Failure Behavior Of System Research Articles

System failure behavior and maintenance decision making using, RCA, FMEA and FM

PurposeThe purpose of this paper is to permit the system reliability analysts/managers/engineers to model, analyze and predict the behavior of industrial systems in a more realistic and consistent manner and plan suitable maintenance strategies accordingly.Design/methodology/approachRoot cause analysis (RCA), failure mode effect analysis (FMEA) and fuzzy methodology (FM) have been used by the authors to build an integrated framework, to facilitate the reliability/system analysts in maintenance planning. The factors contributing to system unreliability were analyzed using RCA and FMEA. The uncertainty related to performance of system is modeled using fuzzy synthesis of information.FindingsThe in‐depth analysis of system is carried out using RCA and FMEA. The discrepancies associated with the traditional procedure of risk ranking in FMEA are modeled using decision making system based on fuzzy methodology. Further, to cope up with imprecise, uncertain and subjective information related to system performance, the system behavior is quantified by fuzzy synthesis of information.Originality/valueThe complementary adoption of the techniques as discussed in the study will help the maintenance engineers/managers/practitioners to plan/adapt suitable maintenance practices to improve system reliability and maintainability aspects after understanding the failure behavior of component(s) in the system.

プラズマ溶射遮熱コーティングシステムのクリープおよび疲労損傷挙動のその場観察(ガスタービン用遮熱/耐環境コーティング技術)

In order to investigate crack initiation sites and the crack propagation behavior in connection with the microstructure of thermal barrier coating (TBC) systems under creep and fatigue loadings, the failure behavior was observed in situ for plasma-sprayed TBC systems by optical microscopy, as a first step for elucidating the thermo-mechanical failure mechanism. Two types of TBC systems with differing top-coat (TC) microstructures were prepared by changing the processing conditions. The mechanical failure behavior of TBC system was found to depend strongly on the loading conditions. Under static creep loading, many segmentation cracks in the TC widened with increasing creep strain in the substrate. However, the propagation of these cracks into the bond-coat (BC) and alloy substrate was prevented due to the stress relief induced by plastic flow in the BC layer at elevated temperatures. As a result, the TBC system exhibited typical creep rupture behavior with nucleation and coalescence of microcracks in the alloy substrate interior regardless of the TC microstructure. Under dynamic fatigue loading, on the other hand, many fatigue cracks initiated not only from the tips of segmentation cracks in the TC layer but also from the TC/BC interface. Furthermore, it was found that the fatigue cracks propagated into the BC and alloy substrate even at elevated temperatures above the ductile-brittle transition temperature of the BC; the fatigue failure behavior under dynamic fatigue loading was dependent on the TC microstructure and the properties of the TC/BC interface.

Effect of Coating Process Condition on High-Temperature Oxidation and Mechanical Failure Behavior for Plasma Sprayed Thermal Barrier Coating Systems

In order to clarify the thermal and/or mechanical failure behavior of the plasma sprayed thermal barrier coating (TBC) system in connection with their coating characteristics depending on the coating process condition, two kinds of the failure analytical tests were conducted for TBC systems processed under different conditions. One was the high-temperature oxidation test, which was conducted at 1100°C under both the isothermal and thermal cycle conditions. The other was the in-situ observation of mechanical failure behavior, which was conducted under the static loadings at ambient temperature; as the most fundamental aspect, by means of an optical microscopy. It was found that the thermal and mechanical failure behavior of TBC system depends strongly on the top-coat (TC)/bond-coat (BC) interfacial condition, the reheat-treatment (RHT) after spraying and so on. For the TBC system with vacuum plasma sprayed (VPS) BC as well as for that with atmospheric plasma sprayed (APS) BC, in particular, the RHT at an appropriate temperature in Ar atmosphere was found to be effective for improving the oxidation property. For the TBC system with APS-BC, however, it was impossible to prevent the crack growth into the BC interior under the tensile loading in spite of conducting the RHT, since the microdefects such as oxides within the APS-BC tend to provide an easy crack propagation path. Furthermore, it was clarified that the smoothening process on the BC surface is able to prevent perfectly the occurrence of the wart-like oxide during oxidation, but at the same time increases also the risk of the TC spalling under the mechanical loading.

FM – a pragmatic tool to model, analyse and predict complex behaviour of industrial systems

PurposeThis paper aims to permit the system reliability analysts/managers/practitioners/engineers to analyze the system failure behavior using fuzzy methodology (FM)Design/methodology/approachIn order to deal with both qualitative and quantitative information related to system performance the authors have adopted failure mode effect analysis (FMEA) and Petrinets (PNs), the well‐known tools for reliability analysis, to build an integrated framework aimed at helping the reliability and maintenance managers in decision‐making.FindingsUsing the proposed framework an industrial case from the paper mill is examined. From the results it is observed that the limitations associated with the traditional procedure of risk ranking in FMEA are efficiently modeled using fuzzy decision‐making system (FDMS) based on FM. Also, the fuzzy synthesis of system failure and repair data helps to quantify the system behavior in a more realistic manner.Originality/valueThe simultaneous adoption of the proposed techniques to model, analyze and predict the uncertain behavior of an industrial system will not only help the reliability engineers/managers/practitioners to understand the behavioral dynamics of system but also to plan/adapt suitable maintenance practices to improve system reliability, availability and maintainability (RAM) aspects.

Modeling and analysing system failure behaviour using RCA, FMEA and NHPPP models

PurposeThe aim of this paper is to permit system reliability analysts/managers/practitioners/engineers to analyse system failure behaviour more consistently and plan suitable maintenance actions accordingly.Design/methodology/approachThe paper adopted three important tools, namely, root cause analysis (RCA), failure mode effect analysis (FMEA), and non‐homogeneous Poisson point process (NHPPP), to build an integrated and helpful framework, able to facilitate the maintenance managers in decision making. The factors contributing to system unreliability were analysed using RCA and FMEA. The failure data related to the components are modelled using NHPPP models and are used to optimise maintenance decisions (repair or replacements) based on cost dimensions.FindingsThe paper finds that the in‐depth analysis of a system using RCA and FMEA helps to create a knowledge base to deal with problems related to process/product unreliability. From the results it is observed that NHPPP models adequately analyse time‐dependent rate of occurrence of failures. Thus, assisting the maintenance analyst in development of suitable maintenance strategy by properly understanding the mechanism of failure (through modeling of failure data); adopting adequate aging management actions (such as predictive or periodic testing) to predict or detect the degradation of components; and performing cost analysis.Originality/valueThe contemporaneous adoption of the three proposed techniques for failure analysis will help system reliability engineers/managers/practitioners not only to understand the failure behaviour of component(s) in the system, but also to plan/adapt suitable maintenance practices to improve system reliability and availability.

OS6-1-2 Effect of coating process condition on high-temperature oxidation and mechanical failure behavior for plasma sprayed thermal barrier coating systems

In order to clarify the thermal and / or mechanical failure behavior of the plasma sprayed thermal barrier coating (TBC) system in connection with their coating characteristics such as the coating microstructures and interfacial natures depending on the coating process condition, two kinds of the failure analytical tests were conducted for TBC systems processed under different conditions. One was the high-temperature oxidation test, which was conducted at 1100℃ under both the isothermal and thermal cycle conditions. The other was the in-situ observation of mechanical failure behavior, which was conducted under the static loadings at ambient temperature; as the most fundamental aspect, by means of an optical microscopy. It was found that the thermal and mechanical failure behavior of TBC system depends strongly on the top-coat (TC) / bond-coat (BC) interfacial condition, the sorts of BC spraying process, the reheat-treatment (RHT) after spraying and so on. For the TBC system with vacuum plasma sprayed (VPS) BC as well as for that with air plasma sprayed (APS) BC, in particular, the RHT at an appropriate temperature in Ar atmosphere was found to be effective for improving the oxidation property. For the TBC system with APS-BC, however, it was impossible to prevent the crack growth into the BC interior under the tensile loading in spite of conducting the RHT, since the microdefects such as oxides and micropores within the APS-BC tend to provide an easy crack propagation path. In addition, it was clarified that the smoothening process on the BC surface is able to prevent perfectly the occurrence of the wart-like oxide (WO) during oxidation, but at the same time increases also the risk of the TC spalling under the mechanical loading. Furthermore, the effect of the coating process condition on the TC spalling resistance was discussed.

Predicting uncertain behavior of industrial system using FM—A practical case

As such the reliability of system is affected by many factors such as design, manufacturing, installation, commissioning, operation and maintenance. Consequently it may be extremely difficult if not impossible to model, analyze and predict the failure behavior of system. To this effect, the authors presented a structured framework which makes use of fuzzy methodology (FM), an approximate reasoning tool to deal with the imprecise, uncertain and subjective information related to system performance. The component related objective events are modeled with the help of the Petri net model of the system. Various parameters of managerial importance such as repair time, failure rate, mean time between failures, availability and expected number of failures are computed to quantify the uncertain behavior of system. Further, to improve upon the reliability characteristics of the system, in-depth qualitative analysis of unit is carried out using failure mode and effect analysis (FMEA) by listing all possible failure modes and their causes. A decision support system based on fuzzy set theory is developed to counter the limitations of traditional FMEA. The framework has been applied to model and analyze a real complex industrial system from paper mill.

An improved decomposition scheme for assessing the reliability of embedded systems by using dynamic fault trees

The theories of fault trees have been used for many years because they can easily provide a concise representation of failure behavior of general non-repairable fault tolerant systems. But the defect of traditional fault trees is lack of accuracy when modeling dynamic failure behavior of certain systems with fault-recovery process. A solution to this problem is called behavioral decomposition. A system will be divided into several dynamic or static modules, and each module can be further analyzed using binary decision diagram (BDD) or Markov chains separately. In this paper, we will show a very useful decomposition scheme that independent subtrees of a dynamic module are detected and solved hierarchically. Experimental results show that the proposed method could result in significant saving of computation time without losing unacceptable accuracy. Besides, we also present an analyzing software toolkit: DyFA (dynamic fault-trees analyzer) which implements the proposed methodology.

Bounds on MTBF of Systems Subjected to Periodic Maintenance

Mean time between failures (MTBF) is a common reliability measure used to assess the failure behavior of repairable systems. In order to increase MTBF, in most systems, it is a common practice to perform preventive maintenance activities at periodic intervals. In this paper: We first discuss the validity of a commonly used equation for computing MTBF of systems subjected to periodic maintenance.) For complex systems where this equation is valid, we propose a simple and better approximation than the exponential approximation proposed in a recent paper. In addition, we prove that for systems with increasing failure rate on average (IFRA) distributions, the exponential approximation proposed in a recent paper always underestimates the MTBF; hence, it is a lower bound at best.) The proposed approximation and bounds are applicable for a wide range of systems because systems which contain components with exponential or any increasing failure rate (IFR) distribution (viz., Weibull with beta>1, gamma, Gumbel, s-normal, and uniform) follow an IFRA distribution. As a special case, the proposed bounds & approximations provide better results for systems that contain only exponential failure distributions

In Situ Observation of Failure Behavior for Plasma Sprayed Thermal Barrier Coating Systems under Static Loadings

In situ observation of the mechanical failure behavior was conducted for different kinds of the plasma sprayed thermal barrier coating (TBC) systems by means of an optical microscopy under the static loadings at room and elevated temperatures; as the fundamental aspect, in order to clarify the thermomechanical failure mechanism of TBC system in connection with various coating characteristics. Mechanical tensile or compressive loading was applied progressively to the TBC specimen by an axial loading mode. It was found that the failure behavior of TBC system depends strongly on the testing temperature under both the tensile and compressive loadings. At the elevated temperature which is higher than the ductile-brittle transition temperature (DBTT) of metallic bond-coat (BC), in particular, the ceramic top-coat (TC) spallation can be prevented by virtue of the stress relief induced by the enhanced plastic flow in the BC layer. At the room temperature which is lower than the DBTT of BC, on the contrary, the TC spalling was inevitably induced, but the initiation site of TC spalling is closely related with the magnitude of local plastic deformation in the alloy substrate. Furthermore, an influence of thermally grown oxides (TGO) layer developed at the TC / BC interface on the crack initiation and propagation behavior was investigated in some detail.

In Situ Observation of Mechanical Failure Behavior for Plasma Sprayed Thermal Barrier Coating System at Ambient and Elevated Temperatures

In situ observation of the mechanical failure behavior was conducted for different kinds of the plasma sprayed thermal barrier coating (TBC) systems by means of an optical microscopy under the static loadings at ambient and elevated temperatures; as the fundamental aspect, in order to clarify the thermo-mechanical failure mechanism in connection with various coating characteristics. Mechanical tensile or compressive loading was applied progressively to the TBC specimen by an axial loading manner. It was found that the failure behavior of TBC system depends strongly on the testing temperature under both the tensile and compressive loadings. Namely, at the elevated temperature which is higher than the ductile-brittle transition temperature (DBTT) of metallic CoNiCrAlY bond-coat (BC), the ceramic yttria-stabilized zirconia (YSZ) top-coat (TC) spalling can be prevented effectively by virtue of the strain accommodation due to the extensive plastic flow in the BC layer. At the ambient temperature which is lower than the DBTT of BC, on the contrary, the TC spalling is more pronounced as a strain increases regardless of stress direction. Such an initiation site of TC spalling is closely related with the magnitude of local plastic deformation in the alloy substrate. Furthermore, the influence of coating microstructures on the crack initiation and propagation behavior was investigated in detail.

A study on the bio-hydro mechanical effects of the tree roots on the Agaclı coal reclaimed – forested land

The research area that is in the north of Istanbul (Turkey) and it is a land of open pit coal mining residuals reclaimed and turned to forest in 1988–1989. The materials that are open pit mine spoils are formed by sandy loam, sandy clay loam, heavy loam and clay (noncalcareous Pliocene I sediments). Pseudoacacia (Robinia pseudoacacia), Maritima Pine (Pinus pinaster) and Stone Pine (Pinus pinea) are planted on these materials. The aims of this research were to determine the strength of the material provided by tree roots and evaluate the performance of the forestation practices at lands especially where open pit coal mining spoil (residual) materials piled up. The research has been performed at two stages. The first one was ‘hydro-mechanical effect’ concerned about material moisture depletion as a result of transpiration and the second one was ‘bio-mechanical effects’ due to strength parameters of the roots and their growth pattern within the material. All results were evaluated in relation to tensile strength and displacement curves due to pre and post failure behaviors of materials and root systems. The results showed the increase of the displacement of the material was the significant indicator of the bio-mechanics tensile strength of the material provided by the tree roots. The fast growing type of tree roots have stabilized the material up to a depth for 80–100 cm by covering the coal residual materials within 12 years.

A new single‐sample failure model and its application to a special CNC system

PurposeThis paper is to present a new failure model that can be applied to single‐sample failure data of a single system under testing.Design/methodology/approachThe Bayesian method is used for the reliability evaluation. The weighted least squares method is used for determining the parameters of the reliability function.FindingsThe authors have observed the operation of a special computer numerical control (CNC) system for a period of over two years, and maintained a reliability database will all the collected failure data, from which the main source of failures can be identified.Research limitations/implicationsPreliminary research results are very encouraging. However, more work will be necessary to validate the new failure model.Practical implicationsThe determination of the parameters of the reliability function of a system under testing helps to identify its failure characteristics and potential quality problems.Originality/valueIt is hoped that the paper can help understand some of the challenges in modeling the failure behavior of special CNC systems.

Analysis and implementation of software rejuvenation in cluster systems

Several recent studies have reported the phenomenon of "software aging", one in which the state of a software system degrades with time. This may eventually lead to performance degradation of the software or crash/hang failure or both. "Software rejuvenation" is a pro-active technique aimed to prevent unexpected or unplanned outages due to aging. The basic idea is to stop the running software, clean its internal state and restart it. In this paper, we discuss software rejuvenation as applied to cluster systems. This is both an innovative and an efficient way to improve cluster system availability and productivity. Using Stochastic Reward Nets (SRNs), we model and analyze cluster systems which employ software rejuvenation. For our proposed time-based rejuvenation policy, we determine the optimal rejuvenation interval based on system availability and cost. We also introduce a new rejuvenation policy based on prediction and show that it can dramatically increase system availability and reduce downtime cost. These models are very general and can capture a multitude of cluster system characteristics, failure behavior and performability measures, which we are just beginning to explore. We then briefly describe an implementation of a software rejuvenation system that performs periodic and predictive rejuvenation, and show some empirical data from systems that exhibit aging

Proactive management of software aging

failures are now known to be a dominant source of system outages. Several studies and much anecdotal evidence point to as a common phenomenon, in which the state of a software system degrades with time. Exhaustion of system resources, data corruption, and numerical error accumulation are the primary symptoms of this degradation, which may eventually lead to performance degradation of the software, crash/hang failure, or other undesirable effects. Software is a proactive technique intended to reduce the probability of future unplanned outages due to aging. The basic idea is to pause or halt the running software, refresh its internal state, and resume or restart it. rejuvenation can be performed by relying on a variety of indicators of aging, or on the time elapsed since the last rejuvenation. In response to the strong desire of customers to be provided with advance notice of unplanned outages, our group has developed techniques that detect the occurrence of software aging due to resource exhaustion, estimate the time remaining until the exhaustion reaches a critical level, and automatically perform proactive software rejuvenation of an application, process group, or entire operating system, depending on the pervasiveness of the resource exhaustion and our ability to pinpoint the source. This technology has been incorporated into the IBM Director for xSeries servers. To quantitatively evaluate the impact of different rejuvenation policies on the availability of cluster systems, we have developed analytical models based on stochastic reward nets (SRNs). For timebased rejuvenation policies, we determined the optimal rejuvenation interval based on system availability and cost. We also analyzed a rejuvenation policy based on prediction, and showed that it can further increase system availability and reduce downtime cost. These models are very general and can capture a multitude of cluster system characteristics, failure behavior, and performability measures, which we are just beginning to explore.

Microstructural features of mechanical failure in thermal barrier coating systems under static loadings

In order to clarify qualitatively and quantitatively the failure mechanism of plasma-sprayed thermal barrier coating (TBC) systems from the microstructural viewpoint, in situ observation of the mechanical failure behavior was conducted for TBC systems under the static loadings at ambient temperature; as the most fundamental aspect, by means of an optical microscopy. Several kinds of TBC systems were prepared by using different sorts of ceramic coating materials. Mechanical tensile loading or compressive loading was gradually applied to the plate shape of TBC specimen using a four-point bending test methodology. It was found that the tensile failure behavior of TBC systems depends strongly on the top-coat microstructures as well as heat treatment after the plasma spraying. The compressive failures were also found rather incidental and depended on the strength of top-coat at the interfacial region. Among different TBC systems, those with the finely segmented top-coat exhibited a good spalling resistance.

Fracture behavior of crumb rubber-filled elastomers

The fracture behavior of a crumb rubber-filled elastomer was observed in optical micrographs. It was found that the failure started from the surface of the unfilled samples. The failure, however, started from a cavity around a crumb in the crumb-filled samples. This paper suggests that the failure mechanism in the crumb-filled elastomers (NR, NBR) was based on the microscopic observation of highly strained samples. This paper also considers the failure behavior of two-component systems: NR/NBR, SBR/NR, and NR/SBR. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3137–3144, 1999

Compression-shear failure of cementitious materials with oblique weak layers

Compressive/shear failure and strain-softening behavior of a bi-material system consisting of two different mortar compositions are studied. The bulk part of the bi-material specimen was made from the stronger mortar and was cast first, and then an oblique weak layer made from the weaker mortar was introduced in the middle of the specimen. By controlling the weak layer angle, thickness and strength, the compressive/shear failure characteristics and Mode-II shear strain-softening behavior have been determined. A bi-linear strain-softening model is proposed to consider both the Mode-II shear strain-softening behavior and the influence of friction due to compression. A linear softening law for the first part of the bi-linear model is sufficient to describe the softening curve after the peak load, but the second linear ‘softening’ relation is required to explain the influence of friction on the load and displacement curve. With the bi-linear model the Mode-II fracture energy G f-ll can be separated from the frictional energy dissipation. It is also found that two different frictional coefficients exist if a load and displacement curve has distinct softening and pure frictional regions.

A general formal approach for fuzzy reliability analysis in the possibility context

In this paper we focus on the fuzzy reliability analysis in the posbist reliability theory. In accordance with this theory the system failure state is defined precisely and the system failure and repair behaviour is fully characterized in the context of possibility measures. To formalize the reliability analysis in the posbist theory we propose a general approach on the basis of a system of functional equations. The solution of the system allows us to obtain fuzzy reliability characteristics of the arbitrary repairable and unrepairable systems. To illustrate the construction and application of the system of functional equations, various examples are given.

FUZZY RELIABILITY OF GRACEFULLY DEGRADING SYSTEMS WITH THE COMPOSITE SOFTWARE

In this paper, we focus on the transient and steady-state reliability behavior of a computer system whose software component as a program executes an infinite loop to provide control function and consists of several subprograms sequentially executed during iterations of the loop. The performance degradation of the system is due to the hardware failure occurrence. For reducing a large number of the system performance levels, we assume that the system success and failure are characterized by the fuzzy success and failure states with the defined membership functions. The system failure behavior is fully characterized in the context of probability measures. All random variables, such as times to hardware failures and mission times of subprograms, are arbitrarily distributed. In fact, we solve two problems: (1) reliability analysing under condition of many states and (2) reducing the state reliability measures to fuzzy success and failure reliability characteristics. The systems of integral and linear equations are used to obtain the unsteady and steady-state reliability characteristics, respectively. A numerical example is provided to illustrate and analyze the results.