HT60급 TMCP강재의 피로설계 파라메터 산정을 위한 실험적 연구
(An )experimental study for assessment of fatigue design parameters on the HT60 grade TMCP steel
v, 64 p.
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This study aimed to investigated the softening effects of welded joints on fatigue crack growth rate of TMCP(Thermo Machanical Control Process) steel. Fatigue test, and quantitatively analyzed fatigue crack growth of base metal and HAZ(Heat Affect Zone) and weld metal have been performed to evaluated the applicability of TMCP steel on steel bridges. The application of the relationship da/dN=C(ΔK)^m is effective to analysis of fatigue crack growth life. The values of material constant C and m have great influences on predicting fatigue life. In this study, HT60 grade TMCP steel were examed. Nine Compact tension(CT) specimens were subtracted from the depths of 2mm, 12mm, 22mm in TMCP steel plate 50mm in thickness, three different types of specimens at each depth are tested. (a) P type - crack has grown to the direction of welding in the base metal. (b) R type - crack has grown to the weld metal from the HAZ. (c) S type - crack has grown to the weld metal through the HAZ from the base metal. The nine CT specimens were installed in a MTS servo-controlled electro-hydraulic fatigue machine and precracked under constant amplitude sinusolidal loading. After precracking, specimens were monotonically loaded(R=0.3) to failure. Crack length was measured by clip-on gauge using Kikukawa-comliance method. The relationship between da/dN and ΔK of each specimen and constant C and m were determined by Paris-Erdogan power law. Barsom proposed relationship of C and m for many structural steels. Although the applicability of the Barsom's relationship has been studied for many steels in U.S and Japan, few similar studies for structural steels have been performed in Korea. To evaluate the material constants of TMCP steel, the relationship of C and m proposed by Barsom have been applied in this study. Results of this study confirmed that the fatigue crack growth behavior of TMCP steel at welded joints is similar to the structural steel's, and the effects of softening on HAZ to fatigue crack growth rate is not noticeable.