Characterization by ultra-micro indentation of an oxidized
epoxy polymer: Correlation with the predictions
of a kinetic model of oxidation
L. Olivier, N.Q. Ho, J.C. Grandidier, M.C. Lafarie-Frenot
Laboratoire de Me´canique et Physique des Mate´riaux, UMR CNRS No. 6617, ENSMA, BP 40109, 86961 Futuroscope-Chasseneuil Cedex, France
Received 8 October 2007; received in revised form 29 October 2007; accepted 11 November 2007
Available online 22 November 2007
This study aims to understand better the inﬂuence of thermo-oxidation on the degradation of an epoxy resin used as the matrix of aeronautical
composite laminates. Neat epoxy resin plates have been aged at 150
C, under vacuum and ambient air. Using an instrumented ultra-micro
indentation device, modiﬁcations of mechanical properties due to oxidation at elevated temperature are characterized through the measurements
of elastic indentation modulus, Vickers hardness and indentation creep. By using a kinetic model of oxidation developed speciﬁcally for this
epoxy resin, the local values of oxidation product concentration are calculated and correlated to experimental indentation measurements.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Epoxy resin; Thermo-oxidation; Oxidized layer; Indentation; Kinetic modelling
In the aerospace industry, widespread use is made of long
ﬁbre carbon/epoxy laminates, as they possess very interesting
speciﬁc mechanical properties. Nowadays, such materials are
used in structural parts subjected to rather severe thermal con-
ditions. Therefore, in the presence of oxygen, oxidation reac-
tions of the polymer can take place and threaten the integrity
of the composite material. Thus, an increased demand for long
lifetime requires better understanding of the oxidation pro-
cesses and their consequences in terms of mechanical degrada-
tion, to have better predictive tools at one’s disposal.
In that context, many studies concerned thermoset poly-
mers, and continuous carbon ﬁbreethermoset matrix compos-
ites (Lafarie-Frenot and Rouquie , Lafarie-Frenot ,
Lafarie-Frenot et al. , Rouquie et al. , Johnson et al.
, Schoeppner et al. , Tandon et al. ). In particular, it
was found that in carbon/epoxy composite laminates,
oxidation induces some matrix shrinkage which generates
high local stresses, leading to ﬁbreematrix debonding and
matrix cracking (Fig. 1) (Lafarie-Frenot and Rouquie ).
For aeronautical engineers, with the objective of assessing
the durability of structural components, the very difﬁcult chal-
lenge is to take into account the ‘local’ modiﬁcations of me-
chanical properties due to oxidation on the microscale, in
‘global’ structural simulations on the mesoscale. On one
hand, scientists have exerted themselves to elaborate multi-
scale predictive models and to propose numerical tools useful
for ‘virtual material testing’ (Lubineau et al. , Schieffer
et al. ). On the other hand, this approach needs some predic-
tive kinetic model of oxidation. For many years, Verdu and
coworkers have elaborated a kinetic model derived from a rad-
ical chain oxidation mechanism, including reactionediffusion
coupling; recently, the parameters of this model have been
identiﬁed for the 977-2 epoxy-amine resin, which is the mate-
rial of the present study (Colin et al. [10e12]). In its present
form, the model predicts, at every time t and for every elemen-
tary thickness layer at the distance x from the surface, various
quantities among which are weight and density variations.
* Corresponding author.
E-mail address: firstname.lastname@example.org (M.C. Lafarie-Frenot).
0141-3910/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
Available online at www.sciencedirect.com
Polymer Degradation and Stability 93 (2008) 489e497