Research On Preparation And Mechanical Behavior Of Composite Folded Hybrid Sandwich Structure

An important consideration in the design of aerospace materials is the dynamic mechanical properties,and structural sandwich panels show better specific stiffness and specific strength performance in impact resistance applications.The pleated structure is a sandwich structure with great potential to replace honeycomb,and it is of great significance to study its mechanical properties.Therefore,this paper improved the design of the folded sandwich structure,and prepared the glass fiber S-shaped folded core by hot pressing.A comprehensive study on the failure mode and impact resistance of foam-filled fold hybrid sandwich panels at different positions is carried out.The influence and law of foam filling,impact position,panel material and other factors on impact performance are analyzed.The main work is as follows:First of all,in this paper,the wall corners of the traditional V-shaped folding structure are curved to obtain an S-shaped folding structure.A 1.5 mm-thick glass fiber folded structure was prepared by a hot press molding process.And the folding core is respectively bonded with the glass fiber composite material and the aluminum alloy panel to complete the preparation of the folding sandwich panel.At the same time,polyurethane foam was used to fill partially folded sandwich panels.The pleated hybrid sandwich panel of foam-filled glass fiber panels and the pleated hybrid sandwich panel of foam-filled and unfilled metal panels were prepared.Secondly,the prepared foam-filled folded sandwich panel was subjected to low-speed impact experiments according to the two positions of the folded core wave peak and wave trough.The impact response and damage mechanism of several folded sandwich panels under low-speed impact are studied,as well as the impact position on the impact resistance of the folded sandwich panels.The influence of foam filling on the impact resistance of the folded sandwich panel is discussed.Studies have shown that the damage mechanism of foam-filled folded sandwich panels is different at different impact positions.For the nodes,the folding structure is mainly caused by the crushing failure of the convex side curved wall.The filling of the foam induces premature fracture of the curved wall.For the base,the sandwich panel is mainly due to the tensile failure of the concave side curved wall,and the foam mainly supports the curved wall.Since the foam-filled provides lateral support to the folded core,the foam-filled sandwich panel has a greater load-bearing capacity.Finally,low-velocity impact experiments were carried out on foam-filled and unfilled metal panel-glass fiber pleated core hybrid sandwich panels.The influence of aluminum alloy panels on the impact resistance of the folded sandwich panel under low-speed impact,and the influence of the impact position and foam filling on the impact resistance of the folded sandwich panel are studied.Studies have shown that the impact position has a significant impact on the damage mechanism of the sandwich panel.When the punch impacts the node position of the folded sandwich panel,the upper metal plate produces radial cracks.The convex side curved wall of the folded core will produce a crush failure,while the concave side curved wall will buckle and fracture.When the punch impacts the base position of the folded sandwich panel,the upper metal plate of the folded sandwich panel will crack in the same direction as the bonding platform.The continuous crushing failure of the curved wall on the convex side of the folded core and the buckling and tensile tearing failure of the curved wall on the concave side are the main damage modes of the folded core.Filling foam has different effects on the impact resistance of different positions of the folded sandwich panel.For node impact,the foam affects the tear mode of the lower metal panel.For the impact of the base,the filling of the foam makes the folded core more prone to breakage of the top bonding surface.