Inelastic Property Research Articles

Finite Element Analysis on Inelastic Mechanical Behavior of Composite Beams Strengthened With Carbon-Fiber-Reinforced Polymer Laminates Under Negative Moment

This work studies the improvement in the inelastic mechanical property of steel-concrete composite beams strengthened by carbon-fiber-reinforced polymer (CFRP) laminates under a negative moment. First, the monotonic loading test was designed and performed on an inverted simply supported beam to simulate the negative moment regions of continuous composite beams. Second, the finite element analysis (FEA) on flexural capacity and cracking resistance in negative moment regions of the composite beams was carried out with ANSYS software. A series of mechanical indexes including the load-deflection curve, component strain, and crack propagation were obtained from the FEA model and verified through the test data. The results showed that the FEA model can accurately predict the general mechanical behavior of composite beams under negative moments, and the calculation results considering the interface slip effect were closer to the experimental values. Finally, based on the FEA model, the parametric study on static behavior in negative moment regions of composite beams strengthened with/without CFRP laminates was conducted. The effects of the CFRP layout width, layout position, layer number, longitudinal reinforcement ratio, and shear connection degree on the bearing capacity of the composite beams were considered. The CFRP laminates can effectively improve the bending resistance of composite beams under negative moments. At a low reinforcement ratio, the bearing capacity was greatly affected by the layout width and layer number of the CFRP laminates, but the rate of increase was not significant when the layer number was more than 3. The reinforcement ratio had a great influence on the bearing capacity of composite beams under negative moments, but the influence of the shear connection degree was not remarkable.

Mixing of non-Newtonian inelastic fluid in a turbulent patch of T-junction

In this paper, we present result from a direct numerical simulation (DNS) of turbulent flow in a converging T-junction for both Newtonian (water) and non-Newtonian inelastic fluid (dilute Xanthan Gum solution). Based on experimental data, the Bird-Carreau law is used to capture the inelastic shear thinning property of the solution. For the Xanthan solution, the viscosity at rest is about 100 times greater than the viscosity at high shear-rate. A passive scalar is introduced in the transverse branch to investigate the mixing in such configuration. The nominal Reynolds number at the exit varies from 4800 to 8000 for the Newtonian cases and for the same inflow rates, the non-Newtonian flow will be necessarily at lower nominal Reynolds number. Two regimes are explored as a function of the inlet velocity ratio r=Ub/Um : the ”deflecting” regime noted DR (r=1) and the ”impinging” regime noted IR (r=4). For the non-Newtonian cases, two viscous cores are observed before the junction. After the junction a laminar state is obtained for the lower flow rate conditions. Surprisingly, in spite of a large viscosity at rest, a self-sustained non-Newtonian turbulence is achieved except for one case. We describe existing vortex mechanisms which pilot the scalar mixing. In addition, we show that in the non-Newtonian cases, the existing peak of turbulence is only shifted in the DR case. The shift is probably due to the nature of the fluid and not to the dynamical regime. After an intense turbulent zone, we show that a re-laminarization zone appears in the non-Newtonian case which reduces the fluctuation as well as mixing. As a result, IR has a better mixing quality than DR.

Properties of a Terpolymer-Treated Soil: A 13C NMR Study

The Young’s modulus and the secant modulus of a terpolymer-treated soil as a function of the polymer’s characteristics are discussed in the context of a more general inelastic property known as the toughness parameter. The soil chosen was a sample of the State of Qatar subsoil. The terpolymer, designated TPAM, was characterized by a backbone structure of acrylamide, anionic carboxylate, and cationic (3-acrylamidopropyl-trimethylammonium chloride) repeat units. The backbone unit ratio was estimated from 13C NMR analyses. TPAM was synthesized by straightforward NaOH hydrolyses of an acrylamide/cationic copolymer. The correlations between the NaOH molarity of the hydrolysis solution, with the corresponding ratio of the anionic and cationic units, were shown to have a significant influence on the value of the toughness parameter. It is speculated that controlling the anionic and cationic ratio of a terpolymer is a general approach to optimize the toughness parameter of treated soils. Measurements of the molecular weight of TPAM were made, and comments on the importance of this feature are given. The equivalent viscosity was also recorded. It is pointed out that the work is particularly relevant to the practical problem of subsoil pavement stabilization in which the terpolymer acts as a soil binder. Suggestions on further work are given.

An elastoplastic fractal model for cylinder in contact with a smooth plane

A mechanical model of which a cylinder-based fractal body in contact with a rigid plat surface presented based on fractal theory. The generalized Weierstrass-Mandelbrot function is employed to derive the formulae of fractal surface asperities formed a smooth cylindrical surface. The existing conditions of which a single asperity is in elastic, elastoplastic or full plastic deformation are derived. When the cylinder-based fractal rough is uniformly divided into N subdivisions, a relation between the N subdivisions and the asperity geometric dimensioning is obtained. A modified size distribution function is adopted to obtain the relation between the dimensionless contact load and the real contact area. The results show: the critical areas of a single asperity are scale dependent. With an increase in the contact load and contact area, a transition from elastic, elastoplastic to full plastic deformation takes place in this order. The mechanical properties of the cylindrical rough surface are related to the range of the asperity frequency indexes. When the first six asperity frequency indexes are less than critical elastic frequency index n ec, the rough surface appears to be elastic property under contact load. When the first six asperity frequency indexes are between the critical elastic frequency index n ec and critical plastic frequency index n pc, the rough surface appears to be elastic property and elastoplastic property, otherwise the rough surface appears to be of inelastic property.

Compression Fatigue Crack Growth in Nacre and Its Implication on the Mechanical Performance of Orthopedic Implants

The aim of the present review is to present some phenomenological observations on compression fatigue crack propagation of nacre samples. The first part of the paper reviews the characteristics of hierarchical structure and the mechanical properties of nacre, which characterize its specific properties. We have investigated the main chemical constituents of nacre and determined their mineral elements. Electron microscopy studies revealed that nacre is composed of a single-crystal aragonite. In the second part of the paper samples of nacre have been tested in compression-compression fatigue under cyclic loading and a Paris curve have been constructed at a fatigue ratio of about 10, subjected to a 30 Hz sinusoidal compressive load. It has been demonstrated that two driving forces ΔK and Kmax mainly govern the overall fatigue crack growth of nacre. Nacre shows considerable ability to stop cracking. By means of axial compression tests, we identified a single elastic and inelastic property. Measurements based on experiments were first done. Mean values of compressive strength and modulus of elasticity were obtained for several samples. A three-point bending test was performed on polished nacre samples according to the international standards for Young’s modulus, bending strength. An attempt is made to explain qualitatively the mechanical behavior of nacre in terms of its submicroscopic structure. It is concluded that the precise geometric arrangement of the plates is highly important. The results obtained provide a director for the design of orthopedic implants.

Random response of vibro-impact systems with inelastic contact

The probability density and statistics of random response are investigated for vibro-impact systems with inelastic contact in this paper. The inelastic contact is described through an empirical model incorporating highly non-linear and inelastic mechanical property of the impact interface, and the system response is determined through the stochastic averaging and energy dissipation balance technique. The inelastic contact force is separated into an elastic restoring component and a dissipative component; the former is expressed as the gradient of the potential energy preserved in the system while the latter is approximated by a damping force with energy-dependent damping coefficient through energy dissipation balance technique. The averaged Itô stochastic differential equation with respect to system total energy is then derived through stochastic averaging. The solution of the associated Fokker–Plank–Kolmogorov equation yields stationary probability density of system total energy, joint probability density of system displacement and velocity, as well as statistics of system response. The agreement between analytical results and Monte-Carlo simulations validates effectiveness of the proposed technique.

The Factors that Influence the Rise of Counterfeit Luxury Products in Egypt

Nothing happens economically, until a customer's perception of value towards a certain product or service surpasses the price of the latter. Meaning, that value or emotion for a product or a service must at a certain point fluctuate high and above the fixed price in order for the transaction to be executed by the customer. The objective of this research is to attempt to explain this emotion consisting of hedonic and utilitarian components that leads Egyptians to perceive luxury product as a necessity casting an inelastic property over the former.They take a considerable amount of social risk to obtain this necessity. Some Egyptians are more and more inclined to purchase counterfeit luxury products. This research attempts to understand the factors behind such behavior. A counterfeit product is a product made with varying quality material using the same design, shapes, symbols, and even logos to resemble the original one but at a fraction of the price.

Experimental Investigation of Strain Rate Dependence of Nanocrystalline Pt Films

A new microscale uniaxial tension experimental method was developed to investigate the strain rate dependent mechanical behavior of freestanding metallic thin films for MEMS. The method allows for highly repeatable mechanical testing of thin films for over eight orders of magnitude of strain rate. Its repeatability stems from the direct and full-field displacement measurements obtained from optical images with at least 25 nm displacement resolution. The method is demonstrated with micron-scale, 400-nm thick, freestanding nanocrystalline Pt specimens, with 25 nm grain size. The experiments were conducted in situ under an optical microscope, equipped with a digital high-speed camera, in the nominal strain rate range 10−6–101 s−1. Full field displacements were computed by digital image correlation using a random speckle pattern generated onto the freestanding specimens. The elastic modulus of Pt, E = 182 ± 8 GPa, derived from uniaxial stress vs. strain curves, was independent of strain rate, while its Poisson’s ratio was v = 0.41 ± 0.01. Although the nanocrystalline Pt films had the elastic properties of bulk Pt, their inelastic property values were much higher than bulk and were rate-sensitive over the range of loading rates. For example, the elastic limit increased by more than 110% with increasing strain rate, and was 2–5 times higher than bulk Pt reaching 1.37 GPa at 101 s−1.

Numerical simulation of time-dependent fracture of graded bimaterial metallic interfaces

Stationary cracks along and near interfaces between two time-dependent materials are simulated using the finite element method (FEM) to examine crack tip fields and candidate driving force parameters for crack growth. Plane strain conditions are assumed. In some cases, a thin transition layer is included between the two materials. This transition layer features a functionally graded blend of properties of the two materials. An example of such a system is that of weld metal (WM) and base metal (BM) in a weldment, with the transition layer corresponding to the heat-affected zone (HAZ). Numerical solutions for the stress and strain fields of homogeneous and heterogeneous Compact Tension (C(T)-type) specimens are presented. The equivalent domain integral technique is employed to compute the J-integral for elastic-plastic cases as well as the C(t)-integral and transition times for creep behavior. Results from parametric studies are curve-fit in terms of transition layer thickness and crack position, inelastic property mismatches, and other independent model parameters. Results indicate that the incorporation of functionally graded transition layer regions leads to less concentrated stress and strain components along interfaces ahead of the crack tip. It is also shown that the computed fracture parameters are influenced by the transition layer properties.

Effect of Cooling Condition on Deformation of Continuously Cast Stainless Steel 304

This work investigated the effect of the cooling condition on the deformation that was found for continuously cast stainless steel 304 slabs. The transient heat-transfer finite element analysis under various cooling conditions yielded temperature distributions within the slab, which were then used for subsequent calculations of the deformed shape. The asymmetric cooling condition in a cooling pit induced non-uniform and asymmetric thermal gradients with elapsed time. The non-zero final deflection and the reversal of curvature for the slab during cooling were attributed to the combined effect of asymmetric temperature profile and inelastic material property. Parametric studies revealed that a slab material of a low thermal conductivity or yield strength resulted in an increase for final deflection. The present analysis explained the physical cause of the deformation reasonably well.

Dense GPS Array observations across the Atotsugawa fault, central Japan

A cross‐fault GPS array is established to reveal the crustal motion around the Atotsugawa fault located in a large strain rate zone, in central Japan. The array has 7 sites along a baseline of 30 km. Four‐year observations delineate a characteristic rate field; the eastward and the westward motions of 5 mm/yr at the sites 25 km apart from the fault gradually decrease and the directions of the motion change towards the ENE‐WSW fault strike, as approaching the fault. These observations are explained by a simple model; two 15‐km thick elastic blocks are obliquely colliding along the Atotsugawa fault with a rate of 20 mm/yr in an EW direction. However, in the zone sandwiched by the Atotsugawa and the Ushikubi faults, the rates are small and the rate vectors have the fault‐normal components, suggesting that the collision boundary forms a zone with lower elasticity or inelastic property.

Simple dynamic models of elastic–plastic structures under impact

The dynamic behaviour of elastic–plastic structures is much more difficult to predict in comparison with the corresponding quasi-static one because of complicated loading conditions and the effect of inertia. If the quasi-static structural and interface behaviour of a structure is specified, by assuming that its dynamic deformation mode is broadly similar to the quasi-static one and the material is strain-rate insensitive, two simple mechanical models, namely the stick model and non-stick model, are proposed in this paper to predict the dynamic response of the structure under a rigid-projectile impact. Each model contains two lumped masses and two inelastic springs. While spring represents the highly non-linear and inelastic mechanical property of the interface between the target structure and the striker, spring represents the elastic–plastic behaviour of the structure itself, with hardening, perfectly plastic or softening in the plastic range. With the complicated deformation history involving loading, unloading and reversed loading being taken into account, the dynamic response can be predicted by these models. A number of numerical examples are given to demonstrate the effects of the mass ratio, energy ratio, structural stiffness/local rigidity and the hardening/softening factor on the maximum and final deformations of the simple models. Finally, the validity of the models proposed for real structures is verified by the impact tests on simply supported beams.

Bending and Shear Properties of Cotton Fabrics Subjected to Cellulase Treatment

Changes in the residual curvature and residual shear strain of eight cotton fabrics after cellulase treatment are compared with those of a polyester staple fabric after alkali treatment. The residual curvature of the cottons decreases less than that of the polyester, and the residual shear strain in the weft measurements of the cottons also decreases less than the polyester. These behaviors can be explained by the fact that cotton fibers are hydrolyzed not only on the fiber surface, but also within the fiber by cellulase treatment. The relation of the change in residual curvature in weft measurements to treatment time and mass/area suggests that the inelastic property decreases less efficiently in the cottons than in the polyester. These observations are consistent with the fact that the inner structure of the cotton fibers is degraded during cellulase treatment.

The inelastic property of amorphous Cu 50Zr 50

Previously we reported that Young's modulus E of amorphous Cu 50Ti 50 increases, showing saturation with increasing strain amplitude ε t below about 25 × 10 −4 (= ε A hereafter), by several tens of a per cent at ε A. The increase in E is found to reflect the saturation behavior of the constituent inelastic strain ε i in ε t, where ε i is found to arise through some athermal process and to decrease with the annealing out of the free volume. In the present work, we further investigated the inelastic property of amorphous Cu 50Zr 50. The general features of the inelastic property observed in amorphous Cu 50Zr 50 are very similar to those in amorphous Cu 50Ti 50, suggesting that they reflect the common property of amorphous alloys. The model for the characteristic inelastic property is discussed.

Analysis program for the design of flexibly jointed frames

To estimate second-order effects on the behavior and strength of steel frames with semi-rigid connections, as well as to perform practical frame design easily and rationally, an attempt was made to develop a structural analysis program considering the characteristics of semi-rigid connections in a direct manner. The program was developed with the following three main routines: 1. 1. The practical procedure for structural analysis is based on a simplified method presented previously. This method uses the closed-form elastic solutions of beam-columns and takes into account the inelastic property of connections. 2. 2. The program PACOM (Parameter Analysis of Connection Models) prepares the parameters of semi-rigid connection models using the program SCDB (Steel Connection Data Bank). 3. 3. The graphic routine draws the general configuration and sectional force diagrams of the overall structure, the hysteresis loop in relation to the connection moment and relative rotation. The development of this system was made on an engineering workstation with a drawing function on a CRT display.

ON THE STABILITY OF SEMI-RIGID ORTHOGONAL FRAMES

Due to the inelastic property of beam-to-column connections, the stability of semirigid frames is affected not only by the loading and the unloading characteristics of connections at the critical points, but also by their load history up to these points, thus resulting in a complicated buckling behavior. Herein, utilizing the accurate method of analysis developed by authors, we precisely examined how the stability of semi-rigid frames is influenced by the modeling of connections, the load conditions and the load history caused by the cyclic wind load. With the information, so obtained, we further discussed the way of stability check to be used in design.

ANALYSIS OF INELASTIC CRITICAL BEHAVIOR OF SEMI-RIGID FRAMES

Different from the frames with rigid or pinned connections, the critical behavior of the semi-rigid frames is rather complicated due to the inelastic property of flexible connections. Thus, up to the present, no accurate method has been developed for its analysis. Herein, we present an accurate method which precisely takes into account the inelastic critical behavior with special emphasis on bifurcation. Further, with this method, rectangular frames with semi-rigid connections are analyzed to examine their critical behavior.

Origin of the incommensurate modulation of the 80-K superconductor Bi2Sr2CaCu2O8.21 derived from isostructural commensurate Bi10Sr15Fe10O46.

The compound ${\mathrm{Bi}}_{10}$${\mathrm{Sr}}_{15}$${\mathrm{Fe}}_{10}$${\mathrm{O}}_{46}$ is shown to be isostructural with the 80-K superconductor ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{O}}_{8.21}$. The incommensurate modulation of the Cu compound is commensurate in the crystal of the Fe compound that was selected. The modulation is caused by the insertion of extra oxygen atoms in the Bi layers and results in corrugated slabs. The structure of the Bi-O layers can be described as roughly 70% of rocksalt type and 30% of oxygen-deficient perovskite type. The results explain the excess oxygen in the superconductor, the mechanism causing the corrugation, and the inelastic bending property displayed by single crystals. They also reconcile apparently discrepant results about the oxygen distribution in the bismuth layers.