Direct comparison of anisotropic damage mechanics to fracture mechanics of explicit cracks

Because damage mechanics modeling involves damage initiation followed by propagation that releases energy, it is often uncritically assumed to be an alternative implementation of fracture mechanics. This paper tests that claim by running side-by-side damage mechanics and explicit crack fracture mechanics simulations within the same code on three separate problems. For a center-notched specimen loaded in tension, damage mechanics can reproduce all features of fracture mechanics, but with three restrictions. First, damage mechanics must implement anisotropic damage mechanics rather then simpler isotropic or scalar damage methods. Second, initiation stress and toughness used in damage mechanics must be calibrated before damage mechanics can reproduce either fracture mechanics or experimental results. Third, damage mechanics properties must scale with absolute size of discretization elements. Two other problems considered were mixed-mode, dynamic fracture and cracking of a brittle coating on a substrate. In each case, anisotropic damage mechanics can be made consistent with fracture mechanics by suitable calibration of properties. An advantage of damage mechanics is its potential to model certain complicated issues better then explicit crack fracture mechanics. Two examples are dealing with a transition to shear failure and modeling of fracture events such as periodic cracking in coatings.