Yufeng Sun

Optimization of maintenance strategy for multi-component system subject to degradation process

The choice of maintenance strategy is a common problem in reliability engineering, and proper maintenance strategies can improve the efficiency of maintenance and save maintenance cost to some extent. There are many papers on the selection and optimization of maintenance strategies. Most of them considered the problem from the system level, and ignored the difference between different components. In fact, the maintenance process of each component is different in many aspects, such as maintenance time and cost. Therefore, it is necessary to analyze the maintenance strategy from the perspective of components. In this paper, the multi-objective optimization model of maintenance cost rate and system availability is established under the constraint of system reliability by mathematical modeling. At the end of this paper, the practicability of the model will be verified by means of numerical analysis.

Degradation process and lifetime evaluation of repairable and non-repairable systems subject to random shocks

This paper studies the degradation process of mechanical systems which are composed of multiple sub-systems which have been subjected to continuous wear and random shocks. We have developed a new mathematical model of series systems and established the function curve of each sub-systems degradation over time to evaluate the systems lifetime. Previous research mainly focused on simple non-repairable systems with multiple sub-systems which suffered from independent degradation processes, and held the view that systems can normally work only when the total degradation of each sub-system is less than the threshold level. This new model extends previous research by considering both a non-repairable system and a repairable system subject to multiple degradation processes, and these two types of systems will also fail when the degradation of the overall system is greater than the threshold level. The model is demonstrated on a specific example by means of Monte-Carlo simulation.

A novel correlative model of failure mechanisms for evaluating MEMS devices reliability

The failure behavior of MEMS can be regarded as the result of certain dependent failure mechanisms in accordance with devices internal attributes and external environment. However, the correlative effects among multiple mechanisms governing the failure process of MEMS have not been well characterized. This paper reviews significant failure mechanisms of MEMS products and proposes a new correlative model for MEMS reliability evaluation. Based on the nature of different failure mechanisms, dependent factors of these correlations are discussed and mathematical models are derived. With a case, reliability of a sort of RF switch is evaluated taking into account the failure mechanism correlative effects, and sensitivity analysis is conducted to assess the effects of the model parameters on reliability function R(t) and failure probability density function f(t).

Temperature-humidity oriented reliability prediction for electronic equipments

This paper presents a practical method of reliability prediction for electronic devices with operating temperature and relative humidity that will not always be in steady state. Since operating temperature (Tu) and relative humidity (RHu) are various in different regions, the authors use temperature probability distribution function f(Tu) to indicate the change of Tu, and humidity probability distribution function g(RHu) is used to indicate the variation of RHu. In order to estimate equipment reliability for the entire area of product usage, this paper uses these two functions to modify prediction model. The proposed method offers a way to predict the average value of failure rate for the entire area of product usage with accelerated test data and climate information.

An improved AGREE method with reliability mathematical model for complex system importance degree computation

During the system design process, there are numerous factors that should be taken into account to incorporate reliability requirements into subsystems. The AGREE method is one of the most applicable methods to achieve system reliability allocation. However, when applied to some complex systems, this traditional method may become invalid. Firstly, the allocation results may become distorted and a computation method for the degree of importance is not proposed. Generally, this method can be only used for systems in series or parallel. To address these issues, the traditional AGREE allocation method needs to be modified. This paper proposes a novel degree computational method for complex system allocation whereby the traditional AGREE method is integrated with a mathematical model of system reliability. A framework for the new reliability allocation method is described. In practice, this novel method is used for the reliability allocation of a ship power system. A sensitivity analysis was conducted across several design requirements. The allocation results were verified, demonstrating the use in practical applications.

Reliability model for load-sharing k-out-of-n system and its numerical algorithms

Dependent failure is a difficult problem, which is not easily solved by traditional reliability models. With an increase in system complexity, dependent failure becomes more and more common. So a special reliability model is needed to describe this kind of problem. A load-sharing system is a typical dependent system. The merits of reliability block diagrams (RBD) include simplicity, intuition and ease of use. This paper builds an extendable RBD model to describe k-out-of-n load-sharing systems. A mathematical reliability model is also set up. A mathematical model with exponential and other distributions is discussed. Then the general mathematic description of the model is provided. On this basis, numerical algorithms for the model are studied. The improved GAUSS quadrature method is then adopted to solve the problem of multiple indefinite integral calculations, solving the general model. Finally, a typical case is used for verifying the correctness and veracity of the model and its algorithms.

An optimization method of efficiency /economy trade-off of complex equipments based on PSO-SVM

The efficiency and economy trade-off of complex equipments is a complicated problem due to its nonlinearity and complexity. How to choose the effective and key method to find the optimal solution is a very important topic. This paper proposes a new method by combining the Particle Swarm Optimization (PSO) and the Support Vector Machines (SVM). The method, on one hand, uses SVM to seek the best balance between efficiency and economy; on the other hand, the penalty factor and kernel function parameter of SVM are optimized by PSO. A example is taken to demonstrate correctness and effectiveness of the proposed approach. The result shows that the method possesses convenience, objectivity and can get the high accuracy of optimal solution.

A solder joint crack — Characteristic impedance model based on transmission line theory

A solder joint crack - characteristic impedance model has been established in this paper. Under high frequency operational condition, signal integrity is important to the reliability of electronic products. Solder joint crack will change the characteristic impedance of transmission channel, and then will affect the signal integrity. So establishing the model of solder joint crack and characteristic impedance could connect solder joint crack with signal distortion together. It is meaningful to determining the failure threshold of the solder joint, so as to achieve the purpose of health monitoring and preventive maintenance. In this paper, the transmission line theory and reflection parameter have been analyzed. And then the physical model of damaged solder joint has been simplified. On these bases, the transmission line electrical model of the solder joint has been established. After that, the characteristic impedance of the damaged solder joint is deduced and the model of solder joint crack - characteristic impedance is obtained. In this process, both skin effect and parasitic effect have been considered. At last, the application process of this model is given. Moreover, this model is verified by experimental data and the result shows that the model is effective and the mean error is fewer.