Fatigue Behavior of Polymers

Abstract

Polymers and polymer‐based composites are increasingly displacing more traditional materials in a wide variety of engineering applications, and as such characterization of their fatigue behavior is of utmost importance. This article presents a general overview of the fatigue behavior of polymers. After a brief introduction that includes general terminology, the effects of test conditions (sample geometry, loading frequency, etc) are discussed. The effects of these conditions are also discussed in relevance to both the high cycle and low cycle fatigue behavior. Current models for predicting fatigue life are also reviewed, including cumulative damage theories and fatigue crack propagation models. Morphological and environmental effects are then discussed over a broad range of semicrystalline, amorphous, and modified polymer systems.

Evolution Equations Based Approach for Modeling Fatigue in Amorphous Glassy Polymers. On the Investigation of Fatigue Damage Development in Polycarbonate

“…hysteresis loops do not show a progressive increase in compliance and irreversible work during evolving fatigue, cf. [23], [18]. The result is a consequence of both neglected temperature effects and physical aging which is a relevant assumption under the applied low frequency loading.…”

“…[18]. It is largely acknowledged that crazing is the governing micro-mechanism that triggers the fatigue damage at the sites following closely the localization of the plastic deformation in the amorphous glassy matrix, [11], [15], [7], [23]. A glance at Fig.…”

“…In the first, initiation step failure is typically attributed to deficiencies or impurities affecting significant stress concentrations which exceed the strength limits of the material, [12], [23]. Under repeated loadings, those defects can nucleate and grow during the service life even at stress levels well below the nominal yield strength, [7], [27].…”

“…Under repeated loadings, those defects can nucleate and grow during the service life even at stress levels well below the nominal yield strength, [7], [27]. This part of fatigue is influenced by the localized yield-like deformation process which provides fatigue crack initiation sites controlling fatigue life (number of cycles N to failure) and thus being of a specific interest in the applied fatigue stress S (S-N curve), [23], [22]. The second, propagation step is characterized by the growth of damage through the coalescence of micro-cracks and propagation of small cracks to form large cracks which ultimately cause component failure, [21], [22].…”

“…The macroscopic mechanical behaviour under such conditions is primarily (visco)elastic being influenced by the defects or inhomogeneities in material, [3], [17]. The fatigue life is relatively long while the ultimate fracture mechanism is rather brittle and influenced by combined mechanisms of the plastic dilatation and coalescence of inclusions or voids, [23], [28]. In thermally dominated mechanisms, at relatively high stresses and frequencies, the physical and mechanical properties of the polymer change due to hysteretic heating.…”