COBEM99

S24 Mecânica dos Sólidos

Title:

ADVANCES IN FINITE ELEMENT MODELLING OF PLASTIC BEHAVIOUR OF PRESSURE VESSELS

Summary :

AN UPPER BOUND FORMULATION FOR ESTIMATING LIMIT AND SHAKEDOWN LOADS FOR PRESSURE VESSELS IS RECOUNTED. THE ERROR ESTIMATOR USING THE ENERGY NORM AND ADAPTIVE STRATEGIES FOR REMESHING ARE ALSO RECALLED. THE MATERIAL IS ASSUMED TO BE ELASTIC-PERFECTLY PLASTIC. A NEW SHELL ELEMENT IS THEN PRESENTED, WHICH IS CAPABLE OF A MUCH BETTER MODELLING OF THE PLASTIC BEHAVIOUR OF PRESSURE VESSELS UNDER ULTIMATE LOADING. THE CLASS OF DISPLACEMENT FIELD PROPOSED TO SIMULATE THE MATERIAL AND ELEMENTAL BEHAVIOUR ALLOWS THE CONSIDERATION OF A MORE REALISTIC PLASTIC STRAIN FIELD. THE CONCEPT OF HINGE CIRCLES NEED NOT TO BE CONSIDERED AND THE BASIC IDEA IS THAT THE NEW ELEMENT CAN, EQUALLY WELL, MODEL MEMBRANE AND BENDING BEHAVIOURS WITHIN ITSELF AND AT THE NODES. THE ENERGY DISSIPATION DUE TO THE CHANGE IN CURVATURE OF THE ELEMENT DURING PLASTIC DEFORMATION IS NOW CONSIDERED GLOBALLY, WITH NO NEED TO SEPARATE ELEMENT FROM NODES, SINCE HINGES NO LONGER EXIST. THE PLASTIC STRAIN FIELD IS DEFINED BY THE FLOW LAW ASSOCIATED TO AN APPROPRIATE LINEARIZED YIELD SURFACE. THE NEW YIELD SURFACE IS ALSO CAPABLE OF INCORPORATING THE VARIATION OF CURVATURE IN THE ELEMENT DURING COLLAPSE. MUCH BETTER COLLAPSE MECHANISMS ARE OBTAINED AND THE SOLUTIONS ARE SUBSTANTIALLY IMPROVED. NEW MINIMIZATION PROCEDURES BASED ON THE ENERGY NORM WERE DEVELOPED TO DETERMINE A CONSISTENT RELATIONSHIP BETWEEN THE TOTAL DISPLACEMENT FIELD AND THE PLASTIC STRAIN FIELD DESCRIBING THE MATERIAL PLASTIC BEHAVIOUR IN TERMS OF PLASTIC MULTIPLIERS. THE DISCRETIZED STRUCTURAL PROBLEM IS REDUCED TO A MINIMIZATION PROBLEM AND THE SOLUTION IS OBTAINED BY LINEAR PROGRAMMING. KEY-WORDS FINITE ELEMENT, PRESSURE VESSELS, ADAPTIVITY

Author :

Barros, Felício Brüzzi
Franco, José Ricardo Queiroz

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