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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Comparative effects of contraction and angiotensin II on growth of adult feline cardiocytes in primary culture

The purposes of this study were 1) to determine whether angiotensin II causes growth of adult feline cardiocytes in long-term culture, 2) to compare the growth effects of angiotensin II with those resulting from electrically stimulated contraction, and 3) to determine whether the anabolic effects of contraction are exerted via the angiotensin type 1 receptor. Adult feline cardiocytes were cultured on laminin-coated trays in a serum-free medium. Cardiocytes were either electrically stimulated to contract (1 Hz, 5-ms pulse duration, alternating polarity) or were nonstimulated and quiescent. Quiescent cells were studied as controls and after treatment with angiotensin II (10(-8) M), losartan (10(-6) M; an angiotensin type 1-receptor antagonist), or angiotensin II plus losartan. Contracting cells were studied in the presence and absence of angiotensin II or losartan. In quiescent cardiocytes, angiotensin II treatment on day 7 significantly increased protein synthesis rates by 22% and protein content per cell by 17%. The effects of angiotensin II were completely blocked by losartan. Electrically stimulated contraction on days 4 and 7 in culture significantly increased protein synthesis rate by 18 and 38% and protein content per cell by 19 and 46%, respectively. Angiotensin II treatment did not further increase protein synthesis rate or protein content in contracting cardiocytes. Furthermore, losartan did not block the anabolic effects of contraction on protein synthesis rates or protein content. In conclusion, angiotensin II can exert a modest anabolic effect on adult feline cardiocytes in culture. In contracting feline cardiocytes, angiotensin II has no effect on growth. Growth caused by electrically stimulated contraction occurs more rapidly and is greater in magnitude than that caused by angiotensin II. Growth of contracting adult feline cardiocytes is not dependent on activation of the angiotensin receptor.

NASA Discipline Cardiopulmonary↗
NASA NTRS1946

Airscrew Gyroscopic Moments

When flying in a turn or pulling out of a dive, the airscrew exerts a gyroscopic moment on the aircraft, In the case of airscrews with three or more blades, arranged symmetrically, the value of the gyroscopic moment is J(sub x) omega(sub x) omega(sub y), where J(sub x) denotes the axial moment of inertia about the axis of rotation of the airscrew, omega(sub x) the angular upeed of the airscrew about its axis, and omega (sub Y) the rotary speed of the whole aircraft about an axis parallel to the plane of the airscrew (e.g., when pulling up, the transverse axis of the aircraft). The gyroscopic moment then tends to rotate the aircraft about an axis perpendicular to those of the two angular speeds and, in the came of airscrews with three or more blades, is constant during a revolution of the airscrew. With two-bladed airscrews, on the contrary, although the calculate gyroscopic moment represents the mean value in time, it fluctuates about this value with a frequency equal to twice the revolutions per minute. In addition, pulsating moments likewise occur about the other two axes. This fact is known from the theory of the asymmetrical gyro; the calculations that have been carried out for the determination of the various gyroscopic moments, however, mostly require an exact knowledge of the gyro theory. The problem will therefore be approached in another manner based on quite elementary considerations. The considerations are of importance, not only in connection with the gyroscopic moments exerted by the two-bladed airscrew on the aircraft, but also with the stressing of the blades of airscrews with an arbitrary number of blades.

Bock, G.↗
NASA NTRS1944

Researches on the Piston Ring

In internal combustion engines, steam engines, air compressors, and so forth, the piston ring plays an important role. Especially, the recent development of Diesel engines which require a high compression pressure for their working, makes, nowadays, the packing action of the piston ring far more important than ever. Though a number of papers have been published in regard to researches on the problem of the piston ring, none has yet dealt with an exact measurement of pressure exerted on the cylinder wall at any given point of the ring. The only paper that can be traced on this subject so far is Mr. Nakagawa's report on the determination of the relative distribution of pressure on the cylinder wall, but the measuring method adopted therein appears to need further consideration. No exact idea has yet been obtained as to how the obturation of gas between the piston and cylinder, the frictional resistance of the piston, and the wear of the cylinder wall are affected by the intensity and the distribution of the radial pressure of the piston ring. Consequently, the author has endeavored, by employing an apparatus of his own invention, to get an exact determination of the pressure distribution of the piston ring. By means of a newly devised ring tester, to which piezoelectricity of quartz was applied, the distribution of the radial pressure of many sample rings on the market was accurately determined. Since many famous piston rings show very irregular pressure distribution, the author investigated and achieved a manufacturing process of the piston ring which will exert uniform pressure on the cylinder wall. Temperature effects on the configuration and on the mean spring power have also been studied. Further, the tests were performed to ascertain how the gas tightness of the piston ring may be affected by the number or spring power. The researches as to the frictional resistance between the piston ring and the cylinder wall were carried out, too. The procedure of study, and experiments conducted by the author, on this subject will be fully described in the following paragraphs.

Ehihara, Keikiti↗
NASA NTRS2004

Bearingless Switched-Reluctance Motor Improved

The Morrison rotor, named after its inventor, is a hybrid rotor for use in a switched reluctance electric motor. The motor is characterized as bearingless in the sense that it does not rely on conventional mechanical bearings: instead, it functions as both a magnetic bearing and a motor. Bearingless switched-reluctance motors are attractive for use in situations in which large variations in temperatures and/or other extreme conditions preclude the use of conventional electric motors and mechanical bearings. In the Morrison motor, as in prior bearingless switched-reluctance motors, a multipole rotor is simultaneously levitated and rotated. In the prior motors, simultaneous levitation and rotation are achieved by means of two kinds of stator windings: (1) main motor windings and (2) windings that exert levitating forces on a multipole rotor. The multipole geometry is suboptimum for levitation because it presents a discontinuous surface to the stator pole faces, thereby degrading the vibration suppression capability of the magnetic bearing. The Morrison rotor simplifies the stator design in that it contains only one type of winding. The rotor is a hybrid that includes both (1) a circular lamination stack for levitation and (2) a multipole lamination stack for rotation. Simultaneous levitation and rotation at 6000 rpm were achieved with a prototype that included six rotor poles and eight stator poles. During normal operation, two of the four pairs of opposing stator poles (each pair at right angles to the other pair) levitate the rotor. The remaining two pairs of stator poles exert torque on the six-pole rotor lamination stack to produce rotation. The relative length of the circular and multipole lamination stacks on the rotor can be chosen to tailor the performance of the motor for a specific application. For a given overall length, increasing the length of the multipole stack relative to the circular stack results in an increase in torque relative to the levitation load capacity and vice versa.

Morrison, Carlos R.↗
NASA NTRS2005

Traction in smooth muscle cells varies with cell spreading

Changes in cell shape regulate cell growth, differentiation, and apoptosis. It has been suggested that the regulation of cell function by the cell shape is a result of the tension in the cytoskeleton and the distortion of the cell. Here we explore the association between cell-generated mechanical forces and the cell morphology. We hypothesized that the cell contractile force is associated with the degree of cell spreading, in particular with the cell length. We measured traction fields of single human airway smooth muscle cells plated on a polyacrylamide gel, in which fluorescent microbeads were embedded to serve as markers of gel deformation. The traction exerted by the cells at the cell-substrate interface was determined from the measured deformation of the gel. The traction was measured before and after treatment with the contractile agonist histamine, or the relaxing agonist isoproterenol. The relative increase in traction induced by histamine was negatively correlated with the baseline traction. On the contrary, the relative decrease in traction due to isoproterenol was independent of the baseline traction, but it was associated with cell shape: traction decreased more in elongated than in round cells. Maximum cell width, mean cell width, and projected area of the cell were the parameters most tightly coupled to both baseline and histamine-induced traction in this study. Wide and well-spread cells exerted larger traction than slim cells. These results suggest that cell contractility is controlled by cell spreading.

Non-NASA Center↗
NASA NTRS1998

Remotely controllable actuating device

An actuating device can change a position of an active member that remains in substantially the same position in the absence of a force of a predetermined magnitude on the active member. The actuating device comprises a shape-memory alloy actuating member for exerting a force when actuated by changing the temperature thereof, which shape-memory alloy actuating member has a portion for connection to the active member for exerting thereon a force having a magnitude at least as large as the predetermined magnitude for moving the active member to a desired position. Actuation circuitry is provided for actuating the shape-memory alloy actuating member by changing the temperature thereof only for the time necessary to move the active member to the desired position. The invention is particularly useful for changing the position of a camber-adjusting tab on a helicopter rotor blade by using two shape-memory alloy members that can act against each other to adjust dynamic properties of the rotor blade as it is rotating.

McKillip, Jr., Robert M.↗
NASA NTRS2006

WISE-2005: LBNP/Treadmill and Resistive Exercise Countermeasures Maintain Aerobic Capacity during a 60-d Bed Rest

We have previously documented that supine treadmill exercise within lower body negative pressure (LBNPex) performed 6 sessions (raised dot) wk(sup -1) during 15- and 30-day bed rests (BR) maintained upright aerobic capacity (VO2pk). In the present study, ure are evaluating whether aerobic capacity is maintained during a 60-d BR when the LBNPex frequency is reduced to 2-4 sessions (raised dot) wk(sup -1) and resistance exercise (REX) is added 2-3 sessions (raised dot) wk(sup -1). Eight healthy women (32 plus or minus 4 yrs; 56.4 plus or minus 3.6 kg; 164 plus or minus 8 cm; mean plus or minus SD) performed maximal-exertion, graded treadmill tests before and 3 days after a 60-d, 6 deg. head-down tilt BR. (Earliest day the medical monitors would permit a maximal exercise test post-BR). During BR, four subjects performed no exercise (CON), while four other subjects (EX) performed LBNPex and REX on separate days. The LBNPex countermeasure employed an intermittent (40-80% pre-BR VO2pk), 40-min protocol against an LBNP pressure (-49 plus or minus 3 mmHg) applied to provide a footward force equivalent to 1.0-1.2 body weight. REX consisted of maximal concentric and eccentric supine leg press and heel raise exercises using a gravity-independent flywheel ergometer. Comparisons were performed using paired (within-group) or non-paired (between-group) t-tests. Three days post-BR, VO2pk of the CON group was reduced significantly from pre-BR (Pre:37.2 plus or minus 1.2, Post: 29.4 plus or minus 2 ml (raised dot) kg(sup -1) (raised dot) min(sup -1), P less than 0.05), while the VO2pk of the EX group was not significantly reduced (Pre: 39.6 plus or minus 1.9, Post: 38.0 plus or minus 0.6 ml (raised dot) kg(sup -1) (raised dot) min(sup -1)). Peak heart rate, ventilation, rating of perceived exertion, and respiratory exchange ratio were not significantly different between the two groups pre- and post-BR. These preliminary results suggest that the combined LBNPex and REX countermeasures may be sufficient to maintain upright aerobic capacity after long-duration space flights.

Schneider, Suzanne M.↗
NASA NTRS2008

Miniature High-Force, Long-Stroke SMA Linear Actuators

Improved long-stroke shape-memory-alloy (SMA) linear actuators are being developed to exert significantly higher forces and operate at higher activation temperatures than do prior SMA actuators. In these actuators, long linear strokes are achieved through the principle of displacement multiplication, according to which there are multiple stages, each intermediate stage being connected by straight SMA wire segments to the next stage so that relative motions of stages are additive toward the final stage, which is the output stage. Prior SMA actuators typically include polymer housings or shells, steel or aluminum stages, and polymer pads between successive stages of displacement-multiplication assemblies. Typical output forces of prior SMA actuators range from 10 to 20 N, and typical strokes range from 0.5 to 1.5 cm. An important disadvantage of prior SMA wire actuators is relatively low cycle speed, which is related to actuation temperature as follows: The SMA wires in prior SMA actuators are typically made of a durable nickel/titanium alloy that has a shape-memory activation temperature of 80 C. An SMA wire can be heated quickly from below to above its activation temperature to obtain a stroke in one direction, but must then be allowed to cool to somewhat below its activation temperature (typically, less than or equal to 60 C in the case of an activation temperature of 80 C) to obtain a stroke in the opposite direction (return stroke). At typical ambient temperatures, cooling times are of the order of several seconds. Cooling times thus limit cycle speeds. Wires made of SMA alloys having significantly higher activation temperatures [denoted ultra-high-temperature (UHT) SMA alloys] cool to the required lower return-stroke temperatures more rapidly, making it possible to increase cycle speeds. The present development is motivated by a need, in some applications (especially aeronautical and space-flight applications) for SMA actuators that exert higher forces, operate at greater cycle speeds, and have stronger housings that can withstand greater externally applied forces and impacts. The main novel features of the improved SMA actuators are the following: 1) The ends of the wires are anchored in compact crimps made from short steel tubes. Each wire end is inserted in a tube, the tube is flattened between planar jaws to make the tube grip the wire, the tube is compressed to a slight U-cross-section deformation to strengthen the grip, then the crimp is welded onto one of the actuator stages. The pull strength of a typical crimp is about 125 N -- comparable to the strength of the SMA wire and greater than the typical pull strengths of wire-end anchors in prior SMA actuators. Greater pull strength is one of the keys to achievement of higher actuation force; 2) For greater strength and resistance to impacts, housings are milled from aluminum instead of being made from polymers. Each housing is made from two pieces in a clamshell configuration. The pieces are anodized to reduce sliding friction; 3) Stages are made stronger (to bear greater compression loads without excessive flexing) by making them from steel sheets thicker than those used in prior SMA actuators. The stages contain recessed pockets to accommodate the crimps. Recessing the pockets helps to keep overall dimensions as small as possible; and, 4) UHT SMA wires are used to satisfy the higher-speed/higher-temperature requirement.

Cummin, Mark A.↗
NASA NTRS2009

Manipulating Neutral Atoms in Chip-Based Magnetic Traps

Several techniques for manipulating neutral atoms (more precisely, ultracold clouds of neutral atoms) in chip-based magnetic traps and atomic waveguides have been demonstrated. Such traps and waveguides are promising components of future quantum sensors that would offer sensitivities much greater than those of conventional sensors. Potential applications include gyroscopy and basic research in physical phenomena that involve gravitational and/or electromagnetic fields. The developed techniques make it possible to control atoms with greater versatility and dexterity than were previously possible and, hence, can be expected to contribute to the value of chip-based magnetic traps and atomic waveguides. The basic principle of these techniques is to control gradient magnetic fields with suitable timing so as to alter a trap to exert position-, velocity-, and/or time-dependent forces on atoms in the trap to obtain desired effects. The trap magnetic fields are generated by controlled electric currents flowing in both macroscopic off-chip electromagnet coils and microscopic wires on the surface of the chip. The methods are best explained in terms of examples. Rather than simply allowing atoms to expand freely into an atomic waveguide, one can give them a controllable push by switching on an externally generated or a chip-based gradient magnetic field. This push can increase the speed of the atoms, typically from about 5 to about 20 cm/s. Applying a non-linear magnetic-field gradient exerts different forces on atoms in different positions a phenomenon that one can exploit by introducing a delay between releasing atoms into the waveguide and turning on the magnetic field.

Aveline, David↗
NASA NTRS2008

Gimballed Shoulders for Friction Stir Welding

In a proposed improvement of tooling for friction stir welding, gimballed shoulders would supplant shoulders that, heretofore, have been fixedly aligned with pins. The proposal is especially relevant to self-reacting friction stir welding. Some definitions of terms, recapitulated from related prior NASA Tech Briefs articles, are prerequisite to a meaningful description of the proposed improvement. In friction stir welding, one uses a tool that includes (1) a rotating shoulder on top (or front) of the workpiece and (2) a pin that rotates with the shoulder and protrudes from the shoulder into the depth of the workpiece. In conventional friction stir welding, the main axial force exerted by the tool on the workpiece is reacted through a ridged backing anvil under (behind) the workpiece. When conventional friction stir welding is augmented with an auto-adjustable pin-tool (APT) capability, the depth of penetration of the pin into the workpiece is varied in real time by a position- or forcecontrol system that extends or retracts the pin as needed to obtain the desired effect. In self-reacting (also known as self-reacted) friction stir welding as practiced heretofore, there are two shoulders: one on top (or front) and one on the bottom (or back) of the workpiece. In this case, a threaded shaft protrudes from the tip of the pin to beyond the back surface of the workpiece. The back shoulder is held axially in place against tension by a nut on the threaded shaft. Both shoulders rotate with the pin and remain aligned coaxially with the pin. The main axial force exerted on the workpiece by the tool and front shoulder is reacted through the back shoulder and the threaded shaft into the friction-stir-welding machine head, so that a backing anvil is no longer needed. A key transmits torque between the bottom shoulder and the threaded shaft, so that the bottom shoulder rotates with the shaft. This concludes the prerequisite definitions of terms.

Carter, Robert↗
NASA NTRS2009

Dewetting and Segregation of Zn-Doped InSb in Microgravity Experiments

In directional solidification, dewetting is characterized by the lack of contact between the crystal and the crucible walls, due to the existence of a liquid meniscus at the level of the solid-liquid interface. This creates a gap of a few tens of micrometers between the crystal and the crucible. One of the immediate consequences of this phenomenon is the dramatic improvement of the quality of the crystal. This improvement is partly due to the modification of the solid-liquid interface curvature and partly to the absence of sticking and spurious nucleation at the crystal-crucible interface. Dewetting has been, commonly observed during the growth of semiconductors in crucibles under microgravity conditions where it appears to be very stable: the gap between the crystal and the crucible remains constant along several centimetres of growth. The physical models of the phenomenon are well established and they predict that dewetting should not occur in microgravity, if sufficient static pressure is imposed on the melt, pushing it towards the crucible. We present the results of InSb(Zn) solidification experiments conducted at the International Space Station (ISS) where, in spite of a spring exerting a pressure on the liquid, partial dewetting did occur. This surprising result is discussed in terms of force exerted .by the spring on the liquid and of possibility that the spring did not work properly. Furthermore, it appears that the segregation of the Zn was not affected by the occurrence of the dewetting. The data suggest that there was no significant interference of convection with segregation of Zn in InSb.

Ostrogorsky, A. G.↗
NASA NTRS2009

T-Rex: A Japanese Space Tether Experiment

Electrodynamic tether (EDT) thrusters work by virtue of the force a magnetic field exerts on a wire carrying an electrical current. The force, which acts on any charged particle moving through a magnetic field (including the electrons moving in a current-carrying wire), were concisely expressed by Lorentz in 1895 in an equation that now bears his name. The force acts in a direction perpendicular to both the direction of current flow and the magnetic field vector. Electric motors make use of this force: a wire loop in a magnetic field is made to rotate by the torque the Lorentz Force exerts on it due to an alternating current in the loop times so as to keep the torque acting in the same sense. The motion of the loop is transmitted to a shaft, thus providing work. Although the working principle of EDT thrusters is not new, its application to space transportation may be significant. In essence, an EDT thruster is just a clever way of getting an electrical current to flow in a long orbiting wire (the tether) so that the Earth s magnetic field will accelerate the wire and, consequently the payload attached to the wire. The direction of current flow in the tether, either toward or away from the Earth along the local vertical, determines whether the magnetic force will raise or lower the orbit. The bias voltage of a vertically deployed metal tether, which results just from its orbital motion (assumed eastward) through Earth s magnetic field, is positive with respect to the ambient plasma at the top and negative at the bottom. This polarization is due to the action of the Lorentz force on the electrons in the tether. Thus, the natural current flow is the result of negative electrons being attracted to the upper end and then returned to the plasma at the lower end. The magnetic force in this case has a component opposite to the direction of motion, and thus leads to a lowering of the orbit and eventually to re-entry. In this generator mode of operation the Lorentz Force serves both to drive the current and then to act on the current to decelerate the system. One of the most important features of tether thrusters is that they use renewable energy sources to drive the electrical current flow in either the orbit-raising or orbit-lowering modes. Sources inherent to Earth orbit are used. To raise the orbit, sunlight can be converted to the electrical energy required to drive the tether current. To lower the orbit, the orbital energy itself (supplied by the Earth-to-orbit launcher when it raises the system into orbit) is the energy source of the tether current via the action of the Lorentz Force. Electrodynamic tethers can be directly applied to a wide spectrum of uses in space. As a propulsion system, they include satellite de-orbit, transfer of a satellite from one orbit to another, altitude maintenance for large spacecraft such as the International Space Station, and since it works wherever there is a magnetic field and an ionosphere planetary exploration missions. An electrodynamic tether upper stage could be used as an Orbit Transfer Vehicle (OTV) to move payloads within low earth orbit. The OTV would rendezvous with the payload and launch vehicle, grapple the payload and maneuver it to a new orbital altitude or inclination without the use of boost propellant. The tug could then lower its orbit to rendezvous with the next payload and repeat the process. Conceivably, such a system could perform several orbital maneuvering assignments without resupply, making it relatively inexpensive to operate.

Johnson, Les↗
NASA NTRS2009

Effect of Changing the Center of Gravity on Human Performance in Simulated Lunar Gravity

Subjective measures of physical exertion, compensation, and controllability while performing tasks in simulated reduced gravity can be affected by changing the center of gravity (CG) of the overall system. The CG of the overall system is defined as the combined CG of the subject, the spacesuit, and the equipment required to change the CG. PURPOSE: To determine if changing the CG affects subjective ratings of suited human performance in simulated lunar gravity. METHODS: A custom weight support structure interfaced with the lunar prototype spacesuit, allowing manipulation of the CG. Weight locations to alter CG were based on a reference subject (81.6 kg, 182.9 cm). Six subjects (80.0 +/- 10.6 kg, 182.3 +/- 6.2 cm) completed 4 tasks (walking, kneel/stand, rock pickup, and shoveling) with system CG at 3 different locations (B=4.8/1.0, C=7.6/14.4, and P=11.2/20.1 cm aft/above the standard subject?s CG). Lunar gravity (0.17-g) was simulated by parabolic flight. Suited testing was performed at 29.6 kPa with a combined suit and structure mass of 181 kg. In all conditions, subjects provided ratings of perceived exertion (RPE) and the gravity compensation and performance scale (GCPS) upon completion of each task. RESULTS: Mean RPE and GCPS were highest at P for all tasks. Variability was greatest at B and lowest at C, and large variations between subjects at the same CG existed for both RPE and GCPS. These trends were not consistent with results from unsuited CG studies performed in other underwater and overhead suspension lunar gravity simulations. CONCLUSION: Modifying CG during suited testing at lunar gravity seems to affect subjective human performance. However, variation in subjective ratings at a given CG location indicates that further study is needed to determine the interactions among lunar gravity simulation, system CG, system mass, and subject characteristics such as anthropometry, strength, and fitness.

Chappell, Steven P.↗
NASA NTRS2007

Several Developments in Space Tethers

Five reports address different aspects of development of tethers to be deployed from spacecraft in orbit around the Earth. The first report discusses proposed optoelectronic tracking of retroreflective objects located at intervals or of retroreflective coats along the entire length of a tether to measure lateral motions. The second report describes digitally controlled spooling machinery that retracts or extends a tape tether at controlled speed and tension in the spool isolated from uncontrolled tension on the outside. The third report discusses part of this machinery that pivots to accommodate misalignments between the deployed and spooled portions of the tether and contains rollers used to exert tension and speed control. The fourth report discusses aspects of designs of proposed electrodynamic tethers, which would be electrically conductive and would interact with the magnetic field of the Earth to exert forces to modify orbits of deploying spacecraft. The fifth report discusses electrical aspects of designs of electrodynamic tape tethers, including the use of solar cells or motional electromagnetic force to generate currents in tethers and the use of electron emitters and electron and ion collectors at opposite ends of tethers to make electrical contact with the thin plasma in surrounding space.

Santangelo, Andrew↗
NASA NTRS2007

Algorithm Optimally Allocates Actuation of a Spacecraft

A report presents an algorithm that solves the following problem: Allocate the force and/or torque to be exerted by each thruster and reaction-wheel assembly on a spacecraft for best performance, defined as minimizing the error between (1) the total force and torque commanded by the spacecraft control system and (2) the total of forces and torques actually exerted by all the thrusters and reaction wheels. The algorithm incorporates the matrix vector relationship between (1) the total applied force and torque and (2) the individual actuator force and torque values. It takes account of such constraints as lower and upper limits on the force or torque that can be applied by a given actuator. The algorithm divides the aforementioned problem into two optimization problems that it solves sequentially. These problems are of a type, known in the art as semi-definite programming problems, that involve linear matrix inequalities. The algorithm incorporates, as sub-algorithms, prior algorithms that solve such optimization problems very efficiently. The algorithm affords the additional advantage that the solution requires the minimum rate of consumption of fuel for the given best performance.

Motaghedi, Shi↗
NASA NTRS2006

Tool for Two Types of Friction Stir Welding

A tool that would be useable in both conventional and self-reacting friction stir welding (FSW) has been proposed. The tool would embody both a prior tooling concept for self-reacting FSW and an auto-adjustable pin-tool (APT) capability developed previously as an augmentation for conventional FSW. Some definitions of terms are prerequisite to a meaningful description of the proposed tool. In conventional FSW, depicted in Figure 1, one uses a tool that includes (1) a rotating shoulder on top (or front) of the workpiece and (2) a rotating pin that protrudes from the shoulder into the depth of the workpiece. The main axial force exerted by the tool on the workpiece is reacted through a ridged backing anvil under (behind) the workpiece. When conventional FSW is augmented with an APT capability, the depth of penetration of the pin into the workpiece is varied in real time by a position- or force-control system that extends or retracts the pin as needed to obtain the desired effect. In self-reacting (also known as self-reacted) friction stir welding (SR-FSW), there are two rotating shoulders: one on top (or front) and one on the bottom (or back) of the workpiece. In this case, a threaded shaft protrudes from the tip of the pin to beyond the back surface of the workpiece. The back shoulder is held axially in place against tension by a nut on the threaded shaft. The main axial force exerted on the workpiece by the tool and front shoulder is reacted through the back shoulder and the threaded shaft, back into the FSW machine head, so that a backing anvil is no longer needed. A key transmits torque between the bottom shoulder and the threaded shaft, so that the bottom shoulder rotates with the shaft. A tool for SRFSW embodying this concept was reported in "Mechanism for Self-Reacted Friction Stir Welding" (MFS-31914), NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 53. In its outward appearance, the proposed tool (see Figure 2) would fit the above description of an SR-FSW tool. In this case, the FSW machine would have an APT capability and the pin would be modified to accept a bottom shoulder. The APT capability could be used to vary the distance between the front and back shoulders in real time to accommodate process and workpiece-thickness variations. The tool could readily be converted to a conventional FSW tool, with or without APT capability, by simply replacing the modified pin with a conventional FSW pin.

Carter, Robert↗
NASA NTRS2004

Heat Control via Torque Control in Friction Stir Welding

In a proposed advance in friction stir welding, the torque exerted on the workpiece by the friction stir pin would be measured and controlled in an effort to measure and control the total heat input to the workpiece. The total heat input to the workpiece is an important parameter of any welding process (fusion or friction stir welding). In fusion welding, measurement and control of heat input is a difficult problem. However, in friction stir welding, the basic principle of operation affords the potential of a straightforward solution: Neglecting thermal losses through the pin and the spindle that supports it, the rate of heat input to the workpiece is the product of the torque and the speed of rotation of the friction stir weld pin and, hence, of the spindle. Therefore, if one acquires and suitably processes data on torque and rotation and controls the torque, the rotation, or both, one should be able to control the heat input into the workpiece. In conventional practice in friction stir welding, one uses feedback control of the spindle motor to maintain a constant speed of rotation. According to the proposal, one would not maintain a constant speed of rotation: Instead, one would use feedback control to maintain a constant torque and would measure the speed of rotation while allowing it to vary. The torque exerted on the workpiece would be estimated as the product of (1) the torque-multiplication ratio of the spindle belt and/or gear drive, (2) the force measured by a load cell mechanically coupled to the spindle motor, and (3) the moment arm of the load cell. Hence, the output of the load cell would be used as a feedback signal for controlling the torque (see figure).

Venable, Richard↗
NASA NTRS2011

An Integrated Musculoskeletal Countermeasure Battery for Long-Duration Lunar Missions

During extended periods of skeletal unloading, losses in strength and density of the proximal femur will occur. In long-duration spaceflight, resistive exercise is used to replace the normal loads exerted on the spine and hip. At the present time, there is no conclusive evidence that hip bone loss has been prevented in this scenario. Our group has recently developed and clinically evaluated a multifunctional exercise system, the Combined Countermeasure Device (CCD). The CCD comprises a low-footprint Stuart Platform for lower-body resistance exercise and balance training, and a cardiovascular exercise bicycle. A consideration for resistance exercise was targeting of the hip abductor and adductor muscles, which attach directly at the hip and which should subject it to the largest loads. In our training study, we found that CCD exercise increased hip adductor and abductor strength, and modeling results suggest that this exercise exerts forces on the hip of approx. 4-6 body weights at 1g, compared to forces of approx.2.5 body weight y squatting exercise. In our current study, we hypothesize that abductor and adductor exercise will increase the density and strength of the proximal femur.

Lang, T. F.↗