The Equilibrium State of the Softened Elastomeric Nanocomposite under Uniaxial Loading and its Independence From the Method of Material Softening

For a mathematical model of an elastomeric material, the researcher must describe its equilibrium curve. This curve can be obtained by very slow stretching or by stress relaxation points at a given deformation. Experimental studies of filled elastomers and the effect of stress relaxation at 100% deformation from the stretching rate were conducted. The aim of the study was to determine how the stretching rate of the material affects the equilibrium state of the nanocomposite. Tests were performed for the specimens of butadiene-nitrile rubber containing 40 parts by weight of black carbon and butadiene-styrene rubber containing 50 parts by weight of black carbon. The specimens were stretched to the strain of 100 % at the rates of 10, 100, 1200 %/min and then aged for 2 hours. The specimens were subjected to tensile-compressive loads up to the strain of 100 % during 200-cycle test, and then were aged at maximum strain for 2 hours. It was found that the tensile rate affects the stress relaxation only at the early stage of aging – up to 15 minutes – after which the stress relaxation curves coincide. In cyclic testing, a decrease in the stress magnitude at the point of maximum strain is very slow and does not coincide with the relaxation curves, but with increasing time of holding one can observe a complete coincidence of the stress and relaxation curves. Such behavior of elastomers is due to their viscoelasticity and the accumulation of damage during stress relaxation at maximum deformation and cyclic testing.