A-POSTERIORI ERROR ESTIMATOR AND ADAPTIVE PROCEDURES FOR COMPUTATION OF SHAKEDOWN AND LIMIT LOADS ON PRESSURE-VESSELS

Adaptive finite element procedures are presented for the computation o f upper bounds estimates of limit and shakedown loads for pressure ves sels. The method consists of an h-type adaptive mesh refinement strate gy based upon an a-posteriori error estimator measured by the energy n orm. The problem is formulated in a kinematic approach using Koiter's shakedown theorem. A constitutive model, for elastic-perfectly plastic materials, relates the plastic strains increments and curvatures to p lastic multipliers through the flow law associated with a shelf piecew ise-linear yield surface (hexagonal prism). A consistent relationship between nodal displacements and nodal plastic multipliers is enforced by minimizing the strain residual between the total strain and the pla stic strain increments, which is measured with respect to the energy n orm. Discretization of the shell into finite elements allows the reduc tion of the problem to a minimization problem which is solved by linea r programming.