SEARCH · Engineering Papers

Results for “Displacement”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

NASA NTRS1978

Measurements of mixed-mode crack surface displacements and comparison with theory

A theoretical and an experimental technique is used to determine crack surface displacements under mixed-mode conditions. Crack surface displacements proved to be quite useful in mode 1 fracture analysis in that they are directly related to strain energy release rate and stress intensity factor. It is felt that similar relationships can be developed for the mixed-mode case. A boundary-integral method was developed for application to two-dimensional fracture mechanics problems. This technique was applied to the mixed-mode problem. A laser interferometry technique, for measurement of crack surface displacements under mixed-mode conditions, is presented. The experimental measurements are reported and the results of the two approaches are compared and discussed.

Altiero, N. J., Jr.↗

NASA NTRS1977

Displacement thickness distributions in transonic flows about 3-D wings

The transonic 3-D inviscid small-perturbation solution of Bailey and Ballhaus is combined with a finite-difference solution for Prandtl's boundary-layer equations in order to include viscous effects. The inviscid-viscous interaction is modeled by means of the displacement surface, which can be thought of as the effective body surface seen by the inviscid flow. Displacement thickness, lift, and pressure distributions resulting from the combined solution are presented for transonic flows about the RAE 101 A wing and a Lockheed transport wing, both at small angles of attack. The influence of changing arbitrarily the start of transition on the displacement surface and lift is discussed for the RAE wing flow.

Kordulla, W.↗

NASA NTRS1979

Optical correlation of surface displacement

A coherent optical correlation technique is used to measure surface displacements. In the event that the surface roughness of the test object is invariant during the object's translation, the correlation intensity peak remains constant. A simple relationship between the displacement of the surface and the displacement of the peak correlation signal is found and experimentally verified.

Owen, R. B.↗

NASA NTRS1980

Simultaneous muscle force and displacement transducer

A myocardial transducer for simultaneously measuring force and displacement within a very small area of myocardium is disclosed. The transducer comprised of an elongated body forked at one end to form an inverted Y shaped beam with each branch of the beam constituting a low compliant tine for penetrating the myocardium to a predetermined depth. Bonded to one of the low compliance tines is a small piezoresistive element for converting a force acting on the beam into an electrical signal. A third high compliant tine of the transducer, which measures displacement of the myocardium in a direction in line with the two low compliant tines, is of a length that just pierces the surface membrane. A small piezoresistive element is bonded to the third tine at its upper end where its bending is greatest. Displacement of the myocardium causes a deformation in curvature of the third tine, and the second small piezoresistive element bonded to the surface of its curved end converts its deformation into an electrical signal.

Feldstein, C.↗

NASA NTRS1982

Load-Displacement Measurement on Pin-Loaded Specimens

Tubes apply as displacement is registered by long armed, double-cantilever gage. Sharp points at ends of arms protrude through holes in tube walls and contact center of area of load applications. Method was devised for determining load point displacement accurately. No extraneous displacement fraction is present in measurement, and data-correction procedures are unnecessary.

Fisher, D. M.↗

NASA NTRS1980

Verification of elastic-wave static displacement in solids

The solution of the nonlinear differential equation which describes an initially sinusoidal finite-amplitude elastic wave propagating in a solid contains a static-displacement term in addition to the harmonic terms. The static-displacement amplitude is theoretically predicted to be proportional to the product of the squares of the driving-wave amplitude and the driving-wave frequency. The first experimental verification of the elastic-wave static displacement in a solid (the 111 direction of single-crystal germanium) is reported, and agreement is found with the theoretical predictions.

Cantrell, J. H., Jr.↗

NASA NTRS1981

Stress-intensity factors and crack-opening displacements for round compact specimens

An improved method of boundary collocation based on the complex variable analysis of Muskhelishvili (1953) is applied to the two-dimensional stress analysis of round compact specimens with pin-loaded holes. Stress intensity factors and crack opening displacements are calculated for various round compact specimens as a function of crack-length-to-specimen-width ratios. A wide-range equation for the stress intensity factors and equations for crack-surface displacements and load-point displacements are developed.

Newman, J. C., Jr.↗

NASA NTRS1983

Laser microspeckle technique in displacement measurement near a crack tip

The laser speckle method has been found quite useful in obtaining in-plane displacement measurements. It is especially useful if the displacement field in a small region can be effectively determined. By obtaining directly the speckle patterns at higher magnifications, a better distinction of the displacements in the vicinity of a crack tip is possible. In this short report some results are obtained and compared with those calculated from linear fracture mechanics and the finite element method for an aluminum crack.

Tang, Z. Q.↗

NASA NTRS1984

Cockpit Window Edge Proximity Effects on Judgements of Horizon Vertical Displacement

To quantify the influence of a spatially fixed edge on vertical displacement threshold, twenty-four males (12 pilots, 12 non-pilots) were presented a series of forced choice, paired comparison trials in which a 32 deg arc wide, thin, luminous horizontal stimulus line moved smoothly downward through five angles from a common starting position within a three second-long period. The five angles were 1.4, 1.7, 2, 2.3, and 2.6 deg. Each angle was presented paired with itself and the other four angles in all combinations in random order. For each pair of trials the observer had to choose which trial possessed the largest displacement. A confidence response also was made. The independent variable was the angular separation between the lower edge of a stable 'window' aperture through which the stimulus was seen to move and the lowest position attained by the stimulus. It was found that vertical displacement accuracy is inversely related to the angle separating the stimulus and the fixed window edge (p = .05). In addition, there is a strong tendency for pilot confidence to be lower than that of non-pilots for each of the three angular separations. These results are discussed in erms of selected cockpit features and as they relate to how pilots judge changes in aircraft pitch attitude.

Haines, R. F.↗

NASA NTRS1985

Pitch change thresholds as influenced by angular rate and duration of the apparent horizon's displacement

The displacement threshold (DT) during voluntary visual tracking of a line and during fixation of a stable spot located at the initial stimulus position was determined to help in the modeling pilot manual dynamics during the nose-up 'flare' maneuver. Forty-six observers made paired comparison, forced choice judgments of the maximal downward displacements of a horizontal line moving at various speeds for the durations of 0.25, 0.50, and 1.00 sec. The results indicated that the DT is significantly lower, the confidence is higher, and the number of errors and guesses is smaller when a fixation dot is present; moreover, increasing both the stimulus velocity and duration significantly improves the accuracy of displacement discrimination and increases mean confidence.

Haines, R. F.↗

NASA NTRS1985

Relative displacement measurements for two-body problems

While high-sensitivity moire interferometry is very effective for displacement measurements in continuous bodies, special difficulties arise with two-body problems. Fringes may become discontinuous at the boundary between the bodies and as a result the relative displacements cannot be extracted from the fringe patterns. In this work, flexible bridges are used between the bodies to provide a continuous path for fringe counting. The bridges are made of relatively low modulus material and have a low stiffness geometry, such that they deform under minimal load. The experimental methods used for obtaining relative displacement measurements in two-body problems are described for the two cases; dovetail joint in turbo-machinery, and thick adherend lap joint.

Post, D.↗

NASA NTRS1987

Sliding Capacitive Displacement Transducer

Simple circuit replaces bridge circuit. Sliding capacitive displacement transducer, capacitance varies linearly with displacement, enables use of simple circuit based on operational amplifier instead of complicated capacitance bridge. With new circuit, transducers as small as 0.05 in. (1.3 mm) square and 0.004 in. (0.1 mm) thick have produced output-voltage changes of about 200 mV per 0.005 in. (0.13 mm) of displacement. Piston-type transducer made quite small for installation in confined spaces.

Bryner, B. D.↗

NASA NTRS1987

Effects of joint rate and displacement constraints on stability regions

A block diagram showing plant dynamics in normal mode coordinates, a linear feedback controller with command limits, and actuator dynamics with rate and displacement limits is given. The objective is to examine the effects of joint rate and displacement saturation limits on the stability regions. An unstable short period dynamic model is transformed into normal mode coordinates and is augmented with actuator dynamics. A linear feedback controller is used to provide closed-loop stability. The stability with constrained actuator rate limits under varying bandwidth, displacement and command limits is examined.

Shrivastava, P. C.↗

NASA NTRS1986

An amplitude modulated laser system for distance and displacement measurement

A laser distance and displacement measurement system is being developed to monitor small displacements in large space structures for strain analysis and structural control. The reflected laser beam is focused on a detector and the detected signal is mixed with the reference. Small displacements are indicated by a change in modulation frequency which is adjusted to maintain quadrature between the received signal and the reference signal from the voltage-controlled oscillator in a phase-locked loop. Measurement of absolute distance is accomplished by sweeping the modulation frequency from a quadrature lock point to an adjacent lock point.

Rogowski, Robert S.↗

NASA NTRS1989

Broad band X-ray telescope (BBXRT) displacement monitor system (DMS) testing and calibration

NASA's shuttle-borne Broad Band X-Ray Telescope (BBXRT) consists of two glancing incidence imaging mirror assemblies mounted on an optical bench which is bolted to the primary structure of the instrument. The X-ray detectors are located in the focal plane of the mirror assemblies approximately 3.5 meters away. It is desirable to monitor the relative alignment of these components throughout ground testing, and to determine the magnitude of launch or thermally induced perturbations to the alignment during flight. The Displacement Monitor System (DMS) was designed to accomplish this task. This paper describes the design of the DMS, the development and optimization of the DMS calibration facility, and the characterization of the system. The characterization of the DMS includes environmental qualification, displacement vs output calibration over the operating temperature range, a detailed error analysis, and the generation of a calibration polynomial which utilizes DMS detector output and thermocouple data to optimize system performance. The DMS accuracy exceeded the requirements of a 15 arc second limit of error, and passed the stringent environmental tests. As such, the DMS is one of the first flight qualified displacement monitor systems with this accuracy to be flown in space.

Hagopian, John G.↗

NASA NTRS1990

Optimal displacement in apparent motion and quadrature models of motion sensing

A grating appears to move if it is displaced by some amount between two brief presentations, or between multiple successive presentations. A number of recent experiments have examined the influence of displacement size upon either the sensitivity to motion, or upon the induced motion aftereffect. Several recent motion models are based upon quadrature filters that respond in opposite quadrants in the spatiotemporal frequency plane. Predictions of the quadrature model are derived for both two-frame and multiframe displays. Quadrature models generally predict an optimal displacement of 1/4 cycle for two-frame displays, but in the multiframe case the prediction depends entirely on the frame rate.

Watson, Andrew B.↗

NASA NTRS1991

Measurements of fuselage skin strains and displacements near a longitudinal lap joint in a pressurized aircraft

Strains and displacements in a small area near a longitudinal lap joint in the fuselage skin of a B737 aircraft were measured during a pressurization cycle to a differential pressure of 6.2 psi while the aircraft was on the ground. It was found that hoop strains were higher than longitudinal strains at each location; membrane strains in the unreinforced skin were higher than in the joint; membrane strains in the hoop direction, as well as radial displacements, tended to be highest at the mid-bay location between skin reinforcements; significant bending in the hoop direction occurred in the joint and in the skin near the joint, and the bending was unsymmetrically distributed about the stringer at the middle of the joint; and radial displacements were unsymmetrically distributed across the lap joint. The interpretation of the strain gage data for locations on the bonded and riveted lap joint assumed that the joint did not contain disbonded areas.

Phillips, Edward P.↗

NASA NTRS1991

Displacement analysis of the interior walls of a pipe using panoramic holo-interferometry

Standard phase-displacement equations, used for both double exposure and real time holo-interferometry, are combined with the geometrical mapping and optical characteristics of panoramic annular lenses to accurately measure surface displacement on the interior wall of a pipe. In this approach, one panoramic annular lens is used to illuminate the surface with coherent light, and the resulting intensity distribution is holographically recorded through a second panoramic annular lens. Interference fringes are obtained in real-time by comparing holograms recorded before and after the pipe is displaced. The annular images and the holographic fringes are acquired and stored digitally in a computer system. Image transformation algorithms are applied to remove optical distortions in the holographic pattern and fringe loci are compared to those predicted on the basis of theory.

Gilbert, John A.↗