Mechanical properties of Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6) metallic glass matrix particulate composites

To increase the toughness of a metallic glass with the nominal composition Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6), it was used as the matrix in particulate composites reinforced with W, WC, Ta, and SiC. The composites were tested in compression and tension experiments. Compressive strain to failure increased by more than 300% compared with the unreinforced Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6), and energy to break of the tensile samples increased by more than 50%. The increase in toughness came from the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area. There was direct evidence of viscous flow of the metallic glass matrix within the confines of the shear bands

Deformation and crystallization of Zr-based amorphous alloys in homogeneous flow regime

The purpose of this study is to experimentally investigate the interaction of inelastic deformation and microstructural changes of two Zr-based bulk metallic glasses (BMGs): Zr_(41.25)Ti_(13.75)Cu_(12.5)Ni_(10)Be_(22.5) (commercially designated as Vitreloy 1 or Vit1) and Zr_(46.75)Ti_(8.25)Cu_(7.5)Ni_(10)Be_(27.5) (Vitreloy 4, Vit4). High-temperature uniaxial compression tests were performed on the two Zr alloys at various strain rates, followed by structural characterization using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Two distinct modes of mechanically induced atomic disordering in the two alloys were observed, with Vit1 featuring clear phase separation and crystallization after deformation as observed with TEM, while Vit4 showing only structural relaxation with no crystallization. The influence of the structural changes on the mechanical behaviors of the two materials was further investigated by jump-in-strain-rate tests, and flow softening was observed in Vit4. A free volume theory was applied to explain the deformation behaviors, and the activation volumes were calculated for both alloys

Dielectric-Recovery Characteristic of Power Arcs in Large Air Gaps

A satisfactory test technique has been developed for studying the rates of dielectric recovery of large air gaps and other types of power-system insulation. This permits the accurate control of the fault conditions so that all practical types of fault currents can be studied. These are: (1) very high magnitude short-duration surges typical of lightning currents; (2) currents of power-system frequencies; and (3) intermediate duration currents such as those which might result from high-frequency current zeros produced by natural system oscillations. Results are presented showing the rate of dielectric recovery of 3-, 6-, and 11-inch standard rod gaps for power frequency fault currents up to 700 amperes. Electrode cooling effects were found important at 3-inch gap spacings but not at six inches or above. The 11-inch gap data are proportionately higher than the 6-inch data indicating that the results can be extrapolated. The data show that for arcs of a few cycles actual duration has little effect on rate of recovery. A range of current magnitudes from 50 to 700 amperes causes only about a 2-to-1 variation in rate of recovery. For the normal ratios of transmission-line insulation level to operating voltage (about four to one) minimum delay times of from 0.025 second for 100-ampere faults to 0.05 second for 700 ampere faults are required before the recovery voltage reaches the magnitude of the normal applied voltage. Time intervals of 0.05 to 0

Effects of Wing and Nacelle Modifications on Drag and Wake Characteristics of a Bomber-Type Airplane Model

An investigation of a model of a large four-engine bomber was conducted in the Langley 19-f'oot pressure tunnel to determine the effects of several wing and nacelle modifications on drag characteristics and air flow characteristics at the tail. Leading-edge gloves, trailing-edge extensions, and modified nacelle afterbodies were tested individual ly and in combination. The effects of the various modifications were determined by force tests, tuft observations, and turbulence s1ITveys in the region of the tail. Tests were made with fixed and natural transition on the wing and with propellers operating and propellers off. Most of the tests were con- ducted at a Reynolds number of approximately 2.6 x 106. The results indicated that application of certain of the modifications provided worth-while improvements in the characteristics or the model. The flow over the wing and flaps was improved, the drag was reduced, and the turbulence in the region of the tail was reduced. Trailing-edge extensions were the most effective individual modification in improving the flow over the wing with wing flaps neutral, cowl and intercooler flaps clos ed. Modified nacelle afterbodies were the most effectiv8 individual edification in reducing drag with either fixed or natural transition on the wing; however, trailin6-edge extensions were slightly more effective with fixed transition. Combinations of either leading or trailing-edge extensions and modified afterbodies were more effective than either modification alone. With cowl and intercooler flaps open, trailing-edge extensions with modified afterbodies provided substantial improvement in flow and drag characteristics. With wing flaps deflected, enclosing the flap behind the inboard nacelle within an extended afterbody or cutting the flaps at the nacelle appeared. to be the most promising methods of improving the f low over the flaps and the tail. Although the results of hot-wire-anenometer surveys were not conclusive in regard to buffeting characteristics, the modifications did educe the turbulence at the tail with wing flaps both neutral and deflected. The modifications, as a rule, were favorable to maximum lift. Appreciable reductions in longitudinal stability of the model were caused by addition of leading -edge gloves and tr ailing -edge extensions

The Red-Cockaded Woodpecker Cavity Tree: A Very Special Pine

The adaptation of red-cockaded woodpeckers (Picoides borealis) to fire-maintained southern pine ecosystems has included the development of behaviors that permit the species to use living pines for their cavity trees. Their adaptation to pine ecosystems has also involved a major adjustment in the species\u27 breeding system to cooperative breeding, probably in response to the extended time period required to excavate a completed cavity in a living pine and the relative rarity of completed cavities for nesting. The characteristics of live pines make them variable in their suitability as cavity trees, leading to the evolution of selection behavior among woodpeckers. Red-cockaded woodpeckers require a very special type of pine for their cavity tree. Potential cavity trees must be sufficiently old because only older pines have heartwood of sufficient diameter to physically house a woodpecker cavity without breaching the resin producing sapwood. Older pines also have a larger diameter of heartwood higher in the pine, permitting higher cavity placement, well away from frequent fires. Older pines also have a higher occurrence rate of red heart fungus (Phellinus pini), which decays the heartwood allowing cavity excavation to proceed more quickly. The potential cavity tree also needs to have relatively thin sapwood, which reduces the time the woodpecker must spend excavating through living xylem tissue that exudes sticky pine resin when pecked. Red-cockaded woodpeckers scale loose bark from the bole of their cavity trees and excavate resin wells above and below cavity entrances. These behaviors create a resin barrier that is very effective in deterring predation by rat snakes (Elaphe spp.). Thus, the ability of pines to produce adequate resin is also important to the woodpecker. Red-cockaded wood- peckers can detect the pine\u27s ability to produce resin and select pines that are high producers. Higher yields of resin likely create better barriers against rat snakes. The socially dominant breeding male red-cockaded woodpecker selects the cavity tree that produces the most resin for its roost tree, which during spring becomes the group\u27s nest tree. Our recent research suggests that red-cockaded woodpeckers also select pines with particular resin chemistries. High concentrations of diterpenes may increase resin viscosity, stickiness, irritability, or other factors that may be important for creating a barrier against rat snakes

The question-behaviour effect: a theoretical and methodological review and meta-analysis

Research has demonstrated that asking people questions about a behaviour can lead to behaviour change. Despite many, varied studies in different domains, it is only recently that this phenomenon has been studied under the umbrella term of the question-behaviour effect (QBE) and moderators of the effect have been investigated. With a particular focus on our own contributions, this article: (1) provides an overview of QBE research; (2) reviews and offers new evidence concerning three theoretical accounts of the QBE (behavioural simulation and processing fluency; attitude accessibility; cognitive dissonance); (3) reports a new meta-analysis of QBE studies (k = 66, reporting 94 tests) focusing on methodological moderators. The findings of this meta-analysis support a small significant effect of the QBE (g = 0.14, 95% CI = 0.11, 0.18, p < .001) with smaller effect sizes observed in more carefully controlled studies that exhibit less risk of bias and (4) also considers directions for future research on the QBE, especially studies that use designs with low risk of bias and consider desirable and undesirable behaviour separately