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The fatigue degradation properties of atomic-layer-deposited alumina, with thickness ranging from 4.2 to 50 nm, were investigated using a silicon micro-resonator on which the coatings were deposited and strained in a static or cyclic manner, with strain amplitudes up to 2.2%, in controlled environments. Based on the measured resonant frequency evolution, post-test scanning electron microscopy observations, and finite element models, it is shown that cracks in the alumina nucleate and propagate under cyclic loading, and that the crack growth rates scale with the strain energy release rates for crack channeling. The implications for the reliability of flexible electronics are discussed.

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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

A microresonator-based interfacial fatigue testing technique was used to investigate the subcritical delamination of atomic-layer-deposited alumina coatings along the sidewalls of deep-reactive-ion-etched monocrystalline silicon thin films. This technique ensures loading conditions relevant to microelectromechanical system devices, including kHz testing frequency and fully reversed cyclic stresses. Four different coating thicknesses (4.2, 12.6, 25, and 50 nm) were investigated in two environments (30 °C, 50% relative humidity (RH) and 80 °C, 90% RH). Fatigue damage, in the form of channel cracks and delamination of the alumina coating, was found to accumulate slowly over more than 1 × 10(8) cycles. The average delamination rates increase with increasing energy release rate amplitude for delamination, modeled with a power law relationship. In the harsher environment, the rates are roughly 1 order of magnitude higher. Additionally, a few tests under static load were conducted for which no delamination (or crack growth) occurred, demonstrating that the governing interfacial fatigue mechanism is cycle-dependent.