Probability of loss of assured safety in systems with weak and strong links subject to dependent failures and random shocks

Abstract Strong link (SL) and weak link (WL) systems are important safety design of high consequence system (HCS). In the accident that continuous time-dependent stress and random shocks occur concomitantly will change the failure mode of SL and WL systems, due to the presences of shock-dependent degradation and competing failure. In this paper, the probability of loss of assured safety (PLOAS) which is the likelihood that WL system will fail to deactivate the HCS before SL system fails, is investigated in the situation that HCS is subject to both continuous stress and random shocks. Four scenarios that the continuous stress is deterministic or stochastic, and continuous stress and random shocks are independent or dependent are analyzed, when SL and WL systems suffer independent random shocks or the same random shocks. It is found that 1) PLOAS is significantly influenced by the Poisson intensity of random shocks, the failure threshold dispersivities and the shock-dependent degradation, which lead to the transform of dominate failure mode; 2) system safety might be enhanced when SL and WL suffer the same random shocks.