Multiple delaminations and their severity in nonlinear circular plates subjected to concentrated loading

Instability problem of multiple penny-shape interlaminar delaminations in circular nonlinear axisymmetric plates subjected to a transverse loading is theoretically studied. It is an idealized problem of damage accumulation in composite laminates due to low velocity impact loading. All the delaminations having a same size are located at a same interval. Nonlinear behaviors of the plates are approximately solved through Rayleigh-Ritz method considering only two mode functions, that is, global and local mode functions which are based upon a linear exact solution. Energy release rate due to a simultaneous propagation of all the delaminations is obtained approximately and the results are compared with those obtained via a finite element analysis. The present solutions agree excellently with the finite element results except when the nonlinear effect is extremely large. The energy release rate significantly decreases with the propagation of the delaminations due to the nonlinear effects, particularly when the number of the delaminations Is large. The load must be increased to keep the delaminations to propagate. The conclusions from the results obtained based on the linear assumption that the more delaminations exist, the easier delaminations propagate, may not be true when the nonlinear effect is considered.