Eduardo Bittencourt

Simulation of 3D metal-forming using an arbitrary Lagrangian–Eulerian finite element method

Abstract The arbitrary Lagrangian–Eulerian (ALE) formulation is an efficient alternative to deal with the finite element mesh distortion that occurs in an updated Lagrangian (UL) formulation when simulating metal-forming processes. Uncoupling mesh movement from material movement, the ALE operator can be split into an UL step followed by an Eulerian step. Deformation due to loading is calculated in the UL step (without convective terms) and the mesh movement (relative to the material) is imposed by nodal relocation techniques in the Eulerian step. In this paper, the authors propose two relocation techniques, similar to an r-refinement, that can move internal and external nodes (including non-planar surface nodes) of eight-node hexahedral elements of structured meshes, while keeping the body volume approximately constant. In this manner, an improved mesh is obtained. Data transfer between the UL mesh and the relocated mesh is performed by using either an expansion of stresses in a Taylor’s series or a new search algorithm that avoids iterative solutions. Two examples, one static and one dynamic, are presented and their results compared with known solutions.

FINITE ELEMENT ANALYSIS OF THREE-DIMENSIONAL CONTACT AND IMPACT IN LARGE DEFORMATION PROBLEMS

Abstract An algorithm that models three-dimensional contact with friction, including cases where large deformations occur is proposed. The algorithm is an extension to three-dimensions of an algorithm for contact previously proposed by Ponthot and Hogge [1] . The present algorithm can be used in implicit or explicit codes, when contact between a rigid and a deformable body or among deformable bodies (multibody contact) is to be determined. The penalty method is used as the contact–friction formulation. Constitutive relations for contact–friction and integration of these relations in a corotational reference system are detailed. In order to provide a good convergence rate, the contact–friction stiffness matrices used are consistent with the time integration process. A simple and fully explicit form was obtained for these matrices. For contact problems involving rigid and deformable bodies, interpenetrations are detected using an iterative procedure. For frictionless multibody contact, a new element that simplifies the gap calculation, eliminating iterative procedures, is proposed. Comparison with benchmark results and the solution of practical examples demonstrate the effectiveness of the algorithm.

Numerical simulation of cracking in reinforced concrete members by an embedded model

Purpose – The purpose of this paper is to describe the development of an embedded crack finite element (FE) model for reinforced concrete (RC) structures, including a bond‐slip methodology to take into consideration the steel contribution in the rupture process, capable of capturing the global behavior of the structure as well as details of cracking phenomenon.Design/methodology/approach – The reinforcement contribution is added in the equilibrium at element level in an embedded crack FE model, based on displacement localization lines inside the elements.Findings – The model is able to determine the steel stress in the crack besides the volumetric average steel stress. It is shown that the steel stress in the crack can be considerable greater than the average value. Other important aspect detected is the contribution of the concrete softening in the steel stress in the crack and in the overall behavior. The number, the distribution and the opening of cracks can be estimated too.Practical implications – Th...

Consideração do esmagamento no concreto armado através de modelos coesivos

In this work, the overlapping crack mode is considered. It permits the modeling of concrete crushing through cohesive surfaces, in a similar way used to simulate fracture. The material is considered in damage when the surfaces interpenetrate each other. Besides simplicity, the big advantage of the methodology is the fact that constitutive relations are independent of the material scale. A generalization is here introduced to consider mixed crushing. Exploratory applications are made considering super-reinforced beams. The effects of the height of the beams, compressive rebars and stirrups are investigated. A good fitting with experiments is obtained.

Análise paramétrica de um modelo de transferência de tensão por aderência em peças de concreto armado fletidas

A propriedade estrutural mais marcante do concreto e sua baixa resistencia a tracao frente a sua resistencia a compressao. Isto faz com que estruturas de concreto funcionem fissuradas ja para baixos niveis de carga. As fissuras reduzem a rigidez da estrutura; quando elas se formam, a distribuicao interna das tensoes e deformacoes e grandemente modificada e o concreto comeca a apresentar comportamento naolinear. Os modelos numericos que pretendam fazer uma analise realistica do funcionamento de estruturas deste material devem reproduzir corretamente este comportamento.O objetivo deste trabalho e fazer uma analise parametrica da influencia que determinadas variaveis de um modelo de transferencia de tensao por aderencia, entre a armadura e o concreto adjacente, tem sobre o comportamento global de pecas de concreto armado fissuradas. Na analise numerica, via metodo dos elementos finitos, sera empregada um modelo de fissura incorporada que leva em consideracao a contribuicao da armadura no equilibrio de forcas interno do elemento. Os modelos incorporados se baseiam no conceito de descontinuidades incorporadas dentro de elementos finitos. As previsoes numericas sao comparadas com resultados experimentais. Palavras-chave: concreto armado, fissuracao, modelo incorporado.