Showing papers on "Flexural rigidity published in 1983"

Generic buckling curves for specially orthotropic rectangular plates

Abstract: Using a double affine transformation, the classical buckling equation for specially orthotropic plates and the corresponding virtual work theorem are presented in a particularly simple fashion. These dual representations are characterized by a single material constant, called the generalized rigidity ratio, whose range is predicted to be the closed interval from 0 to 1 (if this prediction is correct then the numerical results using a ratio greater than 1 in the specially orthotropic plate literature are incorrect); when natural boundary conditions are considered a generalized Poisson's ratio is introduced. Thus the buckling results are valid for any specially orthotropic material; hence the curves presented in the text are generic rather than specific. The solution trends are twofold; the buckling coefficients decrease with decreasing generalized rigidity ratio and, when applicable, they decrease with increasing generalized Poisson's ratio. Since the isotropic plate is one limiting case of the above analysis, it is also true that isotropic buckling coefficients decrease with increasing Poission's ratio.

Low velocity transverse impact behavior of 8-ply, graphite-epoxy laminates

Abstract: This work discusses the behavior of eight-ply, quasi-isotropic, graphite epoxy laminates subjected to low velocity transverse impact loading Large deflection theory of plates was used to predict the load-deflection characteristics during the impact event The impact model considered that the indentation, flexural and shear stiffnesses could be represented by three-equivalent springs in series The analysis of static and dynamic impact loading test-data concluded that the membrane parameter, beta, used in flexural stiffness relation was proportional to the square of the coefficient of restitution, e, of the impactor Use of beta=0443 e-squared was made in load-deflection relations to consider the drop in plate stiffness due to delamination The results of impact tests up to impact velocity 53 m/sec were found in close agreement with the predictions

Periodically Supported Heavy Elastic Sheet

Abstract: A long elastic sheet or cable lies horizontally on equally spaced supports. The sheet sags due to its own weight. The problem is governed by the distance between the supports, 2a, and a nondimensional parameter, K, which represents the relative importance of density and length to flexural rigidity. The heavy elastica equations are solved both analytically and numerically. The design parameters, horizontal force, and maximum moment are found to be sensitive to both a and K.

Some mechanical properties of rigid polyurethane structural foam

Abstract: The mechanical response of integral-skin rigid polyurethane foam, with an average density of 300 to 700 kg/m3, to constant rate and creep loading was determined. Sandwich specimens were modeled by layers of a core material and two skins, whose secant moduli had been determined experimentally by separate tests and approximated by linear functions of the density. The effective rigidities of the sandwich in tension and flexure were calculated and compared favorably to experimental measurements. The sandwich structure improved the flexural rigidity of homogeneous foam by a factor of more than 2.20. Tensile creep tests of sandwich specimens at relatively low stress levels (up to about 38 percent of their strength) showed that the creep was nonlinear, but a single creep curve could represent creep of specimens of various densities, provided the relative load on them was the same. A limited number of flexural creep tests led to similar conclusions, but the creep rate was smaller than in tension. Results from torsion tests of core material, compressive tests of sandwich specimens, and tension and compression tests of nonskin rigid foam are included in this article.

29—yarn-bending and the weighted-ring stiffness test

Abstract: The standard ring-loop test for yarn flexural rigidity is in error unless the yarn bends linearly. The deformation and recovery behaviour of a ring of yarn is therefore recalculated on the basis of non-linear bending behaviour, in which a coercive or frictional couple must be overcome before the yarn bends linearly. Good agreement between theory and experiment is demonstrated.

Structural metal sheet and method for forming the same

Abstract: A structural metal sheet employed as an outer sheet for a railway vehicle, for example, is generally pretensioned in order to prevent buckling. Hitherto, the pretensioning is effected by various methods after or during the assembly of a structure. According to the invention, the metal sheet itself is pretensioned by a plastic working for increasing the flexural rigidity thereof. Thus, there is no fear of buckling, and the workmanship is improved as compared with the prior art.

Free rotation of a circular ring about a diameter

Abstract: A circular ring rotates about a diameter in space. Deformations of the ring depend on a non-dimensional parameterJ which represents the relative importance of centrifugal forces to flexural rigidity. The solutions are found by three methods: series expansion for smallJ, matched asymptotic expansions for largeJ and exact numerical solution using both quasi-Newton and homotopy methods.

Simplified Design Procedures for Composite Plates Under Flexural Loading

Abstract: The paper describes simplified procedures for the design analysis of rectangular plates loaded in flexure and compares predicted results with test data on a range of fibre reinforced plastics plates. Design formulae and design charts are given for determining maximum deflections and bending moments in rectangular orthotropic elastic plates under transverse pressure or point loads. The design methods are based on computed solutions to the orthotropic plate equations whose results are presented as simplified design charts appropriate to composite applications and depending mainly on a single stiffness ratio parameter. Design formulae, derived from approximate variational solutions to the orthotropic plate, are shown to be in good agreement with the computed solutions especially for materials with low and moderate stiffness ratios. Flexure tests are reported on a range of reinforced plastics plates with mat, woven, unidirectional or cross ply reinforcement and subjected to centre point transverse loads. Measured deflections are compared with predicted values and the validity of the design procedures is assessed.

Temperature increase of sheet molding compound (SMC‐R65) in flexural fatigue test

Abstract: The temperature increase in flexural fatigue testing of sheet-molding compound SMC-R65 is investigated within a range of testing frequencies from 1000 cpm to 2200 cpm. Variation of the testing frequency affects the temperature increase and, based on 10 percent reduction in flexural stiffness, the effect of changing frequency on the fatigue lives was not detected. Steady-state temperatures are obtained in the case of specimens tested in air. A temperature analysis is carried out that gives reasonable agreement with experimental values.

Guide rollers for paper, film-treating and printing machines

Abstract: The invention relates to guide rollers for paper, film-treating and printing machines. The guide rollers are to be designed here in such a way that they have a surface which provides good grip and is adapted to the web of paper or film; in addition, a high flexural rigidity combined with a low mass and high transporting speed are required. To meet these requirements, it is proposed according to the invention that a) the jacket of the guide rollers consists of fibre-reinforced plastic and is made up of alternating layers of circumferential and helical windings, and that b) by leaving gaps between individual helical winding strands, rhomboid depressions are made in the surface of the jacket. a

Theory of Shell Structures: The Brazier effect in the buckling of bent tubes

Abstract: Introduction When a drinking-straw is bent between the fingers into a uniformly curved arc of steadily increasing curvature, there comes a point when the tube suddenly collapses locally and forms a kink. If the experiment is repeated with a fresh straw, and the specimen is observed more carefully, it is found that the cross-section of the entire tube becomes progressively more oval as the curvature increases: and the kink or crease which suddenly forms involves a complete local flattening of the cross-section, which then offers virtually no resistance to bending. These observations suggest that the buckling of a thin-walled cylindrical shell which is subjected to pure bending involves behaviour which is of a different kind from that which we have encountered in chapters 14 and 15; for we have previously not come across major changes in geometry, spread over the entire shell, before buckling occurs. The first investigation of this effect was made by Brazier (1927). He showed that when an initially straight tube is bent uniformly, the longitudinal tension and compression which resist the applied bending moment also tend to flatten or ovalise the cross-section. This in turn reduces the flexural stiffness EI of the member as the curvature increases; and Brazier showed that under steadily increasing curvature the bending moment – being the product of curvature and EI – reaches a maximum value. Clearly the structure becomes unstable after the point of maximum bending moment has been passed; and it is therefore not surprising to find that in experiments the tubes ‘jump’ to a different kind of configuration, which includes a ‘kink’.

28—the relation between yarn and fabric properties in plain-knitted structures

Abstract: It is shown that there is a good correlation between the specific stress of a plain-knitted fabric and the parameter G 0/l 3, where G 0 is the yarn flexural rigidity and l is the loop length. In an attempt to determine the contribution of the fabric geometry and structure to the elastic-recovery properties of the plain-knitted fabrics, concepts such as the elastic-recovery ratio (ERR) and elastic-recovery performance index (ERPI) are introduced.

Parameter estimation in truss beams using Timoshenko beam model with damping

Abstract: Truss beams with members having viscous damping are modeled with a Timoshenko beam. Procedures for deriving the equivalent bending rigidity, transverse shear rigidity, and damping are presented. Explicit expressions for these equivalent beam properties are obtained for a specific truss beam. The beam model thus established is then used to investigate the effect of damping in free vibration. Finally, the beam is employed in the estimation of structural parameters in a simply-supported truss beam using a random search algorithm.

Bending Stiffness of Multiwall Sandwich

Abstract: An analytical and experimental study was carried out to understand the extensional and flexural behavior of multiwall sandwich, a metallic insulation composed of alternate layers of flat and dimpled foil. The multiwall sandwich was structurally analyzed by using several simplifying assumptions combined with a finite element analysis. The simplifying assumptions made in this analysis were evaluated by bending and tensile tests. Test results validate the assumption that flat sheets in compression do not significantly contribute to the flexural stiffness of multiwall sandwich for the multiwall geometry tested. However, calculations show that thicker flat sheets may contribute significantly to bending stiffness and cannot be ignored. Results of this analytical approach compare well with test data; both show that the extensional stiffness of the dimpled sheet in he 0 deg direction is about 30 percent of that for a flat sheet, and that in the 45 deg direction, it is about 10 percent. The analytical and experimental multiwall bending stiffness showed good agreement for the particular geometry tested.

Base material for flexible adhesive tape

Abstract: PURPOSE:The titled base material, prepared by drawing a specific laminated sheet having a special flexible resin layer as an intermediate layer provided between polypropylene layers on the surfaces to give a specific thickness, and having improved electrical characteristics, cold resistance, moistureproofness, waterproofness, mechanical strength and flexibility. CONSTITUTION:A laminated sheet having a flexible resin layer, e.g. styrene- butadiene-styrene copolymer, having kg/cm flexural rigidity at 20 deg.C, preferably kg/cm flexural rigidity at -20 deg.C, as an intermediate layer provided between polypropylene layers on both surfaces is drawn preferably at 120-165 deg.C to give 100mu or less total thickness, preferably 30-50mu whole thickness and 50-80%, based on the whole thickness, thickness of the intermediate layer. EFFECT:Well compatible with objects having unevennesses and bent surfaces. USE:Electrical insulation and sealing of cans and openings of decorative cans and bottles.

Composite design method for masonry walls on concrete beams

Abstract: This paper describes a design method for structures consisting of a vertically loaded masonry wall supported by a reinforced concrete beam, taking account of the composite tied-arch action of the wall and beam. Experimental results have shown that the behaviour of walls on reinforced concrete beams is similar enough to that of walls on steel beams to allow the development of a design procedure for the former using similar principles to that for walls on steel beams. Therefore, the design approach is based on the assumption of triangular distributions of vertical stress at the wall–beam interface, where the length of the distributions are a function of the beam-to-wall relative stiffness. In the design method the beam flexural stiffness is designed to give an adequate distribution of the interface stress so that the maximum stress in the wall does not exceed allowable limits. The beam is also designed with flexural and shear reinforcement sufficient to resist the bending moment, tie force, and shear forces...

Refined calculation of the stress state and of the flexural rigidity of lens compensators in the elastoplastic range

Abstract: 1. With the aid of numerical experiments we analyzed the accuracy of the approximate method of the elastoplastic calculation of the state of stress and strain and of the flexural rigidity of lens compensators. 2. A dependence was established of the error of the elastic calculation of the SSS and of the flexural rigidity of typical standardized compensators on the magnitude of their loading. 3. It was demonstrated that elastoplastic calculation of the SSS of compensators subjected to bending is indispensable for evaluating their fatigue strength.