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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.
Assessment of Fracture Characteristics from Revised Small Punch Test Using Pre - cracked Specimen
Jang, Bog Ju,Dongil Kwon 대한금속재료학회(대한금속학회) 1998 METALS AND MATERIALS International Vol.4 No.4
Small punch (SP) test has been utilized to analyze the neutron irradiation damage of nuclear vessels. Mince this technique is easy, simple, and nondestructive, it can be applied to evaluate the mechanical properties and material degradation of in-service components. Conventional SP test has evaluated the ductile-brittle transition temperature and the equivalent fracture strain by the interpretations of load-deflection curve and the change of specimen thickness, respectively. The assumption that fracture occurs at maximum load is, however, not reasonable because the crack initiates at smaller load. In this study, in order to evaluate quantitatively fracture characteristics based on fracture mechanics, the pre-crack is introduced to SP specimen and acoustic emission is used to determine the crack initiation point. Using the load at crack initiation point, the fracture toughness of thin plate is calculated through bending theory. Therefore, the fracture characteristics of thin plate can be evaluated more reliably by using revised SP test.
일부 소규모 시계조립 사업장의 상지 누적외상성장애의 유병률
장은철,김현주,권영준,박시복,이수진,송재철 大韓産業醫學會 2000 대한직업환경의학회지 Vol.12 No.4
목적 : 단순 반복작업을 하는 시계조립 사업장 근로자를 대상으로 상지 누적외상성장애의 자각증상 유병률과 상지 누적외상성장애 유병률을 파악하고자 하였다. 방 법 : 인구학적 특성, 상지의 자각증상, 사회심리적 요인은 자가 설문지법으로, 인간공학적 특성은 점검표를 이용한 면담법으로 조사하였다. 상지의 자각증상 조사와 사회심리적 요인은 각각, N10SH (1993) 설문지와 Karasek(1979)의 Job strain model을 번역하여 조사하였다. 상지 누적외상성장애 판정은 의사가 작업 현장에서 직접 환자 면담과 이학적 검사를 수행한 후, 연구에서 규정한 증례정의에 의해 수행하였다. 수집된 자료는 x2 teat와 exact test로 단별량 분석을 하였고, 이중 의미있는 변수와 위험 인자로 알려진 변수들로 다중 로지스틱 회귀분석을 시행하였다. 결 과 : 대상자들의 자각증상 유병률은 54.2 %였고, 부위별로는 목 34.9 %, 손/손목 31.3 %, 어깨 30.1 %, 팔/팔꿈치 18.0 %순이었다. 상지 누적외상성장애의 유병률은 45.8 %였고, 근막동통증후군이 26명으로 가장 많았고, De Quervain씨 병 8명, 수부/전완부의 건염 및 건활막영 8명, 수근관 증후군 5명, 이두건염 5명, 척골 신경병증 5명, 내상과 염 4명, 외상과염 2명, 경추 디스크 질환 2명, 흥곽 출구 증후군 1명순으로 나타났다. 단변량 분석시 자각증상 유병률은 작업부서 중 완성 부에서, 상지 누적외상성장애 유병률은 여자와 완성 부에서 통계학적으로 유의하게 높았다. 다중 로지스틱 회귀분석 결과 완성부와 근무긴장도가 높은 군이 상지 누적외상 성장애와 통계학적으로 유의한 결과를 보였다. 결 론 : 이 연구에서 상지 누적외상성장애 유병률은 45.8 %으로서 저강도의 단순 반복작업을 하는 시계조립 사업장 근로자에서도 누적외상성장애의 위험이 있는 것으로 생각된다. 또한, 사회심리적 요인과 작업 부서별 공정 및 환경이 유병률에 영향을 미치는 주요 요인으로 생각되며, 향후 이들에 관한 다양한 연구가 진행되어야 할 것이다. 산업보건 현장에서는 시계조립 사업장과 같이 저 강도의 단순 반복작업을 위주로 하는 사업장에 대한 지속적인 관심과 각 사업장별 위험요인을 파악하여 적절한 예방 및 관리 대책을 세워야 할 것이다. Objectives : The prevalence of cumulative trauma disorders of upper extremities mons watch assembly workers in small-scaled industry was studied. Methods. In 83 workers at five watch assembly factories, symptoms and psychosocial questionnaire, ergonomic Interview, physical examination were conducted. Results : Prevalence of self-reported symptoms was 54.2% and neck 34.9%, wrist/hand 31.3%, shoulder 30.1%, elbow/arm 18.0% by anatomical site. Prevalence of cumulative trauma disorders was 45.8%. Most common disease was myofascial pain syndrome (31.3%). The other diseases were De Quervain disease (9.6%), tenosynovitis/tendinitis at wrist/hand (9.6%), bicipital tendinitis(6.0%), fat. epicondylitis(4.8%), meIn. epicondylitis(2.4%), and cervical disc disease(2.4%). As result of ergonomic interview, repetitiveness was 79(98.8%). There were no differences in the prevalence of self-reported symptoms and cumulative trauma disorders for age, sex, marital status, duration of work In the study, The significant factors of cumulative trauma disorders were occupational task and psychosocial stress in the study. The prevalence of cumulative trauma disorders in high strain group was hlgher (68.4%) than other three groups. The prevalence of self-reported symptoms and cumulative trauma disorders in assembly task was higher (70.0%, 64.0%) than other two tasks. Conclusions : Prevalence of self-reported symptoms was 54.2%, prevalence of cumulative trauma disorders was 45.8% in watch assembly workers. In this study, factor related to self-reported symptoms was occupational task and factors relaxed to cumulative trauma disorders were occupational task and psychosocial stress. This results suggest that differences of ergonomics and environment in occupational task cause differences of prevalence of self-reported symptoms and cumulatlve trauma disorders.
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.