Showing papers on "Representative elementary volume published in 1985"

The Elastic Longitudinal Modulus and Poisson's Ratio of Fiber Composites:

Abstract: A simplified theoretical approach for the prediction of the longitudinal elastic modulus and Poisson's ratio in fiber-reinforced composites is developed in this paper. The method considers that the main parameter affecting the elastic behaviour of com posite materials is the existence of the mesophase layer, between fiber and matrix, which possesses different physico-chemical properties than those of the constituent phases. The simplest and most convenient laws of variation are a linear, a parabolic, a hyperbolic and a logarithmic variation of E, and v, for the mesophase material, versus the polar radius from the fiber-surface. In this paper, therefore, these laws are con sidered for evaluating the overall moduli of the composite. Each one of these laws is applied to the representative volume element of the fiber composite and compares favorably with the unfolding model, introduced by one of the authors (PST), as well as with respective data existing in literature.

The unfolding model for the representation of the mesophase layer in composites

Abstract: The adhesion between matrix and inclusions (fibers or particulates) in a composite material is one of principal factors characterizing the mechanical and physical behavior of the modern composite materials. All theoretical models describing these substances neglect to consider the influence of the boundary layer developed between phases during the preparation of the composite. In this paper, two versions of a theoretical model were introduced for the evaluation of this mesophase layer. It had been shown that this thin layer influences considerably the physical properties of the composite. It was assumed that the physical properties of the mesophase unfold from those of the hard-core fibers to those of the softer matrix. Thus, a multicylinder model was assumed, improving the classical two-cylinder model introduced by Hashin and Rosen for the representative volume element of the composite. Based on thermodynamic phenomena appearing at the glass transition temperatures of the composite and concerning the positions and the sizes of the heat-capacity jumps there, as well as on the experimental values of the longitudinal elastic modulus of the composite, the extent of the mesophase and the mechanical properties of the composite may be accurately evaluated. These versions of model are based on a previous one concerning a multilayer model, but they are considerably improved, in order to take into consideration, in a realistic manner, the physical phenomena developed in fiber-reinforced composites.

The mesophase and its influence on the mechanical behaviour of composites

Abstract: A study of the structure of the boundary layer, developed between inclusion and the matrix of composites during their preparation is presented. This thin pseudo-phase was considered as an independent phase, with its own mechanical and physico-chemical properties. A three-layer model was developed, where the composite was considered as composed by three independent phases, with the intermediate phase (mesophase) between matrix and inclusions having properties depending on the properties of the constituent main phases and the mode of preparation of the composite. An improvement of this three-layer model was the multi-layer unfolding model, where the mesophase was assumed as consisting of a series of thin layers of varying mechanical properties from the inclusion- to the matrix-properties. Based on these models, an explanation of the various mechanical and physico-chemical properties of the composites may be given. It was shown, in all cases studied, that the introduction of the mesophase yields a better and more flexible means for interpreting the complicated phenomena, appearing in all composites used in practical engineering applications.