The elastoplastic rate problem is formulated as an unconstrained saddle point problem which, in turn, is obtained by the Lagrange multiplier method from a kinematic minimum principle. The finite element discretization and the enforcement of the min-max conditions for the Lagrangean function lead to a set of algebraic governing relations (equilibrium, compatibility and constitutive law). It is shown how important properties of the continuum problem (like, e.g., symmetry, convexity, normality) carry...
Si considera il problema del mancato adattamento in campo dinamico per strutture elasto-plastiche incrudenti. Si dimostrano una condizione necessaria ed una sufficiente per il verificarsi di fenomeni di inadattamento (plasticità alternata o collasso incrementale) estendendo risultati precedenti ad un'ampia classe di modelli costitutivi a variabili interne in grado di rappresentare comportamenti incrudenti non lineari.
Nell'articolo si tratta il problema dell'adattamento in dinamica elasto-plastica. La trattazione è fondata sulle seguenti basi: si adotta un legame costitutivo elasto-plastico di notevole generalità, basato su di una formulazione a variabili interne in grado di descrivere un comportamento incrudente genericamente non lineare; si fa riferimento ad un modello strutturale discreto, descritto mediante variabili generalizzate. I contributi presentati si possono così riassumere: si estendono risultati...
A homogeneous solid subject to quasi-static loading in the small strain range is considered. The material model assumed is rate-independent, non-associative and incrementally bilinear. The strain localization conditions are analytically solved using a geometric method. The expressions of the critical hardening moduli, their domains of validity and the form of the strain rate discontinuity are obtained. Finally these results, and in particular the role of hydrostatic and deviatoric non-normality,...
For a class of elastic-plastic constitutive laws with nonlinear kinematic and isotropic hardening, the problem of determining the response to a finite load step is formulated according to an implicit backward difference scheme (stepwise holonomic formulation), with reference to discrete structural models. This problem is shown to be amenable to a nonlinear mathematical programming problem and a criterion is derived which guarantees monotonie convergence of an iterative algorithm for the solution...
For a class of elastic-plastic constitutive laws with nonlinear kinematic and isotropic hardening, the problem of determining the response to a finite load step is formulated according to an implicit backward difference scheme (stepwise holonomic formulation), with reference to discrete structural models. This problem is shown to be amenable to a nonlinear mathematical programming problem and a criterion is derived which guarantees monotonie convergence of an iterative algorithm for the solution...
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