【作者】 李娜；

【导师】 刘志明；

【作者基本信息】 北京交通大学 ， 车辆工程， 2022， 硕士

【摘要】 随着高速列车速度的不断提高,为了降低自重,越来越多的结构部件开始采用复合材料结构,复合材料凭借其高强、质轻、可设计性强等优点在轨道交通领域应用广泛。因此开展复合材料在轨道车辆上的应用研究,分析其在服役时易发的失效模式、损伤等问题,具有重要的理论意义和工程意义。本文以碳纤维增强复合材料设备舱结构为研究对象,基于有限元方法、渐进损伤分析理论及疲劳累积损伤理论对设备舱骨架、连接支架和连接接头进行静强度、疲劳强度及冲击损伤分析。主要研究内容如下:建立碳纤维增强复合材料设备舱骨架有限元模型,对设备舱裙板和底板施加7500Pa交变气动载荷,采用Hashin二维失效准则作为失效判据、基于能量耗散的二次应力损伤演化作为材料折减方案进行设备舱静强度评估。分析发现各失效模式下的失效因子均远小于1,且高应力部位主要集中在设备舱连接支架折弯附近的螺栓孔处,同时连接支架螺栓孔、折弯区域为失效起始薄弱区。根据全局模型计算结果,建立连接接头的子模型,重点研究连接支架在螺栓预紧力、铆钉干涉影响下的受力情况。分析发现连接支架在铆钉孔处应力最大,最大值为248.9MPa,螺栓预紧力和铆钉过盈装配带来的干涉对支架结构具有一定影响。根据渐进损伤分析结果,应力集中区域主要是失效区域起始点,失效位置集中在紧固件孔边和支架结构圆弧折弯等薄弱部位。连接支架在当前载荷状态未发生结构破坏,但是在应力集中的薄弱区存在局部失效。支架表面为薄弱区域,会因为载荷作用不平衡、连接结构的变形弯曲等原因加快失效的发生,所以失效因子从表面过渡到面内时会产生突变现象;本文根据复合材料的可设计性,研究了复合材料铺层角度、铺层厚度对支架承载能力的影响。本文结合冲击时结构的受载特性,开发了VUMAT子程序进行冲击过程模拟。对比不同冲击速度下连接支架的损伤,发现随着冲击速度的提高,冲击表面产生永久凹坑,不同冲击速度失效模式均以分层和横向纤维失效为主,得到凹坑深度随冲击速度的变化曲线以及失效因子随铺层变化关系。利用ISIGHT软件对连接支架进行铺层方案优化设计。研究了连接支架承载力在铺层角度、铺层厚度改变时的变化情况,分析得到了连接支架铺层设计的最优方案。对优化后的结构进行强度校核,发现新结构失效因子均小于1,满足使用要求。图75幅,表17个,参考文献111篇。更多还原

【Abstract】 Composite materials,characterised by high strength,light weight and strong designability,have gained their popularity in railway transportation.As EMUs speed up,more components are designed with composite materials to reduce the vehicle’s weight.Therefore,an investigation into how composite materials are applied in railway vehicles and their common failure mode and structural damage during operation can be significant in both a theoretical and an engineering sense.This dissertation targeted the equipment compartment made of carbon-fibrereinforced composite materials as its topic.With a synergy of FEM,progressive damage analysis,and the cumulative damage theory for fatigue,an analysis of static strength,fatigue strength and impact damage of the equipment compartment’s frame,U-shaped bracket and connector is conducted.Main contents of this dissertation are as follows:A finite element model of CFRP equipment cabin is established,and 7500 Pa alternating aerodynamic load is applied to the mass point of the skirt and bottom plate.The Quads damage based on energy dissipation is used as damage degradation criterion,the Hashin failure criterion is used as failure criterion to predict and evaluate static strength.The results show that the failure factors in every failure mode are far less than1,and the stress is mainly concentrated in the bolt hole near the bending of the connecting bracket,and the bolt hole and bending area of the connecting bracket are the weak areas of failure initiation.According to the calculation results of the global model,a sub-model of the joint is built,focusing on the stress of the joint bracket under the influence of bolt pre-tightening force and rivet interference.the maximum stress of the connecting bracket,registering248.9MPa,is found at the rivet hole.Besides,the structure of the bracket is vulnerable to bolt preload and Interference-fit riveting.In general,failure area stems from stress concentration,which is found in flimsy regions such as rivet hole and circular position of U-shaped bracket,as presented in the progressive damage analysis.Current load dose not inflict structural damage in U-shaped bracket,but render weak part of stress concentration locally failed.The surface of the support is a weak area,which will accelerate the failure due to unbalanced load,deformation and bending of the connecting structure and other reasons,so the failure factor will produce a slump phenomenon when it transitions from the surface to the inplane.Otherwise,the effect of composite layer angle and layer thickness on the bearing capacity of the U-shaped bracket is studied according to the designability of composite material.In this paper,a VUMAT subroutine is developed to simulate the impact process.It is found that with the increase of impact velocity,permanent pits are generated on the impact surface.Failure modes at different impact velocities are mainly delamination and transverse fiber failure.The variation curve of pit depth with impact velocity and the relationship of failure factor with layering are obtained.ISIGHT software is used to optimize the layering scheme of the U-shaped bracket.This paper discusses the variation of the bearing capacity of the U-shaped bracket when the layering angle and thickness change,and analyzes the optimal solution of the layering scheme of the U-shaped bracket.The static strength and fatigue strength of the optimized structure are verified,and it is found that there is no damage or crack,which meets the requirements of the test.There are 75 figures,17 tables and 111 references.更多还原