Fracture in polymers

The brittle-ductile transition temperature depends on the characteristics of the sample such as thickness, surface defects, and the presence of flaws or notches. Increasing the thickness of the sample favors brittle fracture a typical example is polycarbonate at room temperature. The presence of surface defects (scratches) or the introduction of flaws and notches in the sample increases Tg. A polymer that displays ductile behavior at a particular temperature can break in the brittle mode if a notch is made in it examples are PVC and nylon. This type of behavior is explained by analyzing the distribution of stresses in the zone of the notch. When a sample is subjected to a uniaxial tension, a complex state of stresses is created at the tip of the notch and the yield stress jy increases, thus increasing Tg. If Tg increases above the temperature at which the test is conducted, the sample will display brittle behavior known as notch brittleness. Brittle behavior is favored by sharp notches and thick samples where plane strain deformation prevails over plane stress deformation. 

Moreover, the brittle-ductile transition temperature depends on the molecular structure and morphology of the polymer sample. The correlation between chemical structure and fracture behavior is not yet well understood. It is recognized that entanglements control the fracture behavior of glassy 

When a sample of polymer is fractured, the creation of the new surfaces must necessarily involve the breakage of primary (covalent) bonds or secondary bonds (van de Waals interactions and hydrogen bonds), or both 

Since the material is assumed to be perfectly elastic, having a modulus E, 

The work done in stressing the sample to fracture will be equal to the surface energy of the new surfaces created, GqI 

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Andrews, E H., "Fracture in Polymers," American Elsevier Publishing Company, New York, 1968. 

Andrews EH (1968) Fracture in polymers. Oliver and Boyd, London... 

Andrews, E. H. Fracture in polymers. London Oliver Boyd 1968... 

Levett RJ, Donald AM (1994) In Proceedings of 9th international conference on deformation, yield and fracture in polymers. 11-14 April 1994, Cambridge, UK 45... 

Andrews EH, "Fracture in Polymers", Oliver and Boyd Ltd, Edinburgh, 1968. 

Andrews, E. H. Fracture, in Polymer Science, Vol. 1 (ed.) Jenkins, A. D., p. 608, Amsterdam— London, North-Holland Publ. Comp. 1972... 

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