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  • Open Access

    ARTICLE

    Matrix Crack Detection in Composite Plate with Spatially Random Material Properties using Fractal Dimension

    K. Umesh1, R. Ganguli1

    CMC-Computers, Materials & Continua, Vol.41, No.3, pp. 215-240, 2014, DOI:10.3970/cmc.2014.041.215

    Abstract Fractal dimension based damage detection method is investigated for a composite plate with random material properties. Composite material shows spatially varying random material properties because of complex manufacturing processes. Matrix cracks are considered as damage in the composite plate. Such cracks are often seen as the initial damage mechanism in composites under fatigue loading and also occur due to low velocity impact. Static deflection of the cantilevered composite plate with uniform loading is calculated using the finite element method. Damage detection is carried out based on sliding window fractal dimension operator using the static deflection. Two dimensional homogeneous Gaussian random… More >

  • Open Access

    ARTICLE

    Polarization Independent Dual-band Metamaterial Based Radar Absorbing Structure (RAS) for MillimeterWave Applications

    Shiv Narayan1, Latha S.1 and R M Jha1

    CMC-Computers, Materials & Continua, Vol.39, No.3, pp. 217-230, 2014, DOI:10.3970/cmc.2014.039.217

    Abstract The EM analysis of multi-layered metamaterial based radar absorbing structure (RAS) with dual-band characteristics in millimeter wave frequency regime has been carried out in this paper using transmission line transfer matrix (TLTM) method for TE and TM polarizations. The proposed metamaterial-based RAS exhibits dual-band characteristics at centre frequencies 120 GHz and 175 GHz with very low power reflection. It absorbs more than 90% power of incidence wave over the frequency range from 111-131 GHz at first resonance and from 164.5-185 GHz at second resonance without metal backing plate, which is desirable for stealth applications. It also showed very low (<… More >

  • Open Access

    ARTICLE

    Toughening Mechanisms in Carbon Nanotube-Reinforced Amorphous Carbon Matrix Composites

    J.B. Niu1, L.L. Li2, Q. Xu1, Z.H. Xia1,3

    CMC-Computers, Materials & Continua, Vol.38, No.1, pp. 31-41, 2013, DOI:10.3970/cmc.2013.038.031

    Abstract Crack deflection and penetration at the interface of multi-wall carbon nanotube/amorphous carbon composites were studied via molecular dynamics simulations. In-situ strength of double-wall nanotubes bridging a matrix crack was calculated under various interfacial conditions. The structure of the nanotube reinforcement -ideal multi-wall vs. multi-wall with interwall sp3 bonding - influences the interfacial sliding and crack penetration. When the nanotube/matrix interface is strong, matrix crack penetrates the outermost layer of nanotubes but it deflects within the nanotubes with certain sp3 interwall bond density, resulting in inner wall pullout. With increasing the sp3 interwall bond density, the fracture mode becomes brittle; the… 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 over 95% both at normal… More >

  • Open Access

    ARTICLE

    Analytical Models for Sliding Interfaces Associated with Fibre Fractures or Matrix Cracks

    L. N. McCartney1

    CMC-Computers, Materials & Continua, Vol.35, No.3, pp. 183-227, 2013, DOI:10.3970/cmc.2013.035.183

    Abstract Analytical stress transfer models are described that enable estimates to be made of the stress and displacement fields that are associated with fibre fractures or matrix cracks in unidirectional fibre reinforced composites. The models represent a clear improvement on popular shear-lag based methodologies. The model takes account of thermal residual stresses, and is based on simplifying assumptions that the axial stress in the fibre is independent of the radial coordinate, and similarly for the matrix. A representation for both the stress and displacement fields is derived that satisfies exactly the equilibrium equations, the required interface continuity equations for displacement and… More >

  • Open Access

    ARTICLE

    Influence of Scale Specific Features on the Progressive Damage of Woven Ceramic Matrix Composites (CMCs)

    K. C. Liu1, S. M. Arnold2

    CMC-Computers, Materials & Continua, Vol.35, No.1, pp. 35-65, 2013, DOI:10.3970/cmc.2013.035.035

    Abstract It is well known that failure of a material is a locally driven event. In the case of ceramic matrix composites (CMCs), significant variations in the microstructure of the composite exist and their significance on both deformation and life response need to be assessed. Examples of these variations include changes in the fiber tow shape, tow shifting/nesting and voids within and between tows. In the present work, the influence of many of these scale specific architectural features of woven ceramic composite are examined stochastically at both the macroscale (woven repeating unit cell (RUC)) and structural scale (idealized using multiple RUCs).… More >

  • Open Access

    ARTICLE

    A Novel Approach to Modeling of Interfacial Fiber/Matrix Cyclic Debonding

    Paria Naghipour1, Evan J. Pineda2, Steven M. Arnold2

    CMC-Computers, Materials & Continua, Vol.35, No.1, pp. 17-33, 2013, DOI:10.3970/cmc.2013.035.017

    Abstract The micromechanics theory, generalized method of cells (GMC), was employed to simulate the debonding of fiber/matrix interfaces, within a repeating unit cell subjected to global, cyclic loading, utilizing a cyclic crack growth law. Cycle dependent, interfacial debonding was implemented as a new module to the available GMC formulation. The degradation of interfacial stresses with applied load cycles was achieved via progressive evolution of the interfacial compliance A periodic repeating unit cell, representing the fiber/matrix architecture of a composite, was subjected to combined normal and shear loadings, and degradation of the global transverse stress in successive cycles was monitored. The obtained… More >

  • Open Access

    ARTICLE

    EM Analysis of Metamaterial Based Radar Absorbing Structure (RAS) for MillimeterWave Applications

    Shiv Narayan1, Latha S.1, R M Jha1

    CMC-Computers, Materials & Continua, Vol.34, No.2, pp. 131-142, 2013, DOI:10.3970/cmc.2013.034.131

    Abstract The EM performance analysis of a multilayered metamaterial based radar absorbing structure (RAS) has been presented in this paper based on transmission line transfer matrix (TLTM) method for millimeter wave applications. The proposed metamaterial-RAS consists of cascaded DPS and MNG layers of identical configurations. It exhibits extremely low reflection (< 42 dB) at 95 GHz and absorbs more than 95% power of incident wave over the frequency range of 90.4- 100 GHz without metal backing for both TE and TM polarizations. In view of aerospace applications, the reflection, transmission, and absorption characteristics of the proposed metamaterial-RAS are also studied at… More >

  • Open Access

    ARTICLE

    Computation of Dyadic Green's Functions for Electrodynamics in Quasi-Static Approximation with Tensor Conductivity

    V.G.Yakhno1

    CMC-Computers, Materials & Continua, Vol.21, No.1, pp. 1-16, 2011, DOI:10.3970/cmc.2011.021.001

    Abstract Homogeneous non-dispersive anisotropic materials, characterized by a positive constant permeability and a symmetric positive definite conductivity tensor, are considered in the paper. In these anisotropic materials, the electric and magnetic dyadic Green's functions are defined as electric and magnetic fields arising from impulsive current dipoles and satisfying the time-dependent Maxwell's equations in quasi-static approximation. A new method of deriving these dyadic Green's functions is suggested in the paper. This method consists of several steps: equations for electric and magnetic dyadic Green's functions are written in terms of the Fourier modes; explicit formulae for the Fourier modes of dyadic Green's functions… More >

  • Open Access

    ARTICLE

    Abrasive Wear Model for Al2O3 Particle Reinforced MMCs Using Genetic Expression Programming

    Metin Kök1,2, Erdogan Kanca3

    CMC-Computers, Materials & Continua, Vol.18, No.3, pp. 213-236, 2010, DOI:10.3970/cmc.2010.018.213

    Abstract In this investigation, a new model was developed to predict the wear rate of Al2O3 particle-reinforced aluminum alloy composites by Genetic Expression Programming (GEP). The training and testing data sets were obtained from the well established abrasive wear test results. The volume fraction of particle, particle size of reinforcement, abrasive grain size and sliding distance were used as independent input variables, while wear rate (WR) as dependent output variable. Different models for wear rate were predicted on the basis of training data set using genetic programming and accuracy of the best model was proved with testing data set. The two-body… More >

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