Haoxuan Yu, The parameters of the Concrete Damaged Plasticity (CDP) model—dilatancy angle, eccentricity, and form factor—are critical for simulating concrete behavior accurately. The dilatancy angle, which measures the volumetric expansion of concrete under shear stress, typically ranges from 30 to 40 degrees for most types of concrete. This parameter is best determined through empirical data from experiments, although values from the literature can serve as a reliable reference when specific data is unavailable. The eccentricity parameter, controlling the shape of the plastic potential surface, is commonly set at 0.1. This value offers a balance between numerical stability and accuracy and is generally less sensitive compared to the dilatancy angle. For the form factor, which dictates the yield surface shape in the deviatoric plane and reflects the compressive-to-tensile strength ratio, a standard value of 0.667 is widely accepted. This ratio is based on the assumption that the second stress invariant on the tensile meridian to the compressive meridian is approximately 2/3. These values can be refined by consulting experimental data, conducting a literature review, and performing calibration simulations to ensure they accurately represent the specific concrete and loading conditions in your study. I hope it is clear now?