JEC COMPOSITES MAGAZINE - Issue #101 - November/December 2015 - 37

Fig. 4: The evolution of interface strength under hygrothermal ageing

continuously with ageing time for both composites and continues
decreasing after one year of ageing, indicating the progressive damage to the interface caused by hygrothermal ageing. The interface
strength retention of pDCPD composites is 60% after one year of
ageing.
During thermo-oxidative ageing, the static tensile properties of
the pDCPD composites were stable, illustrating the exceptional
resistance of pDCPD to thermo-oxidative ageing. Figure 5 shows
a comparison of τapp values from fibres situated far beneath the
surface exposed during ageing ("bulk") and from fibres situated
near the exposed surface ("near-surface"). The value of τapp for
near-surface fibres decreased substantially during ageing because
of surface oxidation (dropped to 37% after 16 weeks). In contrast,
the τapp for bulk fibres was 97% for the same ageing treatment,
indicating that they were largely unaffected by oxidation. Clearly,
high-temperature oxidation degraded the interface strength more
severely than thermal ageing alone.

Fig. 5: The evolution of interface strength under thermal oxidation ageing

Ageing of polymer-matrix composites (PMCs) is a major concern
for structural durability in aggressive service environments. The
present study demonstrates that pDCPD composites exhibit exceptional resistance to both hygrothermal ageing and thermo-oxidative
ageing. These characteristics are well-suited to potential applications, including wind energy structures, offshore oil platforms, oil
pipelines, and both land and marine vehicles. However, before such
composites can be deployed in these applications, investigations are
required to understand other types of ageing and associated damage mechanisms, such as ultraviolet exposure, freeze-thaw cycling,
creep and high pressure. In most practical applications, multiple
types of ageing occur concurrently and the effects couple, resulting
in complex interactions and uncertain longevity. n
Acknowledgements
Support from Materia, Inc. is gratefully acknowledged.
More information:
http://composites.usc.edu

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No101 November - December 2015 /

jec composites magazine 37

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Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #101 - November/December 2015