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Continuum models of fracture should be equipped with a localization limiter to prevent pathological discretization sensitivity of finite element simulations. Moreover, stiffness recovery, called also crack closing effect, should be reproduced in the modelling of quasi-brittle materials when reversed loading is applied. In this paper the efficiency of two different established damage-plasticity models for concrete is assessed from the viewpoint of the two above-mentioned aspects. The first description is the so-called concrete damaged plasticity model, available in the ABAQUS package. In this model the plasticity theory is not only augmented with stiffness degradation and recovery, but also with the crack band approach and viscoplastic regularization. The gradient-enhanced damage description, which is the second one considered, can also be coupled to plasticity. In this model additional averaging equation prevents the pathological discretization sensitivity of fracture simulations. Two fields, displacements and averaged strain measure, are interpolated and suitable finite elements are programmed by the authors in the FEAP package. Basic concepts of the numerical analysis of the crack closing phenomenon are reviewed. Both models are capable of avoiding mesh-sensitivity, but it is achieved in a different manner and it is shown in the paper that the users of ABAQUS should employ the crack band options with particular care. Representative examples in the context of the examined issues are demonstrated: uniaxial tension of a bar and a cantilever beam. The results obtained using both the models are compared and the effects of regularization and crack closing are illustrated. [ABSTRACT FROM AUTHOR]

In this paper, the constraint effect caused by a side-groove on creep crack growth behavior in P92 steel was studied using finite element analysis. Creep crack growth simulations were conducted on compact tension specimens for side-grooves with different depths and angles. The simulated outcome indicated that the creep crack growth rate increased as the depth and the angles of the side-grooves in the specimen increased. Next, the profile of the crack front for the different specimens was discussed. The distribution of the average stress triaxiality and the average equivalent stress on the crack front were studied to investigate the mechanical mechanism describing the constraint effect on creep crack growth behavior. Finally, the creep crack growth rate determined from numerical simulation results was determined to be consistent with existing experimental data. [ABSTRACT FROM AUTHOR]

Computation cost is a key issue for finite element methods to simulate hydraulic fracturing. In this paper a coupled finite element method combined with a condensation technique is proposed to address this issue. Removing the node displacements that have no contribution to fracture widths from the coupled equations, the condensation technique reduces the size of the coupled equations in the proposed method. The numerical method with the condensation technique is verified. Simulations show that the condensation technique can reduce the computation cost effectively, in particular when the fracture propagation regime is viscosity-dominated or the simulation is on the early stage. The effects of the condensation technique on the simulation accuracy, stability, and convergence of the numerical method are discussed. The condensation technique is applicable to other finite element methods that are based on linear elastic fracture mechanics. [ABSTRACT FROM AUTHOR]