Single Failure Mode Research Articles

Load sharing in series configuration

AbstractIn reliability engineering, load sharing is typically associated with a system in parallel configuration. Examples include bridge support structures, electric power supply systems, and multiprocessor computing systems. We consider a reliability maximization problem for a high‐voltage commutation device, wherein the total voltage across the device is shared by the components in series configuration. Here, the increase of the number of load‐sharing components increases component–level reliability (as the voltage load per component reduces) but may decrease system–level reliability (because of the increased number of components in series). We provide the solution for the 2 popular life‐load models: the proportional hazard and the accelerated failure time models with the underlying exponential and Weibull distributions for both a single and dual failure modes.

Optimal failure mode-based preventive maintenance scheduling for a complex mechanical device

This paper addresses the issue of PM scheduling for a complex mechanical with different failure modes. Unlike conventional studies which only consider a single failure mode without prior health information, our work jointly optimizes the failure time estimation and maintenance scheduling for mechanical systems under different failure modes. The proposed approach considers the failure modes which are fatal to the system function and performance. Firstly, the fatal failure modes are identified and divided into two types: the degraded and functional failure modes. The former indicates the one that has an explicit detectable degradation process till the predefined failure threshold is exceeded, while the latter indicates the failure modes that occur suddenly. For both types of failure modes, approaches of failure time estimation are presented to provide the actual health status information for maintenance scheduling. Afterwards, the maintenance scheduling problem is formulated on the estimated failure time distributions of the multiple failure modes. The integer-constrained genetic algorithm (GA) is adopted to optimize the preventive maintenance scheduling by minimizing the life-cycle cost rate. The optimal PM scheduling is derived based on the following: (1) when to perform the intermediate and major maintenance and (2) which failure mode should be maintained at an intermediate maintenance epoch. Finally, the performance of the proposed approach is validated through a real case of the ram subsystem of a boring machine.

Failure Mode Avoidance of Solid Rocket Motor Pressure Monitoring Joint Seals

The sealing joints used for pressure monitoring of solid propellant rocket motors (SRMs) of launch vehicles are very critical, as they are large in number, and leak through any of them is a single point failure mode. Identification of failure modes and its prevention is the key for reliable performance of an SRM. Failure modes are identified and the failure mechanisms of different seals in the pressure monitoring system studied through investigative tests with deliberately induced variations in the design parameters and nonconformance. Systematic analysis is carried out for the proposed designs through a failure mode effects analysis (FMEA), failure modes ranked in accordance with Risk Priority Number (RPN) and reliability of the joints worked out from the data. Design concerns are analyzed, alternate designs explored and innovative design solutions evolved. The effectiveness of the final design is brought out quantitatively by reduced RPN ratings and quantum jump in the reliability. Critical design, process and quality control parameters were identified, and procedures to ensure them evolved for failure mode avoidance.

A linear weighted (n, f, k) system for non-homogeneous Markov-dependent components

ABSTRACTWe study a linear weighted (n, f, k) system, denoted by L(n, f, k, w) system and consider the situation where components are non-homogeneous Markov-dependent. An L(n, f, k, w) system consists of n components ordered in a line, and each component u has a positive integer weight wu for u = 1, 2, …, n and w = (w1, w2, …, wn). The L(n, f, k, w):F (G) system fails (works) if the total weight of failed (working) components is at least f or the total weight of consecutive failed (working) components is at least k. For the L(n, f, k, w):F system with non-homogeneous Markov-dependent components, we derive closed-form formulas for the system reliability, the marginal reliability importance measure of a single component, and the joint reliability importance measure of multiple components using a conditional probability generating function method. We extend these results to the L(n, f, k, w):G systems, the weighted consecutive-k-out-of-n systems, and the weighted f-out-of-n systems. Our numerical examples and a case study on a bridge system demonstrate the use of derived formulas and provide the insights on the L(n, f, k, w) systems and the importance measures. In addition, the two failure modes associated with the L(n, f, k, w):F systems are analyzed by comparing to the single failure mode associated with the weighted consecutive-k-out-of-n:F systems and the single failure mode associated with the weighted f-out-of-n:F systems.

Investigation of some critical scenarios due to various failures of ICSI Cryogenic Distillation System

During normal operation of a CANDU reactor, large amounts of tritiated heavy water are being produced as result of neutron absorption by the heavy water used as moderator and cooling agent. Tritium in the heavy water brings a significant contribution to the personal doses and also represents an environmental hazard if water spills occur.The technology employed in the Pilot Plant for T2 and D2 separation from Rm. Valcea (Romania) is based on Liquid Phase Catalytic Exchange and Cryogenic Distillation (CD) processes and the whole system is in preoperational stage. The CD system consists of a cascade of four columns placed inside a vacuum insulated cold box and a refrigeration unit providing the cooling capacity for the columns condensers.This paper analyzes some critical scenarios due to single failure mode or a combination of failures such as loss of cooling capacity, loss of cooling agent into the columns, and loss of electric power, cases seen as conservative for the system in order to investigate the behavior during abnormal operation or accident.The study presented in the paper is concerning the CD system from Rm. Valcea but gives information and some references for the methodology that can be implemented for ITER Isotope Separation Systems.

Optimal multi-level condition-based maintenance policy for multi-unit systems under economic dependence

The study aims to work on multi -level condition-based maintenance (CBM) policy for multi-unit systems under economic dependence. Failure modes of units are classified as hard failure or soft failure and taken into account in this paper. Unlike previous works which only considered setup cost dependence with a single failure mode, two types of economic dependence are considered, which are setup cost-saving, and additional cost and time that can be saved when identical maintenance tasks and expertise are needed. In this study, hard failure provides an opportunity for additional inspection and repair of soft-type units, and soft failure creates an opportunity for replacement of the hard-type unit as its age exceeds opportunistic threshold. They both undergo preventive maintenance (PM) when the level/age exceeds preventive threshold at inspection epochs. The objective of this study is to determine the optimal opportunistic control limit and preventive control limit for each unit such that the system’s average long-run maintenance cost per unit time is minimized. The optimization problem is formulated in a semi-Markov decision process (SMDP) framework. The explicit formula for the mean residual life is derived for the proposed model which enables the estimation of the remaining useful life and allows maintenance engineers to plan maintenance early based on the observed information. Finally, the method is illustrated by an industrial case study of a feed system of a machine tool. A comparison with other methods is given, which illustrates the effectiveness of our approach.

Integration of reliability analysis into mini-plate fixation strategy used in human mandible fractures: Convalescence and healing periods.

The objective was to assess the reliability level of mini-plate fixation used in fracture mandibles in order to evaluate the structure stability in both convalescence and healing periods. In the convalescence period, the failure scenario is measured by the relative displacement between two fracture surfaces which should not exceed an acceptable value in order to obtain a good stability for rapid bone healing and to limit any trauma. However, in the healing period, it is the objective to obtain an acceptable rigidity. Hereby, the failure scenario is measured by the von Mises stresses being as indicator of mandible fractures. During the surgery operation, some muscles can be cut or harmed and cannot operate at its maximum capability. Thus, there is a strong motivation to introduce the loading uncertainties in order to obtain reliable designs. A 3-dimensional finite element model was developed in order to study the negative effect caused by stabilization of the fracture. The different results were obtained when considering a clinical case of a 35-year-old male patient. The results show the importance of fixation of symphysis fracture by two I-plates with four holes. The structural reliability level was estimated when considering a single failure mode and multiple failure modes. The integration of reliability concepts into mini-plate fixation strategy is considered a novel aspect. The reliability evaluation seams to be a reasonable asset in both convalescence and healing periods.

Review of the Fault Mechanism and Diagnostic Techniques for the Range Extender Hybrid Electric Vehicle

This paper presents a thorough literature review on the fault mechanism and diagnostic techniques for a range extender hybrid electric vehicle, which is one of the most feasible electric vehicles. However, extensive fault diagnosis research has been done on the diesel engine or a generator, but studies on the range extender are still limited, which is a coupling device of an engine-generator shaft. It has many coupling faults except to the single failure mode of the diesel engine or the generator. In this paper, the research development of the fault mechanism and fault diagnosis has been reviewed and analyzed. In addition, the trends in fault diagnosis technologies have been discussed, which provides a theoretical foundation for the engineering application of the condition monitoring and fault diagnosis of the electric vehicle range extender.

Multiple Failure Modes Reliability Modeling and Analysis in Crack Growth Life Based on JC Method

The fatigue crack growth (FCG) phenomenon generally exists in large mechanical structures. Due to the influences of varied kinds of random factors, the safety evaluation of structure in FCG is under great uncertainty. In this paper, based on the reliability theory, the limit state equations of fracture failure and static strength failure were derived firstly, and the parameters in those equations were regarded as random variables that follow the normal distribution or log‐normal distribution. According to the limit state equations, the JC method (equivalent normalizing method) was used to calculate the reliability indexes under the different failure modes of structure in every stress cycle. Based on the reliability indexes and correlation of the two failure modes, the joint failure probability was obtained. In the end, a specific computation example was given, and the curve of joint failure probability in multiple failure modes was used for comparison with the result of single failure mode. The results indicated that the reliability analysis based on multiple failure modes was more reasonable, and the evaluation of reliability could be obtained in fatigue crack growth process.

Multistream sensor fusion-based prognostics model for systems with single failure modes

Advances in sensor technology have facilitated the capability of monitoring the degradation of complex engineering systems through the analysis of multistream degradation signals. However, the varying levels of correlation with physical degradation process for different sensors, high-dimensionality of the degradation signals and cross-correlation among different signal streams pose significant challenges in monitoring and prognostics of such systems. To address the foregoing challenges, we develop a three-step multi-sensor prognostic methodology that utilizes multistream signals to predict residual useful lifetimes of partially degraded systems. We first identify the informative sensors via the penalized (log)-location-scale regression. Then, we fuse the degradation signals of the informative sensors using multivariate functional principal component analysis, which is capable of modeling the cross-correlation of signal streams. Finally, the third step focuses on utilizing the fused signal features for prognostics via adaptive penalized (log)-location-scale regression. We validate our multi-sensor prognostic methodology using simulation study as well as a case study of aircraft turbofan engines available from NASA repository.

Multimodal method for coseismic landslide hazard assessment

Regional-scale coseismic landslide hazard assessments have traditionally been based on infinite-slope analyses, considering only a single mode of failure. Inventories and landslide reconnaissance work have shown a diverse range of coseismic landslide modes with significantly different consequences of failure. This paper presents a multimodal approach for regional-scale coseismic landslide hazard assessment. Through a two-step procedure, the multimodal method explicitly accounts for four general landslide types commonly observed during earthquakes: rock-slope failures, disrupted soil slides, coherent rotational slides, and lateral spreads. First, the susceptibility to each landslide mode is evaluated based on topography. Second, coseismic landslide hazards are assessed using mode-specific geotechnical models. A trial multimodal landslide assessment is presented for the seismically active country of Lebanon. Results show that the computed coseismic landslide hazard closely matches field-verified slope activity across different regions of the country exhibiting a range of failure modes. These results qualitatively demonstrate the efficacy of the procedure and suggest that multimodal coseismic landslide hazard analysis is especially well-suited for regions with varying terrain and where landslide inventories are not available.

Barrier Property of a Ta/MnSi<italic>x</italic>O<italic>y</italic>Layer Formed by a Ta–Mn Alloy for a Cu Interconnect

The advanced back-end module of very-large-scale-integrated-circuits (VLSIs) requires an ultrathin diffusion barrier layer between the Cu interconnect and low-K oxides. In this letter, we investigated the electrical properties of the barrier layer formed by a Ta-Mn alloy on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . A diffusion barrier layer self-formed at the interface during annealing, and the Ta/MnSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> bilayer structures were investigated by standard microscopy. Black's equation and the measured mean-time-to-failure (MTTF) were used to obtain the reliability characteristics under different temperatures and current densities. The reliability is approximately two times better than that of the conventional TaN/Ta counterpart. The confidence intervals at 95% for each MTTF confirmed the single failure mode, and the electromigration phenomenon was observed to be the failure mechanism. Our results provide evidence that Ta/MnSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> is a promising barrier material for Cu interconnects in VLSIs.

Improvement in failure prediction algorithm for textile composites

This study presents an analytical modeling of the mechanical behavior of textile composites. The main objective of this study is to evaluate in-plane and out of plane ultimate strengths for different types of 2D and 3D fabric-reinforced polymer. The proposed analytical model consists of a homogenization method, a failure criterion, and a damaged stiffness model. An improved failure prediction algorithm is presented, which tends to enhance the prediction of ultimate strengths. It is shown that assuming a final failure of undulated yarns for a failure of 90% of subdivisions rather than 100%, alongside assigning a multi-failure mode for the failed subdivision rather than single failure mode is yielding much better results. The predicted elastic properties and ultimate strengths are compared to available experimental and numerical data, where a very good agreement is shown. The proposed model offers a reliable, simple, and easy to use analytical tool.

Evaluating the Effect of Minimizing Screws on Stabilization of Symphysis Mandibular Fracture by 3D Finite Element Analysis.

The objective of this work is to integrate structural optimization and reliability concepts into mini-plate fixation strategy used in symphysis mandibular fractures. The structural reliability levels are next estimated when considering a single failure mode and multiple failure modes. A 3-dimensional finite element model is developed in order to evaluate the ability of reducing the negative effect due to the stabilization of the fracture. Topology optimization process is considered in the conceptual design stage to predict possible fixation layouts. In the detailed design stage, suitable mini-plates are selected taking into account the resulting topology and different anatomical considerations. Several muscle forces are considered in order to obtain realistic predictions. Since some muscles can be cut or harmed during the surgery and cannot operate at its maximum capacity, there is a strong motivation to introduce the loading uncertainties in order to obtain reliable designs. The structural reliability is carried out for a single failure mode and multiple failure modes. The different results are validated with a clinical case of a male patient with symphysis fracture. In this case while use of the upper plate fixation with four holes, only two screws were applied to protect adjacent vital structure. This behavior does not affect the stability of the fracture. The proposed strategy to optimize bone plates leads to fewer complications and second surgeries, less patient discomfort, and shorter time of healing.

Epitaxial nickel disilicide with low resistivity and excellent reliability

Ultra-thin epitaxial NiSi2 was formed, and its structure was examined by electron microscopy and x-ray diffraction. Compared with previous reports, the measured resistivity of the epitaxial NiSi2 was unprecedentedly low, reaching 7 μΩ cm in the experimental results and up to 14.93 μΩ cm after modification. The reliability, which was investigated under different temperatures and current densities to understand its electronic characteristics, was 1.5 times better than that of the conventional polycrystalline counterpart. Black’s equation and the measured mean-time-to-failure (MTTF) were used to obtain the reliability characteristics of epitaxial and poly-NiSi2. Confidence intervals at 95% for each MTTF confirmed the single failure mode. The electromigration phenomenon was observed to be the failure mechanism. Our results provide evidence that epitaxial NiSi2 is a promising contact material for future electronics.

SEISMIC BASE ISOLATION FOR REDUCING SEISMIC RISK OF ARCHITECTURAL HERITAGE BUILDINGS

The paper analyses the applicability of seismic base isolation made of elastomeric bearings for the seismic mitigation of architectural heritage buildings. Due to the inestimable cultural and historical significance any remedial measures into such objects must be selected with care and are usually very limited. In an ideal situation only interventions with minimum visual impacts on the object and maximum potential for restoring its cultural values would be implemented. Historical structures were usually not designed accounting seismic hazard and might be seismically more vulnerable as modern buildings. The paper deals with seismic base isolation as a technique for increasing the seismic resistance of architectural heritage buildings made of unreinforced masonry. Typical base isolation devices represent special bearings that are usually installed bellow the foundations of the structure. If the isolation system is properly designed it can eliminate the need for using more invasive retrofit measures and techniques. The paper presents a relatively simple and computationally less demanding technique for the modelling and analysis of regular unreinforced masonry (URM) structures. This technique is based on the equivalent frame approach, while the complex seismic failure mechanism of masonry piers is expressed by a single failure mode interaction surface (an FMI surface), taking into account the influence of variation in the pier’s vertical loading, and it’s bending moment distribution. A single failure mode interaction plastic hinge (an FMI hinge) for each masonry frame element is introduced by combining specific failure modes, taking into account their minimum envelope. In the final part of the work a case study of using base isolation for the seismic retrofitting of an existing three-story masonry building has been conducted. Some results obtained by the N2 method comparing the damage in fixed based and base isolated variant of the test building demonstrate the potential of used techniques for the seismic protection of masonry heritage buildings.

Numerical integration method for computing reliability index of geotechnical system

ABSTRACTTo account for the uncertainties in the design of a geotechnical system, reliability-based design approach is often adopted, in which the main task is to evaluate reliability index of the system based on a performance function (or limit state function). In this paper, we propose a new method for computing the reliability index, based upon the numerical integration of the cumulative distribution function (CDF) of the performance function. This numerical integration method requires only a deterministic evaluation of the system performance and the joint probability of the uncertain input parameters. The effectiveness and the efficiency of the proposed method, measured in terms of the accuracy and the computational effort, respectively, are demonstrated with two geotechnical problems: a drilled shaft in sand and a semi-gravity retaining wall. The new method is found valid regardless of the type of distribution of uncertain input parameters, whether the correlations exist among these input parameters, whether the system involves single or multiple failure modes, and how the performance function is formulated.

Interactive Multiple-Model Application for Hydraulic Servovalve Health Monitoring

&#x0D; &#x0D; &#x0D; Hydraulic systems are widely used as power source for several different applications. Servovalves are critical components and often subjected to failures. Estimating degradations from these components requires dynamic analysis of their behavior and consequently advanced monitoring techniques. This article proposes an online monitoring method to estimate a degradation parameter of the servovalve using an interactive multiple-model technique considering a bank of Extended Kalman Filters that models not only the valve itself but also the degradation trend. A single failure mode was considered related to the nozzle line clogging. The degradation estimates and the likelihood of the correctness of each model were analyzed in order to evaluate the proposed method.&#x0D; &#x0D; &#x0D;

An approach to optimize the machining accuracy retainability of multi-axis NC machine tool based on robust design

Machining accuracy retainability is considered to be one of the most important aspects in the process of performance evaluation and optimization design of the machine tools. Reliability based design optimization (RBDO) and robust design optimization (RDO) are the tools that search for safe structural systems with minimal variability of response when subjected to uncertainties in design parameters. The aim of this paper is to propose an approach that simultaneously considers reliability and robustness to allocate geometric accuracy of components for improving machining accuracy retainability under certain design requirements. Based on homogenous transformation matrices (HTMs), a comprehensive volumetric model explaining how individual errors in the components of a machine affect its volumetric accuracy (the coupling relationship) was established. By applying high-order moment standardization technique (HOMST), reliability and sensitivity with single failure mode were obtained and then the reliability model and the sensitivity model with multiple failure modes were developed and common methods such as Narrow bounds, AFOSM and Monte Carlo were used for verification and comparison. Meanwhile, a cost model taking manufacturing cost and present worth of expected quality loss into consideration was introduced. By taking the minimum possibility of failure and cost of machine tools as criterions and taking the reliability of machine tools as constraint of optimizing the basic parameters of machine tools, an approach to optimize the machining accuracy retainability of multi-axis NC machine tool based on robust design was developed and an example of improving the machining accuracy retainability for a five-axis NC machine tool was used to demonstrate the effectiveness of this approach. This study implies that it is possible to obtain the relationships between geometric errors and specify the accuracy grades of main feeding components of mechanical assemblies.

Statistical Estimation of Duplex S-N Curves

In recent years, experimental tests investigating properties of materials in gigacycle regime have suggested modifications to well-known statistical fatigue life models. Classical fatigue life models based on a single failure mode and by the presence of the fatigue limit, have been integrated by models that can take into account the occurrence of two failure modes (duplex S-N curve).Duplex S-N models involve a number of unknown parameters that must be statistically estimated from experimental data. The present paper proposes a simplified and automated procedure for statistical parameter estimation. The procedure is applied to experimental datasets taken from the literature. Parameter estimation is carried out by applying the Maximum Likelihood Principle and by taking into account the possible presence of runout specimens with unequal number of cycles. The application of the procedure permits to estimate different key material parameters (e.g., the characteristic parameters of transition stress and fatigue limit), as well as to statistically predict the failure mode of each tested specimen.