THE EFFECTS OF THE FIBRE BRIDGING ON THE ENTIRE STRAIN FIELD OF FATIGUE CRACKS IN FIBRE METAL LAMINATES R.Rodi 1,2 , G.S.Wilson 3,2 , R.C.Alderliesten 2 , R.Benedictus 2 1 Materials Innovation Institute -M2i-, Mekelweg 2, 2628CD Delft, Netherlands 2 Delft University of Technology, Kluyverweg 1, 2629 HS Delft, Netherlands 3 Alcoa Technical Center, 100 Technical Dr., Alcoa Center PA, 15069, USA [email protected] , [email protected] , [email protected] , [email protected] SUMMARY This paper presents both experimental and analytical investigations on the effects of bridging fibres on the entire strain field of fatigue cracks in Fibre Metal Laminates. Digital image correlation provided visualization of both the entire strain fields and delamination shape, which have been compared with those analytically calculated. Keywords: Fibre metal laminates, bridging fibres, digital image correlation, fatigue crack growth INTRODUCTION Fibre Metal Laminates (FMLs) have been developed in the past to improve the fatigue performances of laminated aluminium structures by adding fibres in the bond line. FMLs exhibit failure mechanisms of both metals and composites. The metallic layers show fatigue crack growth similar to monolithic metals, crack initiation and propagation, while the composite layers, which are insensitive to the fatigue loading, show delamination at the metal–composite interfaces. The fibres transfer load over the fatigue crack in the metal layers and restrain the crack opening. This phenomenon is called fibre bridging. These complex mechanisms of crack growth in the metal layers and delamination growth at the interface between metal and fibre layers, if in optimal balance, result in the excellent fatigue characteristics for which FMLs are known. The fatigue crack growth behaviour of FMLs has been investigated extensively during the last two decades for constant and variable amplitude loading sequences [1-4]. In the last decade several analytical prediction methods have been developed to describe the crack growth behaviour in FMLs under constant amplitude loading [5-10]. The bridging fibres, acting as a second load path in the wake of the crack, carry part of the load, reducing the stress intensity at the metal crack tip; consequently, the full field deformation of the metal layers, including the plastic zone ahead the crack tip, reduces. This paper presents both experimental and analytical investigations on the effect of bridging fibres on the deformation field in FMLs. Digital image correlation (DIC) was employed to measure the deformation field of the external metal layer of different FMLs, considering both saw-cut and fatigue crack configurations. The experimental
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