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Fatigue crack growth in polyethylene: Material dependence. II: Effects of time “off‐load”
Author(s) -
Harcup J. P.,
Duckett R. A.,
Ward I. M.,
Capaccio G.
Publication year - 2000
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.11194
Subject(s) - materials science , crack closure , growth rate , composite material , paris' law , polyethylene , constant (computer programming) , crack growth resistance curve , kinetics , fracture mechanics , geometry , mathematics , physics , quantum mechanics , computer science , programming language
Abstract Fatigue crack growth rates have been determined for a series of polyethylenes through the application of various periodic loading and unloading programs in which the load was held constant for t ON seconds and unloaded to a lower constant value for t OFF seconds in each cycle. The crack growth rate, da / dN , was given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{da}}{{dN}} = \gamma t_{ON}[1 + k(1-\exp(-(t_{OFF}/\beta t_{ON})^n))] $$\end{document} where the parameters γ, k , β and n are material dependent and β and n are also geometry dependent. It was found that β and n described the closure of the crack during the unloaded period as well as the kinetics of the increase in crack growth rate. It is proposed that this equation is consistent with a mechanism in which the crack growth rate increases because of damage sustained by the craze during the unloaded period as it closes and is compressed under the recovery of the surrounding material.