Technical Study Of Opening Design And Reinforcement Of Foam Sandwich Composite Laminates

Foam-core sandwich structure is a special form of advanced composites. It has been widely used in aeronautics, astronautics, transportation and medical instruments due to its good properties such as: high specific stiffness and strength, low weight, smooth surface, excellent sound and heat insulation and good erosion resistance. Because of the checking, repairing and the pipe getting across, foam-core sandwich structure should have a series of holes. For composite laminate, holes existing will cut the fiber and cause local stress concentration. So the opening structure especially large opening structure has become an urgent problem for the application of foam-core sandwich structure.This thesis reviews the research status of the mechanical properties and shed design of foam-core sandwich structure and analyzes the problems in this area. Experimental and numerical studies were conducted to design the opening structure of sandwich panels with foam-core and carbon fabric plain weave laminated face-sheets. In particular, the following studies have been completed in this thesis:(a) According to classical laminated plate theory, the practicality of failure criterion and stiffness degradation model of composite laminated plates in the research question was studied in this paper. Based on the Hashin failure and corresponding stiffness degradation models of ABAQUS/Explicit platform, user subroutine VUMAT of three-dimensional progressive damage constitutive model has been developed.(b) Finite software ABAQUS and program VUMAT were used to analyze and compare the mechanical properties of the five kinds of opening (rectangle, square, ovale, round and oval)in the foam-core sandwich composite materials. Then determine the size and location of the reinforcement by the influence of local stress in the opening. Finally, analyze the reinforcement effect and reinforcing the efficiency by compare the simulation results of composite reinforcement and metal reinforcement to determine the most appropriate reinforcement scheme.(c) Vacuum assisted resin infusion(VARI) was used to manufacture the specimen, based on the experimental results, the failure mode of foam sandwich composite laminated plates with rectangular openings, foam sandwich composite laminated plates with oval openings and Insert layer reinforced foam core sandwich composite laminate with oval openings have been studied in this paper. Then compare the tensile strength: rectangle openings and oval openings, oval openings and oval openings with reinforcement under tensile loading. At the same time,comparisons between the analysis results and the testing results are carried out.The research shows: composite foam sandwich structure opening has significant effect on strength of the structure, the distribution of stress and strain and carrying capacity; the influence of oval openings for the foam sandwich laminated plate is relatively small. The reinforcing efficiency of composite reinforcement can significantly increase the strength of the opening in foam-core sandwich structure.