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The part of rail joint becomes the cause of the disadvantage points such as ride discomfort, undesired sound and 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 buckling caused by the axial stress (i.e. the thermal stress which is brought out by the weather conditions or the friction heat between wheel and rail) of the rail have been pointed out. Therefore, some evaluation techniques for buckling management have been proposed. In this study, the relationship between the increase in compressive stress and the behaviors of the characteristics of the wavelet transform (i.e. a kind of time-frequency analysis) results of ultrasonic echoes was researched. The stress was increased in 10 [MPa] interval, and the echo at each stress was detected. From the results of experiment and analysis, it became clear that there is the relatively correlation between three characteristics and the stress. They are RMWC, RWE and RKTW respectively. The value of each RMWC, RWE and RKTW shows the ratio to the initial value (i.e. shows at 0[MPa] in this case) of MWC (i.e. the maximum wavelet coefficient), WE (i.e. wavelet energy) and KTW (i.e. the kurtosis of the time fluctuation waveform of the wavelet coefficient of the frequency that indicates MWC). Therefore, it was able to show the possibility of comparatively accurately predicting the increment of the stress by comparing the transitions of those. 1. 緒 言 レールの継目は「乗心地の悪化」「騒音の発生源」「レールの最弱箇所」となることから,軌道保守での問題点 となっている.このようなことから,複数のレールの継目を溶接して 1本の長いレールにするロングレール化が 進められている.しかし, ・夏季での温度上昇や車輪との摩擦熱で生じる圧縮の軸応力(熱応力)による軌道座屈(張り出し), ・冬季での温度低下で生じる引張りの軸応力(熱応力)によるレール破断(溶接箇所でのき裂発生), などに関するトラブルが報告されている(村田他,2016)(平野他,2014)(浦川,2017).このようなことから,レー ルの軸応力に対する長期的な管理の重要性が高まっている(村田他,2016)(平野他,2014). *1 正員,(株) レールテック(〒532-0011 大阪府大阪市淀川区西中島 5-4-20 中央ビル 3F) *2 正員,関西大学 システム理工学部(〒564-8680 大阪府吹田市山手町 3-3-35) *3 関西大学 システム理工学部 E-mail of corresponding author: t940081@kansai-u.ac.jp 1 Received: 18 May 2019; Revised: 23 August 2019; Accepted: 18 November 2019

Study on evaluation of rail axial stress with ultrasonic wave method (Application of wavelet transform results)