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There are often many reasons for equipment failure. When the performance of a certain aspect drops to a certain threshold, the equipment will fail. Affected by other factors, the threshold is uncertain. A reliability model of uncertain thresholds where degradation and external shocks compete with each other is established, and the reliability of the model are evaluated according to uncertainty theory. Under three different shock types, the reliability of the equipment is obtained. The reliability with uncertain thresholds and the reliability with constants thresholds are compared. The results show that in different periods of equipment operation, the reliability of the uncertain thresholds is different with the reliability of the constants thresholds. If the threshold is simply regarded as a known constant, it will cause inaccuracies in the reliability assessment of the system, and miss the best maintenance time, causing unnecessary losses. Taking the microelectronic mechanical system as an example, the superiority of the proposed model is illustrated.

A system undergoes a failure process in which the internal degradation and external loads are independent and compete with each other. In the reliability model of competitive failure, the threshold of failure is often a dynamic process that changes with time. Based on this, this paper constructs a model in which the failure threshold is an uncertain Liu process and applies it to the competitive failure reliability process, where soft and hard failure thresholds are modeled by different Liu processes. In the absence of a large amount of failure data, uncertainty theory is used as a tool to analyze the belief reliability and mean time to failure of the system. Taking gas-insulated substation (GIS) as an example, the effect of parameters on belief reliability is analyzed, and the reliability under Liu process threshold and constants threshold is compared, which shows the validity of the prosed model.