Experimental observations of fatigue damage in cross-ply laminates using carbon/epoxy ultra-thin plies

Abstract

The damage mechanisms of cross-ply laminates under fatigue loading have been deeply studied during last years. In the case of quasi-static loads the so-called scale effect has recently acquired renewed importance after the appearance of ultra-thin plies. In this work, the experimental observation of the onset of transverse damage and its progression in two different cross-ply laminates under tension–tension cyclic loading is performed. First, a [04/903/04] laminate made of plies with conventional thickness (150 g/m2) is analysed. After looking for the expected fatigue damage mechanisms in this case, a [04/90/04] laminate with a single ultra-thin 90⁰ ply (30 g/m2) is studied. All specimens have been carefully examined by means of an optical microscope, detecting the expected damage mechanisms for [04/903/04] and non-conventional types of damages for [04/90/04]. The change of fatigue damage mechanisms for cross-ply laminates involving an ultra-thin 90⁰ ply is microscopically detailed, meaning the evidence of the delay of transverse damage onset in the 90° layer under cyclic loading. This evidence shows the existence of a scale effect concerning the appearance of the fatigue damage mechanisms.