Design of a novel thin-walled tube specimen for multiaxial loading conditions and a method to estimate the load-train compliance

Additive manufacturing, specifically fused filament fabrication (FFF), is increasingly utilized for end-use parts, but it presents challenges such as weak interlayer bonding and therefore highly anisotropic mechanical behaviour. While the axial (tensile and compressive) mechanical response of 3D-printed polymer parts is well-documented, their response to static or cyclic combined (axial and torsional) loads remains relatively unexplored. This study focuses on designing a novel thin-walled cylindrical specimen geometry for 3D-printed acrylonitrile butadiene styrene (ABS) suitable for testing under tension, compression, torsion, and combined loading conditions. To mitigate structural testing challenges like clamp slippage and premature failure, the specimen incorporates fully dense grip regions, longitudinal surface grooves, and stress-relief transition zones. Because the specimen's size prevented the use of standard extensometers, the study additionally proposes and validates a methodology to correct for load-train and machine compliance. Findings demonstrate that the multiple-length (ML) method yields highly accurate corrections for calculated elastic properties compared to the rigid specimen (RS) method. For example, the ML compressive modulus was estimated at 1685 ± 24 MPa, much closer to the measured elastic modulus of 1731 ± 16 MPa obtained through standard tensile tests, and higher than the value calculated with RS (1185 ± 12 MPa). Furthermore, mechanical analysis confirms that structural failure of these specimens at 47.3 MPa under compression (2.5 times the tensile load) is driven by material densification and plastic collapse rather than geometric buckling. Ultimately, this research establishes a robust, highly accessible, and low-cost framework for accurately evaluating the macroscopic multiaxial properties of 3D-printed polymers, overcoming the limitations of traditional solid-bar specimens and expensive non-contact strain measurement systems.