Study On Bending And Impact Resistance Of Toughened Composite Foam Sandwich Structure

With the strict requirements of the rail transit industry on the lightweight of car body,composite materials are widely used in the car body due to their excellent specific stiffness and strength.Because the composite sandwich structure is formed by resin bonding and curing,its surface core interface performance is weak,and the delamination between the panel and the core may occur during the service,which seriously affects the bearing performance of the structure.In this paper,the Kevlar short fibers were used to toughen the interface between the panel and the core,and the flexural and impact resistance properties of the short fiber reinforced composite foam sandwich structure were studied.The specific work of this paper is as follows:First of all,a corresponding simulation model was established for the three point bending test of short fiber reinforced composite foam sandwich structure in the literature.The accuracy of the test was verified by the experimental curve,and the effect of toughening parameters on the flexural properties of the sandwich panel was studied by changing the length of the short fiber and the surface density.The results show that when the fracture toughness of the toughened interface reaches a certain threshold,the peak load of the composite sandwich panel under three-point bending tends to converge,which is equivalent to the peak load of the perfectly bonded specimen;the increase of the dimensional area density of short fibers can improve the bearing capacity of the composite sandwich panel under three-point bending load,and too long or too short short-fibers will affect the toughening effect.Then,the quasi-static uniaxial compression tests of PMI foam with different densities were carried out.The mechanical properties of PMI foam with different densities were studied.The carbon fiber/PMI foam sandwich panels with or without Kevlar short fibers were prepared and subjected to low-speed impact and impact compression tests under four different impact energies,by comparing peak load,absorbing energy,dent depth and compressive strength after impact.The damage resistance and damage tolerance of Kevlar short fiber reinforced composite sandwich panels were studied.The results show that the short fiber reinforced composite sandwich panel has strong damage resistance,but has little effect on energy absorption and compressive strength after impact.Finally,the finite element models of PMI foam and composite laminates were established.The accuracy of the modeling was verified by experimental data.The damage evolution process of composites was simulated by compiling the VUMAT user subroutine,the rationality of Hashin failure criterion and the linear damage evolution method and the correctness of the subroutine were verified,and the carbon fiber reinforced with / without short fibers was established.PMI foam sandwich panel simulation model is used to analyze its internal damage.The simulation results show that the damage of the short fiber reinforced panel is smaller,and the delamination area of interface between panel and core is less.