Crack initiation and evolution in vulcanized natural rubber
under high temperature fatigue
Gengsheng Weng, Guangsu Huang
, Hangxin Lei, Liangliang Qu, Yijing Nie, Jingrong Wu
State Key Laboratory of Polymer Material Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, PR China
Received 29 May 2011
Received in revised form
24 August 2011
Accepted 8 September 2011
Available online 16 September 2011
Crack initiation and evolution
High temperature fatigue
The nanoscaled crack initiation and evolution of natural rubber under high temperature (85
small strain amplitude (strain maximum
¼ 1) fatigue condition were investigated. It was shown by
scanning electron microscopy (SEM) images that cracks and cavities with dimensions in nanoscale in the
NR matrix appear during the high temperature fatigue. FTIR study indicated that thermal oxidation effect
leads to the crosslinking structure destruction. According to the combined analysis of SEM, energy-
dispersive X-ray (EDX) spectrometer and small angle X-ray scattering investigations, it was deduced
that the destruction of crosslinking structure mainly locates in the vicinity of the ZnS particles with
a diameter of 20.2 nm. The ZnS particles are generated as a byproduct in the vulcanization process.
Further, the real-time SAXS analysis revealed that the cracks are primarily initiated at relative higher
< 1) in the region of ZnS aggregations and larger cavities are derived from the enlarge-
ment of the cracks.
Ó 2011 Elsevier Ltd. All rights reserved.
Crack initiation is a localized deformation process which often
evolves during deformation and ﬁnally leads to complete fracture
or failure for many polymer materials. Prior to fracture, cracks
themselves are detrimental to not only structure integrity but also
other properties, such as thermal conductivity. So, understanding
the crack initiation and evolution is very important to deﬁne the
mechanical robustness of these materials.
Natural rubber (NR) is a unique biomass whose molecular
chains are composed of highly stereoregular 1,4-isoprene units .
Nowadays, it has been recognized as indispensable commercial
rubber material in many applications, such as heavy-duty tires,
essential components of vibration isolation structure against
earthquakes and medical products, because of its high elasticity,
tensile strength and excellent crack growth resistance [2e4].
Although investigation on the crack initiation and evolution of NR
is very important, most of the studies focused on the crack initia-
tion and propagation in elastomers were based on pure mechanical
Nowadays, there are some valuable progresses in studying the
crack initiation and evolution. Hainsworth used the environmental
scanning electron microscopy (SEM) to study the crack initiation
and propagation in elastomers at room temperature .Itwas
found that cracks are initiated at defects associated with the sample
geometry and sample processing. The crack initiation in NR at room
temperature was also described by Le Cam et al. [9,10]. By the use of
in-situ SEM, they proposed that cavitation of NR at room temper-
ature takes place around zinc oxide particles at the poles of metallic
oxide inclusions, due to the decohesion between zinc oxides and
rubber matrix. However, these investigations did not consider the
inﬂuence of temperature. NR vulcanizates are especially sensitive
to thermal oxidation degradation. In most of the applications of NR,
heat generated from cyclic deformations at sufﬁcient magnitude of
amplitude and frequency cannot be easily conducted away,
resulting in the temperature increasing of rubber components
[11e13]. High temperatures accelerate the fatigue of rubbers, so it is
very important to reveal the crack initiation mechanism of NR
during high temperature fatigue loading. Besides, previous inves-
tigation scales are large. In fact, most of the present researches are
limited in the spatial scale level from micron to millimeter. In order
to obtain comprehensive understanding on the crack initiation and
evolution, investigations on the crack initiation and evolution
process in nanometer scale should be achieved.
It is accepted that strain induced crystallization plays a major
role in crack growth at large deformation condition. Trabelsi et al.
conﬁrmed the exact effect of strain induced crystallization on the
crack resistance by positional wide angle X-ray diffraction method
. Le Cam and Saintier et al. also investigated the relevancy of
strain induced crystallization on fatigue crack growth in NR .
E-mail address: email@example.com (G. Huang).
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Polymer Degradation and Stability
journal homepage: www.elsevier.com/locate/polydegstab
0141-3910/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
Polymer Degradation and Stability 96 (2011) 2221e2228