Nonlinear Load-deflection Curves Research Articles

皿ばねを用いた免震用摩擦ダンパーの復元力特性に関する実験的研究

The present report concerns a friction damper constructed with coned disc springs as a part of laminated rubber bearings for base-isolation systems. This friction damper is constructed by keeping coned disc springs against a horizontally placed stainless steel plate on the sliding surface by making use of the rebound from deformation by vertical compression. The examination of non-linear load-deflection curves of the coned disc springs were undertaken by both characteristics tests and analysis. Through dynamic characteristics tests, the reliability of friction dampers constructed with the coned disc spring was confirmed as applicable to a base isolation system.

Nonlinear and First-Ply Failure Analyses of Laminated Composite Cross-Ply Plates

A method is presented to study the nonlinear behaviors and first-ply failure strengths of centrally loaded laminated composite plates with semi-clamped edges. The method which is developed from the von Karman-Mindlin plate theory and the Ritz method is used to construct the nonlinear load-deflection curves of the composite plates with or without considering the reduction in plate stiffness induced by ply failure and predict the first-ply failure loads of the plates based on various commonly used strength-of-material type failure criteria. Experiments on laminated composite plates loaded to failure are performed to construct the experimental load-displacement curves of the plates. During testing, the first-ply failure loads of the plates are identified using the acoustic emission technique. The experimental results are used to investigate the capabilities of the present method in predicting the nonlinear behaviors and first-ply failure loads of the laminated composite plates. It has been found that when compared with the experimental load-deflection curves the present method with the consideration of stiffness reduction can yield reasonable results on load-deflection curve and even for some cases the ultimate strength. As for the determination of first-ply failure load, the inconsistent results predicted by the adopted failure criteria indicate that the strength-of-material approach may be inappropriate for the first-ply failure analysis of laminated composite plates. Hence, more research on failure mechanism and, especially, the development of appropriate failure criteria for composite laminates is needed.

Free vibration steady state response of geometrically nonlinear shallow arches

A study of the large amplitude, free vibration of geometrically non-linear shallow arches is presented. To obtain the non-linear steady state response a combination of finite elements and finite difference methods is employed. Finite elements idealization is used to express the geometrically non-linear and incremental stiffness matrices and the rest of the terms appearing in the equation of motion are expressed by finite difference equations relating displacement, velocity and acceleration. The resulting recurrence formula is then solved by assuming that for the first time interval, the transverse displacement away from the centre of the arch, is in the form of a sinusoidal equation. The complex relationships between frequency and large amplitude for shallow arches having various ratios of radius to thickness are thus obtained and the results are discussed in relation to the elastic geometrically non-linear load-deflection curves which are generally multi valued exhibiting local maximum and minimum and resulting into snap-through between various equilibrium states. These elastic geometrically non-linear curves are based on an analytical solution in which the shape of the arch is expressed in terms of an infinite Fourier series and the thrust in the shallow arch is assumed to be constant.

Mechanical and electrical responses of the squid giant axon to simple elongation.

There is a limited amount of information available on the mechanical and functional response of the nervous system to loading. While deformation of cerebral, spinal, or peripheral nerve tissue can have particularly severe consequences, most research in this area has concentrated on either demonstrating in-vivo functional changes and disclosing the effected anatomical pathways, or describing material deformations of the composite structure. Although such studies have successfully produced repeatable traumas, they have not addressed the mechanisms of these mechanically induced injuries. Therefore, a single cell model is required in order to gain further understanding of this complex phenomena. An isolated squid giant axon was subjected to controlled uniaxial loading and its mechanical and physiological responses were monitored with an instrument specifically designed for these experiments. These results determined that the mechanical properties of the isolated axon are similar to those of other soft tissues, and include features such as a nonlinear load-deflection curve and a hysteresis loop upon unloading. The mechanical response was modeled with the quasi-linear viscoelastic theory (Fung, 1972). The physiological response of the axon to quasi-static loading was a small reversible hyperpolarization; however, as the rate of loading was increased, the axon depolarized and the magnitude and the time needed to recover to the original resting potential increased in a nonlinear fashion. At elongations greater than twenty percent an irreversible injury occurs and the membrane potential does not completely recover to baseline.

Monotonic and cyclic nail connection tests

The results of monotonic and cyclic nail connection lateral tests are presented. The tests are part of an extensive experimental and analytical study to investigate the behaviour of timber shear walls subjected to earthquakes. The results from the nail connection tests were used in a larger study of timber shear walls. The nonlinear load–deflection curves were used for modelling the nail connection between the sheathing and the framing of the shear walls. The dependency of the nail connection on the grain orientation of the timber materials is investigated along with the evidence that the material properties of the nails are the primary parameters for the load–displacement characteristics of the connection made with hot-dipped, galvanized common nails. Both the monotonic and cyclic lateral behaviours of the connections are established. The premise that the hysteresis for the nail connection is contained within an envelope defined by the monotonic load–displacement curve is confirmed. These connection characteristics translate into similar behaviour in nailed timber shear walls. Therefore, an improved undertanding of the principal connection used in the construction of shear walls will also improve the understanding of the behaviour of shear walls. Key words: connections, nails, plywood, waferboard, monotonic, cyclic, shear wall.

Interactive Bending Behavior of Sandwich Beams

A multi-degree-of-freedom nonlinear Rayleigh-Ritz formulation for a sandwich beam is developed and is used to demonstrate the possible sudden destabilizing effects associated with wrinkling on the compressive face. Through-core stretching and core shearing effects are included. Nonlinear load-deflection curves, for various loading conditions including point loads and uniformly distributed loads, are presented.

Interlaminar Fracture of Random Short-Fiber SMC Composite

The interlaminar fracture behavior of a random short-fiber SMC composite is studied both experimentally and analytically. In the experimental phase of the study, the random short-fiber SMC-R50 composite with different thicknesses is used. The commonly used double-cantilever-beam (DCB) fracture test is employed to evaluate the mode-I interlaminar fracture toughness. In the analytical portion of the research, owing to significant deformation in the DCB test, a geometrically nonlinear analysis is introduced to account for large deflection and nonlinear load-deflection curves in the evaluation of the interlaminar fracture toughness. For the SMC-R50 material studied, the interlaminar toughness of the composite is found to be an order of magnitude higher than that of unreinforced neat resin due to unusual damage mechanisms ahead of the crack tip and significant fiber bridging across crack surfaces. The effect of com posite thickness on the interlaminar fracture is appreciable. The influence of the SMC material microstructure on interlaminar crack resistance is discussed in detail.

Elastic energy release rates determined from nonlinear load-deflection curves

The usual experimental determination of elastic energy release rates involves the measurement of load-deflection curves of selected specimen configurations with varying crack lengths. The desired energy release rate, ℐ is then related to the rate of change of the slope of this load-deflection curve with respect to the crack length.