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Results for “BEAMS, CANTILEVER - VIBRATION”

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The influence of gyroscopic forces on the dynamic behavior of rotating blades

The question of divergent oscillatory stability of an axial turbomachine blade when the bladed rotor system is subjected to a forced precessional motion is studied by using two simplified models of the blade. The simplest (lumped) model is a point mass restrained by three orthogonal linear springs attached to the rotor. An improved distributed parameter model represents the blade by a uniform cantilever beam with bending in one plane. In both instances instability is shown to be strongly dependent upon the ratio of blade root radius to blade length and the magnitude of the rotor spin relative to the nonrotating blade natural frequency for realistic values of precession rate. Results are presented on augmented Campbell diagrams. Implications for design and operation are drawn as are the characteristics of needed future studies.

Sisto, F.↗
NASA NTRS1981

Addition polyimide adhesives containing ATBN and silicone elastomers

A study was conducted to determine the effects of added elastomers on the thermal stability, adhesive strength, and fracture toughness of LARC-13, a high-temperature addition polyimide adhesive. Various butadiene/acrylonitrile and silicon elastomers were incorporated into the polyimide resin either as physical polyblends, or by chemically reacting the elastomers with the polyimide backbone. Adhesive single lap-shear and T-peel strengths were measured before and after ageing at elevated temperature. A tapered double-cantilever beam specimen was used to determine the fracture toughness of the elastomer-modified polyimide adhesives.

Saint Clair, A. K.↗
NASA NTRS1980

Elastomer-toughened polyimide adhesives

A study has been conducted to determine the effects of added elastomers on the Tg, thermal stability, adhesive strength, and fracture toughness of LARC-13, a high-temperature addition polyimide adhesive. Various butadiene/acrylonitrile and silicone elastomers were incorporated into the polyimide resin (1) as physical polyblends, and (2) by chemically reacting the elastomers with the polyimide backbone. Adhesive single lap-shear and T-peel strengths were measured before and after aging at elevated temperature. A tapered double-cantilever beam specimen was used to determine the fracture toughness of the elastomer-modified polyimide adhesives.

Saint Clair, A. K.↗
NASA NTRS1981

DC calibration of the strain sensitivity of a single mode optical fiber interferometer

The strain sensitivity of an optical fiber interferometer developed for the detection of pulsed ultrasonic waves in solids has been calibrated. The optical paths in both signal and reference arms of the interferometer are through similar 2 m lengths of ITT-110 single mode fibers mode stripped by index matching at both ends and attached to opposite sides of a 30 cm plexiglas bar 0.3 cm thick. Light from the output ends of both fibers was superimposed to form an interference fringe pattern that was interrogated in the far field to give a signal proportional to the differential optical fiber path length. Strain sensitivity was determined by comparing data obtained by clamping and bending the bar at different lengths to simple cantilever beam theory. Calibration indicates a minimum theoretical detectable strain of less than 10 to the -10.

Claus, R. O.↗
NASA NTRS1981

DC calibration of the strain sensitivity of a single mode optical fiber interferometer

The strain sensitivity of an optical fiber interferometer developed for the detection of pulsed ultrasonic waves in solids was calibrated. Light from the output ends of both fibers was superimposed to form an interference fringe pattern that was interrogated in the far field to give a signal proportional to the differential optical fiber path length. Strain sensitivity is determined by comparing data obtained by clamping and bending the bar at different lengths to simple cantilever beam theory. A minimum theoretical detectable strain of less than 10 to the minus 10th power is indicated.

Claus, R. O.↗
NASA NTRS1980

Behavior of damaged graphite/epoxy laminates under compression loading

The influence of three different resin systems on the damage tolerance of graphite/polymer laminates was evaluated. Testing consisted of both static compression and cyclic compression evaluation of 10.2 by 15.2 by 0.5 cm (4 by 6 by 0.2 in) laminates with circular holes, simulated delaminations, and low velocity impact. Damage growth under steadily increasing compression and cyclic compression loading was monitored. Damage size and impact-induced failures for the three materials were compared. Of the three material systems evaluated, the one most tolerant to impact damage exhibited the least delamination within the cross section due to impact, the highest transverse tension strain to failure, and the largest crack opening force, as determined from double cantilever beam tests.

Byers, B. A.↗
NASA NTRS1982

The influence of Coriolis forces on gyroscopic motion of spinning blades

Turbomachine blades on spinning and precessing rotors experience gyroscopically induced instabilities and forcing. With vehicle-mounted turbomachines, either constant or harmonic precession occurs, depending on vehicle or mount motion. Responses of uniform cantilever beams at arbitrary stagger, subjected to the noted rotor motion, are predicted in both self-excited and forced-excitation modes taking into account Coriolis acceleration.

Sisto, F.↗
NASA NTRS1982

A simple test for the interlaminar fracture toughness of composites

A simple test method for the measurement of delamination resistance is assessed through its application to 11-ply graphite-epoxy laminates whose matrices employ the F185 and 205 resins. The F185 resin has the same base epoxy as the 205, to which liquid and solid elastomers have been added. The critical value of the mixed mode energy release rate, calculated from a closed form equation employing nominal strain measurements from the onset of edge delamination, show that addition of the elastomers to the base epoxy increases interlaminar fracture toughness. Comparison of these results with those of width-tapered double cantilever beam (WTDCB) test data for the two materials shows a similar strain energy release rate, establishing the accuracy of the novel method. Both tests are found to be needed, however, for the quantitative characterization of interlaminar fracture toughness.

Obrien, T. K.↗
NASA NTRS1981

Miniature drag-force anemometer

A miniature drag-force anemometer is described which is capable of measuring unsteady as well as steady-state velocity head and flow direction. It consists of a cantilevered beam with strain gages located at the base of the beam as the force measuring element. The dynamics of the beam are like those of a lightly damped second-order system with a natural frequency as high as 40 kilohertz depending on beam geometry and material. The anemometer can be used in both forward and reversed flow. Anemometer characteristics and several designs are presented along with discussions of several applications.

Krause, L. N.↗
NASA NTRS1983

Performance of a quantitative study of instability-related delamination growth

An experimental program was conducted to quantify instability-induced imbedded delamination growth. Static tests on double cantilever beam (DCB) specimens yielded the critical mode 1 strain energy release rate (G sub 1 C) for T300/5208 graphite/epoxy. Static tests on mixed mode cracked lap shear (CLS) specimens, and a nonlinear finite element analysis (NFEA) of the CLS specimen to separate mode 1 and mode 2 effects, yielded the critical mode 2 strain energy release rate (G sub 2 C) for T300/5208. Constant amplitude fatigue tests on DCB and CLS specimens, along with the NFEA results on CLS specimens, quantified mode 1 and mode 2 contributions to delamination growth rate. Fatigue tests were conducted at a frequency (omega) of 10 Hertz, maintaining the minimum to maximum cyclic load ratio (R) at 0.05. Static compression and constant amplitude compression fatigue tests were also conducted on specimens with imbedded through the width (ITTW) delaminations. Kapton imbeddments were located below 3, 4 or 6 plies in a 64-ply laminate, during layup, to simulate ITTW delaminations.

Ramkumar, R. L.↗
NASA NTRS1983

Design of dry-friction dampers for turbine blades

A study is conducted of turbine blade forced response, where the blade has been modeled as a cantilever beam with a generally dry friction damper attached, and where the minimization of blade root strain as the excitation frequency is varied over a given range is the criterion for the evaluation of the effectiveness of the dry friction damper. Attempts are made to determine the location of the damper configuration best satisfying the design criterion, together with the best damping force (assuming that the damper location has been fixed). Results suggest that there need not be an optimal value for the damping force, or an optimal location for the dry friction damper, although there is a range of values which should be avoided.

Ancona, W.↗
NASA NTRS1984

Approximation techniques for parameter estimation and feedback control for distributed models of large flexible structures

Approximation ideas are discussed that can be used in parameter estimation and feedback control for Euler-Bernoulli models of elastic systems. Focusing on parameter estimation problems, ways by which one can obtain convergence results for cubic spline based schemes for hybrid models involving an elastic cantilevered beam with tip mass and base acceleration are outlined. Sample numerical findings are also presented.

Banks, H. T.↗
NASA NTRS1983

Interlaminar fracture toughness of composites. II - Refinement of the edge delamination test and application to thermoplastics

The mixed mode interlaminar fracture toughness, G(c), is obtained for the two thermoplastic matrices UDEL P1700 polysulfone and ULTEM polyetherimide by means of edge delamination tensile (EDT) tests on unnotched, eleven-ply graphite fiber reinforced composite specimens. A novel method is used to obtain the stiffness parameter employed in the closed form equation for the calculation of G(c), decreasing the number of stiffness measurements required and simplifying the calculations. The G(Ic) values from double cantilever beam (DCB) measurements on composites of the two thermoplastics were similar to each other, but slightly higher than the G(c) data obtained by EDT. Interfacial resin/fiber failures predominated in both the EDT and DCB tests.

Johnston, N. J.↗
NASA NTRS1983

Dynamic fracture toughness of glass

Experimentally determined dynamic crack propagation histories in wedge-loaded, modified tapered, and rectangular double cantilever beam specimens were used to drive a dynamic finite element code in its generation phase. The resultant dynamic fracture toughness versus crack velocity relation, during the initial crack acceleration phase of these dynamic fracture specimens, was erratic but followed the standard Gamma-shaped curves of brittle polymers and metals during subsequent crack propagation at terminal velocity and crack deceleration phases. The distinct initiation phase of dynamic crack propagation, which was not observed in dynamic fracture of brittle polymer and metal specimens, is attributed to the lower stored energy in the glass specimen.

Kobayashi, A. S.↗
NASA NTRS1984

Characterizing Delamination Resistance of Toughened Resin Composites

The delamination resistance of toughened resin composites was studied. Both the edge delamination test (EDT) and the double-cantilever-beam (DCB) test provided a useful ranking of improvements in delamination resistance between brittle and tough resin composites. Several layups were designed for the edge delamination test to cover a wide range of mixed-mode conditions. The DCB and the various layups of the EDT were then used to characterize the interlaminar fracture behavior of brittle and toughened resin composites subjected to both static and cyclic loading.

Obrien, T. K.↗
NASA NTRS1985

Characterization of mode 1 and mixed-mode failure of adhesive bonds between composite adherends

A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

Mall, S.↗
NASA NTRS1985

Stress intensity factor in a tapered specimen

The general problem of a tapered specimen containing an edge crack is formulated in terms of a system of singular integral equations. The equations are solved and the stress intensity factor is calculated for a compact and for a slender tapered specimen, the latter simulating the double cantilever beam. The results are obtained primarily for a pair of concentrated forces and for crack surface wedge forces. The stress intensity factors are also obtained for a long strip under uniform tension which contains inclined edge cracks.

Xue-Hui, L.↗
NASA NTRS1985

Approximation Techniques for Parameter Estimation and Feedback Control for Distributed Models of Large Flexible Structures

Approximation ideas that can be used in parameter estimation and feedback control for Euler-Bernoulli models of elastic systems are discussed. Focusing on parameter estimation problems, the authors outline how one can obtain convergence results for cubic spline-based schemes for hybrid models involving an elastic cantilevered beam with tip mass and base acceleration. Sample numerical findings are also presented.

Banks, H. T.↗