Consistent couple-stress theory for free vibration analysis of Euler-Bernoulli nano-beams made of arbitrary bi-directional functionally graded materials

Mohammad Zamani Nejad,Amin Hadi,Ali Farajpour 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.2

In this paper, using consistent couple stress theory and Hamilton's principle, the free vibration analysis of Euler- Bernoulli nano-beams made of bi-directional functionally graded materials (BDFGMs) with small scale effects are investigated. To the best of the researchers' knowledge, in the literature, there is no study carried out into consistent couple-stress theory for free vibration analysis of BDFGM nanostructures with arbitrary functions. In addition, in order to obtain small scale effects, the consistent couple-stress theory is also applied. These models can degenerate into the classical models if the material length scale parameter is taken to be zero. In this theory, the couple-tensor is skew-symmetric by adopting the skew-symmetric part of the rotation gradients as the curvature tensor. The material properties except Poisson's ratio are assumed to be graded in both axial and thickness directions, which it can vary according to an arbitrary function. The governing equations are obtained using the concept of Hamilton principle. Generalized differential quadrature method (GDQM) is used to solve the governing equations for various boundary conditions to obtain the natural frequencies of BDFG nano-beam. At the end, some numerical results are presented to study the effects of material length scale parameter, and inhomogeneity constant on natural frequency.

Impact of inboard materials on the size of a tokamak fusion reactor

Bong Guen HONG 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2

Impact of inboard materials on the size of a tokamak fusion reactor were studied via a coupled analysis of tokamak systems and neutron transport. The shielding capability was the best for a tungsten carbide (WC), showing smaller reactor size than cases using other shield materials. It was found that the tritium self-sufficiency requirement could be satisfied with an inboard blanket replaced by neutron multiplier and/or reflector materials. An optimum combination of the multiplier and reflector materials can lead to smaller reactor size than the reactor with an inboard blanket.

나노 연/경자성 분말 재료를 이용한 Exchange-coupling 자석의 제조 기술

김종렬(Jongryoul Kim),조상근(Sang-Geun Cho),전광원(Kwang-Won Jeon) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.6

Magnetic materials has been applied to various fields due to their energy convertible properties between electrical and mechanical energy. Particularly, permanent magnets have been currently attracted much attention because they produce external magnetic field without any electrical current. For high efficiency, a demand for permanent magnets containing rare earth elements has been continuously increased, which abruptly raises the price and causes the supply difficulty of rare earth materials. Therefore, the development of permanent magnets with less or without rare earth elements become a urgent issue. In this report, the current trend and major issues on high efficiency permanent magnets, particularly exchange-coupling magnets, are discussed.

An Experimental and Numerical Study on the Stemming Effect of a Polymer Gel in Explosive Blasting

Khaqan Baluch,김정규,고영훈,김승준,정승원,양형식,김용기,김종관 대한화약발파공학회 2018 화약발파 Vol.36 No.4

In this study, several concrete-block blast tests and AUTODYN numerical analyses were conducted to analyze the effects of different stemming and coupling materials on explosion results. Air, sand, and polymer gel were used as both the stemming and coupling materials. The stemming and coupling effects of these materials were compared with those of the full-charge condition. Soil-covered or buried concrete blocks were used for field crater tests. It was found from the concrete block tests and numerical analyses that both the crater size and the peak pressure around the blast hole were higher when the polymer gel was used than when the sand and the decoupling condition were used. The numerical analyses revealed the same trend as those of the field tests. Pressure peaks in concrete block models were calculated to be 37, 30, and 16 MPa, respectively, for the cases of the polymer gel, sand, and no stemming and decoupling condition. The pressure peak was 52 MPa in the case of full-charge condition, which was the highest pressure. But the damage area for the case was smaller than that obtained from the use of polymer gel. Full-charge was also used as a reference test.

An effective solution of electro-thermo-structural problem of uni-axially graded material

J. Murín,V. Kutis,M. Masny 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.28 No.6

The aim of this contribution is to present a new link/beam finite element suitable for electrothermo-structural analysis of uni-axially graded materials. Continuous polynomial variation of geometry and material properties will be considered. The element matrix and relations for solution of Joule’s heat (and its distribution to the element nodes) have been established in the sense of a sequence method of a coupled problem solution. The expression for the solution of nodal forces caused by a continuously distributed temperature field has also been derived. The theoretical part of this contribution is completed by numerical validation, which proves the high accuracy and effectiveness of the proposed element. The results of the performed experiments are compared with those obtained using the more expensive multiphysical link element and solid element of the FEM program Ansys. The proposed finite element could be used not only in the multiphysical analysis of the current paths and actuators but also in analysis of other 1D construction parts made of composite or uni-axially graded materials.

An effective solution of electro-thermo-structural problem of uni-axially graded material

Murin, J.,Kutis, V.,Masny, M. Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.28 No.6

The aim of this contribution is to present a new link/beam finite element suitable for electrothermo-structural analysis of uni-axially graded materials. Continuous polynomial variation of geometry and material properties will be considered. The element matrix and relations for solution of Joule's heat (and its distribution to the element nodes) have been established in the sense of a sequence method of a coupled problem solution. The expression for the solution of nodal forces caused by a continuously distributed temperature field has also been derived. The theoretical part of this contribution is completed by numerical validation, which proves the high accuracy and effectiveness of the proposed element. The results of the performed experiments are compared with those obtained using the more expensive multiphysical link element and solid element of the FEM program Ansys. The proposed finite element could be used not only in the multiphysical analysis of the current paths and actuators but also in analysis of other 1D construction parts made of composite or uni-axially graded materials.

초고강도 강판 성형 시의 스프링백 해석 및 금형 소재 적합성 검토

오인석,윤동렬,조준행,이명규,김헌영,김형종 한국소성∙가공학회 2020 소성가공 : 한국소성가공학회지 Vol.29 No.4

In this study, formability and springback behavior of 1.5 GPa grade ultra-high strength steel (UHSS) sheet were predicted through the finite element simulation, and structural stability of the forming dies was verified by the coupled forming-structural analysis. Uniaxial tension and uniaxial tension-compression tests were performed to obtain experimental data for modeling the springback properties of the sheet material. The springback values predicted by simulation were compared with those from actual measurements. The results calculated from the kinematic hardening model were found to be much more accurate than those from the isotropic hardening model. Deformation of the forming die and springback of the product were calculated by the coupled forming-structural analysis. The higher the strength of the die material, the smaller the surface displacement of the die and the springback of the product. The internal stresses of the dies made of three materials, FC300, FCD550 and STD11 were compared with the yield stress of each material. The results provided a basis for determining the most suitable material for each part of the die set. As a result, simulation techniques have been established for predicting formability and springback in the UHSS sheet forming process.

Stress wave propagation in composite materials

Shen, Siyuan J.,Pfister, Jens C.,Lee, James D. Techno-Press 2001 Structural Engineering and Mechanics, An Int'l Jou Vol.11 No.4

The linear constitutive relations and the failure criteria of composite materials made of thermoviscoelastic solids are presented. The post-failure material behavior is proposed and the dynamic finite element equations are formulated. However, a nonlinear term is kept in the energy equation because it represents the effect of the second law of thermodynamics. A general purpose nonlinear three-dimensional dynamic finite element program COMPASS is upgraded and employed in this work to investigate the interdependence among stress wave propagation, stress concentration, failure progression and temperature elevation in composite materials. The consequence of truthfully incorporating the second law of thermodynamics is clearly observed: it will always cause temperature rise if there exists a dynamic mechanical process.

Buckling analysis of FGM Euler-Bernoulli nano-beams with 3D-varying properties based on consistent couple-stress theory

Amin Hadi,Mohammad Zamani Nejad,Abbas Rastgoo,Mohammad Hosseini 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.6

This paper contains a consistent couple-stress theory to capture size effects in Euler-Bernoulli nano-beams made of three-directional functionally graded materials (TDFGMs). These models can degenerate into the classical models if the material length scale parameter is taken to be zero. In this theory, the couple-stress tensor is skew-symmetric and energy conjugate to the skew-symmetric part of the rotation gradients as the curvature tensor. The material properties except Poisson's ratio are assumed to be graded in all three axial, thickness and width directions, which it can vary according to an arbitrary function. The governing equations are obtained using the concept of minimum potential energy. Generalized differential quadrature method (GDQM) is used to solve the governing equations for various boundary conditions to obtain the natural frequencies of TDFG nano-beam. At the end, some numerical results are performed to investigate some effective parameter on buckling load. In this theory the couple-stress tensor is skew-symmetric and energy conjugate to the skew-symmetric part of the rotation gradients as the curvature tensor.

인장변형에 따른 단층 BrBiAsCl밴드 제어

진영록,이재광 한국물리학회 2023 새물리 Vol.73 No.2

Using first-principle density functional theory calculations involving spin–orbit coupling (SOC), we study the electronic property changes of the BrBiAsCl monolayer under tensile strain. BrBiAsCl features a structure similar to that of monolayer hexagonal boron nitride. BrBiAsCl without SOC features a bandgap of 0.76 eV and exhibits typical semiconductor characteristics. In contrast, in BrBiAsCl with SOC, spin splitting results in downward and upward shifts in the conduction and valence bands, respectively. Consequently, a graphene-like linear band is formed near the Fermi energy level. Furthermore, tensile strain efficiently modifies the band structure of the BrBiAsCl monolayer. Our theoretical studies can guide the design of two-dimensional material-based high-mobility devices. 스핀-궤도 결합 (Spin orbit coupling: SOC)이 고려된 제일원리 계산 (First-principles calculation)을 이용하여, BrBiAsCl 단층 (monolayer) 물질에 대해 인장 변형 (tensile strain)하에서 전자구조 변화를 연구하였다. BrBiAsCl 단층 물질은, 이차원 단층 형태의 육각형 질화 붕소와 유사한 구조를 가진다. 스핀-궤도 결합을 고려하지 않으면 0.76 eV의 밴드 갭을 가지는 전형적인 반도체 특성을 가진다. 그에 반해 스핀-궤도 결합을 고려하면 원자번호가 큰 Bi, As, Br 원자들로 인해 최저 전도대 (conduction band minimum: CBM)가 스핀 갈라짐 (spin splitting)으로 에너지 준위가 내려오고, 최고 가전자대 (valence band maximum: VBM)는 에너지 준위가 올라간다. 이로 인해 페르미 에너지 근처에서 전도대와 가전자대가 만나며, 그래핀과 유사한 선형적인 밴드구조를 가지는 것을 확인하였다. 인장 변형이 가해짐에 따라 밴드 구조가 변화됨을 알 수 있었다. 이 연구 결과는 향후, 이차원 물질 기반 고 이동도 소자 디자인에 이용될 것으로 기대한다.