Effect of longitudinal or inplane deformation and inertia on the large amplitude flexural vibrations of slender beams and thin plates
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Raju, I. S.↗
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The dynamic flexural response of propeller blades
The determination of the torsional constants of three blade models having NACA four-digit symmetrical airfoil cross sections is presented. Values were obtained for these models analytically and experimentally. Results were also obtained for three other models having rectangular, elliptical, and parabolic cross sections. Complete modal analyses were performed for five blade models. The identification of modal parameters was done for cases when the blades were modeled as either undamped or damped multi-degree-of-freedom systems. For the experimental phase of this study, the modal testing was performed using a Dual Channel FFT analyzer and an impact hammer (which produced an impulsive excitation). The natural frequency and damping of each mode in the frequency range up to 2 kHz were measured. A small computer code was developed to calculate the dynamic response of the blade models for comparison with the experimental results. A comparison of the undamped and damped cases was made for all five blade models at the instant of maximum excitation force. The program was capable of handling models where the excitation forces were distributed arbitrarily along the length of the blade.
Djordjevic, S. Z.↗
Constraints on the structure of the Himalaya from an analysis of gravity anomalies and a flexural model of the lithosphere
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Lyon-Caen, H.↗
Unidirectional flexural pivot
A pair of generally coaxial mutually rotatable cylindrical outer ring members are held in spaced-apart relationship by three parallelogram-shaped, relatively thin, flexible, flat planar spring elements. These spring elements are substantially inextensible in length and are joined to the inside of the outer ring members and held in position by arcuate inner ring segments, three for each outer ring members, which respectively span an arc of substantially 120. The parallelogram shape of the spring elements provides a slanted interconnection between the outer ring members. The direction of slant, moreover, determines in which direction the spring elements can flex or bend unidirectionally to relieve the compression stress imparted thereto by any mutual angular rotation of the outer ring members.
Bahiman, H.↗
Dynamic stress analysis of smooth and notched fiber composite flexural specimens
A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.
Murthy, P. L. N.↗
Flexure of the continental lithosphere beneath Apennine and Carpathian foredeep basins
The preservation of foredeep basins after an associated mountain belt has been greatly reduced by erosion suggests that an additional load must act on the subducted slab's lithosphere independently of topography. This hypothesis is presently tested for the case of young orogenic belts, through the construction of transects through the Apennine and outer Carpathian thrust belts of the Mediterranean region. A simple elastic model is used to show that the topographic loads present along the transects are not sufficient to cause the observed plate deflection, suggesting that an additional load or downward force is acting on the plate to generate the plate deflection observed. It is proposed that this extra load is due either to the negative buoyancy contrast between the subducted slab and the asthenosphere, or to the crustal structure's modification by backarc rifling in the hinterland.
Royden, L.↗
Flexure of the North American lithosphere above the subducted Mendocino fracture zone and the formation of east-west faults in the transverse ranges
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Glazner, A. F.↗
Gravity anomalies and flexure of the Brazilian Shield beneath the Bolivian Andes
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Lyon-Caen, H.↗
Possible role of crustal flexure in the initial detachment of extensional allochthons
The existence of low-angle normal faults indicates that the ratio of shear stress (TAU) to normal stress (sigma sub N) needed to cause slip on faults is substantially less than would be predicted based on experimental data. Because the tensional strength of rock at a large scale is exceedingly low, the upper plate of a low-angle normal fault cannot be pulled down the fault ramp, but must be driven down it by its own weight. The active or recently active Sevier Desert detachment fault in western Utah dips regionally at 12 deg. The radio of shear stress to normal stress due to the weight of the upper plate on a 12 deg dipping fault surface is 0.2. In contrast, laboratory experiments indicate that slip on fracture surfaces occurs with almost all rock types when (tau/sigma) reaches values of 0.6 to 0.85, corresponding to normal-fault dips of 30 deg to 40 deg. Seismological data indicate that low deviatoric stresses are associated with movement on faults of other geometrics and are not unique to low-angle normal faults. It thus appears that approximately planar fault zones with surface areas of hundreds to thousands of square kilometers have different mechanical properties than would be predicted based on laboratory studies of fractured rock. Modeling of stresses indicates that deviatoric stresses greater than 5kb exist and are sustainable in oceanic lithosphere, and that failure occurs when tau/sigma sub N approaches 0.6 to 0.85.
Spencer, J. E.↗
Dynamic stress analysis of smooth and notched fiber composite flexural specimens
A detailed analysis of the dynamic stress field in smooth and notched fiber composite (Charpy-type) specimens is reported in this paper. The analysis is performed with the aid of the direct transient response analysis solution sequence of MSC/NASTRAN. Three unidirectional composites were chosen for the study. They are S-Glass/Epoxy, Kevlar/Epoxy and T-300/Epoxy composite systems. The specimens are subjected to an impact load which is modeled as a triangular impulse with a maximum of 2000 lb and a duration of 1 ms. The results are compared with those of static analysis of the specimens subjected to a peak load of 2000 lb. For the geometry and type of materials studied, the static analysis results gave close conservative estimates for the dynamic stresses. Another interesting inference from the study is that the impact induced effects are felt by S-Glass/Epoxy specimens sooner than Kevlar/Epoxy or T-300/Epoxy specimens.
Murthy, P. L. N.↗
Flexurally-resisted uplift of the Tharsis Province, Mars
The tectonic style of Mars is dominated by vertical motion, perhaps more than any of the terrestrial planets. The imprint of this tectonic activity has left a surface widely faulted even though younger volcanism has masked the expression of tectonism in many places. Geological activity associated with the Tharsis and, to a lesser extent, Elysium provinces is responsible for a significant portion of this faulting, while the origins of the remaining features are enigmatic in many cases. The origin and evolution of the Tharsis and Elysium provinces, in terms of their great elevation, volcanic activity, and tectonic style, has sparked intense debate over the last fifteen years. Central to these discussions are the relative roles of structural uplift and volcanic construction in the creation of immense topographic relief. For example, it is argued that the presence of very old and cratered terrain high on the Tharsis rise, in the vicinity of Claritas Fossae, points to structural uplift of an ancient crust. Others have pointed out, however, that there is no reason that this terrain could not be of volcanic origin and thus part of the constructional mechanism.
Phillips, R. J.↗
Nonlinear flexure and torsion of rotating beams, with application to helicopter rotor blades. I - Formulation. II - Response and stability results
The dynamic response and aeroelastic stability of rotating beams such as helicopter blades is investigated analytically. The Hamilton principle is used to formulate the equations of motion for extensional and inextensional beams with precone angles and variable pitch angles, taking higher-order nonlinearities into account. The derivation of the equations and their approximate solution by a Galerkin procedure are explained in detail, and numerical results of equilibrium solutions and stability analyses are presented graphically.
Crespo Da Silva, M. R. M.↗
Active control of flexural vibrations in beams
An analytical model of the feedback control system which estimates the voltage generated by the piezoelectric sensor as a function of the dynamic stress at the sensor location and the force exerted by the driver piezoelectric as a function of signal gain is developed. The analytical results are compared to measured results for a cantilever beam excited to vibrate in its first natural mode. The estimated increase in the first mode damping factor is in good agreement with the measured results.
Gerhold, Carl H.↗
Comparison of Weibull strength parameters from flexure and spin tests of brittle materials
Fracture data from five series of four point bend tests of beam and spin tests of flat annular disks were reanalyzed. Silicon nitride and graphite were the test materials. The experimental fracture strengths of the disks were compared with the predicted strengths based on both volume flaw and surface flaw analyses of four point bend data. Volume flaw analysis resulted in a better correlation between disks and beams in three of the five test series than did surface flaw analysis. The Weibull (moduli) and characteristic gage strengths for the disks and beams were also compared. Differences in the experimental Weibull slopes were not statistically significant. It was shown that results from the beam tests can predict the fracture strength of rotating disks.
Holland, Frederic A., Jr.↗
Investigation of axial positioning for flexural compressors
The testing of the research compressor is presented. The research compressor was assembled and disassembled in order to show the consistency in which the piston and rod could be aligned with a .0004 inch radial gap around the piston. A full set of tests was completed for the first assembly, which is referred to as assembly no. 1. The compressor was disassembled and assembled a second time (assembly no. 2). Assembly no. 2 was only tested statically due to the time constraint. Results are discussed.
Riggle, Peter↗
Flexural deformation of the continental lithosphere
Prior work focused primarily on the Adriatic and northern Ionian regions. The results of these studies have been summarized previously, and so are only briefly discussed. More recent work focuses on two different topics: (1) analysis of foredeep basin geometry, sedimentary style, and thrust belt structure in light of the kinematics at the associated plate boundary and subduction zone dynamics; and (2) the evolution and plate strength of early Proterozoic lithosphere.
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Indentation-flexure and low-velocity impact damage in graphite/epoxy laminates
Static indentation and low velocity impact tests were performed on quasi-isotropic and cross ply graphite/epoxy composite laminates. The load deflection relations in static tests and impact force history in the impact tests were recorded. The damage was assessed by using ultrasonic C-scanning and photomicrographic techniques. The static behavior of the laminates and damage progression during loading, unloading, and reloading were explained by a simple plate delamination model. A good correlation existed between the static and impact responses. It was found that results from a few static indentation-flexture tests can be used to predict the response and damage in composite laminates due to a class of low velocity impact events.
Kwon, Young S.↗
Scaling effects in the flexural response and failure of composite beams
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Jackson, Karen E.↗