M.Z Kabir - Associate Professor
H Zadmehr - Graduate student, Department of Civil and Environmental Engineering, Amirkabir University of Technology,۲۴ Hafez Street, Tehran, Iran

Fiber reinforced composites have some failure mechanisms. One of them is micro buckling that is due to the differences between mechanical properties of fibers and matrix. Micro buckling looks like to longitudinal bending of a beam on an elastic media. This geometrical failure mode depends highly on the fiber content and differences between fiber and matrix mechanical properties. Also, it is sensitive to resin-rich or resin-poor regions, free surfaces, defect fiber-matrix interfaces, etc. These characteristics can have important effects on fiber reinforced composites sections or structures stability. The research on this topic is quite notable since there are not found considerable literature in this direction. In this study, a finite element analysis is performed to consider the compressive strength of unidirectional fiber reinforced polymers. Analyses are carried out for different physical and geometrical properties of fibers. The hypothetical micromechanics were examined for verification of numerical results. The analysis was set based on Eigen values solution of fiber-matrix systems subjected to axial compression loading. The relation between compressive strength and fiber volume fraction was also investigated. The verification between numerical results and analytical methods was satisfaction. According to micromechanics theories and beam on elastic foundation, there are two major failure mode governs in micro-buckling, shear and symmetric flexural modes. Based on the obtained results, the shear mode is the prevailing mode for high fiber volume fractions.

Micro-buckling; Finite element analysis; Compressive strength; Fiber volume fraction