• 소성∙가공
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• 제14권6호
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• pp.559-564
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it is utilized in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. Accurate understanding of material's mechanical properties with various strain rates is required in order to guarantee the reliability of structural parts made of INCONEL 718. This paper is concerned with the dynamic material properties of the INCONEL 718 at various strain rates. The dynamic response of the INCONEL 718 at the intermediate strain rate is obtained from the high speed tensile test and at the high strain rate is from the split Hopkinson pressure bar test. The effect of the strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure is evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of rNCONEL 718.

• Structural Engineering and Mechanics
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• 제13권2호
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• pp.135-154
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• 2002

This paper presents the convected material frame approach to study the nonlinear behavior of inelastic frame structures. The convected material frame approach is a modification of the co-rotational approximation by incorporating an adaptive convected material frame in the basic definition of the displacement vector and strain tensor. In the formulation, each discrete element is associated with a local coordinate system that rotates and translates with the element. For each load increment, the corresponding strain-displacement and nodal force-stress relationships are defined in the updated local coordinates, and based on the updated element geometry. The rigid body motion and deformation displacements are decoupled for each increment. This modified approach incorporates the geometrical nonlinearities through the continuous updating of the material frame geometry. A generalized nonlinear function is used to derive the inelastic constitutive relation and the kinematic hardening is considered. The equation of motion is integrated by an explicit procedure and it involves only vector assemblage and vector storage in the analysis by assuming a lumped mass matrix of diagonal form. Several numerical examples are demonstrated in close agreement with the solutions obtained by the ANSYS code. Numerical studies show that the proposed approach is capable of investigating large deflection of inelastic planar structures and providing an excellent numerical performance.

• Geomechanics and Engineering
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• 제9권6호
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• pp.729-742
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• 2015

The aim of the present work was the study of instability in a loose sand from Les Dunes beach in Ain Beninan, Algeria, where the Boumerdes earthquake occurred in 2003. This earthquake caused significant structural damages and claimed the lives of many people. Damages caused to infrastructures were strongly related to phenomena of liquefaction. The study was based on the results of two drained and six undrained triaxial tests over a local sand collected in a region where liquefaction occurred. All the tests hereby analyzed followed compression stress-paths in monotonic conditions and the specimens were isotropically consolidated, since the objective was to study the instability due to static loading as part of a more general project, which also included cyclic studies. The instability was modeled with the second-order work increment criterion. The definition of the instability line for Les Dunes sand and its relation with yield surfaces allowed the identification of the region of potential instability and helped in the evaluation of the susceptibility of soils to liquefy under undrained conditions and its modeling. The dilatancy rate was studied in the points where instability began. Some mixed tests were also simulated, starting with drained conditions and then changing to undrained conditions at different time steps.

• 반도체디스플레이기술학회지
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• 제9권2호
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• pp.91-96
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• 2010

In recent years there have been considerable attentions on nanoimprint lithography (NIL) by the display device and semiconductor industry due to its potential abilities that enable cost-effective and high-throughput nanofabrication. Although one of the current major research trends of NIL is large-area patterning, the technical difficulties to keep the uniformity of the residual layer become severer as the imprinting area increases more and more. In this paper we consider the roll-to-plate type imprinting process. In the process a glass mold, which is placed upon the 2nd generation TFT-LCD glass sized substrate(370${\yen}$470 mm), is rolled by a rubber roller to achieve a uniform residual layer. The pressure distribution on the glass mold by rolling of the rubber roller is crucial information to analyze mold deformation, transferred pattern quality, uniformity of residual layer and so forth. In this paper the quantitative pressure distribution induced by rolling of the rubber roller was calculated with finite element analysis under the assumption of Neo-Hookean hyperelastic constitutive relation. Additionally the numerical results were verified by the experiments.

• Nuclear Engineering and Technology
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• 제50권8호
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• pp.1330-1338
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• 2018

High-density UMo/Zr monolithic nuclear fuel plates have a promising application prospect in high flux research and test reactors. The solid state welding method called co-rolling is used for their fabrication. Hot co-rolling simulations for the composite blanks of UMo/Zr monolithic nuclear fuel plates are performed. The effects of coupon sizes and mechanical property parameters on the contact pressures between the to-be-bonded surfaces are investigated and analyzed. The numerical simulation results indicate that 1) the maximum contact pressures between the fuel coupon and the Zircaloy cover exist near the central line along the plate length direction; as a whole the contact pressures decrease toward the edges in the plate width direction; and lower contact pressures appear at a large zone near the coupon corner, where de-bonding is easy to take place in the in-pile irradiation environments; 2) the maximum contact pressures between the fuel coupon and the Zircaloy parts increase with the initial coupon thickness; after reaching a certain thickness value, the contact pressures hardly change, which was mainly induced by the complex deformation mechanism and special mechanical constitutive relation of fuel coupon; 3) softer fuel coupon will result in lower contact pressures and form interfaces being more out-of-flatness.

• Advances in aircraft and spacecraft science
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• 제10권3호
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• pp.257-279
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• 2023

This manuscript is dedicated to deriving the closed form solutions of free vibration of viscoelastic nanobeam embedded in an elastic medium using nonlocal differential Eringen elasticity theory that not considered before. The kinematic displacements of Euler-Bernoulli and Timoshenko theories are developed to consider the thin nanobeam structure (i.e., zero shear strain/stress) and moderated thick nanobeam (with constant shear strain/stress). To consider the internal damping viscoelastic effect of the structure, Kelvin/Voigt constitutive relation is proposed. The perforation geometry is intended by uniform symmetric squared holes arranged array with equal space. The partial differential equations of motion and boundary conditions of viscoelastic perforated nonlocal nanobeam with elastic foundation are derived by Hamilton principle. Closed form solutions of damped and natural frequencies are evaluated explicitly and verified with prestigious studies. Parametric studies are performed to signify the impact of elastic foundation parameters, viscoelastic coefficients, nanoscale, supporting boundary conditions, and perforation geometry on the dynamic behavior. The closed form solutions can be implemented in the analysis of viscoelastic NEMS/MEMS with perforations and embedded in elastic medium.

• Advances in nano research
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• 제16권3호
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• pp.265-272
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• 2024

In this paper, the problem of static bending of axially functionally graded (AFG) nanobeam is formulated with the local stress(Lσ)- and strain-driven(εD) two-phase local/nonlocal integral models (TPNIMs). The novelty of the present study aims to compare the size-effects of nonlocal integral models on bending deflections of AFG Euler-Bernoulli nano-beams. The integral relation between strain and nonlocal stress components based on two types nonlocal integral models is transformed unitedly and equivalently into differential form with constitutive boundary conditions. Purely LσD- and εD-NIMs would lead to ill-posed mathematical formulation, and Purely εD- and LσD-nonlocal differential models (NDM) may result in inconsistent size-dependent bending responses. The general differential quadrature method is applied to obtain the numerical results for bending deflection and moment of AFG nanobeam subjected to different boundary and loading conditions. The influence of AFG index, nonlocal models, and nonlocal parameters on the bending deflections of AFG Euler-Bernoulli nanobeams is investigated numerically. A consistent softening effects can be obtained for both LσD- and εD-TPNIMs. The results from current work may provide useful guidelines for designing and optimizing AFG Euler-Bernoulli beam based nano instruments.

• 대한토목학회논문집
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• 제4권3호
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• pp.43-52
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• 1984

본문(本文)은 재생성(再生成)한 해성점토(海成粘土)에 대한 점토(粘土)의 시간효과특성(時間効果特性)과 정규압밀(正規壓密)된 점토(粘土)의 시간의존성거동(時間依存性擧動)을 보편적(普遍的)으로 설명(說明)할 수 있는 구성방정식(構成方程式)과 관계(關係)가 있다. 따라서 본문(本文)에서는 T. Adachi와 F. Oka가 제안(提案)한 구성식(構成式)을 채택(採擇)하였으며 이 구성방정식(構成方程式)은 Cam-clay 이론(理論)을 Perzyna외 탄일점소성연속체이론(彈一粘塑性連續體理論)에 적용(適用)하여 수립(樹立)된 것이다. 그리고 이 구성방정식(構成方程式)이 재생성(再生成)한 무안점토(務安粘土)에 대하여 어떻게 적용(適用)될 것인가를 실험적(實驗的)으로 연구(硏究)한 것이다. 본(本) 연구(硏究)에서 얻어진 결론(結論)의 주요(主要)한 것은 다음과 같다. 1. 등방압밀(等方壓密)과 등방응력완화시험(等方應力緩和試驗)의 결과(結果)로부터 정적(靜的), 동적(動的)인 강복면(降伏面)이 각각 존재(存在)함을 확인(確認)할 수 있었다. 2. 일정변형전단시험(一定變形剪斷試驗)과 응력완화시험(應力緩和試驗)의 결과(結果)로부터 시간효과(時間効果)의 특성(特性) 즉 응력(應力)-변형율(變形率)-시간간(時間間)의 유일(唯一)한 관계(關係)가 존재(存在)함을 알 수 있다. 3. Cam-clay 이론(理論)에 의한 응력경로(應力經路)와 변형율(變形率) 추정(推定)에 있어서 이론치(理論値)와 실험치간(實驗値間)에는 차이(差異)가 있다. 4. Cam-clay 이론(理論)을 Perzyna의 탄일점소성체이론(彈一粘塑性體理論)에 적용(適用)시킨 구성방정식(構成方程式)(6)은 비배수상태(非排水狀態)의 등방응력완화과정중(等方應力緩和過程中) 발생(發生)하는 간극수압(間隙水壓)의 거동(擧動)을 설명(說明)할 수 있다. 그리고, 동일(同一)한 혹은 다른 압밀이력(壓密履歷) 받은 점토(粘土)에 대하여 다른 변형속도(變形速度) 적용(適用)한 비배수(非排水) 3축시험(軸試驗)의 결과(結果)를 예측(豫測)하는데 상당한 적합성(適合性)이 있음을 알았다. 5. 이 구성방정식(構成方程式)에는 8개의 재료상수(材料常數)가 있는데 3축압축시험(軸壓縮試驗)을 통하여 쉽게 얻어진다.

• 대한기계학회논문집A
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• 제26권5호
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• pp.924-931
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• 2002

Vacuum interrupters in order to be used in various switch-gear components such as circuit breakers, distribution switches, contactors, etc. spread the arc uniformly over the surface of the contacts. The electrodes of vacuum interrupters are made of sinter-forged Cu-Cr materials for good electrical and mechanical characteristics. Since the closing velocity is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at the high strain rate is obtained from the split Hopkinson pressure bar test using disc-type specimens. Experimental results from both quasi-static and dynamic compressive tests are Interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the value of five parameters such as the initial velocity of a movable electrode, the added mass of a movable electrode, the wipe spring constant, initial offset of a wipe spring and the virtual fixed spring constant.

• 대한기계학회논문집A
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• 제26권5호
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• pp.939-951
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• 2002

We propose a new multiscale Galerkin method based on interpolation wavelets for two-dimensional Poisson's and plane elasticity problems. The major contributions of the present work are: 1) full multiresolution numerical analysis is carried out, 2) general boundaries are handled by a fictitious domain method without using a penalty term or the Lagrange multiplier, 3) no special integration rule is necessary unlike in the (bi-)orthogonal wavelet-based methods, and 4) an efficient adaptive scheme is easy to incorporate. Several benchmark-type problems are considered to show the effectiveness and the potentials of the present approach. is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at the high strain rate is obtained from the split Hopkinson pressure bar test using disc-type specimens. Experimental results from both quasi-static and dynamic compressive tests are Interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the value of five parameters such as the initial velocity of a movable electrode, the added mass of a movable electrode, the wipe spring constant, initial offset of a wipe spring and the virtual fixed spring constant.