Abstract
Some metro vehicle lifeguard structure cracking emerged during operation, and the reason is due to resonance. In order to simulate the dynamic stress accurately in resonance state, the formula for calculating the dynamic stress under multi-load condition was deduced based on structural dynamics mechanics. During the dynamic stress simulation, firstly, the frequency response function (FRF) of each external load was calculated, which including the phase information. Then, the method was based on Fast Fourier Transform (FFT) to get the frequency domain with real and imaginary part of each external load rather than power spectrum density (PSD) calculation, avoiding loss of the phase information due to PSD method. Finally, the dynamic stress frequency domain data could be calculated by FFT results and FRFs. Based on above, the dynamic stress time history could be acquired by Inverse FFT (IFFT) of stress frequency domain data, and the stress simulation method was verified by the line test result. Compared with the conventional stress PSD calculation method, the method in this paper can retain the phase information of the each external load. Meanwhile, the conventional stress simulation method based on PSD could not get satisfactory result.
Highlights
2.1 Research backgroundlifeguard structure cracking emerged in metro vehicles
Quasi-static superposition method [2] is suitable when the external load frequency is much lower than the structural first elastic modal frequency, but this method is not suitable for dynamic stress prediction when structure is under resonance condition [1]
The external load frequency and amplitude is the system input, and the dynamic stress is predicted according to structure inherent properties
Summary
In dynamic theory, when the frequency of external load on structure is close to the structural mode frequency, and the external load direction is the same with the mode direction at the external load point, it will cause structural resonance which may lead to fracture. Quasi-static superposition method [2] is suitable when the external load frequency is much lower than the structural first elastic modal frequency, but this method is not suitable for dynamic stress prediction when structure is under resonance condition [1]. The external load frequency and amplitude is the system input, and the dynamic stress is predicted according to structure inherent properties. It is a suitable method for vibration and stress prediction of structure under resonance state. When the input loadings are multiple, the phase between the loadings could not be separated It could not simulate the structure dynamic stress factually under multi-load input condition. The simulation method of structural dynamic stress under multi-load input condition was studied, and the phase relationship between the input loadings was considered
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