Abstract
The part of rail joint becomes the causes of the disadvantage points such as the ride discomfort, the undersired sound and the track maintenance, etc. For restraining those points, the long rail made by welding the standard length rails has been developed. However, the problems of the overhang or the breakage caused by bucking have been pointed out. Those phenomena are cause by the axial force (i.e. the thermal stress) that is brought out by the weather conditions or the friction heat of wheel and rail. Therefore, several evaluation techniques for managing those have been proposed. The application of non-destructive method, the quantitative evaluation, the high prediction accuracy and the decrease in work of measures, etc., are desired in that technique. In the previous study, we had presented the relationship between the increases of compression stress and the behaviors of the ultrasonic echo to that stress. Concretely, it was shown that there is high correlation between the increase of the maximum wavelet coefficient of that echo and each applied stress. Here, that coefficient is led from the wavelet transform that is the time-frequency analysis. However, it became a problem that the change ratio of that coefficient by the increase of the stress is very small. In this study, the parameter that indicates a remarkable change to the applied stress is proposed. That parameter is the change ratio of wavelet coefficient evergy (RWE). The RWE is led by the following procedure. (1) Wavelet coefficient energy (WE) which adds the value over 98 % of the maximum coefficient at each applied stress is calculated. (2) By calculating the change ratio of WE in each applied stress for WE at the initial state of which the stress is zero, the RWE at each stress is led. After that, the experimental equation for evaluating the stress from the RWE was built. Also, the ability of that equation was examined. As the result, it became clear that the stress could be estimated in the good precision by RWE.
