• 한국의류산업학회지
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• 제21권3호
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• pp.336-345
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• 2019

This study evaluated the preference and wearing characteristics of existing fitness compression wear for elderly women and identified the problems and improvements of existing fitness apparel. Preference and wearing characteristics for 6 types (A-F) of upper and lower fitness compression wear were evaluated. Photos and drawings as well as the preferred designs and details were investigated after presenting the evaluation clothing. Evaluations were made on a 5 point Likert scale for the fitness, allowance, pressure, ease of movement, fabric material, and overall satisfaction after wearing. The design preference indicated that B type (26.6%) and C type (23.4%) were preferred in the top with C, E and F type preferred to the same ratio of 19.4% in the slacks. The fitness and allowance amount of the top B type were the most appropriate (${\geq}4$), the C type was in close contact (2.86), and the F type was inadequate in the neck circumference (1.77). The feeling of pressure was high in the waist, abdomen, thighs, and knees. The area where the elderly people want to improve their strength was the legs; in addition, a pattern design was needed to strengthen leg muscles when designing fitness compression wear. However, a design with excessive adhesion due to a muscle support band was shown to be not preferred. Therefore, depending on the activity, it is necessary to develop a fitness compression wear that applies an optimum stretching ratio of fabric based on body surface area changes.

• Geomechanics and Engineering
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• 제17권1호
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• pp.81-95
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• 2019

Due to the importance of soil reinforcement using geotextiles in geotechnical engineering, study and investigation into long-term performance, design life and survivability of geotextiles, especially due to installation damage are necessary and will affect their economy. During installation, spreading and compaction of backfill materials, geotextiles may encounter severe stresses which can be higher than they will experience in-service. This paper aims to investigate the installation damage of geotextiles, in order to obtain a good approach to the estimation of the material's strength reduction factor. A series of full-scale tests were conducted to simulate the installation process. The study includes four deliberately poorly-graded backfill materials, two kinds of subgrades with different CBR values, three nonwoven needle-punched geotextiles of classes 1, 2 and 3 (according to AASHTO M288-08) and two different relative densities for the backfill materials. Also, to determine how well or how poorly the geotextiles tolerated the imposed construction stresses, grab tensile tests and visual inspections were carried out on geotextile specimens (before and after installation). Visual inspections of the geotextiles revealed sedimentation of fine-grained particles in all specimens and local stretching of geotextiles by larger soil particles which exerted some damage. A regression model is proposed to reliably predict the installation damage reduction factor. The results, obtained by grab tensile tests and via the proposed models, indicated that the strength reduction factor due to installation damage was reduced as the median grain size and relative density of the backfill decreases, stress transferred to the geotextiles' level decreases and as the as-received grab tensile strength of geotextile and the subgrades' CBR value increase.

• Structural Engineering and Mechanics
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• 제86권2호
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• pp.167-180
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• 2023

This work applies a four-known quasi-3D shear deformation theory to investigate the bending behavior of a functionally graded plate resting on a viscoelastic foundation and subjected to hygro-thermo-mechanical loading. The theory utilizes a hyperbolic shape function to predict the transverse shear stress, and the transverse stretching effect of the plate is considered. The principle of virtual displacement is applied to obtain the governing differential equations, and the Navier method, which comprises an exponential term, is used to obtain the solution. Novel to the current study, the impact of the viscoelastic foundation model, which includes a time-dependent viscosity parameter in addition to Winkler's and Pasternak parameters, is carefully investigated. Numerical examples are presented to validate the theory. A parametric study is conducted to study the effect of the damping coefficient, the linear and nonlinear loadings, the power-law index, and the plate width-tothickness ratio on the plate bending response. The results show that the presence of the viscoelastic foundation causes an 18% decrease in the plate deflection and about a 10% increase in transverse shear stresses under both linear and nonlinear loading conditions. Additionally, nonlinear loading causes a one-and-a-half times increase in horizontal stresses and a nearly two-times increase in normal transverse stresses compared to linear loading. Based on the article's findings, it can be concluded that the viscosity effect plays a significant role in the bending response of plates in hygrothermal environments. Hence it shall be considered in the design.

• 한국염색가공학회지
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• 제35권3호
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• pp.169-178
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• 2023

The extended use of polyester nowadays has increased the amount of waste polyester (PET) released into the environment. Although these materials don't directly harm living things or the ecosystem, their inability to biodegrade remains one of the major global threats, driving up the amount of solid waste made up of PET. Environmental concerns have approved an increasing interest in recycled PET however the production of recycled PET with sufficient mechanical properties is still a challenge. Recycled Polyester (rPET) yarns are inexpensive and have the potential to acquire better mechanical characteristics through physical treatments, particularly by using technically simple method like uniaxial drawing. This study inspected the drawn behavior of virgin PET yarns and rPET yarns under various drawing parameters by first analyzing the initial material characteristics of both yarn. The impact of stretching on mechanical and morphological properties was also investigated. The results showed that virgin PET has better properties than rPET yarn; however, mechanical properties resembling virgin PET are achieved after optimizing the draw ratio.

• Structural Engineering and Mechanics
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• 제90권1호
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• pp.83-96
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• 2024

This paper suggests an analytical approach to investigate the free vibration and stability of functionally graded (FG) beams with both perfect and imperfect characteristics using a quasi-3D higher-order shear deformation theory (HSDT) with stretching effect. The study specifically focuses on FG beams resting on variable elastic foundations. In contrast to other shear deformation theories, this particular theory employs only four unknown functions instead of five. Moreover, this theory satisfies the boundary conditions of zero tension on the beam surfaces and facilitates hyperbolic distributions of transverse shear stresses without the necessity of shear correction factors. The elastic medium in consideration assumes the presence of two parameters, specifically Winkler-Pasternak foundations. The Winkler parameter exhibits variable variations in the longitudinal direction, including linear, parabolic, sinusoidal, cosine, exponential, and uniform, while the Pasternak parameter remains constant. The effective material characteristics of the functionally graded (FG) beam are assumed to follow a straightforward power-law distribution along the thickness direction. Additionally, the investigation of porosity includes the consideration of four different types of porosity distribution patterns, allowing for a comprehensive examination of its influence on the behavior of the beam. Using the virtual work principle, equations of motion are derived and solved analytically using Navier's method for simply supported FG beams. The accuracy is verified through comparisons with literature results. Parametric studies explore the impact of different parameters on free vibration and buckling behavior, demonstrating the theory's correctness and simplicity.

• Advances in nano research
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• 제16권5호
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• pp.473-487
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• 2024

The current study employs the nonlocal Timoshenko beam (NTB) theory and von-Kármán's geometric nonlinearity to develop a non-classic beam model for evaluating the nonlinear free vibration of bi-directional functionally-graded (BFG) nanobeams. In order to avoid the stretching-bending coupling in the equations of motion, the problem is formulated based on the physical middle surface. The governing equations of motion and the relevant boundary conditions have been determined using Hamilton's principle, followed by discretization using the differential quadrature method (DQM). To determine the frequencies of nonlinear vibrations in the BFG nanobeams, a direct iterative algorithm is used for solving the discretized underlying equations. The model verification is conducted by making a comparison between the obtained results and benchmark results reported in prior studies. In the present work, the effects of amplitude ratio, nanobeam length, material distribution, nonlocality, and boundary conditions are examined on the nonlinear frequency of BFG nanobeams through a parametric study. As a main result, it is observed that the nonlinear vibration frequencies are greater than the linear vibration frequencies for the same amplitude of the nonlinear oscillator. The study finds that the difference between the dimensionless linear frequency and the nonlinear frequency is smaller for CC nanobeams compared to SS nanobeams, particularly within the α range of 0 to 1.5, where the impact of geometric nonlinearity on CC nanobeams can be disregarded. Furthermore, the nonlinear frequency ratio exhibits an increasing trend as the parameter µ is incremented, with a diminishing dependency on nanobeam length (L). Additionally, it is established that as the nanobeam length increases, a critical point is reached at which a sharp rise in the nonlinear frequency ratio occurs, particularly within the nanobeam length range of 10 nm to 30 nm. These findings collectively contribute to a comprehensive understanding of the nonlinear vibration behavior of BFG nanobeams in relation to various parameters.

• 한국전산구조공학회논문집
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• 제28권3호
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• pp.301-307
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• 2015

결합 기반 페리다이나믹 모델을 통해 다양한 동적취성파괴 현상을 해석할 수 있었지만, 결합 기반 모델은 다양한 재료 구성 모델을 표현하는데 여러 한계를 보여왔다. 특히 결합 기반 모델은 각 결합들이 서로 독립적으로 작용하도록 가정하였기 때문에 3차원 모델에서 포아송비가 1/4로 고정되며 전단 변형이 표현되지 못하고 체적 변형만이 모사되는 문제점이 있다. 본 연구에서는 상태 기반 페리다이나믹 모델을 통한 동적취성파괴 해석을 제시한다. 상태 기반 모델은 일종의 일반화된 페리다이나믹 모델로서 일반적인 재료 구성모델로부터 직접 페리다이나믹 재료 모델을 구성한다. 또한 연결된 모든 결합의 변형을 통해 각 절점의 재료 응답이 결정되기 때문에 체적 및 전단 변형이 모두 표현된다. 본 논문에서는 선형 탄성체에 대해서 상태 기반 평면 응력 페리다이나믹 모델을 소개하고 상태 기반 모델에 적합한 손상 모델에 대해 논의한다. 페리다이나믹 비국부 영역을 축소시키는 $\delta$-수렴성 연구를 통해 동적파괴 모델을 검증하고 상태 기반 모델이 동적 균열 전파를 모델링하는데 적합함을 확인하였다.

• 대중서사연구
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• 제25권4호
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• pp.73-108
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• 2019

본고는 'SF연극'의 역사와 현재를 논의하고자 하는 시도이다. SF연극은 대중에게 여전히 생소한 장르로, 연극이라는 장르의 특성상 무대는 과학적 상상력을 펼치기에 적절치 않은 공간으로 인지되었다. 연극에 과학적 상상력을 결합한 작품들이 빈번하게 공연되고, SF연극에 대한 인식이 확립되기 시작한 것은 2010년 이후로, 연출자들은 사실적 묘사를 포기하면서 기술의 진보 속에서 고립되는 인간의 심리와 세계의 부조리에 몰두하게 됐고, 이것이 오늘날 한국 SF연극을 개괄하는 바탕이 됐다. 이를 감안하여, SF연극에 대한 연구사와 개념 변화로부터 출발해 식민지시기부터 현재까지 SF극의 공연 현황에 대해 살펴보았다. 현재 SF연극에 대한 함의는 만들어지는 중이며, SF연극의 역사를 검토한 결과 다음의 문제점을 발견할 수 있었다. 첫 번째는 과학적 개연성이나 합리성과 관계없이 미래 사회를 배경으로 하거나 기술의 진보를 언급하면 모두 'SF연극'으로 명명되기에 과학적 상상력이 부재하다는 것이다. 두 번째는 융합을 강조하는 시대에 과학과 무대를 접목했다는 시도 자체가 높이 평가 받으면서, 소재의 진보성에만 천착하고 세계관은 여전히 퇴행적인 경우가 두드러진다는 점이다. 세 번째는 여전히 극본이 SF의 고전이나 일본 원작에 기대어 있는 경우가 많다는 점이다. 그럼에도 불구하고, 장르물에 대한 젊은 창작자들의 다양한 시도가 새로운 소재를 원하는 동시대 관객과 호흡할 수 있다면, 한국형 SF극의 저변은 보다 긍정적인 의미에서 확대될 수 있을 것이다.

• 대한기계학회논문집A
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• 제37권2호
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• pp.271-277
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• 2013

냉간압연 및 소둔공정에서의 조질압연 과정은 강종별로 적정 연신율을 부여함으로서 프레스 가공시 항복점 연신 현상을 제거해주는 중요한 공정이다. 적정 연신율 확보를 위해서는 강종별, 사이즈별 정확한 압연하중 예측이 필수이다. 열간 및 냉간압연과는 달리 조질압연에서는 2%이내의 연신율을 부과하는 공정이므로 압연하중 작용 시 롤 바이트 내 에서의 롤의 탄성변형 거동이 복잡하여 정확한 압연하중을 예측하기가 어려워 예측모델이 정립되어 있지 않다. 그럼에도 불구하고 최근 인장강도 590MPa 급 이상의 자동차용 고강도강 개발이 가속화 됨에 따라 조질압연시 정확한 압연하중의 예측은 더욱더 중요하게 되었다. 따라서 본 연구에서는 조질 압연 시 롤 바이트 내에서 롤의 변형거동이 유사하다고 알려져 있는 호일(foil)압연 이론 식을 이용해 조질 압연 시 전체 생산 강종을 대상으로 압연하중 예측 가능성에 대해 검토하였다. 그 결과 인장강도 350MPa 이상 980MPa 이하의 강종에 대해서는 non circular model 이 circular 모델보다 압연하중 예측 정도가 우수하며, 이 영역에서 압연하중 예측 모델로의 적용이 가능함을 확인하였다.

• 대한치과교정학회지
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• 제33권6호
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• pp.465-474
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• 2003

형상기억효과 및 초탄성 특성을 가진 니켈 타이타늄 와이어는 대단히 다양한 제품들이 출시되어 있어서, 보다 적절하면서도 경제적인 재료를 선택하고자 하는 임상가에게 어려움을 주고 있다. 이때, 교정 선재의 기계적 특성에 대한 실험적 연구는 임상가에게 유용한 정보를 제공해 줄 수 있다. 이 연구에서는 5군으로 나뉘어진 4종의 교정선재(stainless steel, multistranded, superelastic nickel titanium 그리고 themoactivated nickel titanium)에 대한 응력 -변형 실험을 통한 기계적 특성에 대한 비교를 시행하였다. 각 군의 교정선재에 대하여 일련의 여섯 가지 실험이 이루어졌다. 처음에는, 각 군에 대하여 선재가 파절될 때까지, 3차례의 실험이 이루어졌다. 그리고, 각 군에서 세 종류의 실험이 이루어졌는데, 표준하중에서 선재를 신장시켜서, 하중을 주었을 때와 하중을 제거하였을 때의 기계적 특성에 대한 신뢰할 만한 비교를 시행하였다. 각 군간의 차이를 알아보기 위하여 t-test를 시행하였다. 실험결과, 생리적인 치아이동을 위한 기계적 특성, 즉 강성, 탄성률, 힘의 발휘 특성 등을 고려해 볼 때, themoactivated nickel titanium, multistranded wire, stainless steel wire 순으로 바람직하였다. 초탄성은 superelastic nickel titanium에서 나타났다. 섭씨 37도에선 themoactivated nickel titanium의 형상기억효과가 나타났는데, 이것은 온도가 기계적 특성을 증진시키는데 중요하다는 것을 보여준다.