Optimizing mechanical performance of 3D-printed PLA–TPU composites through heat treatment and geometric interlocking

This study investigates the mechanical behavior of 3D-printed layered composites composed of thermoplastic polyurethane and polylactic acid, bonded through a geometric interlocking process. This approach is intended for static-load applications such as orthotic devices, consumer electronics, and automotive interiors, where long-term cyclic loading is not a primary concern. Such applications demand strong interfacial bonding and dimensional stability under single or low-cycle mechanical loads. The objective was to enhance interfacial adhesion using a slit-type penetration pattern and to evaluate the effects of postprint heat treatment on mechanical performance. Five composite specimens were subjected to heat treatment at temperatures ranging from room temperature to 110°C, under controlled pressure via a custom-built mold that ensured uniform heat distribution around the interlock region. Scanning electron microscopy was used to analyze porosity variations, and tensile testing was conducted to assess load–displacement behavior and elastic modulus. An uncertainty analysis was performed to quantify variability in peak load and displacement. The results showed that porosity decreased with increasing heat treatment temperature, and mechanical strength followed a bell-shaped trend, peaking at 80°C. Excessive heating compromised interlock integrity, leading to reduced mechanical performance. Fractographic analysis revealed distinct failure modes across temperature conditions, highlighting the influence of heat treatment on interfacial bonding. The uncertainty study validated the reliability of the mechanical data. Overall, the findings offer valuable insights into optimizing strength in multimaterial 3D printing, presenting geometric interlocking as a robust alternative to fusion-based bonding techniques and contributing to the durability of printed structures.