Review of morphing concepts and materials for wind turbine blade applications

With increasing size of wind turbines, new approaches to load control are required to reduce the stresses in blades. Experimental and numerical studies in the fields of helicopter and wind turbine blade research have shown the potential of shape morphing in reducing blade loads. However, because of the large size of modern wind turbine blades, more similarities can be found with wing morphing research than with helicopter blades. Morphing technologies are currently receiving significant interest from the wind turbine community because of their potential high aerodynamic efficiency, simple construction and low weight. However, for actuator forces to be kept low, a compliant structure is needed. This is in apparent contradiction to the requirement for the blade to be load carrying and stiff. This highlights the key challenge for morphing structures in replacing the stiff and strong design of current blades with more compliant structures. Although not comprehensive, this review gives a concise list of the most relevant concepts for morphing structures and materials that achieve compliant shape adaptation for wind turbine blades.Copyright © 2012 John Wiley & Sons, Ltd.     

The bone diagnostic instrument II: indentation distance increase

The bone diagnostic instrument (BDI) is being developed with the long-term goal of providing a way for researchers and clinicians to measure bone material properties of human bone in vivo. Such measurements could contribute to the overall assessment of bone fragility in the future. Here, we describe an improved BDI, the Osteoprobe IItrade mark. In the Osteoprobe IItrade mark, the probe assembly, which is designed to penetrate soft tissue, consists of a reference probe (a 22 gauge hypodermic needle) and a test probe (a small diameter, sharpened rod) which slides through the inside of the reference probe. The probe assembly is inserted through the skin to rest on the bone. The distance that the test probe is indented into the bone can be measured relative to the position of the reference probe. At this stage of development, the indentation distance increase (IDI) with repeated cycling to a fixed force appears to best distinguish bone that is more easily fractured from bone that is less easily fractured. Specifically, in three model systems, in which previous mechanical testing and/or tests reported here found degraded mechanical properties such as toughness and postyield strain, the BDI found increased IDI. However, it must be emphasized that, at this time, neither the IDI nor any other mechanical measurement by any technique has been shown clinically to correlate with fracture risk. Further, we do not yet understand the mechanism responsible for determining IDI beyond noting that it is a measure of the continuing damage that results from repeated loading. As such, it is more a measure of plasticity than elasticity in the bone.     

Dynamics of gas-phase trichloramine (NCl3) in chlorinated, indoor swimming pool facilities

Trichloramine (NCl(3)) is recognized as an irritant of the human respiratory system and other tissues. Processes that lead to volatilization from the liquid phase allow for human exposure to gas-phase NCl(3) in swimming pool settings. The dynamics of these processes are not well defined. A N,N-diethyl-p-phenylenediamine/potassium iodide (DPD/KI)-based wet-chemistry method for measuring gas-phase NCl(3) concentration was verified and applied in chlorinated, indoor swimming pool facilities. Other gas-phase oxidants in the air of indoor pools provided interference of 15% or less. The DPD/KI method was applied for the measurement of gas-phase NCl(3) in four chlorinated, indoor swimming pool facilities. All results showed a correlation between bather loading and gas-phase NCl(3) concentration. The nature of swimmer activities also influenced air quality, presumably because of the effects of these activities on mixing near the gas-liquid interface. PRACTICAL IMPLICATIONS: The activities of swimmers promote transfer of volatile compounds from water to the surrounding air. For chlorinated, indoor pool facilities, this can lead to exposure to gas-phase chemicals that can cause irritation of the respiratory system and other tissues. The focus of this study was on NCl(3), a common disinfection by-product (DBP) in chlorinated pools. However, the conditions that promote NCl(3) transfer are likely to promote transfer of other volatile chemicals from water to air. As such, it is possible that other DBPs formed in pools may also contribute to diminished air quality.     

Interfacial bonding and optical transmission for transparent fiberglass/poly(methyl methacrylate) composites

Evidence is presented relating the interfacial bonding strength and the optical transmission of transparent glass fiber reinforced PMMA composites. The temperature dependent (20° to 50°C) optical transmission of composites that contained uncoated 13 μm glass fibers and 13 μm glass fibers coated with divinyltetramethyl disilazane or 3-(trimethoxysilyl)propyl methacrylate was found to decrease in the same order as the bond strength of the PMMA/glass fiber interface, namely, trimethoxy silane coated fiber, disilazane coated fiber, and uncoated fiber. SEM photographs showed similar fracture surfaces, clean fiber pull-out, and no apparent bonding of the glass fiber to the PMMA for the composites containing uncoated and disilazane coated fiber, whereas, the composite containing trimethoxy silane coated fiber showed virtually no clean fiber pullout. Additional evidence for differences in the bonding strength is seen in the degradation (penetration of water and fiber whitening) on aging at 23°C in air or water for composites containing uncoated fiber (most degradation), disilazane coated fiber (slight degradation), and trimethoxy silane coated fiber (no degradation). The optical transmission between 20° and 30°C at 600 to 800 nm for the composite containing trimethoxy silane coated fiber decreased the least with increasing temperature (from ∼85% to 70%) while the composite containing uncoated fiber decreased the most (from ∼85% to 32%).     

Preparation and properties of optically transparent,pressure-cured poly(methacrylate) composites

The objective of this work was to develop optically transparent glass fiber reinforced poly(methyl methacrylate) (PMMA) composites by matching the refractive index of the glass fiber reinforcement to that of the PMM, A matrix, thereby minimizing the quantity of light which is normally scattered and reflected at the interface of dissimilar materials. A pressure curing process is described for preparing composites 10 by 15 by 0.6 cm thick and containing up to ∼ 35% glass fiber. By curing at 65°C under 6.9 MPa N₂ for 18 H, composites have been produced with optical quality surfaces and flexural strengths more than seven times that of commercial PMMA of the same thickness. A transparent composite containing 10.4 vol% of 13 μm diameter fiber had an 84% optical transmission (92% maximum for PMMA) at 600 nm and 25°C.