Mechanical, thermal, and formability characterization of additively reinforced polyethylene terephthalate glycol (PETG) composite sheets for thermoforming applications

This study establishes material selection guidelines for localized additive reinforcement of fiber-reinforced polyethylene terephthalate glycol (PETG) composite sheets intended for thermoformed structural components. Three classes of PETG sheets, including neat PETG, short fiber-reinforced (SCF, SGF, and hybrid), and continuous fiber-reinforced (CCF and CGF) composites, were systematically evaluated to identify material architectures that provide an optimal balance between thermoformability, mechanical performance, and compatibility with localized additive lattice reinforcement. Based on the selected material systems, lattice structures were additively deposited to evaluate stiffness enhancement, interfacial bonding, and thermoforming feasibility within a convergent manufacturing framework. CCF sheets exhibited the highest flexural performance (∼860 MPa strength and ∼31.6 GPa modulus) but also the greatest spring-back, limiting thermoformability. In contrast, SCF sheets provided a favorable balance between stiffness (∼140 MPa flexural strength and ∼8.8 GPa modulus) and formability, reducing spring-back by ∼94% relative to CCF, while SGF sheets exhibited the lowest spring-back and the hybrid composites showed intermediate behavior. Localized lattice reinforcement reduced load-normalized displacement by up to ∼98%, and untreated substrates exhibited the highest lap shear strength (∼5.2 MPa) following additive deposition. Collectively, these findings demonstrate the potential of convergent manufacturing for thermoformed structural composite components requiring enhanced stiffness and dimensional stability.