Reliability Growth Program Research Articles

Analysis of correlated multivariate degradation data in accelerated reliability growth

AbstractModern engineering systems have become increasingly complex and at the same time are expected to be developed faster. To shorten the product development time, organizations commonly conduct accelerated testing on a small number of units to help identify failure modes and assess reliability. Many times design changes are made to mitigate or reduce the likelihood of such failure modes. Since failure‐time data are often scarce in reliability growth programs, existing statistical approaches used for predicting the reliability of a system about to enter the field are faced with significant challenges. In this work, a statistical model is proposed to utilize degradation data for system reliability prediction in an accelerated reliability growth program. The model allows the components in the system to have multiple failure modes, each associated with a monotone stochastic degradation process. To take into account unit‐to‐unit variation, the random effects of degradation parameters are explicitly modeled. Moreover, a mean‐degradation‐stress relationship is introduced to quantify the effects of different accelerating variables on the degradation processes, and a copula function is utilized to model the dependency among different degradation processes. Both a maximum likelihood (ML) procedure and a Bayesian alternative are developed for parameter estimation in a two‐stage process. A numerical study illustrates the use of the proposed model and identifies the cases where the Bayesian method is preferred and where it is better to use the ML alternative.

Data analysis and resource allocation in Bayesian selective accelerated reliability growth

The rapid pace of technology advancement has resulted in increasingly complex systems with more potential failure modes. However, it is quite common that multiple key components of such a system may be developed, tested and improved independently during product development. Without taking a holistic approach to system reliability improvement, a significant amount of time and resources may be wasted on over-design of some components, which can be otherwise used for strengthening other under-designed components. The technical challenge is more prominent when accelerated testing is utilized in a reliability growth program in hopes of shortening the system development cycle. To overcome limitations of the traditional reliability growth method using the Crow-AMSAA model, a Bayesian selective accelerated reliability growth method is proposed in this article to accelerate potential failure modes and aggregate component testing results and prior knowledge for predicting system reliability growth and corrective actions. As one of the key steps, the method dynamically allocates limited resources for testing and correcting failures on all system levels. Numerical examples illustrate that the proposed integrated statistical and optimization method is effective in estimating and improving the overall reliability of a system.

RAMI: The main challenge of fusion nuclear technologies

RAMI (Reliability, Availability, Maintainability and Inspectability) is one of the most severe challenges of Fusion Technologies, and it is probably the engineering branch where the fusion community is the least competent. This paper summarizes the RAMI statistics in existing fusion machines, the RAMI approaches adopted in ITER and in DEMO, and the expected availability targets in these two machines. The paper then discusses these approaches and targets and recommends adopting a Reliability Growth program for future fusion devices.

Electric propulsion reliability: Statistical analysis of on-orbit anomalies and comparative analysis of electric versus chemical propulsion failure rates

With a few hundred spacecraft launched to date with electric propulsion (EP), it is possible to conduct an epidemiological study of EP's on orbit reliability. The first objective of the present work was to undertake such a study and analyze EP's track record of on orbit anomalies and failures by different covariates. The second objective was to provide a comparative analysis of EP's failure rates with those of chemical propulsion. Satellite operators, manufacturers, and insurers will make reliability- and risk-informed decisions regarding the adoption and promotion of EP on board spacecraft. This work provides evidence-based support for such decisions. After a thorough data collection, 162 EP-equipped satellites launched between January 1997 and December 2015 were included in our dataset for analysis. Several statistical analyses were conducted, at the aggregate level and then with the data stratified by severity of the anomaly, by orbit type, and by EP technology. Mean Time To Anomaly (MTTA) and the distribution of the time to (minor/major) anomaly were investigated, as well as anomaly rates.The important findings in this work include the following: (1) Post-2005, EP's reliability has outperformed that of chemical propulsion; (2) Hall thrusters have robustly outperformed chemical propulsion, and they maintain a small but shrinking reliability advantage over gridded ion engines. Other results were also provided, for example the differentials in MTTA of minor and major anomalies for gridded ion engines and Hall thrusters. It was shown that: (3) Hall thrusters exhibit minor anomalies very early on orbit, which might be indicative of infant anomalies, and thus would benefit from better ground testing and acceptance procedures; (4) Strong evidence exists that EP anomalies (onset and likelihood) and orbit type are dependent, a dependence likely mediated by either the space environment or differences in thrusters duty cycles; (5) Gridded ion thrusters exhibit both infant and wear-out failures, and thus would benefit from a reliability growth program that addresses both these types of problems.

Allocation of tasks for reliability growth using multi-attribute utility

In reliability growth models in particular, and project risk management more generally, improving the reliability of a system or product is limited by constraints on cost and time. There are many possible tasks which can be carried out to identify and design out weaknesses in the system under development. This paper considers the allocation problem: which subset of tasks to undertake. While the method is applicable to project risk management generally, the work has been motivated by reliability growth programmes. We utilise a model for reliability growth, based on an efficacy matrix, developed with engineering experts in the aerospace industry. We develop a general multi-attribute utility function based on targets for cost, time on test and system reliability. The optimal subset is identified by maximising the prior expected utility. We derive conditions on the model parameters for risk aversion and loss aversion based on observed properties of preference. We give conditions for multivariate risk aversion under the general form of the utility function. The method is illustrated using an example informed by work with aerospace organisations.

Research on Temperature Stress for Contacts Reliability of Electric Connector

Temperature induced degradation is a widely recognized failure phenomenon.However, the basic mechanisms that control the onset and progression of such behavior are not well understood and are a topic of considerable interest in the electrical connector community. In this paper, the simulation analysis of temperature field on this topic are described. The distribution graph of temperature field for the electrical connectors and the highest temperature of the surface of electrical connector was achieved by analyzing a single blade/receptacle contact pair FEA model. A mathematical model was developed that related the early stage temperature levels for the connectors.Additionally, the thermal deformation caused by the temperature had little effect on the contact stress based on temperature - structure coupling field analysis for the electrical connector, the impact of temperature on the electrical connector was mainly reflected in the rate of oxidation of the metal surface. The failure physical process of the electric connector was drawn under temperature stress through the model and theory analysis for the electrical connector , and reliability growth program of the electrical connector was achieved under the temperature influence. The same transfer functions for one type of contact pair were obtained from the simulation, and the results showed that for this limited system, finite element modeling and analysis have great potential for evaluating the influence of design variations on degradation behavior.

R&M Management of a Vehicle Reliability Growth Programme

ABSTRACTMilitary vehicles are required to have high leveis of reliability in order to be fully effective, rapidly deployable, and affordable. Reliability growth programmes are typically used to achieve the desired levels of reliability. A Reliability Growth Test (RGT) is a well-structured process of finding reliability problems by testing, incorporating corrective actions resulting in the elimination of systematic failure modes leading to reliability growth.A review of Ministry of Defence (MoD) vehicle reliability growth programmes [1] concluded that only one of the five vehicle programmes examined, achieved their reliability targets as planned. This paper investigates the reasons for the failings and presents an approach which aims to mitigate the Reliability and Maintainability (R&M) programme risks, which was developed as part of an MSc dissertation entitled “Risk Management of a Reliability Growth Programme” [2].

An analytical framework for reliability growth of one-shot systems

In this paper, we introduce a new reliability growth methodology for one-shot systems that is applicable to the case where all corrective actions are implemented at the end of the current test phase. The methodology consists of four model equations for assessing: expected reliability, the expected number of failure modes observed in testing, the expected probability of discovering new failure modes, and the expected portion of system unreliability associated with repeat failure modes. These model equations provide an analytical framework for which reliability practitioners can estimate reliability improvement, address goodness-of-fit concerns, quantify programmatic risk, and assess reliability maturity of one-shot systems. A numerical example is given to illustrate the value and utility of the presented approach. This methodology is useful to program managers and reliability practitioners interested in applying the techniques above in their reliability growth program.

Médecine nucléaire De la médecine nucléaire à l'imagerie moléculaire

RAMI (Reliability, Availability, Maintainability and Inspectability) is one of the most severe challenges of Fusion Technologies, and it is probably the engineering branch where the fusion community is the least competent. This paper summarizes the RAMI statistics in existing fusion machines, the RAMI approaches adopted in ITER and in DEMO, and the expected availability targets in these two machines. The paper then discusses these approaches and targets and recommends adopting a Reliability Growth program for future fusion devices.

Simulation and comparison of reliability growth models

The Duane reliability growth model has a number of inherent limitations that make it unsuitable for monitoring reliability improvement progress. These limitations are explored and a model based on variance‐stabilizing transformation theory is explained. This model retains the ease of use while also avoiding the disadvantages of the Duane model. It represents a more useful graphical model for portraying reliability improvement at development team meetings. Computer simulations have shown that the new model provides a better fit to the data over the range of Duane slopes normally observed during a reliability growth program. The instantaneous mean time between failures (MTBF) equation for the new model is developed. Computer simulations show that its use results in higher values of instantaneous MTBF than that achieved by the Duane model. The new model also reduces the total test time for achieving a particular specified instantaneous MTBF. Finally, software failure data from an actual project illustrates the calculations and benefits of the new model.

Unreplicated experimental designs in reliability-growth programmes : Claudio Benski and Emmanuel Cabau. IEEE Transactions on Reliability, 44 (2), 199 (June 1995).

Unreplicated experimental designs in reliability-growth programmes : Claudio Benski and Emmanuel Cabau. IEEE Transactions on Reliability, 44 (2), 199 (June 1995).

Unreplicated experimental designs in reliability growth programs

Reliability-growth programs are usually implemented through repairs and modifications aimed at lengthening the system times-between-failures. The many factors that affect system performance suggest that a rational alternative to the common tweaking approach to reliability growth is experimental design techniques. However, economic and time constraints generally impose unreplicated experiments where the response is measured by the times between system failures. We show that statistical analysis of these experiments is more difficult because of this condition. Fortunately, several techniques to detect statistically significant effects in unreplicated experiments are available and can be used to identify which factors and interactions have the strongest influence in lengthening the system up-time. These techniques use a variety of principles and, expectedly, perform somewhat differently under various conditions. We present the results of the most extensive Monte Carlo benchmark ever undertaken to test the performance of these techniques. A new figure of merit is introduced, allowing a 1-quantity summary of the statistical behavior of the tested techniques. A numerical example illustrates the problem and its solution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An integrated missile reliability growth program : George Kasouf and David Weiss. Proc. a. Reliab. and Maintainab. Symp. 465 (1964)

An integrated missile reliability growth program : George Kasouf and David Weiss. Proc. a. Reliab. and Maintainab. Symp. 465 (1964)

Reliability-Growth Programmes For Undersea Communication Systems

This paper deals with the unique problems encountered when managing reliability growth programmes on expensive capital equipment components destined for use in a relatively inaccessible environment. Continuous operation of these components in predominantly non-redundant configurations is required for up to 25 years; and repair costs and/or lost revenues incurred by single failures at anytime during this period can amount to several $100 000. After a brief review of the history and philosophy of reliability growth programmes on components for coaxial cable systems, the planning, development, and implementation of reliability assurance procedures for undersea systems designed for 1.3 ?m optical transmission at 280 Mbit/s are addressed. The challenge involved in proving electro-optic and electronic components suitable for undersea optical PCM systems is not to be underestimated. Even in a relatively benign environment, these systems have specific problems with respect to operating temperatures, voltage stresses, heat dissipation factors, and the lack of escape routes for trapped contaminants. The components themselves are not only relatively new, or just emerging from the development phase, they also demand innovative reliability assessment techniques because of the inadequacy of traditional methods of accelerated testing. This paper gives an insight into some of these problems from a reliability management viewpoint. It is increasingly evident that QC and RA programme leadership cannot now, if it ever could, be accomplished without detailed knowledge of sophisticated component design.

Advanced fuel fusion application to manned space propulsion

With a few hundred spacecraft launched to date with electric propulsion (EP), it is possible to conduct an epidemiological study of EP's on orbit reliability. The first objective of the present work was to undertake such a study and analyze EP's track record of on orbit anomalies and failures by different covariates. The second objective was to provide a comparative analysis of EP's failure rates with those of chemical propulsion. Satellite operators, manufacturers, and insurers will make reliability- and risk-informed decisions regarding the adoption and promotion of EP on board spacecraft. This work provides evidence-based support for such decisions. After a thorough data collection, 162 EP-equipped satellites launched between January 1997 and December 2015 were included in our dataset for analysis. Several statistical analyses were conducted, at the aggregate level and then with the data stratified by severity of the anomaly, by orbit type, and by EP technology. Mean Time To Anomaly (MTTA) and the distribution of the time to (minor/major) anomaly were investigated, as well as anomaly rates.The important findings in this work include the following: (1) Post-2005, EP's reliability has outperformed that of chemical propulsion; (2) Hall thrusters have robustly outperformed chemical propulsion, and they maintain a small but shrinking reliability advantage over gridded ion engines. Other results were also provided, for example the differentials in MTTA of minor and major anomalies for gridded ion engines and Hall thrusters. It was shown that: (3) Hall thrusters exhibit minor anomalies very early on orbit, which might be indicative of infant anomalies, and thus would benefit from better ground testing and acceptance procedures; (4) Strong evidence exists that EP anomalies (onset and likelihood) and orbit type are dependent, a dependence likely mediated by either the space environment or differences in thrusters duty cycles; (5) Gridded ion thrusters exhibit both infant and wear-out failures, and thus would benefit from a reliability growth program that addresses both these types of problems.