Failure Simulation Of Stitched Composite Sandwich Panel Under Mechanical/Thermal Environment

As a typical integrated thermal protection structure,stitched composite sandwich panel(SCSP)is a key subsystem of high-speed aircraft.During its service,it is often subjected to dynamic loads such as vibration and noise.It will produce typical tensile and compressive behavior for the sandwich panel structure.At the same time,due to the friction of air,a large amount of heat will be generated on the surface of the aircraft,resulting in thermal protection of the aircraft surface.The protective structure produces thermal deformation.In order to study the failure behavior of stitched composite sandwich panels under mechanical/thermal loads,a simulation study on the failure behavior of stitched composite sandwich panels under normal/high temperature out-ofplane tension and compression loads was carried out in this paper.The specific work is as follows:(1)The experimental study on the basic mechanical properties of aerogel core layer was carried out.The mechanical behavior of aerogels with different thermal loading under different loading directions is analyzed,and the elastic modulus of compression and stretch under different directions is obtained.The constitutive relationship of stress and strain under external compression load is fitted.The results showed that aerogels did not fail when they were subjected to out of plane compression,and the specimens became thinner along the thickness direction.The stress-strain curves showed a nonlinear relationship.When in plane compression,aerogels showed shear fracture along the loading direction at 40° When out of plane tension,aerogels occurred interlaminar dislocation fracture along thickness direction,and aerogel strength was only 0.028 MPa.(2)The basic mechanical behavior and failure of stitched composite sandwich panels under static loads were studied.Based on numerical analysis method,the failure subprogram of each part of stitched composite sandwich panels was compiled.The failure behavior of stitched composite sandwich panels under out-of-plane compression and tension loads was simulated by taking the overall structure and local structure as the research objects.The results show that the failure modes of suture in stitched composite sandwich panels are the fracture failure along the out-of-plane suture part and the tensile failure in the contact part between the suture and the panel;the local structure simulation can more accurately characterize the stress distribution in the sandwich panels and has higher calculation efficiency.(3)The basic mechanical behavior and failure analysis of stitched composite sandwich panels under mechanical/thermal loads are carried out.The failure behaviors of out-of-plane tension and compression under mechanical/thermal loads are simulated with the whole structure and local structure as research objects,and the results of heat conduction are given.The results show that under the mechanical/thermal load,the failure mode of stitched composite sandwich panel structure is the fracture failure along the out of plane suture part,and the tensile failure of the panel at the contact with the stitches,but the panel is mainly failure on the upper panel.Under the high temperature environment,the aerogel core layer plays a good role in thermal insulation.