Failure Study On Low Velocity Impact And Compression Of Composite Sandwich Panels

The sandwich panel is a multi-layer structure in which a composite laminate is bonded to a low-density core material,and the advantages of the two are combined to provide good bending and compression stability when subjected to out-of-plane and in-plane loads.However,when the sandwich panel is subjected to foreign matter impact,particularly at low speed impact,the impact damage greatly reduces the residual strength and rigidity of the structure.Therefore,it is necessary to study the mechanical behavior of composite sandwich panels under low-velocity impact,especially the compression failure behavior after impact.Based on ABAQUS finite element software,this paper carried out the sandwich panel and low-speed impact test and compression after impact experiment.At the same time,the cohesive element was used to simulate the debonding failure between the panel and the sandwich.The damage of the panel after impact and compression after impact was discussed.In addition,the paper also carried out low-speed impact experiments and numerical analysis of hat-shaped stiffened plates.Firstly,low-velocity impact experiments and numerical simulations of different energy were carried out on the foam sandwich panels.The impact damage morphology,damage size and damage distribution were obtained through experiments.The effects of impact energy and core type on the damage were analyzed.It was found that the depth and area of the pit increase of the impact energy.The impact resistance of the P foam sandwich panel was better than that of the R foam,and the absorbed impact energy was 23.51% and 21.73%,respectively.In the low-velocity impact process,the foam mainly plays the role of absorbing energy in the structure,and the outer panel acts as the main bearing component of the sandwich,directly obtaining the impact force and causing large-area damage.At the point of contact with the impact head,the shape of the damage is generally elliptical,similar to the damage shape in the experiment.Secondly,the compression after impact experiment and numerical simulation of the foam sandwich panel are carried out.Compared to the P foam sandwich structure,the R foam sandwich structure has a lower overall load carrying capacity.Electrical and optical measurements show that no local buckling occurs during axial compression.The numerical simulation results are in good agreement with the experiment results,and the residual compressive strength of the specimen after impact shows a different degree of reduction.The failure mechanism of foam sandwich panel compression after impact is that the impact pit expands laterally in the compression process,and the width remains basically unchanged in the expansion process.When the final specimen is damaged,the damage is almost throughout the whole panel.In the process of pit expansion,the panel was subjected to greater transverse bending,which exceeded the maximum compressive strain of the panel material in the loading direction,and eventually led to the panel fracture and the loss of bearing capacity of the entire structure.Finally,low-velocity impact experiments and numerical simulations were performed on the stiffened panels.The damage zone is round when impacted in the foam core region,and the diamond shape is broken when impacted in the non-foam region.At the same energy,the stiffened plate absorbed about 39% of the impact energy in the foam core area,which was lower than that in the non-foam core area.The failure mode of the wall plate is the peanut shell distribution with the impact point as the symmetrical center.In the foam core impact failure mode for the impact point along ±45°for symmetric center symmetric distribution,stress wave is transmitted to the ribs in a wide range.