Bending and Torsion Load Alleviator With Automatic Reset

A force transmitting load alleviator apparatus and method are provided for rotatably and pivotally driving a member to be protected against overload torsional and bending (moment) forces. The load alleviator includes at least one bias spring to resiliently bias cam followers and cam surfaces together and to maintain them in locked engagement unless a predetermined load is exceeded whereupon a center housing is pivotal or rotational with respect to a crown assembly. This pivotal and rotational movement results in frictional dissipation of the overload force by an energy dissipator. The energy dissipator can be provided to dissipate substantially more energy from the overload force than from the bias force that automatically resets the center housing and crown assembly to the normally fixed centered alignment. The torsional and bending (moment) overload levels can designed independently of each other

Hybrid Inflatable Pressure Vessel

Figure 1 shows a prototype of a large pressure vessel under development for eventual use as a habitable module for long spaceflight (e.g., for transporting humans to Mars). The vessel is a hybrid that comprises an inflatable shell attached to a rigid central structural core. The inflatable shell is, itself, a hybrid that comprises (1) a pressure bladder restrained against expansion by (2) a web of straps made from high-strength polymeric fabrics. On Earth, pressure vessels like this could be used, for example, as portable habitats that could be set up quickly in remote locations, portable hyperbaric chambers for treatment of decompression sickness, or flotation devices for offshore platforms. In addition, some aspects of the design of the fabric straps could be adapted to such other items as lifting straps, parachute straps, and automotive safety belts. Figure 2 depicts selected aspects of the design of a vessel of this type with a toroidal configuration. The bladder serves as an impermeable layer to keep air within the pressure vessel and, for this purpose, is sealed to the central structural core. The web includes longitudinal and circumferential straps. To help maintain the proper shape upon inflation after storage, longitudinal and circumferential straps are indexed together at several of their intersections. Because the web is not required to provide a pressure seal and the bladder is not required to sustain structural loads, the bladder and the web can be optimized for their respective functions. Thus, the bladder can be sealed directly to the rigid core without having to include the web in the seal substructure, and the web can be designed for strength. The ends of the longitudinal straps are attached to the ends of the rigid structural core by means of clevises. Each clevis pin is surrounded by a roller, around which a longitudinal strap is wrapped to form a lap seam with itself. The roller is of a large diameter chosen to reduce bending of the fibers in the strap. The roller also serves to equalize the load in the portions of the strap on both sides of the clevis pin. The lap seam is formed near the clevis by use of a tapered diamond stitch: This stitch is designed specifically to allow fibers in the stitch and strap to relax under load in such a manner that the load becomes more nearly evenly distributed among all fibers in the stitch region. Thus, the tapered diamond stitch prevents load concentrations that could cause premature failure of the strap and thereby increases the strength of the strap/structural-core joint. The lap seam can be rated at >90 percent of the strength of the strap material

The Essential Toxin: Impact of Zinc on Human Health

Compared to several other metal ions with similar chemical properties, zinc is relatively harmless. Only exposure to high doses has toxic effects, making acute zinc intoxication a rare event. In addition to acute intoxication, long-term, high-dose zinc supplementation interferes with the uptake of copper. Hence, many of its toxic effects are in fact due to copper deficiency. While systemic homeostasis and efficient regulatory mechanisms on the cellular level generally prevent the uptake of cytotoxic doses of exogenous zinc, endogenous zinc plays a significant role in cytotoxic events in single cells. Here, zinc influences apoptosis by acting on several molecular regulators of programmed cell death, including caspases and proteins from the Bcl and Bax families. One organ where zinc is prominently involved in cell death is the brain, and cytotoxicity in consequence of ischemia or trauma involves the accumulation of free zinc. Rather than being a toxic metal ion, zinc is an essential trace element. Whereas intoxication by excessive exposure is rare, zinc deficiency is widespread and has a detrimental impact on growth, neuronal development, and immunity, and in severe cases its consequences are lethal. Zinc deficiency caused by malnutrition and foods with low bioavailability, aging, certain diseases, or deregulated homeostasis is a far more common risk to human health than intoxication

Size-dependent mechanical properties and failure study of nickel nanoparticles

The limited number of studies that focus on the size-dependent failure mechanisms of individual nanoparticles and their significance on epoxy composite material properties led to the twofold aim of this research: study the failure modes of nickel nanoparticles and determine the dependence of the mechanical properties of the Ni-epoxy composite on the size of the nickel particles used as reinforcement. Samples of spherical nickel nanoparticles were separated by size based on their densities and the resulting sections used as reinforcement in epoxy composites. The microstructural characterization of the nickel samples were performed on a Scanning Electron Microscope and the mechanical properties of the different Ni-epoxy composite pucks investigated using a nanoindenter. For the failure analysis investigation, an ultrasonic processor was used to induce damage to nickel nanoparticles of diverse sizes dispersed in a solvent. The corresponding effects of the treatment on the nanostructures were analyzed through X-ray diffraction techniques, to determine possible phase transformations, and Transmission Electron Microscopy, to analyze changes in the crystal lattice. Findings indicate that the hardness and Young’s Modulus values for the Ni-epoxy composites increase as filler particle size decreases and follows a normal Hall-Petch relation. The intense energy imparted by the ultrasonic process, along the particle-solvent interface, created a protective NiO coating in the Ni spherical nanoparticles. The latter seems to suppress the complete fracturing of the particle despite the creation of multiple lattice defects.http://archive.org/details/sizedependentmec1094549612Major, United States ArmyApproved for public release; distribution is unlimited