Fatigue of polymers

Similar to metals, polymers can deform plastically and thus can fail in a similar way under cyclic loading. However, the microscopic mechanisms are not the same as in metals. 

If we load a polymer cyclically with a non-zero mean stress, the viscoelastic and viscoplastic deformation causes an increase of the strain. 

This effect can cause failure under cyclic loads, but this is not true fatigue, for it is not the number of cycles, but the total loading time that determines failure. 

FIGURE 4.6 Nonisothennal fatigue behavior of polymers, (a) Stress input and (b) strain response. 

FIGURE 4.8 Cycles to failure versus test frequency. (Glass reinforced PP, initial stress = 8500 psi.) (Adatpted from Cessna, L. C. and J. A. Levens, Proc. 4th Annual Plastics Conf., Eastern Michigan University, September, 1969, pp. 46-73.) 

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Bradley, W.L. (1990). The effeet of resin toughness on delamination toughness and post-impact compression strength. In Proc. "Benihana" Intern. Symp. How to improve the toughness of polymers and composites-toughness, fracture and fatigue of polymers and composites, Yamagata. Japan, pp. 221-230. 

Effect of Molecular Variables on Crazing and Fatigue of Polymers... 

In view of fact that most time-dependent failures, such as the fatigue of polymers, initiate at the surface, more precisely at the interface of the polymer and the surrounding medium, it is to be expected that the application of plasma polymers will contribute to the improvement of the wear characteristics of polymers at least in certain cases. 

J A Sauer and M Hara, Effect of molecular variables on crazing and fatigue of polymers . Crazing in Polymers, Berlin, Springer Verlag, 1990, Volume 2, pp 69-118. 

Standard test method for tension-tension fatigue of polymer matrix composite materials... 

As an illustration of the correctness of mechanochemical representations of the fatigue of polymers, we might cite data on the action of substances active with respect to free radicals, introduced into rubber in small amounts. 

Sauer, J.A., Richardson, G.C. Fatigue of polymers. Int. J. Fract. 16,499-532 (1980) Pegoretti, A. Creep and fatigue behavior of polymer nanocomposites. In Karger-Kocsis, J., Fakirov, S. (eds.) Nano- and Micro-Mechanics of Polymer Blends and Composites, pp. 301-339. Hanser, Munich (2009)... 

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