• Smart Structures and Systems
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• 제31권6호
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• pp.545-559
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• 2023

Nanoparticle strips (NPS) are widely used as external reinforcers for two-way reinforced concrete slabs. However, the Structural Health Monitoring (SHM) of these slabs is a very important issue and was evaluated in this study. This study has been done analytically and numerically to optimize the placement of sensors. The properties of slabs and carbon nanotubes as composite sheets were considered isotopic and orthotropic, respectively. The nonlinear Finite Element Method (FEM) approach and suitable optimal placement of sensor approach were developed as a new MATLAB toolbox called DECOMAC by the authors of this paper. The Suitable multi-objective function was considered in optimized processes based on distributed ECOMAC method. Some common concrete slabs in construction with different aspect ratios were considered as case studies. The dimension and distance of nano strips in retrofitting process were selected according to building codes. The results of Optimal Sensor Placement (OSP) by DECOMAC algorithm on un-retrofitted and retrofitted slabs were compared. The statistical analysis according to the Mann-Whitney criteria shows that there is a significant difference between them (mean P-value = 0.61).

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 봄 학술논문 발표대회
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• pp.195-196
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• 2021

The pore distribution of the cement mortar mixed with carbon nanotubes was found to have a large number of pores at (370~80)㎛, and the distribution ratio was larger as the carbon nanotubes were mixed. However, the pores with a fine particle diameter of (10-0.5) ㎛ were found to be larger as the carbon nanotubes were incorporated. However, the distribution of pores of the test specimens of conductive cement mortar with deterioration damage was found to be distributed in a number of particle diameters of (500 to 100) ㎛ and (10 to 0.5) ㎛. It is judged that the particle diameter of the internal pores increased due to the damage. However, as the mixing ratio of the test specimen with carbon nanotubes increased, the distribution of voids was relatively lower than that of plain, and it was judged to have excellent resistance to deterioration damage.

• Advances in nano research
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• 제14권6호
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• pp.541-555
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• 2023

The extensive use of polymeric matrix composites in the athletic sector may be attributed to its high strength-to-weight ratio, production economy, and a longer lifespan than conventional materials. This study explored the impact of carbon nanotubes on the properties of different composite field sports equipment components. The test specimens were fabricated using the compression molding technique. The insertion of carbon nanotubes increases mechanical properties related to the process parameters to account for an improvement in the stick sections' overall performance. The dynamic response of functionally graded reinforced nanocomposite wire structure is examined in this paper on the bases of high-order hyperbolic beam theory lined to the size-dependent nonclassical nonlocal theory under the external mechanical load due to the physical activities. Finally, the impact of different parameters on the stability of nanocomposite structures is discussed in detail.

• Advances in nano research
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• 제14권5호
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• pp.463-474
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• 2023

The purpose of this paper is to present the analysis of propagating and evanescent waves in functionally graded (FG) nanoplates with the consideration of nonlocal effect. The analytical integration nonlocal stress expansion Legendre polynomial method is proposed to obtain complete dispersion curves in the complex domain. Unlike the traditional Legendre polynomial method that expanded the displacement, the presented polynomial method avoids employing the relationship between local stress and nonlocal stress to construct boundary conditions. In addition, the analytical expressions of numerical integrations are presented to improve the computational efficiency. The nonlocal effect, inhomogeneity of medium and their interactions on wave propagation are studied. It is found that the nonlocal effect and inhomogeneity of medium reduce the frequency bandwidth of complex evanescent Lamb waves, and make complex evanescent Lamb waves have a higher phase velocity at low attenuation. The occurrence of intersections of propagating Lamb wave in the nonlocal homogeneous plate needs to satisfy a smaller Poisson's ratio condition than that in the classical elastic theory. In addition, the inhomogeneity of medium enhances the nonlocal effect. The conclusions obtained can be applied to the design and dynamic response evaluation of composite nanostructures.

• Steel and Composite Structures
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• 제49권3호
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• pp.293-306
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• 2023

This article focuses on the study of the buckling behavior of two-dimensional functionally graded (2D-FG) nanosize tubes, including porosity, based on the first shear deformation and higher-order theory of the tube. The nano-scale tube is simulated using the nonlocal gradient strain theory, and the general equations and boundary conditions are derived using Hamilton's principle for the Zhang-Fu's tube model (as a higher-order theory) and Timoshenko beam theory. Finally, the derived equations are solved using a numerical method for both simply-supported and clamped boundary conditions. A parametric study is performed to investigate the effects of different parameters, such as axial and radial FG power indices, porosity parameter, and nonlocal gradient strain parameters, on the buckling behavior of the bi-dimensional functionally graded porous tube. Keywords: Nonlocal strain gradient theory; buckling; Zhang-Fu's tube model; Timoshenko theory; Two-dimensional functionally graded materials; Nanotubes; Higher-order theory.

• Advances in nano research
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• 제17권1호
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• pp.61-73
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• 2024

This paper presents nonlinear vibration analysis of a composite cylindrical shell. The core of the shell is made of functionally graded (FG) porous materials and layers is fabricated of carbon nanotubes (CNTs) reinforced nanocomposites. To increase the accuracy of results, neutral surface position is considered. First-order shear deformation theory is used as displacement field to derive the basic relations of equation motions. In addition, von-Karman nonlinear strains are employed to account geometric nonlinearity and to enhance the results' precision, the exact position of the neutral surface is considered. To governing the partial equations of motion, the Hamilton's principle is used. To reduce the equation motions into a nonlinear motion equation, the Galerkin's approach is employed. After that the nonlinear motion equation is solved by multiple scales method. Effect of various parameters such as volume fraction and distribution of CNTs along the thickness directions, different patterns and efficiency coefficients of porous materials, geometric characteristics and initial conditions on nonlinear to linear ratio of frequency is investigated.

• 폴리머
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• 제39권1호
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• pp.23-32
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• 2015

상 전이 물질인 파라핀 왁스를 초고분자량 폴리에틸렌(UHMWPE)과의 absorption method를 통해 파우더를 제조 후 hot press를 사용하여 형태안정성 상 전이 물질(SSPCM) composite를 제조하였다. SSPCM composite의 화학, 미세구조, 형태, 열적, 결정구조, 유변학적 특성을 조사하기 위하여 FTIR, SEM, DSC, XRD, ARES 측정을 하였다. FTIR 분석결과 파라핀 및 UHMWPE의 고유 피크들이 나타나고 있는 것을 확인하였고, SEM 분석결과 파라핀의 농도가 40 wt%까지는 표면이 상당히 팽윤되며 거친 특성을 나타냄을 확인할 수 있었고, DSC 분석결과 SSPCM에서 파라핀 및 UHMWPE의 고유 융점들이 나타났고, XRD 분석에서는 파라핀과 UHMWPE의 $2{\theta}$ 값들이 SSPCM에서도 나타남을 확인할 수 있었고, ARES 분석에서는 파라핀 농도에 따른 G', G", $tan{\delta}$ 값의 변화를 확인할 수 있었다. 종합적인 분석 결과를 통해, 파라핀의 농도가 30 wt%일 때, 형태안정성 측면에서 최적의 농도임을 확인할 수 있었다.

• 한국분말재료학회지
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• 제9권6호
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• 대한환경공학회지
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• 제38권9호
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• pp.521-527
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• 2016

나노 영가철은 산화환원기작을 통하여 염소계 유기화합물과 같은 물질을 효과적으로 처리할 수 있다고 알려져 있지만, 작은 사이즈로 인하여 회수가 어려운 단점으로 인하여 실제 수처리 공정에서는 유출 등의 우려로 널리 적용되지 못하였다. 이와 같은 한계를 극복하기 위하여 활성탄과 같은 담체에 고정화 하여 사용하는 연구가 활발히 진행되었다. 본 연구에서는 활성탄에 영가철의 고정화 시 대표적으로 사용되는 고온 및 상온의 두 가지 경로에 대해 평가하였으며, 결과를 바탕으로 최적의 합성 조건을 도출하였다. 효과적인 나노영가철/입상활성탄 복합체를 합성하기 위해서는 높은 철 함량과 더불어 영가철의 분율을 높이는 것이 중요하며, 이를 위해서는 합성 과정에서 형성되는 철 산화물 및 수산화물의 형성을 억제하는 것이 중요한 것으로 나타났다. 또한 영가철의 분율을 높이기 위한 환원 시간 및 중간 건조 과정의 유무 등 합성 조건의 영향을 살펴보았으며, 그 결과 중간 건조 과정 없이 바로 $NaBH_4$를 이용한 환원 조건을 약 2시간 이상 유지하는 것이 최적 조건임을 확인하였다. 합성된 나노영가철/입상활성탄 복합체는 활성탄의 흡착 능력과 영가철의 환원 능력을 동시에 보유함으로써 나이트로벤젠과 같은 환원이 가능한 오염물질의 제거에 효과적으로 나타났다.

• 감성과학
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• 제13권4호
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• pp.687-692
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• 2010

본 연구에서는 원적외선 방출 직불 소재를 개발하기 위해서 나노사이즈 게르마늄 업자와 PET chip을 마스터 배치 칩으로 제조하고 이를 PET와 용융 방사하여 sheath-core conjugate 복합사를 제조하여 이들의 물성과 이들 복합사로 제조한 직물의 원적외선 방출특성을 측정 분석하였다. 또한 게르마늄을 함유한 필라멘트와 직물의 물성을 측정하고 이들 물성이 사가공 공정의 중요공정 인자인 벨트각과 사속비 등의 공정인자와 직물 설계에서의 경사와 위사의 밀도에 관계하는 직물 밀도 계수 등의 설계 조건에 의해 직물 역학 특성과 직물 촉감등의 물성이 어떠한 변화를 가져 오는가에 대한 분석을 하였다. 최적 방사조건에 의한 core부에 게르마늄이 함유된 sheath-core형 PET복합사를 제조하였으며 이들의 절단강신도 모두 일반 PET계(系)의 물성치를 보였으며 DTY는 제직성에 문제가 없는 강신도를 보였고 습건열 수축률은 일반 PET사 보다 높은 값을 보였다. 게르마늄 함유 직물의 원적외선 방사강도는 $5{\sim}20{\mu}m$ 파장 영역에서 $3.53{\times}10^2W/m^2$을 보였으며 방사율은 0.874를 보였다. 그리고 최적 사가공 공정 조건 설정과 최적 직물밀도 설계로 직물의 역학 특성치와 촉감 특성의 저하를 막을 수 있음을 확인할 수 있었다.