Strains expansional

The ingress of water is associated with increased separation between the molecular chains, thereby inducing expansional strains. This phenomenon, called plasticization, enhances chain mobility in a manner akin to that of rising temperature. It was therefore possible to associate the creep and relaxations of wet polymers with concentration dependent a hygral shift factor an(m) analogous to a-iff). Typically, the plasticization process is thermodynamically reversible. 

Earlier data on the uptake of sea water were collected for Divinycell HlOO and H200 closed-cell PVC foams (Li and Weitsman 2004). Weight gains were recorded periodically for samples of thicknesses varying between 2 and 9 mm that were immersed in sea water at room temperature for more than 2 years. In addition, expansional strains were measured periodically and microscopic observations of fluid-induced damage were taken intermittently. 

Moisture expansional strain at saturation, Eh 450 p at 0.5% saturation weight ... 

Constants C2 and Ci are dependent on material properties, expansional strains and the far-field strain. Numerical results are normalized by or , which represents the far-field fiber stress in the absence of expansional strains. In particular ... 

Each of the above elements can be viewed as being transversely isotropic about the common fiber direction, say x, thus characterized by five material constants, say E, E22, G23, Gi2, and V12, where %2 — X3 is the plane of isotropy and V12 is the Poisson s ratio that expresses the strain 62/ i. due to For in-plane problems, say within the Xi — X2 plane, G23 is globally irrelevant. Similarly, only two thermal and two hydral expansional coefficients are of interest, namely i, 2 (=as) and jSi,... 

Whitney and Drzal [87] presented an analytical model to predict the stresses in a system consisting of a broken fiber surrounded by an unbounded matrix. The model (Fig. 8) is based on the superposition of the solutions to two axisymmetric problems, an exact far-field solution and an approximate transient solution. The approximate solution is based on the knowledge of the basic stress distribution near the end of the broken fiber, represented by a decaying exponential function multiplied by a polynomial. Equilibrium equations and the boundary conditions of classical theory of elasticity are exactly satisfied throughout the fiber and matrix, while compatibility of displacements is only partially satisfied. The far-field solution away from the broken fiber end satisfies all the equations of elasticity. The model also includes the effects of expansional, hygrothermal strains and considers orthotropic fibers of the transversely isotropic class. 

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