フェーズドアレイ超音波探傷法による鋼床版デッキプレート進展き裂の非破壊評価

Fatigue cracking in the rib-to-deck weld of the orthotropic steel deck system has been one of the most serious problems in recent years. In Japan, a closed section of U shaped longitudinal rib plate has been employed. Usually, a fatigue crack is initiated at the root of the weld. The fatigue crack cannot be detected by the visual inspection. A phased array ultrasonic testing system was newly developed especially focusing on the nondestructive evaluation for the fatigue cracks in the rib-to-deck weld. In the system, two types of data acquisition process were employed. One was the conventional steering and focusing method. The acquired wave data were superposed in the flaw detector (superposition in hardware). The other was the full matrix capture. Wave forms were acquired one element by one element, and superposed in the computer (superposition in software). Specimen with an artificial slit made by electrical discharge machining was used for the validation. Fatigue test was carried out. The specimen was failed after more than 1 million cycles. Beach marking showed the propagation of the fatigue crack. Both data acquisition methods showed good agreement with the actual crack height. Even the full matrix capture showed better agreement. The minimum crack height was estimated about 2 mm.