Testing of novel joining concepts for improved load application into oscillation-loaded fibre-reinforced plastic structures

Abstract

In the framework of the project KraSchwing, two innovative joining technologies have been developed for the reduction of local stresses with the primary aim of increasing fatigue strength. Firstly, through integration of elastomer layers into laminates the high residual stresses at the end of the overlap length of bond lines are reduced. The second joining method study aims at reducing the bearing forces around bolt holes through the application of rosettes, produced by using wet-winded, pre-impregnated loops, as new options for adapting connection points with bolts. The joining technologies are investigated concerning their quasi-static and fatigue strength. Here, the focus is the methodical and experimental approach testing the joining concepts. A local elastomer integration in the CFRP-laminate shows in the quasi-static loading test no significant increase or decrease of the shear strength. But in the fatigue test, the cycles to fracture can be increase by a factor of 2. Furthermore the application of rosettes, to reduce the bearing force around a bolt hole, show in the quasi-static test an increase of the maximum force by 77%. Compared to the bearing failure of the reference, the reinforced specimens show a delamination of the rosettes. Beyond the characterization of the mechanical behavior, fundamentals for an industrial manufacturing process are illustrated briefly.