Free-Vibration Performance–Robustness Trade-Offs in Hybrid Composite Laminates under Manufacturing Uncertainty: A Probabilistic Decision Framework

Manufacturing variability introduces uncertainty in the vibration response of laminated composites, which can affect decision-making on laminate selection based on nominal parameters. This paper proposes an uncertainty-aware methodology for free vibration evaluation and selection between Kevlar/Epoxy, Glass/Epoxy, and Kevlar-Glass hybrid plates. The first five natural frequencies were determined by propagating uncertainties in the material properties and manufacturing processes using a Mindlin-Reissner FSDT finite-element model in combination with Monte Carlo simulation. Published benchmark frequencies were matched with a maximum absolute relative error of 0.38%. Convergence of mesh and sampling was verified independently. The coefficients of variation for frequency ranged from about 2.8% to 3.3%. The local and global sensitivity analyzes showed that the ply thickness and the longitudinal elastic modulus were the main sources of uncertainty, followed closely by density. The Kevlar laminate had the maximum natural frequencies and Rank-1 probability (61.61%) and continues to be the leader under all nine decision assumptions. The KGGKs with Kevlar outer plies showed a favorable balance between cross-modal performance robustness and stable near-top ranking, while the glass laminate had the least variability in four of five modes, but at lower frequencies. These results indicate that laminate selection under manufacturing uncertainty is priority-dependent and that probabilistic decision measures can offer more insight than deterministic frequency rankings