The Effect Of Impact Velocity And Strain Rate On The Cushioning Properties Of Hexagonal Honeycomb

The hexagonal honeycomb core,as a kind of general cellular material,has the advantages of high specified strength and stiffness,shockproof,soundproof,permeability and aeration,so it is widely applied in the field of packaging,medical science,automobile manufacturing,et al.In order to promote its application,more and more researchers have studied its static and dynamic mechanical properties,and have obtained relevant investigation results.But most of them used different compression rates to get different strain rates,and then studied their effects on the mechanical behavior of cellular materials.But the effects of impact velocity and strain rate have not been distinguished obviously.This paper investigates the influences of impact velocity and strain rate on the fundamental mechanical behavior and cushioning performance of hexagonal honeycomb core,and confirms whether the enhancement of its mechanical properties is caused by impact velocity effect or strain rate effect.The finite element software ANSYS/LS-DYNA is used to establish the reliable finite element model and the corresponding numerical analysis method for the in-plane and out-of-plane cushioning performance of hexagonal honeycomb core.A bilinear strain hardening material model is applied for the honeycomb base materials with strain rate insensitivity or strain rate sensitivity.Through the software LSPREPOSTD,the results of the calculation are processed.The corresponding deformation patterns,stress-strain and energy absorption curves corresponding to the impact process are obtained,and the dynamic peak stress,unit volume energy absorption and other numerical values are further calculated by these curves.By changing the thickness of honeycomb core in the compression direction,different strain rates were achieved at the same impact velocity.When the base material is of bilinear strain hardening and of strain rate insensitivity,the effect of strain rate on the dynamic mechanical properties of honeycomb can beignored,because the mechanical properties of hexagonal honeycomb cores are only influenced by the impact velocity.When the base material is of bilinear strain hardening and of strain rate sensitivity,the influence of strain rate on the in-plane dynamic mechanical properties and cushioning properties of hexagonal honeycomb can be still neglected.Otherwise this strain rate sensitivity affects the out-of-plane dynamic mechanical properties of hexagonal honeycomb.The inertia effect and the micro inertia effect on the in-plane and out-of-plane of the hexagonal honeycomb are studied by changing the base materials density and the impact velocity.Inertia is an important factor that leads to a significant increase in dynamic peak stress.For the hexagonal honeycomb,when the base material is insensitive to the strain rate,the influence of the micro inertia effect on the mechanical properties of the honeycomb can be ignored.When the hexagonal honeycomb base material is of bilinear strain hardening and of strain rate sensitive,the influence of ratio of cell wall thickness to edge length,expanding angle,edge length ratio and impact velocity on dynamic plateau stress and energy absorption per unit volume is studied.With increasing cell wall thickness,the dynamic plateau stress and energy absorption per unit volume of the hexagonal honeycomb increase,and they are related to ratio of cell wall thickness to edge length by power laws.With the increasing expanding angle,the dynamic peak stress and energy absorption per unit volume decrease first and then increase.When other parameters are fixed,the dynamic peak stress and energy absorption per unit volume are related to the expanding angles by quadratic curves.With the increasing edge length ratio,the dynamic peak stress and energy absorption per unit volume decrease.When the other parameters are fixed,the dynamic peak stress and energy absorption per unit volume is related to edge length ratio by the quadratic curves.The dynamic peak stress and the energy absorption per unit volume increase with the increase of the impact velocity and are linear to the square of the impact velocity.