Deformation and Fracture in Polymers

The previous section described the thermodynamics of deformation and fracture in terms of the energy required to elongate and break the sample. This section describes two major experiments to evaluate the deformation and fracture energy stress-strain and impact resistance. In a tensile stress-strain experiment, the sample is elongated until it breaks. The stress is recorded as a function of extension. Stress-strain studies are usually relatively slow, of the order of mm/s. Impact strength measures the material s resistance to a sharp 

A third mechanism of energy absorption is called shear yielding. In shear yielding, oriented regions are formed parallel to the planes of maximum shear 

In order to cause crack growth at a predefined position, many fracture researchers deliberately introduce notches of various kinds before testing. While this presupposes that the early stages of fatigue (Section 11.4) or other types of internal damage can be ignored, notching does produce better controlled experimental conditions. 

Some of the more important methods of failure studies include stress-strain, impact loading, and fatigue. Creep and stress relaxation (Chapter 10) may cause serious damage to engineering materials, but they normally do not result in fracture per se except for creep rupture. Emphasis in this chapter will be on the study of fracture energy, kinetics of crack growth, and molecular mechanisms. The reader is directed to Chapter 13 for a fuller discussion of plastic toughening. 

Toughness as such is measured by the area under the stress-strain curve. This area has the units of energy per unit volume and is the work expended in deforming the material (see Section 11.1). The deformation may be elastic, and recoverable, or permanent (irreversible deformation). Elastic energy is stored in the sample in terms of energy per unit volume. Because of the development of crazes within the strained material, which are microscopic voids. 

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Wignall GC, Crist B, Russell TP, Thomas EL (eds) (1987) Scattering, deformation and fracture in polymers, Materials Research Society Symposia Proceedings, vol 79, MRS, Pittsburgh PA... 

DEFORMATION AND FRACTURE IN POLYMERS 575 Table 11.3 Mechanical strength of several plastics ... 

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... 

Barenblat, G-1. Methods ofthe Combustion Theory in the Mechanics of Deformation, Flow and Fracture of Polymers, in Deformation and Fracture of Polymers (ed. Kausch, H. H., Hassell, J. A., Jaffee, R. I.), New York—London, Plenum 1973, p. 91... 

Plastic deformation and fracture of polymers usually begins in highly localized regions and is initiated at points of stress concentration arising fiom molecular... 

The purpose of this book is to present a coherent picture of the inelastic deformation and fracture of polymers from a mechanistic point of view, addressed to graduate students of material science and mechanical engineering and to professional practitioners in the field. 

The serious entry of the author into the field of deformation and fracture of polymers started in 1971 during a sabbatical leave at Leeds University in Britain with Professor Ian Ward. The friendly association with Ward has continued until the present. For this reason the book is dedicated first of all to him in appreciation of his long-term friendship. Secondly, however, the book is dedicated in equal measure to my wife Xenia for her enduring support. 

Kinetics of Deformation, Relaxation, and Fracture in Polymers over a Wide Temperature Range... 

In this Section, an approach to the descnption of kinetics of deformation, relaxation, and fracture of polymers over a wide temperature range will be elaborated on the basis of kmetic equations with constant activation parameters. A nonuniform distribution of the energy of atoms over the degrees of freedom requires the replacement of T by the F(6/T) quantum function. The resultant (modified) Arrhenius equation describes adequately both deformation and fracture of polymers in the range from 20 K to the melting temperature. 

Zhurkov, S.N., Novak, I.I., Slutsker, A.I. et al. (March/April 1970) Connection between destruction of chain molecules and formation of sub micro cracks in stressed polymers in Proceedings of the Conference on the Yield, Deformation and Fracture of Polymers, Cambridge, Session 3, Talk 3, pp. 1-6. 

G. J. Lake, Conference Proceedings of the Physical Institute, The Yield Deformation and Fracture of Polymers, Cambridge, 1970 . G. J. Lake, P. B. Lindley and A. G. Thomas, in Fracture ed. L. Averbach, Chapman and Hall, London, 1979. 

In their recent monographs on deformation and fracture of polymers Bartenev and Zuyev [51], Andrews [52], and Regel, Slutsker, and Tomashevskii [53] have reviewed a considerable amount of experimental data under this aspect reference to their works should be made if information is sought on the effect of time and temperature on the fracture behavior of polymers of different composition and structure and under various environments. 

Parameters that Govern Slow Crack Growth in Linear Polyethylenes," Cambridge Conference on Deformation and Fracture (rf Polymers, Ajwil 1991 Plastic, Journal Composites Rubber Processing and Applications 17 (4) 1992 255-258. 

The book is based on the editors and authors extensive experience in research, deveiopment, and education in the field of materials science, and especially polymer testing, polymer diagnostics, and failure analysis. A comprehensive coverage of the methods of polymer testing is provided along with the results of the authors work on deformation and fracture behaviorof polymers. 

Breach, C.D. Donald, A.M. Jones, R.A.L. In 9th International Conference on Deformation, Yield, and Fracture of Polymers (Conference Papers). The Institute of Materials London, 1994. 

Suresh S, Pruitt L (1991) Fatigue crack growth in polymers and organic composites under cyclic compressive loads. In Proceedings of the 8th International Conference on Deformation, Yield and Fracture Of Polymers, 32 1-4... 

Doll, W., Schinker, M. G., Konczol, L. in Deformation, Yield and Fracture of Polymers, p. 20.1, Cambridge/London, Plastics and Rubber Institute 1982... 

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