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SUMMARY:Micromechanical modelling of the mechanical behaviour of semi‐cr
 ystalline polymers - Dr Hans van Dommelen\, Eindhoven University of Techno
 logy
DTSTART:20110506T130000Z
DTEND:20110506T140000Z
UID:TALK30041@talks.cam.ac.uk
CONTACT:Ms Helen Gardner
DESCRIPTION:The mechanical performance of semicrystalline materials is str
 ongly dependent on the underlying\nmicrostructure\, consisting of crystall
 ographic lamellae and amorphous layers. An elasto‐viscoplastic\ntwo‐ph
 ase composite inclusion‐based model was developed previously. The concep
 t of a layered\ncomposite inclusion as a representative element is extende
 d with a third phase\, which is also\nreferred to as the interphase or the
  rigid amorphous phase. This phase represents the region\nbetween crystall
 ine and amorphous domains\, having a somewhat ordered structure and a fixe
 d\nthickness. The incorporation of the interphase in the composite inclusi
 on naturally leads to a\ndependence on the lamellar thickness\, i.e. on an
  internal length scale.\nThe micromechanical model is used to describe the
  yield kinetics of polyethylene. For this purpose\,\nthe kinetics of slip 
 of the various physical slip systems are described with an Eyring relation
 . For\npolyethylene\, a double yield point is observed for both tensile an
 d compressive deformation modes.\nIn literature\, several possible mechani
 sms have been proposed to explain this behaviour\, among\nwhich different 
 deformation processes for the first and second yield point\, often associa
 ted with fine\nslip and coarse slip. Even though the model considers only 
 fine slip\, it mimics this complex\nbehaviour\, where it is observed that 
 after the first yield point a change in the mechanisms occurs\nand transve
 rse slip systems become active\, whereas the primary chain slip mechanism 
 was the\ndominant process around the first yield point. Experimental resul
 ts on the yield kinetics of\npolyethylene at different temperatures and st
 rain rates revealed the contribution of two processes\,\nof which the α
 ‐process (at high temperatures or low strain rates) is attributed to the
  crystalline\nphase and the β‐process is related to the amorphous phase
 . In order to predict this behaviour\, the\nslip kinetics and the amorphou
 s yield kinetics are further refined.
LOCATION:Oatley Seminar Room\, Department of Engineering
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