Experimental and Numerical Investigation on the Size of Damage Process Zone of a Concrete Specimen under Mixed-Mode Loading Conditions

The characteristic length of a gradient-dependent damage model is a key parameter, which is usually regarded as the length of damage process zone (DPZ). Value and evolution of the size of DPZ were investigated by both a numerical method and an experimental manner. In the numerical study, the geometrical model adopted was a set of four-point shearing beams; the numerical tool used was the Abaqus/Explicit software. The distance between the front and end of a complete DPZ was obtained. Values of strain components at these points were given out at given time points. The experimental study of the evolution process of a damage process zone was investigated with a set of concrete specimens under mixed-mode loading conditions by using a white-light speckle method. The geometrical parameters of the damage process zone were measured. Double-notched specimens under four-point shear loading conditions were adopted. A series of displacement fields for points on the surface of the specimen were measured and further transferred into a strain field of these points during loading process. With reference to the strain values that occurred at both the front and end of a numerically-obtained DPZ, the length of the DPZ was determined with the experimental results. These results provide an experimental basis for the determination of the value of an internal length parameter for a gradient-enhanced and/or area-averaged non-local model.