35. Characterisation of the Ultimate Tensile Properties of Elastomers by a Dimensionless Hooke Number—A New Approach to Failure Envelopes

The ultimate tensile properties of polymeric materials can be described by different kinds of master curves. Attention is focused mainly on the dimensionless Hooke number He fairly unknown in the literature. This quantity is defined and its utility to characterise the fracture mechanical properties of chemically uncrosslinked thermoplastics as well as very slightly crosslinked rubbers is discussed in detail. Pronounced differences were observed in a double logarithmic plot of the Hooke number versus the elongation at break ε _b for these two types of polymeric materials. The reasons of these discrepancies are explained on a molecular level. Furthermore, the effect of carbon black as reinforcing filler and its influence on the Hooke number is analysed. The presented test results support the idea that the Hooke number is adequate to characterise the fracture mechanical behaviour of polymers in a similar manner as do the well-known failure envelope representations.