XFEM ANALYSIS – INCLUDING BUCKLING – OF COMPOSITE SHELLS CONTAINING DELAMINATION

Based on a first-order shear-deformation theory a four-noded shell element is formulated for composite laminates with and without a delamination.Interlaminar stresses are calculated to evaluate a delamination criterion.The presentation will show how and how accurate.Once the danger of delamination is detected the displacement field is enriched in the sense of the eXtended FEM to account for a discontinuity at an arbitrary position.The remaining strength after starting delamination is simulated by a mixed-mode cohesive zone model based on energy release.Contact when reclosing a discontinuity is included.Large rotations are covered by Green's strain.The developed formulation is tested for shell problems by comparing its results with available benchmark tests for in-and out-of-plane load cases.The feasibility and practicality of the presented model and its advantage over the approach using two shell elements at the predefined plane of the discontinuity, connected by a third one, a cohesive zone element, is demonstrated.Then, linear and non-linear buckling analyses for composite laminates containing a delamination are performed.It is shown how imperfections of the delamination type, i.e. concerning the discontinuity, used for nonlinear analysis are based on the modes from linear buckling.The full process from starting with one layer of elements over detecting a delamination to simulating its growth and its interaction with buckling is outlined.