Trapped crack model

Waples D. W. (1994) Maturity modelling thermal indicators, hydrocarbon generation and oil cracking. In The Petroleum System-from Source to Trap, AAPG Memoir 60 (eds. L. Magoon and W. G. Dow). American Association of Petroleum Geologists, Tulsa, pp. 285-306. 

This model has been tested primarily on polymer systems (a more detailed treatment will be presented in a publication in preparation) but appears to explain to a great extent the observed features of FE, in particular, the time dependence of EE and PIE. In terms of applications involving adhesive failure, such a model would be useful to relate the measured FE characteristics to fracture phenomena of interest i.e., the fragment species, density of trapped electrons, initial concentrations (before decay) and their rate of production all should be closely related to processes occurring at the crack tip. Although the FE model and characteristics outlined above have been observed in a limited number of situations, there appears to be evidence for considerable generality. 

Note that, in this model, the role of dissolution is essential, but indirect. First, vacancies can enhance the plasticity at the crack tip and, second, hydrogen absorption requires the existence of a critical defect in passivated metals. This defect is created by dissolution at the slip band emergence, which is often experimentally observed as the crack initiation step. Vacancies may also act as hydrogen trapping sites, thus increasing its crack tip concentration. 

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