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  • Open Access

    ARTICLE

    A Note on Statistical Strength of Carbon Nanotubes

    X. Frank Xu1,2, Yuxin Jie3, Irene J. Beyerlein4

    CMC-Computers, Materials & Continua, Vol.38, No.1, pp. 17-30, 2013, DOI:10.3970/cmc.2013.038.017

    Abstract This note aims to relate the measured strength statistics of individual carbon nanotubes (CNTs) to the physics of brittle fracture and the weakest link model. By approximating an arbitrary flaw size distribution with a segmented power law, an effort is made to extend applicability of the Weibull distribution to arbitrary flaw populations, which explains why the Weibull distribution fits the experimental data of CNTs and many other brittle materials, and why in other cases it is not so clear. A generalized Weibull distribution is proposed to account for all non-asymptotic cases. The published CNT testing More >

  • Open Access

    ARTICLE

    From Ordered to Disordered: The Effect of Microstructure on Composite Mechanical Performance

    L.B. Borkowski1, K.C. Liu1, A. Chattopadhyay1

    CMC-Computers, Materials & Continua, Vol.37, No.3, pp. 161-193, 2013, DOI:10.3970/cmc.2013.037.161

    Abstract The microstructural variation in fiber-reinforced composites has a direct relationship with its local and global mechanical performance. When micromechanical modeling techniques for unidirectional composites assume a uniform and periodic arrangement of fibers, the bounds and validity of this assumption must be quantified. The goal of this research is to quantify the influence of microstructural randomness on effective homogeneous response and local inelastic behavior. The results indicate that microstructural progression from ordered to disordered decreases the tensile modulus by 5%, increases the shear modulus by 10%, and substantially increases the magnitude of local inelastic fields. The More >

  • Open Access

    ARTICLE

    Soft Computing for Terahertz Metamaterial Absorber Design for Biomedical Application

    Balamati Choudhury1, Pavani Vijay Reddy1, Sanjana Bisoyi1, R. M. Jha1

    CMC-Computers, Materials & Continua, Vol.37, No.3, pp. 135-146, 2013, DOI:10.3970/cmc.2013.037.135

    Abstract The terahertz region of the electromagnetic spectrum plays a vital role in biomedical imaging because of its sensitivity to vibrational modes of biomolecules. Advances in broadband terahertz imaging have been emerging in the field of biomedical spectroscopy. Biomedical imaging is used to distinguish between the infected (cancer) and the non-infected tissue, which requires broad band and highly efficient radar absorbing material (RAM) designs (to obtain high resolution image of the tissue). In this paper, a metamaterial broadband RAM design is proposed towards biomedical spectroscopy applications in the THz region. The particle swarm optimization (PSO) algorithm More >

  • Open Access

    ARTICLE

    A Novel Metamaterial FSS-based Structure for Wideband Radome Applications

    Shiv Narayan1, R M Jha1

    CMC-Computers, Materials & Continua, Vol.37, No.2, pp. 97-108, 2013, DOI:10.3970/cmc.2013.037.097

    Abstract A novel metamaterial based FSS (frequency selective surfaces) structure is presented in this paper for wideband airborne radome applications. The proposed metamaterial-FSS structure consists of three layers, where a DPS (double positive sign) layer is sandwiched between a MNG (μ-negative) and ENG (ε- negative) layer, exhibits very good bandpass characteristics inside the operational band along with excellent roll-off characteristics outside the band. The EM performance analysis of the proposed structure has been carried out using transmission line transfer matrix (TLTM) method, which shows excellent bandpass characteristics over a wide frequency range. The transmission efficiency is More >

  • Open Access

    ARTICLE

    Design of Aligned Carbon Nanotubes Structures Using Structural Mechanics Modeling
    Part 2: Aligned Carbon Nanotubes Structure Modeling

    J. Joseph1, Y. C. Lu1

    CMC-Computers, Materials & Continua, Vol.37, No.1, pp. 59-75, 2013, DOI:10.3970/cmc.2013.037.059

    Abstract The aligned carbon nanotube (A-CNT) structure is composed of arrays of individual CNTs grown vertically on a flat substrate. The overall structure and properties of an A-CNTs are highly dependent upon the designs of various architectures and geometric parameters. In Part 2, we have presented the detailed designs and modeling of various aligned carbon nanotube structures. It is found the A-CNT structures generally have much lower modulus than an individual CNT. The reason is due to the high porosity and low density of the A-CNT structures, since the interstitial space between nanotubes is mostly occupied More >

  • Open Access

    ARTICLE

    Stochastic Macro Material Properties, Through Direct Stochastic Modeling of Heterogeneous Microstructures with Randomness of Constituent Properties and Topologies, by Using Trefftz Computational Grains (TCG)

    Leiting Dong1,2, Salah H. Gamal3, Satya N. Atluri2,4

    CMC-Computers, Materials & Continua, Vol.37, No.1, pp. 1-21, 2013, DOI:10.3970/cmc.2013.037.001

    Abstract In this paper, a simple and reliable procedure of stochastic computation is combined with the highly accurate and efficient Trefftz Computational Grains (TCG), for a direct numerical simulation (DNS) of heterogeneous materials with microscopic randomness. Material properties of each material phase, and geometrical properties such as particles sizes and distribution, are considered to be stochastic with either a uniform or normal probabilistic distributions. The objective here is to determine how this microscopic randomness propagates to the macroscopic scale, and affects the stochastic characteristics of macroscopic material properties. Four steps are included in this procedure: (1)… More >

  • Open Access

    ARTICLE

    Theoretical Modeling of the Radiative Properties and Effective Thermal Conductivity of the Opacified Silica Aerogel

    Zichun Yang1,2,3, Gaohui Su1,4, Fengrui Sun1

    CMC-Computers, Materials & Continua, Vol.36, No.3, pp. 271-292, 2013, DOI:10.3970/cmc.2013.036.271

    Abstract In this paper, we investigate the radiative properties and the effective thermal conductivity (ETC) of the opacified silica aerogel by theoretical method. The radiative properties of the opacified silica aerogel are obtained by the modified Mie Scattering Theory that is used for particle scattering in absorbing medium. The modified gamma distribution is used to take account of the non-uniformity of the particle size. The solid thermal conductivity of the composite material is obtained by considering the scale effect of the particles. Based on these calculated thermophysical properties the coupled heat conduction and radiation through the More >

  • Open Access

    ARTICLE

    Numerical Evaluation of Variation in ‘Characteristic Distance’ due to Fracture Specimen Thickness and Temperature

    Sanjeev Saxena1, Raghvendra Singh2, Geeta Agnihotri2

    CMC-Computers, Materials & Continua, Vol.36, No.3, pp. 257-270, 2013, DOI:10.3970/cmc.2013.036.257

    Abstract The present numerical study is an attempt to understand the dependency of characteristic distance on the fracture specimen thickness and temperature. The presented work will be useful to establish the characteristic distance prediction methodology using three dimensional FEM model. Based on the methods proposed for the numerical prediction of characteristic distance, it comes out that it depends on fracture specimen thickness and finally it converges after a specified thickness of fracture specimen. In Armco iron material, characteristic distance varies in temperature ranges where dynamic strain ageing phenomenon is observed, initially decrease and then increases again. More >

  • Open Access

    ARTICLE

    Thermal-Mechanical and Thermodynamic Properties of Graphene Sheets using a Modified Nosé-Hoover Thermostat

    Ching-Feng Yu1, Wen-Hwa Chen1,2, Kun-Ling Chen1, Hsien-Chie Cheng2,3

    CMC-Computers, Materials & Continua, Vol.36, No.2, pp. 203-229, 2013, DOI:10.3970/cmc.2013.036.203

    Abstract The investigation assesses the thermal-mechanical and thermodynamic properties of various graphene sheets using a modified Nosé-Hoover (NH) thermostat method incorporated with molecular dynamics (MD) simulation. The investigation begins with an exploration of their thermal-mechanical properties at atmospheric pressure, including Young’s modulus, shear modulus, Poisson’s ratio, specific heats and linear and volumetric coefficients of thermal expansion (CTE). Two definitions of the line change ratio (ΔL/L) are utilized to determine the linear CTE of graphene sheets, and the calculations are compared with each other and data in the literature. To estimate the volumetric CTE values, the Connolly… More >

  • Open Access

    ARTICLE

    Estimation of the Mechanical Property of CNT Ropes Using Atomistic-Continuum Mechanics and the Equivalent Methods

    C.J. Huang1, T.Y. Hung1, K.N. Chiang2

    CMC-Computers, Materials & Continua, Vol.36, No.2, pp. 99-133, 2013, DOI:10.3970/cmc.2013.036.099

    Abstract The development in the field of nanotechnology has prompted numerous researchers to develop various simulation methods for determining the material properties of nanoscale structures. However, these methods are restricted by the speed limitation of the central processing unit (CPU), which cannot estimate larger-scale nanoscale models within an acceptable time. Thus, decreasing the CPU processing time and retaining the estimation accuracy of physical properties of nanoscale structures have become critical issues. Accordingly, this study aims to decrease the CPU processing time and complexity of large nanoscale models by utilizing, atomistic-continuum mechanics (ACM) to build an equivalent… More >

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