Showing papers on "Stress–strain curve published in 2021"

Gradient and lamellar heterostructures for superior mechanical properties

Abstract: Heterostructured (HS) materials are a novel class of materials with mechanical properties that are superior over their conventional homogeneous counterparts. They are composed of HS zones with a dramatic difference in mechanical behaviors, which produces a synergistic effect on mechanical properties that are above the prediction by the rule-of-mixtures. Among all heterostructures, the two most studied are grain-size gradient structure and heterolamellar structure. These two heterostructures produce typical heterogeneous deformation during tensile deformation, producing long-range back stress in the soft zones and forward stress in the hard zones, which collectively produces hetero deformation-induced (HDI) stress to enhance the yield strength before yielding, and HDI hardening after yielding to retain ductility. In this article, we will focus on these two types of heterostructures. The issues, concerns, and progress are reviewed with the emphasis on the synergistic effect of mechanical properties, the fundamentals of several special plastic behaviors (e.g., strain gradient, HDI hardening and strain hardening), the plastic deformation mechanism, and the relationship between the microstructure and properties.

An Experimental Investigation into the Stress-Strain Characteristic under Static and Quasi-Static Loading for Partially Embedded Rock Bolts

Abstract: This article deals with a static and quasi-static load using the maximum power of a hydraulic pump. Additionally, quasi-static coefficients for the partially embedded rock bolts were determined. The laboratory tests included 2.2 m long bolts, which were embedded segmentally on the lengths of 0.05 m, 0.3 m and 0.9 m and were tested. To fix the ribbed bolt rods in the steel cylinders, resin cartridges with a length of 0.45 m long were used. The main aim of the research was to determine the load-displacement characteristics. Knowing the bolt rod tensile mechanism, the points of failure in the material continuity were identified, on the basis of which stress-strain characteristics are made. Particular attention was paid to the definition of: tensile stress for the yield point (σ1), maximum stress (σ2), stress at failure (σ3), strain in the elastic range (e1), strain for maximum stress (e2) and strain corresponding to the failure (e3).

Quasi-3D large deflection nonlinear analysis of isogeometric FGM microplates with variable thickness via nonlocal stress–strain gradient elasticity

Abstract: Via the nonlocal stress–strain gradient continuum mechanics, the microscale-dependent linear and nonlinear large deflections of transversely loaded composite sector microplates with different thickness variation schemes are investigated. Microplates are assumed to be prepared from functionally graded materials (FGMs) the characteristics of which are changed along the thickness direction. A quasi-3D plate theory with a sinusoidal transverse shear function in conjunction with a trigonometric normal function was employed for the establishment of size-dependent modelling of FGM microplates with different thickness variation schemes. Then, to solve the nonlocal stress–strain gradient flexural problem, the non-uniform rational B-spline type of isogeometric solution methodology was applied for an accurate integration of geometric discerptions. It was found that the gap between load–deflection curves drawn for linear, concave and convex thickness variation patterns became greater by changing FGM composite microplate boundary conditions from clamped to simply supported. In addition, it was found that by considering only the nonlocal size effect, the plate deflection obtained by the nonlocal strain gradient quasi-3D plate model was greater than that extracted by the classical continuum elasticity because of the softening character of nonlocal size effect, while the strain gradient microstructural size dependency acted in opposite way and represented a stiffening character.

Characterization of toughening mechanisms in UHPC through image correlation and inverse analysis of flexural results

Abstract: The nature of cracking in flexural specimens made using ultra-high-performance concrete (UHPC) is studied in the context of mechanisms of enhanced strength and ductility. The effect of fibers on the suppression of cracking and the attendant toughening mechanisms are addressed at two different fiber contents to elucidate the strain-softening and strain-hardening responses. Results indicate that the first crack strength is directly related to the fiber content, with fibers extending the stable crack growth region at high fiber contents such that flexural strengths as high as 20 MPa are obtained. Fiber bridging results in resistance to crack growth, stabilization, as well as multiple crack formation, all of which contribute to toughening. Using a combination of experimental results, digital image correlation (DIC) measurements of crack extension, and an analytical model for the flexural response, the stress and strain distributions across the depth of the specimens are determined, leading to stress-crack width relationships, and consequently, the relationship between tensile and flexural stresses in fiber-reinforced UHPCs. The results are also used to determine the tensile and compressive strain and stress distributions. Using back-calculated tensile properties from the flexural response and the 3-D DIC results, crack width profile and the stress-crack width relationship in tension are obtained for UHPCs, leading to a comprehensive understanding required for the structural design using such high-ductility materials.

Numerical analysis of the electromechanical behavior of high-field REBCO coils in all-superconducting magnets

Abstract: Despite the excellent improvement of high field by adopting REBa2Cu3Ox (REBCO) coated conductors (CCs), the resulting stress and strain due to winding tension, cooling stress and screening current-induced Lorentz force may lead to severe plastic deformation and degradation of superconductivity. Therefore, it is essential to understand the comprehensive electromechanical behavior and deformation mechanism of high-field REBCO magnets. In this paper, the multi-step finite element analysis is designed to simulate the electromechanical behaviors of REBCO coils after winding, cooling-down, and charging processes. All major constituent materials including mandrel, CCs, co-wind reinforcement and over-banding are considered in mechanical models to emulate contact-separation behavior between them. In addition to the contact nonlinearity, the intrinsic elastoplastic property is introduced to predict the plastic deformation observed by experiments. To reveal the screening current effect, the distributions of screening current and magnetic field are analyzed by solving T-A formulation of Maxwell's equations with homogenous technique. Then, with the electromagnetic load acting as body force, the electromagnetic stress and strain are computed and experimentally validated for pancake coil involving transport current and external field. Finally, the electromechanical behavior under Lorentz load is investigated by considering the accumulation of stress and strain due to winding tension and cooling down. Simulation results reveal that the winding tension and thermal stress affect the final stress-states at fully charged state and therefore the electromechanical properties. Both plastic deformation and possible degradation are more likely to occur in the outermost tape of several pancakes due to the influence of screening current-induced stress and strain. Besides, this work further analyzes the effect of current sweep reversal method, which could be favorable on reducing the screening current-induced high stress and strain at stable state.

Analysis-oriented stress-strain model for FRP-confined predamaged concrete

Abstract: In the area of structural rehabilitation, extensive research has been conducted on stress-strain models for fiber-reinforced polymer (FRP)-confined concrete. Most of the existing models are developed from tests conducted under laboratory conditions. However, structural repair work on concrete structures is usually applied to damaged concrete, which has different mechanical properties compared with those of normal concrete. An analysis-oriented stress-strain model of FRP-confined predamaged concrete columns was studied in this paper for the first time. Two state-of-the-art databases, including the cross-sectional variables, concrete damage degree, and FRP-confined stiffness, were established by collecting 313 test data points from the literature. Parameters in the analysis-oriented stress-strain model were well developed for FRP-confined predamaged concrete. The proposed models are unified in terms of column cross sections, which can predict both FRP-confined circular and square columns by considering the factor of the corner radius ratio. The proposed model shows a good performance by comparison with test data.

Modeling for complete stress-strain curve of circular concrete columns confined with steel spiral and FRP

Abstract: The results of 153 specimens from an experimental study on fiber-reinforced polymer (FRP) and steel spiral-confined (FRP-SS-confined) circular concrete columns were collected from accessible literature to establish a database. The existing models of FRP-SS-confined circular concrete columns were included and evaluated. A new stress-strain model with a simple, continuous, general expression was put forward for FRP-SS-confined circular concrete columns by taking into account various confining conditions during the loading process. Calculation models of the ultimate stress, ultimate strain, peak stress and peak strain were proposed by considering the contributions from both steel spiral confinement and FRP confinement. The comparison showed that the elastic stage, nonlinear transition stage, linear hardening stage and residual stage of the stress-strain curves were well captured by the proposed model for FRP-SS-confined circular concrete columns. Compared with other existing models, the proposed model showed better flexibility and versatility for practical application. In particular, various declining trends in the residual stages corresponding to the different confining conditions were well predicted by the proposed model. Furthermore, the effects of different parameters (steel tube thickness, FRP type, FRP layer and unconfined concrete strength) on the behavior of FRP-SS-confined circular concrete were discussed.

Stress-strain behaviour of cement mortars containing recycled glass during and after exposure to elevated temperatures

Abstract: The present communication investigates the stress-strain behaviour of a self-compacting mortar (SCM) prepared with RG (SCM-Glass) during exposure to elevated temperatures. Unlike a reference SCM prepared with 100% sand (SCM-Sand), which behaved similarly when tested during and after exposure to the elevated temperatures, the SCM-Glass samples suffered up to 83% and 67% decrease of the ultimate strength with a significant gain in the strain capacity during exposure to 600 °C and 800 °C, respectively. This was due to the melting and softening of RG which led to a dramatic deformation of the whole mortar matrix under the dead load. Interestingly, when tested after cooling to room temperature the SCM-Glass samples displayed higher elastic moduli but lower compressive strength than the SCM-Sand samples, indicating the melting and re-solidification of RG induced micro-crack filling effects and the accompanying ITZ improvement had a more beneficial effect on the elastic modulus than on the compressive strength.