In concrete, growth and coalescence of microcracks lead to formation of visible frac- ture process zones that transfer stresses by crack bridging and aggregate interlock. Commonly, the behaviour of the fracture process zones is modelled by nonlinear fracture mechanics approaches…
In concrete, growth and coalescence of microcracks lead to formation of visible frac- ture process zones that transfer stresses by crack bridging and aggregate interlock. Commonly, the behaviour of the fracture process zones is modelled by nonlinear fracture mechanics approaches us- ing stress-strain laws with strain softening. One group of nonlinear fracture mechanics approaches suitable for computational structural analysis are nonlocal models, which lead to regular strain distri- butions over the fracture process zones, independently of the size of finite elements. This is achieved by evaluating the stress at each point based on weighted averages of state variables in the vicinity of that point. However, there is no consensus how the influence of boundaries should be taken into account by the averaging procedures. In the present comparative study, nonlocal damage models with different averaging methods and constitutive laws are investigated, with attention focused on the influence of boundaries. The most common approach of standard scaling is compared to averaging procedures that depend on the stress state and on the distance to boundaries. Firstly, the nonlocal models are calibrated by fitting stress-strain curves of one-dimensional uniaxial tension analyses to the results of mesoscale analyses. Then, the models are applied to two-dimensional simulations of three-point bending tests with a sharp notch, a 45◦ V-type notch and a smooth boundary without a notch. The performance of the nonlocal models is evaluated by comparison of load-displacement curves and dissipated energy profiles along the ligament of the beams with meso-scale results.