Study On Casting Defects And Fracture Mechanism Of High-speed Train Gear Box Materials During Static Loading

In recent years,with the development of China's high-speed railway technology,it has been taking an enormous influence over the way people live and travel.Gear box,a key part of high-speed train,the quality and performance of a gearbox directly affect safety and reliability of railway trains.It is of great significance to study the casting defects and fracture mechanism of gear box.The effects of microstructure and defects of the gear box on crack initiation and propagation during static load fracture were studied.The main research contents of this paper include:(1)X-ray diffraction analysis(XRD),scanning electron microscopy(SEM),energy spectrum analysis(EDS)and other methods were used to study the microstructure of high-speed trains' gear box material.It is found that it is mainly composed of ?-Al matrix,secondary phase particles(Si particles,Fe-rich phase,Mg2Si)in the eutectic region,accompanied by a small amount of Al2O3 generated by oxidation during heat treatment.(2)Crack initiation and propagation of gear box material under external stress were analyzed by in-situ tensile SEM test.Under the action of applied stress,stress concentration is not difficult to occur in the pores,which leads to fracture and initiation of microcracks of the second phase particles in the eutectic region near the pores.As the applied load continues to grow,different microcracks expand and merge in the eutectic region,resulting in macroscopic cracks,which eventually lead to fracture failure.Through SEM observation and analysis of the specimen fracture,it was found that the tensile fracture morphology of gear box material was mainly quasi-cleavage surface,and the tensile fracture mechanism was transgranular brittle fracture.(3)Synchrotron radiation X-ray tomography technology was utilized to collect data of tensile specimens under different loads.Through observation and analysis of reconstructed section diagrams,3d renderings and statistical data,it can be seen that cracks appeared and spread along the region with a large volume fraction of the second phase particles.The number increased and the space volume increased with the extension of time,finally leading to fracture failure of the specimen.(4)Based on the experiment,the material parameters employed in the finite element simulation of ABAQUS were determined.Finite element simulation was used to study the stress distribution in the surrounding area under different pore shapes and its impact on crack initiation and propagation in the process of material stretching.