Stress analysis of short fiber-reinforced polymers incorporating a hybrid interphase region

Abstract

The finite element method is used to investigate the load-carrying characteristics and the stress profiles in unidirectional short fiber polymeric composites. The micromechanics composite model incorporates a hybrid interphase region surrounding the fiber. The new interphase concept involves different domains of interaction between different material properties depending on the corresponding properties of primary constituents, volumetric composition and macroscopic characterization of the composite. Thus, the hybrid interphase is not defined within a unique thickness, its outer radius being a function of the material property under consideration. The model describes also imperfect adhesion conditions by immediate softening of material properties. Numerical results are illustrated and discussed for a variety of the involved parameters. These results referring mainly to hoop and radial stresses along the fiber length confirm the intense variation of stress in this area. Parametric studies have been conducted accounting for different degrees of adhesion and shapes of the fiber tip and where it is possible comparisons with existing theories and experimental results taken from literature are illustrated.

Experimental, analytical, and numerical investigation of interphasial stress and strain fields in MWCNT polymer composites

“…It should be noted that the stress field is known to be sensitive to the fiber tip shape as investigated and confirmed in a previous publication by the authors. 13 Finally, a theoretical model for the computation of the normal and shear stress distribution along the fiber length at the fibermatrix interface developed in a previous publication by Papanicolaou et al 22 was applied and analytical results were compared with respective values derived by means of the finite element model described above. The agreement between the FEM results and the respective ones derived by the analytical model, as presented in Figure 13, is almost perfect and this is because the analytical model is taking into account the adhesion coefficient ''k'' as well as the interface stiffness ''K'' which is a measure of the stiffness of the fiber-matrix boundary measured in GPa and which, in turn, depends upon the fiber-matrix adhesion coefficient, ''k," as well.…”

“…This denotes that the interphase is not simply a geometrical concept; dependent only on the volumetric composition of the composite, but it is mainly a property-dependent concept. [12][13][14] Recent investigations have proved the validity of the above conception.…”

“…The interphase formed during manufacturing of the composite is the so-called structural interphase. 12,13 Within this region a rather complex situation is developed involving areas of imperfect bonding, where mechanical stresses and stress singularities are developed due to the filler's geometry and the constraint imposed to the matrix deformation. This, finally results in the creation of microcracks, voids, and other discontinuities.…”

“…As shown in a recent by the author's investigation, 13 the main factors affecting the interphase thickness are: the adhesion coefficient, k, the reinforcement radius r f and the material's anisotropy coefficient, S. Then, the property-dependent hybrid interphase thickness is given as:…”

Analytical and computational study of the moduli of fiber-reinforced composites and comparison with experiments

“…On the other hand, the existence of the intermediate phase plays an important role in the determination of the elastic constants and in the study of damage tolerance of composite structures under different loadings. [10][11][12][13][14][15] In this investigation, the quality of adhesion between fibers and matrix was studied by a three-phase model which considers the existence of a third phase, the interphase, surrounding the fibers and having different mechanical properties, than the respective properties of the two main phases which were considered as varying between the properties of the fibers to those of the matrix. The laws of variations were assumed to be expressed by polynomials.…”