2008 - present (in progress)
The present research is motivated by the need for accurate simulation of structural steel behavior under strong reverse or cyclic loading conditions, associated with excursions into the plastic range of the steel material. Under such loading conditions, several plasticity related phenomena such as the Bauschinger effect or the accumulation of plastic strain (often reported as ratcheting or cyclic creep) take place and need to be accurately predicted. The study concerns relatively thin-walled structural steel members, with emphasis on cylindrical shells (tubes and pipes). Those structural components, due to their relatively small thickness, often fail due to buckling when excessive compressive stresses are developed. The phenomenon of buckling becomes quite more complicated when cyclic loading is applied; in such a case, a progressive accumulation of plastic deformation occurs, leading to buckling under a relatively low level of loading.
The study is aimed at developing a large-strain plasticity constitutive model, based on the concept of bounding-surface plasticity, and incorporating the model into a nonlinear step-by-step nonlinear finite element solution of the governing equations (e.g. ABAQUS/Standard software). The constitutive model will take into account the accumulation of plastic deformation and possible degradation in every cycle. Subsequently, the numerical formulation and solution technique will be used to solve benchmark problems related to structural behavior and failure of steel structural members, subjected to cyclic loading. The developed methodology is applicable to steel structural components of arbitrary geometry; however, in the present research special emphasis will be given to elongated cylindrical (tubular) members, such as members of tubular lattice structures (e.g. offshore platforms, towers etc.), industrial piping components, steel pipeline segments (onshore and offshore), or steel catenary risers.
In Conference Proceedings
- Varelis, G.E., Vathi, M, Houliara, S., Karamanos, S.A., "Effect of the UOE Manufacturing Process on Pressure Buckling of Thin-walled Pipes.", 2nd South-East European Conference on Computational Mechanics, paper No. SE151, Rhodes, Greece, June 2009
- Varelis, G.E., Vathi, M, Houliara, S., Karamanos, S.A., "Effect of the UOE Manufacturing Process on Pressure Buckling of Thin-walled Pipes.", X International Conference on Computational Plasticity, Barcelona, Spain, September 2009
Figure 1: Basic concept of bounding-surface (two-surface) plasticity (e.g. Dafalias & Popov, 1976).
Figure 2: Cyclic behaviour of a steel material exhibiting hardening using J2 plasticity model with nonlinear kinematic hardening material law; comparison of in-house results with ABAQUS.
Figure 3: Progressive ovalization during cyclic bending of a long thick-walled cylindrical shell; simulation using finite elements and a nonlinear kinematic hardening material law.
Figure 4: Numerical simulation of the UOE pipe manufacturing process.
Figure 5: Stress path at a critical location during the UOE pipe manufacturing process; comparison between isotropic and (linear) kinematic hardening rules.