Simulation Study On Low-speed Lateral Impact Of CFRP Strengthened Steel Tubes

CFRP strengthening technology can effectively improve the energy absorption and anti-impact deformation ability of body structure parts.Now the technology is only in the experimental stage.Because of the long experimental period,the low efficiency and the poor repeatability,the research cost is greatly increased.Therefore,this paper focuses on the failure mechanism and energy absorption mechanism of CFRP strengthened tubes under lateral impact load by numerical simulation.The orthotropic constitutive relation based on continuous damage is selected.On the basis of three-dimensional Hashin failure criterion,an out-of-plane delamination failure criterion based on Linde failure criterion is introduced to determine the damage initiation of four main failure modes of CFRP.Linear continuous stiffness degradation scheme is used to simulate damage evolution until material failure.The material model is written as a Vumat user subroutine in ABAQUS.The transverse impact test of CFRP tubes was carried out.The effects of different collision energies on the failure modes of tubes are studied.The transverse impact model of CFRP tubes is established.The failure modes and load-time curves of the simulation and test are compared,and the accuracy of the model is verified.The mechanism of crack generation under different collision energies is analyzed by combining the nephograms of damage state variables.Finally,the influence of different layers of CFRP on the performance of tubes is studied.The results show that only circumferential cracks occur when the impact energy is small.When the impact energy is large enough,circumferential and longitudinal cracks will occur.The bearing capacity and bending deformation resistance of [+45]3 and [+45/90/0/+45]layered tubes are stronger than those of unidirectional layers.The transverse impact model of CFRP strengthened steel tubes is established to study the failure mechanism and energy absorption characteristics.The results show that the energy absorption of CFRP strengthened steel tubes is mainly from the steel tube in the process of transverse impact,accounting for 92.3%,CFRP accounted for7.36%,and the energy absorption of adhesives was less.The deformation of tubes mainly consists of local depression in the middle part and overall bending deformation.In the compression plane,some CFRP elements are deleted due to the failure of the fiber.Distribution characteristics of damage modes in longitudinal direction and circumferential direction layers are different.Some elements on the tensile surface at the impact point and on both sides of the tubes failed and were deleted.Cracks occur in the middle of the tube and propagate along the axis at both ends.The energy absorption characteristics of tubes are studied.The effects of CFRP fiber orientation and layers’ number on the deformation failure of tube were studied.The results show that the length of debonding crack is not proportional to the number of layers in the same direction.The introduction of layer along circumferential direction can not only effectively reduce the local deformation of the tube,but also effectively reduce the adhesive layer debonding failure on both sides of the tube.The performances of three kinds of tubes,namely,steel tube,CFRP tube and CFRP reinforced steel tube,under the same working conditions were compared from three aspects: bearing capacity,bending resistance and specific energy absorption.The structural design of CFRP reinforced steel tube is emphasized.Two strengthening methods were designed.The influence of different strengthening methods on the performance of tubes were studied.The results show that 1/2L of the axial length of CFRP can meet the performance requirements of the whole span.When the circumferential length of CFRP is 3/4H and 1/2H on the back part of impact side,the performance requirement of the whole circumference can be satisfied.