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 man-ufacturing 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 facto-rial Design of Experiments (DOE) quantified the effects of six variables on single-lap shear strength. Analysis of Variance (ANOVA) established a definitive hierarchy: induction time was the dominant factor, with a sub-optimal 15-minute 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.