Evaluation for thermal shock and hot-humid of material-extruded parts in additive manufacturing

Additive manufacturing (AM) is a technology that enables the direct fabrication of complex geometries from digital 3D data without molds or tooling, offering high design freedom and material efficiency. Among AM technologies, material extrusion (MEX) is widely utilized due to its low equipment cost, simple operation, and broad compatibility with various thermoplastics. However, to apply MEX components in the aerospace and automotive industries, it is essential to verify their reliability under harsh environmental conditions, such as rapid temperature changes and high temperature and humidity that may occur during actual operation. This study evaluates the environmental reliability of polymer specimens fabricated by the MEX process under thermal shock and hot–humid conditions. Bio-based polycarbonate (PC), PC, and acrylonitrile butadiene styrene (ABS) specimens were fabricated in both longitudinal and transverse orientations and subjected to environmental reliability tests. Tensile testing before and after exposure revealed numerically observed increases in tensile strength for most materials. In particular, the ABS specimen fabricated in the transverse direction exhibited statistically significant increases in tensile strength from 14.0 MPa to 24.1 MPa after thermal shock exposure and from 14.0 MPa to 26.7 MPa after hot–humid exposure. In addition, a drone body and wing components fabricated using ABS were assembled before and after the thermal shock test to evaluate application-level assembly reliability, confirming that the components maintained excellent assembly compatibility even after environmental exposure. Optical microscopy analysis confirmed that air gaps between deposited layers disappeared after exposure, resulting in a denser and smoother internal structure. These findings demonstrate that polymer components fabricated through the MEX process can maintain or even improve their mechanical reliability under combined thermal and moisture stresses. The results of this study are expected to serve as a key reference for establishing design and reliability evaluation standards for AM components operating in harsh environments.