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 l oading 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 inter val. Nonlinear behaviors of the plates are approximately solved throug h Rayleigh-Ritz method considering only two mode functions, that is, g lobal and local mode functions which are based upon a linear exact sol ution. Energy release rate due to a simultaneous propagation of all th e delaminations is obtained approximately and the results are compared with those obtained via a finite element analysis. The present soluti ons agree excellently with the finite element results except when the nonlinear effect is extremely large. The energy release rate significa ntly decreases with the propagation of the delaminations due to the no nlinear effects, particularly when the number of the delaminations Is large. The load must be increased to keep the delaminations to propaga te. The conclusions from the results obtained based on the linear assu mption that the more delaminations exist, the easier delaminations pro pagate, may not be true when the nonlinear effect is considered.