The Nonlinear Visco-Hyperelastic Damage Mechanics of Individual Electrospun Polycaprolactone Fibers: Experiments and Modeling

Individual electrospun polycaprolactone (PCL) fibers were mechanically tested using a CellScale MicroTester G2. Single fibers were mounted on a custom collector and loaded using a three-point-bending-style fixture: a steel beam (0.1016 mm diameter for “small strain” tests; 0.1524 mm for “large strain” tests) was manually positioned to the midspan of the fiber and then displaced vertically to bisect and extend the fiber, which the authors modeled as two uniaxially stretched fiber segments. A 200 µm pre-displacement was applied to ensure initial tension, and the setup was submerged in water prior to testing to reduce vibrational noise. The MicroTester executed cyclic loading protocols at prescribed displacement rates (e.g., ~13 µm/s loading and ~7 µm/s unloading for the small-strain set), applying two cycles at each incremental strain level (5%, 10%, 15%, 20% for small-strain; and 20%, 40%, 60%, 80%, 100% for large-strain). Beam kinematics were optically tracked (vertical and horizontal tip motion), and fiber forces were derived from the known beam stiffness and measured tip displacement to generate force–displacement (and force–time) responses used for viscoelastic/damage modeling.