Fatigue behaviour of composite tubes under multiaxial loading

Abstract
Effect of stress ratio on fatigue transverse cracking
in a CFRP laminate
K Ogi a, *, R Kitahara a , M Takahashi a , S Yashiro b
a School of Science and Engineering, Ehime University, 3, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
b Faculty of Engineering, Shizuoka University, 3-5-1, Johoku, Naka-ku, Hamamatsu 432-8561, Japan
This paper presents the effect of stress ratio R on the transverse cracking behavior through theoretical consideration
and experiment results. Firstly, the three subcritical crack growth (SCG) models were formulated in association with the
Weibull's probabilistic failure concept for transverse cracking in a cross-ply laminate. The transverse crack density was
expressed as a function of R , the maximum stress in the transverse ply and the number of cycles. Next, cyclic fatigue
tests were performed for various R to analyze the applicability of the three models. Thirdly, the new crack growth law,
that covers the whole range of R including R = 1,
was proposed. Finally, constant fatigue life diagrams are simulated,
based on the new Paris law.
Keywords: Transverse cracking; Slow crack growth; CFRP
1. Introduction
Since carbon fiber reinforced plastic (CFRP) laminates have been employed in a variety of industrial
fields as structural components, long-term structural reliability has become increasingly important.
Transverse cracking is the first microscopic damage appeared in CFRP laminates during fatigue loading.
This damage leads to reduction of modulus and residual strength of the laminates. Furthermore,
delamination is initiated from the tips of transverse cracks for high-cycle fatigue loading. Therefore, it is
important to quantitatively predict transverse cracking behavior under fatigue loading.
A lot of work has been conducted on modeling of fatigue of composites. A review on modeling of
fatigue in composites was reported by Kaminski [1]. In contrast, the models for transverse cracking
behavior, under static loading as well as fatigue loading, are reviewed by Berthelot [2]. In order to
predict the stable growth of transverse cracks under fatigue loading, a subcritical crack growth (SCG)
model is employed. Ogin and coworkers [3, 4] proposed a fracture mechanics model for fatigue
transverse crack propagation, based on the Paris law. In their model, the stress intensity factor for a
transverse crack depends on the thickness and average applied stress of the transverse ply. In addition,
they assumed that the crack propagation rate, as well as the stress intensity factor, is independent of
crack length. The authors have recently developed probabilistic SCG models for predicting transverse
crack evolution under static [5] and cyclic loading [6, 7] for cross-ply laminates with thick transverse
* Corresponding author.
E-mail addresses: kogi@eng.ehime-u.ac.jp