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Leonid I Slepyan - One of the best experts on this subject based on the ideXlab platform.

  • feeding and dissipative waves in fracture and phase transition i some 1d structures and a square cell lattice
    Journal of The Mechanics and Physics of Solids, 2001
    Co-Authors: Leonid I Slepyan
    Abstract:

    Abstract In the lattice structure considered here, crack propagation is caused by feeding waves, carrying energy to the crack front, and accompanied by dissipative waves carrying a part of this energy away from the front (the difference is spent on the bond disintegration). The feeding waves differ by their wavenumber. A zero feeding wavenumber corresponds to a macrolevel-associated solution with the classical Homogeneous-Material solution as its long-wave approximation. A non-zero wavenumber corresponds to a genuine microlevel solution which has no analogue on the macrolevel. In the latter case, on the crack surfaces and their continuation, the feeding wave is located behind (ahead) the crack front if its group velocity is greater (less) than the phase velocity. Dissipative waves, which appear in both macrolevel-associated and microlevel solutions, are located in accordance with the opposite rule. (Wave dispersion is the underlying phenomenon which allows such a wave configuration to exist.) In contrast to a Homogeneous Material model, both these solutions permit supersonic crack propagation. Such feeding and dissipative waves and other lattice phenomena are characteristic of dynamic phase transformation as well. In the present paper, mode III crack propagation in a square-cell elastic lattice is studied. Along with the lattice model, some simplified one-dimensional structures are considered allowing one to retrace qualitatively (with no technical difficulties) the main lattice phenomena.

Zhenhuan Li - One of the best experts on this subject based on the ideXlab platform.

  • the influence of plasticity mismatch on the growth and coalescence of spheroidal voids on the biMaterial interface
    International Journal of Plasticity, 2002
    Co-Authors: Zhenhuan Li
    Abstract:

    Abstract To investigate the macro-mechanical response and micro-mechanism of damage by void growth and coalescence on the interface in a biMaterial system, detailed finite element computations of a representative cylindrical cell containing a spherical void are performed. By comparison with the response of a Homogeneous Material cell model, significant effects of the matrix plasticity mismatches due to the yield stress and the strain hardening exponent on the void growth and coalescence are revealed: (1) The growth rate of the void on the biMaterial interface is much faster than that in the Homogeneous Material, and the critical coalescence strain of the void on the interface is only about half of that in Homogeneous Material. (2) Due to the difference in the deformation resistance of the matrix Materials in the biMaterial system, all computations indicate that deformed voids are seriously distorted and the linking of adjacent voids takes place in the softer matrix Material. Comparison of the computational results with the classical Rice–Tracey (R-T) model shows that the R-T model cannot make good prediction for the growth of the void on the biMaterial interface. On the basis of large numbers of numerical simulations, a correction coefficient is introduced to improve the R-T model.

Hideki Oshita - One of the best experts on this subject based on the ideXlab platform.

  • MODELING OF WATER MIGRATION PHENOMENON IN CONCRETE AS Homogeneous Material. TECHNICAL NOTE
    Journal of Engineering Mechanics-asce, 2000
    Co-Authors: Hideki Oshita, T Tanabe
    Abstract:

    This technical note develops, in detail, a mathematical model for water migration in concrete as a Homogeneous Material (one that does not contain cracks). In the proposed model, concrete is assumed to be composed of aggregate, cement paste, and water, for which the compressibility is taken into account. Then, the governing equation for water migration in concrete as a Homogeneous Material is developed by coupling the mass conservation law and the force equilibrium equation.

  • Modeling of Water Migration Phenomenon in Concrete as Homogeneous Material
    Journal of Engineering Mechanics, 2000
    Co-Authors: Hideki Oshita, Tada-aki Tanabe
    Abstract:

    A mathematical model for water migration in concrete as a Homogeneous Material (one that does not contain cracks) is developed in detail. In the proposed model, concrete is assumed to be composed of aggregate, cement paste, and water, for which the compressibility is taken into account. Then, the governing equation for water migration in concrete as a Homogeneous Material is developed by coupling the mass conservation law and the force equilibrium equation.

Philippe Lasaygues - One of the best experts on this subject based on the ideXlab platform.

  • Tomography in standing trees: revisiting the determination of acoustic wave velocity
    Annals of Forest Science, 2015
    Co-Authors: Andrés Arciniegas, Loïc Brancheriau, Philippe Lasaygues
    Abstract:

    • Context The quality of acoustic tomographic images in standing trees is mainly function of the accuracy of the acoustic velocity computation. Improving the acoustic velocity determination is, furthermore, of great interest because acoustic tools are widely used in nondestructive testing of wood. • Aims Four different signal processing algorithms were used (1) to study the effect of the signal dynamic on the velocity determination, (2) to determine the validity range of each computation method, and (3) to compare the behavior between a Homogeneous Material and wood. • Methods The experiments were performed using the conventional experimental protocol for the ultrasonic characterization of Materials in a tank (normal incidence transmission at 500 kHz). A polyurethane resin (Homogeneous Material) and two wood species ( Bagassa guianensis Aubl., Milicia excelsa (Welw.) C.C. Berg) were used for the experiments. • Results Computed velocity increased as the noise level increased. The Hinkley method appeared to be the most exact when the noise level exceeded 10 dB. The Fisher method was that most suitable for very noisy signals. No difference was found between the resin and the wood samples. • Conclusion A combination of the Fisher and Hinkley methods in the same algorithm would yield the most accurate acoustic velocity determinations in the tomography of standing trees. Key message Wood acoustic velocity determination is affected by the wavelength and the detection algorithm used. The Fisher algorithm is optimal with high signal attenuation; otherwise, the Hinkley algorithm should be used.

Tada-aki Tanabe - One of the best experts on this subject based on the ideXlab platform.

  • Modeling of Water Migration Phenomenon in Concrete as Homogeneous Material
    Journal of Engineering Mechanics, 2000
    Co-Authors: Hideki Oshita, Tada-aki Tanabe
    Abstract:

    A mathematical model for water migration in concrete as a Homogeneous Material (one that does not contain cracks) is developed in detail. In the proposed model, concrete is assumed to be composed of aggregate, cement paste, and water, for which the compressibility is taken into account. Then, the governing equation for water migration in concrete as a Homogeneous Material is developed by coupling the mass conservation law and the force equilibrium equation.