Analysis of Fatigue Reliability in Aluminum Car Bodies for High Speed Rail

초록

As new high speed trains are being developed, car bodies are being redesigned that achieve high strength with low mass. One concern is in the reliability of the car bodies with respect to vibration- and pressure-induced fatigue. (In South Korea, pressure fluctuations are important due to the large number of tunnels in their HSR system.) This paper summarizes some of the current capabilities in fatigue reliability analysis as applied to car bodies, and also presents some testing procedures for fatigue that are under consideration. There are three main tasks in this work: the development of a stress prediction model, stochastic analysis of fatigue in aluminum, and the investigation of possible load configurations for fatigue testing. To predict stresses, three sources of information are used: the measured accelerations of the bogies and car body, measured pressure on the exterior of the car body and a finite element model. This information is integrated into a stress transfer function. Both the modal and harmonic stress response patterns are used to investigate the relationships between bogie vibrations and car body stresses. It is found that the spatial patterns of stresses vary significantly with frequency. In the analysis of fatigue reliability, the above stress transfer function and the measured data are used to simulate the stress time histories. The focus is on critical locations such as joints and the corners of openings such as windows and doors. The rainflow counting 3D histograms are then obtained with respect to stress amplitudes and mean stresses. The shape of these 3D histograms follows the combined Gaussian-Rayleigh probability distribution that is expected from stochastic fatigue analysis. These results are subsequently used to determine the damage indices for fatigue. The Palmgren-Miner rule is evaluated using a continuous representation of the probability distribution of stresses. It is found that the damage indices for stresses in the current designs of car bodies in the South Korean HSR are very small. Currently, test procedures for the next generation of car bodies are being developed. Since the stress response patterns are complex, fatigue testing becomes a challenging task. To gain insight into the possible fatigue testing procedures, this task is focused on exploring possible load configurations for producing the types of stress patterns observed in the derivation of the stress transfer functions. Both static and dynamic test configuration were considered and a least-squares technique was used to determine the magnitude and direction/phase of the test loads.