Fracture polymer

This topic has been mentioned in Section V, Failure, Defect and Contaminant Analysis, in Chapter 15, where a number of typical practical problem invetsigations were presented. Obviously the potential list of examples exhibiting different characteristics and requiring a different type of analysis is lengthy. When the sample is heterogeneous, e.g., a polymer blend or a composite, the study of the surface of a failed piece of material may reveal whether the problem is the interface of the components or that failure occurred within one of these. In particular in the case of crazing or necking orientation may have been induced, the way this can be analysed is discussed in Chapter 8. 

Because c is typically much greater than h, equals Icjh. Thus, the 

Example 12.4 Estimate the critical crack length using Eq. (12.6.2) and physical property values characteristic of glassy polymers. 

From everyday experience with plastic materials, we know that this calculated value is unrealistically low. Indeed, y needs to be taken to be of the order of 10 -10 ergs/cm to obtain agreement with experimental data [2], 

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Fig. 33. High resolution C(ls) XPS spectra obtained from (A) silver and (B) polymer fracture surfaces of specimens prepared by curing the polyamic acid of PMDA/4-BDAF against polished silver substrates. Reproduced hy permission of the American Chemical Society from Ref. [391.

Kausch, H.H., Polymer Fracture, 2nd edn. Springer-Verlag, Berlin, 1981. 

Marshall, G.P. Design for toughness in polymers - Fracture Mechanics, Plastics and Rubber Proc. and Appl. 2(1982) p 169-182. 

Andrews, E.H. Developments in Polymer Fracture - 1, Applied Science, London (1979). 

Kausch HH (1987) Polymer fracture. 2nd (edn) Springer. Berlin Heidelberg New York, chap 5... 

Polymer fracture studies reported in the recent literature are shown to be in agreement with the conclusions derived from the present model polymers. 

Payne, K.L. Harms, S.D. "Recent Developments in Polymer Fracture Fluid Technology" 1984 AIChE National Meeting, Anaheim, May 20-24. 

Gall, B.L. and Raible, C.J. "Characterization of Degraded Polymer Fracturing Fluids," NIPER-48, National Institute for Petroleum and Energy Research Topical Report, February, 1985. 

Since an understanding of the importance of any one process contributing to the failure in thermoplastics and the control over these processes is only partly attainable, a knowledge and understanding of the nature of endurance Hmits is of extreme importance for successful use of plastics, in particular engineered thermoplastics [27]. In terms of the failure type, polymer fracture may occur as a rapid extension of an initial defect, plastic flow of the matter and the thermally activated flow of the macromolecules. In all these cases, however, fracture is a localized phenomenon characterized by a large inhomogeneity of deformations. 

KinlochAJ, Young RJ (1983) Polymer fracture. Elsevier, London, p 147... 

Williams JG (1984) Polymer fracture. Ellis Norwood, Chichester Voight-Martin IG, Fischer EW, Mandelkern L (1980) J Polym Sci Polym Phys 18 2347 Samuels RJ (1985) Polym Eng Sci 25 864 Barham PJ,Keller A (1977) J Mater Sci 12 2141... 

Young RJ (1979) In Andrews EH (ed) Developments in polymer fracture. Applied... 

Kausch H-H (1987) Polymer Fracture, 2nd ed. Springer, Heidelberg Berlin New York... 

In order to get a quantitative characterisation of fracture, different concepts of fracture mechanics have been developed and we will focus on two of them (i.e. the K c and Gic approaches) which will be defined and briefly considered. More information about polymer fracture is given in the first review of this volume and in [4,5]. 

This approach using LEFM is a very useful tool for polymer fracture characterization and may be extended to impact characterization (determination of KId, GId, in dynamic conditions), and for fatigue crack propagation studies (see Sec. 12.4.4). 

There has been a prevailing theory that oxidative degradation is accelerated by mechanical stress [100]. This theory is based on fracture kinetic work by Tobolsky and Eyring [101], Bueche [102, 103, 104], and Zhurkov and coworkers [105, 106, 107]. Their work resulted in an Arrhenius-type expression [108] sometimes referred to as the Zhurkov equation. This expression caused Zhurkov to claim that the first stage in the microprocess of polymer fracture is the deformation of interatomic bonds reducing the energy needed for atomic bond scission to U=U0-yo, where U0 is the activation energy for scission of an interatomic bond, y is a structure sensitive parameter and o is the stress. 

The establishment of the interrelationships between polymer fracture properties and contact fatigue behaviour requires some knowledge of the contact stress field. The specificity of fretting loading is that, depending on the applied contact load and imposed relative displacement, two different contact conditions can be achieved within the interface [54,55] (Fig. 5) ... 

As the loading rate increases, thermal effects need to be accounted for and the analysis is extended to a coupled thermomechanical framework. Evidence of a temperature effect in glassy polymer fracture is found (e.g., in [2,3]) with a temperature increase beyond the glass transition temperature Tg. The influence of thermal effects on the fracture process is also reported. 

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