McCartney, L N (1999) Model of composite degradation due to fatigue damage. NPL Report. CMMT(A)211

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Abstract

This report first reviews the problems of developing fatigue models for unidirectional composites and then describes a new model that aims to predict the cycle-dependent strength of a unidirectional fibre reinforced composite arising from axial fatigue loading. The model assumes that microstructural damage leads to interfaces that are very weak so that a parallel two bar model can be developed where one bar represents the behaviour of the fibres which are regarded as a loose bundle, and where the second bar represents the matrix. The principal effect of fatigue loading is assumed to be the cycle dependent strength degradation of individual fibres arising from microscopic failure mechanisms within the fibres. The initial strength of the fibres is assumed to be governed by the Weibull distribution which, when combined with a fibre failure criterion, defines an initial statistical distribution of fibre strength characteristics. Composite degradation arising from fatigue loading is assumed to be governed by a damage growth law. The model developed here parallels, but in a more general manner, a recently developed model of composite degradation arising from environmental exposure.
It has been shown that, when the residual strength of the composite is divided by its static strength, the resulting strength ratio is virtually independent of the matrix properties. The strength ratio for a unidirectional composite, where fibres are prone to fatigue damage, is thus predictable from the static strength of the composite, and the cycle dependence of the residual strength of a bundle of loose fibres. The corollary to this is that the fatigue performance of unidirectional composites might be estimated experimentally from the use of static strength data, and an examination of the fatigue behaviour of a bundle of loose fibres.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	CMMT(A)211
Subjects:	Advanced Materials Advanced Materials > Composites
Last Modified:	02 Feb 2018 13:18
URI:	http://eprintspublications.npl.co.uk/id/eprint/2785

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