Development of Allowables for Composite Wrinkles

Wrinkles in composite structure have been a source of concern since the first structural laminates were developed. Identified as out of plane distortions in the fibers of composite laminates, wrinkles are known to dramatically reduce laminate strength. To address these issues, an experimental investigation was undertaken to determine the critical characteristics of wrinkles as related to the static strength of composites. The critical characteristics include wrinkle type, wrinkle aspect ratio, and wrinkle depth. Resulting characterizations were used to determine design allowables for further analysis of discrepant parts. This work also investigated the interlaminar failure mechanisms of two types of wrinkles (outward and inward) and found static tension and inter-laminar tension are critical to failure initiation and propagation. Finite Element Modeling was used to show that numerical methods could predict these types of wrinkle-induced failure mechanisms.