Research On The Strength Of Connection Joints In Composite Equipment Compartment

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.