Optimization of interface layers in the design of ceramic fiber reinforced metal matrix composites

The potential of using an interface layer to reduce thermal stresses in the matrix of composites with a mismatch in coefficients of thermal expansion (CTE) of fiber and matrix was investigated. It was found that the performance of the layer can be defined by the product of the CTE and the thickness, and that a compensating layer with a sufficiently high CTE can reduce the thermal stresses in the matrix significantly. A practical procedure offering a window of candidate layer materials is proposed

Thermo-mechanical coupling of a viscoelastic-viscoplastic model for thermoplastic polymers : thermodynamical derivation and experimental assessment

In this paper, a new constitutive model is proposed for the behavior of thermoplastic polymers under non-isothermal conditions. The model couples linear viscoelasticity, viscoplasticity and thermal effects. It is formulated within the framework of irreversible thermodynamics. The total strain is the sum of viscoelastic, viscoplastic and thermal strains. General hereditary integrals describe the thermo-viscoelastic response. The viscoplastic part accounts for both isotropic and kinematic hardenings. The stress-strain response and the material self-heating are predicted and compared to experimental data on Polyamide 66 (PA66) and Polypropylene (PP). Good agreement between the numerical simulations and experimental data was obtained for the two materials

Coarse-graining microscopic strains in a harmonic, two-dimensional solid and its implications for elasticity: non-local susceptibilities and non-affine noise

In soft matter systems the local displacement field can be accessed directly by video microscopy enabling one to compute local strain fields and hence the elastic moduli using a coarse-graining procedure. We study this process for a simple triangular lattice of particles connected by harmonic springs in two-dimensions. Coarse-graining local strains obtained from particle configurations in a Monte Carlo simulation generates non-trivial, non-local strain correlations (susceptibilities), which may be understood within a generalized, Landau type elastic Hamiltonian containing up to quartic terms in strain gradients (K. Franzrahe et al., Phys. Rev. E 78, 026106 (2008)). In order to demonstrate the versatility of the analysis of these correlations and to make our calculations directly relevant for experiments on colloidal solids, we systematically study various parameters such as the choice of statistical ensemble, presence of external pressure and boundary conditions. We show that special care needs to be taken for an accurate application of our results to actual experiments, where the analyzed area is embedded within a larger system, to which it is mechanically coupled. Apart from the smooth, affine strain fields, the coarse-graining procedure also gives rise to a noise field made up of non-affine displacements. Several properties of this noise field may be rationalized for the harmonic solid using a simple "cell model" calculation. Furthermore the scaling behavior of the probability distribution of the noise field is studied and a master curve is obtained.Comment: 16 pages, 12 figure

Modeling and simulation of an impact test using wavelets, analytical solutions and finite elements

An instrumented falling weight impact test is thoroughly investigated in two cases, that of a rebound and that of a rupture in the sample. First, the force signal is analyzed with four methods: the continuous wavelet transform (with different wavelets: derivatives of a Gaussian and Morlet's), the Gabor transform, the WignerVille transform and the classical Fourier analysis. It is shown how a proper use of the timefrequency methods allows to precisely detect the discontinuities in the signal, the moment of rupture, if any, and the frequencies that are excited at the impact. In a second part, modal and stress analyses are carried out, both by an analytical method and by finite element computations. The results confirm those obtained in the first part and agree with experimental findings

Quantum Smoluchowski equation: Escape from a metastable state

We develop a quantum Smoluchowski equation in terms of a true probability distribution function to describe quantum Brownian motion in configuration space in large friction limit at arbitrary temperature and derive the rate of barrier crossing and tunneling within an unified scheme. The present treatment is independent of path integral formalism and is based on canonical quantization procedure.Comment: 10 pages, To appear in the Proceedings of Statphys - Kolkata I