Broughton, W R; Lodeiro, M J (2000) Fatigue testing of composite laminates. NPL Report. CMMT(A)252

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Abstract

This report provides an assessment of test methods for characterising the fatigue performance of unidirectional and multidirectional laminates. The work was carried out within the “Composites Performance and Design Project - Life Assessment and Prediction (CPD2)”. The project is directed towards the development and validation of test methods and predictive methodologies that can be used for characterising the long-term properties and residual life/strength of polymer matrix composites. Constant amplitude tension-tension fatigue tests have been carried out on glass and carbon fibre-reinforced systems in order to evaluate the suitability of these techniques for generating cyclic fatigue data at accelerated rates. This report provides an assessment of test methods and the data generated for composite laminates under monotonic and cyclic loading conditions. The report considers both dumbbell and straight-sided coupon specimens for testing multidirectional laminates. A discussion of the effects of stress amplitude and methods of end tabbing has been included.
The principal conclusions that can be drawn from the results are: (i) standard test geometries in the international standards IS0527-4 and ISO 527-5 are suitable for assessing fatigue performance under tension-tension loading conditions; (ii) continuous aligned and cross-ply carbon fibre-reinforced laminates have excellent fatigue resistance at loads approaching the tensile strengths for these materials; (iii) normalised S-N curves for unidirectional and cross-ply glass fibre-reinforced laminates show an underlying similarity and can be “approximated” by a simple algebraic relationship, which is dependent on stress amplitude; (iv) waisting coupon specimens results in an improvement in fatigue performance for cross-ply glass fibre-reinforced laminates; and (v) progressive development of damage generally leads to a gradual reduction in laminate stiffness and strength of glass fibre-reinforced laminates. The notable exception is the stiffness of continuous axially aligned laminates, which remains constant for almost the entire life of the coupon specimen. The stiffness and strength of a cross-ply glass fibre-reinforced laminate close to its fatigue life plateaus to a value equivalent to that predicted for a laminate of equal thickness, but with no load-bearing contribution from the 90 ° plies (i.e. full ply discount). The report includes recommendations on preparation, testing and inspection of composite laminates.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	CMMT(A)252
Subjects:	Advanced Materials Advanced Materials > Composites
Last Modified:	02 Feb 2018 13:17
URI:	http://eprintspublications.npl.co.uk/id/eprint/1790

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