Abstract:
The presence of a nonlinear fracture process zone (FPZ) plays a crucial role in governing the
failure response of a quasi-brittle structure. One such influence is the structural size and boundary
effect phenomenon, where the growth and interaction of FPZ with the boundary has a considerable impact on the load-carrying capacity of the structure. In this article, a numerical study is
conducted using a micromorphic stress-based localizing gradient damage model [1], recently
proposed by the authors, to capture the structural size effect phenomenon during quasi-brittle
failure of geometrically similar concrete beams. The main objective is to reproduce the results
of independent experimental investigations on the size effect in quasi-brittle structures using a
single set of material and numerical parameters. Generally, a quasi-brittle fracture process starts
with a diffuse network of microcracks, which eventually localizes in a narrow process zone before
forming a macroscopic crack during the final stages of failure. To comply with this description,
the micromorphic stress-based localizing gradient damage model incorporates evolving anisotropic nonlocal interactions throughout the loading process through an anisotropic interaction
tensor and a damage dependent interaction function. A new arc-length control method based on
rates of the internal and dissipated energy approach [2] is modified as per the localizing gradient
damage formulation and implemented to trace the nonlinear behavior in numerical simulations.
The damage model successfully reproduces the experimental results with localized damage profiles using low-order finite elements for both mode-I and mixed-mode cases.
