Compressive strength of lamina reinforced and fiber reinforced composite materials

Results are presented from a theoretical and experimental investigation on the compressive strength of lamina reinforced and fiber reinforced composite materials when loaded parallel to the reinforcement. An analytical model which replaces the fiber reinforced composite with a laminate containing initially curved laminae has been proposed. By applying the Timoshenko beam equations to each layer of the laminate, an interlaminar shear stress analysis which can be used to predict the behavior of the laminate under compressive loading was developed. Two modes of failure are considered in the analysis, delamination and shear instability, and nonlinear shear stress-strain behavior of the laminae is included.

Axial compression tests were performed on aluminum-wax laminates, boron-epoxy tubes and S-glass-epoxy tubes. In addition, torsion tests and combined compression and torsion tests were conducted on the fiber reinforced tubes. Coordinates of fibers in a boron-epoxy laminate were measured. Experimental results indicate that the aluminum-wax laminates failed by delamination and that failure of the boron-epoxy composite in compression is most likely due to shear instabIlity. In addition it was shown that the shear modulus of boron-epoxy is a function of axial compressive stress and that the fibers in a boron-epoxy composite are not parallel but contain initial curvature.

Adequate correlation between theory and experiment was obtained for both lamina and fiber reinforced test results.