Stress Distribution of Aligned Short-Fiber Composites Under Axial Load

Abstract

The objective of this paper is to investigate the normal and interfacial shear stress distribution of short-fiber composites under a force either parallel to the fiber or mak ing some angle with the fiber. Different geometrical shapes of fiber end were taken into account. The geometrical shapes under investigations were: rectangular, semi-circular, V-shaped and wedge-shaped respectively. Analytical solutions of this problem were achieved by using finite-element numerical scheme. For the cases when the applied load is parallel to the fiber, very small triangular constant strain elements were used near the fiber tip and rectangular elements were used throughout the rest of the region. For the cases of off-axis loading parabolic-isoparametric elements were used throughout the entire domain. Depending upon the fiber volume fractions and fiber end geometry, the total time of calculation for each case is around 18 seconds. Numerical results of normalized normal stress σf and shear stress τ were plotted as a function of the coordinate along the fiber direction. It was observed that, the distribu tions of σ f and τ were in good agreement with existing results obtained experimentally by using photoelasticity method. It was also observed that shear stress concentration is very high near the fiber tip. This phenomenon is particularly true for wedge and V-shaped fiber ends. A possible application of this investigation is to optimize internal damping of short- fiber composites by properly adjusting fiber end geometry. It is believed that the presence of high shear stress concentration at numerous fiber ends in short-fiber com posites will transfer to the viscoelastic matrix. The viscoelastic matrix will then dissipate energy and thus improve internal damping of the composites.