Experimental study on flexural fatigue behavior of glass fibers/epoxy hybrid composites with statistical analysis

Flexural fatigue behaviors were investigated experimentally for unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid composite laminates. Three different hybrid composites, i.e. {[}0.5R/U/U](S), {[}U/0.5R/U](S) and {[}U/U/0.5R](S) were fabricated using hand lay-up technique with 37\% total fiber volume fraction (V-fT), unidirectional glass fiber relative volume fraction (V-fU/V-fT)=0.8 and of 5.5 +/- 0.2mm thickness. Flexural fatigue tests were performed at zero mean stress. A 20\% reduction of the flexural stiffness was taken as a failure criterion. The effects of layer stacking sequences on both initial stress-no. of cycles to failure relationships and the relative surface temperature increase of the mentioned composites were investigated. The specimen failure modes have been recorded and discussed. The S-N curves and fatigue safe workability areas for the fabricated hybrid composites have been constructed as design curves. Two-parameter Weibull distribution function was used to obtain the scatter in the experimental results and to construct the reliability graphs for the fabricated hybrid composites.