A novel safety life analysis method based on equivalent constraint transformation

Equivalent constraint method (ECM) is an efficient method for safety life analysis under target time-dependent failure possibility (TDFP) constraint. However, the efficiency of existing ECM still needs to be improved for problems with complex performance functions. In this paper, an efficient method based on equivalent constraint and sequential Kriging model with fuzzy simulation (EC-SK-FS) is proposed to improve the efficiency of solving safety life. In EC-SK-FS, the TDFP constraint is first equivalently transformed into performance function constraint with respect to target TDFP, which can avoid performance function evaluations under unnecessary membership level. Second, based on the EC of the lower bound of extremum performance function being equal to zero, the traditional dichotomy method is embedded to search for the safety life. For each possible life searched by dichotomy, the Kriging model of time-dependent performance function is sequentially trained in the corresponding candidate sample pool (CSP) for estimating the lower bound of extremum performance function, in which a new stopping criterion is established to improve the efficiency of training Kriging model. The new stopping criterion only requires at least one failure sample point accurately identified by the current Kriging model, which reduces the computational cost while ensuring the accuracy of estimating the lower bound of extremum performance function. In addition, the strategy of reducing CSP is adopted to further improve the efficiency of the proposed method. Compared with the existing ECM, the results of examples fully prove that the proposed EC-SK-FS method is more efficient under acceptable accuracy.