• Advances in materials Research
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• 제5권4호
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• pp.263-277
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• 2016

Mechanical properties of $Al/Al_2O_3$ and $Al/B_4C$ composites prepared through powder metallurgy are estimated up to 50% $Al_2O_3$ and 35% $B_4C$ weight fractions using micromechanics models and experiments. The experimental Young's modulus up to 0.40 weight fraction of ceramic is found to lie closely between Ravichandran's/Hashin-Shtrikman lower/upper bounds, and close to self consistent method/Miller and Lannutti method/modified rule of mixture/fuzzy logic method single value predictions. Measured Poisson's ratio lies between rule of mixture/Ravichandran lower and upper bound/modified Ravichandran upper bounds. Experimental Charpy energy lies between Hopkin-chamis method/equivalent charpy energy/Ravichandran lower limit up to 20%, and close to the reciprocal rule of mixture for higher $Al_2O_3$ content. Rockwell hardness (RB) and Micro-hardness of $Al/Al_2O_3$ are closer to modified rule of mixture predictions.

• Steel and Composite Structures
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• 제17권1호
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• pp.105-121
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• 2014

A fundamental limitation of steel structures is the decrease in their load-bearing capacity at high temperatures in fire situations such that structural members may require some additional treatment for fire resistance. In this regard, this paper evaluates the structural stability of fire-resistant steel, introduced in the late 1999s, through tensile coupon tests and proposes some experimental equations for the yield stress, the elastic modulus, and specific heat. The surface temperature, deflection, and maximum stress of fire-resistant steel H-section columns were calculated using their own mechanical and thermal properties. According to a comparison of mechanical properties between fire-resistant steel and Eurocode 3, the former outperformed the latter, and based on a comparison of structural performance between fire-resistant steel and ordinary structural steel of equivalent mechanical properties at room temperature, the former had greater structural stability than the latter through $900^{\circ}C$.

• 한국정밀공학회지
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• 제19권11호
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• pp.89-95
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• 2002

A shadow mask inside the Braun tube of a TV is sustained by springs attached to the glass panel, its vibration cause the picture image to discolor, which is called the microphonic phenomenon. It is found that it results from resonance when the natural frequency of the shadow mask coincides with that of built-in speaker sound. This paper describes experimental and analytical investigations by using FEM on the vibration problem of the shadow mask assembly. The simulation scheme may be efficiently used to develop a new design for a large-screen flat TV.

• Elastomers and Composites
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• 제38권2호
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• pp.167-174
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• 2003

Thermoplastic vulcanizates (TPV) or dynamic vulcanizates are thermoplastic elastomers produced by simultaneous mixing and crosslinking of a rubber and a thermoplastic. The objective of the present work is to investigate the effects of different types of peroxides as curing agents on the properties of PP/EPDM TPVs. The mechanical properties change significantly with the chemical nature of the peroxides and the extent of crosslinking at a fixed PP/EPDM blend ratio. The tensile strength of the TPVs obtained with the various peroxides can be related to the solubility parameters of the polymers and of the peroxides. The Young's modulus of the peroxide-cured TPVs can be correlated with the delta torque values of equivalent thermoset EPDM vulcanizates, corresponding to the crosslinking efficiencies of the peroxides.

• 터널과지하공간
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• 제22권4호
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• pp.284-295
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• 2012

본 연구에서는 암석 절삭 장비의 마모에 직접적인 영향을 주는 인자인 암석의 마모도(abrasiveness) 측정에 관한 연구를 수행하였다. 몇 가지 방법 중 세르샤 마모 시험(Cerchar abrasiveness test)을 통하여 암석의 마모도에 영향을 미치는 인자를 확인하고 효율적인 시험을 수행하기 위한 조건들을 연구하였다. 국내 19종 암석에 대한 시험 결과를 통하여, 세르샤 마모 지수(CAI, Cerchar Abrasiveness Index)에 영향을 미치는 암석의 역학적 물성(단축압축강도, 간접인장강도, 탄성계수, 포아송비, 공극률, 쇼어경도)과의 상관관계를 찾아보았고 X선 회절 분석을 통하여 암석의 구성 광물 중 마모도에 가장 큰 영향을 미치는 석영 함량, 등가 석영 함량과의 관계도 확인하였다. 그 결과로 암석의 입자 결합 특성보다 광물의 특성이 CAI에 영향을 더 미치는 것으로 관찰되었고, 단축압축강도와 등가 석영함량의 함수로 CAI를 예측하는 모델을 제시하였으며 핀의 경도가 커질수록 CAI값이 선형적으로 작아짐을 확인하였다. 수치해석적 연구를 통해 세르샤 마모 시험을 모사한 결과 초기 긁힘 거리에서 대부분의 마모가 발생함을 확인하였고 하중이 증가할수록 CAI값이 증가함을 확인하였다.

• 지질공학
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• 제32권1호
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• pp.59-72
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• 2022

본 연구는 부산 기장지역의 백악기 흑운모 화강암에 대하여 삼차원 개별체 수치해석 기반의 응력-변형 해석을 수행하고 절리성 암반의 강도 및 변형특성을 평가하였다. 절리성 암반의 역학적 특성에 대한 규모효과 및 REV를 규명하기 위한 워크플로우가 제시되었으며 연구지역에서 결정된 REV(representative elementary volume) 크기의 DFN(discrete fracture network) 큐브 블록에 대한 블록강도, 변형계수, 전단탄성계수, 체적탄성계수 등의 강도 및 변형 파라미터가 산정되었다. 연구지역의 역학적 REV 크기는 15 m 큐브로 평가되었으며 DFN 큐브 블록의 평균 블록강도 및 평균 변형계수는 각각 신선암의 52.8% 및 57.7%로 추정되었다. 연구지역의 절리성 암반은 역학적으로 뚜렷한 직교이방성을 나타내는 것으로 평가되었으며 삼차원 수치해석을 통하여 산정된 변형 파라미터를 이용하여 선형-탄성의 직교이방성 구성모델이 도출되었다. 연구지역에 대한 직교이방성 구성모델은 등가의 연속체 해석을 통한 터널 및 지하공간의 안정성 평가에 활용될 수 있다.

• Structural Engineering and Mechanics
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• 제31권6호
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• pp.697-716
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• 2009

This paper summarizes an experimental and analytical study on the seismic behavior of high strength reinforced concrete columns under cyclic loading. In total six cantilever columns with different sizes and concrete compressive strengths were tested. Three columns, small size, had a $325{\times}325$ mm cross section and the three other columns, medium size, were $520{\times}520$ mm. Concrete compressive strength was 80, 130 and 180 MPa. All specimens were designed in accordance with the Japanese design guidelines. The tests demonstrated that, for specimens made of 180 MPa concrete compressive strength, spalling of cover concrete was very brittle followed by a significant decrease in strength. Curvature was much important for the small size than for the medium size columns. Concrete compressive strength had no effect on the curvature distribution for a drift varying between -2% and +2%. However, it had an effect on the drift corresponding to the peak moment and on the equivalent viscous damping variation. Simple equations are proposed for 1) evaluating the concrete Young's modulus for high strength concrete and for 2) evaluating the moment-drift envelope curves for the medium size columns knowing that of the small size columns. Experimental moment-drift and axial strain-drift histories were well predicted using a fiber model developed by the authors.

• 한국지반신소재학회논문집
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• 제1권1호
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• pp.23-29
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• 2002

1980년대 이래 일본 및 미국등에서 연약지반상에 구축된 기존철도의 보수 및 보강시 지오셀 시스템을 이용하여 철도노반의 지지력을 높이는 보강기법들에 대한 연구가 활발히 진행되고 있다. 본 연구에서는 기존 철도의 보수 및 보강을 위해 지오셀 시스템으로 보강된 철도노반에 대해 국내외에서 이미 수행된 연구결과들을 분석하고 평가 하였다. 그리고 이들 결과를 토대로 지반의 변형계수 Ev를 시용하여 철도노반의 두께를 산정하는 다층이론에 근거를 둔 등가방법에 의한 설계방법을 개발하였다.

• Structural Engineering and Mechanics
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• 제85권4호
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• pp.445-459
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• 2023

The current investigation is the first endeavor to apply the full layerwise finite element method (FEM) in free vibration analysis of functionally graded (FG) composite plates reinforced with graphene nanoplatelets (GPLs) in thermal environment. Unlike the equivalent single-layer (ESL) theories, the layerwise FEM focuses on all three-dimensional (3D) effects. The GPLs weight fraction is presumed invariable in each layer but varies through the plate thickness in a layerwise model. The modified Halpin-Tsai model is employed to acquire the effective Young's modulus. The rule of mixtures is applied to specify the effective Poisson's ratio and mass density. First, the current method is validated by comparing the numerical results with those stated in the available works. Next, a thorough numerical study is performed to examine the influence of various factors involving the pattern of distribution, weight fraction, geometry, and size of GPLs, together with the thickness-to-span ratio, thermal environment, and boundary conditions of the plate, on its free vibration behaviors. Numerical results demonstrate that employing a small percentage of GPL as reinforcement considerably grows the natural frequencies of the pure epoxy. Also, distributing more square-shaped GPLs, involving a smaller amount of graphene layers, and vicinity to the upper and lower surfaces make it the most efficient method to enhance the free vibration behaviors of the plate.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1455-1463
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• 2009

Theoretical mechanics analysis and finite element simulation were performed to investigate creep deformation behavior at the crack tip of transversely isotropic materials under small scale creep (SCC) conditions. Mechanical behavior of material was assumed as an elastic-$2^{nd}$ creep, which elastic modulus ( E ), Poisson's ratio ( ${\nu}$ ) and creep stress exponent ( n ) were isotropic and creep coefficient was only transversely isotropic. Based on the mechanics analysis for material behavior, a constitutive equation for transversely isotropic creep behavior was formulated and an equivalent creep coefficient was proposed under plain strain conditions. Creep deformation behavior at the crack tip was investigated through the finite element analysis. The results of the finite element analysis showed that creep deformation in transversely isotropic materials is dominant at the rear of the crack-tip. This result was more obvious when a load was applied to principal axis of anisotropy. Based on the results of the mechanics analysis and the finite element simulation, a corrected estimation scheme of the creep zone size was proposed in order to evaluate the creep deformation behavior at the crack tip of transversely isotropic creeping materials.