Mechanism of Impact Damage and CAI Strength Reduction of Fiber Reinforced Composite Laminate

A research work is conducted to understand CAI(Compression After Impact)problem and to give a theoretical base for estimating the significance of the foreign object impact on the compressive performance of composite laminated structures。The problem consists of two parts：·Impact damage initiation and development·Compressive behavior of the damaged plateBoth portions are too complex to simply explain the theoretical idealized solution.So the numerical analysis and model experiments are conducted for both parts to identify the effects of the various parameters such as impact energy，stacking sequence etc on the compressive performance。In order to simulate the damage accumulation process in the interface region，a fracture element is proposed and the simulated results well coincides with the existing theory and many new findings are shown using the damage element，such as unstable delamination propagation at the early stage of the damage accumulation，propagation of all embedded delaminations instead of a few delaminations etc。In the compression problem，three dimensional finite element analysis is conducted to investigate the buckling performance and the postbuckling behavior including the calculation of the fracture mechanical parameter(energy release rates GⅠD2，GⅡD2，GⅡD2)along the embedded delaminations.The complex compressive behavior of the delaminated laminate with many delaminations is well simulated，where the contact problem must be considered。The solution well explains the very complex experimental results including damage propagation before the final fracture.Particularly，the first delamination propagation occurred at the delamination expected from the present analysis.

A research work is conducted to understand CAI (Compression After Impact) problem and to give a theoretical base for estimating the significance of the foreign object impact on the compressive performance of composite laminated structures. The problem consists of two parts:・ Impact damage initiation and development・ Compressive behavior of the damaged plateBoth portions are too complex to simply explain the theoretical idealized solution. So the numerical analysis and model experiments are conducted for both parts to identify the effects of the various parameters such as impact energy, stacking sequence etc on the compressive performance. In order to simulate the damage accumulation process in the interface region, a fracture element is proposed and the simulated results well coincides with the existing theory and many new findings are shown using the damage element, such as unstable delamination propagation at the early stage of the damage accumulation, propagation of all embedded delaminations instead of a few delaminations etc. The theory can be incorporated in the analysis of the compressive behavior of the damaged plate. In the compression problem, three dimensional finite element analysis is conducted to investigate the buckling performance and the postbuckling behavior including the calculation of the fracture mechanical parameter (energy release rates GィイD2IィエD2, GィイD2IIィエD2, GィイD2IIIィエD2) along the embedded delaminations. The complex compressive behavior of the delaminated laminate with many delaminations is well simulated, where the contact problem must be considered. The solution well explains the very complex experimental results including damage propagation before the final fracture. Particularly, the first delamination propagation occurred at the delamination expected from the present analysis.