The Dynamic Mechanical Behavior Of Porous Metallic Square Sandwich Panels Under Intensive Loading

With excellent mechanical and physical properties, porous metals are widely used in aerospace, transportation, military industry and construction field. They are multifunction materials which can adapt to different kinds of service environment. The sandwich structure with porous metal as core layer utilized the properties of each component which greatly widen the application range of porous metal materialsis. The mechanical behavior research of porous metal sandwich structure under quasi-static load and dynamic load has become a hot topic research both at domestic and overseas. Currently, the subject has not been formed into systematic study and there are plenty problems urgent to be solved. With the deepening of the study, the porous metal sandwich structure will play an increasingly important role in engineering application and high-tech areas.In this study, we conducted the explosive loading experiment and foam bullet impact test on typical aluminium honeycomb sandwich panels and aluminum corrugated sandwich panels. By changing the parameters such as the equivalent of explosive, distance, and the speed of the foam bullets, failure mode and the plastic dynamic response process of clamped sandwich panels under different impulse were studied. The experimental results show that the ultimate deflection of the rear panel reduced effectively by increasing height and relative density of core layer, however, this will magnify the volume and quality of the structure. Therefore, in sandwich structure design, how to balance the relationship between blast-resistance and the size and quality of sandwich structure is an important consideration. The facesheet of sandwich panels under explosion loading mainly have three failure modes, they are large plastic deformation, tear, and intrusion failure, the deformation region of core layer can be divided into three areas, which are full folded, partial folded and clamped region, obvious shear failure will occur at the boundary. In the projectile impact test, the front sheet fails by mainly local indentation and insertion, and the rear sheet shows the global deformation of "dome" form, local partial tear and even penetration. The mainly deformation area of the core laye is located in the loading area, compared with that under the explosive load, there is no obvious shear failure near the boundary. When the foam projectile has lower or higher relative density, during the impact process the more kinetic energy of projectile will transmit to the the structure which can lead to "embed" failure of sandwich panel. The instantaneous deflection of back face sheet will exceed the ultimate deflection from10%to40%under intensive dynamic load, which will produce severe harm to the protected structures and persons. Strain results indicated that under projectile impact loading the response of sandwich panels can be divided into two stages, one is foam projectile compression stage, the other is foam projectile and sabots combinded action stage.Based on the experiment, numerical simulatons were conducted to investigate the dynamic response of the sandwich panels under explosion and impact loading by using the finite element software AUTODYN. Interaction between load and structure, deformation of the core layer, energy absorption of each part and deformation mechanism of the sandwich panels were analyzed. The results show that compare with sperical shock wave, the center of sandwich panel got a more intensive load when the shock wave obtained from cylinder charge, and the plastic region first occurred in the center of panel and then move to the boundary. The honeycomb core layer buckling immediately when the blast load act on the panel, after it’s full compacted, global response started. But for corrugated core, as the thickness of core is large, the core layer almost accelerates with the front plate in the initial loading stage; buckling of core occurred in the process of front sheet getting the maximum velocity. And in the global response stage, wrinkle appeared in the direction that has a weak bending stiffness. When the sabot-foam projectile impacted the panel, accelerated impact will occurred after the sabot and the densitified foam got the same velocity. When the impact velocity of projectile is low, the influence of accelerated impact to the response of panel is small, however,with high impact velocity, this influence can’t be ignored which will do further harm to the structure. With the increase of the sheet thickness, the core height and cell thickness, the final deflection of back face sheet decreased. The energy absorption of sandwich structure depends on the loading strength, when the loading strength is small, the structure cant express its whole ability, but high loading strengh may exceed the ability of structure.Response models of sandwich panel under intensive loading are also analyzed by unsing AUTODYN. Results demonstrate that when cylinder explosive detonated in near-field, Fleck model may underestimate(core with high compression strength) or over estimate (core with low compression strength) the energy absorption by core layer and panel, thus lead to the distortion of the calculation results. The response of the sandwich panel can be distributed into four stages under foam projectile impact loading, they are foam projectile compression, core layer compression, the common motion of projectile with sandwich panel and projectile apart from panel.