Terms Of Stress-strain Curves Research Articles

Flexural Behaviour of Skinned Beams with Different Shapes of Steel Mesh Confinements

- Jacketing is a popular technique in modern civil engineering for strengthening and modifying structures. It is used to increase bearing load capacity or to restore structural design integrity after the structural design has been altered or after a structural member has failed. This method is typically utilized for horizontal surfaces such as the bottom and sides of beams and vertical surfaces such as walls and columns. This study investigates the flexural performance of high-strength concrete beams reinforced with steel wire mesh in various forms, such as hexagonal steel wire mesh, square wire mesh, and diamond wire mesh, using the concept of dual-layer concrete. At First, three sets of 450 x 50 x 50 mm beams were cast, and three different mesh configurations were confined around the beam and filled with concrete to form 500 x100 x 100 mm beams. The flexural behaviour of these beams was carefully examined under load controlling machine (UTM). The study found that adding steel wire meshes to beams as confinement enhances their total flexural strength and the behaviour of the beams failure mechanism when subjected to two-point stress. The Flexural strength has been increased by an amount of 10%, 23% and 35% respectively for hexagonal, square and diamond meshes. However, the specimen restricted with diamond mesh wrapped around the inner core performs more effectively than the specimen with Square and hexagonal wrapped around the core in terms of Stress-strain curves and Young’s Modulus.

Plasticity and ductility of an anisotropic recrystallized AA2198 Al-Cu-Li alloy in T3 and T8 conditions during proportional and non-proportional loading paths: simulations and experiments

The anisotropic material behaviour of a recrystallized AA2198 Al-Cu-Li alloy in T3 and T8 conditions was assessed by proportional loading of uniaxial-tension specimens in rolling (L), transverse (T) and diagonal (D) orientations. The width and longitudinal strains were measured to quantify plastic anisotropy. Notched-tension samples were tested in L and T directions. The material showed weak anisotropy in terms of stress strain curves and a moderate plastic anisotropy, consistent with its texture obtained by EBSD. An anisotropic Bron-Besson type material model was identified using this data base and a micro shear-only (SO) test. The model succeeded in predicting the behaviour of micro specimens for proportional tension-only (TO) loading and non-proportional load path changes including 'shear to tension' (ST) as well as 'tension to shear' (TS) tests. The non-proportional loading was achieved using a newly designed cross shaped sample. It was loaded in one direction, unloaded and subsequently loaded in the orthogonal direction till fracture. The average stretch to fracture of both alloys measured by a four point frame optical extensometer decreased by 29 % and 16 % for T3 and T8 respectively for the 'shear to tension' experiment compared to the proportional TO experiment. The average stretch to fracture of 'tension to shear' tests was reduced by 10 % for 2198T3 and hardly reduced for 2198T8 compared to the stretch to fracture of the SO tests, but subject to strong scatter. FE simulations showed local accumulated strain to fracture values that were similar for all loading histories for the T8 condition (0.73 − 0.84). Lower strain to fracture values were found in T3 condition (0.45 − 0.73), despite the enhanced macroscopic ductility in tension. This was attributed to larger less localized plastic zones, especially for the ST test. The ductility scatter was attributed to necking and damage development in tension that can affect strain localization, associated fracture path and ductility, as observed by DIC and fractography.

Numerical analysis of anisotropic stiffness and strength for geomaterials

In numerical modelling, selection of the constitutive model is a critical factor in predicting the actual response of a geomaterial. The use of oversimplified or inadequate models may not be sufficient to reproduce the actual geomaterial behaviour. That selection is especially relevant in the case of anisotropic rocks, and particularly for shales and slates, whose behaviour may be affected, e.g. well stability in geothermal or oil and gas production operations. In this paper, an alternative anisotropic constitutive model has been implemented in the finite element method software CODE_BRIGHT, which is able to account for the anisotropy of shales and slates in terms of both deformability and strength. For this purpose, a transversely isotropic version of the generalised Hooke's law is adopted to represent the stiffness anisotropy, while a nonuniform scaling of the stress tensor is introduced in the plastic model to represent the strength anisotropy. Furthermore, a detailed approach has been proposed to determine the model parameters based on the stress–strain results of laboratory tests. Moreover, numerical analyses are performed to model uniaxial and triaxial tests on Vaca Muerta shale, Bossier shale and slate from the northwest of Spain (NW Spain slate). The experimental data have been recovered from the literature in the case of the shale and, in the case of the slate, performed by the authors in terms of stress-strain curves and strengths. A good agreement can be generally observed between numerical and experimental results, hence showing the potential applicability of the approach to actual case studies. Therefore, the presented constitutive model may be a promising approach for analysing the anisotropic behaviour of rocks and its impact on well stability or other relevant geomechanical problems in anisotropic rocks.

Experimental investigation on tensile and shear bond behaviour of Basalt-FRCM composites for strengthening calcarenite masonry elements

The use of Fabric Reinforced Cementitious Matrix (FRCM) composites for structural retrofit has seen an increased interest among the scientific community, during the last decade. Various studies have revealed their effectiveness as external retrofitting technique of masonry elements, offering numerous advantages respect to the well know Fibre Reinforced Polymer (FRP) in terms of compatibility with masonry support, reversibility of intervention and sustainability. Despite the growing use, the characterization of FRCM mechanical behaviour is still an open issue, due to numerous uncertainties involved in test set-up adopted and fibre-mortar combination. The proposed experimental study aims to investigate the tensile and shear bond behaviour of Basalt-FRCM for strengthening calcarenite masonry elements. Calcarenite is a natural stone with sedimentary origin and it is widely present in existing buildings of the Mediterranean areas. Direct tensile tests are performed on two types of Basalt-FRCM coupons, with cement-based and lime-based mortar, adopting two different test-set-up based on clamping and clevis grip methods. Moreover, double shear bond tests are carried out to evaluate the adhesion properties of the two types of Basalt-FRCM with calcarenite support. Experimental outcomes are compared in terms of stress-strain curves, evaluating the influence of mortar grade and test set-up on the mechanical performances of Basalt-FRCM composites. The comparisons provide information about the mechanical stress transfer phenomena that occur at the fibre-to-matrix and FRCM-to-substrate interface level and the failure modes.

Analysis of CFRP Confined Concrete Cylinders by using ABAQUS Software

The fiber-reinforced polymer (FRP) wrapping is widely used in concrete column strengthening, as it can enhance concrete strength and ductility. This study aims to develop finite element numerical model that can capture the behavior of the short cylinder column confined with CFRP. After validating the proposed finite element models with previous experimental works, a series of parametric studies have been conducted, including, CFRP number of layers, concrete grade, confinement configuration, and size of samples are investigated in terms of stress-strain curves, ductility, and volumetric strain. The results indicate a significant improvement in concrete strength after fully CFRP wrapping. However, the partial confinement records less improvement in concrete strength but considerable ductility. By increasing the specimen’s size and maintaining the same confinement ratio, the strength enhancement was decreased. Based on this observation; it can be concluded that; by increasing the samples sizes, it should be escorted with more confining ratio than that of the small size. Moreover, it was concluded that as the number of layers increases the ductility increases whether it was full or partial confinement configuration. The CFRP confinement can control the specimen’s dilation during the axial compression test thus presenting less volumetric strain. The proposed formula by (Lam & Teng, 2003) that can predict the stress-strain response of FRP full confined concrete cylinder was compared with the corresponding values. The results indicated that; a good matching was noticed only for the samples located in the same area that was studied by (Lam & Teng, 2003).

Damage Characteristics of Recycled Aluminium Alloys AA6061 Undergoing Finite Strain Deformation of Tensile Loading

Recycling aluminium alloys has excellent advantages to avoid bad environmental effects while providing significant economic benefits. Many efforts are demanded to identify the appropriate applications, especially in automotive and aerospace fields. It can be observed that various recycling methods have been adopted and examined. However, it is generally agreed that there is still a need for improved recycling methods to fulfil the needs of the required applications as shown by its primary resources. It is amassive challenge and an obvious drawback in such materials due to the degradation of material’s properties related to damage, hence, must be critically analyzed before the potential applications can be identified. Based on this motivation, the present study establishes the effects of temperature and strain rate of hot-forged recycled aluminium alloys AA6061 via uniaxial tensile test implementations. The test is conducted at elevated temperatures of 100°C, 200°C and 300°C, at two different strain rates of 10-4 s-1and 10-3s-1. The tensile behaviour and damage are analyzed in terms of stress-strain curves and microstructural analysis, respectively. The microstructure and fracture surface of such materials are observed using Scanning Electron Microscope (SEM) and Optical Microscope (OM).Generally, the flow stress of recycled AA6061 increases with increasing strain rate and decreases with increasing temperature. The quantity and size of the micro-voids observed is enhanced with the increases in strain rate. It is due to the growth and coalescence of the micro-voids. From the OM analysis, the gap between the grain boundaries become wider with the increases in temperature; thus, the strength of the material decreases.

Performance of concrete beam reinforced with 3D printed Bioinspired primitive scaffold subjected to three-point bending

Concrete exhibits inherently low ductility and tensile strength despite its high compressive strength. Typically, it must be reinforced with steel rebars, yet it still suffers from potential corrosion issues. This work proposes and examines a new method for improving the bending stiffness of cementitious beams by reinforcing with 3D printed plastic TPMS-Primitive scaffolds. Three concrete beams of the same size - including non-reinforced, reinforced with one-layer, and two-layer bioinspired thin-walled molds - are designed and fabricated for three-point bending tests and comparisons. The simulation is found to be in good agreement with the experiment in terms of stress-strain curves and crack propagation. Results show the improved load-bearing capacity of the concrete beam reinforced with 3D-printed TPMS-Primitive shells. The peak load of the two-layer TPMS-Primitive reinforced beam is 35% and 125% higher than that of the one-layer reinforced beam and the non-reinforced concrete beam, respectively. Furthermore, the TPMS-Primitive reinforced concrete beams reveal a smooth softening behavior in bending and increase ductility as well. The scalable and sustainable production of such beams for construction applications could be realized by a combination of 3D printing techniques and recycled plastic.

Materials Characterisation and Fracture Mechanism of Recycled Aluminium Alloy AA6061 Reinforced with Alumina Oxide

This manuscript characterises the tensile behaviour and fracture mechanism of recycled aluminium alloy AA6061 reinforced with alumina oxide undergoing finite strain deformation of a uniaxial tensile test. The tests are conducted at three different strain rates of 6×10−3s−1, 6×10−2s−1, and 6×10−1s−1, at room temperature. The specimens are primarily examined in terms of stress-strain curves and microstructural analysis. The stress strain curve analysis is compared with the primary aluminium alloy AA6061. In general, the flow stress of both materials increases with increasing strain rate. The microstructures are investigated using Field-Emission Scanning Electron Microscopy (FESEM). The analysis on the deformed specimens showed that the deformation is driven by a ductile fracture mechanism via voids nucleation, and sensitive to the strain rate changes. The results of this work provide valuable information to improve the existing recycling process before an appropriate engineering application can be established in relevant areas.

Efficient simulation of single and poly-crystal plasticity based on the pencil glide mechanism

The present work demonstrates that the pencil glide mechanism is a physically reliable and a computationally efficient model to simulate the nonlinear behaviour of b.c.c. single and polycrystals. For that purpose, the pencil glide extension of Schmid’s criterion used by Gilormini [1] is incorporated in a single crystal model and in a homogenized polycrystal model accounting for large elastoviscoplastic deformations. The response of the pencil glide model in terms of stress-strain curves and lattice rotation is compared to the prediction based on the consideration of all ({110}〈111〉+{112}〈111〉) slip systems. In the case of α-iron single crystals both approaches are shown to accurately reproduce recent experimental results [2, 3]. The comparison is extended to α-iron polycrystals behaviour under tension, compression, rolling and simple shear loading conditions. The evolution of crystallographic textures obtained either based on pencil glide or using the 24 slip systems is analyzed and compared to classical experimental results from the literature. Limitations of the approach, especially in the case of simple shear textures, are also pointed out. The pencil glide approach can be viewed as a reduced order model enhancing computational efficiency of crystal plasticity simulations involving many slip mechanisms.

Tensile behaviour and damage characteristic of recycled aluminium alloys AA6061 undergoing finite strain deformation

The effects of temperature and strain rate of hot-forged recycled aluminium alloys AA6061 are examined via uniaxial tensile test implementations in this paper. The tests are conducted at elevated temperatures of 100 °C, 200 °C and 300 °C, at two different strain rates of 10−4 s−1 and 10−3 s−1. The tensile behaviour and damage characteristic are analysed in terms of stress-strain curves and microstructural analysis, respectively. The microstructure and fracture surface of such materials are observed using Scanning Electron Microscope (SEM) and Optical Microscope (OM). The flow stress of recycled AA6061 increases with increasing strain rate and decreases with increasing temperature. ImageJ software is used to quantify void characteristics. It is observed that the quantity and size of the micro-voids are strain-rate sensitive. This is due to the growth and coalescence of the micro-voids. The OM analysis shows the gap between the grain boundaries becomes wider with the increasing temperature that affects the strength of the material. The outcome of this work gives valuable information before the appropriate applications, especially in automotive and aerospace fields, can be established. It can be agreed that there is still a need for improved recycling methods to fulfil the needs in the required applications, as shown by its primary resources. It is a massive challenge and an obvious drawback in such materials due to the degradation of material’s properties related to damage.

Material properties and residual stresses of cold-formed high-strength-steel circular hollow sections

Owing to the development of material processing technologies, high strength steel plates with yield strengths exceeding 460 MPa are commercially available at present. However, experimental investigations on material properties and residual stress distributions of cold-formed high strength steel circular hollow sections (CHSs) are rather limited. This paper therefore presents an experimental investigation to advance the knowledge in this area. In total, 11 steel circular hollow sections were manufactured from steel plates with the measured yield strength varying from 546.5 MPa to 973.3 MPa. A total of 58 tensile coupons taken from parent plates and hollow tubes were tested to examine the effect of cold-forming process on material properties within the cross-section. When compared with parent metals, strength enhancements were found in Q460 sections, while yield strengths remained nearly the same as parent metal in Q690 sections, and a slight strength reduction by around 1% was noticed in Q960 sections. Basic material parameters in existing material models to obtain stress-strain curves were thoroughly calibrated against the coupon test results. Results indicate that the use of the calibrated parameters can give excellent predictions in terms of stress-strain curves. Residual stress measurements on 2 cold-formed CHSs were performed, with 57 strips extracted and 684 readings taken. The maximum tensile membrane residual stress and maximum tensile bending residual stress on the external surface were observed to be 41% and 32% of the material yield strength. A multilinear predictive model for the distribution of membrane residual stresses in cold-formed high-strength-steel CHSs was subsequently proposed.

Brick masonry panels strengthened with textile reinforced mortar: experimentation and numerical analysis

Composites materials comprising textiles embedded in organic or inorganic matrices are receiving great attention for their aptitude to be effectively applied as strengthening systems in existing structural components. The use of a Basalt Textile Reinforced Mortar (BTRM) composite to improve the in-plane shear behavior of brick masonry panels is here studied. The reinforcement is externally bonded to the masonry substrate. An experimental campaign is carried out involving diagonal compression tests on specimens strengthened with the BTRM system applied on one and both panel surfaces, experiencing asymmetric and symmetric reinforcement. The experimental response of unreinforced and reinforced panels is analyzed in terms of stress-strain curves, strength, stiffness and deformation capacity, crack pattern and failure mode. The experimental results are also compared with those obtained from a previous campaign carried out by the authors on tuff masonry panels reinforced with the same BTRM system, with the aim to investigate its effectiveness when applied to different masonry types. Finally, a relatively simple numerical model, suitably calibrated, is used to interpreter and analyze the results of the experimental investigation, leading to a validation of the model itself.

On the Use of Digital Image Correlation (DIC) for Evaluating the Tensile Behaviour of BFRCM Strips

Fibre Reinforced Cementitious Matrix (FRCM) composites are becoming largely adopted for retrofitting masonry structures. These materials offer several advantages in comparison to Fibre Reinforced Polymer (FRP) composites, such as good resistance to fire and high temperatures, vapour permeability, possibility to be applied on wet surfaces, higher compatibility with the masonry substrate. However, the tensile behavior of FRCM materials is more complex compared to FRP composites, due to the limited tensile strength of the cement-based matrix. For this reason, FRCM materials require appropriate tensile characterization and, in this context, the use of non-conventional measurement systems, such as the Digital Image Correlation (DIC), can offer numerous advantages. This work presents an experimental study on the application of the DIC technique for the tensile characterization of Basalt Fibre Reinforced Cementitious Matrix (BFRCM) strips. Tensile tests were carried out on three series of specimens reinforced with one, two or three layers of basalt grid in order to investigate the effect of the reinforcement ratio on the tensile response of the composite strips. The test setup and the calibration of the DIC analyses are discussed. It is shown as the DIC allows obtaining detailed information on the tensile response, including the evaluation of the full strain field on the surface of the BFRCM strips and the location of cracks. Results are discussed also in terms of stress-strain curves and failure modes.

Thermodynamically consistent and scale-dependent phase field approach for crack propagation allowing for surface stresses

A thermodynamically-consistent phase field approach for crack propagation which includes the following novel features is presented. (1) Scale dependency was included by relating the length scale to the number of cohesive interatomic planes at the crack tip. Because of this, the developed theory is applicable from the atomistic to the macroscopic scales. (2) The surface stresses (tension) are introduced by employing some geometrical nonlinearities even in small strain theory. They produce multiple contributions to the Ginzburg-Landau equation for crack propagation. (3) Crack propagation in the region with compressive closing stresses is eliminated by employing a stress-state-dependent kinetic coefficient in the Ginzburg-Landau equation. (4) The importance of analysis of the thermodynamic potential in terms of stress-strain curves is shown. The developed theory includes a broad spectrum of the shapes of stress-strain relationships. The finite element method is utilized to solve the complete system of crack phase field and mechanics equations. The effect of the above novel features is analyzed numerically for various model problems.

Uniaxial compressive tests on ancient brick masonry from heritage buildings under unsaturated freeze-thaw conditions

Freeze-thaw action, as an atmospheric impact, affects masonry by altering its original microstructures, which causes severe damage by decreasing the compressive strength of the masonry. This process, studied mostly under saturated conditions, in reality usually occurs under unsaturated conditions, which are characterized by more complex modes and have not been studied in depth before. To simulate and investigate processes and basic trends of these modes and examine the post-freeze-thaw compressive behaviors, we place our specimens (including ancient bricks and the mortar created and rebuilt masonry specimens) in an environmental chamber before performing compressive tests. We classify all specimens into eight scenarios, varying the numbers of freeze-thaw cycles and corresponding degrees of saturation. We discuss the impacts of these two factors on the compressive behaviors of the test specimens. Our results suggest that freeze-thaw cycles and degrees of saturation have combined effects on both ancient bricks and the mortar created. Under conditions of low saturation degree, freeze-thaw, as the primary factor, improves the strengths of both materials, although to a limited extent, while under conditions of high saturation degree, the degree of saturation becomes the predominant factor that results in the cracking and even failure of the materials, powered by freeze-thaw processes. Using these two factors (i.e., freeze-thaw action and degree of saturation), we summarize three different stages (or classified groups) in terms of stress-strain curves and crack development in masonry specimens based on the slopes of stress-strain curves and the rates of crack development. After studying all test results, we recommend an optimal saturation degree (approximately 50%) that is considered beneficial for ancient masonry in terms of freeze-thaw resistance.

Meso-scale modelling of mechanical behaviour and damage evolution in normal strength concrete

Modelling concrete at the meso-scale has been a topic of intensive research in the last decade, as this approach allows for improved understanding of meso-structure effects on the damage and failure of concrete. The majority of previous works focus on simple stress state, either tension or compression, which does not allow for clarifying the most suitable description of the behaviour of concrete constituents: aggregates, mortar, interfacial transition zones (ITZ) between aggregates and mortar, and entrapped voids. Here all these constituents are represented explicitly and a new combination of their behaviours is explored, applicable to both tension and compression. The work is based on synthetically generated concrete with spherical coarse aggregates and voids randomly packed without overlapping. The meso-structure is meshed and zero-thickness cohesive elements are inserted at ITZs. Aggregates are considered elastic, concrete damage plasticity (CDP) model with both tension and compression hardening is adopted for mortar, and cohesive zone model is used for ITZs. The results presented demonstrate very good agreement with experiments in both tension and compression, in terms of stress-strain curves as well as crack patterns. The proposed development is a promising step towards more realistic representation of concrete behaviour, which is required in practical cases where concrete experiences complex triaxial stress states.

Temperature-dependent crystal-plasticity model for magnesium: A bottom-up approach

A crystal-plasticity model is developed to account for temperature-dependent mechanical behaviour of magnesium in this paper. The constitutive description of plastic deformation accounts for crystalline slip and twining as well as their interactions. The temperature dependence is incorporated into the constitutive equations for both slip and twin modes based on experimental observations. A bottom-up computational modelling framework is proposed to validate the developed constitutive model. First, the crystal-plasticity model is calibrated with experimental results for plane compression at micro-scale. At meso-scale, a three-dimensional representative element volume was adopted to represent the microstructure of polycrystalline magnesium. In the combination with the proposed constitutive theory, the effects of temperature on mechanical response and evolution of twins and texture in polycrystalline magnesium were predicted. Comprehensive experimental validations at meso-scale were performed to consolidate further the developed crystal-plasticity model incorporating temperature dependence in terms of stress-strain curves, the Hall-Petch relationship and texture evolution. This work provides a useful modelling tool for understanding temperature-dependent behaviour of magnesium, which could be used to improve the formability of this family of materials.

Modeling the Mechanical Behavior of Dynamically Deformed Cu using the Theories of Crystal Plasticity

A phenomenological constitutive model for polycrystalline plasticity is evaluated by comparing the predictions for the evolution of deformation response of the material under dynamic compression. Copper (Cu) is selected as the model material. The mechanical response of dynamically deformed single crystal and polycrystalline Cu is simulated in the framework of finite element method. The results are in good agreement with the experiments in terms of stress-strain curves and shape changes albeit with different parameter sets for single crystal and polycrystal Cu. This is suggestive of the key role of other microstructural features like grain boundaries (absent in single crystals) in governing plasticity in polycrystalline materials.

A Physically Based Dynamic Recrystallization Model Considering Orientation Effects for a Nitrogen Alloyed Ultralow Carbon Stainless Steel during Hot Forging

The nitrogen alloyed ultralow carbon stainless steel is a good candidate material for primary loop pipes of AP1000 nuclear power plant. These pipes are manufactured by hot forging, during which dynamic recrystallization acts as the most important microstructural evolution mechanism. A physically based model was proposed to describe and predict the microstructural evolution in the hot forging process of those pipes. In this model, the coupled effects of dislocation density change, dynamic recovery, dynamic recrystallization and grain orientation function were considered. Besides, physically based simulation experiments were conducted on a Gleeble-3500 thermo-mechanical simulator, and the specimens after deformation were observed by optical metallography (OM) and electron back-scattered diffraction (EBSD) method. The results confirm that dynamic recrystallization is easy to occur with increasing deformation temperature or strain rate. The grains become much finer after full dynamic recrystallization. The model shows a good agreement with experimental results obtained by OM and EBSD in terms of stress-strain curves, grain size, and recrystallization kinetics. Besides, this model obtains an acceptable accuracy and a wide applying scope for engineering calculation.

Mechanical and Freeze-Thaw Durability Properties of Recycled Aggregate Concrete Made with Recycled Coarse Aggregate

AbstractThe influence of recycled coarse aggregates (RCAs) on the fresh, hardened, and freeze-thaw durability properties of recycled aggregate concrete (RAC) is investigated in the research reported in this paper. Four different mixes were considered with natural aggregate and three different replacement levels of RCA [i.e., (1) 30%, (2) 40%, and (3) 50%]. The fresh and hardened properties of RAC were investigated according to national standards where the target strength was 35 MPa in 56 days. The compressive strengths of different concrete mixes were determined after 3, 7, 28, 56, and 120 days of moist curing. The results are also presented in terms of stress-strain curves, modulus of elasticity, and Poisson’s ratio. Freeze-thaw durability performance of RAC was studied in accordance with a national standard. This paper shows that the performance of RAC slightly decreases with increasing RCA replacement levels; however, their overall performance is comparable to natural aggregate concrete (NAC). This pap...