Optimization of low velocity impact parameters of thermoplastic based fiber metal laminate composites using Taguchi based desirability function approach

Fiber metal laminates (FMLs) combine the high specific strength and damage tolerance of metals with the light weight and fatigue resistance of fiber-reinforced composites, overcoming key limitations of conventional monolithic materials. Replacing thermoset matrices with thermoplastics further improves recyclability and repairability, yet the low-velocity impact behavior of thermoplastic-based FMLs (T-FMLs) under varying impact energy and ambient temperature, and the systematic identification of optimum parameters, remains insufficiently understood. This study addresses that gap by combining, for the first time for T-FML systems, a Taguchi-based multi-parameter experimental design with a PCA-based composite desirability function to jointly characterize and optimize low-velocity impact response. PP- and PA-6-based T-FMLs were subjected to low-velocity impact tests at three impact energies and three ambient temperatures (−40, 25, and 80°C), and tensile tests at room temperature were additionally performed for both resin systems. A Taguchi L18 orthogonal array was used to evaluate the individual and combined effects of resin type, impact energy, and temperature, with analysis of variance (ANOVA) applied to assess parameter significance and contribution ratios. Impact energy was found to be the dominant factor governing impact response, while resin type and temperature had comparatively minor effects; post-impact examination further revealed interlaminar delamination in PA-6-based T-FMLs under certain conditions. Notably, although not originally targeted in the experimental design, a PP film interlayer was found to improve interfacial properties. The PCA-based desirability function identified PA-6 resin, an impact energy of 30 J, and a temperature of −40°C as the optimum condition for maximizing impact force while minimizing displacement and damage.