Tensile Strain-hardening Behavior Research Articles

MECHANICAL PROPERTIES OF A PVA FIBER REINFORCED ENGINEERED CEMENTITIOUS COMPOSITE

High Performance Fiber Reinforced Cementitious Composites (HPFRCCs) are promising construction materials characterized by tensile strain hardening behavior. Engineered Cementitious Composite (ECC) is a special type of HPFRCC developed with enhanced ductility and durability. Coarse aggregates are usually excluded from the ECC matrix, and the reported ECCs are typically produced with microsilica sand having a maximum grain size of 200 µm. In this paper, a PVA-ECC mixture containing local dune sand with a maximum grain size of 300 µm was developed, and its compressive and tensile properties were experimentally investigated. A dog-bone-shaped specimen and a rectangular-coupon-shaped specimen were both used in the tensile test, and it was found after extensive research that the dog-bone specimen was more suitable than the rectangular coupon specimen. The experimental results from the dog-bone specimens indicated that the newly-developed composite possessed good tensile strain-hardening behavior, with a high ultimate tensile strength, and the compressive strength was comparable to that of existing PVA-ECCs.

Micromechanics-Based Optimization of Pigmentable Strain-Hardening Cementitious Composites

AbstractArchitectural and decorative concrete (ADC) has become an enormously popular product for both building interiors and exteriors, combining an aesthetic finish with structural capabilities. Cracking and chipping of ADC product during handling and transportation, however, is of great concern due to the brittleness of ADC materials. This paper looks at the development of a white strain-hardening cementitious composite (SHCC) as an alternative ADC material to address the above-mentioned challenges. It was found that the replacement of ordinary portland cement and fly ash with white cement altered SHCC microstructure which is unfavorab to the tensile strain-hardening behavior. A micromechanical model was engaged for composite optimization through ingredients selection and component tailoring to reengineer white SHCCs.

Rheology, fiber dispersion, and robust properties of Engineered Cementitious Composites

The capability of processing robust Engineered Cementitious Composites (ECC) materials with consistent mechanical properties is crucial for gaining acceptance of this new construction material in various structural applications. ECC’s tensile strain-hardening behavior and magnitude of tensile strain capacity are closely associated with fiber dispersion uniformity, which determines the fiber bridging strength, complementary energy, critical flaw size and degree of multiple-crack saturation. This study investigates the correlation between the rheological parameters of ECC mortar before adding PVA fibers, dispersion of PVA fibers, and ECC composite tensile properties. The correlation between Marsh cone flow rate and plastic viscosity was established for ECC mortar, justifying the use of the Marsh cone as a simple rheology measurement and control method before fibers are added. An optimal range of Marsh cone flow rate was found that led to improved fiber dispersion uniformity and more consistent tensile strain capacity in the composite. When coupled with the micromechanics based ingredient-tailoring methodology, this rheological control approach serves as an effective ECC fresh property design guide for achieving robust ECC composite hardening properties.

Shear Behavior of Reinforced Ultrahigh Toughness Cementitious Composite Beams without Transverse Reinforcement

AbstractThe shear behavior of reinforced ultrahigh toughness cementitious composite (RUHTCC) beams without transverse reinforcement was investigated in the present paper, in which UHTCC has tensile strain-hardening behavior due to the steady propagation of multiple fine cracks. A total of 15 simply supported beams were subjected to a concentrated load at midspan, of which nine beams were RUHTCC beams and six beams were RC counterpart beams. The varied parameters were shear span-effective depth ratio and longitudinal reinforcement ratio. The experimental results showed that an enhanced ultimate shear strength that was about two times larger than that of an RC beam was obtained for slender beams with use of UHTCC, whereas only a marginal improvement was obtained for short beams. All tested RUHTCC beams presented a diagonal multiple-cracking mode and a stable diagonal crack propagation process. The maximum crack width was controlled within 0.1 mm at the service state and the high postcracking shear reserve s...

High-Early-Strength Engineered Cementitious Composites for Fast, Durable Concrete Repair—Material Properties

The lack of durability in concrete structures worldwide demands fast and durable repairs. To address this need, high-early-strength engineered cementitious composites (HES-ECC) were recently developed for concrete repair applications in which minimum operations disruption is desired. A detailed characterization of HES-ECC’s compressive, tensile, flexural, and shrinkage properties at different ages is reported in this paper. HES-ECC achieves a compressive strength of 23.59 ± 1.40 MPa (3422.16 ± 203.33 psi) in 4 hours and 55.59 ± 2.17 MPa (8062.90 ± 315.03 psi) in 28 days. Under uniaxial tension, HES-ECC exhibits tensile strain-hardening behavior with a strain capacity greater than 2.5%. Its flexural strength exceeds twice that of concrete with similar compressive strength. Under restrained shrinkage conditions, HES-ECC forms microcracks with a self-controlled crack width below 50 μm (0.002 in.). The combination of these properties suggests HES-ECC material is highly suitable for fast and durable concrete repairs with shortened downtime and improved longterm durability.

Crystallization of an ethylene-based butene plastomer: the effect of uniaxial extension

In this paper, the effect of uniaxial extension on the crystallization of an ethylene-based butane plastomer is examined by using rheometry coupled with differential scanning calorimetry (DSC). Uniaxial extension experiments were performed at temperatures below and above the peak melting point of the polyethylene in order to characterize its flow-induced crystallization behavior at extensional rates relevant to processing. The degree of crystallinity of the stretched samples was quantified by DSC, i.e., by analyzing the thermal behavior of samples after stretching. Analysis of the tensile strain-hardening behavior very near the peak melt temperature revealed that crystallization depends on temperature, strain, and strain rate. In addition, it was revealed that a very small window of temperatures spanning just 1–2°C can have a dramatic effect on polymer crystallization. Finally, flow-induced crystallization experiments at temperatures close to the peak melting point have shown the recrystallization of multiple crystalline structures within a polymer matrix, witnessed by double peaks within a narrow window of 89–93°C in the DSC thermographs, with the most demonstrable double peak behavior occurring at a temperature of 91°C, a temperature that is just 1°C cooler than the peak melt temperature of the polymer.

Properties, processability and weldability of a novel affordable creep resistant nickel base superalloy

A recently designed heat resistant alloy for operation ∼750°C in power plant, named FT750DC, of composition Ni–20Cr–5Fe–3·5W–2·3Al–2·1Ti–0·07C–0·4Si–0·005B (wt-%), is fully characterised. Creep rupture and damage is investigated, as well as Charpy impact toughness. The alloy processability is also assessed: castability (comparison between measured microsegregation and Scheil simulation), forgeability (hot tensile ductility, strain hardening and recrystallisation behaviour), γ′ aging heat treatment (gamma-prime precipitation kinetics) and weldability (GTAW/TIG). It is demonstrated that this material, made affordable by avoiding the use of expensive alloying elements, with a creep rupture life in excess of 100 000 h at 750°C under 100 MPa, is easily castable, forgeable and weldable. It can therefore be favourably compared to concurrent alloys for fossil fuel or nuclear power plant applications (like the coal fired ultra supercritical steam power plant, or the nuclear high temperature gas cooled reactor) currently under assessment, such as alloys 230, 617, 625, 740, HX, etc.

Analytical Model for Tensile Strain Hardening and Multiple Cracking Behavior of Hybrid Fiber-Engineered Cementitious Composites

An analytical model for the design of strain-hardening and multiple-cracking behavior of engineered cementitious composites (ECC) containing hybrid fibers is proposed. The model predicts first crack strength and ultimate bridging strength of hybrid fiber ECC. The model also predicts the minimum (critical) volume fraction of fibers required to exhibit strain-hardening and multiple-cracking behavior in uniaxial tension. The model is verified with the experimental results of hybrid fiber ECC specimens. A parametric study is also performed, using this model, to evaluate the effects of fiber length, diameter, and interfacial bond strength on the first crack strength, the ultimate bridging strength and the critical volume fraction of fibers. It is shown that the critical volume fraction of fibers in hybrid fiber composites can be optimized by proper selection of fiber length, diameter, and interfacial bond strength. Low modulus fibers are found to have a more pronounced effect on the strain-hardening and multiple-cracking behaviors of hybrid fiber composites compared to high modulus fibers. The hybrid fiber concept is found to offer additional freedom in the design variables compared to composite containing one type of fiber.

Repair Performance of Engineered Cementitious Composites(ECC) Treated with Wet-Mix Spraying Process

This paper presents an experimental study on the repair performance of sprayed engineered cementitious composites(ECC) serving as a repair material. Sprayable ECC, which exhibit tensile strain-hardening behavior in the hardened state and maintain sprayable properties in the fresh state, have been developed by using a parallel control of micromechanical design and rheological process design. The effectiveness of sprayable ECC in providing durable repaired structures was assessed by spraying the ECC and testing them for the assessment. The experimental results revealed that, when sprayed ECC were used as a repair material, both load carrying capacity and ductility represented by the deformation capacity at peak load of the repaired flexural beams were obviously increased compared to those of commercial prepackaged mortar(PM) repaired beams. The significant enhancement in the energy absorption capacity and tight crack width control of the ECC repair system treated with wet-mix spraying process suggests that sprayed ECC can be effective in extending the service life of rehabilitated infrastructures.

Behavior of Hybrid-Fiber Engineered Cementitious Composites Subjected to Dynamic Tensile Loading and Projectile Impact

The characteristics of engineered cementitious composites (ECCs) subjected to dynamic tensile loading and high-velocity projectile impact have been investigated and are reported in this paper. Hybrid-fiber ECC containing a combination of high-modulus steel fibers and relatively low modulus polyethylene fibers was adopted to achieve a desired balance between the ultimate strength and the strain capacity of the material required for impact- and blast-resistant structures. Dynamic uniaxial tensile tests at varying strain rates of 2× 10−6 to 0.2 s−1 were carried out, and ECC was found to be able to provide much higher enhancement in tensile strength than plain concrete and still be able to maintain pronounced tensile strain-hardening behavior. At higher rates of strain, ECC showed multiple-cracking behavior, similar to that observed from quasi-static tests, with tight crack width of about 0.1 mm . The results from high-velocity (300–750 m∕s) impact tests demonstrated the potential of ECC in providing improved...

Highly Damage-Tolerant Beam-Column Joints Through Use of High-Performance Fiber-Reinforced Cement Composites

//<![CDATA[ var theForm = document.forms['Form']; if (!theForm) { theForm = document.Form; } function __doPostBack(eventTarget, eventArgument) { if (!theForm.onsubmit || (theForm.onsubmit() != false)) { theForm.__EVENTTARGET.value = eventTarget; theForm.__EVENTARGUMENT.value = eventArgument; theForm.submit(); } } //]]>

미세역학이론과 레올로지 제어에 의한 습식스프레이용 고인성 섬유보강 모르타르(ECC)의 개발

Sprayable high ductile fiber-reinforced cementitious composite (ECC), which exhibits tensile strain-hardening behavior in the hardened state, while maintaining sprayable properties in the fresh state, has been developed by employing parallel control of micromechanical design and rheological process design. Initially, micromechanical tools were adopted to properly select the matrix, fiber, and interface properties, and also to exhibit strain-hardening and multiple cracking behaviors in the ECC composites. Within the pre-determined micromechanical constraints, the fluid properties were controlled by the rheological process design to develop flocculations between cementitious particles at a proper rate. The sprayable properties of ECC mix were then developed by the controlled rheological properties of fresh matrix and the uniform dispersion of fibers. A series of spray tests showed the excellent pumpability, sprayability, and rebound property of tile sprayable ECC. Subsequent uniaxial tensile tests demonstrated that the mechanical performance of sprayed ECC is comparable to that of ECC cast with external consolidation, for the same mix design.

습식스프레이공법으로 타설된 고인성 섬유보강 모르타르(ECC)의 역학적 특성과 보수 성능

This paper presents an experimental study on the potential durability enhancement of infrastructures repaired by a sprayed high ductile fiber-reinforced cementitious composite (ECC). For this study, a PVA-ECC which exhibits sprayable properties in the fresh state and tensile strain-hardening behavior in hardened state was sprayed and tested. The experimental results show that the sprayed ECC exhibits mechanical properties with strain capacity comparable to the cast ECC with the same mix design. During loading, the crack widths of ECC are tightly controlled with an average of 30. It is also revealed that when sprayed ECC is used as a repair material, ductility represented by deformation capacity at peak load of repaired beams in flexure are obviously increased in comparison to those of commercial prepackaged mortar (PM) repaired beams. In addition to high delamination resistance, the significant enhancement of energy absorption capacity and crack width control in ECC repair system suggest that sprayed ECC can be effective in extending the service life of rehabilitated infrastructures.

Constitutive rheological control to develop a self-consolidating engineered cementitious composite reinforced with hydrophilic poly(vinyl alcohol) fibers

A self-consolidating engineered cementitious composite (ECC), which exhibits tensile strain-hardening behavior in the hardened state, while maintaining self-consolidating properties in the fresh state, has been developed by employing hydrophilic poly(vinyl alcohol) (PVA) fibers. The constitutive rheological design approach is adopted to separately control the aggregation between cement particles and sedimentation behavior with a combination of a strong polyelectrolyte and non-ionic polymer. This study suggests an effective formulation approach of fresh cementitious mix to maximize its fluidity without segregation, regardless of solids concentration employed. The resulting self-consolidating PVA-ECC exhibits tensile strain up to 5%. Besides, the methodology of constitutive rheological control can be extended to formulating other self-consolidating cementitious materials with various types of polymeric admixtures.

Tensile Strain-Hardening Behavior of Polyvinyl Alcohol Engineered Cementitious Composite (PVA-ECC)

A high-performance polyvinyl alcohol fiber-reinforced engineered cementitious composite (PVA-ECC) was developed for structural applications under the performance-driven design approach. Fiber, matrix, and fiber/matrix interfacial properties were tailored to micromechanics models to satisfy the pseudo strain-hardening condition. This research experimentally investigated the effects of fiber surface treatment and sand content on the composite performance. Results from uniaxial tensile tests show an ultimate strain exceeding 4%, as well as an ultimate strength of 4.5 MPa for the composites, with a moderate fiber volume fraction of 2%. The specimens reveal saturated multiple cracking with crack width at ultimate strain limited to below 100 nanometers. The underlying reason of the distinctly different tensile behavior between normal fiber-reinforced concrete and PVA-ECC is highlighted by the comparison of complementary energy from their fiber bridging stress and crack opening curves.

Tensile Strain Hardening Behavior of Cementitious Composites Reinforced with Short Steel Fibres

Tensile Strain Hardening Behavior of Cementitious Composites Reinforced with Short Steel Fibres

Processing, microstructure, and mechanical behavior of cast magnesium metal matrix composites

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. This article presents a liquid mixing and casting process that can be used to produce SiC particulate-reinforced magnesium metal matrix composites via conventional foundry processes. Microstructural features, such as SiC particle distribution, grain refinement, and particle/matrix interfacial reactions of the cast magnesium matrix composites, are investigated, and the effects of solidification-process parameters and matrix alloys (pure Mg and Mg-9 pct Al-1 pct Zn alloy AZ91) on the microstructure are established. The results of this work suggest that in the solidification processing of MMCs, it is important to optimize the process parameters both to avoid excessive interfacial reactions and simultaneously achieve wetting, so that a good particle distribution and interfacial bonding are obtained. The tensile properties, strain hardening, and fracture behavior of the AZ91/SiC composites are also studied and the results are compared with those of the unreinforced AZ91 alloy. The strengthening mechanisms for AZ91/SiC composite, based on the proposed SiC particle/matrix interaction during deformation, are used to explain the increased yield strength and elastic modulus of the composite over the magnesium matrix alloy. The low ductility found in the composites is due to the early appearance of localized damages, such as particle cracking, matrix cracking, and occasionally interface debonding, in the fracture process of the composite.