Abstract: The decay function for the free-surface effect is constructed by treating a target as an incompressible Mohr-Coulomb material and assuming that the cavity expansion produces a plastic-crack-elastic response region. The semi-empirical forcing function of brittle targets for oblique penetration is obtained by multiplying the semi-empirical forcing function of brittle targets with the decay function. Then the projectile is modeled with an explicit transient dynamic finite element code and the target is represented by the forcing function as the pressure boundary condition. This methodology eliminates the need for discretizing the target as well as the need for the contact and erosion algorithms, which reduces the computer time and memory requirements. The oblique penetration of 4340（RC44.5）steel into limestone target is simulated. The comparisons of the final forms of projectile and the final positions of tip in simulation and experiment demonstrate the effectiveness and advantage of the proposed method.

Key words: ordnance science and technology, oblique penetration, free-surface effect, finite cavity expansion, numerical simulation