Development of a New Testing Procedure for Characterizing Adhesion Quality in Fabric-Reinforced Laminates—Yarn Pullout in Laminate Test

Fabric-reinforced laminates (FRLs) require strong fiber-matrix adhesion to prevent delamination in demanding applications such as inflatable aerospace structures. Conventional adhesion tests, such as the T-peel and lap shear methods, often fail to capture localized interactions at the yarn-matrix interface. These methods suffer from inconsistent failure modes, poor reproducibility, and limited relevance to actual delamination behavior. This study introduces the yarn pullout in the laminate test, a novel method that isolates and extracts a single yarn from within a laminate to directly assess interfacial adhesion. Kevlar-based laminates bonded with ethylene vinyl alcohol and polyurethane adhesives were fabricated, and key parameters such as yarn tail length, laminate length, and crosshead speed were optimized. Load-displacement analysis revealed distinct failure modes and adhesive behaviors. A linear relationship between cross yarn count and peak pullout force highlighted the role of mechanical interlocking. Method precision was validated through a gage repeatability and reproducibility (R&R) study simulating interlaboratory conditions, with R&R falling within ASTM-acceptable limits. Compared with the T-peel test, this method offers greater consistency, stronger relevance to service conditions, and practical ease of implementation. The yarn pullout in laminate test provides a sensitive and reproducible tool for evaluating adhesion in flexible composites, bridging the gap between microscale bonding and real-world laminate performance.