Showing papers on "Stress–strain curve published in 2009"
TL;DR: More accurate expressions for the ultimate axial strain and the compressive strength are proposed for use in this model in this paper, which can be easily incorporated into Lam and Teng's model for more accurate predictions.
Abstract: This paper presents the results of a recent study conducted to refine the design-oriented stress–strain model originally proposed by Lam and Teng for fiber-reinforced polymer (FRP)-confined concrete under axial compression. More accurate expressions for the ultimate axial strain and the compressive strength are proposed for use in this model. These new expressions are based on results from recent tests conducted by the writers’ group under well-defined conditions and on results from a parametric study using an accurate analysis-oriented stress–strain model for FRP-confined concrete. They allow the effects of confinement stiffness and the jacket strain capacity to be separately reflected and accounts for the effect of confinement stiffness explicitly instead of having it reflected only through the confinement ratio. The new expressions can be easily incorporated into Lam and Teng’s model for more accurate predictions. Based on these new expressions, two modified versions of Lam and Teng’s model are present...
437 citations
TL;DR: The results indicate that the physiological elastic modulus depends strongly on the definition of the stress-strain curve, mixing ratio, and the strain rate, and for various mixing ratios and strain rates.
Abstract: Tensile tests on Polydimethylsiloxane (PDMS) materials were conducted to illustrate the effects of mixing ratio, definition of the stress-strain curve, and the strain rate on the elastic modulus and stress-strain curve. PDMS specimens were prepared according to the ASTM standards for elastic materials. Our results indicate that the physiological elastic modulus depends strongly on the definition of the stress-strain curve, mixing ratio, and the strain rate. For various mixing ratios and strain rates, true stress-strain definition results in higher stress and elastic modulus compared with engineering stress-strain and true stress-engineering strain definitions. The elastic modulus increases as the mixing ratio increases up-to 9:1 ratio after which the elastic modulus begins to decrease even as the mixing ratio continues to increase. The results presented in this study will be helpful to assist the design of in vitro experiments to mimic blood flow in arteries and to understand the complex interaction between blood flow and the walls of arteries using PDMS elastomer.
224 citations
TL;DR: In this paper, a stress-strain model for FRP-confined concrete under cyclic axial compression is presented, and the model consists of the following major components: (a) a monotonic stress −strain approach for predicting the envelope curve; (b) new algebraic expressions for predicting unloading and reloading paths; and (c) predictive equations for determining the permanent strain and stress deterioration, with the effect of loading history duly accounted for.
215 citations
TL;DR: In this article, a servo-hydraulic test jig and a fixture were designed and manufactured for testing composites under uni-axial loading at quasi-static and intermediate strain rates of 0.001−100−1.
197 citations
TL;DR: In this article, the stress-strain behavior of extruded AA6xxx and AA7xxx aluminium alloys in T6 temper was studied at a wide range of strain rates, and the experimental data were used to identify the parameters of a thermo-viscoplastic constitutive relation for the extruded alloys.
197 citations
15 Nov 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors used finite element modeling (FEM) to evaluate the influence of the specimen dimensions and strain measurement methods on the tensile curves obtained from miniature specimens, and they demonstrated that the values of strain obtained from the crosshead displacement are critically influenced by the sample dimensions such that the uniform elongation and the postnecking elongation both increase with decreasing gauge length and increasing specimen thickness.
Abstract: Miniature tensile specimens, having various sizes and geometries, are often used to measure the mechanical properties of bulk nanostructured materials. However, these samples are generally too small for use with conventional extensometers so that the strains are usually calculated from the crosshead displacements. This study uses experimental results and finite element modeling (FEM) to critically evaluate the influence of the specimen dimensions and strain measurement methods on the tensile curves obtained from miniature specimens. Using coarse-grained Cu as a model material, the results demonstrate that the values of strain obtained from the crosshead displacement are critically influenced by the specimen dimensions such that the uniform elongation and the post-necking elongation both increase with decreasing gauge length and increasing specimen thickness. The results provide guidance on the optimum procedures for the tensile testing of miniature specimens of both coarse-grained and nanostructured materials.
191 citations
TL;DR: In this article, the natural strain (volume change divided by rock volume at the current stress state) was used in Hooke's law for accurate modeling the elastic deformation of that part of the pore volume subject to a relatively large degree of relative deformation (i.e., cracks or fractures).
178 citations
TL;DR: In this article, a micromechanical analytical model is proposed to address the problem of stiffness and yield stress prediction in the case of nanocomposites consisting of silica nanoparticles embedded in a polymer matrix.
157 citations
TL;DR: In this article, a servo-hydraulic type high speed tensile testing machine was used to obtain stress-strain curves of mild steel and advanced high strength steels at strain rates ranged from 1/sec to 200/sec.
Abstract: This paper presents stress-strain curves of steel sheets for an auto-body obtained at intermediate strain rates with a servo-hydraulic type high speed tensile testing machine. The apparatus has the maximum stroke velocity of 7.8 m/sec to obtain the tensile material properties at a strain rate of up to 500/sec. A special jig fixture is specially designed for accurate acquisition of tensile loads with reduction of the load-ringing phenomenon induced by unstable stress wave propagation at high strain rates. Tensile testing of steel sheets for an auto-body was carried out to obtain stress-strain curves of mild steel and advanced high strength steels at strain rates ranged from 1/sec to 200/sec. The test results provide interesting information regarding the stress-strain curves at intermediate strain rates ranged from 1/sec to 200/sec and demonstrate that strain rate hardening is strongly coupled with strain hardening.
147 citations
TL;DR: In this article, the effect of an increase in the oil volume fraction ( φ ) on the Young's modulus was studied for all gels according to the Van der Poel theory, and the relative impact was related to the viscoelastic properties of the gels and to droplet-matrix interaction.
119 citations
TL;DR: In this article, the authors used the Caputo fractional derivatives and a linear relation between stress and strain measures to obtain an integro-differential equation of motion, which is solved in the space of tempered distributions by using the Fourier and Laplace transforms.
Abstract: We study the motion of a one-dimensional continuum whose deformation is described by a strain measure of nonlocal type. In particular, we use the Caputo fractional derivatives and a linear relation between stress and strain measure to obtain an integro-differential equation of motion. This equation is solved in the space of tempered distributions by using the Fourier and Laplace transforms. The properties of the solution are examined and compared with the classical case.
TL;DR: In this paper, the Softened Membrane Model for Torsion (SMMT) is extended to reinforced concrete (RC) membrane elements under shear, which takes into account the strain gradient of concrete struts in the shear flow zone.
TL;DR: In this paper, the authors studied the micromechanical behavior of dual-phase alloys using the in-situ high-energy X-ray diffraction (HEXRD) technique and established a method to separate the stress and strain in the ferrite and martensite during loading.
Abstract: The direct measurement of the stress or strain partitioning during deformation in the materials, consisting of two phases with the same crystallographic structure and different microstructures, is still difficult so far. This is due to the fact that no effective characterization tool is available with the ability to distinguish the local strain and stress at microscale level. In this article, we studied the micromechanical behavior of ferrite/martensite dual-phase (DP) alloys using the in-situ high-energy X-ray diffraction (HEXRD) technique. We established a new method to separate the stress and strain in the ferrite and martensite during loading. Although the ferrite and martensite exhibit the same crystal structure with similar lattice parameters, the dependence of (200) lattice strains on the applied stress is obviously different for each phase. A visco-plastic self-consistent (VPSC) model, which can simulate the micromechanical behavior of two-phase materials, was used to construct the respective constitutive laws for both phases from the experimental lattice strains and to fit the macro-stress-strain curve. The material parameters for each phase extracted from our experiments and simulations could be used for designing other DP alloys and optimizing some complex industrial processes.
TL;DR: In this paper, the authors examined the performance of one mechanical strain relief technique particularly suitable for large section components, the deep hole drilling (DHD) technique, for estimating the magnitude of residual stress work by measuring strains or displacements when part of the component is machined away.
Abstract: Mechanical strain relief techniques for estimating the magnitude of residual stress work by measuring strains or displacements when part of the component is machined away. The underlying assumption is that such strain or displacement changes result from elastic unloading. Unfortunately, in components containing high levels of residual stress, elastic-plastic unloading may well occur, particularly when the residual stresses are highly triaxial. This paper examines the performance of one mechanical strain relief technique particularly suitable for large section components, the deep hole drilling (DHD) technique. The magnitude of error is calculated for different magnitudes of residual stress and can be substantial for residual stress states close to yield. A modification to the technique is described to allow large magnitudes of residual stress to be measured correctly. The new technique is validated using the case of a quenched cylinder where use of the standard DHD technique leads to unacceptable error. The measured residual stresses using the new technique are compared with the results obtained using the neutron diffraction technique and are shown to be in excellent agreement.
TL;DR: In this article, a finite element analysis (FEA) model was used to study the flexural performance of circular concrete-filled thin-walled steel tubular (CFST) beam.
Abstract: This paper presents a finite element analysis (FEA) modeling to study the flexural performance of circular concrete-filled thin-walled steel tubular (CFST) beam. A set of test data was used to verify the FEA modeling; generally, good agreement was achieved. The FEA modeling was then used to investigate the stress and strain distributions across the composite section in the whole loading procedure. The composite action between the steel tube and its concrete core was analyzed. A strut–tie model was proposed for the load transfer mechanism of the circular composite member subjected to pure bending.
TL;DR: In this paper, Fibre Reinforced High Performance Concrete (FR-HPC) subjected to high temperatures were experimentally investigated, and three different concretes were prepared: a normal strength concrete (NSC) and two High Performance Concretes (HPC1 and HPC2).
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01 Jan 2009
TL;DR: In this paper, the modified Wohler curve method was used for fatigue assessment of composite materials and the modified Manson-Coffin curve was used to assess the fatigue of welded structures.
Abstract: Useful stress quantities used in fatigue problems Fundamentals of fatigue assessment The modified Wohler curve method in fatigue assessment Fatigue assessment of notched components according to the modified Wohler curve method Multiaxial fatigue assessment of welded structures The modified Wohler curve method and metallic materials cracking behaviour under fatigue loading The modified Manson-Coffin curve method in fatigue assessment Multiaxial fatigue of composite materials.
TL;DR: In this article, the authors investigated the suitability of using an existing stress-strain model originally proposed by Popovics for OPC concrete to predict the load-deflection behavior and strength of geopolymer concrete structural members.
Abstract: Ordinary portland cement (OPC) has been traditionally used as the binding agent in concrete. However, it is also necessary to search for alternative low-emission binding agents for concrete to reduce the environmental impact caused by manufacturing of cement. Geopolymer, also known as inorganic polymer, is one such material that uses by-product material such as fly ash instead of cement. Recent research has shown that fly ash-based geopolymer concrete has suitable properties for its use as a construction material. Since the strength development mechanism of geopolymer is different from that of OPC binder, it is necessary to obtain a suitable constitutive model for geopolymer concrete to predict the load–deflection behaviour and strength of geopolymer concrete structural members. This article has investigated the suitability of using an existing stress–strain model originally proposed by Popovics for OPC concrete. It is found that the equation of Popovics can be used for geopolymer concrete with minor modification to the expression for the curve fitting factor, to better fit with the post-peak parts of the experimental stress–strain curves. The slightly modified set of stress–strain equations was then used in a non-linear analysis for reinforced concrete columns. A good correlation is achieved between the predicted and measured ultimate loads, load–deflection curves and deflected shapes for 12 slender test columns.
TL;DR: In this paper, the effects of stress and strain on the optical sensor were decoupled and analyzed independently, and it was shown that the effect of stress (as opposed to strain), and the relaxation of stress in the optical fibre during loading have a minimal effect.
Abstract: Optical fibre sensors have conventionally been made of silica. Polymers however have a much lower Young's modulus and higher elastic limit than silica, and can be incorporated into a larger range of materials. Whilst these properties make them attractive for using in mechanical sensing, using polymers also brings complexity because of their viscoelastic response. In this work, we use long period gratings (LPG) in microstructured polymer optical fibre (mPOF) as a mechanical optical sensor. The effects of stress and strain on the sensor are decoupled and analysed independently. Through experiments and modelling we show that the effect of stress (as opposed to strain), and the relaxation of stress in the optical fibre during loading have a minimal effect.
TL;DR: In this paper, the compressive properties of unidirectional glass-fiber reinforced polymeric composites using a servo-hydraulic testing apparatus at varying strain rates, ranging from 0.001 to 100 s−1.
TL;DR: In this paper, a model that regards the evolution behavior of the friction coefficient in the cylindrical compression test as a function of true strain on the basis of experimental results, allowing the effect of friction on the deformation curve at extremely high strain level to be evaluated and corrected for the first time.
Abstract: This article provides a model that regards the evolution behavior of the friction coefficient in the cylindrical compression test as a function of true strain on the basis of experimental results, allowing the effect of friction on the deformation curve at extremely high strain level to be evaluated and corrected for the first time. The compressive tests were carried out at a stroke rate of 1.2 mm/s on IHS38MSV hypoeutectoid steel with various lubricants at temperatures ranging from 800 °C to 1200 °C. The results showed that the friction coefficient for the compressive process was not constant and the variation could be approximated by an exponential equation along with the true strain. Microstructure observation showed that the stress increase in the later stages of process should be closely related to the large increase in the friction coefficient. The corrected curves were found to correlate well with the microstructure observation.
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08 Jan 2009
TL;DR: In this article, the authors discuss the effect of failure and failure on Axial Members and Pressure Vessels, Torsion Members, Bending Members, Beams and Combined Loading.
Abstract: Opening Remarks.- Statics.- Strain and Stress.- Axial Members and Pressure Vessels.- Torsion Members.- Bending Members: Beams.- Combined Loading.- Transformation of Stress and Strain.- Failure Criteria.- Buckling.- Energy Methods.- Ductile Materials and Design.- Effect of Flaws: Fracture.- Joints.- Composites.- Smart Systems.
TL;DR: In this article, parallel molecular dynamics simulations have been performed to study the deformation behavior of nanocrystalline copper samples with embedded nanotwins under approximately uniaxial tensile load.
TL;DR: In this paper, an experimental study of the stress corrosion cracking (SCC) process on 8mm-diameter wires which are used industrially in precast concrete prestressed by pre-tension is presented.
TL;DR: In this paper, the effects of deformation temperatures on the strain/stress distribution and microstructural evolution of 42CrMo steel during hot upsetting process were simulated by integrating the thermo-mechanica1 coupled finite element model.
TL;DR: In this article, a Viscous Pressure Bulge (VPB) test is described, which yields the equibiaxial stress point and r-value, as well as a plastic hardening curve for large values of plastic strain.
Abstract: The importance of an accurate material modeling for the accuracy and reliability of sheet forming simulations has become increasingly evident during the last years. More advanced material models have, however, to be supported by novel methods for material characterization. The recent eight parameter yield functions Yld2000-2d and BBC2003 demand, besides data from the ordinary uniaxial tensile tests, also equibiaxial data. In the present paper a Viscous Pressure Bulge (VPB) test is described. The test yields the equibiaxial stress point and r-value, as well as a plastic hardening curve for large values of plastic strain. The test setup is based on an ARGUSS™ optical measuring system, and provides the desired result data in a very smooth and easy way. In order to verify the results from the current test, comparisons have been made with compression tests performed at Corus RD&T and hydraulic bulging tests performed at RWTH in Aachen. A discussion on how to determine the equibiaxial yield stress and how to transform the biaxial stress-strain curve to an effective stress-strain curve is included in the paper.
TL;DR: Finite element analysis was used to predict the compressive impact response of low-density closed-cell polyethylene and polystyrene foams, and the predicted yield stresses were close to experimental data, for a range of foam densities as mentioned in this paper.
TL;DR: In this paper, a novel approach is presented for converting spherical nanoindentation load-displacement data into indentation stress-strain curves, without the need for continuous stiffness measurement (CSM).
TL;DR: In this paper, a polynomial formulation of the traction separation law and hydrogen dependent critical stress was applied to a 25%Cr duplex stainless steel and best agreement with the experiments was found for an initial critical stress of 2200 MPa and a critical separation of 0.005 mm.
TL;DR: In this article, a finite element-based model with quantized crystal plasticity (QCP) was developed to study distinctive features of nanocrystalline (nc) metal behavior, including an enhanced flow stress, extended plastic transition strain and propensity for strain localization.