Study On The Stitching Process And Properties Of Foam Sandwich Composites

Foam core sandwich composites have the advantages of light weight,heat insulation,shockproof,sound insulation,heat preservation,etc.Currently,the foam core sandwich composites are widely used in ships,automobiles,aerospace and other fields.However,the interface stress concentration usually occurs due to the anisotropy of the composite material and the different mechanical properties of the face/core material.The immature manufacturing process and inhomogeneity of the material always cause the residual stress and initial defect.These will lead to the interfacial delamination and the cracking of the foam core during service.The interfacial delamination and cracking will seriously affect the bearing capacity of the structure,and sometimes lead to premature failure and damage of the integral structure,which seriously affects the mechanical properties of the structure.Therefore,it is great significance to strengthen foam core sandwich composites by stitching method in order to expand the application range of sandwich composites.In this paper,the interfacial fracture process of stitched foam sandwich composites is studied by means of combining experiment and simulation.The specific work is as follows:Firstly,a set of stitching auxiliary device for foam core sandwich composite was designed and built.The preform of stitched foam core sandwich composite material was prepared.The VARI molding technology was used to manufacture the stitched foam core sandwich composite material,and the influence of different molding processes on the specimen quality and the demoulding process were discussed.Secondly,in order to study the fracture behavior of meso-fiber column in the stitched foam sandwich composites,the ITT specimen containing a single stitch column was prepared.The failure process of specimen was analyzed.The influence of thread thickness on the failure process of specimen was studied.The failure process of the resin deficient specimen was discussed,and compared with the resin sufficient specimen.Then,the Asymmetric Double Cantilever Beam(ADCB)specimen of the stitched foam core sandwich composites was prepared,and the failure process is compared between the stitched specimen and the unstitched specimen.The effects of process parameters such as thread thickness,stitching angle,stitching spacing on the interfacial fracture behavior of stitched foam sandwich composites were discussed.Finally,based on the above experimental results,the finite element model of the ADCB was established in ABAQUS.The effects of thread thickness and stitching spacing on the crack propagation process were studied by using the Extended Finite Element Method(XFEM).The research results will provide theoretical and experimental basis for the stitching process,failure mechanism and simulation analysis of foam core sandwich composites.