Numerical And Experimental Investigation On Energy-absorbing Characteristics Of CFRP Strengthened Thin-walled Aluminum Beams

Nowadays, it is necessary that vehicles become more environmental friendly while meet the needs of passenger safety and comfort. The former tends to better safety performance and multifunctional components, which demands for a larger vehicle mass. the latter tends to higher oil efficiency and less emission, which demands for lightweight of vehicles. The solution of this conflict is adopting new structures and materials.Carbon fiber reinforced plastic(CFRP) has shown extremely well performance in energy absorption and has been widely used for energy-absorbing components in vehicles. when combining thin-walled metal beams with CFRP, the failure modes of CFRP can be guide by progressive deformation of metal beams, which is important when designing energy absorption components such as vehicle front side rails. In this paper, based on the outstanding energy absorbing performances of metal-CFRP beams and metal beams strengthened with aluminum foam and plastics, a new structure of thin-walled aluminum beam with CFRP laminates inserted was developed. The energy-absorbing characteristics of thin-walled structures were investigated through axial impact simulations and tests.Firstly, the geometry configuration of CFRP strengthened thin-walled aluminum beams were introduced and mechanical properties of CFRP and aluminum were tested. Nodal displacements were introduced to simulate the geometry imperfection of aluminum beam. The extended Hashin failure criterion and damage evolution law was developed through user subroutine to simulate the failure progress of CFRP. Axial impact procedures of pure aluminum beam and aluminum beams strengthened with varied CFRP structures and thicknesses.Secondly, energy absorption, specific energy absorption and crash force efficiency were introduced to evaluate the energy-absorbing characteristics of pure aluminum beam and aluminum beams strengthened with varied CFRP structures and thicknesses. The progressive buckling process and load/energy-displacement curves of typical thin-walled structures were analyzed. Reliability of simulation results were proved through energy parameters and a summary was made. Numerically simulations showed that the energy absorption and specific energy absorption were improved.Finally, CFRP and aluminum beam specimen were cured based on simulation results and put into axial impact tests through a drop tower. Based on experimental results, axial collapse behavior of plain aluminum beam was analyzed along with the load-displacement curve. The influence of boundary conditions and laminate thicknesses of CFRP core on energy-absorbing characteristics of aluminum beam was analyzed based on failure mechanisms of CFRP. The progressive buckling behavior, load-displacement curves, mean crushing loads and specific energy absorption from numerical simulations were compared with those from the tests. Empirical formulas were given to predict the peak loads of CFRP strengthened thin-walled aluminum beams based on existing buckling theories of thin-walled metal beams and ultimate strength theories of CFRP.