Modeling compression failure after low velocity impact on laminated composites using interface elements

Low velocity impact damage can significantly reduce the residual strength of laminated composites. This kind of damage (mostly delaminations) is very dangerous for the structures because it is not apparent to the naked eve and, in some case, it can reduce the compressive residual strength up to 60%. In this work, a numerical model For predicting the compression failure of laminated composites containing delamination caused by low velocity impact was developed. An interface finite element, previously developed by the authors, was used. This element is compatible with twenty-seven node isoparametric hexahedral elements and enables modeling the behavior of the damaged interface, taking into account a three-dimensional stress state, the interpenetration constraint and the propagation of delamination. In order to verify the numerical model, some experimental work was done. The experimental work, performed on carbon-epoxy (0(4), 90(4))(s) and (90(4), 0(4))(s) laminates, included low velocity impact tests using a drop weight testing machine, followed by X-Ray damage characterization and compression tests using a fixture system similar to IITRI system. The numerical and experimental results were compared and good agreement was obtained.