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Advanced Indentation System을 이용한 연성 파괴인성 평가식의 모델링
주장복,이정석,심홍석,이승건,권동일 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.1
Fracture properties of various structural steels were determined non-destructively using the advanced indentation system (AIS), which is developed on the basis of continuous indentation technique. In this study, conventional critical strain model was modified to predict the ductile fracture toughness from the AIS data. In deriving the ductile fracture toughness model, fracture strain and characteristic length were estimated using the stress triaxiality and the work-hardening exponent. AIS tests were conducted on carbon steels, stainless steels, aluminum alloys and copper alloys. For all these materials, the results of indentation test were compared to those of the standard fracture toughness test methods, which shows that the present analysis can predict successfully the ductile fracture toughness of structural steels.
손상평가도를 이용한 용접구조물의 균열형 결함에 대한 사용적합성 평가
李精錫,朱章福,張宰溢,金禹植,고영대,權東一 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.10
Flaws nucleated during operation of structures such as nuclear power plants, petroleum facilities and gas equipment raise many safety problems, and thus the integrity assessment of crack-like flaws in structures has been very important. Since large-scale structures include weldments with complex micro-structures and inhomogeneous material properties, it is essential to consider both metallurgical and mechanical factors. In this study, a methodology for integrity assessment in welded structures was developed based on API 5L X65 grade natural gas pipeline (an approximately 2400 ㎞ pipeline in Korea). A failure assessment diagram(FAD), which includes all failure modes from linear elastic fracture to plastic collapse, was used for integrity and fitness-for-service(FFS) assessment of the pipeline. Since tensile properties and fracture toughness of base metal, weld metal and heat affected zone(HAZ) are required for the FAD, tensile tests and fracture toughness tests were performed on each region. In particular, the evaluation of representative properties of HAZ make it possible to assess FFS accurately by using the HAZ-based FAD when crack-like flaws exist in HAZ. This HAZ-based FAD is different from current codes, which assess integrity by the material properties of weld metal or base metal even when flaws exist in HAZ.
소형펀치 시험의 선형탄성 파괴역학적 분석을 통한 파괴이성 평가
권동일,장재일,주장복,이백우 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.1
Small punch test is used to assess the reliability of industrial facilities such as fusion reactor structures and power generation systems. Conventional small punch tests evaluate transition temperature and fracture strain by analyzing the load-deflection curves and deformation behaviors, respectively. However, previous research did not consider fracture mechanical concepts such as flaw, stress analysis and fracture toughness. In this study, to obtain more reliable fracture characteristics based on linear elastic fracture mechanics in small punch tests, a pre-crack was introduced to small punch specimen. Stress and deformation behaviors near the crack tip were analyzed and the stress intensity factor was derived. Using the load at crack initiation point, the fracture toughness of SA 508 Cl.3 steel was successfully evaluated.