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Communication Dans Un Congrès Année : 2014

Evolution of the Hysteresis area during fatigue tests of a synthetic rubber

Résumé

The hysteresis area as a fatigue criterion has been studied in the framework of the fatigue behavior of the elastomers since the early 2000. Lacroix in 2004 [1] has shown that it was a relevant parameter to be investigated and Poisson in 2012 [2] showed that for a given framework it could be an efficient fatigue life criterion. As a characteristic value must be measured during a given fatigue test, in [2], the hysteresis area is measured at the end of each test, regardless if the sample failed or not. The issue is that in a previous communication, Cruanes et al. [3] showed that the self-heating could have an impact on the mechanical behavior. Therefore it is necessary to study in detail the evolution of the hysteresis area during a fatigue test. This evolution has been studied during a load controlled fatigue campaign on polychloroprene rubber dumbbells, known for being subjected to strain induced crystallization. It appears that two phases can be observed: a first one where the hysteresis area increases and reaches a threshold. Then, in a second phase, a faster increasing is observed. This behavior could be explained by the competition between the propagation of cracks and the strain-induced crystallization (SIC). For this kind of elastomer, those properties are well known (Le Cam and Toussaint [4] for example). In our case, the propagation of the crack during the first phase seems to get slower as the SIC sees its impact increasing. However, the dumbbell is subjected to a non-negligible self-heating and this raise of temperature makes the creation of crystallites harder. Therefore, at the beginning of the second phase, the propagation of the crack seems to override the SIC, which could explain the important increase of the hysteresis area. In order to detail this behavior, a new campaign has been carried out. Each test is divided in three steps: the first one is at a given maximum load F1 and last Nblock1 cycles. During the second step, the sample is put to rest in order to see its temperature comes back to the ambient. The third step consists in a fatigue test at a given maximum load F2 conducted until failure of the sample. With this protocol, two settings were used. The first setting investigated consisted in taking the maximum loads F1 and F2 equals and the impact of the length of the first block Nblock1 has been studied. It has been observed that when Nblock1 reach a given value, an increase of fatigue life during the second block is observed (up to seven times the life of a classical fatigue test). In this case, the first step seems to produce cracks and the second step allows the sample to come back to the ambient temperature. At the beginning of the third step, there seems to be cracks in the sample at an ambient temperature, meaning that there should be many sites (the tip of the cracks) where the SIC will could appear and therefore reinforce the sample. The second setting investigated consisted in fixing the duration of the first block and the maximum load F1 and studying the impact of the evolution of F2. It was observed that if F2 is lower than F1, the fatigue life is improved. This could mean that one may only need to damage enough the sample to see an increase of the fatigue life as long as the load is lower in this last step. To summarize, the study of the evolution of the hysteresis area during a fatigue test lead to an experiment showing an increase of fatigue life for elastomers which are subjected to SIC.
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Dates et versions

hal-01240024 , version 1 (08-12-2015)

Identifiants

  • HAL Id : hal-01240024 , version 1

Citer

C. Cruanes, F. Lacroix, Gaelle Berton, Stéphane Méo, Narayanaswami Ranganathan. Evolution of the Hysteresis area during fatigue tests of a synthetic rubber. International Elastomer Conference, 186th Technical Meeting, Oct 2014, Nashville, United States. ⟨hal-01240024⟩
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