Reliability Evaluation of CNC Machine Tools Considering Competing Failures of Fault Failure Data and Machining Accuracy Degradation Data

Traditional reliability evaluation of CNC machine tools usually considers a single failure mode of fault failure or degradation failure, or considers fault failure and degradation failure to be independent of each other. However, in the actual working conditions, fault failure and degradation failure are mutually affected, and the reliability evaluation of the competing failure models of CNC machine tools by considering the two failure modes comprehensively can get more accurate evaluation results. Therefore, this paper proposes a reliability evaluation method for CNC machine tools considering fault failure data competing with machining accuracy degradation data. A fault failure model of CNC machine tools is established based on a non-homogeneous Poisson process. The fault failure model is updated according to the different effects of each maintenance result of the failure on machining accuracy. By integrating multiple geometric errors of CNC machine tools through multi-body system theory, the amount of machining accuracy degradation is extracted. A machining accuracy degradation failure model is established using the Wiener process. Considering the correlation between fault failure and degradation failure, a competing failure model based on the Coupla function is developed for evaluating the reliability of CNC machine tools. Finally, the effectiveness of the proposed method is verified by example analysis.

Competing failure analysis of aircraft connecting-rod-type cabin door retraction mechanism with intermission considered

A novel competing failure model considering intermission is established in this paper, which is appropriate for aircraft connecting-rod-type cabin door retraction mechanism. Poisson process, Archard wear model and failure functions are integrated to describe the catastrophic failure and degradation failure of the aircraft mechanism. Intermission is introduced in the novel competing failure model after considering the actual working condition and working factors. Based on the analysis of mechanism working principle and failure characteristics, a certain aircraft connecting-rod-type cabin door retraction mechanism is studied as an example. The case results indicate that this mechanism has an unusual degradation process. Besides, the novel competing failure model with intermission is effective in engineering project.

Modeling a sequentially inspected system prone to degradation and shocks

PurposeIn certain environments, the system may not fail completely, but undergoes degradation, and the system productivity might decrease. Meanwhile, at the same time, the system may be vulnerable to shocks. A single-unit system prone to degradation and shocks is proposed in this study, and emphasis is placed upon determining its availability and cost rate.Design/methodology/approachThe considered single-unit system is expected to have three states, namely, normal, degraded and failed. As the system enters the degraded state, it is said to be partially failed. The degraded state incurs higher degradation than the normal state and is more prone to shocks. Inspections are used to determine the state and failure type of the system. Inspections are predetermined to be carried out sequentially at time I, I+aI, I+aI+a2I,… where 0 < a ≤ 1, until the detection of degradation/failure. Perfect repairs are conducted instantly on spotting the partial/complete failure. Two cases have been considered of repair taking constant times and random times.FindingsExplicit results on the reliability, availability (both point and limiting availability) and long-run average cost rate (LRACR) of a sequentially inspected single-unit system prone to degradation and shocks under constant and random repair times are given. Numerical example of an oil pipeline system is taken to clarify the acquired results.Originality/valueA sequentially inspected single-unit system prone to degradation and shock is studied unlike done previously.

Reliability analysis for dependent competing failure of harmonic drive with strength failure and stiffness degradation failure

Purpose The purpose of this paper is to analyze the dependent competing failure reliability of harmonic drive (HD) with strength failure and degradation failure. Design/methodology/approach Based on life tests and stiffness degradation experiments, Wiener process is used to establish the accelerated performance degradation model of HD. Model parameter distribution is estimated by Bayesian inference and Markov Chain Monte Carlo (MCMC) and stiffness degradation failure samples are obtained by a three-step sampling method. Combined with strength failure samples of HD, copula function is used to describe the dependence between strength failure and stiffness degradation failure. Findings Strength failure occurred earlier than degradation failure under high level accelerated condition; degradation failure occurred earlier than strength failure under medium- or low-level accelerated condition. Gumbel copula is the optimum copula function for dependence modeling of strength failure and stiffness degradation failure. Dependent competing failure reliability of HD is larger than independent competing failure reliability. Originality/value The reliability evaluation method of dependent competing failure of HD with strength failure and degradation failure is first proposed. Performance degradation experiments during accelerated life test (ALT), step-down ALT and life test under rated condition are conducted for Wiener process based step-down accelerated performance degradation modeling.

Research Progress of Proton Exchange Membrane Failure and Mitigation Strategies

Proton exchange membrane (PEM) is critical for the efficient, reliable and safe operation of proton exchange membrane fuel cells (PEMFC). The lifetime of PEM is the main factor restricting the commercialization of PEMFC. The complexity of operating conditions, such as open-circuit/idling, dynamic load and startup-shutdown under automotive conditions, on PEMFC will cause the mechanical and chemical degradation of PEM and affect the service life of PEMFC. In order to understand the degradation behavior and durability of PEM, this paper presents an overview of the degradation failure mechanism and mitigation strategies of PEM. The mechanical and chemical degradation behavior of PEM and its causes, as well as the mitigation strategies are discussed in order to give a direction for PEM design and fuel cell system control strategy. It is proposed as a primary principle in order to further develop and promote the durability of PEM, to focus on the material improvement and system engineering.

Reliability Demonstration Method for Competing Failure System

In order to improve the accuracy of reliability assessment for the system with multiple failure modes, a reliability modeling method based on the s-dependent competing risk of degradation failures and traumatic failures was proposed. A condition space model was applied to evaluate the degradation degree of system by fusing multivariate degradation data, and then Gamma process was utilized to establish the degradation failure model of system. A conditional Weibull distribution was used to establish the traumatic failure model of system. The reliability model based on dependent competing risk was established by assuming that the probability of traumatic failure depends on the degradation degree of system. An illustrative example was provided to validate the effectiveness of the proposed method.

Minimization of the volume of reliability tests of the machines under development taking into account the reliability functions for certain types of failures

A method of minimizing the volume of reliability tests for non-recoverable machines at the stage of their development by increasing the test time and using forced modes is described. Keywords tests, degradation failure, reliability, scattering parameters, random variables [email protected]