Improved Nonlinear Model for Concrete Fracture

A nonlinear model for the fracture process zone (FPZ) that exists at the tip of a crack in concrete is developed through the interactive use of experimental data and finite element analysis of crack‐line‐wedge‐loaded double‐cantilever‐beam (CLWL‐DCB) specimens. That model relates the clamping stress to the crack opening displacement (COD) and is characterized by three straight‐line stress variations segmented by three critical CODs. In the first segment the clamping stress equals the concrete's tensile strength. In the second segment the crack closure decreases sharply with increasing CODs from the tensile strength at about $0.4\times {10}^{-3}$ in. (0.01 mm) to 0.3 times that stress at about $2.0\times {10}^{-3}$ in. (0.05 mm). The validity of that model is demonstrated by showing that it can predict the results of tests on five different groups of CLWL‐DCB specimens subjected to mode I loadings.