Impact Analysis of Sandwich Composites

A finite element simulation of impacts on sandwich composites with laminated faces is presented; it is based on a refined multilayered plate model with a high-order zig-zag representation of displacements, which is incorporated through a strain energy updating process. This allows the implementation into existing commercial finite elements codes, preserving their program structure. As customary, the Hertzian law and the Newmark implicit time integration scheme are used for solving the contact problem. The contact radius and the force are computed within each time step by an iterative algorithm which forces the impacted top surface to conform, in the least-squares sense, to the shape of the impactor. Nonlinear strains of von Karman type are used. As appearing by the comparison with experimental results, the present model is able to accurately predict the impact force, the core damage and the damage of face sheets in sandwich composites with foam and or honeycomb core. Moreover, this paper also assesses the accuracy and the range of application of stress based criteria in predicting the onset and evolution of delamination in service. These criteria are widespread by virtue of their low run time and storage costs, although no exhaustive proofs are known weather they are accurate enough for a reasonably wide range of applications. Since where highly iterative solutions are involved (e.g., impact and geometric, or material nonlinear problems) they are the only currently affordable failure models, it appears of primary importance to fill this gap. Aimed to contribute to the knowledge advancement in this field, a comparison is presented with more sophisticate fracture mechanics and progressive delamination models.