Gower, M R L (2009) Project ACLAIM (Advanced Composite Life Assessment and Integrity Management): measurement of Mode I and II fracture toughness for mixed material systems used in ACLAIM case studies. NPL Report. MAT 19

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Abstract

A range of processing, machining and in-service defects typically found within advanced composite structures have previously been reviewed within the ACLAIM project [1]. Due to the large number of defects that can occur, and the fact that not all defects represent a serious threat to loss of structural integrity, the focus of definitions for failure modes has been on the "crack-like" defects, such as delamination and matrix micro-cracking, that give real cause for concern over remnant performance.

This report details experimental work that has been carried out to measure the Mode I and II fracture toughness values, GIC and GIIC respectively, for three case studies undertaken within ACLAIM that are concerned with delamination or interfacial de-bonding. The measurement of Mode I and II fracture toughness data for these material systems is not an easy task, with Mode II data being particularly difficult to measure. Existing test standards or protocols for measuring fracture toughness properties for composites and adhesives have been developed for configurations where the material on each side of the delamination tip is the same and in the case of composites is continuous and unidirectional in format. The material systems tested in this study consisted of bi-material interfaces, of various formats and where in some instances a degree of curvature in the specimens existed due to differences in coefficients of thermal expansion. Hence the stress state at the delamination tip is more complicated than for the ideal cases catered for in the test methods used. Data have been produced although it is emphasised that all values, and in particular the Mode II values, should be treated as approximate.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MAT 19
Keywords:	composites, Mode I, Mode II, fracture toughness
Subjects:	Advanced Materials Advanced Materials > Composites
Last Modified:	02 Feb 2018 13:15
URI:	http://eprintspublications.npl.co.uk/id/eprint/4435

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