An energy based damage model for thin laminated composites

The present paper outlines an unconventional energy based composite damage model capable of modelling woven and unidirectional composite materials. The damage model has been implemented into the LLNL-DYNA3D and LS-DYNA3D finite element codes for shell elements (plane stress), relevant to tensile, compressive and shear damage failure modes. The damage model uses five damage variables assigned to tensile, compressive and shear damage at a laminae level. The evolution of damage in each mode is controlled via a series of damage-strain equations, thus allowing the total energy dissipated for each damage mode to be controlled during a dynamic or impact event.The materials under investigation were a uni-directional (UD) carbon-epoxy and a woven carbon epoxy composite. Recent experimental test results from the CEC HICAS project have also been used to verify the behaviour of the model at elevated strain rates. Experimental data for the 0° and 90° tensile response indicates effectively rate independent, while matrix dominated modes, such as the shear response is highly rate dependent.The 0° and 90° tensile response and the tensile shear response have been modelled at a coupon level, including relevant strain rate effects, with the proposed damage model. Results show very good agreement with the available coupon experimental data. Suggestions are also presented for additional non-standard experimental tests to derive the material model parameters.A follow on paper describes the results of a series of simulations using the proposed material model on a number of experimental plate impact tests performed on the CEC HICAS project.