Material model for finite element modelling of fatigue crack growth in concrete

Although fatigue damage of concrete is an important problem in structures subjected to cyclic loading, there are not many high-cycle fatigue models available for use in conjunction with advanced concrete material models and nonlinear finite element analysis. The available models that are published in the literature (for instance [1]) usually deal with the low cycled fatigue when it is necessary to perform the numerical nonlinear analysis for all investigated cycles. This approach is definitely not applicable when it comes to high-cycle fatigue when it is usually necessary to consider millions of cycles. The available models (for instance [2]) for high-cycled fatigue are based on linear elastic fracture mechanics considerations and they are not readily applicable to the finite element analysis using the smeared crack approach. The three-dimensional fracture-plastic model [3] in the finite element software ATENA has been extended to capture fatigue damage in tension (however, the model can be easily modified to also consider damage from compressive and tensile-compressive loads). The damage can result in new cracks or growth of existing ones. To keep the material model as simple as possible, the implementation is based on a classical stress based model (S-N or Wohler curve). The S-N criterion is translated into material damage, which is introduced into the material model on the basis of stress increments at each material point and the number of cycles. The S-N criterion is suitable to initiate damage into the intact material. However, in order to facilitate the necessary crack propagation and extension of a pre-existing damage an additional damage needs to be introduced. It is advantageous to base this damage not on stress cycles but rather on the cycles of crack opening displacements (delta COD). The paper will present the formulation of the new model for the high-cycle fatigue in a form that is suitable for the smeared crack model formulation and the finite element analysis. The model behaviour will be documented on small theoretical examples as well as by comparison with experimental data. (C) 2010 Published by Elsevier Ltd.