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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

A survey of load methodologies for shuttle orbiter payloads

Loads methods currently being used to design shuttle orbiter payloads are summarized. Methods used for the design of payloads launched by expendable launch vehicles are described in historical perspective. Experiences gained from expendable launch vehicle payloads are used to develop methodologies for the space shuttle orbiter payloads. The objectives for the development of a new methodology for the shuttle payloads are to reduce the cost and schedule for the payload load analysis by decoupling the payload analysis from the launch vehicle to the maximum extent possible. Methods are described for payload member load estimation or obtaining upper bounds for dynamic loads, as well as load prediction or calculating actual transient member load time histories.

Chen, J. C.↗
NASA NTRS1981

A survey of load methodologies for shuttle orbiter payloads

Loads methods currently being used to design planetary spacecraft to be launched on the shuttle orbiter are summarized. Experiences gained from expendable launch vehicle payloads are used to develop methodologies for the space shuttle orbiter payloads. The objectives for the development of a new methodology for the shuttle payloads are to reduce the cost and schedule for the payload load analysis by decoupling the payload analysis from the launch vehicle to the maximum extent possible. Methods are described for payload member load estimation or obtaining upper bounds for dynamic loads, as well as load prediction or calculating actual transient member load time histories.

Chen, J. C.↗
NASA NTRS1979

Accelerated development and flight evaluation of active controls concepts for subsonic transport aircraft. Volume 1: Load alleviation/extended span development and flight tests

Active wing load alleviation to extend the wing span by 5.8 percent, giving a 3 percent reduction in cruise drag is covered. The active wing load alleviation used symmetric motions of the outboard ailerons for maneuver load control (MLC) and elastic mode suppression (EMS), and stabilizer motions for gust load alleviation (GLA). Slow maneuvers verified the MLC, and open and closed-loop flight frequency response tests verified the aircraft dynamic response to symmetric aileron and stabilizer drives as well as the active system performance. Flight tests in turbulence verified the effectiveness of the active controls in reducing gust-induced wing loads. It is concluded that active wing load alleviation/extended span is proven in the L-1011 and is ready for application to airline service; it is a very practical way to obtain the increased efficiency of a higher aspect ratio wing with minimum structural impact.

Johnston, J. F.↗
NASA NTRS1980

Spacecraft loads methodology - Transient vs. shock spectra method

The methodology for the establishment of spacecraft loads is strongly influenced by project constraints which include the cost, schedule and allowable weight. The most rigorous approach is the transient loads analysis which requires a composite mathematical model of the spacecraft and launch vehicle. The structural member loads for the entire composite structure are computed by applying the forcing functions, which represent various dynamic environments during the mission, to the composite model. Although this method ideally leads to a lightweight design, it is costly and time consuming due to complex interfaces involving many organizations. To reduce complexity and cost a shock spectra method has been used to design spacecraft structures. This method utilizes envelopes of shock spectra of launch vehicle accelerations obtained from analysis and/or flight measurements. Since only limited information on the launch vehicle model is involved in this process the design loads iteration cycle can be rapidly performed within the payload organization. In the present paper, these two methods will be evaluated by comparing the loads for several spacecraft. Flight measured loads will also be used in the evaluation.

Chen, J. C.↗
NASA NTRS1981

Unsteady environments and responses of the shuttle combined loads orbiter test

Both separate and combined wind tunnel and vibration shaker tests were conducted on two structural panels representative of the Shuttle orbiter in the NASA LaRC 8-foot transonic pressure tunnel (TPT) to determine the effects of combined loads on the thermal protection system (TPS). The primary objective of this test was to provide a combined full-scale load environment and realistic time history of the dynamic pressures, Mach numbers (through transonic), and dynamic structural responses of these panels. The panels were selected from orbiter locations where interactive load sources such as aerodynamic shock waves, turbulent boundary layers, strut-induced vorticity, and substrate deformation combined to provide high bonding loads between the TPS and the orbiter structure. The test panels for this program were highly instrumented with static and dynamic pressure gages, accelerometers, deflectometers, strain gages, Schileren and high-speed photography, and special instrumentation necessary to determine TPS/structure interface loads and tile motions. Two test specimens of each orbiter panel were utilized. Both were high-fidelity representations of the selected orbiter location. The first panel (calibration panel) for each test was utilized to calibrate the tunnel and shaker system as well as provide a data-gathering source for applied static and dynamic loads. The second panel (test panel) for each test was subjected to flight time exposures only so that TPS characteristics as a function of flight mission exposure could be determined. These tests were the last in a series that was suce6ssfully completed and necessary to certify the TPS prior to the first launching of the Shuttle.

P. H. Schuetz↗
NASA NTRS1983

Loads environment for payload/cargo integration

Space Shuttle users are required to design their payload to the Shuttle loads environment. This loads environment covers mission phases from prelaunch to landing. Transient response loads analyses are required for lift-off and landing events. Other mission events are analyzed statically because they result in payload loads that either change slowly or are lower than lift-off and landing loads. Response data from flight instrumentation located on the orbiter and payloads have been compared to preflight design conditions and to nominal predictions. The results have verified that the design loads envelop flight responses.

Frederick, D. H.↗
NASA NTRS1984

Large deflections of circular isotropic membranes subjected to arbitrary axisymmetric loading

Circular membranes with fixed peripheral edges, subjected to arbitrary axisymmetric loading are analyzed. A single governing differential equation in terms of radial stress is used. This nonlinear governing equation is solved using the finite difference method in conjunction with Newton-Raphson method. Three loading cases, namely (1) uniformly loaded membrane, (2) a membrane with uniform load over an inner portion, and (3) a membrane with ring load, are analyzed. Calculated central displacement and the central and edge radial stresses for uniformly loaded membrane, agree extremely well with the classical solution.

Kelkar, A.↗
NASA NTRS1984

Response of long shallow cylindrical panels to radial line loads

The large displacement static response of shallow orthotropic panels subjected to lateral loading is examined both theoretically and experimentally. The panels are circular cylindrical open shells which are also thin and long. The straight edges are simply supported at a fixed distance apart, and the curved edges are free. The lateral load is a spatially uniform line load acting along the generator direction of the cylinder, and is directed radially inward toward the center of curvature. The load induces a circumferential thrust, and the panel can, and does, snap-through to an inverted configuration at the buckling load. The effect of load position on the response is also examined. The test panels discussed in the paper are /(90/0)3/S graphite-epoxy laminates. Nominal dimensions are a radius of 60 in., a thickness of 0.060 in., and an arc length of 12 in. Very good agreement between theory and experiment is achieved.

Johnson, E. R.↗
NASA NTRS1985

Learjet Model 55 Wing Analysis with Landing Loads

The NASTRAN analysis was used to determine the impact of new landing loads on the Learjet Model 55 wing. These new landing loads were the result of a performance improvement effort to increase the landing weight of the aircraft to 18,000 lbs. from 17,000 lbs. and extend the life of the tires and brakes by incorporating larger tires and heavy duty brakes. Landing loads for the original 17,000 lb. airplane landing configuration were applied to the full airplane NASTRAN model. The analytical results were correlated with the strain gage data from the original landing load static tests. The landing loads for the 18,000 lb. airplane were applied to the full airplane NASTRAN model, and a comparison was made with the original Model 55 data. The results of this comparison enable Learjet to determine the difference in stress distribution in the wing due to these two different sets of landing loads.

Boroughs, R. R.↗
NASA NTRS1985

Planetary reorientation by surface loads

Non-hydrostatic concentrations of mass at the surface of the planet have been suggested as mechanisms of permanent reorientation for all of the terrestrial planets and for the Moon. In order for such a load to control planetary orientation, three conditions must be satisfied. The surface load must be non-hydrostatically supported; the surface load must be large compared to internal departures from a hydrostatic mass distribution; and the load must be large compared to hydrostatic departures of the planetary figure from a sphere. The third condition comes from the consideration that if the load is non-hydrostatically supported, then the same processes which support the load will also the hydrostatic figure.

Willemann, R. J.↗
NASA NTRS1985

Large deflections of circular isotropic membranes subjected to arbitrary axisymmetric loading

Circular membranes with fixed peripheral edges, subjected to arbitrary axisymmetric loading were analyzed. A single governing differential equation in terms of radial stress was used. This nonlinear governing equation was solved using the finite difference method in conjunction with Newton-Raphson method. Three loading cases, namely: (1) uniformly loaded membrane, (2) a membrane with uniform load over an inner portion, and (3) a membrane with ring load, were analyzed. Calculated central displacement and the central and edge radial stresses for uniformly loaded membrane, agreed extremely well with the classical solution.

Kelkar, A.↗
NASA NTRS1986

Analyzing Static Loading of Complex Structures

Critical loading conditions determined from analysis of each structural element. Automated Thrust Structures Loads and Stresses (ATLAS) system is series of programs developed to analyze elements of complex structure under static-loading conditions. ATLAS calculates internal loads, beam-bending loads, column- and web-buckling loads, beam and panel stresses, and beam-corner stresses. Programs written in FORTRAN IV and Assembler for batch execution.

Gallear, D. C.↗
NASA NTRS1986

Combined bearing and bypass loading on a graphite/epoxy laminate

A combined experimental and analytical study was conducted to determine the behavior of a graphite/epoxy laminate subjected to combined bearing and bypass loading. Single-fastener quasi-isotropic specimens were loaded at various bearing-bypass ratios until damage was produced at the fastener hole. Damage-onset strengths and damage modes were then analyzed using local hole-boundary stresses calculated by a finite-element analysis. The tension data showed the expected linear interaction for combined bearing and bypass loading with damage developing in the net-section tension mode. However, the compression bearing-bypass strengths showed an unexpected interaction involving the bearing mode. Compressive bypass loads reduced the bearing strength by decreasing the bolt-hole contact arc and thus increasing the severity of the bearing loads. The bearing stresses at the hole boundary were not accurately estimated by superposition of the stress components for separate bearing and bypass loading. However, superposition produced reasonably accurate estimates for tangential stresses especially near the specimen net-section.

Crews, J. H., Jr.↗
NASA NTRS1986

Effects of state recovery on creep buckling under variable loading

Structural alloys embody internal mechanisms that allow recovery of state with varying stress and elevated temperature, i.e., they can return to a softer state following periods of hardening. Such material behavior is known to strongly influence structural response under some important thermomechanical loadings, for example, that involving thermal ratchetting. The influence of dynamic and thermal recovery on the creep buckling of a column under variable loading is investigated. The column is taken as the idealized (Shanley) sandwich column. The constitutive model, unlike the commonly employed Norton creep model, incorporates a representation of both dynamic and thermal (state) recovery. The material parameters of the constitutive model are chosen to characterize Narloy Z, a representative copper alloy used in thrust nozzle liners of reusable rocket engines. Variable loading histories include rapid cyclic unloading/reloading sequences and intermittent reductions of load for extended periods of time; these are superimposed on a constant load. The calculated results show that state recovery significantly affects creep buckling under variable loading. Structural alloys embody internal mechanisms that allow recovery of state with varying stress and time.

Robinson, D. N.↗
NASA NTRS1985

Linear and nonlinear dynamic analysis of redundant load path bearingless rotor systems

The bearingless rotorcraft offers reduced weight, less complexity and superior flying qualities. Almost all the current industrial structural dynamic programs of conventional rotors which consist of single load path rotor blades employ the transfer matrix method to determine natural vibration characteristics because this method is ideally suited for one dimensional chain like structures. This method is extended to multiple load path rotor blades without resorting to an equivalent single load path approximation. Unlike the conventional blades, it isk necessary to introduce the axial-degree-of-freedom into the solution process to account for the differential axial displacements in the different load paths. With the present extension, the current rotor dynamic programs can be modified with relative ease to account for the multiple load paths without resorting to the equivalent single load path modeling. The results obtained by the transfer matrix method are validated by comparing with the finite element solutions. A differential stiffness matrix due to blade rotation is derived to facilitate the finite element solutions.

Murthy, V. R.↗
NASA NTRS1986

A compressive failure model for anisotropic plates with a cutout under compressive and shear loads

The paper introduces a failure model for laminated composite plates with a cutout under combined compressive and shear loads. The model is based on kinking failure of the load-carrying fibers around a cutout, and includes the effect of local shearing and compressive stresses. Comparison of predictions of the model with available experimental results for quasi-isotropic and orthotropic plates with a circular hole indicated a good agreement. Predictions for orthotropic plates under combined loading are compared with the predictions of a point-stress model. The present model indicates significant reductions in axial load-carrying capacity due to shearing loads for plates with principal axis of orthotropy oriented along the axial load direction. A gain in strength is achieved by rotating the axis of orthotropy to counteract the shearing stress, or by eliminating the compressive-shear deformation coupling.

Gurdal, Z.↗
NASA NTRS1986

Unsteady aerodynamic load estimates on turning vanes in the national full-scale aerodynamic complex

Unsteady aerodynamic design loads have been estimated for each of the vane sets in the National Full-Scale Aerodynamic Complex (NFAC). These loads include estimates of local loads over one vane section and global loads over an entire vane set. The analytical methods and computer programs used to estimate these loads are discussed. In addition, the important computer input parameters are defined and the rationale used to estimate them is discussed. Finally, numerical values are presented for both the computer input parameters and the calculated design loads for each vane set.

Norman, Thomas R.↗
NASA NTRS1986

Observations of fatigue crack growth rate and closure behavior in 7475-T731 aluminum under variable amplitude loading

Simultaneous measures of fatigue crack propagation rate and crack closure were taken from 7475-T731 aluminum alloy center cracked tensile specimens under variable amplitude loading conditions. Results indicate the presence of load interaction in a variety of repeated variable amplitude loading blocks. Load interaction results in retardation of the propagation rate for most loading blocks examined in the study. Closure did not explain observed delay behavior associated with high stress ratio and single peak overloads. Primary influences on the crack opening stress intensity level include the maximum stress intensity of the repeated loading block, the minimum stress intensity of the block, and the number of fatigue cycles between overloads of the block.

Turner, Charles C.↗