Berechnung dynamischer Delaminationsvorgaenge in Faserverbundplatten

In this thesis, a finite element model originally formulated for static delamination analyses of fibre-reinforced composite plates is extended to include inertial effects. The applicability of the model to three typical problem classes in dynamic fracture mechanics is investigated, namely cases with stationary cracks and dynamic loading, cases with known or prescribed crack histories, and cases with unknown crack histories. Simple strategies for the simulation of the three problem classes are implemented. In the stationary-mesh approach employed, crack propagation is modelled by releasing the element nodes successively. The use of the modified crack closure technique for stationary cracks and nodal release forces for propagating cracks allows dynamic energy release rates to be computed along the crack front. In the case of unknown crack histories, a secant procedure is used for the element-wise, iteractive calculations of the crack speed. Rayleigh damping is included, and the time integration is carried out using the Newmark method with constant average acceleration, which did not cause stability problems even in the geometrically nonlinear analyses. In the examples studied, it is found that the contact between the sub- and baselaminate can in some circumstances have a very strong influence. The system response can also react quite sensitively to the applied damping ratio. For the case of a buckling specimen with a through-width delamination, the hypothesis that similar initial buckling shapes of the sublaminate lead to initially similar crack histories is confirmed. A significant variation of the dynamic energy release rate along the delamination front is not found in any of the cases investigated, and hence a strong curvature of the front in the crack propagation phase would not be expected. For DCB-specimens with a constant displacement loading rate, this has in fact been confirmed experimentally. The extended model allows a good description of the dynamic influences as long as the deformation of the structure can be represented realistically by the simplified plate kinematics on which the model is based. However, even when the respective conditions are not satisfied, sufficiently accurate simulations of the physical processes may be able to be achieved at least for parts of an analysis. (orig.)SIGLEAvailable from TIB Hannover: RR 7887(1999,30) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman