Humidity influence on crashworthiness performance of paper corrugation and honeycomb composite sandwich structure

Corrugation and honeycomb paperboards are two kinds of important and popular packaging materials worldwide for transporting and protecting goods. The paper composite sandwich structure with corrugation and honeycomb cores is an innovative energy-absorbing component for the shock protection of civilian and military products. This study is to analyze the influence of relative humidity on the drop impact response characteristics, compression deformation feature, and crashworthiness performance by experiment approach and finite element simulation. The results indicate that, under the same drop impact condition, with the increase of relative humidity from RH 70% to RH 90%, the drop impact acceleration of the composite sandwich structure increases by 5%–79%, while the impact duration decreases by 1%–14%. With the increase of honeycomb thickness in the composite sandwich structure, the peak acceleration decreases by 23%–80%, and the impact duration rises by 52%–115%. Throughout compression, higher humidity level results in the reduction of initial peak stress, impact resistance and energy absorption capacity of the composite sandwich structure. With the increase of relative humidity from RH 70% to RH 90%, the yield stress and the plastic plateau stress decrease from 2.5% to 50%, and 1.3% to 51.6%, respectively. The unit volume energy absorption gradually decreases from 7% to 59%, and the stroke efficiency increases slightly with a range from 0.2% to 4.0%. There is good agreement between the deformation patterns of simulation and experiment, however, a little discrepancy regarding the deformation mode of paper honeycomb core layer may be possibly attributable to the variation in material model with hygro-mechanical properties and parameter. The simulation and experimental stress and strain curves all exhibit four stages, yet, the initial peak stress and the densification stress obtained by simulation are higher than those of the drop experiment.