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  • STRUCTURAL MECHANICS  (7)
  • Mechanical Engineering  (4)
  • 1
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    Composite Structures and Materials Research at NASA Langley Research Center (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-28
    Description: A summary of recent composite structures and materials research at NASA Langley Research Center is presented. Fabrication research to develop low-cost automated robotic fabrication procedures for thermosetting and thermoplastic composite materials, and low-cost liquid molding processes for preformed textile materials is described. Robotic fabrication procedures discussed include ply-by-ply, cure-on-the-fly heated placement head and out-of-autoclave electron-beam cure methods for tow and tape thermosetting and thermoplastic materials. Liquid molding fabrication processes described include Resin Film Infusion (RFI), Resin Transfer Molding (RTM) and Vacuum-Assisted Resin Transfer Molding (VARTM). Results for a full-scale composite wing box are summarized to identify the performance of materials and structures fabricated with these low-cost fabrication methods.
    Keywords: Mechanical Engineering
    Type: Low Cost Composite Structures and Cost Effective Application of Titanium Alloys in Military Platforms; 17-1 - 17-11; RTO-MP-069(II)
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    NASA TECHNICAL REPORTS
  • 2
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    Active Blade Vibration Control Being Developed and Tested (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: Gas turbine engines are currently being designed to have increased performance, lower weight and manufacturing costs, and higher reliability. Consequently, turbomachinery components, such as turbine and compressor blades, have designs that are susceptible to new vibration problems and eventual in-service failure due to high-cycle fatigue. To address this problem, researchers at the NASA Glenn Research Center are developing and testing innovative active blade vibration control concepts. Preliminary results of using an active blade vibration control system, involving a rotor supported by an active magnetic bearing in Glenn's Dynamic Spin Rig, indicate promising results (see the photograph). Active blade vibration control was achieved using feedback of blade strain gauge signals within the magnetic bearing control loop. The vibration amplitude was reduced substantially (see the graphs). Also, vibration amplitude amplification was demonstrated; this could be used to enhance structural mode identification, if desired. These results were for a nonrotating two-bladed disk. Tests for rotating blades are planned. Current and future active blade vibration control research is planned to use a fully magnetically suspended rotor and smart materials. For the fully magnetically suspended rotor work, three magnetic bearings (two radial and one axial) will be used as actuators instead of one magnetic bearing. This will allow additional degrees of freedom to be used for control. For the smart materials work, control effectors located on and off the blade will be considered. Piezoelectric materials will be considered for on-the-blade actuation, and actuator placement on a stator vane, or other nearby structure, will be investigated for off-the-blade actuation. Initial work will focus on determining the feasibility of these methods by performing basic analysis and simple experiments involving feedback control.
    Keywords: Mechanical Engineering
    Type: Research and Technology 2002; NASA/TM-2003-211990
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    NASA TECHNICAL REPORTS
  • 3
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    Measurement and analysis of critical crack tip processes during fatigue crack growth (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The mechanics of fatigue crack growth under constant-amplitudes and variable-amplitude loading were examined. Critical loading histories involving relatively simple overload and overload/underload cycles were studied to provide a basic understanding of the underlying physical processes controlling crack growth. The material used for this study was 7091-T7E69, a powder metallurgy aluminum alloy. Local crack-tip parameters were measured at various times before, during, and after the overloads, these include crack-tip opening loads and displacements, and crack-tip strain fields. The latter were useed, in combination with the materials cyclic and monotonic stress-strain properties, to compute crack-tip residual stresses. The experimental results are also compared with analytical predictions obtained using the FAST-2 computer code. The sensitivity of the analytical model to constant-amplitude fatigue crack growth rate properties and to through-thickness constrain are studied.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-172597 , NAS 1.26:172597
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  • 4
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    Fatigue crack growth with single overload - Measurement and modeling (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: This paper compares experiments with an analytical model of fatigue crack growth under variable amplitude. The stereoimaging technique was used to measure displacements near the tips of fatigue cracks undergoing simple variations in load amplitude-single overloads and overload/underload combinations. Measured displacements were used to compute strains, and stresses were determined from the strains. Local values of crack driving force (Delta-K effective) were determined using both locally measured opening loads and crack tip opening displacements. Experimental results were compared with simulations made for the same load variation conditions using Newman's FAST-2 model. Residual stresses caused by overloads, crack opening loads, and growth retardation periods were compared.
    Keywords: STRUCTURAL MECHANICS
    Type: Effects of load and thermal histories on mechanical behavior of materials; Feb. 25, 26, 1987; Denver, CO; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Buckling of conical shell with local imperfections (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Small geometric imperfections in thin-walled shell structures can cause large reductions in buckling strength. Most imperfections found in structures are neither axisymmetric nor have the shape of buckling modes but rather occur locally. This report presents the results of a study of the effect of local imperfections on the critical buckling load of a specific axially compressed thin-walled conical shell. The buckling calculations were performed by using a two-dimensional shell analysis program referred to as the STAGS (Structural Analysis of General Shells) computer code, which has no axisymmetry restrictions. Results show that the buckling load found from a bifurcation buckling analysis is highly dependent on the circumferential arc length of the imperfection type studied. As the circumferential arc length of the imperfection is increased, a reduction of up to 50 percent of the critical load of the perfect shell can occur. The buckling load of the cone with an axisymmetric imperfections is nearly equal to the buckling load of imperfections which extended 60 deg or more around the circumference, but would give a highly conservative estimate of the buckling load of a shell with an imperfection of a more local nature.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-2991 , L-9331
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  • 6
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    Automated preliminary design of simplified wing structures to satisfy strength and flutter requirements (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A simple structural model of an aircraft wing is used to show the effects of strength (stress) and flutter requirements on the design of minimum-weight aircraft-wing structures. The wing is idealized as an isotropic sandwich plate with a variable cover thickness distribution and a variable depth between covers. Plate theory is used for the structural analysis, and piston theory is used for the unsteady aerodynamics in the flutter analysis. Mathematical programming techniques are used to find the minimum-weight cover thickness distribution which satisfies flutter, strength, and minimum-gage constraints. The method of solution, some sample results, and the computer program used to obtain these results are presented. The results indicate that the cover thickness distribution obtained when designing for the strength requirement alone may be quite different from the cover thickness distribution obtained when designing for either the flutter requirement alone or for both the strength and flutter requirements concurrently. This conclusion emphasizes the need for designing for both flutter and strength from the outset.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-6534 , L-7876
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  • 7
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    A Comparison Study of Magnetic Bearing Controllers for a Fully Suspended Dynamic Spin Rig (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: NASA Glenn Research Center (GRC) has developed a fully suspended magnetic bearing system for the Dynamic Spin Rig (DSR) that is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust bearing and the associated control system were integrated into the DSR to provide noncontact magnetic suspension and mechanical excitation of the 35 lb vertical rotor with blades to induce turbomachinery blade vibration. A simple proportional-integral-derivative (PID) controller with a special feature for multidirectional radial excitation worked very well to both support and shake the shaft with blades. However, more advanced controllers were developed and successfully tested to determine the optimal controller in terms of sensor and processing noise reduction, smaller rotor orbits, and energy savings for the system. The test results of a variety of controllers we demonstrated up to the rig's maximum allowable speed of 10,000 rpm are shown.
    Keywords: Mechanical Engineering
    Type: ISMB-8-Paper-0160 , 8th International Symposium on Magnetic Bearings; Aug 26, 2002 - Aug 28, 2002; Mito; Japan
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  • 8
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    Analytical investigation of an inflatable landing system having omnidirectional and multiple impact capabilities (1969)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Inflatable landing system investigated for impact normal to smooth surface
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-5236
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  • 9
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    Modelling and measurement of crack closure and crack growth following overloads and underloads (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Ignoring crack growth retardation following overloads can result in overly conservative life predictions in structures subjected to variable amplitude fatigue loading. Crack closure is believed to contribute to the crack growth retardation, although the specific closure mechanism is dabatable. The delay period and corresponding crack growth rate transients following overload and overload/underload cycles were systematically measured as a function of load ratio and overload magnitude. These responses are correlated in terms of the local 'driving force' for crack growth, i.e. the effective stress intensity factor range. Experimental results are compared with the predictions of a Dugdale-type (1960) crack closure model, and improvements in the model are suggested.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics (ISSN 0013-7944); 33; 6 19
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  • 10
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    Adaptive Variable Bias Magnetic Bearing Control (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Most magnetic bearing control schemes use a bias current with a superimposed control current to linearize the relationship between the control current and the force it delivers. With the existence of the bias current, even in no load conditions, there is always some power consumption. In aerospace applications, power consumption becomes an important concern. In response to this concern, an alternative magnetic bearing control method, called Adaptive Variable Bias Control (AVBC), has been developed and its performance examined. The AVBC operates primarily as a proportional-derivative controller with a relatively slow, bias current dependent, time-varying gain. The AVBC is shown to reduce electrical power loss, be nominally stable, and provide control performance similar to conventional bias control. Analytical, computer simulation, and experimental results are presented in this paper.
    Keywords: Mechanical Engineering
    Type: NASA/TM-1998-206975 , NAS 1.15:206975 , E-11127 , 1998 American Controls Conference; Jun 24, 1998 - Jun 26, 1998; Philadelphia, PA; United States
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