Determination of the Loading Mode Dependence of the Proportionality Parameter for the Tearing Energy of Embedded Flaws in Elastomers Under Multiaxial Deformations

In this paper, the relationship between the tearing energy and the far-field cracking energy density (CED) is evaluated for an embedded penny-shaped flaw in a 3D elastomer body under a range of loading modes. A 3D finite element model of the system is used to develop a computational-based fracture mechanics approach which is used to evaluate the tearing energy at the crack in different multiaxial loading states. By analysing the tearing energy’s relationship to the far-field CED, the proportionality parameter in the CED formulation is found to be a function of stretch and biaxiality. Using a definition of biaxiality that gives a unique value for each loading mode, the proportionality parameter becomes a linear function of stretch and biaxiality. Tearing energies predicted through the resulting equation show excellent agreement to those calculated computationally

Some revisions of fatigue crack growth characteristics of rubber

Fatigue crack growth (FCG) characteristic of rubber materials is a very important factor in determining the durability of the rubber products. Slight variations in compounding ingredients, mixing and the curing process or even in the loading conditions and several physical factors have an impact on the final FCG behaviour of rubber vulcanisates. Thus, possible inaccuracies in the experimentally determined FCG characteristics can have direct consequences on the development of durable rubber compounds. Therefore, the aim of this work is focused on the experimental validation of the FCG characteristics of rubber in comparison with the recently customary theoretical background and functions describing the relationship between the FCG rate and the tearing energy. From the literature survey, the weak points directly influencing the accuracy of the FCG characteristics in the experimental approach were identified. The first weak point is the transient point or discontinuity of the FCG characteristics within the region of the stable FCG. To follow on, a visible deviation of the experimentally determined data within the region of the stable FCG from the theoretical function is necessary to be validated. FCG analyses of plane strain tension samples based on ethylene propylene diene monomer (EPDM) rubber filled with a varied content of carbon black were performed using a Tear and Fatigue Analyzer (TFA (c), Coesfeld GmbH & Co. KG, Germany). The FCG characteristics were plotted for a broad range of tearing energies. The intrinsic strength and the ultimate strength were determined. The region of the stable FCG was studied in detail. The continuous function of the stable FCG within the region was found, and thus, the presence of a transient point was refuted. Moreover, a specific equation was validated to fit the data into the region of the stable FCG compared to a previously preferred power-law with a higher accuracy.Ministry of Education, Youth and Sports of the Czech Republic - DKRVO [RP/CPS/2020/004

Photo of John Ducey's workbench

Workbench inside John Ducey's store; various tools for woodworking and fishing either on, hanging above, or nearby the workbenc