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As basic components, springs are widely used in aerospace, mechanical and electrical fields. Due to their various functions such as buffer, energy storage and polarization, springs are playing an increasingly important role in various fields. In the long-term storage process, due to environmental factors such as temperature, the spring will be degraded, manifested as the stress relaxation phenomenon, and the process is that as the storage time increases, the elasticity of the spring slowly declines, and the load capacity slowly decreases, the torque changes while the spring is released. In this paper, the variation of spring torque under different stress is taken as the degradation of the spring, and the reliability analysis of the springs' experimental data based on the degradation distribution is analyzed by using the stochastic process degradation modeling method and the generalized degenerate modeling method respectively. The advantages and disadvantages of different methods will be given, it provides a reliable and effective way to analyze the degradation process of springs.

This paper proposed a design method for force-limited vibration testing conditions based on the complex two degrees of freedom system (TDFS) model. This method adopted the dynamic sub-structure theory to calculate the modal effective mass and the residual mass of the test article structure and the supporting structure, determined the specific parameters of the complex TDFS model in different bands depending on their distributions. The force spectrum and the acceleration spectrum of the contact surface between test article and supporting structure were defined with the excitation conditions of supporting structure. On the basis of the envelope, the force limited vibration test profile was obtained. Simulation results showed that the force-limited vibration testing conditions given by this method reflect the vibration environment of the test article much more realistically compared to the conservative testing conditions of the traditional acceleration-controlled vibration test.

Proportional hazards model is introduced into dealing with accelerated degradation test data, and a model based on proportional degradation hazards model (PDHM) is proposed, the only assumption is that the logarithm of the degradation hazard function is a linear function of the stress covariates. The PDHM is established with degradation data, then the probability density function and Likelihood function of the model are derived, and maximum likelihood estimate (MLE) and Newton-Raphson method are utilized to estimate the model parameters. According to the relationship between failure threshold and degradation measure, the reliability model of the product is established, with which the reliability is assessed. The model in this paper is demonstrated correct and valid by assessing the reliability of percent increase in resistance over time of carbon-film resistors.