Showing papers on "Flexural rigidity published in 1981"

Observations of flexure and the rheology of the oceanic lithosphere

Abstract: Observations of flexure indicate that the effective flexural rigidity of oceanic lithosphere is a function of the age of the lithosphere at the time of loading, and hence temperature. We have used a yield stress envelope model constrained by data from experimental rock mechanics to determine how the flexure parameters and rheologic properties of oceanic lithosphere are related. The results of our model for seamounts and oceanic island loads in the interior of plates suggest that following loading, rapid stress relaxation occurs as the plate 'thins' from its short-term to its long-term (>10/sup 6/ years) mechanical thickness. The mechanical thickness, which determines the effective flexural rigidity of the plate, is strongly dependent on temperature and weakly dependent on load size and duration (>1-10 m.y.). The results of our model for convergent plate boundaries suggest that changes in the shape of the Outer Rise along an individual trench system may be due to variations in the horizontal load acting across the boundary (<1 kbar). The model predicts a narrow zone of high strain accumulation seaward of a trench which is in agreement with variations in crustal velocities and seismicity patterns observed along some trench systems.

Performance tests of full span panel form bridges

Abstract: An experimental program to determine the effects of repetitive loading on the serviceability and strength of full span composite panel form bridges is described. Six simply supported bridge decks were tested. The specimens consisted of three precast, pretensioned panels composite with a cast-in-place topping slab. Bond between the topping slab and the roughened interface surfaces of the panels provided the only means of shear connection. Items considered in the study include the topping slab thickness, panel joint type (flat or bevelled-edge), and the effect of longitudinal cracks in the topping slab. The specimens were loaded repetitively with 2,000,000 cycles of design load (HS20-44 axle load with allowance for impact). The loading arrangement was such that maximum transverse shear stresses and maximum longitudinal bending stresses were produced during each cycle. Performance was evaluated primarily on the basis of flexural rigidity, differential deflection between panels, and the strength and ductility of the composite system. Visible cracks in the concrete, extension of prestressing strands and strains in transverse steel were also considered in evaluating the specimens. Recommendations are made regarding the minimum topping slab thickness, type of panel joints and quantity of transverse reinforcement to be provided in the topping slab. (FHWA)

Unfolding a Curved Elastic Sheet

Abstract: A curved elastic sheet is flattened on a rigid flat plate by vertical end forces. The problem is governed by a non-dimensional parameter, B, which signifies the relative importance of flexural rigidity to the applied force and the natural radius. The elastica equations are solved by elliptic functions, perturbation for small B, and numerical integration. Force-displacement characteristics and sheet configurations are found. The results may be applied to sandwiched leaf springs.

New materials for loudspeaker diaphragms and cones—An overview

Abstract: Desirable properties of materials for loudspeaker diaphragms are high specific Young's modulus (E/ρ), large flexural rigidity and large internal loss (tanδ). In order to obtain large flexural rigidity, honeycomb structured diaphragms or porous metal diaphragms have been used. For the purpose of realizing ideal loudspeaker diaphragms which can be easily produced, however, the material itself should have high values of E/ρ and tanδ This paper is a review on recent developments of materials for loudspeaker diaphragms in Japan, such as beryllium, boronized titanium, carbon fiber reinforced olefin, and polymer‐graphite composite diaphragms.

A Study of Tensile and Bending Properties of Woven Cotton Fabrics

Abstract: The uniaxial tensile and bending characteristics of a series of cotton and cotton-blend fabrics have been examined. The fabrics tested encompass' a wide range of tightness of construction by including three different groups of cotton woven structure, viz. canvas fabrics, sheeting fabrics and handloom outer wear fabrics. The fabric load-extension curves and yarn decrimping curves are ana lysed and discussed in terms of the following dimensionless parameters: the normalized tension per thread (the applied tension divided by the yarn bending rigidity and multiplied by the square of curvilinear length in the extended direction), the relative yarn or fabric extension (the yarn or fabric extension divided by the yarn crimp), the initial fabric tensile modulus, the yarn decrimping modulus and the ratio of the curvilinear lengths in the two principal directions of woven fabric. The inelastic and elastic parameters for the fabric bending hysteresis curve are described. The effects of fabric weave construction. weave tightness and fabric finishing or wet relaxation treatments on the fabric tensile and bending behaviour are studied and related to the cross-thread interaction effects determined as the ratios offabric bending parameters (expressed per bending thread) to the yarn bending parameters and the ratio of the initial fabric tensile modulus to the yarn decrimping modulus. The mechanisms of viscoelasticity are evaluated by studying the stress relaxation behaviour of bent cotton fabrics under conditions of both stable and changing relative humidity. It is observed that the yarn interference effects in cotton fabrics are generally higher than those in worsted outerwear fabrics, although the hand loom fabrics show yarn interference effects similar to those of wool fabrics. There is a good correlation between yarn interference effects as measured by pure bending and tensile deformations of fabrics. The- stress-relaxation of cotton fabrics during changing conditions of relative humidity is more sensitive to structure than in the case of wool. The stress-relaxation in cotton fabrics is more severe than in wool,

Stability of unfigured and stiffened shells made of fibrous composites

Abstract: Within the known generalizations of the theory of thin shells, formulas were obtained for calculating critical loads of unfigured and stiffened cylindrical shells made of fibrous composite materials under an external pressure and axial compression, taking into account not only the longitudinal (compressive) and flexural rigidity, but also the torsional and shear rigidities. From an analysis of the testing results of unfigured shells made of fiber-glass material, the divergence between the calculated and experimental data has been estimated by introducing into the formulas correction functions 0.181 In λ + 1.32 and a coefficient 0.697. The values of the safety factor were determined, which with a given reliability guarantee the selection of the geometrical parameters of the shells, amounting to (for a 0.95 reliability) 1.244 and 1.45.