Mechanical Behavior Of Honeycombs And Sandwich Panels Under Impact Loading

Due to their superior specific strength and stiffness,excellent performance in designability and energy absorption,honeycombs and honeycomb sandwich structures have been widely used in many engineering industries,such as aerospace,transportation and personal protective equipment,etc.Honeycombs and sandwich structures are susceptible to various impact loadings during the period of their serves.Mechanical behavior of honeycombs under combined compression-shear loadings,crushing of hierarchical tubes and hierarchical honeycombs,drop-weight impact of honeycomb sandwich panels are respectively investigated.Relationship between mechanical properties and structural characteristics,crushing behaviors and energy absorption mechanisms of honeycombs and honeycomb sandwich structures under impact loadings are explored by means of experimental,theoretical and numerical methods.A combined compression-shear crushing test system is proposed,which can measure the compression and shear forces individually.A series of combined compression-shear crushing tests are conducted on hexagonal honeycombs.Two deformation modes are identified during the tests,deforming cell walls non-inclined and inclined.Deformation modes have significant effect on crushing responses,specifically,negative shear forces being observed for the inclined mode.Loading angles and loading planes influence deformation modes,crushing responses and plateau stresses differently.Initial yield surface is estimated and is found to take the form of an ellipse envelop in the stress space.Two types of hierarchical circular tubes are constructed by replacing the wall of a single cell circular tube fully or partially with micro-cell tubes.Investigations on crushing behaviors and energy absorption properties are proposed subsequently.Relationships between the hierarchical parameters,i.e.size and number of micro-cell tubes,and deformation modes,mean crushing forces and energy absorption are explored.It is indicated that crashworthiness and energy absorption capacity can be highly improved by selecting suitable hierarchical parameters.Analytical models are established based on the Super Folding Element Method to predict the mean crushing forces of self-similar vertex-based hierarchical honeycombs.Effect of hierarchical orders on the mean crushing forces is specifically discussed.Results show that hierarchy can significantly improve the out-of-plane crashworthiness of honeycombs.When the hierarchical order is sufficiently large,the amplification of the mean crushing force from one generation to the next approaches a constant,which is?_n?1.26.Non-self-similar vertex-based hierarchical honeycombs are constructed by replacing vertexes of a hexagonal honeycomb with triangular micro-lattices.Numerical models are established to explore the in-plane and out-of-plane crushing behaviors of the honeycombs.During which,two cell models and two corresponding modified cell models are proposed for out-of-plane crushing analysis.Results show that hierarchy affects in-plane deformation significantly but has little effect on out-of-plane deformation.Non-self-similar hierarchy not always improve the crashworthiness of honeycombs,and the improvement performs better in in-plane than out-of-plane.Experiments and numerical analysis are conducted on drop-weight impact of honeycomb sandwich panels.Indentation characteristics and energy absorption properties are investigated.Analytical model and modified energy balance model are established to explore the deformation mode,generation of indentation and energy dissipation mechanisms.Results show that honeycomb sandwich panels performs excellent in energy absorption.Most of the impact energy is absorbed and dissipated by the top facesheet and core as plastic dissipation energy.Impact energy obtained through changing mass of the impactor or impact velocity have different influence on indentation and energy absorption.Semi-empirical models are overfitted to estimate the residual dent depth and energy absorbed during a drop-weight impact event on a honeycomb sandwich panel.