Linear Stress-strain Relationship Research Articles

Earthquake Response of RC Infilled Frame with Wall Openings in Low-rise Hotel Buildings

To study the earthquake response of RC infilled frame structures with variable wall opening, 3-D computer models were made for 3, 4, and 5 storey typical hotel buildings consisting of six frames of 3 bays. In X-direction, the middle bay was open and the side bays were in-filled with full (solid) walls. In Y-direction, the interior walls consisted of door opening in the corner and the exterior walls consisted of window openings with variable ratios of 20%, 40%, 60%, 80%, and 100%. Prior to modeling the 3-D structure, 2-D validation models using diagonal strut and shell element were made based on test results of simple infilled frames with various openings. For the strut model, the wall with opening was modeled using diagonal strut of reduced width. For the shell element model the wall was modeled as is with gap element at the interface between the frames and the wall. Considering crack development and non linear stress-strain relationship of the materials, the lateral load-displacement diagrams of the shell element models fit the test result better than the strut ones. Models with lintels around the wall openings were also created for validation and the results show that lintels stiffen the frame and strengthen the wall around the openings. The shell element model was then used to create 3-D models of the hotel building with lintels around the wall openings. Analysis and design of the 3-D models show that the earthquake responses of RC frames infilled with walls of opening ratios 20% to 60% are significantly stiffer and stronger than that without infill wall. However, the contribution of infill walls with 80% opening in reducing storey drift and frame reinforcement was much smaller. Accordingly, the infill walls with opening ratios of less than 80% should be considered in the structural modeling to obtain a more accurate analysis and efficient design.

A mathematical model of the growth of uterine myomas.

Uterine myomas or fibroids are common, benign smooth muscle tumours that can grow to 10cm or more in diameter and are routinely removed surgically. They are typically slow- growing, well-vascularised, spherical tumours that, on a macro-scale, are a structurally uniform, hard elastic material. We present a multi-phase mathematical model of a fully vascularised myoma growing within a surrounding elastic tissue. Adopting a continuum approach, the model assumes the conservation of mass and momentum of four phases, namely cells/collagen, extracellular fluid, arterial and venous phases. The cell/collagen phase is treated as a poro-elastic material, based on a linear stress-strain relationship, and Darcy's law is applied to describe flow in the extracellular fluid and the two vascular phases. The supply of extracellular fluid is dependent on the capillary flow rate and mean capillary pressure expressed in terms of the arterial and venous pressures. Cell growth and division is limited to the myoma domain and dependent on the local stress in the material. The resulting model consists of a system of nonlinear partial differential equations with two moving boundaries. Numerical solutions of the model successfully reproduce qualitatively the clinically observed three-phase "fast-slow-fast" growth profile that is typical for myomas. The results suggest that this growth profile requires stress-induced resistance to growth by the surrounding tissue and a switch-like cell growth response to stress. Analysis of large-time solutions reveal that while there is a functioning vasculature throughout the myoma, exponential growth results, otherwise power-law growth is predicted. An extensive survey of the effect of parameters on model solutions is also presented, and in particular, the enhanced growth caused by factors such as oestrogen is predicted by the model.

Flexural Behaviour of Reinforced Concrete Beam with Glass Fiber Reinforced Polymer (GFRP) Bar Strengthened with Carbon Fiber Reinforced Polymer (CFRP) Plate

The use of glass-fiber-reinforced polymer (GFRP) bar to replace steel reinforcement in concrete structures is a relatively a new technique. The GFRP bars possess mechanical properties different from steel bars, including high tensile strength combined with low elastic modulus and linear stress–strain relationship up to failure. Therefore, design procedures and process should account for these properties. This paper presents the experimental work on the flexural behavior of concrete beam reinforced with GFRP bars and strengthen with CFRP plate. A total of ten reinforced concrete beams reinforced with either steel and GFRP bars were cast and tested under four point loads. Eight concrete beams (200x250x2800mm) were reinforced with 13mm diameter GFRP bars together with strengthening using CFRP plate and two control beams reinforced with 12mm diameter steel bars were tested. The experimental results show that although the stiffness of the beams reduced but the ultimate load of the GFRP reinforced concrete beam is bigger than steel reinforced beam. It was also found that strengthening using CFRP plate will further enhanced the flexural performance of the beams with GFRP bars.

Compressible Direct Numerical Simulation of Low-Pressure Turbines—Part II: Effect of Inflow Disturbances

In the present paper, direct numerical simulation (DNS) studies of the compressible flow in the T106 linear cascade have been carried out. Various environmental variables, i.e., background turbulence level, frequency of incoming wakes, and Reynolds number, and a combination of these were considered for a total of 12 fully resolved simulations. The mechanisms dictating the observed flow phenomena, including the mixing and distortion of the incoming wakes, wake/boundary layer interaction, and boundary layer evolution impact on profile loss generation, are studied systematically. A detailed loss generation analysis allows the identification of each source of loss in boundary layers and flow core. Particular attention is devoted to the concerted impact of wakes distortion mechanics and the intermittent nature of the unsteady boundary layer. Further, the present study examines the validity of the Boussinesq eddy viscosity assumption, which invokes a linear stress–strain relationship in commonly used RANS models. The errors originating from this assumption are scrutinized with both time and phase-locked averaged flow fields to possibly identify shortcomings of traditional RANS models.

Constitutive model of single root system's resistance to tensile stress - taking Pinus tabulaeformis, Betula platyphylla, Quercus mongolica and Larix gmelinii as experimental objects.

A constitutive model for the stress-strain relationship of single forest root system was developed in order to provide theoretical foundations for the mechanisms of soil-reinforcement by root system and offer a reliable basis for the analysis of root tensile strength character. This study started a general form of linear and non-linear stress-strain relation that was mathematically defined by four boundary conditions observed in typical tensile tests of single roots. The parameters of the model were determined by experiment data and had definite physical meaning. The model was verified by experiment data, which showed that the calculated values were in good agreement with the experimental single root tensile test results. The constitutive model was validated and found to be feasible for modeling single root tensile stress.

FRP Slab Capacity Using Yield Line Theory

Fiber reinforced polymer (FRP) bars have been increasingly used in bridge deck slabs over the last decades to overcome corrosion issues. However, there is still a critical need for a rational method to analyze the load capacity of such bridge deck slabs. Because FRP bars possess a linear stress-strain relationship, the moment-curvature response of FRP concrete section, either reinforced or prestressed, does not exhibit a distinct yield-plateau, thus it is unclear if conventional yield line theory is applicable. Therefore, the concept of an equivalent plastic moment capacity for FRP concrete sections is introduced and applied in yield line theory for bridge deck slabs. A full-scale bridge deck slab with precast panels reinforced and prestressed with aramid fiber reinforced polymer (AFRP) bars is experimentally tested under different wheel and axle load configurations on either interior spans or overhangs. The results confirm the high accuracy of the failure analysis using the yield line theory, where the load capacity predictions are within 3% accuracy of the experimentally observed results.

Ductility of externally prestressed continuous concrete beams

Ductility is a desirable structural property that allows stress redistribution and provides warning of impending failure. Factors affect the ductility of beams prestressed with external FRP tendons are different than those affect the ductility of ordinary bonded prestressed concrete beams due to lack of bond and linear stress-strain relationship of FRP tendons. This paper investigated the effect of several variables on the ductility of continuous concrete beams, externally strengthened using Parafil ropes. The test variables included external prestressing force value, depth of external prestressing tendons, loading pattern, tendon profile and location of deviators. Test results show that the ductility of the externally prestressed concrete beams significantly reduced due to prestressing. Also, the eccentricity of the prestressing force and the tendon profile had the main influence on ductility of the externally prestressed beams, while the variation in prestressing force value, loading pattern and location of deviators had a less effect.

Connective tissue lung: different composition between male and female

Abnormal elasticity of lung tissue has a major impact on the clinical progression and outcome of many lung diseases including respiratory distress syndrome, asthma, emphysema and pneumothorax post thoracic injury. The major components of lung connective tissue are elastin, collagen and together provide the lung with its elasticity and tensile strength. Elastin is composed of flexible cross-linked polypeptides and has a linear stress-strain relation up to 200% strain; collagen has a more organized structure with both crystalline and amorphous phases and exhibits a highly unlinear stress-strain curve. The thoracic injury is responsible for about 25% of death for injury and in particular it represent 12% of all death in man in comparison to 7% of dealt in female. This different in death rate is due to the different hormone levels between man and female. On the other hand female sex hormones, estrogens (e.g. 17b-estradiol) exert important biological actions, both protective and undesirable. In particular in addition to their primary function as reproductive hormones, estrogens (e.g. 17b-estradiol) influence a wide range of other physiological processes in humans and other mammals, including cardiovascular, respiratory, and neuronal function, and bone density.. With special respect to the cardiorespiratory system, estrogens promote lung development and differentiation and exhibit pulmonary and cardiovascular protective properties. However, very little is known about the different composition of the two major constituents of the connective tissue of the female and men lung. We have studied by CLSM the elastin an collagen in man and female lung. All proteins tested are present in lung tissue of male and female and they are localized in the peribronchiolar and in the interalveolar septum. The reaction to elastin shows very differences staining in the basal laminae of small and medium bronchioles in two sexes, in particular these structures stained very strongly in female but not in male. Opposite behavior we have showed to collagen type IV reactions. In male the collagen type IV is localized as a continuous network throughout the lung parenchymal tissue and in the basal laminae it shows strongly staining.

Synthesis and Properties of Thermosensitive Poly(N-Isopropylacrylamide)/Waterborne Polyurethane Graded Concentration Hybrid Films

Temperature-sensitive hybrid films were synthesized with a concentration gradient by casting and UV curing of N-isopropylacrylamide (NIPAAm) monomers (0%–70%) on the free surface of waterborne polyurethane (WPU) films on a Teflon substrate. The surface hardness and contact angle of the free surface with a water drop increased asymptotically with the addition of NIPAAm, whereas those on the substrate side were virtually unchanged. The diffusion coefficient (D), rates of swelling at 20°C (below the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM)) and deswelling at 50°C (above the LCST) increased with increasing NIPAM content, showing favorable thermosensitivity. In addition, the glassy state modulus and glass transition temperature (Tg) of the film increased with increasing NIPAM content, whereas the rubbery modulus decreased due to the increased molecular weight between the crosslinks. In addition, as the NIPAM content increased, the film showed a positive yield with an increased yield and fracture stress and decreased ductility. Above 50% NIPAM, the film became brittle, showing a linear stress–strain relationship.

Numerical Evaluation of Strain Rate Effect on Mechanical and Electromechanical Coupling Responses in BaTiO3 Single-Crystal Nanofilm

The mechanical and electromechanical coupling responses of a ferroelectric single-crystal nanofilm under displacement loading at different strain rates have been simulated using the molecular dynamics method based on the shell model. While the linear stress–strain relation is independent of the strain rate, strong strain rate dependence is exhibited in the electromechanical coupling response for strain rates between 0 ns−1 and 0.5 ns−1. There is an approximate semilogarithmic linear relationship between the polarization stability strain and the strain rate. With increasing strain rate, local 180° domain switches take place sequentially from inside to outside in the stable domain structure evolution, and the number of domain walls increases. However, after the strain rate exceeds 0.5 ns−1, it has almost no effect on the␣domain structure. This work is helpful for improving ferroelectric device design and expanding ferroelectric application fields.

Investigation of Nanomechanical Properties of β-Si3N4 Thin Layers in a Prismatic Plane under Tension: A Molecular Dynamics Study.

We report molecular dynamics simulations of the nanomechanical properties and fracture mechanisms of β-Si3N4 thin layers in a prismatic plane under uniaxial tension. It is found that the thin layers in the y loading direction display a linear stress-strain relationship at ε < 0.021, and afterward, the stress increases nonlinearly with the strain until fracture occurs. However, for the z direction, the linear response is located at ε < 0.051. The calculated fracture stresses and strains of the thin layers increase with strain rates both in both directions. The thin layers exhibit the higher Young's modulus of 0.345 TPa in the z direction, higher than that in the y direction. The origins of crack derive from N(2c-1)-Si and N(6h-1)-Si bonds for the y and z loading directions, respectively.

Essential work of fracture: An approach to study the fracture behavior of acrylic bone cements modified with comonomers containing amine groups

The fracture behavior of acrylic bone cements modified with comonomers containing amine groups was studied using the essential work of fracture approach. The cements were prepared with either 2-(diethylamino)ethyl-acrylate (DEAEA), 2-(dimethylamino)ethyl-methacrylate (DMAEM) or 2-(diethylamino)ethyl-methacrylate (DEAEM) as comonomer in the liquid phase. Double-Edge-Notched Tensión (DENT) specimens were tested in a universal testing machine at 5 mm/min. The results showed that the essential work (we) and nonspecific value of fracture (βwp) of bone cements modified with all percentages of comonomer were notably increased compared with unmodified bone cement. From Scanning Electron Microscopy (SEM) micrographs, ductile behavior was observed for modified bone cements, i.e. the crack propagation is stable, whereas the unmodified cement exhibited brittle behavior indicating unstable crack propagation. The use of the essential work of fracture approach is suggested to determine the fracture behavior of cements that do not exhibit a linear stress-strain relationship.

Analysis of the Flexible PDMS Capacitive Microsensor for the 3-axis Force Measurement

Analysis of a flexible capacitive microsensor is described to measure both normal and shear forces simultaneously and instantaneously for the potential application of gait analysis. The microsensor consists of two pairs of sensing electrodes and an in-between dielectric layer. When normal force is applied to the microsensor, the capacitances of two sensing electrodes increase because of the uniform compression of the dielectric layer. When shear force is applied, deformation of the dielectric layer induces the capacitance difference between two sensing electrodes. Therefore, by measuring the capacitance values and capacitance difference, the normal and shear force can be determined directly and simultaneously. Since the microsensor is designed for measuring large forces, polydimethylsiloxane (PDMS) is selected as the material of the dielectric layer because it has the advantages of high dielectric constant and tunable elasticity. But PDMS is an elastic material that has highly non-linearity of stress-strain relationship. In this work, PDMS characterization was conducted to investigate the stiffness under different mixing ratios of PDMS pre-polymer and the curing agent. PDMS in 16:1 mixing ratio was selected since it has the most linear stress-strain relationship with the highest elasticity based on our results. Hence, analysis of mechanical and electrical properties of the microsensor was performed and the capacitance changes under normal and shear stresses were calculated. The microsensor was design to support the maximum normal stress of 1.39MPa and shear stress of 85KPa based on the requirement of foot pressure measurement. The microsensor is designed using flexible materials and it is easy to access to the curved surface to measure its interfacial force with minimum disturbance. It has the potential to develop portable real time microsensor for many biomechanical applications.

Development of a flexible PDMS capacitive pressure sensor for plantar pressure measurement

Graphical abstractDisplay Omitted Highlights? A flexible capacitive sensor was developed for plantar pressure measurement. ? PDMS material was used for the dielectric layer of the sensor. ? The stiffness of PDMS was investigated under different mixing ratios. ? The sensor can measure the pressure up to 945KPa. A flexible capacitive pressure sensor has been developed for plantar pressure measurement in biomechanical application. Polydimethylsiloxane (PDMS) material was selected as the material of the dielectric layer because of its advantages of high dielectric constant and tunable elasticity. In this work, PDMS characterization was conducted to investigate the stiffness under different mixing ratios of PDMS pre-polymer and the curing agent. PDMS in 16:1 mixing ratio was selected since it has the most linear stress-strain relationship with the highest elasticity within our pressure region of interest. Since the sensor was designed for the measurement of the plantar pressure, it can measure the pressure up to 945kPa. Moreover, flexible printed circuit film was utilized as the sensor substrate for the minimum disturbance of the measurement to the curved surface and reservation of the electronic circuit integration. Because of the miniaturization and flexibility of the sensor, it has the potential to develop shoe-integrated sensor system for long-distance data collection for gait analysis.

Dilatation parameterization for two-dimensional modeling of nearly incompressible isotropic materials

A new method to model the stress–strain relationship in two dimensions is proposed, which is particularly suited for analyzing nearly incompressible materials, such as soft tissue. In most cases of soft tissue modeling, plane strain is reported to approximate the deformation when an external compression is applied. However, it is subject to limitations when dealing with incompressible materials, e.g., when solving the inverse problem of elasticity. We propose a novel 2D model for the linear stress–strain relationship by describing the out-of-plane strain as a linear combination of the two in-plane strains. As such, the model can be represented in 2D while being able to explain the three-dimensional deformation. We show that in simple cases where the applied force is dominantly in one direction, one can approximate the sum of the three principal strain components in a plane by a scalar multiplied by the out-of-plane strain. 3D finite-element simulations have been performed. The proposed model has been tested under different boundary conditions and material properties. The results show that the model parametrization is affected mostly by the boundary conditions, while being relatively independent of the underlying distribution of Young's modulus. An application to the inverse problem of elasticity is presented where a more accurate estimate is obtained using the proposed dilatation model compared to the plane-stress and plane-strain models.

Strain-based modeling of fatigue crack growth – An experimental approach for stainless steel

This study aimed at correlation of the crack growth rates to the strain range and assessment of the fatigue life by crack growth prediction. First, the fatigue crack growth rate was investigated using Type 316 stainless steel specimens. Cylindrical specimens were subjected to a fully reversed load in order to apply cyclic plastic strain. The crack growth during the tests was monitored by taking replicas. Then, the crack growth rates were correlated to a parameter derived using the strain range. It was shown that, under the same stress intensity factor range, crack growth rates obtained by the fully reversed fatigue tests were more than ten times those obtained using compact tension specimens under the small scale yielding condition, and the strain intensity factor derived assuming the linear stress–strain relation (strain hardening exponent of n=1) correlated well with the growth rates obtained under various conditions. That the strain intensity factor could represent the fatigue crack growth driving force was reasonably explained by the strain field at the crack tip as examined by finite element analyses. Finally, the relationship between the crack growth rates and the fatigue life was discussed. It was found that the fatigue life could be predicted by integrating the crack growth rates represented by the strain intensity factor without considering the incubation period before the crack initiation. The emergence of a crack with a depth of 0.1mm indicated the remaining fatigue life was less than 0.3Nf regardless of the applied strain range.

Finite Element Modeling of Reinforced Concrete Column under Monotonic Lateral Loads

response of reinforced concrete columns under lateral load has always been an area attracting research and practical interest. The importance of columns in building frame in terms of lateral stiffness has been subjected to growing attention in relation to soft storey phenomena and other seismic response analysis over times. Various numerical approaches has been attempted to correlate deflection with lateral load according to theories and field performance. A numerical analysis has been carried out in this study on column behavior subjected to lateral load. Cantilever columns have been modeled using finite element analysis package ANSYS considering non linear stress-strain relationship of concrete and bilinear behavior of steel. Effect of lateral reinforcement in terms of confinement has also been associated. For simplicity of analysis, only rectangular columns with single story height have been considered. The results have been compared with field experimental data. The response of load-deflection curve to change in column geometry has also been discussed. The load deflection curve found in this manner is almost linear with constant stiffness initially as suggested by ACI in the elastic zone. However stiffness gradually decreases in the plastic zone and finally tends to zero. Column response to change in column geometry is also according to the prescribed relations in ACI. Increase in stiffness has been found with decrease in height and increase in cross section. Finally the test results are compared with field experimental value where they show almost similar behavior.

Soft Projectile Impacts on Thin Reinforced Concrete Slabs: Tests, Modelling and Simulations

Numerical simulations of reinforced concrete structures subjected to high velocity impacts and explosions remain a difficult task today. Since ten years and more now, the CEA-Gramat has maintained a continuous research effort with the help of different French universities in order to overcome encountered difficulties in modelling the behaviour of concrete structures under severe loading. These difficulties are related to numerical aspects (convergence difficulties of the non linear stress strain relation in 3D configuration, efficiency of the numerical procedure and robustness), but also due to the ability of the material model to simulate the accurately behaviour of a very complex and heterogeneous material like concrete. A new concrete model, named PRM model, has been developed at CEA-Gramat (Pontiroli, Rouquand &amp; Mazars, [1], [2], [3]) to predict the concrete response under a large range of dynamic loadings.

J043023 繊維不連続部を有するCFRP積層板の損傷挙動([J04302]高分子基複合材料の加工と評価(2))

In fabricating complicated laminated composite structure by using prepregs, there may be fiber discontinuity in the structure which may influence the mechanical response of the structure. The fiber discontinuity also may act as a source of stress concentration and damage. In this regard, it is very important to understand the effect of fiber discontinuity. In the present study, the effect of fiber discontinuity in CFRP laminate is investigated experimentally. The damage initiation and growth near the fiber discontinuity are also discussed. Laminates which contain fiber discontinuity with different thicknesses are prepared. Tensile tests were conducted to investigate the mechanical response of the laminates. We observed the edge surface of the specimen around the fiber discontinuity. The strain away from fiber discontinuity show almost linear stress-strain relation until a certain stress level. The strain increases rapidly at a stress point, and after that, stress-strain curve shows almost linear stress-strain relation. The strain at the center of the specimens (fiber discontinuity site) shows nonlinear stress-strain relation at relatively low stress range. After the strain away from fiber discontinuity rapidly increased, the stress-strain curves of both points almost agreed with each other. The nonlinear stress-strain relation at the fiber discontinuity site implies that interfacial debonding initiate and progress around the fiber discontinuity in the relatively low stress range. The coincidence of the stress-strain curves from the two points after the sudden increase in the strain implies the delamination development and progress between the continuous and discontinuous layers.

Out-of-plane seismic analysis of Bozdogan (Valens) aqueduct in Istanbul

The Bozdogan (Valens) aqueduct in Istanbul is one of the most prominent water supply structures inherited from the Byzantine period. The paper investigates the out-of-plane seismic resistance of the aqueduct. The structural system of the aqueduct is composed of a series of piers connected to each other with arches at two tier levels. Taking advantage of the structural periodicity, only one pier of the highest part of the aqueduct is considered for the analysis instead of the whole structure. This pier is modelled as a cantilever prismatic element subjected to gravity load and increasing lateral load representing out-of-plane seismic loading. It is assumed that the pier is made of a no-tension material, with a linear stress-strain relationship in compression, and has infinite compression strength. To accomplish the solution, an efficient numerical model and solution procedure developed by La Mendola and Papia for investigating the stability of masonry piers under their own weight and an eccentric top load, is utilised and adapted to the problem at hand. The analysis showed that, although, the aqueduct can withstand out-of-plane earthquake ground motions of medium size and usually encountered periods, it is vulnerable to the ones containing long-period pulses. Key words: Bozdogan (Valens) aqueduct, seismic, out-of-plane resistance, numerical model.