Showing papers on "Stress–strain curve published in 2020"

Stress-strain curves of metallic materials and post-necking strain hardening characterization: A Review

Abstract: Fatigue Fract Eng Mater Struct. 2019;1–17. Abstract For metallic materials, standard uniaxial tensile tests with round bar specimens or flat specimens only provide accurate equivalent stress–strain curve before diffuse necking. However, for numerical modelling of problems where very large strains occur, such as plastic forming and ductile damage and fracture, understanding the post‐necking strain hardening behaviour is necessary. Also, welding is a highly complex metallurgical process, and therefore, weldments are susceptible to material discontinuities, flaws, and residual stresses. It becomes even more important to characterize the equivalent stress–strain curve in large strains of each material zone in weldments properly for structural integrity assessment. The aim of this paper is to provide a state‐of‐the‐art review on quasi‐static standard tensile test for stress–strain curves measurement of metallic materials. Meanwhile, methods available in literature for characterization of the equivalent stress–strain curve in the post‐necking regime are introduced. Novel methods with axisymmetric notched round bar specimens for accurately capturing the equivalent stress–strain curve of each material zone in weldment are presented as well. Advantages and limitations of these methods are briefly discussed.

Direct Tensile Properties and Stress–Strain Model of UHP-ECC

Abstract: This research developed an ultra-high-performance engineered cementitious composite (UHP-ECC), which combines the properties of strain-hardening, multiple cracking, and high mechanical stre...

Stress-strain behavior of polyethylene terephthalate fiber-reinforced polymer-confined normal-, high- and ultra high-strength concrete

Abstract: Polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites, which are made from recycled PET products and exhibit large rupture strain (LRS), have gained more and more attention in recent years on account of their environmentally friendly origin. One promising application of such fibers is in the confinement of concrete. Research is, however, limited and particularly for the stress-strain behavior of PET FRP-confined concrete. In light of such a knowledge gap, this paper presents an experimental investigation on the stress-strain behavior of PET FRP-confined normal-, high- and ultra high-strength concrete cylinders. It is found that the stress-strain behavior of the confined high-strength (as well as ultra high-strength) concrete specimens exhibits a strain hardening-softening-hardening behavior, while the confined normal-strength concrete specimens generally exhibit a monotonic ascending behavior. In addition, all concrete grades confined with the PET fibers exhibit a typical axial strain-hoop strain curve with an inflection point. A new design-oriented stress-strain model is then proposed based on a comprehensive review of experimental data for PET FRP-confined normal-, high- and ultra high-strength concrete. Comparisons between experimental results and predictions show that the proposed model provides satisfactory predictions for PET FRP-confined concrete.

Material Model Parameters for the Giuffrè-Menegotto-Pinto Uniaxial Steel Stress-Strain Model

Abstract: The uniaxial Giuffre-Menegotto-Pinto (GMP) constitutive steel model is widely used in nonlinear modeling of reinforced concrete components. However, the parameters characterizing this const...

Mechanical Properties and Stress Strain Relationship Models for Bamboo Scrimber

Abstract: In order to investigate the basic mechanical properties and stress strain relationship model for bamboo scrimber manufactured based on a new technique, a large quantities of experiments have been carried out. Based on the analysis of the test results, the following conclusions can be drawn. Two main typical failure modes were classified for bamboo scrimber specimens both under tension parallel to grain and tension perpendicular to grain. Brittle failure happened for all tensile tests. The slope values for the elastic stages have bigger discreteness compared with those for the specimens under tensile parallel to grain. The failure modes for bamboo scrimber specimens under compression parallel to grain could be divided into four. Only one main failure mode happened both for the bending specimens and the shear specimens. With the COV values of 28.64 and 25.72 respectively, the values for the strength and elastic modulus under tensile perpendicular to grain have the largest discreteness for bamboo scrimber. From the point of CHV values, the relationship among the mechanical parameters for bamboo scrimber were proposed based on the test results. Compared with other green building materials, bamboo scrimber manufactured based on a new technique has better mechanical performance and could be used in construction area. Three stress strain relationship models which are four-linear model, quadratic function model, and cubic function model were proposed for bamboo scrimber specimens manufactured based on a new technique. The latter two models gives better prediction for stress strain relationship in elastic plastic stage.

Femur auxetic meta-implants with tuned micromotion distribution

Abstract: Stress shielding and micromotions are the most significant problems occurring at the bone-implants interface due to a mismatch of their mechanical properties. Mechanical 3D metamaterials, with their exceptional behaviour and characteristics, can provide an opportunity to solve the mismatch of mechanical properties between the bone and implant. In this study, a new porous femoral hip meta-implant with graded Poisson’s ratio distribution was introduced and its results were compared to three other femoral hip implants (one solid implant, and two porous meta-implants, one with positive and the other with a negative distribution of Poisson’s ratio) in terms of stress and micromotion distributions. For this aim, first, a well-known auxetic 3D re-entrant structure was studied analytically, and precise closed-form analytical relationships for its elastic modulus and Poisson’s ratio were derived. The results of the analytical solution for mechanical properties of the 3D re-entrant structure presented great improvements in comparison to previous analytical studies on the structure. Moreover, the implementation of the re-entrant structure in the hip implant provided very smooth results for stress and strain distributions in the lattice meta-implants and could solve the stress shielding problem which occurred in the solid implant. The lattice meta-implant based on the graded unit cell distribution presented smoother stress-strain distribution in comparison with the other lattice meta-implants. Moreover, the graded lattice meta-implant gave minimum areas of local stress and local strain concentration at the contact region of the implants with the internal bone surfaces. Among all the cases, the graded meta-implant also gave micromotion levels which are the closest to values reported to be desirable for bone growth (40 µm).

Bounding surface plasticity model for stress-strain and grain-crushing behaviors of rockfill materials

Abstract: Crushing of grains can greatly influence the strength, dilatancy, and stress-strain relationship of rockfill materials. The critical state line (CSL) in the void ratio versus mean effective stress plane was extended to the breakage critical state plane (BCSP). A state void-ratio-pressure index that incorporated the effect of grain crushing was proposed according to the BCSP. Rowe’s stress-dilatancy equation was modified by adding the breakage void-ratio-pressure index, which was also incorporated into the formulations of the bounding stress ratio and plastic modulus. A BCSP-based bounding surface plasticity model was proposed to describe the state-dependent stress-strain behaviors and the evolution of grain crushing during shearing process of rockfill materials, and was shown to sufficiently capture the breakage phenomenon.

Measurement Modulus of Elasticity Related to the Atomic Density of Planes in Unit Cell of Crystal Lattices

Abstract: Young's modulus (E) is one of the most important parameters in the mechanical properties of solid materials. Young's modulus is proportional to the stress and strain values. There are several experimental and theoretical methods for gaining Young's modulus values, such as stress-strain curves in compression and tensile tests, electromagnetic-acoustic resonance, ultrasonic pulse echo and density functional theory (DFT) in different basis sets. Apparently, preparing specimens for measuring Young's modulus through the experimental methods is not convenient and it is time-consuming. In addition, for calculating Young's modulus values by software, presumptions of data and structures are needed. Therefore, this new method for gaining the Young's modulus values of crystalline materials is presented. Herein, the new method for calculating Young's modulus of crystalline materials is extracted by X-ray diffraction. In this study, Young's modulus values were gained through the arbitrary planes such as random (hkl) in the research. In this study, calculation of Young's modulus through the relationship between elastic compliances, geometry of the crystal lattice and the planar density of each plane is obtained by X-ray diffraction. Sodium chloride (NaCl) with crystal lattices of FCC was selected as the example. The X-ray diffraction, elastic stiffness constant and elastic compliances values have been chosen by the X'Pert software, literature and experimental measurements, respectively. The elastic stiffness constant and Young's modulus of NaCl were measured by the ultrasonic technique and, finally, the results were in good agreement with the new method of this study. The aim of the modified Williamson-Hall (W-H) method in the uniform stress deformation model (USDM) utilized in this paper is to provide a new approach of using the W-H equation, so that a least squares technique can be applied to minimize the sources of errors.

Neutron diffraction analysis of stress and strain partitioning in a two-phase microstructure with parallel-aligned phases.

Abstract: By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′ ) phases on the partitioning of stress and strain between these phases was investigated. Initially, tensile specimens of a Co-added stainless steel were heat treated by quenching and partitioning (Q&P) processing. Tensile specimens were subsequently loaded at 350 °C parallel to the length of the bands within the apparent elastic limit of the phase mixture. Lattice parameters in both axial and transverse directions were simultaneously measured for both phases. The observation of a lattice expansion for the γ phase in the transverse direction indicated a constraint on the free transverse straining of γ arising from the banded microstructure. The lateral contraction of α′ imposed an interphase tensile microstress in the transverse direction of the γ phase. The multiaxial stress state developed in the γ phase resulted in a large deviation from the level of plastic strain expected for uniaxial loading of single phase γ. Since segregation-induced banded microstructures commonly occur in many engineering alloys, the analysis of stress and strain partitioning with the present Q&P steel can be used to interpret the observations made for further engineering alloys with two-phase microstructures.

Stress strain performance of steel spiral confined recycled aggregate concrete

Abstract: Improvement of concrete strength owing to confinement by lateral reinforcement is disregarded in the current concrete design practice. The focus of this study is to use the pre-existing lateral reinforcement to enhance the behaviour of recycled aggregate concrete (RAC). The stress strain performance of steel spiral confined concrete specimens with different confinement pressure, recycled aggregates (RA) replacement ratio and target strength is studied. The results show a decrease in compressive strength of concrete with the rise in RA replacement ratio. Around 43, 37 and 33% drop in the strength is observed for 100% RA replacement ratio having different target strengths of NAC (i.e., 25, 40 and 60 MPa). However, steel confinement has a positive role to offset the negative effect of RA on strength. The rise in the confinement pressure results in improved ductility and stress strain behaviour of RAC. Due to scant research work related to steel spiral confined RAC, existing models cannot estimate the stress strain performance of steel spiral confined RAC effectively. Therefore, a new model is developed in this study, considering a large experimental program. The newly developed model can be effectively used to predict the stress strain performance of both steel spiral confined normal aggregate concrete and RAC, which provides guidelines for the design of RAC members. Furthermore, a relationship is also developed to determine the allowable content of RA for given confinement without affecting the concrete strength, which may be used to decide the allowable content of RA in designing the RAC compression members.

WS2 Nanotubes: Electrical Conduction and Field Emission Under Electron Irradiation and Mechanical Stress.

Abstract: This study reports the electrical transport and the field emission properties of individual multi-walled tungsten disulphide (WS2 ) nanotubes (NTs) under electron beam irradiation and mechanical stress. Electron beam irradiation is used to reduce the nanotube-electrode contact resistance by one-order of magnitude. The field emission capability of single WS2 NTs is investigated, and a field emission current density as high as 600 kA cm-2 is attained with a turn-on field of ≈100 V μm-1 and field-enhancement factor ≈50. Moreover, the electrical behavior of individual WS2 NTs is studied under the application of longitudinal tensile stress. An exponential increase of the nanotube resistivity with tensile strain is demonstrated up to a recorded elongation of 12%, thereby making WS2 NTs suitable for piezoresistive strain sensor applications.

Stress–strain relationship model of glulam bamboo under axial loading:

Abstract: Glulam bamboo has been preliminarily explored for use as a structural building material, and its stress–strain model under axial loading has a fundamental role in the analysis of bamboo components....

Effect of Freezing on Stress–Strain Characteristics of Granular and Cohesive Soils

Abstract: To investigate the stress–strain behavior of frozen soils, a program of triaxial compression tests was designed and carried out on samples of unfrozen and frozen cohesive (CL) and granular...

Radial-shear rolling of high-strength aluminum alloys: Finite element simulation and analysis of microstructure and mechanical properties

Abstract: The effect of high-temperature radial-shear rolling (RSR) on the strain and stress distributions in the cross-sections of processed rods has been studied using finite element method simulation for the industrial 7075 alloy and compared with that for the new Al7Zn2.8Mg0.7Ni0.55Fe0.2Zr alloy. The simulation has revealed a gradient strain distribution along the cross-section of the processed rods for both alloys. The lowest stress has been observed in the central part of the rods, whereas the peripheral zones have had the highest strain with a factor of more than 1.5. For both alloys, the maximum true strain localized in the peripheral zones of the rods (~10) has proven to be substantially higher than the true strain (~2.1) caused by change in the overall (linear) dimensions of the rods. The results of numerical simulation of the stress and strain distributions have been in a good agreement with the as-deformed structure. For example, we have observed the formation of a gradient structure consisting of deformed fibrous grains in the central parts of the rods (in the vicinity of their axes) whereas in the middle of rod diameter and in the surface layers that are exposed to the highest stress and strain the structure contained more equiaxed and finer grains formed during dynamic recrystallization. The results of uniaxial tensile tests have revealed that the mechanical properties of the 7075 alloy (UTS ~ 390 MPa, YS ~ 280 MPa and δ ~ 9.9%) after RSR are comparable to those of the new alloy the microstructure of which additionally contains fine intermetallic particles. Thus, radial-shear rolling can be considered as an efficient industrial technology of high-strength aluminum alloys allowing one to achieve a combination of high strength and ductility in as-processed materials with a gradient grain structure.