Microfocused Beam SAXS and WAXS Mapping at the Crack Tip and Fatigue Crack Propagation in Natural Rubber
We investigated crack propagation in cyclic fatigue in filled (50 phR of N347 carbon black), highly crosslinked, natural rubber pure shear samples and, in parallel, mapped in detail the microstructure present at the crack tip with a microfocused X-ray syn
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Microfocused Beam SAXS and WAXS Mapping at the Crack Tip and Fatigue Crack Propagation in Natural Rubber Quentin Demassieux, Daniel Berghezan, and Costantino Creton
Contents 1 Introduction 2 Materials and Methods 2.1 Materials and Sample Preparation 2.2 Cyclic Fatigue Testing 2.3 Design of the Crack Tip Characterizations 2.4 DIC Experiments 2.5 In Situ Mapping of Fatigue Crack Tips 3 Results 3.1 Effect of Crosslinking Density 3.2 Effect of Temperature 3.3 On the Presence of Cavities at the Crack Tip 3.4 Comparison between Digital Image Correlation (DIC) and X-Ray Absorption: Mapping the Thickness at the Crack Tip 4 Conclusions References
Abstract We investigated crack propagation in cyclic fatigue in filled (50 phR of N347 carbon black), highly crosslinked, natural rubber pure shear samples and, in parallel, mapped in detail the microstructure present at the crack tip with a microfocused X-ray synchrotron beam. We acquired data by wide-angle X-ray scattering (WAXS) to characterize strain-induced crystallization (SIC) and by small-angle X-ray scattering (SAXS) to detect nano-cavitation. Crack propagation Q. Demassieux and C. Creton (*) Laboratoire de Sciences et Ingénierie de la Matière Molle, ESPCI Paris, PSL University, Sorbonne University, CNRS, Paris, France e-mail: [email protected] D. Berghezan Michelin Research Center, Ladoux, Clermont-Ferrand, France
Q. Demassieux et al.
experiments were carried out for a range of maximum energy release rates during the cycles varying from 1 to 4 kJ/m2. Each material was tested at two temperatures: room temperature and 100 C and in new and aged conditions (10 days at 100 C in an inert atmosphere). We found that although significantly less SIC at the crack tip was present at the crack tip at 100 C, the resistance to crack propagation under cyclic loading was barely affected. In aged samples SIC at the crack tip was significantly lower than in new samples at room temperature, and was not detectable at all in aged samples at 100 C. The crack propagation rate, however, only increased with aging for the more crosslinked sample at 100 C and never increased catastrophically. Finally, a few percent of nano-cavities were detected at the crack tip and the comparison of X-ray transmission and digital image correlation suggested the presence of a significant fraction of large cavities at the very crack tip. In conclusion while strain-induced crystallization in NR may be affecting fatigue resistance we could not establish a quantitative correlation between the volume crystallized at the crack tip and the crack propagation rate in cyclic fatigue. Keywords Cavitation · Crack propagation · Crystallization · Fatigue · Mechanical properties · Natural rubber · X-ray scattering
1 Introduction Although strain-induced crystallization (SIC) is a very well-known and well-studied phenomenon in natural rubber (NR) several questions remain in terms of its role as a toughening mechanism. In this study we explore in more detail, and for realistic carbon black filled materials, the conn
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