Biaxial fatigue behavior of a polychloroprene rubber Jean-Louis Poisson ⇑ , Florian Lacroix, Stephane Meo, Gaëlle Berton, Naranayaswami Ranganathan CERMEL, Laboratoire de Mécanique et Rhéologie, Université François Rabelais de Tours, 7 Avenue Marcel Dassault, 37200 Tours, France article info Article history: Received 30 September 2010 Received in revised form 20 January 2011 Accepted 24 January 2011 Available online 23 February 2011 Keywords: Multiaxial fatigue Dissipated energy density Fatigue criterion Haigh diagram Crystallization abstract Understanding phenomenon induced by complex fatigue loadings is an important issue for the concep- tion of industrial components. Rubber materials, thanks to their abilities to withstand high deformations, are more and more used in industry. In an ongoing study, an experimental investigation is being carried out to study the effect of multiaxial loadings on the fatigue life of polychloroprene rubber. This material is used for pulleys. Specimen used is a dumbbell type, axisymetric geometry with a reduced section at mid- height. The experimental results indicate that under uniaxial tensile loading a kink in the conventional Haigh diagrams is observed leading to high lives at high R-ratio loading as compared to low R-ratios. Frac- tographic studies indicate the presence of crystallographic tongues under high R-ratio loading. To repro- duce multiaxial conditions on this specimen, combined axial displacements and torsion rotation fatigue tests are performed, according to three different paths, depending on the phase angle between the two axes. Different multiaxial fatigue criteria are used to analyze experimental results. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Elastomers are more and more used in industrial applications (tires, belts, pulleys, etc.) thanks to their interesting mechanical behavior and their diversity. In service conditions, rubber compo- nents are subjected to multiaxial loadings. Most studies have been carried out to understand multiaxial fatigue phenomena in a natu- ral rubber (NR). This material is well known to induce reinforce- ment under tension strain state accompanied by crystallization. This phenomenon results in the creations of structures [1] which improve the resistance of such a material to rupture or tear. Previ- ous works [2,3] were aimed to quantify the crystallization rate by X-ray diffraction studies. Toki and Hsiao [4] determined crystalli- zation rate of different elastomers at 0 °C, using a pre-cracked specimen installed in an X-ray device. They observed crystalliza- tion of synthetic elastomers and they proposed a scheme to de- scribe the strain induced crystallization in rubbers. Three different phases were present in their scheme: crystalline struc- tures, oriented amorphous chains and non-oriented amorphous chain. They also concluded in another work [5] that the stress– strain hysteresis loop of rubber-like materials is attributed to strain induced crystallization. Saintier et al. [6,7] developed a uni- axial fatigue criterion, based on principal stress formulation, with a factor that takes into account the amount of crystallization deter- mined by X-ray diffraction. Cadwell et al. [8] observed an increase of fatigue life of a NR compound as the minimum strain increases. This statement is verified until a critical value for the minimum strain up to 300%. Moreover, in this work, at a fixed minimum strain, they noticed a decrease of fatigue life for an increase of strain range. This highlighted the importance of R-ratio on the fa- tigue behavior of natural rubber, where R = r max /r min . Mars [9] worked on the influence of crystallization of NR compounds on the fatigue behavior. He developed a formula taking into account the effect of crystallization on the fatigue crack growth behavior of NR. While NR is well known to involve crystallization, Legorju- jago [10] suggested that such crystallization could be activated in polychloroprene rubber under tension strain state. Crystallization, heterogeneous formulation, complex mechani- cal behavior makes the estimation of fatigue life of rubber-like materials difficult. Some Energy based criteria were introduced and used by many researchers to estimate multiaxial fatigue lives of rubber components. Alshuth and Abraham [11] displayed ten- sion fatigue results for a filled EPDM rubber. They noticed that en- ergy based criterion was able to unify all the fatigue results, with an interesting correlation, while the stress and strain based crite- ria’s results were depending on the fatigue conditions. Mars and Fatemi [12] formulated a new multiaxial fatigue criterion, the Cracking Energy Density (CED), which is the strain energy density available on the cracking plane. Payne and Whittaker [13] found a relationship between the fatigue crack growth of amorphous rub- ber and hysteresis at break in tension loading. Also, Lu [14] and Lacroix et al. [15] used dissipated energy density as a fatigue crite- rion under uniaxial fatigue tests, showing encouraging results with this criterion. Such approach for uniaxial fatigue of elastomers was inspired from the work of Ellyin [16] and Ellyin and Golos [17] on 0142-1123/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijfatigue.2011.01.014 ⇑ Corresponding author. Tel.: +33 2 47 36 12 03. E-mail address: jean-louis.poisson@etu.univ-tours.fr (J.-L. Poisson). International Journal of Fatigue 33 (2011) 1151–1157 Contents lists available at ScienceDirect International Journal of Fatigue journal homepage: www.elsevier.com/locate/ijfatigue