Bending,Buckling And Free Vibration Behavior Of Composite Sandwich Structure With Graded Truss Core

The composite truss core sandwich structure has potential applications in the fields of astronautics,aeronautics and ship-building,because of its high specific strength and high specific stiffness.The composite sandwich structure with graded truss core has higher payload under the concentrated and non-uniform load.Compared to the traditional truss core sandwich structure,the sequential variation of geometry of the truss core leads to the graded distribution of density and mechanical properties in the structure.Due to the features of the composite sandwich structure with graded truss core,they show advantages in bending strength,stiffness,stability and vibration properties.However,there is little thorough study about the influence of the gradient on the mechanical behavior,and the optimal gradient is needed.In this dissertation,a series of composite sandwich beam/plate with graded corrugated truss core are systematically designed.The influence of gradient design on bending,linear and nonlinear buckling and free vibration behavior of the composite corrugated truss core sandwich structure are studied by theoretical prediction,numerical simulation and experimental measurement.The optimal gradient for different loads is obtained to solve the problem of low bearing capacity caused by variation of weight and geometry.The influence mechanism of the gradient design is revealed.The main contents are as follows:Firstly,considering the deformation of the bonding area of the corrugated truss core,the equivalent shear model for single-layer and double-layer composite corrugated truss core is established by simplifying the truss core and the bonding area as beam.The composite sandwich beam with corrugated truss core is fabricated by cutting and mould-pressing method.The three-point bending tests are carried out to reveal the failure mechanism,and the theoretical model is validated.This work provides theoretical foundation for the subsequent study on mechanical behavior of the composite sandwich structure with graded corrugated truss core.The results show that the deformation of the bonding area can't be ignored.Secondly,the bending behavior of the composite sandwich beam with graded corrugated truss core is studied by theoretical model and finite element model.A series of single-layer and double-layer sandwich beams with graded corrugated truss core are designed by alternating the width of core bar along the beam.The graded discrete truss core is equivalent to continuum graded materials by presenting a gradient function.Based on the principle of minimum potential energy,the theoretical model is established to predict the bending strength and stiffness of the sandwich beam with graded corrugated truss core under concentrated and uniform load.Considering the anisotropy of the composite,a progressive damage model based on Hashin criteria is built to simulated the bending strength and failure mode.The influence of gradient on the bending strength,stiffness and failure mode of the composite corrugated truss core sandwich beam is systemically studied to obtain the optimal gradient design for both single-layer and double-layer sandwich beam.The results show that the gradient design distributes the shear stiffness and density of the truss core appropriately to improve the bending behavior.Then,the buckling,post-buckling and free vibration behavior of composite sandwich plate with graded corrugated truss core are investigated systematically.The influence mechanism of gradient design is revealed and an optimal gradient design is obtained.Considering the anisotropy of the corrugated truss core sandwich plate,a series of graded corrugated truss core sandwich plates with the same weight are designed by alternating the width of core bar along the length and width direction of the plate.On the basis of first-order shear deformation and Von Karman nonlinear deformation relation,the influence of gradient on buckling strength and natural frequency of the composite corrugated truss core sandwich plate is studied.The results show that the gradient design can improve the buckling strength and natural frequency for the corrugated truss core sandwich plate with an aspect ratio greater than 2.The gradient design solve the problem of low bearing capacity caused by the increase of the weight.This work provides important references for the design and application of the graded truss core sandwich plate.Finally,considering the nonlinear behavior and the reduction mechanical properties of composite caused by temperature variation,an incremental governing equation for nonlinear buckling of the composite sandwich structure with graded corrugated truss core is deduced based on plasticity model.The influence of gradient design on buckling strength of the composite corrugated truss core sandwich plate is studied with respect to temperature variation.The results show that ignoring the plastic deformation will overestimate the buckling strength of the sandwich plate under high temperature.The gradient design can improve the buckling strength of the composite corrugated truss core sandwich plate with aspect ratio greater than 1.5 and relative density of core greater than 0.0993 before the glass transition temperature.