LeVaDi

Fatigue analysis for bonded joints in large-scale FRP structures with varying adhesive layer thicknesses

The fatigue behavior of large bonded fiber reinforced plastic composite (FRP) structures, such as those used in wind turbines and ships, is largely determined by the cracking behavior in the bonded layer. However, it is particularly in these industries that large manufacturing tolerances meet high requirements in terms of reliability under service load. Production-related imperfections, such as adhesive layer thickness variations and undefined edge geometries, have a significant influence on crack initiation and propagation, which has not yet been taken into account in the design. The aim of the project was therefore to analyze and mathematically describe the influence of various production-related geometric imperfections of the adhesive layer on the service life of large FRP structures.

For this purpose, the adhesive layer thickness variations and edge geometries found in practice were first examined and classified, from which test and simulation plans were derived. The dominant failure modes – normal and peel stress-induced failure – were reproduced in real and virtual tests on different scales (substructure, coupon and submodel). The efficient combination of real tests with numerical, parametric submodel simulations allowed a large parameter space typical of large structures to be investigated for the first time. Based on the results, reliable findings on the influence of imperfections could be developed and made available to the industry. In addition, practical testing methods and design guidelines were derived.