Fatigue characterization of polyethylene fiber reinforced polyolefin biomedical composites

Filament wound flat strip composites of polyethylene fiber reinforced ethylene-butene copolymers were produced and their fatigue behavior under cyclic loading was studied. Three different copolymer compositions and two different winding angles were employed in order to study the effects of branching density in the polymeric matrix and of reinforcement angle on the fatigue response of the composite. The results were in agreement with published fatigue models, showing that the short-term fatigue behavior, at relatively high stress levels, was controlled by the static properties of the materials, exhibiting better fatigue resistance for lower branching density of the copolymer and for a smaller reinforcement angle. However, the long-term fatigue behavior, at moderate stress levels, was governed by the fatigue rate of degradation, which decreased with the branching density and winding angle. The fatigue induced creep resulted in fiber reorientation in the loading direction, which in turn generated high residual properties. It was concluded that various polymer/angle combinations could result in fatigue-proof composites of significant residual properties at 10⁶ fatigue cycles.