Research On Stability And Load Carrying Capacity Of Foam-core Composite Sandwich Panels

Composite sandwich structures have many superior mechanical characteristics,making it widely applied in aerospace and other fields.In practical applications,sandwich panels are sensitive to buckling as under compression and shear loads,but they usually have good carrying capacity after buckling.The compression and shear stability experimental programs have been developed to deeply investigate the buckling behavior and failure mechanism of the sandwich panels.Further,the 3D FE models are established based on the relevant theory and specimens’ parameters,then FE analysis and verification are performed.The results can provide data support and theoretical reference for composite sandwich structural stability design.The main contents are as follows:(1)The analytical solutions of the overall stiffness and buckling load of sandwich structures are derived.A damage evolution model of composite skins is established by UMAT subroutine.The 3D Hashin criterion is selected as the damage initiation criterion,and various damage variables are introduced to describe the damage evolution.The interfaces between the composite skins and the foam core are modeled by the cohesive zone model.The quadratic damage criterion is used as the damage initiation criterion of the interface,and the quadratic energy criterion is used to model its damage propagation.(2)Experimental study and FE analysis are conducted on stability and failure mechanisms of foam core sandwich panels under compression.The results show that the panels are in the linear elastic stage and no damage occurs before buckling.The load-strain curves are nonlinear after the buckling stage.The sandwich panels contain initial bending moment due to the tapered region,and they tend to buckle at lower loads.The buckling load and load carrying capacity of the sandwich panels can be improved by the increase of the thickness of the core.Local stress concentrations cause localized damage to the tapered region.The interfaces of skins-core damage would cause local buckling and decrease carrying capacity.(3)Sandwich panels under shear load are studied experimentally and numerically.Different from the situation of compression,the shear buckling waveform appears along the tensile direction and the damage occurs mainly in its peaks and valleys since the buckling deformation causes the tensile stress and compressive stress concentrating in the peaks and valleys,respectively.