In metals and alloys, generally when the stress generated exceeds yield (ductile) strength, it is implied yielding or failure occurs.
Similarly, in the case of finite element analysis of elastomers, what is the best parameter used to predict failure of elastomer under static loading?
1. Stress
2. Strain or
3. Strain energy
Third, similar to the Goodman relation in metals, what is the industrially used relation for fatigue life prediction of elastomers?
Many elastomers can be modelled by limiting chain extensibility constitutive models. An invariant of the stretch is a natural failure criterion for these materials. (For large deformations stretch is a better deformation measure than strain).
Stress, usually is used alongside stretch as a measure to know the behaviour of a specific elastomer. But failure is a broad term, as far as I comprehend I wouldnt like to use it as we often do in metals etc. Elastomers used in industrial applications are usually reinforced with tension cords or other reinforcing agents and thus they also have to be taken into account when reaching a decision. Also shear loading could play a part so its really difficult to make a failure criteria in a generic way!
I know that critical plane theory is being used in calculating the fatigue life of rubber but there might be other approaches well...
The traditional thinking is in stress limits and small deformations. The stretch-strain curve of elastomers becomes quite steep when approaching the limiting stretch. Therefore, the stress at rupture is less certain. But the limiting stretch is. Unfortunately you will hardly find tabulated values.
However, you can find some large deformation theories for limiting chain extensibility material models like the van der Waals rubber model. Then you can find that the square root of the trace of the left and right Cauchy Green tensor is limited to approx. 8.8. (The eigenvalues/proper values of this tensor are the squares of stretch.)
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