The Influence of Crystalline Structure on the Necking-Fracture Behaviour of Polyethylene
At high strain rates, large stresses concentrate to the taut tie chains between the crystallites, favouring fracture processes. At lower strain rates, the molecules rearrange in a way that distributes the local stresses more evenly over the structure which then deforms further rather than fracturing.
Owing to the high concentration of the chains in the high density, high molecular weight polyethylenes, the transfer of stresses and deformations between adjacent crystallites is very efficient. Therefore the structure has a good resistance towards fracture and the deformation of different lamellar regions occurs cooperatively.
The marked transition is a result of both (a) the rapid formation of high strength fibrillar structure, which is partly due to reasons given in item 2 of this hypothesis, and (b) the influence on the strength of the strain rate in accordance with item 1 of the hypothesis. At the marked transition, the maximum in the local strain rate is about the highest tolerable for the actual structure without macroscopic fracture. When an element of the specimen passes the maximum in local strain rate the probability for fracture of this element decreases due to the decreasing strain rate and to the continuous formation of a high strength fibrillar structure. In addition, e.g. the rise in local temperature in the neck caused by dissipation of deformation energy,may affect the necking and fracture behaviour.
KeywordsHigh Strain Rate High Density Polyethylene Lower Strain Rate Lamellar Thickness Macroscopic Fracture
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- 2.U.W. Gedde and J-F. Jansson, to be published in Polym.Eng.Sci.Google Scholar
- 3.U.W. Gedde and J-F. Jansson, to be published in PoTym.Eng.Sci.Google Scholar
- 6.B. Wunderlich, “Macromolecular Physics, Part 2”, Academic Press, New York (1976).Google Scholar
- 9.M.J. McCready, J.M. Schultz, J.S. Lin and R.W. Hendricks, J.Polym.Sci., Polym.Phys.Ed., 17:725 (1979)Google Scholar
- 10.J. Peterman, M. Miles and H. Gleiter, J.Macromol.Sci.-Phys., B 12: 393 (1976).Google Scholar