Strain-hardening Behavior Research Articles

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.

In-situ study of anisotropic strain-hardening and grain boundary mediated deformation in commercially pure titanium

In this study, we investigated the anisotropy in tensile deformation behaviour of CP-Ti plate in the rolling (RD) and transverse direction (TD), using in-situ SEM-EBSD testing and stress-relaxation method. The EBSD-assisted slip trace analysis was conducted to examine the slip systems activated within individual grains. It was found that the prismatic slip is dominant in the RD sample, whilst the activity of non-prismatic slip systems is higher in the TD sample. The slip transfer significantly occurred in the TD sample, thereby promoting the activity of multiple slips and dislocation interactions at the grain interiors. However, the limited occurrence of slip transfer in the RD sample indicates the strong dislocation pinning at the grain boundaries (GBs). Combined with the EBSD analysis, the SEM observations revealed that the GBs with ledge character are formed in the slip-favourable and -unfavourable grain pairs, and the GBs with sink character are created in the grain pairs whose c-axes are equally inclined to the loading direction, but the sign of c-axis inclination angles is opposite with each other. The formation of GB ledges and GB sinks was pronounced in the RD and TD sample, respectively. The GB-dislocation interactions and GB-mediated deformation arising from the orientation relationship between the particular grain pairs led to the anisotropy in strain-hardening behaviour of polycrystalline α-Ti.

Microstructural Understanding of Hydroxyapatite Addition on Age Hardening, Internal Friction, and Mechanical and Electrochemical Response of Resorbable Magnesium Alloys with Good Cytocompatibility

The present work aims to assess the age hardening of microalloyed Mg-Zn-Mn alloy reinforced with Ca10(PO4)6(OH)2 (hydroxyapatite, HAp) particles to impart mechanical strength without deteriorating their degradation and biocompatibility behavior for their suitability toward resorbable fixation devices. The hydroxyapatite powder was synthesized with high purity. Mg-Zn-Mn (ZM31) and Mg-Zn-Mn/HAp (ZM31/HAp) were stir-cast, homogenized, and solution-treated to achieve uniform dissolution. Further, they were given a range of aging treatments (175 °C for 0, 5, 10, 25, 50, and 100 h), and the age hardening was measured as Vickers microhardness. The solution-treated and peak-aged (175 °C × 50 h) samples were further investigated using optical and electron microscopy, tensile testing, electrochemical corrosion testing, dynamic mechanical analysis, and biocompatibility. The peak-aged ZM31 sample revealed the highest ultimate strength (134.09 ± 5.46 MPa). The aging treatment resulted in notable improvement in ductility in ZM31 (8.72 ± 1.38%) and yield strength in ZM31/HAp (82.50 ± 1.43 MPa). The rapid strain-hardening behavior was distinctly visible in peak-aged samples in the initial stage of deformation. The amplitude-dependent internal friction confirmed the active solute and age-hardening mechanisms in agreement with the Granato-Lücke model. All samples displayed favorable cell viability (>80%) and cell adhesion behavior; however, their hemocompatibility and biodegradation need further consideration.

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.

Microcellular extrusion foaming of long-chain branched polyamide 6 composites

In this study, by introducing the long-chain branched (LCB) structure into the polyamide 6 (PA6) matrix, low-density microcellular PA6 composite foams with favorable cell morphology were prepared using supercritical CO2 extrusion foaming. PA6/talc composites with varying degrees of LCB were prepared using a twin-screw extruder. Rheological tests showed that the LCB-4.0 T sample with an ultra-high LCB degree had more apparent strain-hardening behavior and higher instantaneous elongational viscosity of 4.40 × 108 Pa·s. Isothermal crystallization tests revealed that LCB-4.0 T had lower crystallization rate. The effect of the degree of LCB on the gas solubility of CO2 in the PA6 composites was also examined. The foamability of the PA6/talc composites was verified via continuous extrusion foaming. High-performance PA6 composite foams with an average cell size as low as 66.7 µm, cell density as high as 2.53 × 107 cells/cm3, expansion ratio as high as 11.8, and foaming temperature window as wide as 16 °C were successfully obtained.

Reinforcement effect of cutting process on machined surface quality and performance of aviation aluminum alloy 7075 based on Oxley-Welsh theory

Aiming at the difficult problem of regulating the mechanical properties of the machined surface in the dry cutting of aviation aluminum alloy 7075, and the deviation of the solution caused by the idealized assumption of stress-strain in the shear zone in the previous cutting models, the effect of cutting parameters on the average width of the shear zone and stress-strain behavior of aviation aluminum alloy 7075-T651 in the dry turning process, and the effect of strain-hardening behavior on the cutting model were studied based on the Oxley-Welsh theory. In addition, relationship models between shear flow stress and hydrostatic stress in cutting zone, hydrostatic-shear difference of material unit, microhardness of machined surface, as well as surface roughness were established, which reasonably explains the size effect and strain-hardening effect in the shear zone of workpiece material during dry turning of 7075-T651 aluminum alloy. The results showed that the slope K of the relationship model between shear flow stress and hydrostatic stress is the result of the combined effect of the size effect and the strain-hardening effect in the shear zone of workpiece material. When the 7075-T651 aluminum alloy is produced under the cutting conditions of cutting velocity vc = 240 m/min, feed rate f = 0.05 mm/r, and cutting depth ap = 0.15 mm, the machined workpiece had the best uniform plastic deformation, relatively highest surface hardness, up to 174.1 HV, relatively best surface quality, with roughness up to 0.78 μm, and relatively strongest load-bearing capacity in the service process.

High volume of slag and polypropylene fibres in engineered cementitious composites: microstructure and mechanical properties

The use of engineered cementitious composite (ECC) is increasing owing to its high tensile strength and ductility; however, little attention has been paid to substitutes for its ingredients. Blast furnace slag instead of fly ash and polypropylene (PP) fibres instead of polyvinyl alcohol (PVA) fibres may be considered to be appropriate alternative substitutes. Therefore, the present study aimed to produce an ECC with a large proportion of slag and PP fibres that would achieve high strength and ductility characteristics and create controlled microcracking behaviour under tensile stresses (i.e. strain-hardening behaviour). The specimens made from ECC thus prepared were subjected to compressive, four-point bending, X-ray diffraction (XRD) and scanning electron microscope (SEM) tests. The results showed that a slag/cement ratio of 0.5 in ECC led to the highest compressive strength (55.6 MPa) and modulus of rupture (MOR) (7.0 MPa), while the corresponding energy absorption was fairly high. The results of XRD and SEM analyses indicated that applying the slag/cement ratio of 0.5 led to a homogenous cement matrix and produced the highest calcium-silicate-hydrate (C-S-H) in the ECC microstructure. Finally, to predict the load–deflection of specimens, a three-part model was proposed and verified with other available data.

Tensile Behavior of Titanium-Clad Bimetallic Steel Butt-Welded Joints

Because of the promising corrosion resistance and load-bearing capacity, titanium-clad (TC) bimetallic steel has gained increasing attention in ocean/coastal civil and structural engineering. Due to the double-layer nature of TC bimetallic steel, the characteristics of the structural member’s geometry and weld details are considerably different from that of conventional steel members. Even though previous studies have conducted systematical clarifications on parent material of TC bimetallic steels, the mechanical behaviors of weld joints are still vague. This paper firstly describes the manufacture features of TC bimetallic steel welded joints and welded members. Subsequently, the type II and type III butt-welded joints provided by GB/T 13149-2009 are selected to study the corresponding tensile mechanical behavior. Two butt-welded TC bimetallic steel plates were fabricated from hot-rolled bonding TA2 + Q355B TC bimetallic steel and welding wire of ER55-Ni1 and ERTA2ELI. Eight tensile coupons were then extracted from the two welded plates and loaded to failure monotonically. The failure mechanism, stress–strain curves and key mechanical properties are studied and compared with that of parent material. It is found that both types of welded joints possess two fracture points. The first one refers to the fracture of weld joint between the clad layer and titanium cover plate, whilst the second one is the eventual fracture of substrate metal. When the first fracture point is reached, the stress–strain relation exhibits a sharp drop in stress value. Thereafter, a strain-hardening behavior can still be observed prior to the ultimate strength point. The first fracture-induced stress drop of type II joint is less than that of type III joint, whilst the strain-hardening amount of type II joint is more outstanding than that of type III joint. The fracture elongations of type II joint and type III joint are respectively 37% and 57% that of the parent material, whilst the proportions between the ultimate strengths of welded joints and parent material are, respectively, 90% and 93%. In general, the two types of TC bimetallic steel weld joints investigated herein exhibit favorable load-bearing capacity but unfavorable ductility and deformability. Based upon the experimental results, the structural design methodology of welded TC bimetallic steel structure is discussed. The investigations conducted in this paper can provide reference for development of structural design theory of welded TC bimetallic steel structure.

Influence of curing conditions on mechanical and microstructural properties of ultra-high-performance strain-hardening cementitious composites with strain capacity up to 17.3%

This study investigated the mechanical properties and microstructural characteristics of ultra-high-performance strain-hardening cementitious composites (UHP-SHCC). The mechanical properties were thoroughly analyzed based on the shrinkage behavior, thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopic images. Three relative humidity (RH) conditions and curing ages were set as the test variables. Relative to the specimens cured at 30% RH, the specimens cured at 60% and 100% RH conditions showed 29.9% and 37.6% higher 91-day compressive strengths. Excellent strain-hardening behaviors with very high strain capacities, ranging between 6.0% and 17.3%, were obtained for all UHP-SHCC specimens tested. The highest strain capacity and energy absorption capacity of 17.3% and 1310.7 kJ/m3 were obtained when cured under RH conditions of 30% and 60% for 7 days, respectively. The strain capacity and energy absorption capacity of UHP-SHCC rather decreased as the RH condition and curing age increased to 100% and 91 days, respectively.

Effect of ECAP processing temperature on an austenitic TWIP steel's microstructure, texture and mechanical properties

The development of microstructure and texture of twinning-induced plasticity (TWIP) steel sheet during ECAP at two temperatures (250° and 350°) up to four passes were investigated. The high chromium content is the differential of this TWIP steel, a chemical element that reduces the stacking-fault energy and increases corrosion resistance. By imposing ECAP, the volume fraction of twins, dislocation density, and yield strength significantly increase while ductility decreases. This study compared the effect of temperature during applied severe plastic deformation (SPD). Thin parallel slip bands’ high density was observed, and in addition to an intense micro shear, banding took place when pressing was continued by increasing the number of passes. The martensitic transformation was not detected in the deformation-twinning microstructure after more passes. The relationship between the microstructure, strain-hardening behavior, and mechanical properties was investigated after two different deformation schedules of ECAP. The best balance between high strength and good ductility (1915 MPa and 7%) was obtained after four passes at 250 °C and 350 °C. It was found that the quantity of ECAP pass affects the displacement substructure with the formation of shear bands, subgrains, and various variants of twins. These also influenced strain-hardening behavior, microhardness, texture, and ultimate strength.

Effect of woven geotextile reinforcement on mechanical behavior of calcareous sands

The mechanical properties of calcareous sands are critical as potentially important material sources for marine geotechnical constructions. Brittleness and large deformations created in calcareous sands can affect the stability of marine structures and geosynthetic reinforcement is a promising new approach. In this study, a series of consolidated-drained (CD) tests were conducted to evaluate the mechanical properties and deformation of woven geotextile-reinforced calcareous sand. For this purpose, the effect of geotextile layers, relative density, type of woven geotextile, and confining pressure were investigated. The results show that the strength of the reinforced specimens increases markedly compared to the unreinforced calcareous sand and the deviatoric stress-strain curves change from slight softening to hardening and dilatancy. Also, by increasing the number of woven geotextile layers and applying a confining pressure, the shear deformation shifts toward strain-hardening behavior. Overall, woven geotextiles significantly improve the apparent cohesion strength of calcareous sand soil. The woven geotextile, relative density, and confining pressure all contribute to volumetric changes and dilatancy of reinforced specimens, but particle breakage is more affected by confining pressure.

Construction of fully biodegradable poly(L-lactic acid)/poly(D-lactic acid)-poly(lactide-co-caprolactone) block polymer films: Viscoelasticity, processability and flexibility

Development of biodegradable polymer films is essential for sustainable energy conservation and ecological protection. In this work, to improve the processability and toughness of poly(lactic acid) (PLA) films, poly(lactide-co-caprolactone) (PLCL) segments were introduced into poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) chains via chain branching reactions during reactive processing, and fully biodegradable/flexible PLLA/D-PLCL block polymer with long-chain branches and stereocomplex (SC) crystalline structure was prepared. Compared with neat PLLA, PLLA/D-PLCL exhibited much higher complex viscosity/storage modulus, lower tanδ values in terminal region and obvious strain-hardening behavior. Through biaxial drawing, PLLA/D-PLCL films were prepared, which showed improved uniformity and non-preferred orientation. With increasing draw ratio, the total crystallinity (Xc) and Xc for SC crystal both increased. By introduction of PDLA, the two phases of PLLA and PLCL penetrated and entangled with each other, and the phase structure transformed from “sea-island” structure to “co-continuous network” structure, which was beneficial for exerting the toughening effect of flexible PLCL molecules on PLA matrix. The tensile strength and elongation at break of PLLA/D-PLCL films increased from 51.87 MPa and 28.22 % of neat PLLA film to 70.82 MPa and 148.28 %. This work provided a new strategy for developing fully biodegradable polymer films with high performance.

Extremely Robust and Multifunctional Nanocomposite Fibers for Strain-Unperturbed Textile Electronics.

Textile electronics are needed that can achieve strain-unaltered performance when they undergo irregular and repeated strain deformation. Such strain-unaltered textile electronics require advanced fibers that simultaneously have high functionalities and extreme robustness as fabric materials. Current synthetic nanocomposite fibers based on inorganic matrix have remarkable functionalities but often suffer from low robustness and poor tolerance against crack formation. Here,wepresent a design for a high-performance multifunctional nanocomposite fiber that is mechanically and electrically robust, whichwasrealized by crosslinking titanium carbide (MXene) nanosheets with a slide-ring polyrotaxane to form an internal mechanically-interlocked network. This inorganic matrix nanocomposite fiber featured distinct strain-hardening mechanical behavior and exceptional load-bearing capability (toughness approaching 60 MJ m-3 and ductility over 27%). It retained 100% of its ductility after cyclic strain loading. Moreover, the high electrical conductivity (>1.1 × 105 S m-1 ) and electrochemical performance (>360 F cm-3 ) of the nanocomposite fiber can be well retained after subjecting the fiber to extensive (>25% strain) and long-term repeated (10 000 cycles) dimensional changes. Such superior robustness allowed for the fabrication of the nanocomposite fibers into various robust wearable devices, such as textile-based electromechanical sensors with strain-unalterable sensing performance and fiber-shaped supercapacitors with invariant electrochemical performance for 10 000 strain loading cycles.

Crimped fiber composites: mechanics of a finite-length crimped fiber embedded in a soft matrix.

Composites comprising crimped fibers of finite length embedded in a soft matrix have the potential to mimic the strain-hardening behavior of tissues containing fibrous collagen. Unlike continuous fiber composites, such chopped fiber composites would be flow-processable. Here, we study the fundamental mechanics of stress transfer between a single crimped fiber and the embedding matrix subjected to tensile strain. Finite element simulations show that fibers with large crimp amplitude and large relative modulus straighten significantly at small strain without bearing significant load. At large strain, they become taut and hence bear increasing load. Analogous to straight fiber composites, there is a region near the ends of each fiber which bears much lower stress than the midsection. We show that the stress-transfer mechanics can be captured by a shear lag model where the crimped fiber can be replaced with an equivalent straight fiber whose effective modulus is lower than that of the crimped fiber, but increases with applied strain. This allows estimating the modulus of a composite at low fiber fraction. The degree of strain hardening and the strain needed for strain hardening can be tuned by changing relative modulus of the fibers and the crimp geometry.

High Ductile Medium Mn Lightweight Alloy: The Role of Intensive Quenching and Deep Cryogenic Treatment

Medium Mn lightweight steels with a relatively higher Mn content of 9–12 wt% have been actively developed recently to meet the demands of crashworthiness and lightweight vehicles. In this study, a combined intensive quenching (IQ) and deep cryogenic treatment (DCT) was first proposed to achieve the microstructural homogeneity as well as the final strength–ductility synergy of medium Mn lightweight steels with Mn segregation bands, together with a comparison with the conventional intercritical annealing. The proposed IQ and DCT process induced the formation of finer large fractioned plate-like martensite in the austenite matrix and thereby contributed to finer and uniform austenite grains after subsequent intercritical annealing. The martensitic transformation rate (dVγ/dε) and transformation kinetics (k value) were used to evaluate the mechanical stability of retained austenite, showing that the D700&750 sample exhibited a similar dVγ/dε value and extremely low k value when compared to the conventional IA650–850 samples, implying that the former had the higher mechanical stability of austenite. The higher mechanical stability of austenite enabled the TRIP effect to occur in a larger strain range, leading to continuous strain hardening behavior. Thus, the highest yield strength (728 MPa) and the largest total elongation of 61.6% were achieved in the D700&750 sample, where the ductility was more than three times higher than that of the conventional IA samples. The grain size and morphologies of retained austenite were believed to be the main factors influencing the strain-hardening behavior of this type of ultrafine lamellar and equiaxed ferrite and austenite duplex structure.

3D cohesive fracture of heterogeneous CA-UHPC: A mesoscale investigation

Ultra high performance concrete with coarse aggregates (CA-UHPC) exhibits complicated damage and failure mechanisms due to intricate interactions of irregular mesoscale phases, including random aggregates, fibres, mortar, and interfaces. This work proposes a 3D numerical framework to investigate the complex cohesive fracture of CA-UHPC at mesoscale for the first time. Automatic algorithms are proposed to model realistic aggregates, mortar, aggregate-mortar interfaces and steel fibres in large quantities. Zero-thickness cohesive interface elements are automatically inserted in the mortar and on the aggregate surfaces to capture potential cracks, and an efficient non-conforming methodology is developed to model the fibre-mortar bond-slip behaviour using orientation-dependant pullout force-slip relations. The proposed models are validated using typical uniaxial tension tests, and elucidate that the progressive interactions of aggregate barrier, interfacial cracking and fibre bridging govern the early cracking, strain-hardening behaviour, fibre activation and final crack networks. Quantitative analyses are performed to optimize the mechanical properties of CA-UHPC: as the aggregate content increases, there are more torturous crack surfaces and fewer activated fibres with lower load-carrying capacities, but the downside of coarse aggregates can be alleviated by increasing fibre content, especially when needing aggregates to reduce carbon footprints and improve anti-shrinkage performance.

Local electropulse-induced gradient and hierarchical architecture of soft-hard phase in 35CrMo steel

To improve the comprehensive mechanical properties while avoiding the overall heat treatment, this study provided a method to prepare structural steel with soft-hard phases arranged in complex gradient, hierarchical structures via processing a homogenous material using local electropulsing treatment (LEPT). The results show that ultimate tensile strength, elongation-to-failure, and curves area of the structural steel plate are about 1400 MPa, 15.93%, and 19,100 MPa·%, respectively, which are 16.5%, 34.7%, and 47.5% higher than the conventional quenched and tempered steel. The excellent mechanical properties of LEPTed specimens are mainly due to the local strengthening caused by the effects of pulse current, and the synergistic effect of hard and soft phases. The designed hardened units produced by LEPT exhibit hierarchical structure and gradient variations in texture and grain size. There also exists gradient hardness distribution in hardened units. These structures are produced due to the multi-scale effects of current and the gradient current density distribution. Moreover, due to the introduction of hardened units at another scale, there were four stages in the strain-hardening behavior of LEPT based on differential Crussard-Jaoul (DC-J) analysis, which deviates from the three stages of two-phase or multi-phase steels.

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%.

Dependency of work-hardening behavior of a metastable austenitic stainless steel on the nucleation site of deformation-induced martensite

Effects of the nucleation site and morphology of deformation-induced martensite on the work-hardening behavior of transformation-induced plasticity (TRIP)-assisted austenitic stainless steel with different austenite grain sizes were examined. By increasing grain size from the ultrafine-grained (UFG) range to the coarse grained (CG) regime, the nucleation site of α′-martensite changed from the grain boundaries to the interior of the deformed grains (i.e., shear bands and their intersections), where the nucleation on the ε-martensite was also observed. The nucleation site was found to be responsible for the morphology of the α′-martensite, which changed from blocky shape to film-like by increasing the grain size from the UFG range to the CG regime. The strengthening effect brought by the strain-induced martensite formation was quantified based on the deviation of the work-hardening behavior from the conventional strain-hardening behavior (by the generation and interaction of dislocations, as represented by the Hollomon law). Film-like α′-martensite formed on the shear bands and their intersections led to a higher work-hardening rate compared to the blocky α′-martensite formed on grain boundaries.

Experimental study on flexural performance of steel-UHTCC composite bridge decks considering different shear connection degrees

Traditional steel–concrete composite bridge deck (CBD) is prone to crack in the concrete layer, which reduces its flexural capacity and durability. Due to the excellent crack resistance behavior and characteristic of tensile strain hardening, ultra-high toughness cementitious composite (UHTCC) has become a promising material to solve this problem. In this study, the flexural performance of bridge decks composed of steel and UHTCC using shear studs is analyzed by means of experimental research and finite element (FE) analysis. Five steel-UHTCC CBDs with different shear connection degrees and rib dimensions were fabricated and tested. Then, FE models of steel-UHTCC CBDs were established by ABAQUS, involving FE examples for comparing with the tests and 10 groups of models to conduct a parametric study. The flexural resistant performance of steel-UHTCC CBDs was studied concerning the key design parameters, including stud number, span length, rib dimension, thickness of UHTCC and longitudinal reinforcement ratio. The effect of shear connection degree on the flexural resistance of CBDs was discussed in detail. Finally, a modified theoretical formula was proposed for predicting the flexural resistance of steel-UHTCC CBDs.