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  • 1
    Electronic Resource
    Electronic Resource
    Effect of volume fraction and morphology of reinforcing phases in composites (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1155-1170 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Computer modeling has been employed to study the effect of volume fraction and morphology of second-phase constituents on composite stiffness and strength. It is found that the efficiency of load transfer to the second-phase constituent increases with volume fraction vf for particulate composites. For aligned short-fiber composites, the efficiency of load transfer reaches a limiting value with increasing volume fraction for homogeneous fiber dispersions, while for fiber distributions which allow for fiber-rich and matrix-rich regions, the efficiency of load transfer decreases. The saturation or decrease in load transfer efficiency is due to fiber confinement, by which the interfiber matrix material is constrained by the presence of neighboring fibers. Hence, the amount of shear tractions and load transferred to a given fiber is altered by the local fiber distribution, as compared to the case of an isolated fiber (dilute limit). The strength of brittle particulate composites is reduced for most particulate volume fractions considered, while the strength of aligned short-fiber composites with a homogeneous fiber dispersion is marginally increased only for vf(approximately-greater-than)0.2. The composite strength has a downward concave shape, as a function of vf. This is accounted for by both the saturation in load transfer due to fiber confinement and the lower composite strain at failure (embrittlement) as vf is increased. The strength of viscoelastic aligned short-fiber composites with a homogeneous fiber dispersion displays a higher strength at high fiber volume fractions, as compared to a perfectly brittle matrix, which suggests that matrix toughness plays a key role in the strengthening of short-fiber composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356501
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  • 2
    Electronic Resource
    Electronic Resource
    The Young's modulus of silica beads/epoxy composites: Experiments and simulations (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1442-1455 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of particulate volume fraction vp and diameter dp on the composite Young's modulus Ec is studied both experimentally, using a silica bead/epoxy system, as well as with the help of computer simulations. The experimental and simulation results show that for a given particulate size, the overall Ec vs vp curve displays a concave upward shape and not a linear shape. This superlinear trend of the data implies that the average strain normalized to the applied strain λ=ε¯p/εc transferred to the particulates increases with volume fraction. The above finding is explained in terms of a mean-field picture, where a single particle interacts with an effective medium consisting of the remaining particles embedded in the matrix. As the modulus of the effective medium surrounding a reference particle increases with vp, the modulus mismatch between the reference particulate and the medium is consequently reduced. This leads to an overall increase in the normalized average strain λ transferred to each particulate as vp is increased. The experimental results using silica particulates with various sizes dp, as well as the simulation results, show that smaller particulates provide an increased composite modulus as compared to larger particulates, at constant vp. General equations are developed, which relate the composite modulus to the average particle stress or strain, given only information about the volume fraction and the Young's modulus of each of the phases present.Through the application of these relations, it is found that smaller particulates display a greater amount of normalized average strain λ transferred than larger particulates. The effect of particulate Young's modulus Ep in combination with particulate size on the resulting Ec is also studied using simulations only. It is found that for a low particulate to matrix modulus ratio Ep/Em, the particulate size has very little influence on Ec. Moreover, the shape of the Ec vs vp curve can be well approximated by a straight line up to large values of vp. On the other hand, as the ratio Ep/Em is increased, the superlinear trend of the composite modulus Ec vs vp data is more apparent. This results in a smaller range of the Ec vs vp curve, which can be approximated by a linear function. It is also found that the extent of this linear region also decreases with particle size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356378
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo study of the effect of perturbations on critical droplets (1992)
    Springer
    Journal of statistical physics 66 (1992), S. 117-132 
    Details
    ISSN: 1572-9613
    Keywords: Nucleation ; perturbation ; growth and saddle point study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a Monte Carlo study of the effect of perturbations on critical or nucleation droplets in both classical and spinodal nucleation. Locating the saddle point with an intervention technique, we determine that the effect of perturbations at the saddle point depends on their location in the droplet. We find that the most effective perturbations occur at the location of the maximum growth rate where the droplet is allowed to nucleate and grow unperturbed. Moreover, the decay of sufficiently perturbed droplets follows a path that can be best characterized as a growth mode in reverse, specifically the decay of classical droplets is at the surface and that of spinodal droplets at the center independent of the location of the perturbation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01060062
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of modulus and cohesive energy on critical fibre length in fibre-reinforced composites (1992)
    Springer
    Journal of materials science 27 (1992), S. 4393-4405 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The effect of fibre modulus and cohesive energy on critical fibre length and radius in ceramic-fibre-reinforced brittle composites has been investigated employing both analytical theory and computer simulation. The theory consists of a shear-lag analysis in which an energy failure criterion is incorporated. The simulation consists of a two-dimensional computer model based upon a discrete network of grid points. Failure is also defined in terms of an energy criterion, where the energy is calculated on the basis of a two- and three-body interaction between the grid points. Both theory and simulation show that a minimum critical aspect ratio is found as a function of the elastic moduli ratio, E f/E m, with a divergence occurring at both low- and high-modulus values. As the modulus ratio is increased, there is a transition in failure mechanism from tensile-dominated failure in the matrix to shear-dominated failure at the fibre-matrix interface. In addition, families of critical aspect ratio curves are obtained as a function of the cohesive energy ratio, U f/U m. Larger cohesive energy ratios shift the critical aspect ratio curve to larger values. These features potentially explain trends in the experimental results reported by Asloun et al., where the critical fibre aspect ratio was measured for fibre/matrix systems having different modulus and toughness ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00541572
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of interphase modulus and cohesive energy on the critical aspect ratio in short-fibre composites (1993)
    Springer
    Journal of materials science 28 (1993), S. 79-99 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The effect of interphase modulus and cohesive energy on critical fibre length in short-fibre reinforced brittle composites has been investigated employing computer simulation. The simulation consists of a two-dimensional computer model based upon a discrete network of grid points. Failure is defined in terms of an energy criterion, where the energy is calculated on the basis of a two- and three-body interaction between the grid points. Simulation results show that for a whisker-type fibre, a thick interphase (i.e. A i〉Af where A represents the cross sectional area) with an elastic modulus less than that of the matrix in combination with an increased interphase toughness greatly reduce the critical aspect ratio, for both metal-matrix and ceramic-reinforced brittle polymer composites. The results also show a variation in the failure mode from tensile failure in the matrix to tensile and shear failure in the interphase as a function of the fibre-interphase modulus ratio. In particular, a significant increase in the load transfer efficiency in metal-matrix composites is found, for an interphase modulus E i less than the matrix modulus E m. Better load transfer properties in metal-matrix composites cause the yield point to occur at higher values of applied strain, and hence may significantly increase the toughness (area under the stress-strain curve) for certain metal-matrix composites. The computer results are compared with the predictions of Cox's shear-lag theory as well as with a new theoretical development presented in this work. The new theory is found to provide a better description of the fibre and matrix stress distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349037
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  • 6
    Electronic Resource
    Electronic Resource
    The meaning of the critical length concept in composites: Study of matrix viscosity and strain rate on the average fiber fragmentation length in short-fiber polymer composites (1993)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 14 (1993), S. 101-115 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Computer modeling is used in order to provide a theoretical understanding of the concept of critical length in composites, and of the factors influencing the critical aspect ratio. The effects of interphase and matrix properties have been investigated. We have identified the interphase parameters which minimize the critical length. Contrary to the assumption that the critical aspect ratio is related to interfacial shear strength and fiber strength only, we find a significant dependence on matrix viscosity and strain rate, for fixed interphase properties. We therefore conclude that the fragmentation test, which relates the measured critical aspect ratio to a value for the interfacial shear strength, has to be reinterpreted in terms of more parameters than those simply present in the Kelly-Tyson formalism. Moreover, the significance of the concept of critical length for tailoring mechanical properties of composites needs to be reassessed.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750140204
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  • 7
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    Spinodal nucleation as a coalescence process (1992)
    American Physical Society
    Details
    Publication Date: 1992-04-13
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 8
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    Effect of interphase modulus and cohesive energy on the critical aspect ratio in short-fibre composites (1993)
    Springer
    Details
    Publication Date: 1993-01-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 9
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    Effect of modulus and cohesive energy on critical fibre length in fibre-reinforced composites (1992)
    Springer
    Details
    Publication Date: 1992-01-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 10
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    Projected changes to precipitation extremes for northeast Canadian watersheds using a multi-RCM ensemble (2012)
    Wiley
    Details
    Publication Date: 2012-07-04
    Description: This study focuses on projected changes to seasonal (May–October) single- and multiday (i.e., 1-, 2-, 3-, 5-, 7-, and 10-day) precipitation extremes for 21 Northeast Canadian watersheds using a multi-Regional Climate Model (RCM) ensemble available through the North American Regional Climate Change Assessment Program (NARCCAP). The set of simulations considered in this study includes simulations performed by six RCMs for the 1980–2004 period driven by National Centre for Environmental Prediction reanalysis II and those driven by four Atmosphere-Ocean General Circulation Models (AOGCMs) for the current 1971–2000 and future 2041–2070 periods. Regional frequency analysis approach is used to develop projected changes to selected 10-, 30- and 50-yr return levels of precipitation extremes. The performance errors due to internal dynamics and physics of the RCMs and those due to the lateral boundary data from driving AOGCMs are studied. The use of a multi-RCM ensemble enabled a simple quantification of RCMs' structural and AOGCM related uncertainties in terms of the coefficient of variation. In general, the structural uncertainty appears to be larger than that associated with the choice of the driving AOGCM for majority of the precipitation characteristics and watersheds considered. Analyses of ensemble-averaged projected changes to various return levels show an increase for most of the watersheds, with smaller changes and higher uncertainties over the southeasternmost watersheds compared to the rest. It is expected that increases in return levels of precipitation extremes will have important implications for water resources related activities such as hydropower generation in this region of Canada.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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