Mechanical Responses And Energy Absorption Characteristics Of GF/PP Hierarchical Honeycomb Structures

Composite energy absorbing components are widely applied in engineering fields such as aerospace,navigation,and transportation.The key in energy absorption design is to reduce the initial peak load and improve the plateau load-carrying capacity to achieve high crushing force efficiency and energy absorption.Conventional designs with the brittleness of thermoset composite and high sensitivity of local defects go against effective prevention and high energy absorption.In contrast,thermoplastic composites have the advantages of high damage tolerance,a short manufacturing cycle,recycling,and reprocessing.Hierarchical design can enhance structural toughness and stability under low density,which is a primary means of losing structural weight and improving their performance.Based on the hierarchical thermoplastic composite,a reasonable design method for energy-absorbing is of great scientific value and engineering significance.This paper studies the static/dynamic mechanical behaviors and energy absorption of the continuous glass fiber reinforced polypropylene composite(GF/PP)hierarchical honeycomb lattice structures through analytical design,numerical simulation,and experimental tests.The specific work is as follows:Firstly,design methods and effective fabrication techniques of GF/PP hierarchical honeycomb lattice structures were put forward.The failure analysis model were established and failure maps drawn,which revealed the mechanism of the technique on equivalent stiffness,failure mode,and load-carrying capacity.Structural failure modes,critical load,and compression load-displacement response curves were predicted.The sandwich facesheet and structural gradient were proposed to reduce initial peak load and achieve high crushing force efficiency,which is increased to above 0.8.Secondly,the mechanical behavior and repeated energy absorption property of composite hierarchical cylindrical structures under multiple/cyclic compression were studied.The deformation processes,failure responses and energy absorption of each load cycle under cyclic compression were studied by multiple compressive tests of the thermoplastic composite hierarchical cylindrical structure(TCHCS).The mechanism of the technique on deformation recovery and repeated energy absorption were revealed.A prediction model on energy absorption of the cylindrical structure was derived according to the energy conservation and simplified super folding theory.Finally,the low-velocity impact behaviors and dynamic crushing responses of thermoplastic composite hierarchical structures were studied,taking TCHCS as the research object.Drop hammer impacting tests and hydraulic dynamic crushing tests were performed on the mechanical responses of TCHCS under varying impact energy and crushing rates,respectively.Low-velocity impact time history responses like load-time curves,response time,failure and damage modes,and fracture characteristics were discussed.Crushing modes,crack behavior,and energy absorption mechanism of medium strain rate crushing were explored.The loading rate effect on structure failure modes and the deformation mode transformation range of low-velocity impact and dynamic crushing were discussed with and without strain rate effect of core material and derived a mean crushing force prediction model to cor-validated the effect.