The integration of shear-thickening fluids (STFs) into composite structures has been investigated with the aim of tuning part stiffness and damping capacity under dynamic deformation. Results from oscillatory rheological measurements for a STF based on concentrated fused silica in polypropylene glycol were correlated with results from vibrating beam tests on model sandwich structures containing layers of the same STF sandwiched between polyvinyl chloride (PVC) beams. Above a critical amplitude, the relative motion of the PVC beams provoked shear thickening of the silica suspensions, and the vibration and damping properties were significantly modified. These changes were related to the rheological response of the STF through analytical calculations of strains in the STF layers, an approach that was verified experimentally by replacing the STF with a slow-curing epoxy resin. The potential for integrating STFs into structures exposed to dynamic flexural deformation, with the aim of controlling their vibrational response, has thus been demonstrated.
Pulsed laser deposition (PLD) and magnetron sputter deposition (MSD) have been used to prepare different types of Mo/Si multilayers for the extreme ultraviolet (EUV) spectral range. In the case of PLD prepared Mo/Si multilayers the deposition of 0.3-0.5 nm thick carbon barrier layers at the interfaces leads to a substantial improvement of the interface quality. This can be deduced from Cu-Kα reflectivity measurements and HRTEM observations. Consequently the EUV reflectivity has been substantially increased. For pure Mo/Si-multilayers prepared by MSD the deposition parameters have been optimized so that a normal incidence reflectivity of R EUV = 68.7% could be realized. Although this is one of the best experimental results achieved so far, there is still a gap between this experimental value and the theoretical limit (R EUV = 75.5%). One of the main reasons for this discrepancy is the formation of intermixing zones at the interfaces. With B 4 C and C barrier layers at the interfaces interdiffusion can be reduced. The resulting EUV reflectivity of this new type of EUV multilayers is 69.8% (λ = 13.42 nm, α = 1.5 •) and 71.4% (λ = 12.52 nm, α = 22.5 •).
Earlier investigations of steady two-dimensional marginally separated laminar boundary layers have shown that the non-dimensional wall shear (or equivalently the negative non-dimensional perturbation displacement thickness) is governed by a nonlinear integro-differential equation. This equation contains a single controlling parameter $\Gamma$ characterizing, for example, the angle of attack of a slender airfoil and has the important property that (real) solutions exist up to a critical value $\Gamma_c$ of $\Gamma$ only. Here we investigate three-dimensional unsteady perturbations of an incompressible steady two-dimensional marginally separated laminar boundary layer with special emphasis on the flow behaviour near $\Gamma_c$. Specifically, it is shown that the integro–differential equation which governs these disturbances if $\Gamma_c\,{-}\,\Gamma\,{=}\,O(1)$ reduces to a nonlinear partial differential equation – known as the Fisher equation – as $\Gamma$ approaches the critical value $\Gamma_c$. This in turn leads to a significant simplification of the problem allowing, among other things, a systematic study of devices used in boundary-layer control and an analytical investigation of the conditions leading to the formation of finite-time singularities which have been observed in earlier numerical studies of unsteady two-dimensional and three-dimensional flows in the vicinity of a line of symmetry. Also, it is found that it is possible to construct exact solutions which describe waves of constant form travelling in the spanwise direction. These waves may contain singularities which can be interpreted as vortex sheets. The existence of these solutions strongly suggests that solutions of the Fisher equation which lead to finite-time blow-up may be extended beyond the blow-up time, thereby generating moving singularities which can be interpreted as vortical structures qualitatively similar to those emerging in direct numerical simulations of near critical (i.e. transitional) laminar separation bubbles. This is supported by asymptotic analysis.
Abstract-This paper presents a concept for the wafer-scale manufacturing of microactuators based on the adhesive bonding of bulk shape memory alloy (SMA) sheets to silicon microstructures. Wafer-scale integration of a cold-state deformation mechanism is provided by the deposition of stressed films onto the SMA sheet. A concept for heating of the SMA by Joule heating through a resistive heater layer is presented. Critical fabrication issues were investigated, including the cold-state deformation, the bonding scheme and related stresses and the TitaniumNickel (TiNi) sheet patterning. Novel methods for the transfer stamping of adhesive and for the handling of the thin TiNi sheets were developed, based on the use of standard dicing blue tape. First demonstrator TiNi cantilevers, wafer-level adhesively bonded on a microstructured silicon substrate, were successfully fabricated and evaluated. Intrinsically stressed silicon dioxide and silicon nitride were deposited using plasma enhanced chemical vapor deposition to deform the cantilevers in the cold state. Tip deflections for 2.5 mm long cantilevers in cold/hot-state of 250/70 µm and 125/28 µm were obtained using silicon dioxide and silicon nitride, respectively. The bond strength proved to be stronger than the force created by the 2.5 mm long TiNi cantilever and showed no degradation after more than 700 temperature cycles. The shape memory behavior of the TiNi is maintained during the integration process.Index Terms-Adhesive bonding, blue tape, contact printing, microactuator, microelectromechanical systems (MEMS), nitinol, shape memory alloy (SMA), stress layers, titanium-nickel (TiNi), integration, transfer stamping, wafer-scale integration, wet etching.
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