Study On Fatigue Property For L-type Joint Of Composite Ship Structure

Compared with the complete composite laminated plate,the addition of core material can reduce the structural weight and increase the stiffness of the structure.In the case of comprehensive balance structure strength,stiffness and weight,the strength function of laminated plate can be effectively utilized to carry large tonnage loads.It has become a trend of the future development to build a large ship superstructure with lightweight sandwich structure.Composite connector as the main components in composite material structures is a kind of complex structure and always under static load and cyclic fatigue load combination.The designer of connector structure is usually focused on its fatigue life and damage failure.In order to make the own potential of composite materials could be fully made use of,a good method to predict fatigue life and failure damage is especially important,at the same time,it is urgent need to solve engineering problems.For the above these problems,first of all,the comprehensive summary and analysis on the loading characteristics of sandwich composite material structure have been finished.Combined with the existing fatigue life model and the hypothesis condition and application range of the gradient cumulative damage method,the cumulative damage failure process of the composite materials of local damage has been analyzed under static load and fatigue loading cycle.Integrated the local damage of material and the overall failure correlation effect of many factors,Hashin three-dimensional rule of fatigue failure analysis has been applicated to determine the composites material damage in three orthogonal directions.Finally,the material performance step degradation criterion has been put forward.Secondly,on the basis of the fatigue test,the structure fatigue creep cumulative damage process has been extended to sandwich composite plate.Acoustic emission crack detection technology has been used to record the fatigue crack propagation and cumulative damage in the period of the accumulated fatigue failure process.Relying on the sandwich composite material structure fatigue cumulative failure analysis,material performance under fatigue loads,the data law of material performance degradation criterion and cumulative damage tracking process under fatigue load,In this paper,the prediction mechanics model of structural fatigue life of sandwich composite plate has been derived.Finally,using the fatigue life prediction model of sandwich composite material plate and cumulative damage simulation path,the research results are promoted to the fatigue characteristic analysis process of the "L" sandwich composite joint.In the synchronous fatigue test,based on the principle of load and time increment,the expression of regularized fatigue life in each main direction is obtained by combining the stress-strain analysis with the least square method in cumulative damage.Considering the effect of configuration on structural stress state change,the configuration coefficient ? is introduced in the paper to correct the expressions of fatigue state variables and the expressions of residual fatigue stiffness,which improve the degradation process of fatigue performance of the "L" type connecting joint of sandwich composite material.In the end,the fatigue cumulative damage model and fatigue life prediction model of the "L" type joint are presented.