이동절점모드를 사용한 직교이방성 적층평판의 층간분리해석

안재석,Ahn, Jae-Seok 한국전산구조공학회 2012 한국전산구조공학회논문집 Vol.25 No.4

본 논문에서는 직교이방성 적층평판에서의 균열생성 및 전파로 이루어진 층간분리해석을 다룬다. 기존의 p-유한요소가 가지고 있는 요소의 강건성을 균열진전해석에 적용하여, 균열진전시 모델링을 재구성하지 않고, 균열 선단부에 해당되는 꼭지점 모드의 위치만을 이동하도록 하여, 요소망을 단순화시켰다. 이와 같은 층간분리해석에 대해서 이 논문에서의 주요 목적은 다음 두 가지이다. 첫째, 적층복합 재료의 층간분리해석 시, 일반적인 유한요소 모델과 비교하여 매우 간단한 요소망을 가지는 모델을 제안하는 것이다. 모델의 타당성을 평가하기 위해 적층 복합재료로 구성된 이중 외팔보 해석을 통하여, 기존 참고문헌 값과의 비교를 수행하였다. 둘째, 제안된 모델을 내부균열을 갖는 적층평판의 층간분리해석에 적용하여 여러 가지 거동 양상에 대한 평가이다. 이와 같은 목적을 수행하기 위하여 로바토 형상함수를 이용한 완전층별요소가 고려되었으며, 선형탄성파괴역학에 기초한 3차원 가상균열닫힘법을 이용하여 에너지 방출률을 산정하였다. In this study, the delamination analysis has been implemented to investigate the initiation and propagation of crack in composite laminates composed of orthotropic materials. A simple modeling was achieved by moving nodal technique without re-meshing work when crack propagation occurred. This paper aims at achieving two specific objectives. The first is to suggest a very simple modeling scheme compared with those applied to conventional h-FEM based models. To verify the performance of the proposed model, analysis of double cantilever beams with composite materials was implemented and then the results were compared with reference values in literatures. The second one is to investigate the behavior of interior delamination problems using the proposed model. To complete these objectives, the full-discrete-layer model based on Lobatto shape functions was considered and energy release rates were calculated using three-dimensional VCCT(virtual crack closure technique) based on linear elastic fracture mechanics.

치과용 Ti-Xwt%Cu 합금의 연삭성

안재석,Ahn, Jae-Seok 대한치과기공학회 2009 대한치과기공학회지 Vol.31 No.4

This study evaluated the grindability of series of Ti-Cu alloys in order to develop a Ti alloy with better grindability than commercially pure titanium(CP Ti). Experimental Ti-Xwt%Cu alloys(X=2, 5, 10) were made in an argon-arc melting furnace. Slabs of experimental alloys were ground using a SiC abrasive wheel on an electric handpiece at circumferential speed(15000, 30000rpm) by applying a force(250, 300gr). Grindability was evaluated by measuring the amount of metal volume removed after grinding for 2 minutes. Data were compared to those for CP Ti and Ti-6wt%Al-4wt%V alloy. From results, It was observed that the grindability of Ti-Cu alloys increased with an increase in the Cu concentration compared to CP Ti, particularly the 10wt%Cu alloy exhibited the highest grindability at all speeds. By alloying with Cu, the Ti exhibited better grindability at high speed. The continuous precipitation of $Ti_2Cu$ among the ${\alpha}$-matrix grains made this material less ductile and facilitated more effective grinding because small segments more readily formed. The Ti-10wt%Cu alloy has a great potential for use as a dental machining alloy.

p-Version 비선형 유한요소모델링과 실험적 검증에 의한 팻취 보강된 RC보와 슬래브의 극한강도 산정

안재석,박진환,우광성,Ahn Jae-Seok,Park Jin-Hwan,Woo Kwang-Sung 한국전산구조공학회 2004 한국전산구조공학회논문집 Vol.17 No.4

팻취 보강된 철근콘크리트 구조물 해석을 위한 p-version 비선형 유한요소 모델이 제시되었다. 이방성 적층평판이론에 기초를 둔 제안된 모델은 Total Lagrangian기법에 기초한 von Karman의 대변형-소변형률 이론과 증분소성이론(incremental theory of plasticity)을 적용하였다. 콘크리트의 경화법칙(hardening rule)과 그에 따른 파괴기준을 고려하고, 단부 계면 층분리 모델(plate-end interfacial debonding model) 즉, 보강판 끝 부분에서의 콘크리트 탈락에 대한 기준으로서 Oehlers Model과 Raoof and Zhang Model을 사용하였다. 콘크리트는 두께 방향으로 층상화기법(layered model)이 이용되며, 철근과 보강판은 환산층(smeared reinforcing layer)으로 계산되도록 하였다 적분형 르장드르 다항식이 형상함수로 사용되며, 절점에서의 응력값 산출을 위해 Gauss Lobatto 수치적분법을 사용하였다. 본 연구의 목적은 p-version 유한요소법을 사용하여 RC구조물에 대한 수피해의 정확도 및 모델의 단순성을 높인 수 있도록 하였다. 따라서, 철근과 콘크리트모델에 대한 이론적 근거는 기존의 연구문헌에 근거를 두었으며, 수치해석의 적정성은 팻취 보강된 RC보와 슬래브에 대한 문헌의 실험치 및 해석치와 비교 분석되었다. A new finite element model will be presented to analyze the nonlinear behavior of RC beams and slabs strengthened by a patch repair. The numerical approach is based on the p-version degenerate shell element including theory of anisotropic laminated composites, theory of materially and geometrically nonlinear plates. In the nonlinear formulation of this model, the total Lagrangian formulation is adopted with large deflections and moderate rotations being accounted for in the sense of von Karman hypothesis. The material model is based on hardening rule, crushing condition, plate-end debonding strength model and so on. The Gauss-Lobatto numerical quadrature is applied to calculate the stresses at the nodal points instead of Gauss points. The validity of the proposed p-version nonlinear finite element model is demonstrated through the load-deflection curves, the ultimate loads, and the failure modes of RC beams or slabs bonded with steel plates or FRP plates compared with available result of experiment and other numerical methods.

직교이방성 적층구조 해석을 위한 부분-선형 층별이론에 기초한 저매개변수요소

안재석,우광성,Ahn, Jae-Seok,Woo, Kwang-Sung 한국전산구조공학회 2009 한국전산구조공학회논문집 Vol.22 No.2

본 논문에서는 적층구조 해석을 위해 부분 선형 층별이론에 의해 정식화된 저매개변수 유한요소 모델을 제안한다. 얇은 직교이방성 문제뿐만 아니라, 두꺼운 식교이방성 적층판 해석을 위해 제안된 모델은 2차원 세분화 기법에 기초를 두고 있다. 즉, 이 모델은 두께방향으로의 면내거동에 대해서는 선형변화로 가정하는 층별분리 이론이 적용되고, 두께방향으로의 면외거동에 대해서는 상수로 가정하는 등가단층이론이 사용된다. 변위장을 정의하기 위해 적분형 르장드르 다항식이 사용된다. 또한 가우스-로바토 적분법을 사용하여, 적층평판의 종래의 가우스적분점이 아닌 절점의 위치에 발생하는 최대응력값을 별도의 외삽법을 사용하지 않고 바로 산출하였다. 제안된 모델의 정당성과 특성은 직교이방성 다층적층판 문제를 사용하여 검증되었으며, 그 결과는 출판된 참고문헌의 값들과 비교되었다. 이 연구에서는 최적의 유한요소 적층모델을 결정하기 위해 응력과 최대처짐을 사용한 수렴성조사가 수행되었다. 또한, 적층 수의 증가에 따른 두께방향으로의 변위와 응력분포의 변화가 조사되었다. This paper presents the subparametric finite element model formulated by partial-linear layerwise theory for the analysis of laminate composites. The proposed model is based on refined approximations of two dimensional plane for orthotropic thick laminate plate as well as thin case. Three dimensional problem can be reduced to two dimensional case by assuming piecewise linear variation of in-plane displacement and a constant value of out-of-plane displacement across the thickness. The integrals of Legendre polynomials are chosen to define displacement fields and Gauss-Lobatto numerical integration is implemented in order to directly obtain maximum values occurred at the nodal points of each layer without other extrapolation techniques. The validity and characteristics of the proposed model have been tested by using orthotropic multilayered plate problem as compared to the values available in the published references. In this study, the convergence test has been carried out to determine the optimal layer model in terms of central deflection and stresses. Also, the distribution of displacements and stresses across the thickness has been investigated as the number of layer is increased.

폐 방사선 치료 후 발생한 우측 유방의 혈관육종

안재석(Jae Seok Ahn),강선희(Sun Hee Kang),권선영(Sun Young Kwon) 대한외과학회 2008 Annals of Surgical Treatment and Research(ASRT) Vol.75 No.6

Angiosarcoma of the breast is an uncommon, extremely hostile neoplasm of vascular origin. A 55-year-old female visited our hospital for a right breast mass, which had been initially noticed 6 months previously. She had a history of previous squamous cell lung cancer (T4, N2, M0) with radiation therapy 9 years earlier. Physical examination revealed a 10 cm sized slightly movable firm mass and edematous overlying skin with congested superficial veins and retracted nipple. Mammography showed asymmetrically increased opacity in central right breast. Ultrasonography showed a indistinctly demarcated, heterogenous, complex less-echogenic mass in upper central right breast. Core needle biopsy suggested poorly differentiated carcinoma. Chest computed tomography and whole body bone scan showed no evidence of distant metastasis. On June 29, 2007, modified radical mastectomy was performed and revealed angiosarcoma of the right breast. Adjuvant therapy was not given.

복합재료 팻칭에 의한 중앙경사균열에서 2단계 확장 가상균열닫힘법을 사용한 혼합모우드해석

안재석(Ahn Jae-Seok),우광성(Woo Kwang-Sung) 대한토목학회 2012 대한토목학회논문집 A Vol.32 No.1A

This paper deals with the numerical determination of the stress intensity factors of cracked aluminum plates under the mixed mode of KⅠ and KⅡ in glass-epoxy fiber reinforced composites. For the stress intensity factors, two different models are reviewed such as VCCT and two-step extension method. The p-convergent partial layerwise model is adopted to determine the fracture parameters in terms of energy release rates and stress intensity factors. The p-convergent approach is based on the concept of subparametric element. In assumed displacement field, strain-displacement relations and 3-D constitutive equations of a layer are obtained by combination of 2-D and 1-D higher-order shape functions. In the elements, Lobatto shape functions and Gauss-Lobatto technique are employed to interpolate displacement fields and to implement numerical quadrature. Using the models and techniques considered, effects of composite laminate configuration according to inclined angles and adhesive properties on the performance of bonded composite patch are investigated. In addition to these, the out-of-plane bending effect has been investigated across the thickness of patch repaired laminate plates due to the change of neutral axis. The present model provides accuracy and simplicity in terms of stress intensity factors, stress distribution, number of degrees of freedom, and energy release rates as compared with previous works in literatures. 이 논문에서는 유리-에폭시 섬유 보강 복합재료판에 KⅠ과 KⅡ에 의한 혼합모우드 상태의 균열된 알루미늄판의 응력확대계수의 수치해석 산정을 다루고 있다. 응력확대계수 산정을 위한 가상균열닫힘법과 2단계 확정법이 고려된다. 에너지 방출률과 응력확대계수의 항으로 표현되는 파괴역학 매개변수 계산을 위하여, p-수렴 부분 층별모델이 채택된다. 고려되는 p-수렴 방식은 저매개변수 요소의 개념에 기초한다. 1개 층에 대해 가정된 변위장, 변위-변형률 관계, 그리고 3차원 구성방정식은 2차원과 1차원 고차 형상함수의 조합으로 정의된다. 고려되는 요소는 변위장의 보간과 수치적분을 수행하기 위해 로바토 형상함수와 가우스-로바토 적분법이 사용된다. 언급된 모델과 기법들을 사용하여, 경사각도의 변화에 따른 적층판 형상의 효과와 접착제의 강도가 팻치보강 시스템에 미치는 영향이 조사된다. 중립축 변화에 따른 팻치보강 적층판의 면외 휨 효과도 분석된다. 고려되는 모델의 정확성과 단순성 등에 관해서 응력확대계수, 응력분포, 자유도 수, 에너지 방출률 등의 항목을 가지고서 평가된다.

대상포진 후 신경통에 시행된 실험적 척수자극술시 예측치 못한 추간판 탈출증 증상의 개선 - 증례 보고 -

안재석(Jae Seok Ahn),한석희(Seok Hee Han),김태형(Tae Hyeong Kim),박학수(Hahck Soo Park),임영진(Young Jin Lim),이상철(Sang Chul Lee) 대한통증학회 2001 The Korean Journal of Pain Vol.14 No.1

In controlling chronic intractable pains, the current therapeutic methods used are exercise, over the counter medication, cognitive-behavioral therapy, opioid medication, neural blockade, operation, etc., spinal cord stimulation being the last resort. Spinal cord stimulation was initiated when Shearly and others clinically tested the Gate control theory of Melzack and Wall. This had triggered the advancement of theoretic research on the mechanism and hardware necessary and has resulted in an accumulation of clinical experiences. This is known to be effective for treating sympathetic pain, arachnoiditis, failed back pain syndrome, radiculopathy, peripheral vascular disease, phantom limb syndrome, post-herpetic neuralgia, peripheral neuropathy, and angina pectoris. This report describes our experience in experimental spinal cord stimulation in patients with simultaneous post-herpetic neuralgia and herniated intervertebral disc. There wasn`t any improvement in the post-herpetic neuralgia but the symptoms of a herniated intervertebral disc was much ameliorated. This was quite an unexpected result. The patients back pain returned when the stimulation stopped.

임상연구 : Sevoflurane이 자율신경계에 미치는 영향

안재석 ( Jae Seok Ahn ),박희진 ( Hee Jin Park ),황창환 ( Chang Hwan Hwang ),김상태 ( Sang Tae Kim ),김희수 ( Hee Soo Kim ),임승운 ( Seung Woon Lim ) 대한마취과학회 2003 Korean Journal of Anesthesiology Vol.44 No.6

조기 유방암에서 삼중복 음성군의 임상 병리학적 특징 및 예후

안재석(Jae Seok Ahn),조지형(Jihyoung Cho),권선영(Sun Young Kwon),강선희(Sun Hee Kang) 대한외과학회 2009 Annals of Surgical Treatment and Research(ASRT) Vol.77 No.1

Purpose: Triple negative breast cancer (estrogen receptor-negative, progesterone receptor-negative, and HER2/neu negative) is associated with high risk of recurrence and poor prognosis. We investigated the characteristics and prognosis of triple negative early-stage breast cancer. Methods: We reviewed the records of 821 early-stage breast cancer patients treated at our hospital from 1995 to 2005. We studied the differences between a triple negative group compared with a non-triple negative group. Results: Of 821 early-stage breast cancer patients, 200 (24.4%) were classified as triple negative. Large tumors (>2 cm) in the triple negative group were significantly more than those in the non-triple negative group (P=0.042). Histologic and nuclear grade of the triple negative group were significantly higher than those of the non-triple negative group (P<0.001). The median follow-up time is 50 months (1∼135). There have been 50 local recurrences, 98 distant metastases, and 65 deaths. There were high rates of local recurrence in the triple negative group but no difference in 5-year disease free survival rates (P=0.178). The 5-year overall survival rate showed 85% in the triple negative group but 92.8% in the non-triple negative group (P=0.008). The relative risk for overall survival was 1.93 times higher in the triple negative group. Conclusion: Triple negative breast cancer patients in early stages have poor pathologic findings and prognoses. Careful treatment and follow-up are important and further investigation is necessary for triple negative breast cancer.

Push-Shear Bond Strength of Veneering Ceramics and Zirconia Ceramic

Jae-Seok Ahn(안재석),Hyeong-Rok No(노형록),Jung-Hwan Lee(이정환) 한국콘텐츠학회 2015 한국콘텐츠학회논문지 Vol.15 No.9

본 연구에서는 원통형 지르코니아 코어에 다섯 종류의 지르코니아 비니어 세라믹을 축성하여 push-전단결합강도를 측정하고, 비니어 세라믹의 이축굽힘강도와 지르코니아 글라스 라이너 처리에 따른 전단결합강도 차이를 알아보고자 하였다. 지르코니아 비니어 세라믹은 piston-on-three-ball test로 이축굽힘강도를 측정하였고, 지르코니아 실린더 코어와 비니어 세라믹은 push-shear test로 결합강도를 측정하였으며, 결과값은 이원분산분석을 사용하여 분석하였다. 이축굽힘강도는 Cercon ceram kiss (CE)군에서 가장 높게 측정되었고 전단결합강도는 글라스 처리군과 Triceram(TR)군이 높게 측정 되었으며 Creation ZI(CR)군에서 가장 낮은 값이 측정 되었다. 실험군에서 지르코니아 라이너 처리군이 라이너 처리하지 않는 군보다 전단결합강도가 높게 나타났으며 통계적으로 유의한 차이를 보였다(P<0.05). 따라서 지르코니아 라이너 처리는 지르코니아와 비니어 세라믹의 결합강도를 향상시킬 수 있는 것으로 사료된다. The purpose of this study was to evaluate the push-shear bond strength between five commercial zirconia veneering ceramics and zirconia core cylinder, and to investigate the effect of biaxial flexural strength and zirconia liner glass treatments. The biaxial flexural strengths of the veneering ceramics were evaluated by a piston-on-three-ball test. The bond strengths between the Y-TZP cylinder and zirconia veneering ceramics were evaluated using the push-shear bond strength test. The data was analyzed using two-way ANOVA and Scheffes test. The biaxial flexural strength of Cercon ceram kiss (CE) was higher than those of the other groups. The glass-treated and Triceram zirconia groups showed the highest value and the Creation ZI(CR) showed the lowest. In all groups, the liner glass treatment groups showed significantly higher push-shear bond strength than those without(P<0.05). The liner glass treatments of zirconia can improve the bond strength between the zirconia ceramic core and veneering ceramics.