Experiment and Modelling on Biaxial Deformation of PLLA Materials Under Designed Strain History for Stretch Blow Moulding

Stretch blow moulding in manufacturing bioresorbable vascular scaffold (BVS) from poly (l-lactic acid) (PLLA) provides a biaxial deformation process of raw materials to enhance the mechanical performance. Current knowledge on the mechanical behaviour of PLLA materials in this deformation process is still lacked and trial-and-error tests are relied to develop a successful operation, causing significant waste of material and cost. Motivated by this circumstance, mechanical properties of PLLA materials were investigated by biaxial stretching test at designed strain history mimicking the stretch blow moulding process. A nonlinear viscoelastic material model, i.e. Glass-rubber model was calibrated based on the experimental data from equal biaxial (EB) and constant-width (CW) stretching tests. Material anisotropy was implemented into the original model by introducing the initial orientation factor from the extrusion process. Biaxial deformation process of PLLA materials under variable strain history was modelled by the calibrated and modified model. Modelling results exhibited good agreement with the experimental data, highlighting the potential application of material modelling in improving the understanding on stretch blow moulding of PLLA materials in the industrial manufacture.