Anisotropic Elastic-Viscoplastic Properties at Finite Strains of Injection-Moulded Low-Density Polyethylene

Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injectionmoulding process, are therefore examined in the present work. Test specimens were punched out from injectionmoulded plates and tested in uniaxial tension. Three in-plane M. Kroon [email protected] E. Andreasson [email protected] E. Persson Jutemar [email protected] V. Petersson [email protected] L. Persson [email protected] M. Dorn [email protected] P.A.T. Olsson [email protected] 1 Linnaeus University, Växjö, Sweden 2 Tetra Pak, Lund, Sweden 3 Malmö University, Malmö, Sweden 4 Blekinge Technical University, Karlskrona, Sweden material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elasticviscoplasticity law. The components of the anisotropic compliance matrix were determined together with the directionspecific plastic hardening parameters.