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Creep characteristics of molybdenum at high temperature and stress are utilized to compress tungsten foil liner against inner surface of tantalum alloy cylinder to form bond at interface. Temperature and pressure can be accurately controlled and size of workpiece is limited only by furnace size.
A Thermal Control Valve (TCV) has been in development for the Exploration Extravehicular Mobility Unit Portable Life Support System (xEMU PLSS). The xEMU PLSS TCV controls flow going to the liquid cooling and ventilation garment that the crew member wears during extra-vehicular activity to expel waste heat. A previous TCV version with a linear actuator and diverter valve has been tested to attempt to control the flow accurately. The previous valve has a non-linear flow response relative to valve position and has struggled to meet the setpoints desired for precise thermal control. While many diverter valve design variations have been attempted, all previous designs have had difficulty meeting set points. Additionally, high precision machining is required to create a metal-on-metal seal which has its own drawbacks and does not always meet requirements for internal leakage. This metal seal also requires stalling a linear actuator to load the seal in compression or tension which has caused sticking failures when stalled. A new approach and design for a TCV has been developed which uses a rotational ball to control flow and has demonstrated a much more precise and linear flow control. The design functions like a two-way ball valve with two Teflon seats that cradle and compress the ball for sealing. The ball outlet has a unique geometric design to create a set-able orifice like hole which is more predictable at controlling flow. Additionally, the Teflon seat performs much better for preventing internal leakage than the metal seal and prevents sticking by having a large range in which it is sealed without having to stall the actuator. This paper will review a new proposed xEMU PLSS TCV ball design and compare it with previous iterations of the design.
A Thermal Control Valve (TCV) has been in development for the Exploration Extravehicular Mobility Unit Portable Life Support System (xEMU PLSS). The xEMU PLSS TCV controls flow going to the liquid cooling and ventilation garment that the crew member wears during extra-vehicular activity to expel waste heat. A previous TCV version with a linear actuator and diverter valve has been tested to attempt to control the flow accurately. The previous valve has a non-linear flow response relative to valve position and has struggled to meet the setpoints desired for precise thermal control. While many diverter valve design variations have been attempted, all previous designs have had difficulty meeting set points. Additionally, high precision machining is required to create a metal-on-metal seal which has its own drawbacks and does not always meet requirements for internal leakage. This metal seal also requires stalling a linear actuator to load the seal in compression or tension which has caused sticking failures when stalled. A new approach and design for a TCV has been developed which uses a rotational ball to control flow and has demonstrated a much more precise and linear flow control. The design functions like a two-way ball valve with two Teflon seats that cradle and compress the ball for sealing. The ball outlet has a unique geometric design to create a set-able orifice like hole which is more predictable at controlling flow. Additionally, the Teflon seat performs much better for preventing internal leakage than the metal seal and prevents sticking by having a large range in which it is sealed without having to stall the actuator. This paper will review a new proposed xEMU PLSS TCV ball design and compare it with previous iterations of the design.
After measuring ultrasonic velocity and density, the molecular compressibility values from Wada's formula were calculated, for alkali metal halide solutions in methyl, ethyl, butyl, and glycol alcohol. The temperature and concentration dependence were studied, finding deviations due to the hydrogen bonds of the solvent.
A gripping system has been developed to test uniaxial, 0 deg orientation PMR 15/Celion 6000 composites at elevated temperatures. The method involves compression of grit-blasted laminate between grit-blasted metal to give a non-slipping interface for load transfer. Tensile testing at both 316 C and room temperature indicated that deformation was elastic to fracture and that the variation in tensile properties for one laminate is the same as that for several panels. In addition, the tensile properties for uniaxial PMR 15/Celion 6000 are identical at 316 C and room temperature. For nominally 51 volume percent fiber, the elastic modulus is 119.6 GPa, the fracture stress is 1370 MPa, and the strain to fracture is about 1.15 percent. In addition, data are presented which indicate that the gripping system can be used for long term, elevated temperature testing of composite materials.
The present report deals with the development of a thermometer for recording stagnation temperature in compressible mediums in turbulent flow within 1 to 2 percent error of the adiabatic temperature in the stagnation point, depending upon the speed. This was achieved by placing the junction of a thermocouple near the stagnation point of an aerodynamically beneficial body, special care being taken to assure an uninterrupted supply of fresh compressed air on the junction together with the use of metals of low thermal conductivity, thus keeping heat-transfer and heat-dissipation losses to a minimum. In other experiments the use of the plate thermometer was proved unsuitable for practical measurements by reason of its profound influence in the reading by the Reynolds number and by the direction of flow.
Amplified mechanical displacement effects, similar to those observed in the recently reported Rainbow actuators, have also been found to exist in prestressed ceramic/metal composite structures coined as CERAMBOW's - an acronym for CERamic And Metal Biased Oxide Wafer. Mimicking the Rainbows in many ways, the intentionally created internal compressive and tensile stresses within the Cerambows are used to amplify their displacement properties via the combined effects of piezoelectric d31 strain and domain reorientation. They are fabricated from ferroelectric, piezoelectric or electrostrictive materials and metal substrates of significantly different thermal expansions which are largely responsible for the creation of the stress. Typical ceramics used in Cerambows are PZT, PLZT, PBZT, PSZT and PMN and some typical metal substrates are Al, Ag, Ni, brass, steel and Be/Cu foil. Shapes can vary from round disks to square plates and rectangular bars. Formed at an elevated temperature of approximately 250 C, the stresses on cooling to room temperature are generally sufficient to produce displacements as large as 0.125mm (5 mils) when activated unipolar and 0.25mm (10 mils) when operated bipolar at 450 volts in a dome mode. Comparing equal structures of a Cerambow with a Rainbow, the Cerambow was found to achieve approximately 70% of the displacement that would normally be obtained with a Rainbow. Although this difference in displacement is sufficient to prefer a Rainbow for many applications, there are some advantages for the Cerambow. Among these are (1) the processing temperatures are lower, (2) high lead-containing ceramics are not required and (3) in some instances the metal substrate is more convenient to interface with other elements of a device. However, the disadvantages include (1) lower displacement in the dome mode of operation, (2) the higher displacement saddle mode has not yet been demonstrated with a Cerambow and (3) the ceramic/metal bond interface is a possible failure area when operated for extended periods of time. The applications for Cerambows are considered to be similar to Rainbows, i.e., actuators, pumps, deflectors, vibrators, speakers, hydrophones, hydroprojectors, switches, etc.
A reusable metal clamp for retaining a fused quartz ampoule during temperature cycling in the range of 20 deg C to 1000 deg C is described. A compressible graphite foil having a high radial coefficient of thermal expansion is interposed between the fused quartz ampoule and metal clamp to maintain a snug fit between these components at all temperature levels in the cycle.
Tension-compression fatigue properties under axial loading for aluminum and titanium sheet metal
Reinforced fluorocarbon cupseal, which provides an integral lip-type seal, replaces the metal piston rings in piston-cylinder configurations used in the compression of low density gases. The fluorocarbon seal may be used as cryogenic compressor piston seals.
Finite element analyses of thermal buckling of thin metallic plates with prescribed spatial temperature distributions are described. Thermally induced compressive membrane stresses and transverse plate displacement imperfections initiate plates buckling. A finite element formulation based on von Karman plate theory is presented. The resulting nonlinear equations are solved for incremental temperature increases by Newton-Raphson iteration. The computational method is used to investigate the buckling response of rectangular plates with steady and unsteady spatially varying temperature distributions. The role of initial plate imperfections and temperature distributions on the nonlinear response of plate displacements and stresses is described. The relatively high levels of stress induced by spatial temperature gradients should be considered carefully in the postbuckling design of panels for aerospace vehicles subjected to combined mechanical and thermal loads.
In the late 1990s, Lambda Research Inc., of Cincinnati, Ohio, received Small Business Innovation Research (SBIR) awards from Glenn Research Center to demonstrate low plasticity burnishing (LPB) on metal engine components. By producing a thermally stable deep layer of compressive residual stress, LPB significantly strengthened turbine alloys. After Lambda patented the process, the Federal Aviation Administration accepted LPB for repair and alteration of commercial aircraft components, the U.S. Department of Energy found LPB suitable for treating nuclear waste containers at Yucca Mountain. Data from the U.S. Food and Drug Administration confirmed LPB to completely eliminate the occurrence of fretting fatigue failures in modular hip implants.
In 1954, Salpeter calculated nuclear reaction rates would increase via weak and strong electron screening in stars. Astrophysical observations and laboratory astrophysics experiments have confirmed that electron screening reduces the Coulomb Barrier between charged particles. Fermi degenerate strong screening occurs when the electron density exceeds 10e23 electrons/cm3 in the cores of gas giant planets, White Dwarf Stars, the conduction bands of metals, deuterated LENR materials and Inertial Confinement Fusion targets at maximum compression. We have modelled these quantum mechanical effects with Density Functional Theory codes.
Lightweight honeycomb sandwich construction using a wide variety of metal and fibrous composite faceskins was used in the design of a typical Space Tug skirt structure. Relatively low magnitude combined loading of axial compression and torsion resulted in designs using ultrathin faceskins, lightweight honeycomb cores, and thin faceskin/core adhesive bond layers. Two of the designs with metal faceskins (aluminum and titanium) and four with fibrous composite faceskins (using combinations of fiberglass, boron, and graphite) were evaluated through the fabrication and structural test of a series of small development panels. The two most promising concepts with aluminum and graphite/epoxy faceskins, were further evaluated through the fabrication and structural test of larger compression and shear panels. All panels tested exceeded design ultimate load levels, thereby, verifying the structural integrity of the selected designs. Projected skirt structural weights for the graphite/epoxy and aluminum concepts fall within original weight guidelines established for the Space Tug vehicle.
From 1995 to the present the friction stir welding (FSW) process has been under study at Marshall Space Flight Center (MSFC). This is an account of the progressive emergence of a set of conceptual tools beginning with the discovery of the shear surface, wiping metal transfer, and the invention of a kinematic model and making possible a treatment of both metallurgical structure formation and process dynamics in friction stir welding from a unified point of view. It is generally observed that the bulk of the deformation of weld metal around the FSW pin takes place in a very narrow, almost discontinuous zone with high deformation rates characteristic of metal cutting. By 1999 it was realized that this zone could be treated as a shear surface like that in simple metal cutting models. At the shear surface the seam is drawn out and compressed and pressure and flow conditions determine whether or not a sound weld is produced. The discovery of the shear surface was followed by the synthesis of a simple 3- flow kinematic model of the FSW process. Relative to the tool the flow components are: (1) an approaching translational flow at weld speed V, (2) a rotating cylindrical plug flow with the angular velocity of the tool , and (3) a relatively slow ring vortex flow (like a smoke ring) encircling the tool and driven by shoulder scrolls and pin threads. The rotating plug flow picks up an element of weld metal, rotates it around with the tool, and deposits it behind the tool ( wiping metal transfer ); it forms plan section loops in tracers cut through by the tool. Radially inward flow from the ring vortex component retains metal longer in the rotating plug and outward flow expels metal earlier; this interaction forms the looping weld seam trace and the tongue and groove bimetallic weld contour. The radial components of the translational and ring vortex flows introduce parent metal intrusions into the small grained nugget material close to the tool shoulder; if this feature is pronounced, nugget collapse may result. Certain weld features, in particular internal banding seen in transverse section as onion rings and associated surface ridges called tool marks , have long implied an oscillation flow component, but have only recently been attributed in the literature to tool eccentricity. Rotating plug shape, typically a hollow cylinder flared at the end where it sticks to the shoulder, varies as pressure distribution on the tool determines where sticking occurs. Simplified power input estimates balanced against heat loss estimates give reasonable temperature estimates, explain why the power requirement changes hardly at all over a wide range of RPM s, and yield isotherms that seem to fall along boundaries of parameter windows of operation.
Strain range components and creep fatigue behavior of metals related independently to cyclic life by equations in both tension and compression
The definition of Poisson's ratio for nonlinear behavior of metal matrix composite laminates is discussed and experimental results for tensile and compressive loading of five different boron-aluminum laminates are presented. It is shown that there may be considerable difference in the value of Poisson's ratio as defined by a total strain or an incremental strain definition. It is argued that the incremental definition is more appropriate for nonlinear material behavior. Results from a (0) laminate indicate that the incremental definition provides a precursor to failure which is not evident if the total strain definition is used.
Tool locally expands small-diameter tubes. Tube expander locally expands and deforms tube: Compressive lateral stress induced in elastomeric sleeve by squeezing axially between two metal tool parts. Adaptable to situations in which tube must have small bulge for mechanical support or flow control.