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열사이클에 따른 금속배선/보호층에서의 유한요소 모델에 의한 응력 분석
권동일,정증현,이소윤 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.8
Electronic pads and interconnects consisting of a passivation layer (hard layer) and a metal layer (ductile layer), e.g. SiN/Al/SiO₂/Si, are very important in many electronic devices. However, they are likely to fail due to cracking of the passivation layers during operation of the devices. This study investigates the failure mechanism through finite-element analysis(FEA). FEA calculations reveal that residual stress is produced in the passivation layer as a result of thermal cycling and increases as cycling continues. During thermal cycling, the multilayer films are deformed by various stresses due to differential thermal expansion of adjacent materials, particularly shear stresses applied to the chip (or die) surface by the large thermal mismatch between substrate and chip (or die). The cyclic shear stress leads to accumulation of asymmetric plastic deformation (called the ratcheting effect) in the metal layers. The residual strain or stress in the passivation layer may be induced by the ratcheting deformation of metal layer. The effects of the thickness and the yield stress of the passivation and metal layers were analyzed through FEA and discussed. The residual stress in the passivation layer decreases with passivation layer thickness and metal layer yield strength, which is closely related to the likelihood of plastic yielding in the metal layer.
권동일,고기영,김종우,고흥규,윤현기,성규보 대한영상의학회 2018 Korean Journal of Radiology Vol.19 No.2
Objective: To investigate the technical safety and clinical efficacy of a double-stent system with long duodenal extension in patients with malignant extrahepatic biliary obstruction. Materials and Methods: This prospective study enrolled 48 consecutive patients (31 men, 17 women; mean age, 61 years; age range, 31−77 years) with malignant extrahepatic biliary obstructions from May 2013 to December 2015. All patients were treated with a double-stent system with long duodenal covered extension (16 cm or 21 cm). Results: The stents were successfully placed in all 48 patients. There were five (10.4%) procedure-related complications. Minor complications were self-limiting hemobilia (n = 2). Major complications included acute pancreatitis (n = 1) and acute cholecystitis (n = 2). Successful internal drainage was achieved in 42 (87.5%) patients. Median patient survival and stent patency times were 92 days (95% confidence interval [CI], 61−123 days) and 83 days (95% CI, 46−120 days), respectively. Ten (23.8%) of the 42 patients presented with stent occlusion due to food impaction with biliary sludge, and required repeat intervention. Stent occlusion was more frequent in metastatic gastric cancer patients with pervious gastrectomy, but did not reach statistical significance (p = 0.069). Conclusion: Percutaneous placement of a double-stent system with long duodenal extension is feasible and safe. However, this stent system does not completely prevent stent occlusion caused by food reflux.
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.