• 대한기계학회논문집A
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• 제40권8호
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• pp.731-736
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• 2016

본 연구에서는 의용생체공학에 널리 사용되는 미소바늘과 같은 3차원 고종횡비 미소구조물을 용이하게 제작할 수 있는 하이브리드 자외선 노광법에 대해 기술한다. 하이브리드 자외선 노광법은 기존에 사용되고 있는 경사노광, 회전노광 및 역노광을 혼합한 방법으로, 경사 및 회전노광은 경사진 축대칭 형상을 가지는 3차원 미소구조물의 제작이 가능하도록 하고 역노광은 자외선 노광공정 중 필연적으로 발생하는 하부기판에서의 자외선 반사를 최소화 시킨다. 자체 개발한 자외선 노광시스템과 SU-8 음성감광제를 이용하여 하이브리드 자외선 노광법의 다양한 공정조건이 최종 제작된 3차원 고종횡비 미소구조물 형상(종횡비, 선단의 곡률반경 등)에 미치는 효과를 확인한다. 또한 SU-8의 소프트 베이킹(soft baking) 조건과 미소구조물 선단 형상 사이의 관계에 대해서도 논의한다.

• Structural Engineering and Mechanics
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• 제72권6호
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• pp.713-722
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• 2019

Micromechanics is a technique for the analysis of composites or heterogeneous materials which focuses on the components of the intended structure. Each one of the components can exhibit isotropic behavior, but the microstructure characteristics of the heterogeneous material result in the anisotropic behavior of the structure. In this research, the general mechanical properties of a 3D anisotropic and heterogeneous Representative Volume Element (RVE), have been determined by applying periodic boundary conditions (PBCs), using the Asymptotic Homogenization Theory (AHT) and strain energy. In order to use the homogenization theory and apply the periodic boundary conditions, the ABAQUS scripting interface (ASI) has been used along with the Python programming language. The results have been compared with those of the Homogeneous Boundary Conditions method, which leads to an overestimation of the effective mechanical properties. According to the results, applying homogenous boundary conditions results in a 33% and 13% increase in the shear moduli G₂₃ and G₁₂, respectively. In polymeric composites, the fibers have linear and brittle behavior, while the resin exhibits a non-linear behavior. Therefore, the nonlinear effects of resin on the mechanical properties of the composite material is studied using a user-defined subroutine in Fortran (USDFLD). The non-linear shear stress-strain behavior of unidirectional composite laminates has been obtained. Results indicate that at arbitrary constant stress as 80 MPa in-plane shear modulus, G₁₂, experienced a 47%, 41% and 31% reduction at the fiber volume fraction of 30%, 50% and 70%, compared to the linear assumption. The results of this study are in good agreement with the analytical and experimental results available in the literature.

• Imaging Science in Dentistry
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• 제37권1호
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• pp.27-33
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• 2007

Purpose : The research was done to investigate the effectiveness of 2D bony morphometry and microstructure of micro-computed tomography (micro-CT) on the osteoporotic bony change. We performed the bone morphometric analysis of proximal femur in ovariectomized rabbits with BMD and micro-CT examination. Materials and Methods : Twenty-one female (Newzealand, about 16 weeks old, 2.9-3.4kg) rabbits were used. Three rabbits were sacrificed on the day when experiment began (Baseline). The remaining 18 rabbits were divided into two groups. One group was ovariectomized bilaterally (OVX) and the other animals were subjected to sham operation (Sham). Bone specimens were obtained from the right and left femur of sacrificed rabbits. At intervals of 1, 2, 3, 5, 6 months respectively, BMD tests were performed on the proximal femur by using PIXlmus 2 (GE Lunar Co. USA), 2-dimensional bone morphometric analysis by custome computer program and 2D/3D bone structure analysis by micro-CT (Skyscan 1072, Antwerpen, Belgium). Statistical analysis was carried out for the correlation between bone morphometry, micro-CT and BMD Result : BV/TV, Tb.Th, Tb.N of micro-CT parameters showed higher values in sham group than OVX group. N.Nd/Ar.RI, N.NdNd, N.NdTm, N. TmTm, PmB/Ar.RI, 3-D BoxSlope of 2D morphometric parameters showed higher values in Sham group than OVX group. The micro-CT parameters of Tb.Sp, Tb.N were statistically significant correlated with BMD respectively. Several 2D morphometric parameters were statistically significant correlated with BMD respectively. Conclusion : Several parameters of 2D bony morphometry and micro-CT showed effective aspects on the osteoporotic bony change.

• International Journal of Oral Biology
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• 제38권3호
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• pp.87-92
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• 2013

Periodontal inflammation increases the risk of tooth loss, particularly in cases where there is an associated loss of alveolar bone and periodontal ligament (PDL). Histological and morphometric evaluation of periodontal inflammation is difficult. Especially, the lengths of the periodontal ligament and interdental alveolar bone space have not been quantified. A quantitative imaging procedure applicable to an animal model would be an important clinical study. The purpose of this study was to quantify the loss of alveolar bone and periodontal ligament by evaluation with micro-computed tomography (micro-CT). Another purpose was to investigate differences in infections with systemic E. coli LPS and TNF-${\alpha}$ on E. coli lipopolysaccharide (LPS) in loss of alveolar bone and periodontal ligament model on mice. This study showed that linear measurements of alveolar bone loss were represented with an increasing trend of the periodontal ligament length and interdental alveolar process space. The effects of systemic E. coli LPS and TNF-${\alpha}$ on an E. coli LPS-induced periodontitis mice model were investigated in this research. Loss of periodontal ligament and alveolar bone were evaluated by micro-computed tomography (micro-CT) and calculated by the two- and three dimensional microstructure morphometric parameters. Also, there was a significantly increasing trend of the interdental alveolar process space in E. coli LPS and TNF-${\alpha}$ on E. coli LPS compared to PBS. And E. coli LPS and TNF-${\alpha}$ on E. coli LPS had a slightly increasing trend of the periodontal ligament length. The increasing trend of TNF-${\alpha}$ on the LPS-induced mice model in this experiment supports the previous studies on the contribution of periodontal diseases in the pathogenesis of systemic diseases. Also, our findings offer a unique model for the study of the role of LPS-induced TNF-${\alpha}$ in systemic and chronic local inflammatory processes and inflammatory diseases. In this study, we performed rapidly quantification of the periodontal inflammatory processes and periodontal bone loss using micro-computed tomography (micro-CT) in mice.

• Journal of the Optical Society of Korea
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• 제18권1호
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• pp.55-59
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• 2014

Sarcopenia, or reduced muscle mass and volume, is due to various factors such as senile change, neuronal degeneration, drug, malignancy, and sepsis. Sarcopenia with the aging process has been evidenced by the decline in muscle mass by 0.5 to 1% per year with 3-5% reduction in muscle strength for 10 years between the ages of 40 and 50, and a 1-2% of decline of mass every year in people aged 60-70. Therefore, early diagnosis and understanding the mechanism of sarcopenia are crucial in the prevention of muscle loss. However, it is still difficult to image changes of muscle microstructure due to a lack of techniques. In this study, we developed an animal model using denervated rats to induce a rapid atrophy in the tibialis anterior (TA) and imaged its structural changes using optical coherence tomography (OCT) along with histologic and ultrasound analyses. Ultrasound showed changes of overall muscle size. Histology revealed that the atrophic TA muscle displayed an increased size variability of muscle fiber and inflammatory changes. Three dimensional OCT imaged the changes of perimysial grid and muscle fiber structure in real time without sacrifice. These observed advantages of multimodal imaging using OCT and ultrasound would provide clinical benefits in the diagnosis of sarcopenia.

• 센서학회지
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• 제18권3호
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• pp.239-244
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• 2009

We fabricated nano-templates by low temperature BCP(block copolymer) process at 180 $^{\circ}C$, then we deposited 10 nm-thick $TiO_2$ layers with ALD(atomic layer deposition) at low temperature of 150 $^{\circ}C$. Through FE-SEM analysis, we confirmed the successful formation of the groove-type(width of crest : 30 nm, width of trough : 18 nm) and the cylinder-type(diameter : 10 nm, distance between hole : 25 nm) templates. Moreover, after $TiO_2$-ALD processing, we confirmed the deposition of the uniform nano layers of $TiO_2$ on the nano-templates. Through AFM analysis, the pitches of the crest-through(in groove-type) and hole-hole(in cylinder-type) were the same before and after $TiO_2$-ALD processing. In addition, we indirectly determined the existence of the uniform $TiO_2$ layers on nano-templates as the surface roughness decreased drastically. We successfully fabricated nano-template at low temperature and confirmed that the three-dimensional nano-structure for sensor application could be achieved by $TiO_2$-ALD processing at extremely low temperature of 150 $^{\circ}C$.

• 한국분말재료학회지
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• 제25권6호
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• pp.475-481
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• 2018

Selective laser melting (SLM), a type of additive manufacturing (AM) technology, leads a global manufacturing trend by enabling the design of geometrically complex products with topology optimization for optimized performance. Using this method, three-dimensional (3D) computer-aided design (CAD) data components can be built up directly in a layer-by-layer fashion using a high-energy laser beam for the selective melting and rapid solidification of thin layers of metallic powders. Although there are considerable expectations that this novel process will overcome many traditional manufacturing process limits, some issues still exist in applying the SLM process to diverse metallic materials, particularly regarding the formation of porosity. This is a major processing-induced phenomenon, and frequently observed in almost all SLM-processed metallic components. In this study, we investigate the mechanical anisotropy of SLM-produced 316L stainless steel based on microstructural factors and highly-oriented porosity. Tensile tests are performed to investigate the microstructure and porosity effects on mechanical anisotropy in terms of both strength and ductility.

• Elastomers and Composites
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• 제58권1호
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• pp.44-56
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• 2023

Additive manufacturing (AM) or three-dimensional (3D) printing of metals has been drawing significant attention due to its reliability, usefulness, and low cost with rapid prototyping. Among the various AM technologies, fused deposition modeling (FDM) or fused filament fabrication is receiving much interest because of its simple manufacturing processing, low material waste, and cost-effective equipment. FDM technology uses metal-filled polymer filaments for 3D printing, followed by debinding and sintering to fabricate complex metal parts. An efficient binder is essential for producing polymer filaments and the thermal post-processing of printed objects. This study involved an in-depth investigation of and a fabrication route for a novel multi-component binder system with steel alloy powder (45 vol.%) ranging from filament fabrication and 3D printing to debinding and sintering. The binder system consisted of polyvinyl pyrrolidone (PVP) as a binder and thermoplastic polyurethane (TPU) and polylactic acid (PLA) as a carrier. The PVP binder held the metal components tightly by maintaining their stoichiometry, and the TPU and PLA in the ratio of 9:1 provided flexibility, stiffness, and strength to the filament for 3D printing. The efficacy of the binder system was examined by fabricating 3D-printed cubic structures. The results revealed that the thermal debinding and sintering processes effectively removed the binder/carrier from the cubic structures, resulting in isotropic shrinkage of approximately 15.8% in all directions. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) patterns displayed the microstructure behavior, phase transition, and elemental composition of the 3D cubic structure.

• Composites Research
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• 제37권1호
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• pp.40-45
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• 2024

본 연구에서는 고분자 전해질막 연료전지용 가스확산층의 투과도를 예측하기 위해 삼차원 합성곱 신경망 모델을 사용하는 방법론을 소개한다. 먼저, 기계학습 모델을 학습시키기 위해 X-선 단층 촬영을 통해 얻은 실제 가스확산층 이미지에서 형태학적 특성을 추출해 가스확산층의 대표 체적 요소로 이루어진 인공 데이터셋을 생성한다. 이러한 형태학적 특성은 다공성, 섬유 배향, 직경의 통계적 분포가 포함된다. 구축한 인공 데이터셋 대표 체적 요소들의 투과도를 평가하기 위해 격자 볼츠만 방법이 사용되었으며 각각의 대표 체적 요소들의 투과도를 도출하였다. 이러한 인공 데이터셋을 통해 삼차원 합성곱 신경망 모델을 학습시켰으며 인공 데이터셋을 학습한 삼차원 합성곱 신경망 모델이 실제 가스확산층의 대표 체적 요소 투과도 또한 잘 예측하는 것을 확인하였다.

• 콘크리트학회논문집
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• 제14권6호
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• pp.813-822
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• 2002

본 연구에서 초기재령 콘크리트의 단면 내 수화도와 온도 및 습도분포를 구하는 3차원 유한요소 해석 프로그램을 개발하기 위한 수화도에 따른 재료 모델을 제시하고, 수치해석 절차에 관하여 정립하였다. 재료물성이 급격히 변화하는 초기재령 콘크리트의 거동을 모사하는 과정에서 온도 및 습도에 관련된 재료 물성이 수화도에 따라 결정하였다. 또한 수분거동 연구는 경화한(mature) 콘크리트에 대해서는 여러 연구자에 의해 수행되었지만, 초기재령 콘크리트의 전달계수, 수분용량에 관한 연구는 제대로 정립되지 않은 실정이다. 또한 일반적으로 보통콘크리트에서 무시되는 수분감소항은 고강도 및 고성능 콘크리트의 자기건조(self-desiccation)와 관련된 자기수축(autogenous shrinkage)을 유발하고, 이는 구조물의 장기 내구성 및 사용성 측면에서 중요한 관심사이다. 따라서 본 연구는 초기재령 콘크리트의 온도 및 수축에 의한 응력을 평가하기 위하여, 고강도 및 고성능 콘크리트를 포함한 초기재령 콘크리트의 온도 및 수분거동을 적절히 표현하는 수학적 재료 모델을 제시하고, 콘크리트의 단면 내 수화도와 온도 및 습도분포를 결정하는 3차원 유한요소 해석 프로그램을 개발하였다. 개발된 해석프로그램을 이용한 수치해석 결과는 실험결과와의 비교를 통하여 그 타당성을 검증하였다.