Study On Fatigue Crack Propagation Of The Al Alloy Crossbeam In High Speed Emu Carbody

As a mature light metal material,aluminum alloy has been widely used in the body of high-speed motor train units.It has been recognized as an important way to achieve the lightweight of vehicle body.At present,the A7N01-T5 aluminum alloy large extrusion profiles are used for the crossbeams of high-speed trains,and these beams are used for installation of the equipment to ensure the normal operation of vehicles.But with the increase of high-speed train,the bearing vertical dynamic load of Aluminum Alloy crossbeam is growing,some high-speed EMU crossbeams appeared fatigue crack problems,by studying fatigue crack propagation life and crack propagation path of beam structure will have significance for improving the safety and reliability of Chinese emu.In this paper,the A7N01-T5 aluminum alloy bottom crossbeam which commonly used in China’s high-speed EMU trains is selected as the object,and the fatigue crack growth test is combined with ABAQUS and NASGRO software to study the fatigue crack propagation behavior.First,the installation stress test and the actual line dynamic stress test on the bottom crossbeam of the vehicle are carried out.The installation stress test is carried out for the possible matching gap between the traction converter equipment and the crossbeam.The results show that the stress on each hanging point of the crossbeam is not the same,and the stress value is dispersive.With the increase of the simulation gap,the mounting stress at the hanging point beam is also increasing.The actual line dynamic stress data of the crossbeam in the high-speed EMU are measured,based on nCode software,the stress spectrum of each measuring point is obtained,and the equivalent stess of 12 million km is calculated.The results show that the dynamic stress level of each measuring point on the cross beam is relatively small.Then,the stress condition of the crossbeam is simplified,and some crossbeams are taken to make samples.The MTS fatigue test machine is used in the calibrate test to confirm the load magnitude of the crossbeam.In the most easily occurring crack position,the inside corner of the T groove of the beam,a crack is prefabricated and the fatigue crack propagation test of the beam specimen was carried out.Under the plane strain condition and under different vertical amplitude cyclic loading,Studying on the beam structure crack propagation path and the fatigue crack propagation life,the results show that under the same the mean load,the crack propagation life increases with the decrease of load amplitude,the crack propagation path is similar along the beam flange level extension.In ABAQUS,by using its extended finite element function,we insert the precast initial crack on the finite element model of the crossbeam specimen,and establish the actual constraint and load of the specimen to observe the crack growth.The results show that the XFEM method can effectively simulate the fatigue crack growth behavior of the beam structure,and accurately calculate the crack growth life,which provides a convenient and effective way to solve the practical problems of the engineering structure.The fatigue crack growth of crossbeam specimens is analyzed by fracture mechanics analysis software NASGRO.The results show that NASGRO software can easily calculate the fatigue crack growth life.And then consider the beam and bolt geometric mismatch,analysis the crack propagation and crack instability by NASGRO combined with ABAQUS software.Results show that the out of tolerance of the beam has great influence over the crack propagation.