Study On Characteristics And Applications Of On-track Load Of Welded Bogie Frame

The increasing needs of society promoted the transport capacity of railway vehicles, the quantity of new products of rail vehicles, and made the operational security issues of the vehicles face the unprecedented challenges. Passenger vehicles normally use welded frame, which is the main frame structure of bogie. The fatigue strength of the frame is directly related to the operation safety of the vehicle, and loads are the basis for fatigue strength analysis. However, a large number of on-track tests showed that dynamic load actions of the bogie frame on actual running lines had large difference from the prescribed standards, such as UIC, JIS, TB, etc. Therefore the bogie frame fatigue strength assessment results according to standards might deviate from the fatigue damage in practical application conditions.Aiming at studying the on-track loads characteristics of welded bogie frame in practical application, and establishing the relationship between on-track loads and structural fatigue damage, this thesis launched research on many respects, such as on-track loads test of welded bogie frame, characteristic analysis of on-track loads, fatigue damage assessment of bogie frame in operational condition, formation method of bench test load spectrum based on on-track loads, influence degree assessment of each on-track load to the fatigue damage of bogie frame, etc. All the researches above were supported by the Natural Science Found:"Formation method and experimental verification of structural damage consistency load spectrum of high speed train bogie". The main works of this thesis are as follows:(1) The load identification theories of mode decomposition method, inverse pseudo excitation method, load time domain integral method, and quasi-static method were studied and the limitations of these methods in load identification applications of bogie frame were discussed. For the first time, stress response transfer function method was studied to apply in the identification of the bogie frame loads, and the accuracy of this method was verified by cantilever test. The results showed that the accuracy could be improved by reasonable measuring point selection, signal noise removal, and smooth technology transfer function processing. Then the on-track tested load and stress data was used to verify the feasibility of the stress response transfer function method to apply in bogie frame load identification. The results showed that this method had a high accuracy and good engineering application value. Based on the study of the load identification methods, the bogie frame on-track loads test plan of CRH380BJ type EMU was fixed.(2) The loads data of CRH380BJ type EMU motor bogie frame was obtained by on-track test, and the response characteristics of the loads under different conditions were analyzed. Through the research, the repeatability of the bogie frame loads, the "reverse" consistency of the vertical loads, etc. were found as the important features of on-track loads. A new method was used to reconstruct vertical loads based on the force balance principle, and the application result showed that the vertical loads were mainly composed of roll and nod ingredients. Compared with the traditional method, the new one can realize the conversion between original loads and reformed loads. The relationship between different loads of the bogie frame was found after the vertical load reconstruction, and the "load couple" was used to represent this relationship for the first time. This representation type can retain more characteristic of the on-track loads in a damage consistency calibration, and provide an important experiment basis for the further bench test load spectrum formation.(3)According to the randomness feature of equivalent stress amplitude and the less difference feature of welded bogie frame on-track loads in the same condition, a modified method based on the error analysis theory, S-N curve and Miner guidelines was proposed to improve the mathematical model used to calculate the consistency damage equivalent stress amplitude. This method considered that the equivalent stress amplitude obey normal distribution, which was verified by on-track tested data of dynamic, and revealed the variation rules of the equivalent stress amplitude of welded bogie frame. This modified method was used in several engineering applications, such as equivalent stress amplitude evaluation of the bogie frame, fatigue damage injury prediction of the bogie frame in whole service life, and optimization of the on-track test program. And these practical applications showed that the modified method provided a strong technical support for the structural fatigue evaluation, on-track test research program, etc. in future.(4)According to the frequency characteristic of the bench test equipment in working condition and the spectral property of the on-track loads of welded bogie frame, a method was proposed to establish the bench test load spectrum of the welded bogie frame based on the low-frequency part of on-track loads according to the consistency fatigue damage principle of the key parts of the frame. The load spectrum established by this method could retain as much features of the on-track loads as possible, and had obvious advantages in assessment veracity compared to current standard. The damage consistency bench test load spectrum of CRH380BJ type EMU bogie frame was established by the method proposed, which covered the fatigue damage of all the focused test points, and retained as much on-track load features as possible.(5)To compare the influence of on-track loads on the fatigue damage of welded bogie frame, a method was proposed. Firstly, the dynamic stress response of each on-track load in the response coupling area was extracted. Secondly, the equivalent stress amplitude ratio or fatigue damage ratio under load-full and the load-missing conditions of each on-track load was calculated. Thirdly, the influence degree of each on-track load was compared quantitatively by the ratios calculated. This method offers a new idea to further analyze the on-track loads. It was also applied in the tested data analysis of high-speed EMU and metro vehicle bogie frame, and was verified to have a good prospect in engineering applications.