FATIGUE CRACK GROWTH BEHAVIOUR OF FIBRE-METAL LAMINATE GLARE-1 AND METAL LAMINATE 7475 WITH DIFFERENT BLUNT NOTCHES

Abstract— The fatigue crack growth behaviour of the fibre metal laminate "GLARE-1" has been investigated for different blunt notches in Constant Amplitude (CA) tests. In order to investigate the influence of the fibres, the same laminate material but containing no fibres (Laminate 7475) was also tested. The fatigue crack growth properties of GLARE-1 are superior to those of Laminate 7475. GLARE-1 shows lower crack growth velocities at the same K_nom values and in addition the crack growth rates decrease with increasing crack length. The Laminate 7475 shows typical metal behaviour for single crack propagation and accelerating crack growth with increasing crack length. In GLARE-1, multiple crack propagation takes place. The cracks propagate independent of each other and have similar crack growth rates, in part due to closure effects caused by the unbroken fibre layers.
The crack growth rates of specimens having a small root radius are higher in both materials than in specimens with a large notch radius. In GLARE-1, the superiority of a larger notch radius is more pronounced than in the Laminate 7475 and is attributed to a stronger crack closure effect owing to fibre bridging. The reason for the higher bridging capability in specimens containing larger notches is that less fibres are broken or damaged in the notch vicinity.