The degradation of braking torque in elevator block brakes, resulting from the coupled effects of brake shoe wear and spring stress relaxation, poses a critical challenge to operational safety. In this study, a reliability model is developed to characterize the joint degradation behavior of these two mechanisms. The monotonic and irreversible processes of wear and stress relaxation are modeled using two independent gamma processes, and their combined effect on braking force is formulated based on Hooke’s law. The relationship between braking force and braking torque is established through experimental identification. Model parameters are estimated and validated using degradation data obtained from field inspections. The results indicate that the reliability evolution exhibits a two-stage characteristic, consisting of an initial stable phase with high reliability (approximately 45 months), followed by a rapid degradation phase. The reliable life, defined as the duration corresponding to a reliability level exceeding 0.9, is approximately 50 months. Sensitivity analysis demonstrates that the equivalent friction coefficient (as represented in the torque–force relationship) and the initial spring stiffness are the dominant factors affecting the service life. The proposed model provides a quantitative framework for reliability assessment and offers theoretical support for condition-based maintenance and life prediction of elevator block brake systems.
Wei et al. (Mon,) studied this question.