Energy-Based Interpretation and GLM Analysis of Yarn Pullout in Laminate Test for Bonding Assessment of Woven Fabric-Reinforced Laminates

Woven fabric-reinforced laminates (FRLs) are widely used in flexible composite structures where fabric-adhesive bonding strongly influences load transfer, energy dissipation, and structural integrity. Recently, our team developed a yarn pullout in laminate (YPiL) test for bonding assessment in woven FRLs to overcome the limitations of the cumbersome T-peel test, with a focus on maximum pullout force. This study advanced the YPiL with an energy-based framework in which the force–displacement curve is interpreted using three zones: bonding, interfacial debonding, and drag friction/sliding associated with four metrics: maximum pullout force (Fmax), pre-peak energy (E1), energy to the slope-break point (E2), and total pullout energy (Etotal). A dataset of 187 specimens covering four plain-woven Kevlar structures and five fabric-to-adhesive weight ratios (r = 0.67–2.83) was analyzed using a numeric general linear model (GLM). The dominant factor was r, with Fmax, E1, E2, and Etotal all decreasing as r increased. The interaction between pullout yarn width and r ranked second in every model, confirming a stronger r effect in fabrics with wider pullout yarns. The energy-based metrics, particularly Etotal, were more sensitive than Fmax to structural and bonding differences, and the Etotal model achieved R2 = 0.94 with Root Mean Square Error (RMSE) = 12.42 mJ.