Delamination and Failure at Ply Drops in Carbon Filter Laminates Under Static and Fatigue Loading

Abstract

Delamination at ply drops in composites with thickness tapering has been a major concern in aerospace applications of carbon fibers, where the plies are typically very thin. This study explored the resistance to delamination in fatigue of hybrid carbon fiber and glass fiber prepreg laminates containing various ply drop geometries, and using thicker plies typical of wind turbine blades. Strain levels to produce significant delamination at both carbon and glass fiber ply drops were determined and compared in terms of a simple delamination model. The carbon fiber laminates with ply drops, while performing reasonably well under static loads, delaminated in fatigue at low maximum strain levels except for the thinnest ply drops. The lower elastic modulus and higher interlaminar toughness of the glass fiber prepreg resulted in much higher strains to produce delamination at equivalent ply drops, compared with carbon fiber prepreg using the same resin system. The results indicate that the thickness of ply drops with carbon fibers should be much less than those commonly used for glass fibers.

Materials and Innovations for Large Blade Structures: Research Opportunities in WInd Energy Technology

“…Ply drop delamination at high fatigue cycles occurs at low strains regardless of R-value, position through the thickness or overall laminate thickness. The thickness of material dropped at a single position is an important geometric parameter; improvements have been demonstrated [16,18,21] for treatments of the ply drop edge, including chamfering and pinking.…”