This paper aims to predict fatigue life and fatigue limit of fiber-reinforced ceramic-matrix composites (CMCs) with different fiber preforms, i.e. unidirectional, cross-ply, 2D-…
Abstract
Purpose
This paper aims to predict fatigue life and fatigue limit of fiber-reinforced ceramic-matrix composites (CMCs) with different fiber preforms, i.e. unidirectional, cross-ply, 2D-, 2.5D- and 3D-woven, at room and elevated temperatures.
Design/methodology/approach
Under cyclic loading, matrix multicracking and interface debonding occur upon first loading to fatigue peak stress, and the interface wear appears with increasing cycle number, leading to degradation of the interface shear stress and fibers strength. The relationships between fibers fracture, cycle number, fatigue peak stress and interface wear damage mechanism have been established based on the global load sharing (GLS) criterion. The evolution of fibers broken fraction versus cycle number curves of fiber-reinforced CMCs at room and elevated temperatures have been obtained.
Findings
The predicted fatigue life S–N curve can be divided into two regions, i.e. the Region I controlled by the degradation of interface shear stress and fibers strength and the Region II controlled by the degradation of fibers strength.
Practical/implications
The proposed approach can be used to predict the fatigue life and fatigue limit of unidirectional, cross-ply, 2D-, 2.5D- and 3D-woven CMCs under cyclic loading.
Originality/value
The fatigue damage mechanisms and fibers failure model were combined together to predict the fatigue life and fatigue limit of fiber-reinforced CMCs with different fiber preforms.
Details
Keywords
Longbiao Li, Suyi Bi and Youchao Sun
– The purpose of this paper is to develop a method to predict the multi-failure risk of aero engine in service and to evaluate the effectiveness of different corrective actions.
Abstract
Purpose
The purpose of this paper is to develop a method to predict the multi-failure risk of aero engine in service and to evaluate the effectiveness of different corrective actions.
Design/methodology/approach
The classification of failure risk level, the determination of hazard ratio and the calculation of risk factor and the risk per flight have been proposed. The multi-failure risk assessment process of aero engine has been established to predict the occurrence of failure event and assess the failure risk level. According to the history aero engine failure data, the multi-failure risk, i.e., overheat, blade wounding, pump failure, blade crack, pipe crack and combustor crack, has been predicted considering with and without corrective action. Two corrective actions, i.e., reduce the maintenance interval and redesign the failure components, were adopted to analyze the decreasing of risk level.
Findings
The multi-failure risk of aero engine with or without corrective action can be determined using the present method. The risk level of combustor crack decreases from high-risk level of 1.18×1e−9 without corrective action to acceptable risk level of 0.954×1e−9 by decreasing the maintenance interval from 1,000 to 800 h, or to 0.912×1e−9 using the redesign combustor.
Research limitations/implications
It should be noted that probability of detection during maintenance actions has not been considered in the present analysis, which would affect the failure risk level of aero engine in service.
Social implications
The method in the present analysis can be adapted to other types of failure modes which may cause significant safety or environment hazards, and used to determine the maintenance interval or choose appropriate corrective action to reduce the multi-failure risk level of aero engine.
Originality/value
The maintenance interval or appropriate corrective action can be determined using the present method to reduce the multi-failure risk level of aero engine.
Details
Keywords
Somayeh Mireh, Ahmad Khodadadi and Firoozeh Haghighi
The purpose of this paper is the reliability analysis for systems with dependent gamma degradation process and Weibull failure time.
Abstract
Purpose
The purpose of this paper is the reliability analysis for systems with dependent gamma degradation process and Weibull failure time.
Design/methodology/approach
Consider a life testing experiment in which a sample of n devices starts to operate at t=0 and the data are available on failure time and failure-evolving process on each individual, called in some contents wear or degradation. Ignoring the between performance characteristics dependency structure may lead us to different reliability estimations, while the dependency justly exists. In previous research, dependency between the degradation process and hard failure time has been studied in limited detail (special closed form expression). Thereafter, the dependency between two degradation processes with the same structure (gamma process) in a system is considered using the copula function.
Findings
The results indicate that ignoring the dependency structure may lead us to different reliability estimations while the dependency justly exists.
Originality/value
This study gives some contributions that evaluate reliability metrics with more than one failure mechanism that may not be independent and possibly follow a different distribution function. The authors have used the copula function as a basis to develop a proposal model and analysis methods. In addition, the authors discussed the identifiability of the copula. Finally, simulation data were used to review the suggested approach.