Showing papers on "Flexural rigidity published in 1999"

Growing C57Bl/6 mice increase whole bone mechanical properties by increasing geometric and material properties.

Abstract: In vivo murine models are becoming increasingly important in bone research. To establish baseline data for researchers using these models, we studied the long bones from C57BL/6 female mice, a strain that is widely used in bone research. We determined the femoral structural and material properties in both torsion and four-point bending for mice at ages 4-24 weeks. Measurements of femoral cross-sectional geometry and tibial densitometric properties were also obtained. Results indicated that all structural properties (except ultimate energy), changed significantly with age (p < 0.001). Ultimate torque, ultimate moment, torsional rigidity, and bending rigidity all increased to peak values at 20 weeks, whereas ultimate rotation and ultimate displacement decreased to minimum values at 20 weeks. Our data indicate that increases in the material properties contributed more than increases in cross-sectional geometry to the changes in structural rigidity and ultimate load. For example, from 4-20 weeks torsional rigidity increased 1030%, while shear modulus increased 610% and the polar moment of inertia (a measure of the geometric resistance to rotation) increased by only 85%. Changes in the cross-sectional geometry with age were due to increases in periosteal diameter and decreases in endosteal diameter. In general, both torsion and bending techniques revealed large changes in structural and material properties with age. We conclude that peak bone strength is not achieved before 20 weeks in C57BL/6 female mice, and that torsion and four-point bending tests are equally well suited for evaluating mechanical properties of murine long bones.

Analysis of Fiber-Reinforced Elastomeric Isolators

Abstract: An analysis is given for the mechanical characteristics of multilayer elastomeric isolation bearings where the reinforcing elements-normally steel plates-are replaced by a fiber reinforcement. The fiber-reinforced isolator, in contrast to the steel-reinforced isolator (which is assumed to be rigid both in extension and flexure), is assumed to be flexible in extension, but completely without flexural rigidity. The influence of fiber flexibility on the mechanical properties of the fiber-rein-forced isolator, such as vertical and horizontal stiffness, is studied, and it is shown that it should be possible to produce a fiber- reinforced isolator that matches the behavior of steel-reinforced isolator. The fiber-reinforced isolator will be significantly lighter and could lead to a much less labor intensive manufacturing process.

Properties of high-strength steel fiber-reinforced concrete beams in bending

Abstract: This paper presents research results of ten high-strength reinforced concrete beams and steel fiber-reinforced high strength concrete beams, with steel fiber content of 1% by volume. The enlarged ends of mild carbon steel fibers with three different dimensions were selected. This research shows that the flexural rigidity before yield stage and the displacement at 80% ultimate load in the descending curve are improved, and crack number and length at comparable loads is reduced after the addition of steel fibers. The descending part of the load-displacement curve of the concrete beams without steel fibers is much steeper than that with steel fibers, which shows that the addition of steel fibers makes the high strength concrete beams more ductile.

Effects of mechanical fatigue on the bending properties of the porcine bioprosthetic heart valve.

Abstract: The mechanisms underlying the failure of porcine bioprosthetic aortic heart valves are not well understood. One possible explanation is that delaminations of the layered leaflet structure occur through flexion, leading to calcification and further delaminations, and finally resulting in valve failure. We investigated the changes in flexural rigidity of the belly of aortic valve cusps subjected to accelerated durability testing. We used three-point bending wherein a load was applied to the center of each specimen by a thin stainless steel bar calibrated to a known load-displacement relationship. Ten circumferential and 15 radial specimens from valves fatigued to 0, 50, 100, and 200 million cycles were flexed both with and against the curvature of the cusp. Linear beam theory was applied as a means to compare the relative bending stiffness between groups. Although specimens aligned to the circumferential direction were stiffer when bent against the cuspal curvature, the radial oriented specimens exhibited no bending directional dependence. Both the radial and circumferential specimens experienced a significant decrease in the bending stiffness with an increased number of accelerated test cycles. Overall, our results suggest that it is the fibrosa that experiences the greatest loss of stiffness with mechanically induced fatigue damage.

Optimisation of hollow glass fibres and their composites

Abstract: Hollow glass fibre reinforced plastics have a structural performance niche in a class of their own. They offer increased flexural rigidity compared to solid glass fibre reinforced plastics, they of...

Flexural strength of reinforced concrete T-beams with steel fibers

Abstract: The ultimate strength of reinforced concrete T-beams reinforced with conventional steel bars and short discontinuous steel fibers are studied. It is found that the presence of steel fibers reduced effectively the deflection, width of cracks and also improved the ductility and flexural rigidity of the concrete beams. Hence, an appreciable increase to the ultimate compressive strain is observed as well as the increase in the ultimate compressive strength. These are reflected by an increase in the value of the compressive block parameters. In addition, an increase in tensile strength is achieved and a rectangular tensile stress distribution is proposed. It was found that a negligible difference in moment capacity between overreinforced and underreinforced concrete beams. Therefore, it may be economical to use more amount of tension reinforcement than that allowed by the codes. Theoretical equations are developed to calculate the ultimate strength of reinforced concrete T-beams taking into account the effect of amount of compression reinforcement and amount of steel fibers. Theoretical equations show good agreement when compared with experimental results.

Manufacture, testing and numerical analysis of an innovative polymer composite/concrete structural unit

Abstract: A study of a novel advanced composite/concrete duplex beam is presented, including a four-point-load experimental beam-bending test and a numerical finite-element (FE) analysis. The manufacturing process for the beam, which uses Advanced Composites Group Ltd's optimized low-temperature-cure vacuum process prepreg technology with preimpregnated carbon and glass fibre composites, is outlined. The basic components of this beam consist of a concrete section in the compressive region, a glass-fibre-reinforced polymer (GFRP) composite sandwich foam core web section and a GFRP flange interleaved with high-strength unidirectional carbon fibre tape. The beam was designed such that the neutral axis was situated at the soffit of the concrete to prevent tensile forces developing in the concrete. In an attempt to achieve composite action between the concrete and GFRP composite, indents were placed in the vertical faces of the shuttering. During the loading test certain areas of the shuttering separated from the concrete prematurely; however, the indents did provide continued partial composite action to failure. The failure of the beam occurred by flexural crushing of the concrete followed by failure of the webs in shear. Prior to the separation of the shuttering and concrete the behaviour of the beam was as predicted by the FE analysis. The composite/concrete beam had half the flexural rigidity, a similar ultimate bending-load capacity and a weight reduction of approximately 75% compared to a singly reinforced concrete beam of the same dimensions with a 2% area of reinforcement. The low flexural rigidity can be increased by the use of higher-strength concrete, thus enhancing the modulus of elasticity of the concrete and the flexural rigidity of the whole beam.

Negative electrostatic contribution to the bending rigidity of charged membranes and polyelectrolytes screened by multivalent counterions.

Abstract: Bending rigidity of a charged membrane or polyelectrolyte screened by monovalent counterions is known to be enhanced by electrostatic effects. We show that in the case of screening by multivalent counterions the electrostatic effects reduce the bending rigidity. This inversion of the sign of the electrostatic contribution is related to the formation of two-dimensional strongly correlated liquids ~SCL! of counterions at the charged surface due to strong lateral repulsion between them. When a membrane or a polyelectrolyte is bent, SCL is compressed on one side and stretched on the other so that thermodynamic properties of SCL contribute to the bending rigidity. Thermodynamic properties of SCL are similar to those of Wigner crystal and are anomalous in the sense that the pressure, compressibility and screening radius of SCL are negative. This brings about substantial negative correction to the bending rigidity. For the case of DNA this effect qualitatively agrees with experiment. @S1063-651X~99!16011-2#

Characterizing and Modeling Bending Properties of Multiaxial Warp Knitted Fabrics

Abstract: The bending behavior of multiaxial warp knitted (MWK) fabrics is quite different from that of plain weaves and other apparel materials. According to the bending hysteresis curves obtained from KES-FB-2 (Kawabata's evaluation system), MWK fabric bending involves not only the spreading of filaments in inserting yarns, but also the buckling of inserting yams, which accounts for the more remarkable irregularity and nonsymmetry of MWK fabric bending hysteresis curves compared with those of plain weaves. Furthermore, the inserting yarns not completely parallel to the applied bending moment direction will undergo both bending and torsional deformation during a bending cycle. Experimental observation and theoretical study has shown that the bending paths of those non- orthogonally bent yarn systems follow different cylindrical helices. In this paper, a predictive bending model proves to be applicable in assessing the bending behavior of MWK fabrics in different bending directions, and the bending rigidity corresp...

Experimental investigation of compression moulding of glass/PA12-PMI foam core sandwich components

Abstract: The manufacturing of sandwich components from pre-consolidated glass/polyamide 12 faces and polymethacrylimide foam core by compression moulding has been studied. A statistical experiment design was used initially to identify the dominant process parameters in terms of interfacial bond strength, evaluated using the transverse tensile test method. In a subsequent extended study, the influence of face temperature and moulding pressure on the mechanical properties of the face–core interface and the sandwich construction as a whole, were characterised in terms of mode I interfacial fracture toughness, shear strength, shear stiffness, and flexural rigidity. These properties were evaluated using a modified double cantilever beam test, shear test, and four point bend test.

Low-profile versus conventional metacarpal plating systems: a comparison of construct stiffness and strength.

Abstract: Smaller, lower-profile plates for metacarpal fixation may have the potential to reduce extensor tendon irritation and adhesions, but their sufficiency for stabilizing metacarpal fractures has not been studied. We investigated the relative stiffness and strength of low-profile and conventional plating systems. For apex dorsal bending (bending closed), no plates broke or had notable plastic deformation. The conventional plates exhibited higher overall bending rigidity than all other plates, but had a lower maximum bending moment than the smaller plates. In apex volar bending (bending open) and torsion, the conventional plates were remarkably more rigid and developed remarkably higher torque. In vivo metacarpal loads are primarily apex dorsal bending, and all plates performed well in this mode. Thus, the smaller, low-profile plates may be sufficient for metacarpal fixation, although patient compliance and the use of supplemental stabilization with a cast or splint should be considered.

Flexural Stiffness of Composite Columns Subjected to Major Axis Bending

Abstract: The ACI Building Code permits a moment magnifier approach for design of slender composite steel-concrete columns. This approach is strongly influenced by the effective flexural stiffness (EI) of the column which varies due to cracking, creep, and nonlinearity of the concrete stress-strain curve among other factors. However, the EI expressions given in ACI 318-95 are approximate when compared with the values of EI derived from axial load-moment-curvature relationships. The study reported herein was undertaken to determine the influence of a full range of variables on EI of slender tied rectangular composite columns in which steel shapes are encased in concrete. The columns studied were subjected to bending about the major axis of the steel section in symmetrical single curvature under short term loads. Approximately 12,000 simulated columns, each with a different combination of variables, were used to generate the stiffness data. The EI expressions were then developed for use in slender composite column designs. Two design equations are proposed in this paper.

The effect of the bending rigidity of a wall on lateral pressure distribution

Abstract: A two-dimensional model retaining wall system was developed to investigate the effect of the bending rigidity of a wall, supported at the top and bottom, on the lateral pressure distribution at com...

Pneumatic radial tire for motorcycle

Abstract: A pneumatic radial tire for a motorcycle capable of increasing steering stability in cornering at high speeds while holding various performances such as high-speed durability and straight running stability. The radial tire (1) comprises a tread part (2), side wall parts (3), bead parts (4), a carcass layer (5), and at least one layer of steel spiral belt (6) formed by spirally winding substantially parallel with the equatorial plane of the tire. The flatness ratio (SH/TW) of the height of the tire in cross section (SH) to the maximum tread surface width (TW) is 0.50 to 0.85. The lateral out-plane bending rigidity (Sb) of the bending rigidity of the tread part (2) is 4.9 to 7.7 N/mm, the peripheral in-plane bending rigidity (Sa) is 5.1 to 7.8 N/mm, and the equilibrium value (K) of a belt surface rigidity expressed by a bending rigidity ratio (Sa/Sb) is within the range of 0.90 to 1.10.

Fluctuation route to the bending rigidity

Abstract: A comparison is made of two routes for the calculation of the rigidity constant of bending: the fluctuation route and the equilibrium route. In the fluctuation route the rigidity constant is determined from the calculation of the curvature energy of the fluctuating planar interface, while in the equilibrium route the free energy of curved surfaces in equilibrium is considered. It is known that the expressions for the surface tension of a planar interface in the fluctuation and equilibrium routes, leading to the Triezenberg—Zwanzig and Kirkwood—Buff formula, respectively, are indeed equivalent. Within the context of a squared-gradient density functional theory, we find that, although the form of the expressions for the rigidity constant of bending are similar following both routes, the thermodynamic conditions necessary to bend the interface are different, leading to different values for the rigidity constant of bending.

Flexible plate and a flywheel assembly employing the flexible plate

Abstract: A flexible plate is formed with a first rigidity about a first axis and a second rigidity about a second axis where the first and second axis are each perpendicular to a central axia about which the flexible plate is rotatable. The first rigidity is greater than the second rigidity such that the flexible plate may flex more easily about the second axis than the first axis, thus providing the flexible plate with an anisotropic flexural rigidity. In one embodiment, the flexible plate is formed with an eliptical intermediate portion. In another embodiment, the flexible plate includes first and second plates. Each plate has a central portion. The first plate has first foot portions and the second plate has second foot portions. The first and second foot portions have differing circumferential widths.

RC Flat Plate Under Combined In-Plane and Out-of-Plane Loads

Abstract: A numerical study using nonlinear finite-element analysis is performed to investigate the behavior of reinforced-concrete flat plates subject to combined in-plane compressive and out-of-plane floor loads. For the nonlinear finite-element analysis, a computer program addressing material and geometric nonlinearities is developed. The flat plates to be studied are designed according to the direct design method. Through studies on the effects of different load combinations and loading sequence, the load condition that governs the strength of the flat plates is determined. And, for the flat plates under the governing load condition, parametric studies are performed to investigate the variations of the buckling coefficient and the effective flexural rigidity. As a result, this paper provides rational design rules for the moment magnifier method that is applicable to the flat plates.

Behaviour of stud connectors in wood-concrete composite beams

Abstract: The stiffening and strengthening of wooden floors with a thin collaborating concrete slab is a recent technique, which appears particularly suitable for restoration of ancient buildings. In this experimental research work a simple kind of connection is studied, suitable for practice, using materials that are normally available in the ordinary restoration yard. Tests are carried out both for studying the global behaviour of the composite beams and the local behaviour of the connections. They are conducted on two different composite beams, one with the concrete slab in direct contact with the wood beam, the other with interposed planks. Stud connectors are used which are obtained by ordinary smooth steel bars simply forced into calibrated holes drilled in the wooden beam. For the evaluation of the stiffness and resistance of the connectors pure shear tests were carried out. Experimental results concern both the local shear behaviour of the single connector and the global flexural behaviour of the composite beams. The effectiveness of the proposed technique on the flexural stiffness and strength of the composite beams is shown. Ultimate load values are in a good agreement with those calculated by classical approaches.

Vesicle adhesion and microemulsion droplet dimerization : Small bending rigidity regime

Abstract: To study the vesicle-substrate unbinding transition and the onset of microemulsion aggregation, we calculate the curvature free energy of a vesicle adhered to a substrate and of two microemulsion droplets forming a dimer. Analytical expressions are derived in the small bending rigidity regime in which the length (k/σ)1/2, constructed from the rigidity constant of bending k and surface tension σ, is small compared to the typical size of the vesicle (droplet), (k/σ)1/2≪R. The leading contribution to the curvature free energy is shown to be proportional to k1/2. The formulas derived are used to understand the experimentally observed aggregation of microemulsion droplets occurring in the direction of vanishing spontaneous curvature. In this way we intend to bridge the gap between the liquid state theories used to describe aggregation processes in microemulsion systems and the bending energy concept originally introduced by Helfrich to describe vesicles shapes and fluctuations as well as phase diagrams of micr...

Flexural stiffness of composite columns subjected to bending about minor axis of structural steel section core

Abstract: American Concrete Institute (ACI) 318-95 permits a moment magnifier approach for design of slender composite steel-concrete columns. This approach is strongly influenced by the effective flexural stiffness (EI) of the column that varies with cracking, creep, and nonlinearity of the concrete stress-strain curve, among other factors. However, the EI expressions given in ACI 318-95 are approximate when compared with the values of EI computed from axial load-moment-curvature relationships. This study was undertaken to determine the influence of different variables on EI of slender, tied, rectangular composite columns in which steel shapes are encased in concrete. The columns studied were subjected to bending about the minor axis of the steel section in symmetrical single curvature under short-term loads. Approximately 12,000 simulated columns, each with a different combination of variables, were used to generate the stiffness data. The EI expressions were then developed for use in slender composite column designs. A design equation for EI is proposed.

Cantilever for detecting normal force for atomic force microscope

Abstract: PROBLEM TO BE SOLVED: To detect a normal force without being affected by a torsional deflection by improving a torsional rigidity of a cantilever for detecting the normal force for an AFM without affecting a flexural rigidity. SOLUTION: A plurality of parallel leaf springs 3 in parallel to a surface of a sample 1 to be tested are set via a space to be opposite to each other, thereby constituting a cantilever ? body 2. A base end of the body is fixed to a base 7 mounted to an AFM, and a block-shaped head 4 is set to a leading end part of the cantilever body 2. A probe 5 is set to a face of the head 4 directed to the sample 1, so that a shift or an angle of the cantilever body 2 can be detected.

Effect of soil-structure interactions on column moment of building frames

Abstract: Very little information is available on quantitative effect of soil-structure interaction on design force quantities of members of multi-storeyed space frames. The present study focuses on investigating quantitatively such effects on building frames with isolated footings. The effect of soil-structure interaction on column axial forces of such building frames are broadly quantified. Hence, the scope of the present work is restricted only to the effect of soil-structure interaction on column moments of such frames. A limited case study conducted proves the importance of considering the change in column moment due to the effect of soil-structure interaction, as this change is found to be of the order of a few times that of the actual column moment obtained in no settlement condition under dead loads and live loads. The study summarises the effect of various framing action parameters, namely, ratio of flexural stiffness of columns and beams, number of storeys and number of bays on change in column bending moments. Besides this, an approximate formulation is proposed which helps to predict the change in column moments from the value ofchange in column axial force, knowing the ratio of flexural stiffness of columns and beams and number of storeys in a frame. The conclusions and approximate formulation may prove useful for designing building frames considering the effect of soil-structure interaction.

Door for a vehicle comprises a load-carrying high-strength, high-stiffness frame bounded by an outer skin and an inner shell which are not load-carrying elements but possess certain flexural stiffness

Abstract: The door for a vehicle comprises an outer skin, a load-carrying structure and an inner shell, and is characterized by the following facts: a) the load-carrying structure (3) is a high-strength, high-stiffness frame which also satisfies crash protection requirements; b) the outer skin (4) and the inner shell (2) are not load-carrying structural elements, but possess a flexural stiffness which is adequate for practical purposes.

Method and equipment for measuring flexural rigidity of rod-like material

Abstract: PROBLEM TO BE SOLVED: To provide a method and an equipment for measuring the flexural rigidity of a rod-like material accurately in which the flexural rigidity of a rubber hose can be measured quantitatively at a low temperature and at the application of pressure. SOLUTION: The flexural rigidity measuring equipment 10 comprises a semicircular, planar bending mender 12 having a radius of curvature R secured vertically and removably onto a supporting table 11 by means of screws 13. The planar bending mandrel 12 is fixed, on the side face thereof, with the supporting arm 15 of a pressing means provided with a detector turning, at a constant speed, along the side face of the planar bending mandrel 12. The supporting arm 15 has a base end part 15a fixed to a turning shaft 16 located in the center O of the bonding mandrel 12 and a forward end 15b fixed, through a bracket 17, with rotatable guide rollers 18a, 18b provided with a guide groove 30 covering the substantially semicircular part of a rod-like measured material W, and flexure detectors 19a, 19b, e.g. load cells, for measuring the flexural rigidity (normal force).

Elastic bending behavior analytical system of golf club shaft in swinging

Abstract: PROBLEM TO BE SOLVED: To provide an analytical system of elastic bending behavior including bending, curvature distribution, and rate of change of curvature distribution of a golf shaft in swinging as indexes of a sense to feel and evaluate how the shaft is bending and changing as a feeling. SOLUTION: Bending, curvature distribution and rate of change of curvature distribution of a shaft at a specific time of swinging are visualized as indexes of a sense to feel and evaluate how the shaft is elastically bent and changed, using the calculated bending rigidity distribution of the shaft of high measuring precision, the distribution data of the bending moment applied on the shaft, and the data of various conditions in swiing measurement.

Instability regions of a prestressed compound column subjected to a follower force

Abstract: The influence of prestressing and bending rigidity distribution between rods of a non-linear column on its natural vibrations and stability is studied. The perturbation method is used for solving the problem. Regions of divergence and flutter instabilities for a column have been determined on the basis of courses of eigencurves as a function of bending rigidity ratio and prestress rate. Discontinuities of the critical force have been observed for certain values of the investigated parameters leading to instability of the column, even for small values of the external load. Although each prestress reduces the critical force, it can be applied to passive vibration control.

Cinématique et transfert de contraintes dans des réseaux quasi plans aléatoires de fibres

Abstract: The mechanics of paper is considered from the standpoint of fibre networks. It is shown that the classical model of paper, based on a network of infinitely long fibres capable of carrying only axial forces [1], having the geometry of a Poisson line field, does not possess generic rigidity. This pathological behaviour can be removed by the introduction of rigid fibre-fibre bonds (justified by the presence of hydrogen bonding between cellulose fibres) and fibre flexural stiffness.

Flexural stiffness envelopes for planar multilayered systems containing two dissimilar materials

Abstract: The flexural stiffness of multilayer systems, using two dissimilar materials, namely a high-strength titanium alloy and titanium metal matrix alloy, has been determined. The development of different types of symmetric and asymmetric layered systems is presented and stiffness envelopes are determined for the systems. It is demonstrated that there are several layered structures, which can provide the same flexural stiffness. The results are discussed in the context of other mechanical properties such as the strength, impact toughness and damping capacity.