University of Cambridge > > Engineering - Mechanics and Materials Seminar Series > Micromechanical modelling of the mechanical behaviour of semi‐crystalline polymers

Micromechanical modelling of the mechanical behaviour of semi‐crystalline polymers

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The mechanical performance of semicrystalline materials is strongly dependent on the underlying microstructure, consisting of crystallographic lamellae and amorphous layers. An elasto‐viscoplastic two‐phase composite inclusion‐based model was developed previously. The concept of a layered composite inclusion as a representative element is extended with a third phase, which is also referred to as the interphase or the rigid amorphous phase. This phase represents the region between crystalline and amorphous domains, having a somewhat ordered structure and a fixed thickness. The incorporation of the interphase in the composite inclusion naturally leads to a dependence on the lamellar thickness, i.e. on an internal length scale. The micromechanical model is used to describe the yield kinetics of polyethylene. For this purpose, the kinetics of slip of the various physical slip systems are described with an Eyring relation. For polyethylene, a double yield point is observed for both tensile and compressive deformation modes. In literature, several possible mechanisms have been proposed to explain this behaviour, among which different deformation processes for the first and second yield point, often associated with fine slip and coarse slip. Even though the model considers only fine slip, it mimics this complex behaviour, where it is observed that after the first yield point a change in the mechanisms occurs and transverse slip systems become active, whereas the primary chain slip mechanism was the dominant process around the first yield point. Experimental results on the yield kinetics of polyethylene at different temperatures and strain rates revealed the contribution of two processes, of which the α‐process (at high temperatures or low strain rates) is attributed to the crystalline phase and the β‐process is related to the amorphous phase. In order to predict this behaviour, the slip kinetics and the amorphous yield kinetics are further refined.

This talk is part of the Engineering - Mechanics and Materials Seminar Series series.

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