A localizing gradient enhanced isotropic damage model with Ottosen equivalent strain for the mixed-mode fracture of concrete

Standard isotropic damage models are simple to implement, but they may be inadequate for the mixed-mode fracture of concrete. A new equivalent strain based on the four-parameter failure criterion by Ottosen [1] is proposed here for incorporation into a standard isotropic damage model for mixed-mode fracture, and its performance benchmarked against three other commonly used equivalent strain definitions (Mazars, modified von Mises, Rankine). Departing from the original approach [1], shear failure is utilized here as one of the states for the determination of the four parameters. Numerically, mesh sensitivity is resolved by adopting the localizing gradient enhancement to obtain sharp damage profiles at failure [2]. For the numerical analysis, a series of tests done on Double-Edge-Notched (DEN) specimens of different sizes [3] and the interactive test with multi axial loadings for Single-Edge-Notched (SEN) specimen [4] are considered. These examples illustrate that a simple isotropic damage model in conjunction with new equivalent strain measure is able to capture mixed-mode fracture accurately.

Automated summary

A new equivalent strain based on the four-parameter failure criterion by Ottosen is proposed to enhance standard isotropic damage models for mixed-mode fracture, benchmarked against other commonly used equivalent strain definitions. Shear failure is utilized as one of the states for determining the four parameters, with mesh sensitivity resolved by adopting localizing gradient enhancement. Numerical analysis includes tests on Double-Edge-Notched (DEN) specimens and interactive tests with multi axial loadings for Single-Edge-Notched (SEN) specimens, demonstrating accurate capture of mixed-mode fracture by a simple isotropic damage model combined with the new equivalent strain measure.