Pressure dependent yield criteria applied for improving design practices and integrity assessments against yielding of engineering polymers

Conventional yield criteria for ductile materials, such as Tresca and von Mises, predict that yielding is independent on the hydrostatic stress state (pressure), which means that tensile and compressive stress-strain behaviors are considered equal and are equally treated. This approach is reasonable for ductile metallic materials but sometimes inaccurate for polymers, which commonly present larger compressive yield strength, therefore being characterized as uneven. As a step in the direction of improving design practices taking advantage of unevenness, this work presents two key-activities: i) four selected polymers were tested under tension and compression to identify unevenness and assess its levels; ii) in the sequence, results were incorporated in adapted design practices using modified yield criteria. Results show that mass reductions up to 40% could be reached even with simple geometric changes, while keeping original safety and stiffness levels.