2007 - present (in progress)
The research is aimed at developing advanced numerical tools for the simulation of shell buckling and post-buckling behavior, in the plastic range. This work describes a J2 non-associative plasticity model, which takes into account the "corner-like" effects at the loading point on the yield surface, and is suitable for shell buckling calculations.
Analytical and numerical predictions of structural buckling in the inelastic range are in closer agreement with test results when deformation-plasticity theory moduli are employed, instead of flow-plasticity moduli. This is attributed to the "softer" moduli of the deformation theory, simulating a "vertex" or "corner" (i.e. a high-curvature region on the yield surface at the point of loading on the yield surface), denoted in experimental observations.
The present work focuses on the numerical implementation of the plasticity model based on the von Mises yield surface (J2 plasticity) and the rate form of J2 deformation theory, leading to a non-associated flow rule. The numerical implementation follows an Euler-backward substitution numerical scheme, developed for elastic-plastic shell analysis, where stress and strain are described in curvilinear coordinates, with the extra constraint of zero normal stress through the shell thickness. The previous model is incorporated within an in-house special-purpose finite element technique for the nonlinear analysis of cylindrical shells, with emphasis on buckling of cylindrical shells under uniform axial compression and bending.
In Conference Proceedings
- Pappa, P., and Karamanos, S. A., 'Numerical Implementation of J2 Non-Associative Flow Plasticity Models' 10th International Conference on Computational Plasticity, COMPLAS X, Barcelona, September 2009
Figure 1: Buckled shapes from experiments on thick-walled cylinders under axial compression (Bardi & Kyriakides 2006), and bending (Ju & Kyriakides 1992).