Monotonic and cyclic torsion of vat-photopolymerized tough resin: characterization of governing parameters and ultraviolet post-curing effects

Purpose This study aims to address the absence of research on the torsional behavior of vat-photopolymerized (VPP) resin polymers, particularly under cyclic and reversed cyclic loading. No systematic investigations have previously examined the cyclic torsional response of VPP-ultraviolet (UV)-LED specimens. The aim is to establish reliable experimental data, evaluate the influence of UV post-curing and propose simplified constitutive models for numerical simulations. Design/methodology/approach Seventy-five Anycubic UV Tough resin specimens were fabricated in a vertical orientation and post-cured for 0, 60, 120, 180 and 240 min. Monotonic, cyclic, and reversed cyclic torsion tests were performed at a constant rate until failure. Torque–revolution data were converted into shear stress–strain curves, from which shear modulus, peak shear stress, energy absorption and torsional rigidity were quantified. Logistic regression was applied to predict parameter evolution, and normalized multilinear models were developed to represent shear stress–strain envelopes for different torsional regimes. Findings Results showed that UV post-curing improved stiffness, strength and energy absorption, with the most significant gains up to 180 min. All specimens failed in a ductile manner, with more than 90% of strain energy absorbed in the plastic range. Compared with monotonic tests, cyclic and reversed cyclic torsion reduced ultimate strain but preserved high ductility. Damage indices confirmed progressive stiffness degradation, while fracture consistently followed 45° shear planes. Originality/value To the best of the authors’ knowledge, this work provides one of the first comprehensive data sets on VPP resin polymers under torsion and introduces empirical relationships and normalized multilinear models suitable for direct integration into numerical simulations.