Ultimate Strength Analysis For Marine Composite Sandwich Frame Plate

Light-weight is a major trend in the development of modern engineering,which makes the advanced composite materials widely used in the field of ships.Sandwich structures,as a special form among them,have been responsible for the main load in the ship owing to their light quality,high flexural rigidity and strength.Nevertheless,composite materials often exhibit brittle failures that tend to result in the loss of structural load-carrying capacity and even induce the collapse of structure with the propagation of damage,such as matrix cracks,fiber breaking,fiber/matrix shear failures and delaminating.Therefore,in order to improve the design performance of the sandwich structure to ensure the safety and economy,it is the essential significance to carry out the initial exploration for the ultimate strength of this structure.In the present paper,firstly,a simplified Zig-zag model was established based on laminate theories for buckling analysis of composite sandwich plate.Secondly,the subroutine about a progressive failure analysis was developed to predicte the damage mechanism and ultimate strength of sandwihc plate.Finally,an initial exploration was performed for the sandwich frame plates when these structural forms were applied to the ship structures.Specific works were mainly included as follows:(1)It was mainly studied by three laminate theories that the effect of ply scheme(ply orientation,stacking ply sequence)on critical load.Then,a simplified Zig-zag model was presented based on laminate theories.First-order shear deformation theory was used for face sheets,and third-order shear deformation theory from Reddy was adopted for core,respectively.Continuity conditions for displacements and transverse shear stresses at the interfaces were satisfied.(2)According to the kinematic equation derived from the present theory,solving program was developed by MATLAB for buckling analysis of composite sandwich plate.The comparison of results with the existing results could verify the accuracy of this theory.Subsequently,the influences of design parameters(the thickness of face-sheet and core,load ratio,ply scheme)on critical load were studied.Meanwhile,finite element analysis was performed as a comparison.(3)A subroutine,including the stress transformation relationship,Hashin criterion and degredation model,is coded using the ANSYS-APDL.This program took into account matrix tensile and compressive failure,fiber tensile and compressive failure and second failure for predicting the damage mechanism and final failure strength of composite sandwich plate,and the effects of design parameters on ultimate strength were obtained.(4)In order to explore the application of sandwich structure in ships,a progressive failure analysis was performed for sandwich frame plate to determine its failure initiation,propagation and ultimate strength.Then,it was studies on the sandwich frame plate subjected to combined loads.