National Physical Laboratory

Feasibility of moisture and humidity determination using optical fibre sensing in polymer matrix composites.

Author(s):
Lodeiro, M J, Young, T, Gower, M R L
Source:
NPL Report MN 11, January 2013
ISSN:
1754-3002
ISBN:
NPL Doc. Ref:
PDB: 6631 | DDB: 5698
Document Type:
NPL Report
DOI:

Note: An asterisk after an author's name indicates a non-NPL author.

Abstract:

Knowing the distribution and level of moisture uptake in polymer composites is essential for determining the long-term property retention in aggressive environments. The deleterious effects of moisture on the interface, matrix and occasionally on the reinforcing fibres themselves results in changes to the mechanical behaviour and life expectancy of the material. Ultimately, the uncertainty in moisture content and distribution contributes to conservative design practices to compensate for the worst case scenario property reductions. With fuel/energy savings driving the demand for lightweight structures, more economical designs which still ensure satisfactory lifetime and performance are important. The high strength-to-weight ratio of polymer composites make them ideal candidates for lightweight construction.Bulk material data on moisture absorption can be applied to component design, but doesn't take into consideration local variations in the moisture content from region to region in the structure or from surface to core. In order to minimise design requirements, a system for measuring moisture locally within a composite structure, both in-situ and real-time, would be advantageous.This Measurement Note provides an evaluation of the most viable optical fibre techniques which could potentially be robust enough to be embedded within a composite. All aspects of experimentation are covered, from specimen preparation through testing procedures and results to data analysis. The methods were assessed both in humid air environments at different temperatures and subsequently within a thermosetting epoxy resin to determine any additional problems caused by the embedding process.

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