Low velocity impact on CFRP plates with compressive preload: Test and modelling

When laminated composite materials in modern aircraft structures are subject to impact loads, they are typically not unloaded but under a certain state of prestress. Therefore, in this study the effect of a compressive preload on the low velocity impact behaviour of three different carbon fibre-reinforced plastic (CFRP) materials is investigated. An experimental test programme is documented first, including the design of a preload test device, the specimen manufacture and the results description. An increased deflection and energy absorption for composite plates with a preload of 80% of the buckling load could be observed. Non-destructive inspections showed a large extent of delaminations occurring between individual plies, being an important energy absorption mechanism. The development of numerical simulation methods for this impact scenario using the commercial explicit finite element code LS-DYNA is described in detail. The focus is on the composite material, delamination and preload modelling. The final simulation results showed a good correlation to the experimental data in terms of force and energy plots or the evaluated interlaminar and intralaminar damage, although these numerical results proved to be strongly influenced by simulation parameters like mesh size or the number of shell element layers.