Hi,
Yes, the idea with the reference time, is the same. Using it avoids non-integer time units in the coefficient.
The offset in time serves two purposes, both related to that the Norton-Bailey law has very fast changes in the strain rate for small times.
1. A small value can be used to avoid the infinite strain rates that you could get at t=0. That part of the Norton-Bailey law is not well behaved in the numerical sense. Note that the time integral of the strain rate is still bounded, since the singularity is weak, so the physics is sound. The solver will however experience severe problems with infinite strain rates.
2. It is possible to start up a simulation for a material which has already been subjected to part of the primary creep period.
For anything but linear problems it would be optimistic to say that the default solver settings always work. For a creep problem the default settings will however in most cases work well. Just keep in mind that you should not have too large creep strain increments within a single time step. If required, this can be controlled either by limiting time steps, or by sharpening tolerances.
Regards,
Henrik
Yes, the idea with the reference time, is the same. Using it avoids non-integer time units in the coefficient.
The offset in time serves two purposes, both related to that the Norton-Bailey law has very fast changes in the strain rate for small times.
1. A small value can be used to avoid the infinite strain rates that you could get at t=0. That part of the Norton-Bailey law is not well behaved in the numerical sense. Note that the time integral of the strain rate is still bounded, since the singularity is weak, so the physics is sound. The solver will however experience severe problems with infinite strain rates.
2. It is possible to start up a simulation for a material which has already been subjected to part of the primary creep period.
For anything but linear problems it would be optimistic to say that the default solver settings always work. For a creep problem the default settings will however in most cases work well. Just keep in mind that you should not have too large creep strain increments within a single time step. If required, this can be controlled either by limiting time steps, or by sharpening tolerances.
Regards,
Henrik
