Fatigue effect of elastocaloric properties in natural rubber

In the framework of elastocaloric (eC) refrigeration, the fatigue effect on the eC effect of natural rubber (NR) is investigated. Repetitive deformation cycles at engineering strain regime from 1 to 6 results in a rapid rupture (approx. 800 cycles). Degradation of properties and fatigue life are then investigated at three different strain regimes with the same strain amplitude: before onset strain of strain-induced crystallization (SIC) (strain regime of 0-3), onset strain of melting (strain regime of 2-5) and high strain of SIC (strain regime of 4-7). Strain of 0-3 leads to a low eC effect and cracking after 2000 cycles. Strain of 2-5 and 4-7 results in an excellent crack growth resistance and much higher eC effect with adiabatic temperature changes of 3.5 K and 4.2 K, respectively, thanks to the effect of SIC. The eC stress coefficient index γ (ratio between eC temperature change and applied stress) for strains of 2-5 and 4-7 are γ2-5=4.4 K MPa(-1) and γ4-7=1.6 K MPa(-1), respectively, demonstrating the advantage of the strain regime 2-5. Finally, a high-cycle test up to 1.7×10(5) cycles is successfully applied to the NR sample with very little degradation of eC properties, constituting an important step towards cooling applications.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.