Research On Design And Mechanical Properties Of Composite Sandwich Structure Of Special-shaped Core

The composite sandwich structure has many advantages such as high specific strength,high specific modulus,high specific stiffness and fatigue resistance.Therefore,the sandwich structure is often used as a lightweight and high-strength structure to be widely used in aerospace,military facilities,engineering buildings,and Traffic track and other fields.Although the composite sandwich structure can achieve the effect of light weight and high strength through the design of the sandwich layer,the traditional preparation process is cumbersome,the molding cycle is long,the efficiency is low,and the type of production is single.At the same time,most of the structure manufacturing requires molds,and the cost is high.Therefore,the development of composite sandwich structures is limited.Additive manufacturing technology is also known as 3D printing technology.It has a high degree of design freedom.It can quickly manufacture complex structures through layer-by-layer stacking.These structures are difficult to form with traditional manufacturing techniques.Therefore,this topic uses 3D The printing technology prepares the sandwich structure of special-shaped core material composite material,and the influence of different core parameters and skin parameters on the mechanical properties of the sandwich structure is studiedIn this thesis,based on the grid structure,a special-shaped core material composite sandwich structure is designed by changing the core angle,using fused deposition(Fused Deposition Modeling,FDM)printing technology,using polylactic acid material as a 3D printing consumable through FDM3D printing The sandwich structure is prepared by the technology,the carbon fiber prepreg is molded to prepare the sandwich structure skin,and the special-shaped core material composite sandwich structure is prepared through the secondary bonding technology.Different core angles(a=60°,a=70°,a=80°,a=90°),different core heights(H=6mm,H=7mm,H=8mm,H=9mm,H=10mm),As well as the influence of different skin layer angles(0°/90° and±45°)and thickness(4 layers,6 layers,8 layers,10 layers)on the mechanical properties of the composite sandwich structure,the three-point bending of the composite sandwich structure is analyzed.Mechanical properties and failure modes under plane compression load.Simultaneously,a simulation model for the sandwich structure of special-shaped core material composite was established.After optimizing the simulation parameters,the three-point bending and flat compression performance simulation of the sandwich structure was performed,and the mechanical properties of the composite sandwich structure under three-point bending and plane compression load were analyzed.And failure mode.The main conclusions are as follows:(1)Changing the height or angle of the core can improve the strength of the composite sandwich.When the sandwich structure is subjected to bending load,when the core angle is constant,the ultimate load that the sandwich structure can bear increases with the increase in the height of the core layer,and the bending strength increases;when the height of the core layer is constant,with the core layer As the angle increases,the ultimate load that the sandwich structure can bear decreases and the bending strength decreases.The ultimate load of the sandwich structure composed of core angle ?=60° and core height H=10mm reaches 2350N,and the bending strength is 186.75MPa.The failure modes of the 3D printed special-shaped core sandwich structure under bending load are the shear failure of the core and the buckling and instability of the skin.(2)Affected by the properties of the PL A material of the core layer and 3D printing parameters,the compressive performance of the sandwich structure is mainly related to the side length of the core unit cell.The smaller the unit cell side length,the denser the core lattice per unit volume and the compression resistance.The stronger.It can be seen from the comparison between the experimental results and the simulation results that the failure mode of the 3D printed special-shaped core sandwich structure designed in this paper is the buckling instability of the core when subjected to out-of-plane compression loads(3)Three-point bending test and simulation were carried out on the 3D printed special-shaped core sandwich structure with different skin parameters(including skin fiber angle and layup thickness).The research found that the skin was laid when the fiber layup angle was 0°/90°.The thickness of the layer has little effect on the maximum bending load that the sandwich structure can withstand,and with the increase of the layer thickness,the bending strength of the structure gradually decreases;when the layer angle of the skin fiber is±45°,with the thickness of the skin as the layer thickness increases,the maximum bending load that the sandwich structure can withstand gradually increases.When the thickness of the skin layer is constant,the ultimate load of a sandwich structure with a fiber layer angle of 0°/90° is greater than that of a sandwich structure with a fiber layer angle of±45°.can be seen that the failure mode of the sandwich structure is the core shear failure.