Study On Multi-Crack Stochastic Growth Characteristics Based On Monte-Carlo Method

Continuous and effective safety assessment of civil aircraft is a key task for improving the level of flight safety.Widespread fatigue damage,as a special metal structure damage,is a serious threat to the operational safety of civil aircraft,and is the focus of civil aircraft structural safety assessment.If no actions are taken in time,the cracks will be connected in a short time when widespread fatigue damage occurs,thus causing structural failure.Therefore,it is of great engineering application value to study the growth characteristics of multiple cracks and predict the failure probability of multi-crack structures.By combining the stochastic crack growth process with the deterministic structural residual strength analysis,taking the multi-hole and multi-crack flat structure as the research object,the failure probability prediction of the multi-crack structure is realized through the Monte-Carlo method.The main research contents are as follows:Firstly,the log-normal distribution of crack initiation life distribution of multi-hole flat is obtained through fatigue test,which provides support for multi-crack initiation analysis;the static tensile test shows that the rivet hole diameter,rivet hole spacing and crack initiation angle all have certain effects on the residual strength of the structure.Secondly,with the influence of three kinds of boundary conditions taken into account,namely,crack initiation hole,adjacent hole and adjacent crack,the combined method is used to obtain the analytical expression of the stress intensity factor of multi-crack structure,and then the stochastic crack growth is simulated;based on the experimental data,the traditional residual strength prediction method is improved,and the improved net section yield criterion and the improved Irwin plastic zone linkup criterion are proposed.Finally,a multi-crack failure probability prediction process based on the Monte-Carlo method is established to predict the failure probability of multi-crack structures by combining the stochastic crack initiation and growth process with the residual strength prediction method.