ABSTRACT of the Doctoral Thesis
The aim of the present work is to develop modelling strategies by means of advanced methods within the framework of the Finite Element Method (FEM), which are capable of predicting the impact behaviour of fabric reinforced laminated composites. Not only the total energy absorption of the laminate, but also the share of energy absorbed by individual mechanisms is predicted, where fibre rupture, matrix cracking, delamination and the accumulation of inelastic strains are considered. Within the present work, mainly high energy impact scenarios with intermediate impact velocities are considered. Hence, a dynamic impact response and penetration of the laminate are expected. Modelling strategies at different geometrical length scales are developed which on the one hand, aim at gaining a detailed insight into the impact behaviour of fabric reinforced laminates and on the other hand, aim at simulating the impact behaviour of entire composite components.
A shell element based modelling strategy, which resolves the fabric topology at the level of individual tows (i.e. impregnated bundles of fibres) is developed. It proves to be efficient enough to conduct simulations of the highly dynamic, nonlinear behaviour of fabric reinforced composite coupon specimens under impact loading within reasonable computational resources. The modelling approach is verified based on experimental drop weight impact tests of carbon/epoxy laminates carried out by cooperation partners. Very good agreement between the simulation results and the experimental data is found. Furthermore, the predictions give detailed insight into the impact behaviour of fabric reinforced composites.
Also, a ply-level based strategy for modelling and simulating the impact behaviour of fabric reinforced laminates up to complete perforation is developed. Special attention is directed towards numerical efficiency in order to open up the possibility for simulating impact on structural components much larger than coupon specimens within reasonable computation time. The modelling approach is verified based on experimental drop weight impact tests of carbon/epoxy laminates carried out by cooperation partners. The predicted damage and failure behaviour is in very close agreement with the experimental observations. Furthermore, the approach is found to be of exceptional numerical efficiency. A detailed comparison of the predicted energy absorption behaviour between the ply-level and the tow-level modelling approach is conducted in order to evaluate the effect of different modelling length scales.
Finally, a modelling approach for simulating the impact behaviour of large laminated composite components impacted by large deformable bodies within reasonable computation time and resources is presented. Another focus is set on the simulation of high energy impact on glass fabric reinforced epoxy laminates up to complete perforation. Thereby, the developed ply-level modelling approach is used in combination with an embedding approach. In a first step, the applicability of the ply-level approach to the simulation of high energy impact on glass/epoxy laminates is verified based on a comparison with experimental drop weight impact tests carried out by cooperation partners. Then, to demonstrate an application, two configurations of a generic composite fan containment casing of a jet engine subjected to fan blade out are investigated, where detailed insight into the components' behaviour during the fan blade out event is gained.