Effect of crystalline content on ratchetting of ultra-high molecular weight polyethylene polymers: Experimental investigation and constitutive model

The uniaxial multi-level loading-unloading-recovery, uniaxial creep-recovery and uniaxial and non-proportional multi-axial stress-controlled cyclic tests were first performed to study the recoverable viscoelastic and irrecoverable viscoplastic deformation of ultra-high molecular weight polyethylenes (UHMWPEs) with different crystalline contents. The results illustrate that the uniaxial and non-proportional multi-axial ratchetting of UHMWPEs, which denotes the cyclically accumulated viscoelastic and viscoplastic strains, depends on the crystalline content significantly. Meanwhile, the influences of loading level, rate and path on the ratchetting of UHMWPEs with different crystalline contents were addressed. Based on the experimental observations, an extended viscoelastic-viscoplastic constitutive model was constructed to predict the significant dependence of uniaxial and non-proportional multi-axial ratchetting of UHMWPEs on the crystalline content. It is demonstrated that the newly constructed model can predict the uniaxial and non-proportional multi-axial ratchetting of UHMWPEs with different crystalline contents.