without overlapping or contacting. The effect of reinforcement particle properties on the fracture process aact mechanism of composite with brittle matrix, furthermore, the influence of the particle volumetric fraction is also investigated. Numerical results present the different failure mode and re-produce the crack initiation, propagation aurl coalescence in brittle aurl heterogeneons matrix. The mechanism of sach failure was also elucidated.

Two-Stage Inspection Model Based on a Three-Stage Failure Process

As the non-periodic inspections are common in practice,a two-stage inspection model based on a three-stage failure process is proposed. The two-stage inspection means that the system is inspected with the first inspection interval T_1 and the second inspection interval T_2. Because of the three color schemes commonly used in industry,three stages are divided by the system lifetime:normal, minor defective and severe defective stages. Upon the failure of the system,replacement is carried out. Maintenance is done once identifying the severe defective stage. However,when the minor defective stage is identified by the second inspection interval T_2,action of halving the subsequent inspection interval is adopted.Otherwise,no action is required. Our objective function is to optimize the inspection intervals so as to minimize the expected cost per unit time. Finally,a numerical example is presented to illustrate the effectiveness of the proposed model.

RFPA Realistic Failure Process Analysis

RFPA is a numerical testing tool for realistic failure process analysis(RFPA)of rock,concrete,composites,and engineering structures.The RFPA solution offers perfect simulation tools for robust modelling of brittle material failure and engineering structural damage.The RFPA family of 2D and 3D core products offers the full depth of analysis tools—from a conceptual simulation to advanced

Numerical modeling of the failure process of the heterogeneous karst rock mass using the DDA-SPH method

The sanding process caused by karstification in dolomite creates a special sandy dolomite stratum,where the frequent catastrophic instability of the surrounding rock occurred during tunnel construction.In this study,the micro-origin and macro-performance of the sandy dolomite stratum are first discussed.Then,a numerical model based on the coupling method between the discontinuous deformation analysis and smoothed particle hydrodynamics is proposed to depict the heterogeneous dolomite formation with different sanding degrees.Following,the mechanical behaviors of the heterogeneous dolomite samples under uniaxial compression are studied after calibrating the numerical parameters with the two single materials sampled from the tunnel site respectively.Further,the instability disasters of the dolomite surrounding rock with different sanding degrees are reproduced,and the failure behaviors of tunnels are explained with respect to the stress distribution and plastic zone.The obtained results show that the rotation and dislocation of the remained dolomite block contribute to the unsmooth stress–strain curve and deterioration in uniaxial compressive strength.However,the block serves as the skeleton in the transmission of field stress in underground space,which improves the stability of the formation.

Numerical investigation of hydro-morphodynamic characteristics of a cascading failure of landslide dams

A cascading failure of landslide dams caused by strong earthquakes or torrential rains in mountainous river valleys can pose great threats to people’s lives,properties,and infrastructures.In this study,based on the three-dimensional Reynoldsaveraged Navier-Stokes equations(RANS),the renormalization group(RNG)k-εturbulence model,suspended and bed load transport equations,and the instability discriminant formula of dam breach side slope,and the explicit finite volume method(FVM),a detailed numerical simulation model for calculating the hydro-morphodynamic characteristics of cascading dam breach process has been developed.The developed numerical model can simulate the breach hydrograph and the dam breach morphology evolution during the cascading failure process of landslide dams.A model test of the breaches of two cascading landslide dams has been used as the validation case.The comparison of the calculated and measured results indicates that the breach hydrograph and the breach morphology evolution process of the upstream and downstream dams are generally consistent with each other,and the relative errors of the key breaching parameters,i.e.,the peak breach flow and the time to peak of each dam,are less than±5%.Further,the comparison of the breach hydrographs of the upstream and downstream dams shows that there is an amplification effect of the breach flood on the cascading landslide dam failures.Three key parameters,i.e.,the distance between the upstream and the downstream dams,the river channel slope,and the downstream dam height,have been used to study the flood amplification effect.The parameter sensitivity analyses show that the peak breach flow at the downstream dam decreases with increasing distance between the upstream and the downstream dams,and the downstream dam height.Further,the peak breach flow at the downstream dam first increases and then decreases with steepening of the river channel slope.When the flood caused by the upstream dam failure flows to the downstream dam,it can produce a surge wave that overtops and erodes the dam crest,resulting in a lowering of the dam crest elevation.This has an impact on the failure occurrence time and the peak breach flow of the downstream dam.The influence of the surge wave on the downstream dam failure process is related to the volume of water that overtops the dam crest and the erosion characteristics of dam material.Moreover,the cascading failure case of the Xiaogangjian and Lower Xiaogangjian landslide dams has also been used as the representative case for validating the model.In comparisons of the calculated and measured breach hydrographs and final breach morphologies,the relative errors of the key dam breaching parameters are all within±10%,which verify the rationality of the model is applicable to real-world cases.Overall,the numerical model developed in this study can provide important technical support for the risk assessment and emergency treatment of failures of cascading landslide dams.

Impact Failure of Flattened Brazilian Disc with Cracks——Process and Mechanism

Split Hopkinson pressure bar(SHPB)has been used to study the dynamic failure pattern of flattened mortar Brazilian disc under impact load.Each disc contains several prefabricated cracks paralleled to each other.Dynamic FEM has also been adopted to simulate such failure behavior.The mechanism of crack initiation,propagation and cut-through have been scrutinized with both experimental and numerical approaches.Influence of the number of the prefabricated cracks on the specimen strength and acoustic emission(AE)performance can be observed and studied.The results show that the strength decreases and AE counts increases,when the number of the prefabricated cracks increases.

Reliability modeling of mutual DCFP considering failure physical dependency

Degradation and overstress failures occur in many electronic systems in which the operation load and environmental conditions are complex.The dependency of them called dependent competing failure process(DCFP),has been widely studied.Electronic system may experience mutual effects of degradation and shocks,they are considered to be interdependent.Both the degradation and the shock processes will decrease the limit of system and cause cumulative effect.Finally,the competition of hard and soft failure will cause the system failure.Based on the failure mechanism accumulation theory,this paper constructs the shock-degradation acceleration and the threshold descent model,and a system reliability model established by using these two models.The mutually DCFP effect of electronic system interaction has been decomposed into physical correlation of failure,including acceleration,accumulation and competition.As a case,a reliability of electronic system in aeronautical system has been analyzed with the proposed method.The method proposed is based on failure physical evaluation,and could provide important reference for quantitative evaluation and design improvement of the newly designed system in case of data deficiency.

Model for Failure Point Process of a Repairable System and Application

A engineering system is usually repairable, and failure process of a repairable by a failure point process. The power law model is a commonly used approach to model syst the em is often described failure point process. This paper introduces the concept and model for the failure process of repairable system. The method of parameter estimation is developed, and failure observations are fitted into a power-law model by using the least square method. Two applications of the pressent model are discussed according to the practical failure data of the central cooling system of a nuclear power plant. One application is determining the optimal overhaul time, and the other is evaluating the quality of maintenance. This paper provides references for the overhaul decision making and maintenance quality evaluation in reality.

Mitigating the negative catalytic effect of CuO by FAS-17 coated Al nanopowder:Isothermal ageing of Al/CuO nanothermite at 71°C and 60%relative humidity

The safety and reliability of weapon systems would be significantly affected by changes in the performance of energetic materials due to ambient temperature and humidity.Nanothermites have promising applications due to their excellent reactivity.Therefore it becomes extremely important to understand their aging and failure process in the environment before using them.Here,the aging and failure process of Al/CuO in 71°C/60%RH were investigated,and showed that CuO nanoparticles negatively catalyze Al nanopowders,resulting in rapid hydration.The anti-aging effect of FAS-17-coated Al nanopowder was also examined.The aging process of Al,Al/CuO,and Al@FAS-17/CuO in high humidity and heat environment were revealed by quasi-in situ SEM and TEM methods.Compared with the aging of pure Al,the Al nanopowder in the nanothermites strongly agglomerated with the CuO nanopowder and hydrated earlier.This may be caused by CuO catalyzed hydration of Al nanopowder.The energy release experiments showed that the performance of Al/CuO decreased rapidly and failed to ignite after 4 h of aging.In contrast,the Al@FAS-17/CuO thermite can achieve long-term stability of up to 60 h in the same environment by simple cladding of FAS-17.It is found that FAS-17 coated Al nanopowder can prevent both particle agglomeration and water erosion,which is an effective means to make nanothermites application in high humidity and heat environment.

Influence of Intersection Angle of Prefabricated Cracks on Impact Failure of Flattened Brazilian Disc

Both experimental and numerical approaches were used to study dynamic failure properties and patterns of flattened Brazilian discs,containing two prefabricated cracks intersected at a varying angle.Mechanism of crack initiation,propagation,and cut-through were scrutinized and influences of the intersection angle on specimen strength and acoustic emission performance were also studied.All primary cracks initialize near the middle or the tip points of the upper prefabricated crack,and they continue to develop along the load direction and finally cut through the specimen.The secondary cracks could be observed in directions almost horizontal or parallel to the directions of prefabricated cracks.Furthermore,it is found that stress intensity factor reaches its maximum for specimen with intersection angle of 0 degree.

Experimental and numerical studies on progressive debonding of grouted rock bolts

Understanding the mechanism of progressive debonding of bolts is of great significance for underground safety.In this paper,both laboratory experiment and numerical simulation of the pull-out tests were performed.The experimental pull-out test specimens were prepared using cement mortar material,and a relationship between the pull-out strength of the bolt and the uniaxial compressive strength(UCS)of cement mortar material specimen was established.The locations of crack developed in the pull-out process were identified using the acoustic emission(AE)technique.The pull-out test was reproduced using 2D Particle Flow Code(PFC^(2D))with calibrated parameters.The experimental results show that the axial displacement of the cement mortar material at the peak load during the test was approximately 5 mm for cement-based grout of all strength.In contrast,the peak load of the bolt increased with the UCS of the confining medium.Under peak load,cracks propagated to less than one half of the anchorage length,indicating a lag between crack propagation and axial bolt load transmission.The simulation results show that the dilatation between the bolt and the rock induced cracks and extended the force field along the anchorage direction;and,it was identified as the major contributing factor for the pull-out failure of rock bolt.

Joint optimization of inspection, maintenance, and spare ordering policy considering defective products loss

This paper proposes a joint inspection-based maintenance and spare ordering optimization policy that considers the problem of integrated inspection,preventive maintenance,spare ordering,and quality control for a four-state single-unit manufacturing system.When an inspection detects a minor defect,a second phase inspection is initiated and a regular order is placed.Product quality begins to deteriorate when the system undergoes a severe defect.To counter this,an advanced replacement of the minor defective system is carried out at the Jth second phase inspection.If a severe defect is recognized prior to the Jth inspection,or if system failure occurs,preventive or corrective replacement is executed.The timeliness of replacement depends on the availability of spare.We adopt two modes of ordering:a regular order and an emergency order.Meanwhile,a threshold level is introduced to determine whether an emergency order is preferred even when the regular order is already ordered but has not yet arrived.The optimal joint inspection-based maintenance and spare ordering policy is formulated by minimizing the expected cost per unit time.A simulation algorithm is proposed to obtain the optimal two-phase inspection interval,threshold level and advanced replacement interval.Results from several numerical examples demonstrate that,in terms of the expected cost per unit time,our proposed model is superior to some existing models.

Joint optimization of inspection-based and age-based preventive maintenance and spare ordering policies for single-unit systems

This paper presents a joint optimization policy of preventive maintenance(PM)and spare ordering for single-unit systems,which deteriorate subject to the delay-time concept with three deterioration stages.PM activities that combine a non-periodic inspection scheme with age-replacement are implemented.When the system is detected to be in the minor defective stage by an inspection for the first time,place an order and shorten the inspection interval.If the system has deteriorated to a severe defective stage,it is either repaired imperfectly or replaced by a new spare.However,an immediate replacement is required once the system fails,the maximal number of imperfect maintenance(IPM)is satisfied or its age reaches to a pre-specified threshold.In consideration of the spare’s availability as needed,there are three types of decisions,i.e.,an immediate or a delayed replacement by a regular ordered spare,an immediate replacement by an expedited ordered spare with a relative higher cost.Then,some mutually independent and exclusive renewal events at the end of a renewal cycle are discussed,and the optimization model of such a joint policy is further developed by minimizing the long-run expected cost rate to find the optimal inspection and age-replacement intervals,and the maximum number of IPM.A Monte-Carlo based integration method is also designed to solve the proposed model.Finally,a numerical example is given to illustrate the proposed joint optimization policy and the performance of the Monte-Carlo based integration method.

Comparison between the electrical resistance and the shear strength of brazed cemented carbides

Brazing is a suitable technology to join different materials such as cemented carbides and steel. Even though this technology has been investigated for many years, insufficient joints can occur easily, as the brazing process is very sensitive concerning the handling parameters. Defects such as voids and cracks are hard to detect by commonly used visual inspection methods. Other nondestructive methods such as radiography or ultrasonic testing are usually not economical for the examination of these joints. Studies proved that the electrical resistance has the potential to serve as an effective alternative for the evaluation of brazed joints. In this study, the authors have compared the electrical resistance and the shear strength. For this, cemented carbides were brazed to steel by means of induction heating at an ambient atmosphere. A silver-based filler metal （ BrazeTec 4900 / Ag 449 ） and a flux （ BrazeTec spezial h / FH12） were selected to enable the brazing process. The brazing time and the temperature were varied in order to produce different joint qualities. After brazing, the resistance was measured on each joint with the 4-point probe method to facilitate a high accuracy. The results underline the possibility to use electrical resistance measurements as an effective tool for a quality control of brazed joints.

Prediction and analysis of process failures by ANN classification during wire-EDM of Inconel 718

Wire breakages and spark absence are two typical machining failures that occur during wire electric discharge machining(wire-EDM),if appropriate parameter settings are not maintained.Even after several attempts to optimize the process,machining failures cannot be eliminated completely.A n offline classification model is presented herein to predict machining failures.The aim of the current study is to develop a multiclass classification model using an artificial neural network(ANN).The training dataset comprises 81 full factorial experiments with three levels of pulse-on time,pulse-off time,servo voltage,and wire feed rate as input parameters.The classes are labeled as normal machining,spark absence,and wire breakage.The model accuracy is tested by conducting 20 confirmation experiments,and the model is discovered to be 95%accurate in classifying the machining outcomes.The effects of process parameters on the process failures are discussed and analyzed.A microstructural analysis of the machined surface and worn wire surface is conducted.The developed model proved to be an easy and fast solution for verifying and eliminating process failures.

A compositional method to model dependent failure behavior based on PoF models

In this paper, a new method is developed to model dependent failure behavior among failure mechanisms. Unlike the existing methods, the developed method models the root cause of the dependency explicitly, so that a deterministic model, rather than a probabilistic one, can be established. Three steps comprise the developed method. First, physics-of-failure（PoF） models are utilized to model each failure mechanism. Then, interactions among failure mechanisms are modeled as a combination of three basic relations, competition, superposition and coupling. This is the reason why the method is referred to as ＂compositional method＂. Finally, the PoF models and the interaction model are combined to develop a deterministic model of the dependent failure behavior. As a demonstration, the method is applied on an actual spool and the developed failure behavior model is validated by a wear test. The result demonstrates that the compositional method is an effective way to model dependent failure behavior.

UNCERTAINTY ANALYSIS OF ROCK FAILURE BEHAVIOUR USING AN INTEGRATION OF THE PROBABILISTIC COLLOCATION METHOD AND ELASTO-PLASTIC CELLULAR AUTOMATON

The Karhunen-Loeve （KL） expansion and probabilistic collocation method （PCM） are combined and applied to an uncertainty analysis of rock failure behavior by integrating a self- developed numerical method （i.e., the elastic-plastic cellular automaton （EPCA））. The results from the method developed are compared using the Monte Carlo Simulation （MCS） method. It is concluded that the method developed requires fewer collocations than MCS method to obtain very high accuracy and greatly reduces the computational cost. Based on the method, the elasto- plastic and elasto-brittle-plastic analyses of rocks under mechanical loadings are conducted to study the uncertainty in heterogeneous rock failure behaviour.

Optimal Inspection and Replacement Strategy for Systems Subject to Two Types of Failures with Adjustable Inspection Intervals

The inspection activities are often carried out to detect possible indication of failures in plant systems.This paper considers a single unit system subject to two types of failures, where one failure mode is the traditional0-1 logic failure and the other failure mode is described by a two-stage failure process. Adjustable inspections are used to detect the defective stage of the latter. We assume that the inspection duration gets shorter and shorter with a constant ratio. At the same time, preventive replacement is used to avoid the possible failure due to the former failure mode. The renewal process of this system is analyzed and the expected long-run cost per unit time(ELRCUT) is derived. The optimal inspection period and the preventive replacement interval to minimize ELRCUT are studied. At last, a numerical example is presented to illustrate the proposed model.

Catastrophic failure mechanism of rock masses system and earthquake prediction based on percolation theory

The failure of rocks is a complicated process as the mechanical properties of the rock are governed by loading history and cumulative ruptures.The geometric aspects of fractures,such as the size and shape of the fractures,the spatial distribution of the fracture networks,and the relations among these aspects also depend on the loads acting on rock mass.In general,the fractures are randomly generated in space which is difficult to be described using mathematical methods.In this paper,the failure processes of rock have been analyzed using the percolation theory.The results indicate that the failure process of rock is a transition from a stable state to an unstable state.This phenomenon is essentially consistent with the phase transition in the percolation theory.Based on this consistency,a theoretical model of percolation for earthquake prediction is proposed.A large number of seismic data provided strong evidence in support of the reliability and applicability of this model.