Instantaneous Failure Research Articles

Reliability assessment of an optical current sensor based on accelerated aging tests

The operational reliability directly affects the practical application of optical current transformers (OCTs) in smart substations. As the key component of the OCT, the reliability of the optical current sensor (OCS) largely determines the reliability level of the OCT. This paper proposes a reliability assessment method of the OCS based on accelerated aging tests. The failure modes and failure mechanisms of the OCS are analyzed, and the concept of OCS insertion loss variation is proposed. An allowable range of insertion loss variation is selected as the failure criterion of the OCS. From the viewpoint of the OCS measurement error generated by the quantization error of the analog-to-digital converter, the allowable range of insertion loss variation is obtained. By selecting a high temperature as the accelerated thermal stress, we design the accelerated aging test scheme of the OCS and analyze the sample test data to obtain the activation energy of the OCS insertion loss failure. Based on this activation energy, the median time to failure and instantaneous failure rate curve of the OCS at normal temperature are obtained. The results indicate that the designed OCS has an expected service life of 50 years and a low instantaneous failure rate at normal temperature. This paper provides basic critical reliability analysis data for the system reliability assessment of OCTs.

Effects of Laminate Arrangement on the Failure Behaviour of Hybrid Composite Plates under Transverse Sinusoidal Load

The present work deals with the effects of laminate arrangement on the failure behaviour of hybrid composite plates under transverse sinusoidal load. Failure analysis has been a subject under study for many years, especially for composite materials. This is largely due to the spontaneous nature of composite materials when it fails without warning. Hybrid composite are commonly utilized to improve the unexpected and instantaneous failure mode of composites. Nevertheless, the failure behaviour of hybrid composites is still not well understood. Moreover, studies have not exploited the effects on sinusoidal transverse loading on hybrid composites. Therefore, the first and last ply failure of the hybrid composite laminate was simulated and analysed using built in failure criteria function in ANSYS. The hybrid composite consisted of graphite (GR) and glass (GL), with lamination schemes of [GL/GL/GL/GL], [GL/GL/GL/GR] and [GR/GL/GL/GL] were subjected of transverse sinusoidal loading. The laminate failure was predicted using the Maximum Stress Theory. Prior to determining the first and last ply failure of the hybrid composite plate, numerical validation was conducted to ensure the accuracy of the finite element software. The failure curves of the first ply failure and last ply failure were plotted and the results showed significant difference in the correlation of loadings that caused first and last ply failures and the lamination scheme of the hybrid composite plates. Thus, it can be said that the present work proves to be of importance and valuable in the field of study as well as enriching the knowledge regarding the failure behaviour of hybrid composite plate under transverse sinusoidal load of different laminate arrangement.

A Distribution for Instantaneous Failures

A new one-parameter distribution is proposed in this paper. The new distribution allows for the occurrence of instantaneous failures (inliers) that are natural in many areas. Closed-form expressions are obtained for the moments, mean, variance, a coefficient of variation, skewness, kurtosis, and mean residual life. The relationship between the new distribution with the exponential and Lindley distributions is presented. The new distribution can be viewed as a combination of a reparametrized version of the Zakerzadeh and Dolati distribution with a particular case of the gamma model and the occurrence of zero value. The parameter estimation is discussed under the method of moments and the maximum likelihood estimation. A simulation study is performed to verify the efficiency of both estimation methods by computing the bias, mean squared errors, and coverage probabilities. The superiority of the proposed distribution and some of its concurrent distributions are tested by analyzing four real lifetime datasets.

Non-Destructive Damage Assessment of Five Layers Fiber Glass / Polyester Composite Materials Laminated Plate by Using Lamb Waves Simulation

Composite materials are widely used in the engineered assets as aerospace structures, marine and air navigation owing to their high strength/weight ratios. Detection and identification of damage in the composite structures are considered as an important part of monitoring and repairing of structural systems during the service to avoid instantaneous failure. Effective cost and reliability are essential during the process of detecting. The Lamb wave method is an effective and sensitive technique to tiny damage and can be applied for structural health monitoring using low energy sensors; it can provide good information about the condition of the structure during its operation by analyzing the propagation of the wave in the plate. This paper presented the results and conclusions of a theoretical, numerical and experimental study of this method which was used for damage detection in the five layers fiberglass/polyester composite laminated plate, the fiber layer type is plain woven (0o/90o). The numerical analysis has been carried out by FEM using ABAQUS software for intact and cracked test specimen with the various boundary conditions and excitation frequencies, the results obtained have been confirmed experimentally by using piezoelectric wafer transducers (PZT) as actuator and sensor for both cases of experiments, it has been noted as a good agreement between experimental and numerical results.

An extended proportional hazards model for interval-censored data subject to instantaneous failures.

The proportional hazards (PH) model is arguably one of the most popular models used to analyze time to event data arising from clinical trials and longitudinal studies. In many such studies, the event time is not directly observed but is known relative to periodic examination times; i.e., practitioners observe either current status or interval-censored data. The analysis of data of this structure is often fraught with many difficulties since the event time of interest is unobserved. Further exacerbating this issue, in some such studies the observed data also consists of instantaneous failures; i.e., the event times for several study units coincide exactly with the time at which the study begins. In light of these difficulties, this work focuses on developing a mixture model, under the PH assumptions, which can be used to analyze interval-censored data subject to instantaneous failures. To allow for modeling flexibility, two methods of estimating the unknown cumulative baseline hazard function are proposed; a fully parametric and a monotone spline representation are considered. Through a novel data augmentation procedure involving latent Poisson random variables, an expectation-maximization (EM) algorithm is developed to complete model fitting. The resulting EM algorithm is easy to implement and is computationally efficient. Moreover, through extensive simulation studies the proposed approach is shown to provide both reliable estimation and inference. The motivation for this work arises from a randomized clinical trial aimed at assessing the effectiveness of a new peanut allergen treatment in attaining sustained unresponsiveness in children.

A Level-Fall Wave in the Headwater of a Hydroelectric Complex After a Partial Instantaneous Dam Failure

Results of experimental studies of the current in the upper pool after an emergency partial instantaneous dam failure are examined.

An Experimental Study of the Uniaxial Failure Behaviour of Rock‐Coal Composite Samples with Pre‐existing Cracks in the Coal

Many hazards encountered during coal mining can be caused by the instability and failure of the composite structure of the coal seam and the surrounding rock strata. The defects present in the coal affect the structural stability of the composite structure. In this study, uniaxial compression tests were conducted on sandstone‐coal composite samples with pre‐existing cracks in the coal, combined with tests performed with an acoustic emission (AE) device and a digital video camera. The strength, macrofailure initiation (MFI), and failure characteristics of composite samples, as influenced by the coal’s pre‐existing cracks, were analysed. The coal’s pre‐existing cracks were shown to reduce the strength, promote the occurrence of MFI, and affect the failure characteristics of the samples. Vertical penetration cracks had much more pronounced effects on strength and MFI occurrence, especially vertical penetration cracks that penetrated through the centre of the coal. Horizontal penetration cracks had a much reduced effect on strength and MFI occurrence. The MFI caused a step shape in the stress‐strain curve accompanied with a peak energy index signal and occurred around the original coal cracks. The MFI models predominantly exhibited crack initiation from the pre‐existing coal cracks and surface spalling caused by crack propagation. The intact composite sample failure presented as an instantaneous failure, whereas the composite samples containing the pre‐existing cracks showed a progressive failure. The failures of composite samples occurred predominantly within the coal and displayed an X‐typed shear failure accompanied by a small splitting failure. Both the coal and sandstone were destroyed in the composite sample with vertical penetration cracks through the centre of the coal. Failure of the coal occurred through a splitting failure accompanied by a small X‐typed shear failure, while the sandstone showed a splitting failure induced by crack propagation in the coal.

Modelling and Experimental Testing of Thick CFRP Composites Subjected to Low Velocity Impacts

The present paper investigates a modelling approach of experimentally tested thick panels made of Carbon Fibre Reinforced Polymers (CFRP). The coupons were made of 24 unidirectional (UD) laminae with a layup [45/0/-45/90]3s. The specimens were subjected to low velocity impact using a drop tower system. Several sensors, including a load cell and strain gauge, were utilized both for analysing the behaviour of the material against the impact and for performing a validation of the numerical models. Three energy levels were adopted: 8J, 10J and 12J.Numerical models were implemented into the finite element (FE) software LS-DYNA. A linear - elastic constitutive law with an instantaneous failure material was selected for mimicking the intralaminar behaviour of the carbon fibre composite. Enhanced Chang – Chang was adopted as the onset-of-failure criterion. This criterion is able to capture damage in different directions and permits the consideration (or not) of the shear behaviour in the failure equations. The capability of the model to capture the correct interface failure process was particularly emphasized and therefore cohesive elements with a bilinear traction – separation law were chosen for the reproduction of delamination. Finally, the experimental – numerical results were compared using first and foremost the overall delamination area and the curves force – time, force – displacement and absorbed energy – time as well as the strain measures obtained by the sensors.

Use of an Additional Nonlocking Screw in Olecranon Fracture Osteosynthesis Changes Failure Mechanism.

Hardware-related complications can occur when plate fixation is used to stabilize osteoporotic fractures involving the olecranon. The use of an additional nonlocking screw, placed retrograde into the proximal fracture segment, may improve stability under load. The purpose of this study was to conduct a biomechanical comparison of olecranon repair constructs with and without this additional retrograde screw. Nine matched pairs of elderly fresh-frozen cadaveric upper extremities were used. Two-part olecranon fractures were modeled, and fracture stabilization was performed. Olecranon plates were implanted either with the standard surgical technique (CTRL) or with an additional retrograde screw (EXPT). Dynamic extensions of increasingly loaded forearms were performed, and comparisons of sustained cycles, maximum load, and total work were made. Relative motion of bone segments was tracked, and modes of failure were assessed. Seventy-eight percent of specimens from the CTRL group failed due to relative fragment displacement exceeding 3 mm, while 78% of EXPT specimens failed due to instantaneous catastrophic failure. There were no significant differences in terms of number of survived cycles, maximum load, or work performed between the groups. The addition of a retrograde screw in this plating technique changes the failure mode from fracture displacement to catastrophic failure. The use of a 3.5-mm retrograde screw in the relatively small proximal ulnar fragment should be avoided, but screws with a smaller diameter may still have potential to improve fixation. Further biomechanical and clinical research is necessary to improve strategies for plate fixation of olecranon fractures in the elderly population. [Orthopedics. 2019; 42(1):e74-e80.].

A real-time and reliable dynamic migration model for concurrent taskflow in a GPU cluster

High performance GPU clusters are widely used for massive amount of concurrent dataflow processing, and have higher requirements for real-time, reliability and flexibility. However, the higher computational intensiveness and resources utilization lead to excessively high system temperature and power consumption, and even result in instantaneous failures. In this paper, we present a real-time and efficient dynamic taskflow migration approach (DTMA) based on a computing cluster. Firstly, we propose our basic theoretical models. Among them, the cluster communication model elaborates on all the communication paths and calculates the communication overhead of different migration modes. Secondly, on the basis of theoretical models and multiple instances analysis, our taskflow migration rules are summarized, and the rules help to balance cluster resources utilization and improve the overall performance of GPUs. Thirdly, the DTMA adjusts the cluster task allocation by utilizing performance and power consumption aware migration approach. This is done to reduce single node power consumption and enhance system reliability by shifting the current GPU load to other available GPU (GPUs). Moreover, the DTMA uses a circular queue to store resources information of available GPUs for better task scheduling. We evaluate the effect of DTMA through analyzing power consumption, temperature, fan speed and migration cost with different experiments. The experiment results demonstrate that DTMA is able to improve the performance and reliability of our cluster computing system, and reduce instantaneous failures.

Evaluation of the Role of Metallic Matrix on Environmentally Assisted Embrittlement of Austempered Ductile Iron (ADI) Using High Si Steel

The objective of this work stems from the environmentally assisted embrittlement suffered by austempered ductile iron (ADI) when its surface is submerged in water. This phenomenon leads to a drop in elongation and ultimate tensile strength of about 75% and 10%, respectively, while the 0.2% offset strain stress remains unaffected. Heat-treating a high Si steel, an ausferritic matrix similar to that present in the ADI under study is obtained, yielding giving a very good combination of tensile strength and elongation. In this manner, it was possible to examine the influence of the metallic matrix such as that present in ADI, though without nodules and cell boundaries, also called last to freeze zones (LTF). Tensile test evaluations on ADI and steel samples under dry and wet conditions were carried out. Additionally, a very specific test, introducing surface cracks, was conducted with the purpose of expanding the current knowledge on this particular kind of fracture. Earlier investigations on ADI have suggested that the process of embrittlement starts in a surface crack generated at the early stages of plastic deformation in LTF zones, which results from the solidification process, where pores, inclusions and unreacted austenite are present. In this manner, water penetrates and weakens the material strength, making the crack grow very fast and leading to an instantaneous samples failure. The main results obtained in this work include the confirmation of the deleterious effect of the LTF zones in the embrittlement process and the fracture surface analysis showing characteristic features of this kind of failure.

Phase modulation failsafe system for multi-kJ lasers based on optical heterodyne detection.

Amplification of the transverse scattered component of stimulated Brillouin scattering (SBS) can contribute to optical damage in the large aperture optics of multi-kJ lasers. Because increased laser bandwidth from optical phase modulation (PM) can suppress SBS, high energy laser amplifiers are injected with PM light. Phase modulation distributes the single-frequency spectrum of a master oscillator laser among individual PM sidebands, so a sufficiently high modulation index β can maintain the fluence for all spectral components below the SBS threshold. To avoid injection of single frequency light in the event of a PM failure, a high-speed PM failsafe system (PMFS) must be employed. Because PM is easily converted to AM, essentially all PM failsafes detect AM, with the one described here employing a novel configuration where optical heterodyne detection converts PM to AM, followed by passive AM power detection. Although the PMFS is currently configured for continuous monitoring, it can also detect PM for pulse durations ≥2 ns and could be modified to accommodate shorter pulses. This PMFS was deployed on the Z-Beamlet Laser (ZBL) at Sandia National Laboratories, as required by an energy upgrade to support programs at Sandia's Z Facility such as magnetized liner inertial fusion. Depending on the origin of a PM failure, the PMFS responds in as little as 7 ns. In the event of an instantaneous failure during initiation of a laser shot, this response time translates to a 30-50 ns margin of safety by blocking a pulse from leaving ZBL's regenerative amplifier, which prevents injection of single frequency light into the main amplification chain. The performance of the PMFS, without the need for operator interaction, conforms to the principles of engineered safety.

System-reliability-based design and topology optimization of structures under constraints on first-passage probability

For the purpose of reliability assessment of a structure subject to stochastic excitations, the probability of the occurrence of at least one failure event over a time interval, i.e. the first-passage probability, often needs to be evaluated. In this paper, a new method is proposed to incorporate constraints on the first-passage probability into reliability-based optimization of structural design or topology. For efficient evaluations of first-passage probability during the optimization, the failure event is described as a series system event consisting of instantaneous failure events defined at discrete time points. The probability of the series system event is then computed by use of a system reliability analysis method termed as the sequential compounding method. The adjoint sensitivity formulation is derived for calculating the parameter sensitivity of the first-passage probability to facilitate the use of efficient gradient-based optimization algorithms. The proposed method is successfully demonstrated by numerical examples of a space truss and building structures subjected to stochastic earthquake ground motions.

Study design with staggered sampling times for evaluating sustained unresponsiveness to peanut sublingual immunotherapy.

In this work, we delineate an altered study design of a pre-existing clinical trial that is currently being implemented in the Department of Pediatrics at the University of North Carolina at Chapel Hill. The purpose of the ongoing investigation of the desensitized pediatric cohort is to address the effectiveness of sublingual immunotherapy in achieving sustained unresponsiveness (SU) as assessed by repeated double-blind placebo-controlled food challenges (DBPCFC). With scarce published literature characterizing SU, the length of time off-therapy that would represent clinically meaningful benefit remains undefined. We use the new design features to assess time to loss of SU, an important efficacy endpoint, that to our knowledge, no prior study has investigated. Our work has two-fold objectives: first is to propose and discuss aspects of the altered design that would allow us to study SU and second is to explore methodology to evaluate the time to loss of SU and its association with risk factors in the context of the data originating from the trial. The salient feature of the new design is the allocation scheme of study subjects to staggered sampling timepoints when a subsequent DBPCFC is administered. Due to this feature, the time to loss of SU is either left or right censored. Additionally, some participants at study entry fail the DBPCFC, leading to what can be construed as an instantaneous failure. Through in-depth numerical studies, we examine the performance and power of a recently proposed mixture proportional hazards model specifically designed for the analysis of interval-censored data subject to instantaneous failures.

Simulation of nonhomogeneous degradation process in the system with gradual and instantaneous failures

The paper deals with the heterogeneous degradation process of the system with gradual and instantaneous failures. For the case when the times in the degradation stages are independent and distributed exponentially with different parameters, analytical expressions are obtained for the probability of a failure on the regeneration cycle, average time before the failure on the cycle, the average cycle length with and without failure, the average total cycle length. For the case of arbitrary distributions in highly reliable systems, where failure is a rare event, an simulation splitting algorithm is proposed to speed up the construction of regeneration cycles. The results of experiments obtained by the splitting and Monte-Carlo methods are presented and compared with analytical solutions

Reliability Analysis of DKNCP Systems with a Mixture of Degrading Components Subjected to Different Types of Shocks

This paper attempts to model the reliability of dynamic k-out-of-n systems with component partnership (DKNCP) in which a mixture of deteriorating components and multiple types of shocks are inflicted on the system. Previous studies were merely focused on the DKNCP systems affected by one type of shock that influenced all its components. In practice, however, shocks do not necessarily affect all the components. Hence, shocks may be classified based on their magnitude, specifications, and the components they affect. In this paper, random shocks are classified into distinct sets based on the components affected. DKNCP or adaptive KNCP is a new redundancy system that can be applied when a specific number of high-performance components is required which cannot be replaced by lower-performance components even if the number of these components is high. In a DKNCP system, the components contribute to the system operation in different ways and can make partnership groups for the system to survive when a component failure occurs. Also, we consider two failure mechanisms: accumulating degradation and random shocks. Two types of random shocks are also considered in the model: critical shocks, that cause instantaneous component failure, and non-critical ones, that increase natural degradation by a random amount.

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.

Surficial sediment failures due to the 1929 Grand Banks Earthquake, St Pierre Slope

Abstract A M w 7.2 earthquake centred beneath the upper Laurentian Fan of the SW Newfoundland continental slope triggered a damaging turbidity current and tsunami on 18 November 1929. The turbidity current broke telecommunication cables, and the tsunami killed 28 people and caused major infrastructure damage along the south coast of Newfoundland. Both events are believed to have been derived from sediment mass failure as a result of the earthquake. This study aims to identify the volume and kinematics of the 1929 slope failure in order to understand the geohazard potential of this style of sediment failure. Ultra-high-resolution seismic reflection and multibeam swath bathymetry data are used to determine: (1) the dimension of the failure area; (2) the thickness and volume of failed sediment; (3) fault patterns and displacements; and (4) styles of sediment failure. The total failure area at St Pierre Slope is estimated to be 5200 km 2 , recognized by escarpments, debris fields and eroded zones on the seafloor. Escarpments are typically 20–100 m high, suggesting failed sediment consisted of this uppermost portion of the sediment column. Landslide deposits consist mostly of debris flows with evidence of translational, retrogressive sliding in deeper water (>1700 m) and evidence of instantaneous sediment failure along fault scarps in shallower water (730–1300 m). Two failure mechanisms therefore seem to be involved in the 1929 submarine landslide: faulting and translation. The main surficial sediment failure concentrated along the deep-water escarpments consisted of widely distributed, translational, retrogressive failure that liquefied to become a debris flow and rapidly evolved into a massive channelized turbidity current. Although most of the surficial failures occurred at these deeper head scarps, their deep-water location and retrogressive nature make them an unlikely main contributor to the tsunami generation. The localized fault scarps in shallower water are a more likely candidate for the generation of the tsunami, but further research is needed in order to address the characteristics of these fault scarps.

Characteristics of shear-induced asperity degradation of rock fractures and implications for solute retardation

Direct shear tests on a series of fractured Beishan granite samples were performed under different normal stresses, to investigate the characteristics of asperity degradation during shear and to quantify their effects on solute retardation in fractures. A three-dimensional laser scanner and a laser diffraction particle size analyzer were used to examine the shear-induced asperity volume loss and the size distribution of sheared-off fragments. The results identified two main modes of asperity degradation during shear, i.e., instantaneous failure of asperities occurring at the peak shear stress, and crushing of the generated fragments with further shear displacement. Based on the volume of asperity degradation, a new joint damage coefficient was proposed. The size of the sheared-off fragments under different normal stresses was found to follow a Weibull distribution. Combining the proposed joint damage coefficient and the Weibull size distribution of the sheared-off fragments can approximately predict the potential effects of sheared-off fragments on solute retardation coefficient in rock fractures. The results showed that the shear-induced asperity degradation significantly increases the values of the solute retardation coefficient, by offering more sorption surfaces in fracture voids.

Time-variant reliability-based design optimization using sequential kriging modeling

This paper presents a sequential Kriging modeling approach (SKM) for time-variant reliability-based design optimization (tRBDO) involving stochastic processes. To handle the temporal uncertainty, time-variant limit state functions are transformed into time-independent domain by converting the stochastic processes and time parameter to random variables. Kriging surrogate models are then built and enhanced by a design-driven adaptive sampling scheme to accurately identify potential instantaneous failure events. By generating random realizations of stochastic processes, the time-variant probability of failure is evaluated by the surrogate models in Monte Carlo simulation (MCS). In tRBDO, the first-order score function is employed to estimate the sensitivity of time-variant reliability with respect to design variables. Three case studies are introduced to demonstrate the efficiency and accuracy of the proposed approach.