Load reversals and damage in magnesium alloys during stent crimping and expansion: Experiments and modelling

Biodegradable magnesium alloys are promising materials for next-generation degradable vascular stents, yet their limited ductility and strong tension-compression asymmetry pose major challenges for device deployment. This study investigates the mechanical response and failure behaviour of three magnesium alloys - Mg-2Gd, Mg-4Y-3Gd, and ZX10 - under load reversals representative of stent crimping and expansion. Cyclic tension-compression tests were performed to quantify strength asymmetry, twinning/de-twinning effects, and residual ductility. A constitutive framework combining the Cazacu-Plunkett-Barlat yield criterion with a Gurson-Tvergaard-Needleman damage model was calibrated for each alloy to accurately represent cyclic plasticity and ductile failure. The validated material model was implemented into a finite element simulation of the full crimping-expansion sequence of a balloon-expandable stent. Mg-2Gd and Mg-4Y-3Gd exhibited high tensile ductility after load reversals and maintained structural integrity during simulated deployment, with moderate springback and recoil. In contrast, ZX10 showed early void nucleation, rapid damage accumulation, and premature segment failure during expansion, preventing full deployment. The modelling framework provides detailed insight into local strain paths, damage evolution, and critical design regions, enabling reliable in silico assessment of stent performance.