A Rational Analytic Theory of Fatigue
Materials Science and Engineering A 528 (2011) 1078–1086
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Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea
Cyclic loadings and crystallization of natural rubber: An explanation of fatigue crack propagation reinforcement under a positive loading ratio
N. Saintier a,∗ , G. Cailletaud b , R. Piques b a b
LAMEFIP, Arts et Métiers ParisTech, Esplanade des Arts et Métiers, 33405 Talence Cedex, France Centre des matˇeriaux P.M. FOURT, Ecole Nationale Supˇerieure des Mines de Paris, UMR CNRS 7633, Evry Cedex 91003, France ı ı
a r t i c l e
i n f o
a b s t r a c t
Natural rubber is known to have excellent fatigue properties. Fatigue crack propagation studies show that, under uniaxial tension loading, fatigue crack growth resistance increases with the loading ratio, even if the peak stress increases. Studies dealing with crack initiation confirm this trend. If strain induced crystallization is believed to play a major role in this reinforcement process, it is not clear yet by which mechanism this reinforcement takes place. Using SEM investigation, it is shown here that the reinforcement process is associated with strong crack branching in the crack tip region. From experimental results it is shown that under particular reinforcing loading condition a cyclic strain hardening process can be observed on the natural rubber which is able to overcome classically observed softening effects. A cumulative strain induced crystallization process is proposed to explain the stress ratio effect on fatigue crack initiation and propagation properties of natural rubber. © 2010 Elsevier B.V. All rights reserved.
Article history: Received 30 June 2010 Received in revised form 22 September 2010 Accepted 27 September 2010
Keywords: Natural rubber Fatigue Crystallization Crack branching
1. Introduction Natural rubber’s resistance to crack growth and its ability to withstand large strains
Contents lists available at ScienceDirect
Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea
Cyclic loadings and crystallization of natural rubber: An explanation of fatigue crack propagation reinforcement under a positive loading ratio
N. Saintier a,∗ , G. Cailletaud b , R. Piques b a b
LAMEFIP, Arts et Métiers ParisTech, Esplanade des Arts et Métiers, 33405 Talence Cedex, France Centre des matˇeriaux P.M. FOURT, Ecole Nationale Supˇerieure des Mines de Paris, UMR CNRS 7633, Evry Cedex 91003, France ı ı
a r t i c l e
i n f o
a b s t r a c t
Natural rubber is known to have excellent fatigue properties. Fatigue crack propagation studies show that, under uniaxial tension loading, fatigue crack growth resistance increases with the loading ratio, even if the peak stress increases. Studies dealing with crack initiation confirm this trend. If strain induced crystallization is believed to play a major role in this reinforcement process, it is not clear yet by which mechanism this reinforcement takes place. Using SEM investigation, it is shown here that the reinforcement process is associated with strong crack branching in the crack tip region. From experimental results it is shown that under particular reinforcing loading condition a cyclic strain hardening process can be observed on the natural rubber which is able to overcome classically observed softening effects. A cumulative strain induced crystallization process is proposed to explain the stress ratio effect on fatigue crack initiation and propagation properties of natural rubber. © 2010 Elsevier B.V. All rights reserved.
Article history: Received 30 June 2010 Received in revised form 22 September 2010 Accepted 27 September 2010
Keywords: Natural rubber Fatigue Crystallization Crack branching
1. Introduction Natural rubber’s resistance to crack growth and its ability to withstand large strains
References: [1] N. Saintier, G. Cailletaud, R. Piques, Int. J. Fatigue 28 (2006) 530–539. [2] N. Saintier, G. Cailletaud, R. Piques, Int. J. Fatigue 28 (2006) 61–72. [3] S. Trabelsi, P.A. Albouy, J. Rault, Macromolecules 35 (2002) 10054–10061.