Modified K&C model for cratering and scabbing of concrete slabs under projectile impact

- Four modifications are made to the K&C model for the parameters of the strength surfaces, the dynamic increase factor for tension, the relationship between yield scale factor and damage function, and the tensile damage accumulation.
- Improved performances of the modified K&C model are demonstrated by single element tests including the unconfined uniaxial compression, triaxial compression, dynamic uniaxial tension as well as the biaxial and triaxial tensions.
- New tensile failure erosion criterion for FE-simulations are proposed.
- The modified K&C model can well predict cratering and scabbing phenomena of concrete slabs subjected to projectile impact.

The K&C material model, which was originally developed for the structural response subjected to blast loadings, is modified to improve its numerical prediction capability for cratering and scabbing phenomena in concrete slabs subjected to projectile impact. Four modifications are made for the parameters of the strength surfaces, the dynamic increase factor for tension, the relationship between yield scale factor and damage function, and the tensile damage accumulation. Single element tests of the unconfined uniaxial compression, triaxial compression, dynamic uniaxial tension as well as the biaxial and triaxial tensions are used to demonstrate the improved performances of the modified K&C model. The modified concrete strength model is implemented into the finite element code LS-DYNA through user-defined material model. The improved predictions for cratering and scabbing phenomena under projectile impact using the modified K&C model are demonstrated by comparisons with the perforation tests and the corresponding simulation results from the original K&C model. Furthermore, sensitivity analyses of five parameters that control the dynamic tensile behaviour of the modified K&C model are carried out to understand the influence of each individual parameter on the cratering and scabbing phenomena.