Dissipative Heating, Fatigue and Fracture Behaviour of Rubber Under Multiaxial Loading

Nowadays, different concepts to investigate the crack propagation in rubber materials are used. Most of them are based on the investigation of uniaxial loaded specimens and without taking into account the dissipative aspects of deformation. Rubber parts are used for different kinds of applications like tires, vibration damper, sealing parts, gaskets, diaphragms, etc. These parts are often subjected to multiaxial cyclic loading during operation. To utilize the whole mechanical potential of the rubber, it is necessary to investigate and characterize the material and crack behaviour under application relevant conditions. This study will work out that regardless of the deformation state (equibiaxial, asymmetrical biaxial, "pure shear", uniaxial) the same amount of energy is dissipated if the amount of the equivalent strain (von Mises) is equal. The present paper investigates, how different states of deformation possibly differently triggers the competitive dissipative processes of the material with the aim, to work out the different amount of dissipative effects as a function of the deformation state. It will be further shown how these effects influence the situation at the crack tip during cyclic loading. The correlations between von Mises equivalent strain, dissipative heating and crack propagation were analysed and used for the characterization of the material behaviour at the crack tip. It is shown how the dissipated energy can be estimated and how the data describe the heating of the and the heat transfer to the surrounding in detail. The dissipated conditions in the whole sample and in the vicinity of the crack tip correlate with the crack behaviour. The dependence of the crack growth rate and thermal state at the crack tip from the von Mises strain is discussed in detail. A physically motivated model approximates the strain at the crack tip and, finally, estimates the relationship between strain, energy dissipation and temperature state of the rubber material in the vicinity of the crack tip. The used rubber is a solution-SBR loaded with 50 phr carbon black. The experiments were performed on a biaxial test machine from Coesfeld GmbH & Co. KG. The measurements were done using an optical digital image correlation (DIC) system ARAMIS from GOM, Germany, to measure and analyse the strain. The thermal behaviour was determined by infrared thermography from InfraTec, Germany.