aquis_mech's blog

Dear Sir or Madam, dear colleagues, 

with deep sadness and regret we inform you Prof. Dr.-Ing. Christian  Miehe passed away last  Sunday, August 14th, 2016th.

Professor Miehe held the chair for Mechanics and Material Theory at the Institute of Applied Mechanics, Faculty of Civil and Environmental Engineering of the University of Stuttgart and has been one of the directors of the institute. He has been greatly appreciated by his colleagues and his co-workers, and students always found him receptive to their concerns.

  I have written a Fortran code for nonlinear viscoelasticity according to the Hughes' recurrence algorithm based on a total Lagrangian formulation.  And a relaxation test is made. There is some deviation from the analytical solution(Theoretically the stress response should be an exponential decay plus a constant, isn't it?). The numerical ultimate stress is larger than the analytical one. As a larger initial strain is applied, the deviation is smaller. For a inital strain of 10%, there is almost no difference between the num. and analy. solution. What can account for this?

  The difference to the common model used is the f,g terms. The 3D FEM formulation has been derived and a new fortran program is written. The derivative matrix is symmetric. But the calculation result does not converge. I have tried every means to get a converging result. But it doesn't work, the residual norm always increases.