Tensile Stress-strain Relationship Research Articles

Fracture evaluation of ultra-high-performance fiber reinforced concrete (UHPFRC)

The development of numerical simulation for Ultra-high-performance concrete (UHPC) and Ultra-high-performance fiber-reinforced concretes (UHPFRC) is fundamental for the design and construction of related structures. The simplified engineering stress-strain relationship and the input values are necessary in the finite element modeling. Four-linear curves and modified Kent–Park model were proposed to describe the engineering tensile and compressive stress-strain relationship, respectively. An attempt was made to simulate the fracture of UHPC and UHPFRC using concrete damaged plasticity model and element deletion strategies. The predicted tensile and compressive behaviors of UHPC and UHPFRC were successfully validated by the test results in the literature. For a better understanding of the mechanical behavior of UHPC and UHPFRC exposed to biaxial loadings, mixed-mode crack propagation simulation on the double-notched specimens exposed to combined shear-tensile and shear-compressive forces was discussed.

Non-Linear Finite Element Analysis of RC Deep Beam Using CDP Model

Finite element analysis (FEA) is widely adopted these days to investigate relatively heavy structures such as reinforced concrete (RC) deep beam, which requires a higher investment of resources. This research aims to investigate a numerical modeling technique applicable to study the nonlinear behavior of RC deep beams by using FEA based on the software, ABAQUS. The nonlinear behavior of an RC deep beam adapted from an earlier research work is captured by using the uniaxial compressive and tensile stress-strain relationship and damage parameters of concrete. The response of the FE model is verified with the experimental results in terms of the load to midspan deflection curve and damage distribution. The ultimate shear capacity predicted by the FE model is 0.75% lower, and the corresponding displacement is 6.92% higher than the experimental results. The adopted modeling technique and the constitutive concrete models demonstrate the promising results indicating its possibilities for the investigation of RC structures.

A nonlinear uniaxial stress-strain constitutive model for viscoelastic membrane materials

Membrane materials with the excellent thermal, optical, electrical and chemical properties have attracted significant attention in numerous research fields recently. However, while being used to construct the membrane structures, the mechanical behaviors of membrane materials are more foundational than the other properties in evaluating the structure safety. This paper thus proposes a nonlinear stress-strain constitutive model for revealing the viscoelastic behaviors of membrane materials under uniaxial tensile loading. To this end, the constitutive equations for expressing the uniaxial tensile stress-strain relationships of viscoelastic materials are established gradually from the kinematic equations of the generalized Maxwell model that includes several basic Maxwell models and one basic spring element. Meanwhile, the uniaxial tensile tests of two typical viscoelastic membrane materials were carried out in order to examine the proposed constitutive model. The constitutive model parameters of the stress-strain properties of both membrane materials are accurately identified using the least square method. By comparing the true stress-strain curves between experimental results and constitutive models, good agreements with the maximum differences of 4.67% and 3.41% are acquired for the two employed viscoelastic membrane materials, respectively. These observations are able to validate the accuracy and efficiency of this proposed constitutive model in predicting the uniaxial stress-strain behaviors of viscoelastic membrane materials, which are significant in the nonlinear structural analysis of membrane structures.

Mechanical and self-healing behavior of low carbon engineered cementitious composites reinforced with PP-fibers

While the ultrahigh tensile ductility and superior durability of Engineered Cementitious Composites (ECC) have been demonstrated, the relatively high energy and carbon intensity, as well as high material cost present potential impediments to broader ECC applications. The objective of this research is to develop a more sustainable and cost-effective ECC. The ordinary Portland cement (OPC) and the commonly used PVA fiber in conventional ECC were replaced by limestone calcined clay cement (LC3) and polypropylene (PP) fiber, respectively. The ECC compressive strength, tensile stress-strain relationship, and microcrack self-healing behavior were studied at three water to binder ratios (0.3, 0.2, 0.16). The novel LC3-PP-ECC showed a tensile strain capacity of greater than 6% and an intrinsically tight crack width below 82 μm when loaded to 1% tensile strain. Further, the LC3-PP-ECC demonstrated efficient recovery of the composite tensile ductility and ultimate tensile strength through self-healing. Compared to typical ECC made with OPC and PVA fiber, the material cost, embodied energy and carbon footprint of LC3-PP-ECC are reduced by 61%, 45%, and 48%, respectively. The superior mechanical properties and durability combined with the low environmental impact and cost for material production promote LC3-PP-ECC as a sustainable material for structural and non-structural applications.

Effect of functionalized nano-SiO2 addition on bond behavior of adhesively bonded CFRP-steel double-lap joint

The mechanical properties of adhesives significantly influence the bond behavior of steel structures strengthened by carbon fiber-reinforced polymer (CFRP) composites. In order to improve the toughness of the adhesive and the ductile behavior of adhesively bonded CRFP-steel joint, functionalized nano-sized silica (hereafter refer as nano-SiO2) toughening agent were added into the adhesive. Firstly, the effects of functionalized nano-SiO2 toughening agent on the mechanical properties of the adhesives after curing at room temperature were tested and analyzed. Then, a total of 19 adhesively bonded CFRP-steel double-lap joints were fabricated and tested under shear loading to investigate the effect of functionalized nano-SiO2 on the bonding behaviors, including the failure modes, bond–slip relationships, bond strength and so on. The test results indicate that tensile stress–strain relationship of the adhesive changes from linear to nonlinear with the increase of functionalized nano-SiO2 toughening agent, the elongation at break, strain energy and shear strength of functionalized nano-SiO2-toughened adhesive (ZR14-weight ratio of 1% functionalized nano-SiO2) was improved by 202.88%, 292.10% and 133.12% respectively in comparison to the adhesive without functionalized nano- SiO2 toughening agent. Moreover, the tensile strength, elongation at break, and strain energy of functionalized nano-SiO2-toughened adhesive ZR14 are much higher than those of commercial adhesives (e.g. Sika30, 330) without Nano-SiO2. In addition, the failure mode of CFRP-steel joints changed from interface failure to CFRP plate delamination, when the weight ratio of functionalized nano-SiO2 to adhesive increasing from 0 to 1%. The bond-slip curves could be simplified into a bilinear model (triangle-shape) for CFRP-steel joints without and with only weight ratio of 0.5% functionalized nano-SiO2, however, the bond-slip curves change to simplified trilinear model (trapezoidal shape) for the joints with 1% functionalized nano-SiO2 and the toughness of bonding interface is significantly improved. In all, the CFRP-steel lap joints bonded by adhesive with appropriate amount functionalized nano-SiO2 (i.e., wt. of 1%) shows superior interfacial performance.

Experimental study on the engineering properties of alkali-activated GGBFS/FA concrete and constitutive models for performance prediction

This study focuses on elucidating the engineering properties of alkali-activated GGBFS/FA concrete. In order to consume more industrial by-products, water-quenched slag (WQS) is used as an alternative to river sand in alkali-activated concrete (AAC). In particular, this study examines the responses of AACs under different loading conditions, including static compression and tension loads and dynamic impact pressures. The static compressive stress-strain relationship, modulus of elasticity, direct tensile stress-strain relationship and dynamic response under impact loads of ambient-cured AACs are studied experimentally. Moreover, constitutive models are established by fitting the test results of the AACs. Compared with the existing models recommended for OPC-based concrete, the inclusion of new material parameters in the new proposed models achieves more realistic and reliable predictions for the AACs. It is found that AACs incorporating WQS particles exhibit better deformability in elastic range and ductility in stress descending range compared to OPC concrete.

Stress–strain relationship model of glulam bamboo under axial loading

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. To study the tension and compression behaviour of glulam bamboo, the bamboo scrimber and laminated bamboo as two kinds of typical glulam bamboo materials were tested under axial loading. Their mechanical behaviour and failure modes were investigated. The results showed that the bamboo scrimber and laminated bamboo have similar failure modes. For tensile failure, bamboo fibres were ruptured with sawtooth failure surfaces shown as brittle failure; for compression failure, the two modes of compression are buckling and compression shear failure. The stress–strain relationship curves of the bamboo scrimber and laminated bamboo are also similar. The tensile stress–strain curves showed a linear relationship, and the compressive stress–strain curves can be divided into three stages: elastic, elastoplastic and post-yield. Based on the test results, the stress–strain model was proposed for glulam bamboo, in which a linear equation was used to describe the tensile stress–strain relationship and the Richard–Abbott model was employed to model the compressive stress–strain relationship. A comparison with the experimental results shows that the predicted results are in good agreement with the experimental curves.

A comparative study on the mechanical properties of polymeric monofilaments

This paper presents a comparative study on the mechanical properties of seven monofilaments of 0.12 mm diameter made with different polymeric materials including PET, PBT, PE, PP, and PA6 in order to assess their suitability for being spacer yarns for developing high-quality spacer fabrics. Their support capability and elasticity corresponding to fabric compression resistance and resilience, respectively, were evaluated by analyzing the tensile stress–strain relationships and residual strains of monofilaments subjected to cyclic tensile loading. Slack and taut heat setting on the monofilaments were also considered to select a proper heat setting method for their spacer fabrics. The mechanical properties of the monofilaments were explained by using the supramolecular structure information from X-ray diffraction and sonic orientation tests. The results showed that PET monofilaments have much higher moduli than the other monofilaments and possess better support capability as spacer yarns for spacer fabrics. PET monofilaments also have better elasticity under small deformation below 5% strain than the other monofilaments, but their elasticity is inferior under large deformation above 5% strain. PET monofilaments are suitable for being spacer yarns to achieve high compression resistance and resilience for spacer fabrics. The PET monofilament with higher molecular weight possessed the lower Young’s modulus which is good for the knitting process. PET monofilaments with high molecular weight and taut heat setting are recommended for producing spacer fabrics with high compression resistance and resilience, especially for small fabric deformation.

STRESS-STRAIN RELATION FOR CONCRETE IN NONUNIFORM TENSION

Discrepancy between reported in the literature tensile stress-strain relations for concrete is addressed. A conclusion is reached that in the post-peak (softening) range of deformation the stress-strain relation is not unique and depends on the gradient of stress. A simplified variant of such a relation, intended for analysis of concrete beams with regard to the effect of size (the depth of section), is proposed.

Tensile stress-strain characteristics of rubberised concrete from flexural tests

The tensile characteristics of rubberised concrete are practically impossible to obtain from direct tensile tests, due to the non-uniform distribution of aggregates and stiffness. In this paper, notched three-point bending tests are used to characterise Mode I fracture behaviour of concrete incorporating high volume of rubber particles obtained from post-consumer tyres. The test results show that rubber particles enhance energy absorption capacity and ductility of concrete. Inverse finite element analysis is performed to indirectly determine tensile stress-strain curves of rubberised concrete. The key material parameters introduced in the constitutive model are tensile strength, fracture energy and crack band width. The spurious mesh dependency is resolved by adopting a simple modification to the softening modulus as a function of element size. The performance of the proposed tensile stress-strain relation is compared with that of Model Code 2010 using ABAQUS concrete damaged plasticity model and shows considerably better accuracy. The proposed model can be used to improve the reliability of numerical analyses of rubberised concrete elements and structures.

Effect of Water on the Dynamic Tensile Mechanical Properties of Calcium Silicate Hydrate: Based on Molecular Dynamics Simulation

To study the effect of water on the dynamic mechanical properties of calcium silicate hydrate (C–S–H) at the atomic scale, the molecular dynamics simulations were performed in uniaxial tension with different strain rates for C–S–H with a degree of saturation from 0% to 100%. Our calculations demonstrate that the dynamic tensile mechanical properties of C–S–H decrease with increasing water content and increase with increasing strain rates. With an increase in the degree of saturation, the strain rate sensitivity of C–S–H tends to increase. According to Morse potential function, the tensile stress-strain relationship curves of C–S–H are decomposed and fitted, and the dynamic tensile constitutive relationship of C–S–H considering the effect of water content is proposed. This reveals the strain rate effect of the cementitious materials with different water content from molecular insights, and the dynamic constitutive relationship obtained in this paper is necessary to the modelling of cementitious materials at the meso-scale.

The constitutive behavior of Ti–5Al–3V–2Cr–2Fe under high-velocity impact: Experimental, modeling, and validation

The compressive and tensile stress–strain relationship and fracture behavior of a new low-cost titanium alloy Ti–5Al–3V–2Cr–2Fe (Ti–5322) at 286–573 K, a strain rate of 0.0001–4300 s−1 and a stress triaxiality of 0.43–1.6 were studied. Based on the experimental data, the flow and fracture behavior of Ti–5322 was established based on the Johnson–Cook (J–C) equation. Ballistic impact tests were used to study the ballistic performance of a 7-mm-thick Ti–5322 target and the accuracy of the constitutive model was verified from the ballistic test results. The experimental results showed that the yield strength and strain rate of the Ti–5322 were related logarithmically. As the strain rate increased, the rate-strengthening behavior of the material weakened gradually. The material had an obvious thermal-softening behavior and the yield strength decreased linearly with an increase in deformation temperature. The stress triaxiality and strain rate had a significant effect on the fracture behavior of Ti–5322. The material fracture strain decreased with the stress triaxiality and an increase in strain rate. The J–C constitutive model was a good predictor for the ultimate penetration velocity of the Ti–5322 target and the velocity decay of fragments during penetration. The ballistic limit velocity of the 10-mm-diameter tungsten-alloy ball to the 7-mm-thick Ti–5322 target at 0° and 30° was 416.0 m/s and 484.8 m/s, respectively.

The effect of elevated temperatures on the mechanical properties of laminated bamboo

The steady-state test method is employed to determine the stress-strain relationship and reduction factors for the strength and elastic modulus of laminated bamboo in different directions at temperatures from 20 °C to 280 °C. The experimental results indicate that the compressive stress-strain curves of the laminated bamboo have pronounced elastic deformation stage, plastic deformation stage and descending stage. The compressive strength and elastic modulus of the bamboo in both the flatwise and edgewise directions are similar, and the compressive strength and elastic modulus decrease with increasing temperature from 20 °C to 280 °C. The tensile stress-strain relationship of the bamboo is generally linear from loading to failure, and the failure is obviously brittle. The tensile strength and elastic modulus of the bamboo in both the flatwise and edgewise directions are similar, and the tensile strength and elastic modulus decrease with increasing temperature. A formula describing the stress-strain relationships of the bamboo is proposed. Compared with the bamboo scrimber and timber specifications in Eurocode 5 and the literature, the reduction factors of laminated bamboo have a similar change tendency with those of the timber addressed in Eurocode 5, but the rules are not fully applicable for laminated bamboo. The formulas for the tensile and compressive strength and elastic modulus reduction factors of the bamboo with temperature are statistically regressed and established. This work provides an important reference to understand and predict the performance of laminated bamboo members in fire conditions.

Effect of pre-cyclic damage and high temperature on residual tensile behavior of concrete

In view of devastating outcomes of post-earthquake fires, it is imperative to propose a model for the fire-resistance capacity of a seismically-damaged concrete structure. For this purpose, the effects of cyclic damage and high temperature on residual tensile behavior of normal strength concrete are investigated in this paper. Monotonic tensile tests are performed on cylindrical concrete specimens which have been initially subjected to strain-controlled cyclic tensile load or have been exposed to high temperature. Residual mechanical behaviors are expressed in terms of cyclic damage or high temperature, respectively. Test results indicate that the residual tensile strength and stiffness decrease while residual peak strain and post-peak strain increase with the increase of damage and temperature. Finally, a modified stress-strain model is proposed to describe the residual tensile stress-strain relationship of concrete considering the effect of cyclic damage and high temperature. The modeling results fits well with the experimental curves.

Strain effects on the mechanical properties of Group-V monolayers with buckled honeycomb structures

Based on first-principles calculations, we study systematically the ideal tensile stress-strain relations of three monoatomic group-V monolayer two dimensional (2D) materials with buckled honeycomb lattices: blue phosphorene, β-arsenene, and β-antimonene. The ideal strengths and critical strains for these 2D materials are investigated under uniaxial and equibiaxial strains. It is found that the ideal strengths decrease significantly as the atomic number increases, while the critical strains change not so much. In particular, the ideal strength of antimonene along armchair direction is found to exceed Griffith strength limit. The distributions of charge density, buckling heights, bond lengths and bond angles are also studied under different types of strains. It can be concluded that the critical strain is determined by the stretch and rotation of bonds simultaneously. Furthermore, the phonon dispersions, phonon instabilities, and failure mechanism of these materials under three types of strains are also calculated and explored.

Transverse Deformations and Structural Phenomenon as Indicators of Steel Fibred High-Strength Concrete Nonlinear Behavior

As known, high-strength compressed concrete elements have brittle behavior, and elastic-plastic deformations do not appear practically up to their ultimate limit state (ULS). This problem is solved in modern practice by adding fibers that allow development of nonlinear deformations in such elements. As a rule, are applied steel fibers that proved high efficiency and contribute ductile behavior of compressed high-strength concrete (HSC) elements as well as the desired effect at long-term loading (for other types of fibers, the second problem is still not enough investigated). However, accurate prediction of the ULS for abovementioned compression elements is still very important and current. With this aim, it is proposed to use transverse deformations in HSC to analyze compression elements' behavior at stages close to ultimate. It is shown that, until the appearance of nonlinear transverse deformations (cracks formation), these deformations are about 5-6 times lower than the longitudinal ones. When cracks appear, the tensile stress-strain relationship in the transverse direction becomes nonlinear. This fact enables to predict that the longitudinal deformations approach the ultimate value. Laboratory tests were carried out on 21 cylindrical HSC specimens with various steel fibers content (0, 20, 30, 40, and 60 kg/m3). As a result, dependences of transverse deformations on longitudinal ones were obtained. These dependences previously proposed by the authors’ concept of the structural phenomenon allow proper estimation of the compressed HSC state up to failure. Good agreement between experimental and theoretical results forms a basis for further development of modern steel fibered HSC theory and first of all nonlinear behavior of HSC.

Tensile mechanical characteristics of CF/PEEK biocomposites with different surface modifications

Carbon fibre reinforced polyetheretherketone (CF/PEEK) biocomposites were prepared by the method of hot casting under pressure. The influences of CF surface treatment methods on the tensile strength and modulus of CF/PEEK biocomposites were investigated. The results indicated that the CF modified with concentrated nitric acid was beneficial to improve the tensile strength of CF/PEEK composites. On the contrary, the surface of CF treated by KH-560 silane couple agent has a little or unfavourable influence on the tensile mechanical properties of CF/PEEK composite. Furthermore, the CF surface treatment methods and CF content have a synergistic effect on the mechanical properties of the biocomposites. With the CF content rising, the difference of the effect of different treatment methods on the tensile mechanical properties of CF/PEEK composites is more and more significant. Meanwhile, the tensile stress-strain relationship of the composites showed linear variation and the break strain of the CF/PEEK composites decreased with increasing CF content. The fracture mechanism of the biocomposites gradually changed from ductile to brittle fracture with the increase of CF content. The tensile strength of the biocomposites first increased and then decreased with the increasing CF content. However, the tensile modulus increased monotonically with CF content rising.

Two-dimensional finite element analysis of the flexural resistance of LVL Sengon non-prismatic beams

Laminated veneer lumber (LVL) Sengon is nowadays industrialized in Indonesia as an innovative utilization of Sengon wood, a fast growing timber species. The presence applications of this LVL Sengon is very limited yet to simple one-storey dwelling houses, challenges for other structural applications including in the form of non-prismatic members are essential to be discovered. This study evaluates the flexural behavior of laminated veneer lumber (LVL) non-prismatic beams by developing a finite element algorithm that can be implemented in MATLAB software under a plane stress assumption and the assumption that the LVL is an orthotropic elastoplastic material. This algorithm is capable of modeling different values of the modulus of elasticity in both tension and compression, as generally exhibited by timber. The mechanical properties of the LVL was obtained from previous studies, except for its tensile stress–strain relationship. Hill’s yield criterion in combination with an associated flow rule was used in the computation. The numerical results were compared with the experimental data of a previous study that used three non-prismatic (tapered) beams having a length of 4000 mm and cross-sectional dimensions of 200 mm by 200 mm at one end and 200 mm by 400 mm at the other end. The finite element analysis results showed that, after the outermost compression fibers plastically deformed, failure of the beam at the tensile side caused failure of the beam. This phenomenon was also observed in the tests of previous studies.

Mechanical Behavior of a PBX Substitute Material under Static and Dynamic Loading

Abstract A polymer-bonded explosive substitute material (PBX) composed of sugar granules and polymer binder was fabricated with a weight proportion of 90:10. Static Brazilian tests accompanied by high-speed photography, digital image correlation (DIC) technology, and dynamic mechanical analysis (DMA) were carried out. The tensile stress-strain relation is quasi-linear until failure with a tensile strength of about 0.89 MPa, elastic modulus of 35 MPa, and Poisson’s ratio of 0.392. Microscopically, interfacial debonding and intergranular fractures are the main mechanisms of damage. By DMA, the storage modulus and tan δ show a strong dependence on temperature and less dependence on frequency; the glass transition temperature is found to be about 50°C. These results are helpful for understanding the behavior of PBX under tensile and dynamic loading.

Fabrication and modification of wavy multicomponent vascular grafts with biomimetic mechanical properties, antithrombogenicity, and enhanced endothelial cell affinity.

A mismatch of mechanical properties and a high rate of thromboses are two critical challenges of creating viable artificial small-diameter vascular grafts (SDVGs). Herein, we propose a method to fabricate wavy multicomponent vascular grafts (WMVGs) via electrospinning using an assembled rotating collector. The WMVGs consisted of a wavy silk/poly(lactic acid) (PLA) inner layer and a thermoplastic polyurethane (TPU) outer layer, which mimic the structures and properties of collagen and elastin in native blood vessels, respectively. Attributed to the wavy structure and the combination of rigid silk/PLA and elastic TPU biomaterials, WMVGs are capable of mimicking the nonlinear tensile stress-strain relationship and "toe region" of native blood vessels. In addition, they have sufficient mechanical strength to meet implantation requirements in terms of tensile strength, suture retention, and burst pressure. Further modification of silk/PLA fibers with dopamine and heparin gave the grafts antithrombogenic properties and greatly enhanced endothelial cell affinities. Human umbilical vein endothelial cells (HUVECs) cultured on modified silk/PLA showed high viability, high proliferation rate, and favorable cell-substrate interactions. Moreover, HUVECs were able to fully cover and freely migrate upward on the lumen of the modified WMVGs without needing a special circulation bioreactor. Therefore, the modified WMVGs possessed biomimetic properties, antithrombogenicity, and enhanced endothelialization, making them a promising candidate for SDVGs. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2397-2408, 2019.