A Quantitative Framework for Process Control in the Structural Bonding of Aerospace Composites with MGS L418 Epoxy

The structural integrity of adhesively bonded composites is critically dependent on manufacturing process fidelity. While the MGS L418 epoxy system is widely used in aerospace applications, a quantitative hierarchy of its process variables is absent from the literature, leading to reliance on qualitative guidelines and inherent performance variability. This study closes this gap through a comprehensive sensitivity analysis. A 26-2 fractional factorial Design of Experiments (DOE) quantified the effects of six variables on single-lap shear strength. An Analysis of Variance (ANOVA) established a definitive hierarchy: induction time was the dominant factor, with a sub-optimal 15 min period causing a 74% strength reduction (p < 0.000). Surface preparation was the second most significant factor, with mechanical abrasion increasing strength by 17% (p = 0.000). Ambient humidity was a marginal factor (p = 0.013), linked to amine blush formation. The interaction effects were statistically insignificant, simplifying the control strategy. This work provides a validated, quantitative model that defines a robust process window, prioritizing induction time and surface preparation to de-risk manufacturing and ensure the reliability of safety-critical bonded structures.