Showing papers on "Stress–strain curve published in 2019"
TL;DR: In this article, the authors introduce a guideline on determining deformation and failure characteristics of rocks subjected to true triaxial compression on different stress path. But this guideline is not applicable to all types of rocks.
Abstract: The purpose of this ISRM Suggested Method is to introduce a guideline on determining deformation and failure characteristics of rocks subjected to true triaxial compression on different stress path. The true triaxial testing apparatus was reviewed by means of the function and engineering application. Some key techniques, such as stress and strain measurements, and reduction of end effect between specimen and metal platens, preventing metal platens interference, were stated and suggested in detail. Methodology of specimen processing, specimen shape, and testing procedure are characterized. There is an explanation of the experimental data processing on stress–strain curves, strength, and fracture mode.
78 citations
TL;DR: In this article, the authors developed a stress-strain model to describe the complete stressstrain curve consisting of the four stages of a concrete-filled FRP-confined steel tube.
Abstract: An FRP (fiber-reinforced polymer) -confined concrete filled steel tube is formed by the combination of FRP material and a concrete filled steel tube, and it combines the advantages of FRP-confined concrete and a concrete filled steel tube (CFT); however, there is still no effective model to generally describe the complete stress-strain curve of a concrete filled FRP-confined steel tube. The stress-strain response of a concrete filled FRP-confined steel tube features the dual characteristics of both FRP confined concrete and steel confined concrete. In this paper, ninety-six test results of FRP confined circular CFT columns under axial compression were collected from different researchers. The steel tube confinement index is taken as an additional key influencing parameter on the strength and deformation, and calculation methods for the ultimate strain, ultimate stress, peak strain and peak stress of a concrete filled FRP-confined steel tube are established by taking into account the steel tube confinement index. Moreover, the stress-strain model was developed to describe the complete stress-strain curve consisting of the four stages of a concrete filled FRP-confined steel tube. The proposed model reflects the characteristics of the stress-strain behavior of a concrete filled FRP-confined steel tube with good accuracy and simplicity.
76 citations
TL;DR: In this article, a design-oriented stress-strain model for FRP ring-confined concrete is proposed, and the results of an experimental program aiming to investigate the effect of the specimen size on the axial compressive behavior of circular concrete columns wrapped with FRP rings are presented.
68 citations
TL;DR: In this article, the authors investigated the mechanical properties and full stress-strain curve of lightweight aggregate concrete reinforced with steel and carbon fibres, involving specimens of strength classes ranging from LC40 to LC60 and fibre volume fractions from 0% to 0.9%.
58 citations
TL;DR: In this article, the authors investigated the direct tensile behaviors including tensile strength, stress-strain curve, energy absorption, and crack patterns of soil reinforced by cement and natural fiber, and proposed an empirical formula following three parameters (cement content, fiber content, and curing time) by using regression analysis.
Abstract: The present work was conducted to investigate the direct tensile behaviors including tensile strength, stress-strain curve, energy absorption, and crack patterns of soil reinforced by cement and natural fiber. In order to archive this, the direct tension test was designed to use for both reinforced and unreinforced specimens. The compacted 8-shaped samples with a wide range of cement content (0%, 4%, 8%, and 12%), fiber content (0%, 0.25%, 0.5%, and 1%), and curing days (7, 14, and 28 days) were prepared at optimum moisture content and maximum dry unit weight for the direct tension test. From experimental data, an empirical formula following three parameters (cement content, fiber content, and curing time) was proposed by using regression analysis. In addition, the effective degree of cement content, fiber content, and curing time on direct tensile strength was also examined based on the sensitive analysis. The experimental results showed that tensile properties (tensile strength, energy absorption capacity, and stress-strain curve) of cemented soil at low cement content and curing time were significantly improved with fiber inclusion. Direct tensile strength equaled to 0.483 and 0.071 times of splitting tensile strength and unconfined compressive strength, respectively. An acceptable regression model for predicting direct tensile strength was established. According to sensitive analysis, the ascending orders of effective parameters on direct tensile strength were fiber content, curing time, and cement content.
57 citations
TL;DR: In this paper, a finite element elastic-plastic contact model is developed which takes the gradients of hardness and initial residual stress into account, and the stabilized stress strain field is carried out by considering the shakedown state under the heavy load conditions.
54 citations
TL;DR: In this article, the authors compared the results of indentation plastometry with those obtained from uniaxial stress-strain plots via iterative FEM modeling of the process in which the plasticity is represented using a constitutive law.
53 citations
TL;DR: In this paper, a stress-strain model for fiber reinforced polymer (FRP) confined concrete cylinders were tested under six typical cyclic load patterns and the test results reveal that the partial cyclic stressstrain behavior is different from that under full cyclic loading.
Abstract: Most existing stress-strain models for fiber reinforced polymer (FRP) confined concrete are applicable to monotonic loading or complete cyclic loading where unloading/reloading is a continuous process between envelope curve and zero stress. However, load cycling is mostly incomplete or partial in practical problems where reverse of loading occurs before the previous load cycle is completed, and this unloading and reloading process is random. Cyclic model allowing for random partial load cycling is rare, if any, due to the lack of experimental data, and the insufficient understanding on the behavior of confined concrete under partial cyclic loading. In this study, FRP confined concrete cylinders were tested under six typical cyclic load patterns. The test results reveal that the partial cyclic stress-strain behavior is different from that under full cyclic loading. The key parameters determining unloading/reloading curves, such as reloading modulus, plastic strain, and tangent unloading modulus are related to loading history and axial stress level. It is found that the key parameters will change, or accumulative damage to concrete will occur, only under certain condition which is defined as effective partial cyclic loading in this work. A simple method is proposed to define the effective partial cyclic loading. Based on an existing complete cyclic model, a stress-strain model for FRP confined concrete under random partial cyclic loading is developed in this work. The proposed model performs well under different load patterns.
53 citations
52 citations
31 Mar 2019
TL;DR: In this paper, the relationship between the components of deformation rates and stresses is established, which allows to obtain a direct numerical solution of plastic deformation problems without FED iterative procedures, taking into account the real properties of the metal during deformation.
Abstract: It is shown that when modeling the processes of forging and stamping, it is necessary to take into account not only the hardening of the material, but also softening, which occurs during hot processing. Otherwise, the power parameters of the deformation processes are precisely determined, which leads to the choice of more powerful equipment. Softening accounting (processes of stress relaxation) will allow to accurately determine the stress and strain state (SSS) of the workpiece, as well as the power parameters of the processes of deformation. This will expand the technological capabilities of these processes. Existing commercial software systems for modeling hot plastic deformations based on the finite element method (FEM) do not allow this. This is due to the absence in these software products of the communication model of the component deformation rates and stresses, which would take into account stress relaxation. As a result, on the basis of the Maxwell visco-elastic model, a relationship is established between deformation rates and stresses. The developed model allows to take into account the metal softening during a pause after hot deformation. The resulting mathematical model is tested by experiment on different steels at different temperatures of deformation. The process of steels softening is determined using plastometers. It is established experimentally that the model developed by 89 ... 93 % describes the rheology of the metal during hot deformation. The relationship between the components of the deformation rates and stresses is established, which allows to obtain a direct numerical solution of plastic deformation problems without FED iterative procedures, taking into account the real properties of the metal during deformation. As a result, the number of iterations and calculations has significantly decreased.
44 citations
TL;DR: In this article, a finite element model of the borehole system and sealing equipment was built to study the stress and strain under internal pressure, and failure mechanisms of the sealing integrity of the cement sheath were obtained by combining the test results with the finite element calculations.
TL;DR: In this paper, the effect of fiber hybridization on concrete reinforced with metallic and non-metallic fibres on 30MPa concrete was investigated, where three hybrid combinations were considered, i.e., polyester (PO)-polypropylene (PP), 50% PO+50% PP and 25% PO +25% PP at a total fiber volume of 0.15%.
TL;DR: In this article, both strengthening and strain hardening were investigated in a dual-phase steel, consisting of ductile γ-austenite and almost non-deformable B2 intermetallic phase as the second phase of volume fraction of 23%.
TL;DR: In this article, the behavior of predamaged concrete prisms that were strengthened with fiber-reinforced polymer (FRP) jackets was investigated and the results of an experimental study was presented.
Abstract: This paper presents the results of an experimental study on the behavior of predamaged concrete prisms that were strengthened with fiber-reinforced polymer (FRP) jackets. Tests were conduct...
TL;DR: In this paper, the authors measured various characteristic parameters, such as stress-strain curve and acoustic emission under axial compression, for the frost-damaged coal gangue concrete, and found that the damaged layer thickness and peak strain increased, whereas the initial elastic modulus, peak stress and toughness decreased.
TL;DR: In this article, hot compression tests up to 60% deformation were carried out on both the equiaxed and lamellar morphologies in the temperature range of 750-950 °C and strain rates range of 0.001-10 s−1.
TL;DR: In this paper, a series of uniaxial/triaxial compression tests was conducted to understand the effects of concrete density, confining stress and strain rate on the mechanical properties of foamed concrete.
Abstract: Foamed concrete has a good energy absorption capability and can be used as seismic isolation material for tunnels. This study aims to investigate the mechanical properties and associated seismic isolation effects of foamed concrete layer in rock tunnel. For this, a series of uniaxial/triaxial compression tests was conducted to understand the effects of concrete density, confining stress and strain rate on the mechanical properties of foamed concrete. The direct shear tests were also performed to investigate the effects of concrete density and normal stress on the nonlinear behaviors of foamed concrete layer-lining interface. The test results showed that the mechanical properties of foamed concrete are significantly influenced by the concrete density. The foamed concrete also has high volumetric compressibility and strain-rate dependence. The peak stress, residual stress, shear stiffness and residual friction coefficient of the foamed concrete layer-lining interface are influenced by the foamed concrete density and normal stress applied. Then, a crushable foam constitutive model was constructed using ABAQUS software and a composite exponential model was also established to study the relationship between shear stress and shear displacement of the interface, in which their parameters were fitted based on the experimental results. Finally, a parametric analysis using the finite element method (FEM) was conducted to understand the influence of foamed concrete layer properties on the seismic isolation effect, including the density and thickness of the layer as well as the shear stiffness and residual friction coefficient of the interface. It was revealed that lower density and greater thickness in addition to smaller shear stiffness or residual friction coefficient of the foamed concrete layer could yield better seismic isolation effect, and the influences of the first two tend to be more significant.
TL;DR: A series of cyclic torsional shear tests using hollow cylinder apparatus (HCA) were performed to investigate the effect of principal stress rotation (PSR) on the stress-strain behaviors of saturated soft clay as discussed by the authors.
TL;DR: In this article, a constitutive model for Ti6Al4V titanium alloy is proposed that considers both material plasticity and damage, including the effects of strain hardening, strain-rate and the state of stress.
TL;DR: In this paper, extensive research has been conducted on FRP (fiber-reinforced polymers)-confined concrete columns under concentric compression, leading to many stress-strain models for such concrete.
Abstract: Extensive research has been conducted on FRP (fiber-reinforced polymers)-confined concrete columns under concentric compression, leading to many stress-strain models for such concrete. Thes...
TL;DR: In this article, the compressive response of confined concrete greatly depends on the mechanical properties of the confining material, and various stress-strain models have been proposed based on these materials.
Abstract: The compressive response of confined concrete greatly depends on the mechanical properties of the confining material. Based on these materials, various stress–strain models have been propos...
TL;DR: In this article, a modified local-to-global methodology was introduced to understand the effect of fiber reinforced polymer (FRP) confinement on square concrete section, which led to a methodology to evaluate the stress-strain behavior of concrete subject to arbitrary FRP confinement stress ratio at a local level.
TL;DR: In this paper, a comprehensive solution for the calculation of ground reaction curve (GRC) of circular tunnels is presented, considering all the affecting parameters including the previously studied ones and the new features, including intermediate principle stress, exponential decaying dilation parameter, weight of the damaged rock and Young's modulus variation in the excavation damaged zone (EDZ) on the GRC development.
TL;DR: In this paper, the local stress and strain in a heterogeneous microstructure induced by compression of aluminium rings under nearly full sticking conditions were analyzed using three complementary techniques: microhardness, electron microscopy (electron backscatter diffraction) and finite element modelling.
TL;DR: In this article, the uniaxial compressive stress-strain constitutive relation of corroded concrete in saline soil area of Western China is studied, and the constitutive model based on ion diffusion, chemical reaction and mechanical analysis was also given.
TL;DR: In this article, an analytical model for the response behavior of reinforced concrete beams strengthened in shear with FRP is presented, based on the Modified Compression Field Theory and can reproduce the whole load-displacement curve.
TL;DR: In this paper, the authors evaluated the viability and performance of concrete columns confined with the hybridization of jute and polyester composite sheets to utilize its superior properties, and showed that JPFRP confinement increased the strength, strain and ductility index.
Abstract: The strengthening and rehabilitation of concrete members is an important issue which arises worldwide. Carbon, aramid and glass fiber reinforced polymer (FRP) composites are mainly used for strengthening and rehabilitation. However, its use is limited on a small scale because of its high price, lack of availability and environmental impacts. The solution of this issue gives rise to the use of locally available natural fibers and low-cost synthetic fibers. This paper presents the experimental and analytical results of circular and square concrete columns confined with jute–polyester hybrid FRP composites. The main objective of this study is to evaluate the viability and performance of concrete confined with the hybridization of jute and polyester (FRP) composite sheets to utilize its superior properties. A novel hybrid technique has been applied for the wrapping of fiber sheets. The fiber sheets were applied in such a way that a uniform bond between the inner and outer layer was achieved. A total of 32 plain, standard size circular and square concrete specimens, externally wrapped with a jute–polyester FRP (JPFRP) composite, were tested under monotonic axial compressive loads. The result shows that JPFRP confinement increased the strength, strain and ductility index ranged between 1.24 and 2.61, 1.38 and 8.97, and 4.94 and 26.5 times the un-jacketed specimen, respectively. Furthermore, the wrapping has a significant effect on the low-strength specimens, having a circular cross-section. For high strength specimens, the post-peak stress-strain behavior was dominated by the outer polyester jacket because of its large rupture strain. Additionally, the test results were used to evaluate the existing strength-strain models derived for conventional FRPs. The models predicted values either underestimating or overestimating the compressive strength and strain of JPFRP-confined specimens. However, the strength models performed better than the strain models. The JPFRP wrapping significantly enhanced the strength, fracture energy, ductility index, and post-peak response. Therefore, JPFRP confinement can be used for a small-scale application, where little strength and high ductility is demanded. Moreover, it can be used to prevent the peeling of the concrete cover and moisture penetration into the concrete.
TL;DR: In this paper, thermal softening is used to generate ductile shear zones in the one-dimensional (1D), 2D and 3D models of viscous flow.
TL;DR: In this paper, the tension tests are systematically conducted on a polyurea by Instron and split Hopkinson tension bar apparatuses for strain rate ranging from 0.0001s −1 to −3000s−1, to investigate its mechanical behaviors.
TL;DR: In this paper, the authors proposed new theoretical and experimental stress-strain-damage correlation procedures for hard rock constitutive models, which can be used to predict the damage and stress states for compressive stress regimes.