<FLOW> gsell

Description

This is a viscoplastic model appropriate for some polymer materials. It includes some hardening behavior using the cumulated viscoplastic multiplier \(v\).

\[\dot{\lambda} = \left<\frac{f}{K \left(1-e^{-w v}\right) e^{h v^n}}\right>^{m_1}\]

Note that at \(v = 0\) the term \(1-e^{-w v}\) in the denominator will become zero, setting the denominator to zero (infinite initial strain rate). To alleviate this numerical difficulty, the term is modified to be \(1-e^{-w (v+e_0)}\)

Example

A simple example of purely viscoplastic material follows. Because the yield radius R0 is zero, the material is always flowing. The use of elasticity in this case is also a pseudo-elasticity, attempting to model a purely viscous material in a displacement based FEA model. The higher the modulus, the more \(\ten \varepsilon_{in}\) approaches \(\ten \varepsilon_{to}-\ten \varepsilon_{th}\).

***behavior gen_evp
 **elasticity isotropic
      young 100000.
      poisson 0.48
 **potential gen_evp ev
  *isotropic constant
     R0 0.0
  *flow gsell
      e0  1.e-5
      K   40.0
      w   65.
      h   0.75
      n   1.75
      m   0.08
***return