Proc. of European Conference on Computational Mechanics
Munich, Germany, August 31 - September 3, 1999
ed. W. Wunderlich (CD-ROM)


Milan Jirásek
Swiss Federal Institute of Technology
LSC -DGC, EPFL, 1015 Lausanne, Switzerland


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 elements.



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 /