Proc. of European Conference on Computational Mechanics
Munich, Germany, August 31 - September 3, 1999
ed. W. Wunderlich (CD-ROM)
COMPUTATIONAL ASPECTS OF NONLOCAL MODELS
Swiss Federal Institute of Technology
EPFL, 1015 Lausanne,
This paper deals with several issues related to computational analysis
of strain localization problems using nonlocal continuum models of the
integral type. Stress oscillations appearing for low-order elements are
described, their source is detected, and possible remedies are proposed.
The exact ``nonlocal'' tangential stiffness matrix is derived and its properties
and the corresponding assembly procedure are discussed. Spurious shifting
of the localization zone at late stages of the stiffness degradation process
is described, and it is remedied by combining the nonlocal continuum description
with explicitly modeled displacement discontinuities embedded in finite
Stress oscillations arising in finite element simulations with nonlocal
models have been described and their source has been detected. The possible
remedies are still under investigation and shall be discussed in more detail
in the conference presentation.
The exact, fully consistent global stiffness matrix has been derived
for the nonlocal isotropic damage model with damage energy release rate
as the variable driving the growth of damage. Due to the long-distance
interaction, the stiffness matrix has a larger bandwidth than for a local
model and is in general nonsymmetric. Nonstandard contributions must be
taken into account during the assembly procedure. Nevertheless, a fully
consistent tangential stiffness matrix can be constructed and exploited
in the global equilibrium iteration procedure.
Spurious shifting of the fracture process zone due to gravity forces
has been described and it has been demonstrated that the transition from
nonlocal continuum to a directly modeled displacement discontinuity embedded
in finite elements can remedy the problem.
The complete paper can be downloaded in the PostScript
format (7MB) or PDF format (210kB).
EPFL / 13 September1999 / firstname.lastname@example.org