SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The first phase of a series of evaluations of a vision-based welding control sensor for the Space Shuttle Main Engine Robotic Welding System is described. The robotic welding system is presently under development at the Marshall Space Flight Center. This evaluation determines the standard control response parameters necessary for proper trajectory of the welding torch along the joint.
A method is disclosed for joining segments of the skin of an aircraft. The ends of the skin are positioned in close proximity or abutt each other. The skin is of constant thickness throughout the joint and is sandwiched between splice plates, which taper in thickness from the last to the first bolt rows in order to reduce the stiffness of the splice plate and thereby reduce the load transfer at the location where bypass loads are the highest.
Adhesives are commonly characterized only by their static strength even though they are used in structural joints that are subjected to fatigue loads. This paper reviews the relationship between static and fatigue strength for four different specimen types: single-lap-shear, edge-delamination, double cantilever beam, and cracked-lap-shear. It was found that the ratio of static strength to fatigue strength varied from 2.3 to 4.7, depending on the adhesive and specimen configuration.
A dedicated altimetry mission has been proposed to be conducted jointly by the U.S. National Aeronautics and Space Administration (NASA) and the French Centre National d'Etudes Spatiales (CNES). The mission goal would be focused on advancing the understanding of the general circulation of the global oceans. The mission would involve a U.S. satellite carrying U.S. and French sensors and launched by a French Ariane launch vehicle. Launch would occur in 1990, and the mission would be planned as an integral part of oceanographic programs being proposed under the auspices of the World Climate Research Program.
A combined experimental and analytical investigation of an adhesively-bonded composite joint was conducted to characterize the fracture mode dependence of cyclic debonding. The system studied consisted of graphite/epoxy adherends bonded with EC 3445 adhesive. Several types of specimens are tested which provide the cyclic debond growth rate measurements under various load conditions: mode 1, mixed mode 1 to 2, and mostly mode 2. This study shows that the total strain-energy-release rate is the governing factor for cyclic debonding.
Load-transfer capacities and resistances to fatigue increased. Series of high-strength bonded-stud designs developed for joining laminated wood to metal. Test results for bonded-stud designs demonstrated joint strengths approaching 10,000 to 12,000 psi (69 to 83 MPa) in ultimate strength and 5,000 psi (34 MPa) in high cycle fatigue strength of wood/epoxy composite achieved.
Report describes evaluation of factors influencing minimum-gap requirement for robot-welded joint. Evaluations part of series on vision-based welding-control system.
The mechanism which will be used on the space station to position the solar arrays and radiator panels for Sun pointing and Sun avoidance is described. The unique design features will be demonstrated on advanced development models of two of the joints being fabricated under contract to NASA-MSFC.
O-ring response and sealing in pressurized shell structures is examined. The study found that the key elements in the failure of the seal to be joint opening and rotation, assembly out of roundness, and O-ring seal response.
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.
A discussion of current standard durability prediction methodology for bonded joints is given. The influence of time-dependent adhesive properties on lap shear stress distributions and interfacial stresses is presented. It is suggested that these effects may be important in durability considerations. Test geometries from which better durability information can be obtained are outlined and a general mechanics approach for durability prediction is suggested.
A study was conducted to investigate the stress ratio effect on cyclic debond growth behavior in adhesively bonded composite joints. The system studied consisted of graphite/epoxy adherends bonded with a toughened epoxy adhesive. This study showed that the strain energy release rate range was the driving factor for cyclic debonding of the tested bonded system when subjected to cyclic loads with different stress ratios for both mode I and mixed mode I-II loadings.
Input gain weighting added to existing adaptive-control algorithm. Report discusses concept for adaptive control of rotations of various appended structures about joints on space station, with suppression of vibrations in both station and appendages. Concept relevant to such terrestrial applications as control of aircraft, suppression of vibrations in large buildings, and robotics.
The Combined Release and Radiation Effects Satellite (CRRES) program is a two-phase joint USAF/NASA program consisting of a low Earth orbit (LEO) phase and a geosynchronous transfer orbit (GTO) phase. The mission has been carefully planned to help clarify the geospace environment picture and its effects on space hardware, communications, and man. CRRES instruments were selected for synergism, accuracy, and applicability, and will be cross-calibrated for consistency. They will provide data to fill the gaps in geospace modeling data already obtained, and will update and correct existing models. The chemical release experiments and low altitude instruments will clarify the character of the ionosphere in low Earth orbit and the high altitude chemical release experiments will improve knowledge of how trapped particle populations behave out as far as synchronous altitudes. The ionospheric studies will lead to significantly improved Earth-space intercommunications.
To evaluate the potential for spacecraft damage caused by activation of pyrotechnic mechanisms, pyrotechnic shock tests were conducted on three configurations: pin-pullers on an orthogonal double Hopkinson bar arrangement, pin-pullers on a mock-up of the HALOE (Halogen Occultation Experiment) structure, and a section of separation joint on a single Hopkinson bar. Strains and accelerations were measured. The strains were converted to output stresses, forces and moments. Acceleration shock response spectra are presented for both acceleration- and force-time signals. The devices were attached to the Hopkinson bars with adaptors, which are typical of attachments used in practice. In order to predict the effect of the adaptors, finite element models of the adaptor-bar combinations were analyzed and results are presented with regard to grid size, time interval, and frequency range required to predict the response to pulses of 10 and 100 microsecond duration.
Aircraft and ground vehicle friction data collected during the Joint FAA/NASA Runway Friction Program under winter runway conditions are discussed and test results are summarized. The relationship between the different ground vehicle friction measurements obtained on compacted snow- and ice-covered conditions is defined together with the correlation to aircraft tire friction performance under similar runway conditions.
Problems of joining involving structural components made of aluminum alloys with boron-fiber reinforcements are discussed, giving attention to a diffusion-welding process. The tension characteristics and weight factors in the case of various types of welded joints are considered. Diffusion-welding equipment used in the experimental investigation is described. The strength characteristics obtained in various cases of weld and component design are examined, taking into account static and dynamic stresses.
An efficient Navier-Stokes analysis was successfully applied to simulate the complex flow field in the vicinity of a slot in a solid rocket motor with segment joints. The capability of the computer code to resolve the flow near solid surfaces without using a wall function assumption was demonstrated. In view of the complex nature of the flow field in the vicinity of the slot, this approach is considered essential. The results obtained from these calculations provide valuable design information, which would otherwise be extremely difficult to obtain. The results of the axisymmetric calculations indicate the presence of a region of reversed axial flow at the aft-edge of the slot and show the over-pressure in the slot to be only about 10 psi. The results of the asymmetric calculations indicate that a pressure asymmetry more than two diameters downstream of the slot has no noticeable effect on the flow field in the slot. They also indicate that the circumferential pressure differential caused in the slot due to failure of a 15 deg section of the castable inhibitor will be approximately 1 psi.