Simulation Research Of Locomotive Carbody Structure Fatigue Based On Multibody Dynamics And Finite Element Method

Nowadays,the research of foreign and domestic locomotive and vehicle carbody structure fatigue strength and analysis under dynamical loads is almost blank. The main reason may be that the car body structure is one large complex structure and its durability test is too expensive. If only imposing constant amplitude load spectra and static load test results to evaluation of fatigue strength of the whole carbody structure, it maybe result in serious problems, although the method is simple. Because stochastic variable dynamic loads cause the service locomotive carbody structure fatigue failure. With the more higher vehicle velocities running on the real railway lines, the main research trend in modern locomotive vehicle industry is to produce safe and reliabilities and lightweight carbody structure. So research of car-body structure fatigue life evaluation method has become one of most important tasks and research projects. This paper is developed one system research method to perform carbody structure fatigue life simulation with Multibody System (MBS) dynamics and Finite Element Analysis (FEA) by absorbing some reference newer algorithm.Obviously, the research scope is pay attention to MBS (Multibody System), FEA (Finite Element Analysis) and structure fatigue life prediction. The detail processes include: obtaining the track irregularities excitation through time-frequency transform technology of vehicle excited spectra; Rigid and flexible bodies hybrid modeling and simulation of full locomotive system with SIMPACK (include rigid carbody and flexible one); Stress analysis of carbody structure fatigue life evaluation with ANSYS (Mode analysis and substructure analysis); Fatigue life evaluation with material S-N curve and fatigue damage summary theory.When dynamic behavior of locomotive system is analyzed with MBS, It is very important how to transform track spatial spectra to time domain track excited signal and guarantee the main character describing excited spectra to be correct, such as frequency, phase and amplitude. On the basis of James Andrew terrain PSD technology, one method frequency-time transform technology for excited spectra is constructed in this paper; the problem of spectral distribution characters is solved successfully. And it is useful for the locomotive system dynamic simulation.Multibody dynamic simulation with analysis software SIMPACK is carried out to the full locomotive system, the anti-fatigue character of carbody can be understood in depth. And it can be also analyzed to find structure dynamic character and the universal influence law of the carbody structure fatigue. The suspension dynamic parameter and structure optimization can be performed and finally the carbody anti-fatigue character can be improved. The typical case in operating condition of locomotive has been designed to perform multibody dynamics simulation, which include straight running, curve passing and traction etc. The 35 load histories has been calculated here of typical case in MBS, which include forces, velocities, accelerate and angular velocities etc. And in order to take account of the implementation of elastic carbody, the interface program FEMBS between finite element analysis codes and SIMPACK is used here to generate input data for flexible bodies for MBS simulation.The starting point for carbody fatigue analysis is the response of the carbody structure, which is usually expressed as a stress or strain time history. Some dynamic stress method is discussed here in time domain and frequency domain, and the idea based on MBS-FEM method to obtain dynamic stress is introduced here in detail. The detail method is that structural quasi-static stress analysis with ANSYS would be required and the stress influence coefficient (SIC) of 35 typical load case are multiplied with the load histories from MBS to obtain the total dynamic stress of carbody. And mode analysis and sub-structure analysis are also performed here.Finally, with rainflow matrix and Markov chain theory, S-N curve, structure dynamic stress, and Palmgren-Miner damage summary theory, carbody structure fatigue life can be evaluated based on WAFO technology. Safety factor analysis based on stress can be performed to obtain the damage distribution and stress safety factor of carbody structure. These results validity are also compared with the test results if real line locomotive dynamic stress. The comparison proves the MBS-FEM method to evaluate the carbody structure is correct.In conclusion, this paper introduces the method based on MBS-FEM to evaluate carbody structure fatigue. This integrated method can be used in early stage in structure design to predict correctly carbody structure property. It is beneficial to understand the complex structure fatigue life prediction and support the theory base for carbody structure durability validity test.