Tensile Strain-hardening Behavior Research Articles

Numerical Approach to Determine the Resistance of Threaded Anchors in Ultra-High-Performance Fiber-Reinforced Cementitious Composite

Due to their relatively high tensile strength and dense matrix, UHPFRCs have proven to be a highly effective building material for both strengthening existing reinforced concrete structures and constructing new ones. In both cases, the use of fasteners is prevailing, with threaded anchors being frequently employed. The thicknesses of structural components made of UHPFRCs are relatively thin, i.e., at least 30 mm, typically 50 to 100 mm, and exceptionally 100 to 200 mm. Therefore, the aim is to use fasteners with short anchorage lengths. In this study, the structural behavior of a short threaded anchor with a 20 mm diameter and an embedment length of 50 mm (2.5 Ø) in a UHPFRC is investigated using non-linear finite element models. The UHPFRC is assumed to exhibit tensile strain-hardening behavior, with tensile strengths of 7 MPa and 11 MPa, respectively. The modeled anchor was subjected to a continuously increasing uniaxial pull-out force. The results indicate that the fracture mechanism of threaded anchors in UHPFRCs is primarily characterized by the formation of a tensile membrane within the UHPFRC, which acts as the main resisting element against the pull-out force. Additionally, the influence of the UHPFRC’s tensile properties on the pull-out behavior and ultimate resistance of the threaded anchors was determined.

Limestone calcined clay-based engineered cementitious composites (LC3-ECC) with recycled sand: Macro performance and micro mechanism

Limestone calcined clay cement (LC3) contributes to the development of sustainable cement-based materials. In this study, LC3 was combined with fly ash (FA) and recycled sands (RS) to develop engineered cementitious composites (ECC). Three FA/LC3 ratios (1, 1.5, and 2) and three RS particle sizes (0.15–1.18 mm, 0.15–2.36 mm, and 0.15–4.75 mm) were studied. Compared to ordinary Portland cement (OPC)-based paste, the LC3 substitution resulted in higher hydration heat and hydration degree, forming more hydration products. Although LC3 substitution produced a slightly lower compressive strength, a more robust tensile strain-hardening behavior than OPC-based ECC was achieved. The increasing FA/LC3 ratios gradually reduced compressive strength, tensile strength, and crack width. The multiple cracking behavior with controlled widths of LC3-based ECC was found to be more stable, which could be traced to the superior properties of fiber/matrix interfacial transition zone. In addition, utilizing RS as fine aggregates with various particle sizes could achieve an ultra-high tensile strain capacity exceeding 8 % for LC3-based ECC, thereby enhancing its utilization efficiency. Furthermore, the utilization of LC3 resulted in 28.6–47.1 % and 6.6–22.0 % reductions in carbon emission and embodied energy, respectively. The combination of LC3 and RS holds a promising approach to developing sustainable ECC with desirable mechanical performance.

PET particles modify strain hardening cementitious composites: An approach to introduce defects to enhance deformation capacity

Enhancing deformation capabilities remains a critical direction in the research of Strain-Hardening Cementitious Composites (SHCC). This investigation introduces Polyethylene Terephthalate (PET) particles as a novel method to induce micro-defects within SHCC, aiming to reduce the material's initial crack strength and improve its deformability. Through the exploration of various PET particle volumetric substitutions for traditional aggregates, the development of PET particle-modified SHCC (PMSHCC) was achieved. The paper examines the impact and mechanisms of different PET volumetric substitution rates (0 %, 5 %, 10 %, 15 %, 20 %, and 25 %) on the workability, axial compression strength and tensile properties of PMSHCC. By employing Digital Image Correlation techniques, the progression of crack width and density in PMSHCC under tensile load was documented, facilitating an analysis of the influence mechanisms of varying PET volumetric substitution rates on the tensile strain-hardening behavior of PMSHCC. The findings indicate that the increased Interfacial Transition Zone (ITZ) thickness between PET particles and the cement matrix, combined with the lower elastic modulus of PET particles compared to the cement matrix and quartz sand, collectively contribute to a reduction in tensile initial crack strength and an enhancement in ultimate tensile strain of PMSHCC. Within the examined range, an increase in the PET volumetric substitution rate significantly improves the ultimate tensile strain of PMSHCC by up to 76.0 %, with a minimal reduction in tensile strength of only 3.99 %. Moreover, the study proposes a tensile linear strengthening elasto-plastic model for PMSHCC incorporating the PET substitution rate, enabling accurate prediction of the material's tensile stress-strain behavior. These findings not only offer a novel pathway for the utilization of waste plastics but also provide significant insights for enhancing the deformability of SHCC.

Numerical and analytical investigations on punching shear performance of UHTCC-enhanced RC slab-column joints

The excellent tensile strain-hardening behavior of ultra-high toughness cementitious composite (UHTCC) makes it applicable for enhancing the punching shear performance of reinforced concrete (RC) slab-column joints. However, construction of an entire slab-column structure employing UHTCC would inevitably lead to uneconomical designs. To balance the economic benefits with the punching performance, utilizing UHTCC in the core region of a slab-column joint is a promising approach. In this study, the impact of UHTCC application range (UAR) on the punching shear performance of UHTCC-enhanced RC slab-column joints (USCJs) was investigated, and an approach for determining the optimal UAR was also presented. Two USCJ specimens with different UAR were tested, and experimental results were compared with the counterpart numerical results to validate the finite element (FE) models. Twenty FE USCJ models with different UAR were established. Then the impact of UAR on development of critical cracks, ultimate resistance, and ductile behavior was examined. Analytical approaches based on the critical shear crack theory as well as on the combination of critical shear crack theory and yield line theory were adopted to predict the ultimate and flexural resistances, respectively. The failure mode was determined by comparing these two resistances and considering the ductile coefficient, based on which the effect of UAR on the failure mode was determined. The results show that the location of critical shear cracks and the appearance of flexural cracks vary with UAR. By increasing UAR, the ultimate resistance increases, but the ductile coefficient first increases and then slightly decreases. Provided that the UAR is increased to some extent, the growth rate of the ultimate resistance evidently slows down and the ductile coefficient peaks, indicating the optimal UAR considering both the economic efficiency and the punching performance. The presented approach shows promise for determining the optimal UAR in practical engineering designs.

Tensile strain-hardening behavior and related deformation mechanisms of pure titanium at cryogenic temperature

The tensile strain-hardening behavior of pure Ti at 100 K was investigated using X-ray diffraction line-profile analysis and plasticity simulation. The strain hardening was significantly increased at 100 K, compared with that observed at 298 K. Thus, at 100 K, necking was suppressed during tensile testing, which greatly increased material ductility. The remarkable increase in strain hardening at 100 K was attributed to the dominant activation of prismatic <a> slip and the exceptionally increased rate of its activation stress with tensile strain at 100 K. This finding significantly advances the understanding of the strain-hardening behavior of pure Ti at low temperatures, and it can also guide the development of texture-engineering strategies to increase the low-temperature ductility of pure Ti.

Punching shear behavior and strength prediction of UHTCC-enhanced RC slab-column joints

RC flat slabs are widely employed in medium-height buildings due to their constructional and architectural advantages. However, due to the tensile brittleness of normal concrete, an RC slab-column structure may suffer progressive collapse induced by punching shear failure of slab-column joints. Considering the excellent tensile strain-hardening behavior of ultra-high toughness cementitious composite (UHTCC), the punching shear behavior of slab-column joints enhanced by UHTCC could be substantially improved. Three slab-column joint specimens with different UHTCC application ranges were tested under vertical monotonic loading. The cracking development process, peak bearing capacity, ductility, and post-punching capacity were recorded and analyzed. Yield line theory and critical shear crack theory were adopted to estimate the flexural capacity and punching shear capacity of the specimens, respectively, and the post-punching capacity was also calculated. Finally, the failure patterns of the specimens were determined by comparing the estimated flexural capacity with the estimated punching shear capacity and taking into account the ductile coefficient. The main conclusions are as follows: (1) applying UHTCC can considerably enhance the peak bearing capacity and ductility of a joint, and a more significant improvement effect is achieved by increasing the UHTCC application range; (2) adopting UHTCC affects the failure pattern of a slab-column joint from premature punching shear failure to flexural-triggered punching shear failure achieving better ductile performance, and flexural behavior becomes more evident with the increase of the UHTCC application range; (3) the post-punching capacity of a joint is improved when the UHTCC application range covers the entire punching shear region. Therefore, the progressive collapse resistance of the RC slab-column structures could be substantially improved by introducing the UHTCC-enhanced joints.

Effects of Pre-Treated Crumb Rubber as Sand Partial Replacement on Compressive Strength of Engineered Cementitious Composites (ECC)

This study was conducted to determine the surface morphology of crumb rubber (CR) treated with 10% Sodium Hydroxide (NaOH) solution at different periods and the compressive strength of the treated rubberised engineered cementitious composites (R-ECC). R-ECC is a type of engineered cementitious Composite (ECC) with CR as partial sand replacement. In contrast to the quasi-brittle nature of conventional concrete, engineered cementitious Composite (ECC) is distinguished for its tensile strain-hardening behaviour and tensile ductility. However, adding crumb rubber (CR) in ECC as partial sand replacement reduces the composites’ compressive strength owing to its smooth surface. The Scanning Electron Microscopy (SEM) test was conducted on the CR samples, which had been treated with 10% NaOH for 1, 2 and 3 days. Meanwhile, the compressive strength test was conducted on 45 cubes consisting of standard ECC, untreated R-ECC and treated R-ECC. The results discovered that 2 and 3 days of 10% NaOH treatment on CR enhanced its surface roughness, and 2 days NaOH treated R-ECC is the optimum duration for the highest compressive strength reduction. Therefore, the enhanced surface roughness of the CR used as partial sand replacement in the ECC can lessen the compressive strength reduction owing to better bonding between CR and cement matrix in the composites.

Engineering properties of sustainable engineered cementitious composites with recycled tyre polymer fibres

To lower the material cost and environmental impact of polyvinyl alcohol (PVA) fibre reinforced engineered cementitious composite (ECC), recycled tyre polymer (RTP) fibres were adopted to partially replace PVA fibres in ECC in this study, with an overall aim to develop sustainable ECC with RTP fibres without significantly affecting the engineering properties. A series of tests were conducted to investigate the effect of RTP fibre content on the engineering properties of ECC, with special focus on tensile strain-hardening behaviour and dynamic compressive behaviour. Results indicate that the incorporation of RTP fibres can improve the drying shrinkage resistance of PVA fibre reinforced ECC by 5–13% at 28 d while no positive influences are found on the workability and quasi-static compressive properties. There exists clear strain-hardening behaviour for all studied ECC mixes even when 50% of PVA fibre is substituted with RTP fibre. Based on the results of the micromechanical investigation, all mixtures satisfy the criteria for achieving a robust strain-hardening behaviour. All ECC specimens are characterised by a pronounced strain rate effect under dynamic compression and ECC incorporating RTP fibres shows a stronger sensitivity as opposed to ECC with 2.0% PVA fibre. The material cost and energy consumption of ECC are reduced by about 11–45% and 5–18%, respectively, when RTP fibres are present. This study proves the feasibility of utilising RTP fibres in ECC to improve its sustainability and maintain acceptable static and dynamic mechanical properties while the incorporated fibre volume fraction should be limited to 0.5%.

Investigation of continuous surface cap model (CSCM) for numerical simulation of strain-hardening fibre-reinforced cementitious composites against low-velocity impacts

This study calibrated the parameters of the continuous surface cap model (CSCM) for ultra-high toughness cementitious composites (UHTCC) with compressive strength from 25 MPa to 75 MPa, and the calibrated parameters could describe the mechanical behaviour of UHTCC, including the deviatoric response, volumetric response, tensile strain-hardening behaviour, strain rate effect, as well as the reduction of tensile strain-hardening behaviour at higher strain rate. The drop-weight impact tests on the reinforced concrete slab and reinforced UHTCC slab were proceeded to validate the soundness of the calibrated CSCM. The results show that the calibrated CSCM could accurately predict the impact response of reinforced UHTCC slab, and the most accurate simulation results were achieved in the model of the hexahedral elements with a mesh size of 10 mm. The calibrated CSCM parameters for UTHCC are expected to extend the application of UHTCC in the field of impact engineering.

Tailoring strain-hardening behavior of high-strength Engineered Cementitious Composites (ECC) using hybrid silica sand and artificial geopolymer aggregates

Hybrid artificial geopolymer aggregates (GPA) and natural silica sand were used to strategically tailor the tensile strain-hardening behavior of high-strength engineered cementitious composites (HS-ECC). With such hybridization, the weaknesses of GPA (i.e., relatively low strength and stiffness) were utilized in the performance-based design of HS-ECC, while the advantages of GPA were retained (e.g., the utilization of industrial by-products/wastes through chemical activation and conservation of natural resources). In this study, a comprehensive experimental program was conducted at multiple scales on the HS-ECC. It was found that increasing the replacement ratio of silica sand by GPA improved the tensile ductility, crack control ability, and energy absorption of HS-ECC, although its compressive and tensile strengths were reduced. GPA with low alkalinity were observed to react with the cementitious matrix, and the pozzolanic reaction provided additional chemical bond and thus enhanced the GPA/matrix interface. In addition, GPA could be regarded as “additional flaws” in the HS-ECC system. According to the Weibull-based modeling, it was found that GPA could play a crack-inducing role in activating more inactive initial flaws. Therefore, GPA can tailor the active flaw size distributions in HS-ECC matrix. The findings of this study provide a new avenue for the utilization of GPA.

Eco-Friendly, High-Ductility Slag/Fly-Ash-Based Engineered Cementitious Composite (ECC) Reinforced with PE Fibers

Engineered cementitious composites (ECCs) are a special class of ultra-ductile fiber-reinforced cementitious composites containing a significant amount of short discontinuous fibers. The distinctive tensile strain-hardening behavior of ECCs is the result of a systematic design based on the micromechanics of the fiber, matrix, and fiber–matrix interface. However, ECCs require extensive cement content, which is inconsistent with the goal of sustainable and green building materials. Consequently, the objective of this study is to investigate the mechanical performance of slag/fly-ash-based engineered cementitious composites (ECCs) reinforced with polyethylene (PE) fiber under axial compressive loading, as well as direct tensile and flexural strength tests. The composites’ microstructure and mineralogical composition were analyzed using images obtained from scanning electron microscopy (SEM), X-ray energy diffraction spectroscopy (EDS), X-ray powder diffraction (XRD), and X-ray fluorescence (XRF). The experimental results reveal that a slag-containing composite mixture shows strain-hardening behavior and comparable ductility properties to those of fly-ash-based composite mixtures. A ternary system of binder materials with 5% and 15% slag can increase the compressive strength of ECC by 3.5% and 34.9%, respectively, compared to slag-free ECC composite. Moreover, the microstructural results show that the slag-based cementitious matrix has a more closely cross-linked and dense microstructure at the matrix–aggregate interface. In addition, the concentration of particles on the surface of the fibers was higher in the slag-based cementitious composites than in the fly ash-based composite. This supports the concept that there is a stronger bonding between the fibers and matrix in the slag-based cementitious matrix than in fly-ash-based matrix.

Correlation between tensile properties, microstructure, and processing routes of an Al–Cu–Mg–Ag–TiB2 (A205) alloy: Additive manufacturing and casting

This paper aims at assessing microstructure/processing route/mechanical property correlation of a high-strength TiB2/Al–Cu–Mg–Ag aluminum alloy, namely A205 alloy, additively manufactured via laser powder bed fusion (LPBF) versus the cast counter material. To this end, high magnification advanced microstructural characterization in connection with the tensile flow and strain hardening (i.e., work hardening) behavior of the materials were studied. Ambient temperature uniaxial tensile tests, based on ASTM E8/E8M, were conducted on the LPBF and cast as well as post-heat treated (T7: overaged and stabilized) materials were performed systematically. Results show a pronounced discontinuous yielding for the LPBF material along with extended ductility. The tensile curve of the LPBF T7 heat-treated material showed some plastic instabilities (Portevin–Le Chatelier effect) in the inelastic region. However, none of these phenomena were observed in the cast material, while ductility is limited. These responses were attributed to the very high cooling/solidification rates experienced by the LPBF materials, which result in a very fine equiaxed and supersaturated aluminum grain structure as compared with the coarse-grained structure of the cast counter material.

Curvature-Deflection Relations for Polypropylene Fiber-Reinforced Deflection-Hardening Alkali- Activated Slag Composite

To obtain a tensile strain-hardening behavior by using the ordinary polypropylene (PP) fiber, the micromechanical model recommends the increase of the fiber low interfacial bond with an ordinary cementitious matrix. It was predicted that the alkali-activated slag (AAS) composite high drying shrinkage performance would affect the fiber interface frictional bond during the pullout.

Mechanism study of crack propagation in river sand Engineered Cementitious Composites (ECC)

While incorporation of river sands improves the volume stability and lowers the cost of ECC, distinct multiple cracking and tensile strain-hardening behavior of the resulting river sand ECC (RS-ECC) with different strength grade were observed. This paper investigates the effects of river sand inclusion on crack propagation in RS-ECC. It concludes that crack deflection at RS/matrix interface prevails in the normal strength RS-ECC while crack penetration through RS dominates in the high strength RS-ECC. As a result, crack path in the normal strength RS-ECC is more tortuous which increases matrix fracture toughness and lead to less saturated multiple cracking and reduced tensile strain capacity. Crack branching can occur when the crack propagates through the RS in the high strength mix, resulting in more saturated multiple cracking in the high strength RS-ECC with improved tensile strain capacity.

Modeling the Tensile Strain Hardening Behavior of a Metastable AISI 301LN Austenitic Stainless Steel Pre-strained in Compression

Modeling the Tensile Strain Hardening Behavior of a Metastable AISI 301LN Austenitic Stainless Steel Pre-strained in Compression

Effect of Fibre Types on the Tensile Behaviour of Engineered Cementitious Composites

Engineered cementitious composite (ECC) is a group of ultra-ductile fibre-reinforced cementitious composites, characterised by high ductility and moderate content of short discontinuous fibre. The unique tensile strain-hardening behaviour of ECC results from a deliberate design based on the understanding of micromechanics between fibre, matrix, and fibre–matrix interface. To investigate the effect of fibre properties on the tensile behaviour of ECCs is, therefore, the key to understanding the composite mechanical behaviour of ECCs. This paper presents a study on the fibre-bridging behaviour and composite mechanical properties of ECCs with three types of fibres, including oil-coated polyvinyl alcohol (PVA) fibre, untreated PVA fibre, and polypropylene (PP) fibre. The experimental result reveals that various fibres with different properties result in difference in the fibre-bridging behaviour and composite mechanical properties of ECCs. The difference in the composite mechanical properties of ECCs with different fibres was interpreted by analysing the fibre-bridging behaviour.

Effects of shear deformation via torsion on tensile strain-hardening behavior of SCM415 low-alloy steel

The effect of shear deformation via torsion on tensile strain-hardening behavior of SCM415 low-alloy steel was investigated. Hot-rolled SCM415 rods were machined into round tensile-test specimens based on ASTM E8M. SCM415 round tensile specimens were subjected to shear deformation using a free-end torsion testing machine at a constant rotational speed of 0.1 rpm. The specimens were torsionally deformed at room temperature to four different angles: 0.314 rad, 0.628 rad, 1.256 rad, and 2.512 rad. Tensile tests of torsionally deformed specimens were then carried out. The engineering stress-strain curves indicated that yield strength and ultimate tensile strength increased while ductility decreased with a higher degree in shear deformation via torsion. From true stress-strain curves generated using engineering stress and strain values, it was found that the strain hardening rates were lower in specimens with a higher degree of shear deformation via torsion. A power law was applied to curve fit the true stress-strain data in the uniform plastic deformation region. The strength coefficient and strain hardening exponent were lower in specimens with a higher degree of shear deformation via torsion. The decrease in strain hardening exponent and work hardening capacity of specimens with a higher degree of shear deformation via torsion was presumably caused by a combination of high dislocation density and grain refinement after severe plastic deformation.

Investigation of matrix cracking properties of engineered cementitious composites (ECCs) incorporating river sands

Typical ECC mix design omits normal aggregates and adopts only fine micro silica sands. Few studies report the possibility of using river sands in ECC mix design. While the resulting ECC is more economical with improved time-dependent properties, a very different tensile strain-hardening behavior is also observed. The current study reveals the fundamental mechanisms by investigating the matrix cracking properties ECC incorporating river sands. Results show that the use of river sands alters the matrix fracture toughness and introduces microcracks along the aggregate/matrix interface. As a result, the matrix cracking strength of the high strength ECC with river sands is reduced, which favors multiple cracking and tensile strain-hardening. In contrary, the matrix cracking strength of the normal strength ECC with river sands is increased, which hinders multiple cracking and tensile strain-hardening.

Properties of modified engineered geopolymer composites incorporating multi-walled carbon Nanotubes(MWCNTs) and granulated blast furnace Slag(GBFS)

Engineered cementitious composites (ECC) are widely used owing to their high tensile capacity and strain-hardening behavior; however, the use of large quantities of cement require huge amount of resources and pollutes the environment. Fly ash-based geopolymer has been considered as a promising alternative for the development of high-ductility eco-friendly engineered materials. To improve the tensile capacity of engineered geopolymer composites (EGC), an ultra-high-ductility engineered geopolymer composite has been developed with the incorporation of functionalized multi-walled carbon nanotubes and polyvinyl alcohol fiber. This paper reports the mixture process and mechanical tests on EGC with different mixtures. Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction were used to investigate the characteristics of the reaction products in the geopolymer matrix. The microscopic morphology of the geopolymer matrix were characterized using field emission scanning electron microscopy. The excellent saturated multiple cracking properties and strain hardening of the ultra-high EGC (UHEGCs) were demonstrated by uniaxial tension testing. At the maximum limit, the residual crack width and crack spacing of UHEGCs were generally less than 70 μm and 2 mm, respectively. Tensile strain-hardening behavior with an ultimate tensile strain greater than 8% was experimentally demonstrated for the UHEGC. Meanwhile, the compressive strength of the UHEGC was greater than 45 MPa. The pseudo-strain hardening (PSH) indexes of UHEGC were used to determine the tensile capacity formation. Analysis demonstrated that the tensile capacity of UHEGC can be quantified using the classic PSH criterion, whereas ultra-high crack-bridging capacity was attributed to the ultra-high-ductility of UHEGC. The XRD studies demonstrated that for the reaction products of the geopolymer matrix, new crystalline phases are insignificant. The FT-IR analyses revealed that the amorphous aluminosilicate phases were mainly reaction products, i.e., N-A-S-H. Most importantly, the multi-scale (micro- and meso-scale) modification mechanisms of the material through the addition of two fibers were revealed.

Highly ductile ultra-rapid-hardening mortar containing oxidized polyethylene fibers

This study aims to develop a strain-hardening ultra-rapid-hardening mortar (URHM). A mixture of calcium sulfoaluminate (CSA) cement, ordinary Portland cement (OPC), and gypsum was used to prepare the ultra-rapid hardening cement along with 2% (by volume) polyethylene (PE) fibers. The PE fibers were oxidized by plasma and chromic acid treatments to achieve a robust strain-hardening characteristic. Test results indicated that the tensile strain-hardening behavior of the URHM was achieved in only 4 h of air-drying curing and further improved through surface treatments. The compressive strength of the URHM with untreated PE fibers at 4 h and 28 d of air-drying curing was found to be 37.9 and 60.0 MPa, respectively, and it was slightly enhanced by using the treated PE fibers. Tensile strength and energy absorption capacity of about 5.1 MPa and 124.8 kJ/m3, respectively, were achieved for the URHM at an early age (4 h) using the plasma-treated PE fibers. The tensile performance of the URHM improved with the increase in the air-drying curing age and by using oxidized PE fibers. It was identified that the plasma treatments were more effective than the chromic acid treatment. Finally, the highest tensile strength and energy absorption capacity of approximately 9.95 MPa and 381.1 kJ/m3 were observed in the URHM containing oxygen-gas-treated PE fibers after 28 d of curing.