Periodic imperfect preventive maintenance with two categories of competing failure modes

A maintenance policy is studied for a system with two types of failure modes: maintainable and non-maintainable. The quality of maintenance actions is modelled by its effect on the system failure rate. Preventive maintenance actions restore the system to a condition between as good as new and as bad as immediately before the maintenance action. The model presented permits to study the equipment condition improvement (improvement factor) as a function of the time of the preventive maintenance action. The determination of the maintenance policy, which minimizes the cost rate for an infinite time span, is examined. Conditions are given under which a unique optimal policy exists.     

Reliability analysis of electronic devices with multiple competing failure modes involving performance aging degradation

This paper presents an extension of reliability analysis of electronic devices with multiple competing failure modes involving performance aging degradation. The probability that a product fails on a specific mode is derived. Using this probability, the dominant failure mode on the product can be predicted. A practical example is presented to analyze an electronic device with two kinds of major failure modes–solder/Cu pad interface fracture (a catastrophic failure) and light intensity degradation (a degradation failure). Reliability modeling of an individual failure mode and device reliability analysis is presented and results are discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

A map of competing buckling-driven failure modes of substrate-supported thin brittle films

Our in situ experiments of polyimide-supported thin indium tin oxide (ITO) films reveal buckling-driven film cracking in some samples and buckling-driven interfacial delamination in other samples. Although studies of individual buckling-driven failure mode exist, it still remains unclear what governs the competition between these two different failure modes in a given film/substrate structure. Through theoretical analysis and numerical simulations, we delineate a map of competing buckling-driven failure modes of substrate-supported thin brittle films in the parameter space of interfacial adhesion and interfacial imperfection size. Such a map can offer insight on the mechanical durability of functional thin films. For example, interestingly, we show that strongly bonded thin brittle films are more prone to buckling-driven cracking, a more detrimental failure mode for thin brittle ITO transparent conductors widely used in displays and flexible electronics.     

Optimal Bayesian maintenance policy for a gearbox subject to two dependent failure modes

Most maintenance optimization models of gear systems have considered single failure mode. There have been very few papers dealing with multiple failure modes, considering mostly independent failure modes. In this paper, we present an optimal Bayesian control scheme for early fault detection of the gear system with dependent competing risks. The system failures include degradation failure and catastrophic failure. A three‐state continuous‐time–homogeneous hidden Markov model (HMM), namely the model with unobservable healthy and unhealthy states, and an observable failure state, describes the deterioration process of the gear system. The condition monitoring information as well as the age of the system are considered in the proposed optimal Bayesian maintenance policy. The objective is to maximize the long‐run expected average system availability per unit time. The maintenance optimization model is formulated and solved in a semi‐Markov decision process (SMDP) framework. The posterior probability that the system is in the warning state is used for the residual life estimation and Bayesian control chart development. The prediction results show that the mean residual lives obtained in this paper are much closer to the actual values than previously published results. A comparison with the Bayesian control chart based on the previously published HMM and the age‐based replacement policy is given to illustrate the superiority of the proposed approach. The results demonstrate that the Bayesian control scheme with two dependent failure modes can detect the gear fault earlier and improve the availability of the system.     

A periodic inspection and replacement policy for systems subject to competing failure modes due to degradation and traumatic events

This paper deals with the condition-based maintenance of single-unit systems which are subject to the competing and dependent failures due deterioration and traumatic shock events. The main aim is to provide a model to assess the value of condition monitoring information for the maintenance decision-making. A condition-based periodic inspection/replacement policy is developed and compared with a benchmark time-based block replacement policy.Numerical results show that it is indeed useful to follow closely the actual evolution of the system to adapt the maintenance decisions to the true system state to improve the performance of maintenance policies. The analysis of the maintenance costs savings can be used to justify or not the choice to implement a policy based on condition monitoring information and to invest in condition monitoring devices.     

Exact equations for analysing thickness-twist trapped-energy modes in monolithic filters

Summary Thickness-twist vibrations with energy trapping in a monolithic filter consisting of an infinite piezoceramic plate withN infinitesimally thin electrodes evaporated on to each face are analysed. By applying the Fourier transform technique, the linear three-dimensional equations for a piezoceramic plate are reduced to integral equations for the charge distributions on the electrodes. An approach for solving these equations and numerical results for a dual are given.     

Duality of fatigue failures of materials caused by Poisson defect statistics of competing failure modes

The statistical nature of failures of components subjected to fatigue loading is a major challenge in engineering applications. Here, we report an interesting fatigue phenomenon in which there is a 'duality' of the S-N fatigue data (S is stress and N is cycles to failure)--the grouping of data into two distinct S-N curves as a result of two competing failure modes. The proportions of failure by either mode are about the same and one cannot predict which failure mode will eventually dominate. This means that fatigue lives may be unpredictable in materials under certain application conditions and the consequences can be disastrous. Based on Poisson defect statistics and Monte Carlo simulations, we show that this phenomenon can arise from the Poisson distribution of low populations of microscale defects. An unexpected finding is that there should be a combination of average defect density and specimen area at which this phenomenon is observable in materials having sparsely populated defects.     

Testing and analysing capability performance for products with multiple characteristics

Process capability analysis is a vital part of an overall quality improvement programme. Numerous techniques and tools have been proposed for process capability analysis. Among these, indices and charts of process capability are simple and effective tools and widely used in the manufacturing industry. Many scholars have revealed numerous valuable aspects of previously developed tools and methods. Due to the rising demands of product quality, the current tools and methods are insufficient for enabling managers to make informed decisions. To address this gap, this study proposes a hypothesis testing procedure which determines whether the process capabilities satisfy the target level. Furthermore, this study proposes an integrated quality test chart (IQTC), which can display the process potential and performance for an entire product with smaller-the-better, larger-the-better and nominal-the-best specifications. The proposed procedure and IQTC incorporate the quality-level concept of the Six Sigma model and can be used to quantitate the relationships among the quality level, capability indices and process yield. They can be applied to assist managers in measuring, monitoring, analysing and improving process performance in a timely manner which will help ensure that the quality levels of their products meet customer demands. Finally, an example is provided to illustrate how to use the proposed procedure and IQTC.     

A new combinatorial model for deterministic competing failure analysis

Components in many engineering and industrial systems can experience propagated failures, which not only cause the failure of the component itself but also affect other components, causing extensive damage to the entire system. However, in systems with functional dependence behavior where failure of a trigger component may cause other components (referred to as dependent components) to become unusable or inaccessible, failure propagation originating from a dependent component could be isolated if the corresponding trigger component fails first. Thus, a time-domain competition exists between the failure propagation effect and the failure isolation effect, which poses a great challenge to the system reliability modeling and analysis. In this work, a new combinatorial model called competing binary decision diagram (CBDD) is proposed for the reliability analysis of systems subject to the competing failure behavior. In particular, special Boolean algebra rules and logic manipulation rules are developed for system CBDD model generation. The corresponding evaluation algorithm for the constructed CBDD model is also proposed. The proposed CBDD modeling method has no limitation on the type of component time-to-failure distributions. A memory system example and a network example are provided to demonstrate the application of the proposed model and algorithms. Correctness of the proposed method is verified using the Markov method.     

Metrological maintenance of means for measuring liquid levels

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 29–30, May, 1992.     

Bayesian models and ageing indicators for analysing random changes in failure occurrence

The paper introduces ageing models of repairable components based on Bayesian approach. Models for the development of both failure rate and the probability of failure on demand are presented. The models are based on the assumption that the failure probability or rate has random changes at certain time points. This is modelled by assuming that the successive transformed failure probabilities (or rates) follow a Gaussian random walk. The model is compared with a constant increment model, in which the possible ageing trend is monotone. Monte-Carlo Markov Chain sampling is applied in the determination of the posterior distributions. Ageing indicators based on the model parameters are introduced, and the application of these models is illustrated with case studies.     

Interference methods for measuring surface roughness

Conclusions It is possible without incurring large expenditure, to apply under production conditions methods of interference microscopy by means of appropriately designed instruments for checking the production of components with a required degree of surface finish; in the first instance in lapping operations.The equidensity line, immersion, and Zehender methods extend the range of roughness which can be measured by means of interferometer microscopes.From a report by H. Trumpold D. Sc. (Eng) (Higher Technical School, Karl-Marxstadt, GDR) read at the Bauman Moscow Higher Technical School. The report was arranged for publication in Measurement Techniques by O. Ya. Egor'ev.     

Reliability modeling for multistage systems subject to competing failure processes

In this paper, a novel multistage reliability model is provided as systems are often divided into many stages according to system degradation characteristics. Multistage hard failure (caused by random shock) process (MHFP) and multistage soft failure (caused by random shock and continuous degradation) process (MSFP) are introduced to describe the competing failure processes, where either the MSFP or MHFP would break down the system. The shock processes impact the system in three ways: (1) fatal load shocks cause hard failure immediately in the hard failure process; (2) time shocks cause a hard failure threshold changing; (3) damage load shocks cause degradation level increasing in the soft failure process. In this paper, a density function dispersion method is carried out to address the multistage reliability model, and the effectiveness of the proposed models is demonstrated by reliability analysis with the one-stage model. Finally, the multistage model is applied to a case study, the degradation process is divided into three stages, and the hard failure threshold can be transmitted twice. The proposed model can be applied in other multistage situations, and the calculation method can satisfy the accuracy requirements.     

δ冲击条件下相关性竞争失效过程的系统可靠性建模

研究系统受到δ冲击时,考虑系统自然退化和冲击两个竞争性失效过程间具有相关性时,系统可靠性的建模问题。相关性一方面表现为冲击造成系统退化量的增加,另一方面表现为系统的自然退化程度对冲击结果的影响。假设系统因冲击而失效的过程是δ冲击过程,通过系统自然退化过程和冲击过程的分布函数,导出了系统的可靠度函数,建立了系统可靠度模型的一般形式,并给出一种特例的具体形式,最后利用文献中的具体参数进行仿真,以验证模型的正确性和有效性。     

Optoelectronic methods and devices for measuring bullet velocity

Optoelectronic methods and devices are considered for measuring bullet velocity. The main sources of errors are analyzed. A model is developed for forming the photoelectric signal by which measurement error is determined. Curves are provided for the dependence of measurement error on structural parameters. __________ Translated from Izmeritel’naya Tekhnika, No. 3, pp. 45–48, March, 2006.     

多类型冲击的竞争失效过程可靠性建模研究

针对连续性退化过程中同时存在多种类型冲击的问题,在变失效阈值模型的基础上,建立考虑多种类型冲击的竞争失效模型。首先,基于变阈值失效模型分析多种冲击类型同时存在时对系统可靠性的影响,给出模型的主要失效模式;然后结合极值冲击模型给出竞争失效可靠性建模的一般方法,求解竞争失效可靠性模型的解析表达式;最后,以某微型发动机为研究对象,对该文提出的方法进行对比验证,证明该方法能有效防止对系统可靠性的盲目乐观估计,防止突发故障的发生。     

Precision methods for measuring ocean physicochemical characteristics

This survey analyzes the current state of measuring equipment for basic ocean physicochemical characteristics, its metrological capabilities, and standards support.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 56–64, September, 1993.