A multimethod experimental investigation on HDPE materials and butt-welded joints for marine structural applications

High-Density Polyethylene (HDPE) is increasingly considered for marine structural applications due to its corrosion resistance, weldability, and recyclability; however, its mechanical performance—particularly in recycled form and in welded joints—remains insufficiently characterized within the framework of ship classification society requirements. This study addresses these gaps through a comprehensive experimental investigation of virgin, recycled, and welded HDPE specimens. Two butt‑welding techniques—machine‑based fusion and manual extrusion welding—were applied to virgin HDPE panels and examined using consistent specimen geometries to enable a direct comparison between industrial and field‑applicable processes. The mechanical behaviour of all specimen types was assessed through tensile testing, supported by Digital Image Correlation for full‑field strain analysis and Infrared Thermography for detecting early damage and monitoring thermal energy release. Additional optical microscopy and Fourier-transform infrared spectroscopy provided insights into fracture morphology and chemical structure. The results demonstrate that recycled HDPE exhibits yield stress and stiffness comparable to those of virgin material within the linear-elastic range. Both welding technologies maintain the essential load‑bearing capacity of the polymer, with extrusion welding showing enhanced joint stiffness—reflected in the increased Young’s modulus of the welded region. By integrating mechanical, thermal, and chemical characterization with a critical examination of ship classification society requirements, this study expands the current framework for evaluating HDPE assemblies and offers new evidence supporting the use of recycled HDPE and alternative welding techniques in sustainable marine structural applications.