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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Torque-Limiting Infinitely-Variable CAM Release Mechanism for a Rotatable Joint

The invention relates to a mechanism for permitting convenient manual or servo-powered control of a boom assembly, which is rotatably positionable about yaw and pitch axes by means of releasably locking, yaw and pitch torque-limiting mechanisms, each of which may be locked, unlocked, and positioned by respective yaw and pitch levers. The boom may be longitudinally projected and withdrawn by rotating a boom extension/retraction crank. Torque limiting is provided by spring loaded clutch mechanisms, whereby positioning forces applied to the handles are effective to move the boom unless overcome by greater opposing forces, sufficient to overcome the torque applied by the torque limiting clutch mechanisms. In operation, a structure positionable by the invention (e.g., and end-effector or robot arm) may be rotatably moved about yaw and pitch axes by moving a selected one of the three levers.

Moetteli, John B.↗
NASA NTRS2011

Robotic Scaffolds for Tissue Engineering and Organ Growth

The aim of tissue engineering (TE) is to restore tissue and organ functions with minimal host rejection. TE is seen as a future solution to solve the crisis of donor organs for transplant, which faces a shortage expected only to increase in the future. In this innovation, a flexible and configurable scaffold has been conceived that mechanically stresses cells that are seeded on it, stimulating them to increased growth. The influence of mechanical stress/ loading on cell growth has been observed on all forms of cells. For example, for cartilages, studies in animals, tissue explants, and engineered tissue scaffolds have all shown that cartilage cells (chondrocytes) modify their extracellular matrix in response to loading. The chondrocyte EMC production response to dynamics of the physical environment (in vivo cartilage development) illustrates a clear benefit (better growth) when stressed. It has been shown that static and dynamic compression regulates PRG4 biosynthesis by cartilage explants. Mechanical tissue stimulation is beneficial and (flexible) scaffolds with movable components, which are able to induce mechanical stimulation, offer advantages over the fixed, rigid scaffold design. In addition to improved cell growth from physical/mechanical stimulation, additional benefits include the ability to increase in size while preserving shape, or changing shape. By making scaffolds flexible, allowing relative movement between their components, adding sensing (e.g., for detecting response of cells to drug release and to mechanical actions), building controls for drug release and movement, and building even simple algorithms for mapping sensing to action, these structures can actually be made into biocompatible and biodegradable robots. Treating them as robots is a perspective shift that may offer advantages in the design and exploitation of these structures of the future.

Stoica, Adrian↗
NASA NTRS1989

Composite laminate free-edge reinforcement with U-shaped caps. I - Stress analysis. II - Theoretical-experimental correlation

The present generalized plane-strain FEM analysis for the prediction of interlaminar normal stress reduction when a U-shaped cap is bonded to the edge of a composite laminate gives attention to the highly variable transverse stresses near the free edge, cap length and thickness, and a gap under the cap due to the manufacturing process. The load-transfer mechanism between cap and laminate is found to be strain-compatibility, rather than shear lag. In the second part of this work, the three-dimensional composite material failure criteria are used in a progressive laminate failure analysis to predict failure loads of laminates with different edge-cap designs; symmetric 11-layer graphite-epoxy laminates with a one-layer cap of kevlar-epoxy are shown to carry 130-140 percent greater loading than uncapped laminates, under static tensile and tension-tension fatigue loading.

Howard, W. E.↗
NASA NTRS1991

Contact dynamics testing of automated three-point docking mechanism

An evaluation of an OMV docking mechanism, based on an adaptation of the Shuttle Flight Support System Pallet Berthing Mechanism was completed. The mechanism uses automatically actuated motorized latches to engage towel bars on the target satellite. LED sensors establish the towel bar position within the capture envelope and the latch capture commands are issued. Then, locking pawls engage the bar, locking and pre-loading the mechanism. Two series of tests were conducted to test nominal and failure mode captures and to evaluate design parameters such as LED sensor locations, automatic closure algorithms, latch closure velocity, position/velocity entry envelopes, and closure method. The first test series involved single latch testing on the Flat Floor Facility, the 6 DOF Facility, and an analytic simulation model. The intent was to compare results in order to validate the various facilities. Reasonably good agreement was achieved. The second test series repeated the single latch testing on the refurbished 6 DOF Facility to validate the facility modifications. The individual latches were tested under free-drift conditions for functionality and performance. Next, the three-latch configuration underwent parametric testing. Test results validated the improved fidelity of the 6 DOF Facility and verified successful docking at the required entry velocity. The tests determined the 'best' design parameter definitions and concluded that the locking pawls should not lock until all three latches completely close.

Rourke, Kenneth H.↗
NASA NTRS1988

Dynamic remapping of parallel computations with varying resource demands

The issue of deciding when to invoke a global load remapping mechanism is studied. Such a decision policy must effectively weigh the costs of remapping against the performance benefits, and should be general enough to apply automatically to a wide range of computations. The authors propose a general mapping decision heuristic, then study its effectiveness and its anticipated behavior on two very different models of load evolution. Assuming only that the remapping cost is known, this policy dynamically minimizes system degradation (including the cost of remapping) for each computation step. This policy is quite simple, choosing to remap when the first local minimum in the degradation function is detected. Simulations show that the decision obtained provides significantly better performance than that achieved by never remapping. The authors also observe that the average intermapping frequency is quite close to the optimal fixed remapping frequency.

Nicol, David M.↗
NASA NTRS2005

Mechanical Properties of Nanostructured Materials Determined Through Molecular Modeling Techniques

The potential for gains in material properties over conventional materials has motivated an effort to develop novel nanostructured materials for aerospace applications. These novel materials typically consist of a polymer matrix reinforced with particles on the nanometer length scale. In this study, molecular modeling is used to construct fully atomistic models of a carbon nanotube embedded in an epoxy polymer matrix. Functionalization of the nanotube which consists of the introduction of direct chemical bonding between the polymer matrix and the nanotube, hence providing a load transfer mechanism, is systematically varied. The relative effectiveness of functionalization in a nanostructured material may depend on a variety of factors related to the details of the chemical bonding and the polymer structure at the nanotube-polymer interface. The objective of this modeling is to determine what influence the details of functionalization of the carbon nanotube with the polymer matrix has on the resulting mechanical properties. By considering a range of degree of functionalization, the structure-property relationships of these materials is examined and mechanical properties of these models are calculated using standard techniques.

Clancy, Thomas C.↗
NASA NTRS2008

10.2 Thermal-Structural Testing

Objective: Test a C/SiC Ruddervator Subcomponent under relevant thermal, mechanical & dynamic loading a) Thermal-structural mission cycling for re-entry and hypersonic cruise conditions; b) High-temperature modal survey to study the effect of heating on mode shapes, natural frequencies and damping. Supports NASA ARMD Hypersonics Material & Structures Program. Partners: NASA Dryden / Langley / Glenn, Lockheed-Martin, Materials Research & Design, GE CCP Test Phases - Phase 1: Acoustic-Vibration Testing (LaRC) completed - Phase 2: Thermal-Mechanical Testing (DFRC) in assembly - Phase 3: Mechanical Testing (DFRC) in assembly

Hudson, Larry D.↗
NASA NTRS2003

Ventricular filling slows epicardial conduction and increases action potential duration in an optical mapping study of the isolated rabbit heart

INTRODUCTION: Mechanical stimulation can induce electrophysiologic changes in cardiac myocytes, but how mechanoelectric feedback in the intact heart affects action potential propagation remains unclear. METHODS AND RESULTS: Changes in action potential propagation and repolarization with increased left ventricular end-diastolic pressure from 0 to 30 mmHg were investigated using optical mapping in isolated perfused rabbit hearts. With respect to 0 mmHg, epicardial strain at 30 mmHg in the anterior left ventricle averaged 0.040 +/- 0.004 in the muscle fiber direction and 0.032 +/- 0.006 in the cross-fiber direction. An increase in ventricular loading increased average epicardial activation time by 25%+/- 3% (P < 0.0001) and correspondingly decreased average apparent surface conduction velocity by 16%+/- 7% (P = 0.007). Ventricular loading did not significantly alter action potential duration at 20% repolarization (APD20) but did at 80% repolarization (APD80), from 179 +/- 7 msec to 207 +/- 5 msec (P < 0.0001). The dispersion of APD20 was decreased with loading from 19 +/- 2 msec to 13 +/- 2 msec (P = 0.024), whereas the dispersion of APD80 was not significantly changed. These electrophysiologic changes with ventricular loading were not affected by the nonspecific stretch-activated channel blocker streptomycin (200 microM) and were not attributable to changes in myocardial perfusion or the presence of an electromechanical decoupling agent (butanedione monoxime) during optical mapping. CONCLUSION: Acute loading of the left ventricle of the isolated rabbit heart decreased apparent epicardial conduction velocity and increased action potential duration by a load-dependent mechanism that may not involve stretch-activated channels.

NASA Program Biomedical Research and Countermeasur↗
NASA NTRS1986

Vibration and structureborne noise in space station

Analytical models and computer programs for structural response calculations under action of mechanical point loads were developed for single wall shells (composite or aluminum), double wall shells (composite or aluminum), and single wall or double wall circular plates (aluminum). The design configuration of the habitability modules of the space station concept are expected to be discretely stiffened cylindrical shells with truncated cone type end caps or flat but stiffened circular end plates. Analytical formulations and response calculations were performed for the case where the stiffened shell is represented by an orthotropic shell model. The natural frequencies can be calculated. For application to low frequency (below 1000Hz) vibrations and noise generation, such a model might be adequate to evaluate vibration and noise transmission characteristics of space station habitability modules. Parametric studies are now being performed to assess interior noise environment inside a habitability module to mechanically induced vibrations.

Vaicaitis, R.↗
NASA NTRS1977

Load regulating latch

A load regulating mechanical latch is described that has a pivotally mounted latch element having a hook-shaped end with a strike roller-engaging laterally open hook for engaging a stationary strike roller. The latch element or hook is pivotally mounted in a clevis end of an elongated latch stem that is adapted for axial movement through an opening in a support plate or bracket mounted to a structural member. A coil spring is disposed over and around the extending latch stem and the lower end of the coil spring engages the support bracket. A thrust washer is removably attached to the other end of the latch stem and engages the other end of the coil spring and compresses the coil spring thereby preloading the spring and the latch element carried by the latch stem. The hook-shaped latch element has a limited degree of axial travel for loading caused by structural distortion which may change the relative positions of the latch element hook and the strike roller. Means are also provided to permit limited tilt of the latch element due to loading of the hook.

Appleberry, W. T.↗
NASA NTRS1972

Fluid operated quick release mechanism

Gas operated release mechanism releases load by fluid pressure to provide positive action quick release. Method can be used with large loads and is useful in repetitive cycling functions where shear pins and similar devices would be cumbersome.

Brown, R. A.↗
NASA NTRS1973

Fiber composite materials: A survey of fiber matrix interface mechanics

Report is described which discusses mechanism of load transfer from matrix to fiber through interface and effects of interface on composite structural integrity. Theoretical considerations are supplemented with experimental data. General trends and significant points are illustrated graphically.

Chamis, C. C.↗
NASA NTRS1973

Structural control interaction

The basic guidance and control concepts that lead to structural control interaction and structural dynamic loads are identified. Space vehicle ascent flight load sources and the load relieving mechanism are discussed, along with the the characteristics and special problems of both present and future space vehicles including launch vehicles, orbiting vehicles, and the Space Shuttle flyback vehicle. The special dynamics and control analyses and test problems apparent at this time are summarized.

Ryan, R. S.↗
NASA NTRS1973

Erythrocyte volume in acidified venous blood from exercising limbs.

Five male volunteers performed arm exercises in the sitting position by cranking the pedals of a bicycle ergometer at 50 revolutions per min. The initial mechanical work load of 0 kgm/min was increased every minute by 75 kgm/min until exhaustion occurred. The data obtained show a significant acidification of the venous blood from the working arms and a substantial increase in venous pCO2 during this type of muscular activity. However, the erythrocyte volume remained unaltered during the exercise.

Van Beaumont, W.↗
NASA NTRS1974

Mechanical coupling for high cyclic loading

One-piece cylindrical coupling with ""necked-down'' regions at each end form flexures allowing small misalignments between actuator and load. Coupling has zero backlash, low mass, close spacing between actuator and load, high stiffness in direction of motion, and allowance for misalignments and deflections without causing high side loading on components.

Dustin, M. O.↗
NASA NTRS1975

Opto-mechanical subsystem of a 10 micrometer wavelength receiver terminal. Waveguide laser local oscillator. Servo system

An engineering model opto-mechanical subsystem for a 10.6-micrometer laser heterodyne receiver is developed, and a CO2 waveguide local oscillator and servo electronics are provided for the receiver. Design goals are presented for the subsystems and overall package design is described. Thermal and mechanical distortion loading tests were performed and the results are included.

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