【作者】 吴迪；

【导师】 庄蔚敏；

【作者基本信息】 吉林大学 ， 机械工程（车身工程）， 2019， 硕士

【摘要】 碳纤维复合材料(CFRP)强化技术可有效提高车身结构件的能量吸收和抗冲击变形能力。目前对其研究仅处于试验阶段,周期长、效率低、重复性较差,研究成本大大提高。本文重点通过数值模拟方法来研究CFRP强化管件在横向冲击载荷作用下的失效机理和吸能机制。本文建立基于连续损伤的CFRP正交各向异性本构关系,在三维Hashin失效准则的基础上,引入基于Linde失效准则的面外分层损伤失效准则共同来判定CFRP四种主要失效模式的损伤起始,选用线性连续刚度退化方案来模拟损伤演化直至材料失效。在ABAQUS中将此材料模型编写为Vumat用户子程序。进行CFRP圆管横向冲击试验,研究不同冲击能量对管件破坏形式的影响。建立CFRP圆管横向冲击模型,对比仿真与试验的试件破坏形式和载荷-时间曲线,验证模型准确性,并结合各损伤状态变量云图分析不同冲击能量工况下裂纹产生的机理。研究CFRP不同铺层形式对管件性能的影响。研究表明,当冲击能量较小时只产生环向裂纹,当冲击能量足够大时会产生环向裂纹和纵向裂纹;相较于单向铺层,[±45]3、[±45/90/0/±45]铺层形式管件承载能力和抗弯曲变形能力均较强。建立CFRP强化钢管横向冲击模型,研究强化管件的吸能特性和失效机理。CFRP强化钢管在横向冲击过程中主要由钢管吸能,占比约92.3%,其次为CFRP,占比7.36%,粘接剂吸能较少。管件变形主要是中部的局部凹陷和整体的弯曲变形,在冲击处压缩面,部分CFRP纤维断裂,轴向和环向铺层损伤模式特点不同;在冲击处拉伸面,胶层脱粘,裂纹从管件中部产生并向两端沿轴向扩展。研究CFRP纤维方向、铺层层数等对管件变形失效的影响。胶层脱粘裂纹长度与相同方向铺层层数并不成正比,引入环向铺层不仅可有效降低管件局部变形程度,而且能有效减少管件两侧产生胶层脱粘失效。基于管件承载能力、抗弯曲变形能力以及比吸能对比了钢管、CFRP管、CFRP强化钢管三种材料圆管在相同工况下的管件性能。重点针对CFRP强化钢管进行结构设计,设计了2种强化方式,研究不同强化方式对管件性能的影响规律。研究表明,粘贴CFRP轴向长度1/2L即可满足完全粘贴整个跨距段的管件性能要求;在冲击侧背面部分粘贴CFRP环向长度为3/4H、1/2H时,即可满足完全粘贴整个圆周的管件性能要求。更多还原

【Abstract】 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.更多还原