Impact fracturing of materials driven by the release of kinetic energy of shear strain rate field in forming particles

The paper reviews recent work at Northwestern University in which the apparent increase of strength of concrete at very high strain rates experienced in projectile impact (10 per second to 10 million per second), called `dynamic overstress', is explained by the release of local kinetic energy of shear strain rate field in finite-size particles that about to be produced by interface fracture. The theory predicts the particle size and the additional kinetic energy density that must be dissipated in finite element codes. The additional energy dissipation explains the so-called “dynamic overstress” - an apparent drastic increase of strength that had to be introduced to fit the data on deceleration of missile penetrating concrete or rock.