JEC COMPOSITES MAGAZINE - Issue #88 - April 2014 - Special JEC Americas Spring Edition - 56

ATM
reference static strength sLBo is the static
strength sLB at To = 25°C. The lifetime
during which the static strength decreases to 60% of the reference static strength
sLBo can be predicted as 5.5 years for dry
specimens. The lifetime decreases drastically to 3.5 days for wet specimens.

Conclusion
Fig. 1: Master curves of resin creep compliance and time-temperature shift factors

and 0.6%.
Creep compliance and time-temperature shift factors of the resin
The master curves of creep compliance
Dc versus the reduced time t' at reference temperature To and the time-temperature shift factor aTo(T) for the matrix
resin are shown in Figure 1 for dry and
wet conditions.
Static strength for various
directions of CFRP
Figure 2 shows the master curves of
static strength for longitudinal tension
X, longitudinal bending X', transverse
bending Y, and transverse compression
Y' for dry and wet unidirectional CFRP
specimens, obtained from strength
data at various temperatures using the
time-temperature shift factors aTo shown
in Figure 1. The solid and dotted curves
in these figures show fitting curves by
Equation (1) using the master curves of
matrix resin creep compliance in Figure

1. Figure 2 shows that the static strength
of unidirectional CFRP decreases
concomitantly with increasing time,
temperature, and water absorption. The
time, temperature, and water absorption dependency of the static strength of
unidirectional CFRP differs according to
the loading direction.

Life prediction of CFRP
Figure 3 shows the dimensionless static
strength sLB/sLBo for longitudinal bending
versus the reduced time t' at the reference temperature To = 25°C, where the

A general and rigorous advanced accelerated testing methodology (ATM) for
the long-term life prediction of polymer
composites exposed to actual loading
and having a general stress and temperature history were applied to the static
strengths in the four directions of unidirectional CFRP (longitudinal tension
and bending, transverse bending and
compression) under dry and wet conditions. The static strengths in these four
directions decrease with the increase in
water absorption as well as time and temperature. The effect of water absorption
on the time and temperature dependence
of these static strengths can be characterized by the viscoelastic behaviour of
the matrix resin. The lifetime decreases
drastically with water absorption, which
remarkably influences the viscoelastic
behaviour of the matrix resin. n

More information:
www.kanazawa-it.ac.jp/ekit/
Fig. 3: Dimensionless static strength sLB/sLBo for
longitudinal bending

Fig. 2: Master curves of static strength for various loading directions of CFRP

56 jec composites magazine / No88 April 2014

Acknowledgements
The authors would like to thank the US
Office of Naval Research for supporting this work through an ONR award
(N000140611139) with Dr. Yapa Rajapakse
as the ONR Program Officer. The authors
also thank Professor Richard Christensen
from Stanford University, who acted as
a consultant for this project, and Toray
Industries Inc. as the supplier of carbon
fibres.
References
[1] Y. Miyano, M. Nakada and H. Cai. J.
Composite Materials, pp.42, pp.1897
(2008)
[2] R. M. Christensen and Y. Miyano. Int.
J. Fracture, pp.137, pp.77 (2006)
http://www.kanazawa-it.ac.jp/ekit/
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