Low Tensile Ductility Research Articles

Ultrahigh Tensile Ductility of Ag2Te Nanowire at Room Temperature

AbstractTensile ductility is one of the key concerns in the field of flexible devices. Ag2Te is a promising flexible thermoelectric (TE) material due to its high TE properties and compressive ductility, but low tensile ductility blocks its flexible application. In this work, a low‐dimensional strategy is adopted to find that Ag2Te nanowires exhibit an exceptional tensile fracture strain of 75.7% at room temperature, several times higher than other ceramic and semiconductor nanowires, and even comparable to some metals. By in situ transmission electron microscope (TEM) observations and density functional theory (DFT) calculations, the tensile ductile mechanism has been successfully revealed. First, the emissions of partial dislocations from the surface lead to the slipping band along (100) plane, which is attributed to the atomic rearrangement along (100) plane. Then, the surface steps occur, and deformation twinning forms along (001) plane at the slip region, which inhibits the crack initiation. Finally, Ag particles precipitate around the slip region and then form Ag nanobridges to further resist the external deformation, achieving extraordinary tensile ductility. This work provides some insights into the mechanical behaviors of Ag2Te at the nanoscales, which is beneficial for the development of reliable micro‐devices.

Exploration of high-ductility ternary refractory complex concentrated alloys using first-principles calculations and machine learning

BCC-based refractory complex concentrated alloys (RCCAs) are attracting attention as high-temperature materials because of their exceptional strength at high temperatures, but suffer from low tensile ductility. To search for alloys with improved ductility, it is necessary to investigate the properties of RCCA systems thoroughly, however, an experimental investigation of these vast constitutional spaces is impractical. This study employed data-driven approaches that combined first-principles calculations with machine learning. We first calculated the lattice parameters and elastic constants of 1693 ternary RCCAs, subsets of RCCAs alloys consisting of Ti, Zr, Hf, Nb, Mo, V, Ta, and W, using the exact muffin-tin orbitals method with coherent potential approximation (EMTO-CPA), and generated ductility-related parameters, including Pugh's ratio, Poisson's ratio, and Cauchy pressure. Machine learning models that could predict the three parameters were searched and trained using the generated data. Subsequently, an inverse design based on optimization algorithms was performed to identify optimal alloy systems with high Pugh's ratios. The ductility of the searched alloys was verified by calculating Pugh's ratio using EMTO-CPA, followed by thermodynamic calculations to investigate their structural stability.

Influence of interface on deformation compatibility of a heterogeneous Cu/Al nanoscale multilayer

The incompatible deformation among the constituent layers usually results in extremely low tensile ductility in nanoscale metallic multilayers. Here, molecular dynamics simulations are conducted to investigate the deformation compatibility of a heterogeneous Cu/Al multilayer with various interface structures under compression. The results show that, by selecting an appropriate thickness of thin interlayers, the heterogeneous Cu/Al nanolayered composite with (1¯1¯1) interface exhibits excellent compatible deformation between the soft and hard layers while the homogeneous counterpart does not. The excellent deformation compatibility of the heterogeneous structure originates from the presence of the thin soft interlayer that can enhance the dislocation activities of the hard layers. Unlike that with (1¯1¯1) interface, the heterogeneous structure with (001) interface shows obvious incompatible deformation among the component layers. Such a scenario can be attributed to the stable dislocation network on the (001) interface, making the dislocations in the soft phase difficult to cross the interface into the hard phase. These findings may deepen our understanding of the deformation compatibility of heterogeneous nanoscale metallic multilayers.

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy.

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy's behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m1/2, which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

Investigations on GUJCON-CRF Nylon 6 fiber based cement concrete for pavement

Plain concrete has very low tensile strength, limited ductility, and poor resistance to cracking. Due to its poor tensile strength and cracking propagation, concrete eventually leads to brittle failure on the application of heavy loads. Hence, fiber reinforcement is used to improve the physical properties of plain cement concrete. This study aims to investigate the behavior of concrete when GUJCON-CRF Nylon 6 fibers are incorporated in varying quantities as secondary reinforcement in cement concrete to alter its brittle nature and reduce plastic shrinkage cracking. The fresh characteristics (slump cone test and compaction factor test), mechanical characteristics (compressive strength test and flexural strength test), and durability characteristics (abrasion test, sulfate attack test, acid attack test, and water permeability test) of concrete were investigated experimentally in this study using a superplasticizer (Structuro 202), based on polycarboxylic technology and GUJCON-CRF Nylon 6 fiber. In this study, GUJCON-CRF Nylon 6 fiber was included in concrete in amounts of 0.2 %, 0.25 %, 0.30 %, 0.35 %, and 0.40 % by cement weight, maintaining a consistent water-to-cement ratio of 0.38. An M40-grade concrete mix design was prepared for our exploration and testing. The concrete specimens (cubes and beams) prepared from each type of mix were tested at 7 days and 28 days, respectively, to study the mechanical properties of hardened concrete. The test results of all specimens were analyzed, and it was observed that the mix with 0.25 % replacement of the weight of cement provided the most competitive concrete mix. Compared to ordinary concrete, the compressive and flexure strength increased by 16.8 % and 36.59 %, respectively. It was discovered that abrasion resistance increased significantly up to 0.30 % replacement, then it became insignificant. A minimum value of permeability and water absorption was also reported for 0.25 % of cement weight replacement by GUJCON fiber.

Controllable tensile performance of additively manufactured Al–Fe alloy

Achieving both high strength and ductility is challenging in additive manufacturing of Al alloys using the laser powder bed fusion (L-PBF) process by altering the laser conditions to control the microstructural characteristics. The current work focuses on the influence of varying laser energy density (ED), which is adjusted by different sets of laser power (P) and scan speed (v), on the microstructure-tensile property relationships of the L-PBF-fabricated Al–2.5%Fe alloy under varying laser conditions (P = 204–230 W, v = 450–600 mm/s) with a fixed powder layer thickness (t = 30 μm) and hatch distance (h = 30 μm). With increasing ED (= P/v·t·h), a slight increase in the average size of the columnar α-Al grains was found in the experimental samples concurrently with a higher fraction of <001>-oriented grains. Nanosized particles of the Al6Fe phase with an increased tendency to interconnect were observed in the matrix inside the melt pool, and the θ phase formed within the submicron-sized cellular structure along the melt pool boundaries (MPBs). A low tensile ductility, induced by the local microstructural inhomogeneities across MPBs, was found in all specimens tensile-deformed along the building direction, which was characterized by a preference fracture along the MPBs. At higher applied ED, the tensile ductility of the experimental Al–2.5Fe alloy was significantly improved with only a slight decrease in tensile strength. The difference in concentration of Fe across the MPBs in the matrix was also moderately diminished, which is consistent with the reduced local difference in microhardness across the MPBs under higher ED conditions. Therefore, the present results demonstrate that local microstructural inhomogeneities across MPBs can be controlled by the laser conditions, thereby producing both high strength and good ductility in the L-PBF processed Al–Fe alloys.

Shaking table tests on a 5-storey unreinforced masonry structure strengthened by ultra-high ductile cementitious composites

Multi-storey unreinforced masonry structures have been widely used as residential building structures in China during the decade of 1970–1980. Recent earthquake events have shown that these buildings may exhibit severe damages due to their relatively brittle seismic resistance mechanism. The use of ultra-high ductile cementitious composites (UHDCC) layers can be an attractive minimal-disturbance strengthening option for masonry structures resulting in low intervention costs and quick construction. UHDCC is a high-performance engineered cementitious composite that offers a tensile strain capacity higher than 5%, thus significantly improving the low tensile strength and ductility of the masonry wall. To investigate the seismic behavior of UHDCC-strengthened masonry structures, shaking table tests were carried out on two three-dimensional 5-storey masonry structures including a conventional test structure (CS) and a strengthened test structure (SS). The results show that the proposed strengthening method can effectively improve the seismic performance of multi-storey unreinforced masonry structures due to the excellent cohesion achieved between the existing masonry walls and the UHDCC external strengthening layers. The strengthened method changes the damage state of masonry structures from shear failure to a more ductile failure, and the strengthened masonry walls can exhibit a multi-cracking response. The initial natural period of the SS specimen was found 0.58 times that of the CS specimen. The base shear and maximum roof drift of the SS specimen are 4.8 and 3.4 times that of the CS model, respectively. This study provides reference results for the application of UHDCC layers to strengthen multi-storey unreinforced masonry structures.

Characterization on the glass forming ability of metallic nano-glasses by the dynamic scaling for mechanical loss in supercooled liquid state

Metallic nano-glasses (NGs) are promising in solving the issues of metallic glasses (MGs) such as the intrinsic size limitation and low tensile ductility, while the understanding on the forming ability of glassy structures in NGs is still lacking. Herein, an exponent β is proposed to characterize the glass forming ability (GFA) of NGs, as well as MGs, which is determined by dynamic scaling for mechanical losses (Q − 1) with the frequency ω of external perturbation in their supercooled liquid states as Q − 1~ω−β. The results suggest β is more accurate and sensitive than other commonly used parameters in measuring GFAs, and confirm NGs with a higher volume fraction of glass-glass interfaces (GGIs) have more thermodynamically stable glass phases and enhanced GFAs with higher β values. Our findings provide solid evidence that the introduction of GGIs in NGs could resolve the longstanding issue of size limitation on MGs.

Experimental and modeling investigation on the viscoelastic-viscoplastic deformation of polyamide 12 printed by Multi Jet Fusion

The viscoelastic-viscoplastic deformation of Multi Jet Fusion-printed polyamide 12 (MJF PA12) was investigated with experimental and numerical approaches. Multi-loading–unloading–recovery tests were conducted to distinguish between the viscoelastic and viscoplastic deformations. The influence of the void defects on deformation of PA12 was investigated through the micro-computed tomography (μCT) and field emission scanning electron microscope. A finite-strain viscoelastic-viscoplastic constitutive model based on the logarithmic stress rate for the matrix of MJF PA12 was developed within the thermodynamic framework as well as an introduction of the accumulated plastic deformation–induced damage into the proposed model. A representative volume element was modeled based on the μCT results of MJF PA12. The simulated results, such as stress–strain and strain–time curves, agreed with the experimental results. Moreover, the model revealed the mechanism that the low tensile ductility of MJF PA12 is caused by the increase in strain localization and narrowing of the shear band.

Experimental Investigation of Shear Strength for Steel Fibre Reinforced Concrete Beams

Aims:The aim of this paper is to investigate the influence of the volume fraction of fibres, the depth of the beam and the shear span-to-depth ratio on the shear strength of steel fibre reinforced concrete beams.Background:Concrete is a material widely used in structures, as it has high compressive strength and stiffness with low cost manufacturing. However, it presents low tensile strength and ductility. Therefore, through years various materials have been embedded inside it to improve its properties, one of which is steel fibres. Steel fibre reinforced concrete presents improved flexural, tensile, shear and torsional strength and post-cracking ductility.Objective:A better understanding of the shear performance of SFRC could lead to improved behaviour and higher safety of structures subject to high shear forces. Therefore, the influence of steel fibres on shear strength of reinforced concrete beams without transverse reinforcement is experimentally investigated.Methods:Eighteen concrete beams were constructed for this purpose and tested under monotonic four-point bending, six of which were made of plain concrete and twelve of SFRC. Two different aspect ratios of beams, steel fibres volume fractions and shear span-to-depth ratios were selected.Results:During the experimental tests, the ultimate loading, deformation at the mid-span, propagation of cracks and failure mode were detected. From the tests, it was shown that SFRC beams with high volume fractions of fibres exhibited an increased shear capacity.Conclusion:The addition of steel fibres resulted in a slight increase of the compressive strength and a significant increase in the tensile strength of concrete and shear resistance capacity of the beam. Moreover, these beams exhibit a more ductile behaviour. Empirical relations predicting the shear strength capacity of fibre reinforced concrete beams were revised and applied successfully to verify the experimental results obtained in this study.

Mechanical Reinforcement of Lime Pastes by Electrospun Cellulose Acetate Polymer Fibers

Lime-based composites have been extensively used throughout the years as plasters/renders and jointing mortars in building construction. However, the low flexural strength and tensile ductility of these composite building materials, that are currently still used in the structural and thermal upgrading of existing structures of high cultural and architectural significance, have been a significant drawback. Therefore, researchers have been focusing on the development of novel composites involving the use of additives to enhance the tensile and flexural capacity of lime-based materials. For the first time in this study, naturally-derived polymer fibers produced by electrospinning have been successfully introduced as additives in lime pastes aiming to investigate their effect on the mechanical performance of the end composites. More precisely, the introduction of electrospun cellulose acetate (CA) microfibers within lime pastes resulted to a tremendous improvement of the mechanical properties of the latter. Consequently, the present study paves the pathway towards the use of electrospun fibrous additives in the development of advanced composite lime-based building materials, which is currently an unexplored area.

Prediction of Flexural Behavior of Woven Reinforced for Concrete Reinforcement

Plain concrete possesses very low tensile strength, limited ductility and little resistance to cracking. Fibers glass-reinforced concrete supposed to improve the strain properties well as crack resistance, ductility, as flexural strength and toughness. This paper aims to predict the flexural behavior of fiber-glass reinforced concrete and optimize the beam design by applying woven layer in M35 grade concrete using finite element method. The several techniques were implemented to study flexural performance, woven position on bottom, middle and upper surface and several woven thickness layers employed to investigate flexural performance such as 5, 10, 20, 30, 40 and 50 mm for beam size of 100 × 100 × 500 mm. It found that the flexural strength increased by positioned the woven on the bottom side and it given the improvement in designing when the layer thickness of fiber varied. It is because the fiber usually reduces the brittleness of concrete by providing post cracking ductility and increase toughness. The difference flexural strength between 50mm and 40mm thickness of fiberglass is about 1.29%.

Microstructures and Tensile Fracture Behavior of 2219 Wrought Al–Cu Alloys with Different Impurity of Fe

The Fe-rich intermetallic phases have a broadly detrimental effect on the mechanical properties of Al–Cu alloy. In this paper, the continuous evolution of Fe-rich intermetallics and their effects on mechanical properties, especially the tensile fracture behavior of 2219 wrought Al–Cu alloys as a function of Fe content against different processing approaches (i.e., as-cast, homogenization, multidirectional forging, and solution-peak aging treatment) were investigated using optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that needle-like Al7Cu2Fe or Al7Cu2(Fe, Mn) intermetallics mainly presented in the final microstructures of all alloys with various Fe contents. The size and number of Al7Cu2Fe/Al7Cu2(Fe, Mn) intermetallics increased with the increase of Fe content. The increase of Fe content had little influence on the ultimate tensile strength and yield strength, while obvious deterioration in the elongation, because fracture initiators mainly occurred at the Al7Cu2Fe/Al7Cu2(Fe, Mn) particles or particles–matrix interface. Therefore, the 2219 Al–Cu alloy with 0.2 wt.% Fe content presented relatively low tensile ductility. The tensile fracture mechanism has been discussed in detail.

Ultrahigh strength and ductility in newly developed materials with coherent nanolamellar architectures

Nano-lamellar materials with ultrahigh strengths and unusual physical properties are of technological importance for structural applications. However, these materials generally suffer from low tensile ductility, which severely limits their practical utility. Here we show that markedly enhanced tensile ductility can be achieved in coherent nano-lamellar alloys, which exhibit an unprecedented combination of over 2 GPa yield strength and 16% uniform tensile ductility. The ultrahigh strength originates mainly from the lamellar boundary strengthening, whereas the large ductility correlates to a progressive work-hardening mechanism regulated by the unique nano-lamellar architecture. The coherent lamellar boundaries facilitate the dislocation transmission, which eliminates the stress concentrations at the boundaries. Meanwhile, deformation-induced hierarchical stacking-fault networks and associated high-density Lomer-Cottrell locks enhance the work hardening response, leading to unusually large tensile ductilities. The coherent nano-lamellar strategy can potentially be applied to many other alloys and open new avenues for designing ultrastrong yet ductile materials for technological applications.

Effect of Fibers on Durability of Concrete: A Practical Review.

This article reviews the literature related to the performance of fiber reinforced concrete (FRC) in the context of the durability of concrete infrastructures. The durability of a concrete infrastructure is defined by its ability to sustain reliable levels of serviceability and structural integrity in environmental exposure which may be harsh without any major need for repair intervention throughout the design service life. Conventional concrete has relatively low tensile capacity and ductility, and thus is susceptible to cracking. Cracks are considered to be pathways for gases, liquids, and deleterious solutes entering the concrete, which lead to the early onset of deterioration processes in the concrete or reinforcing steel. Chloride aqueous solution may reach the embedded steel quickly after cracked regions are exposed to de-icing salt or spray in coastal regions, which de-passivates the protective film, whereby corrosion initiation occurs decades earlier than when chlorides would have to gradually ingress uncracked concrete covering the steel in the absence of cracks. Appropriate inclusion of steel or non-metallic fibers has been proven to increase both the tensile capacity and ductility of FRC. Many researchers have investigated durability enhancement by use of FRC. This paper reviews substantial evidence that the improved tensile characteristics of FRC used to construct infrastructure, improve its durability through mainly the fiber bridging and control of cracks. The evidence is based on both reported laboratory investigations under controlled conditions and the monitored performance of actual infrastructure constructed of FRC. The paper aims to help design engineers towards considering the use of FRC in real-life concrete infrastructures appropriately and more confidently.

A molecular dynamics investigation into deformation mechanism of nanotwinned Cu/high entropy alloy FeCoCrNi nanolaminates

High-entropy alloys (HEA) present high hardness, but low tensile ductility. Here, deformation behaviour of the nanotwinned Cu/HEA FeCoCrNi nanolaminates prepared by the previous experiment is investigated using atomic simulations. The result shows the nucleation and glide of lattice dislocations in the Cu layers dominate the initial plastic deformation in Cu/HEA multilayers, and these gliding dislocations are deposited at the twinning boundary. With the increasing strain, the dislocations are activated in HEA layer, and deposited in the Cu-HEA interface, finally facilitate slip transmission from the HEA layer to the Cu layer. The flow stress decreases and keeps a constant value with increasing nanotwinned Cu/HEA FeCoCrNi layer number, which depends upon the slip transmission and interfacial dislocation to govern strain hardening.

Early-age behavior of blast-furnace slag cement pastes produced with carbon nanotubes grown directly on clinker

Abstract Carbon nanotubes are a promising material to solve the low tensile strength and ductility of Portland cement-based materials. Carbon nanotubes (CNTs) synthesized directly on cement clinker particles can also reduce production costs and help dispersion. In this scenario, this paper analyzes the fresh state rheological behavior, as well as the initial hydration period of blast-furnace slag (Brazilian CP III 40 RS) cement pastes produced with CNTs grown directly on clinker. CP III 40 RS was selected since it is one of the most used cement by the construction industry in Brazil. Cement pastes containing 0.1% and 0.3% of CNTs with respect to cement content were compared with CNT-free pastes. No chemical admixtures were used as a dispersant in all cases. The yield stress, plastic viscosity, temperature profile and evolved accumulated heat during the initial hydration period as well as setting times are the properties investigated. The results show that the addition of CNTs does not alter the rheological behavior of the cement pastes considering the employed concentrations, although the yield stress values were larger. The presence of CNTs in the cement pastes did not change the evolved accumulated heat during the first 72 hours of the hydration period.

Effect of boron addition on the microstructure and mechanical properties of K4750 nickel-based superalloy

The effect of boron addition at 0, 0.007 wt. % and 0.010 wt. % on the microstructure and mechanical properties of K4750 nickel-based superalloy was studied. The microstructure of the as-cast and heat-treated alloys was analyzed by SEM, EPMA, SIMS and TEM. Lamellar M5B3-type borides were observed in boron-containing as-cast alloys. After the full heat treatment, boron atoms released from the decomposition of M5B3 borides were segregated at grain boundaries, which inhibited the growth and agglomeration of M23C6 carbides. Therefore, the M23C6 carbides along grain boundaries were granular in boron-containing alloys, while those were continuous in boron-free alloys. The mechanical property analysis indicated that the addition of boron significantly improved the tensile ductility at room temperature and stress rupture properties at 750 ℃/430 MPa of K4750 alloy. The low tensile ductility at room temperature of 0B alloy was attributed to continuous M23C6 carbides leaded to stress concentration, which provided a favorable location for crack nucleation and propagation. The improvement of the stress rupture properties of boron-containing alloys was the result of the combination of boron segregation increased the cohesion of grain boundaries and granular M23C6 carbides suppressed the link-up and extension of micro-cracks.

Microstructure evolution and deformation mechanism of amorphous/crystalline high-entropy-alloy composites

High-entropy amorphous alloys present high hardness, but low tensile ductility. Here, deformation behavior of the amorphous/crystalline FeCoCrNi high-entropy alloy (HEA) composite prepared by the previous experiment is investigated using atomic simulations. The result shows the partial dislocations in the crystal HEA layer, and the formation of shear bands in the amorphous HEA layer occurs after yielding. The strength of the amorphous/crystalline HEA composite reduces with increasing the thickness of the amorphous layer, agreeing with the previous experiments. The coupled interaction between the crystal plasticity and amorphous plasticity in amorphous/crystalline HEA composites results in a more homogeneous redistribution of plastic deformation to cause interface hardening, due to the complex stress field in the amorphous layer. The current findings provide the insight into the deformation behavior of the amorphous/crystalline HEA composite at the nanoscale, which are useful for optimizing the structure of the HEA composite with high strength and good plasticity.

The cryogenic mechanical property deviation of Ti-based bulk metallic glass composite induced by interstitial element

Although most bulk metallic glass composites (BMGCs) will undergo ductile-to-brittle transition at cryogenic temperature, significant low temperature compression and tensile ductility have been found in a BMGC with the composition of Ti48Zr20Nb12Cu5Be15. In present work, the cryogenic mechanical behavior of BMGCs containing interstitial element was studied for understanding the multiple reinforcement of BMGCs in low temperature environment and for explaining the differences in cryogenic properties of BMGCs. Results show that the Ti-based BMGC will be much more sensitive to impurity elements in cryogenic environment than that at room temperature. Besides, the increase in yield strength of BMGCs with the decrease of temperature is not simply due to the dislocations motion in the dendrites becomes more difficult. Low temperature environment can strengthen the glassy matrix as well as increase the strength of dendrites. Results imply Ti48Zr20Nb12Cu5Be15 BMGC can be a kind of promising materials for low-temperature applications.