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Jang Chang-Heui The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.3
A simple approximation method for the stress intensity factor at the tip of the axial semielliptical cracks on the cylindrical vessel is developed. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite element analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. For these, 3-D finite-element analyses are performed to obtain the stress intensity factors for various surface cracks with t/R=0.1. The approximation solutions are within $\pm2.5%$ of the those of finite element analysis using symmetric model of one-forth of a vessel under pressure loading, and 1-3% higher under pressurized thermal shock condition. The analysis results confirm that the approximation method provides sufficiently accurate stress intensity factor values for the axial semi-elliptical flaws on the surface of the reactor pressure vessel.
A Study on the Microscopic Fracture Characteristics of A533B-1 Nuclear Pressure Vessel Steels
Jang, Chang-Heui,Kim, In-Sup,Park, Soon-Pil Korean Nuclear Society 1989 Nuclear Engineering and Technology Vol.21 No.3
The strain rate effects on fracture toughness and fracture resistance characteristics of A533B-1 nuclear pressure vessel steels were examined in the quasi-dynamic test conditions through the microscopic investigation of the intense strain region around crack tip and the microroughness of fracture surface. J-value calculated from the recrystallization etch technique was the same as calculated from the modified-J when the crack extension is less than 1.5mm in a 1/2T-CT specimen. Local fracture strain was calculated from the fracture surface micro-roughness. The local strains were calculated to be the values of 1.8 and 2.0 and were much higher than the macroscopically measured values. It was nearly independent on strain rate and was regarded as a material constant in ductile dimpled rupture. The fracture toughness increased with increase in strain rate while the tearing modulus showed little variation.
Jang, Hun,Cho, Hyun-Chul,Jang, Chang-Heui,Kim, Tae-Soon,Moon, Chan-Kook Korean Nuclear Society 2008 Nuclear Engineering and Technology Vol.40 No.3
To understand the effect of the cyclic strain rate on the environmentally assisted cracking behaviors of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$, the fatigue surface and a sectioned area of specimens were observed after low cycle fatigue tests. On the fatigue surface of the specimen tested at a strain rate of 0.008 %/s, unclear ductile striations and a blunt crack tip were observed. Therefore, metal dissolution could be the main cracking mechanism of the material at this strain rate. On the other hand, on the fatigue surfaces of the specimens tested at strain rates of 0.04 and 0.4 %/s, brittle cracks and flat facets, which are evidences of the hydrogen induced cracking, were observed. In addition, a tendency of linkage between the main crack and the micro-cracks was observed on the sectioned area. Therefore, at higher strain rates, the main cracking mechanism could be hydrogen induced cracking. Additionally, evidence of the dissolved MnS inclusions was observed on the fatigue surface from energy dispersive x-ray spectrometer analyses. Thus, despite the low sulfur content of the test material, the sulfides seem to contribute to environmentally assisted cracking of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$.
최장석(Jang Seok Choi),곽희철(Heui Chul Gwak),김정한(Jung Han Kim),이창락(Chang Rack Lee) 대한정형외과학회 2009 대한정형외과학회지 Vol.44 No.2
골관절 결핵은 전체 결핵의 약 1-3%로 매우 드물며, 주로 척추에 호발하고 족부에 있어서 결핵성 골수염은 매우 드문 것으로 알려져 있다. 임상 양상이 비특이적이고, 다양한 병리학적 형태를 보이므로 진단과 치료에 많은 과정과 시간이 걸린다. 골관절 결핵 진단시에는 철저한 변연절제술과 함께 항결핵요법이 병행되어져야 한다. 저자 등은 영아에서 발생한 족저골의 결핵성 골수염 2예를 경험하여 진단 및 치료 과정에 대한 증례를 보고하는 바이다. Osteoarticular tuberculosis is a rare condition and it makes up 1-3% of all cases of tuberculosis. It usually occurs at the vertebra and it is common knowledge that tuberculous osteomyelitis is very rare at the foot. The clinical symptoms are nonspecific, and it can also mimic a wide range of pathologies, so it takes a lot of time to diagnosis and treat this illness. When osteoarticular tuberculosis is diagnosed, it should be gone through side to side with thorough debridement and chemotherapy. The author has experience 2 case of tuberculous osteomyelitis, so I report here on the diagnosis and treatment of this illness.
곽희철(Heui Chul Gwak),김주용(Joo Yong Kim),최장석(Jang Seok Choi),김창완(Chang Wan Kim),김정한(Jung Han Kim),박대현(Dae Hyun Park) 대한정형외과학회 2010 대한정형외과학회지 Vol.45 No.6
목적 : 거골의 연골 병변에 대하여 관절정적 연골 성형술, 미세 골절술 및 자가 골연골 이식술을 시행 후 임상 결과 비교 및 결과에 영향을 미치는 인지를 평가하고자 하였다. 대상 및 방법 : 1998년 3월부터 2007년 12월까지 거골의 연골 병변으로 진단받은 환자들 중 관절경적 연골 성형술, 미세 골절술 또는 자가 골연골 이식술 시행 후 12개월 이상 추시가 가능했던 35명(36예)을 대상으로 하였다. 연골 성형술이 14예(13명), 미세 골절술이 12예(12명), 자가 골연골 이식술이 10예(10명)에서 시행되었다. 병변의 단계는 단순 방사선 산진 상 Berndt와 Harty 분류 및 Anderson 자기 공명 영상 분류를 사용하였다. 전 예에서 술 전 및 최종 추시에서 VAS score 및 AOFAS score를 측정하여 각각의 술식에 따른 임상적 결과를 평가 및 비교하였다. 병변의 위치, 크기, 단계 및 나이에 따른 임상적 결과를 평가하였다. 결과: 연골 병변 위치는 외측이 13예, 내측이 23예였으며 연골 병변의 평균 크기는 1.9 ㎠(1-4㎠)였다. 병변의 단계는 Berndt와 Harty 분류 및 Anderson 분류 2단계가 8예, 3단계가 21예, 4단계가 7예였다. 평균 추시관찰 기간은 15개월(12-30개월)이었으며, 전체 환자에서 VAS score 및 AOFAS score의 유의한 호전이 관찰되었으나, 각 술식 간의 의미있는 차이는 없었다. 병변 위치, 크기, 단계 및 나이에 따른 환자 군의 비교에서 유의한 차이는 나타나지 않았다. 결론: 관절경을 이용한 연골 성형술, 미세 골절술 및 자가 골연골 이식술 모두 거골의 연골 병변에서 유용한 치료 방법으로 사료되며, 병변 위치, 크기, 단계 및 나이에 따른 분류에서는 각 군별로 유의한 차이가 나나나지 않았다. Purpose: To compare clinical results and to evaluate the factors affecting the clinical results after performing arthroscopic chondroplasty, microfracture, and osteochondral autologus transplantation (OAT) due to a chondral defect of the talus. Materials and Methods: This study enrolled 35 patients (36 cases) diagnosed with a chondral defect of the talus and who could be followed over 12 months after arthroscopic chondroplasty, microfracture, or OAT between March 1998 and December 2007. The arthroscopic chondroplasties were carried out in 14 cases (13 patients), the microfractures were carried out in 12 cases (12 patients) and OAT was carried out in 10 cases (10 patients). The lesion staging used Berndt and Harty classification on simple radiographs and Anderson's classification on magnetic resonance images. Clinical results were evaluated and compared by measuring VAS and AOFAS scores at the time of operation, before the operation, and at the time of follow up Clinical evaluation included location, size, and stage of each lesion as well as the age of individual patient. Results: There were 13 medial and 23 lateral lesions. The average size of the chondral defects were 1.9 ㎠ (range 1-4 ㎠). According to the classification of Berndt and Harty and Anderson, there were 8 stage Ⅱ, 21 stage Ⅲ, and 7 stage Ⅳ cases. The average follow up period was 15 months (range: 12-30 months). VAS and AOFAS scores showed significant improvement in all treatment groups. However, clinical results according to the operative methods did not show any differences. Lesion size, stage and location, as well as of age of patient had no significant impact on clinical results. Conclusion: We concluded that all three procedures, arthroscopic chondroplasty, microtracture. and OAT, are useful for treating a chondral defect of talus. Location of lesion, size, stage and age of patient did not make a significant difference.