Fatigue damage development in new fibre metal laminates made by the VARTM process

Abstract

A B S T R A C T This paper investigates the tensile and fatigue properties of a newly developed fibre metal laminate (FML) manufactured using the vacuum assisted resin transfer moulding (VARTM) method. This manufacturing method allows the glass fibre reinforced epoxy and 2024-T3 aluminium FML to be prepared at lower cost than conventionally manufactured FMLs. However, in order for the resin to infiltrate the FML, the metal sheets need to be perforated. These perforation holes act as crack initiators and reduce the FML's performance. Tension and fatigue test results of three different designs are reported and compared to mechanical property predictions. Additionally, single sheet Al alloy specimens were tested in order to analyse the influence of the drilling method.Keywords fatigue; fibre metal laminate (FML); hybrid composite; tensile behaviour; vacuum assisted resin transfer moulding (VARTM). N O M E N C L A T U R E ARALL= aramid reinforced aluminium laminate CLT = classical lamination theory exp. = experiment E = Young's modulus/elastic modulus E Al = Young's modulus of the aluminium alloy E c = Young's modulus of the composite FML = fibre metal laminate GLARE = glass reinforced fibre metal laminate h = height R = stress ratio = min. stress/max. stress ROM = rule of mixtures VARTM = vacuum assisted resin transfer moulding α Al = thermal expansion coefficient of the aluminium alloy α C = thermal expansion coefficient of the composite ε = strain ε Al = strain of the aluminium alloy ε c = strain of the composite ε f = maximum strain/strain at failure ε total = overall specimen strain ν = Poisson's ratio σ = stress σ Al = stress in the aluminium alloy layer of the specimen

Investigation of fatigue crack growth rate in CARALL, ARALL and GLARE

“…GLARE shows UTS of 167 MPa with maximum elongation of 2.55%, and CARALL shows UTS of 215 MPa with maximum elongation of 1.35%. Elastic modulus of ARALL, GLARE and CARALL are 68, 58 and 85 GPa, respectively, which are in good correlation when compared with already published data . CARALL shows superior tensile behaviour because of high strength layer of carbon fibre.…”

“…Fatigue crack growth rate of FMLs is characterized by the growth of two damage systems (crack growth in metal layer and delamination growth between metal layer and composite core) which are inter related to each other during fatigue loading . Fatigue crack initiates in metal layers earlier than they initiate in reinforcing fibre layers . Remote applied loads are responsible for fatigue crack initiation and propagation in metal layers of laminate .…”

“…24 Fatigue crack initiates in metal layers earlier than they initiate in reinforcing fibre layers. 25 Remote applied loads are responsible for fatigue crack initiation and propagation in metal layers of laminate. 22 Stress cycles in metal layers of FML can be used to determine the fatigue crack initiation of whole laminate.…”

On the notch sensitivity of flax fibre metal laminates under static and fatigue loading

“…[26][27][28] The transference of fatigue loads across the cracks in aluminium, subsequently leading to delamination at the crack edges, reduces the stress intensity at the crack tip, thus constraining further crack growth. However, during the crack propagation phase, a significant proportion of the applied fatigue load is transferred across the cracks formed within the aluminium layer via the intact glass fibres.…”

“…The transference of fatigue loads between the aluminium layer and the glass/epoxy laminate induces cyclic shear stresses, which cause delamination at the aluminium/adhesive interface. [26][27][28] The transference of fatigue loads across the cracks in aluminium, subsequently leading to delamination at the crack edges, reduces the stress intensity at the crack tip, thus constraining further crack growth. This crack-bridging ability of glass fibres considerably reduces the crack propagation rate, hence the enhanced fatigue performance of the notched glass-FMLs.…”