High Elongation Research Articles

Dynamic recrystallization-dependent high-temperature tensile properties and deformation mechanisms in Al-Mg-Sc-Zr alloys

This research elucidates discontinuous dynamic recrystallization (DDRX)-dependent high-temperature tensile properties and deformation mechanisms in simply extruded Al-7Mg alloys tailored by Sc/Zr ratios. The bimodal-grained Al-7Mg-0.4Sc alloy presents a high elongation to failure of ∼540% at 400 °C and 5 × 10−4 s−1. However, such superplastic behavior has not been observed in both coarse-grained Al-7Mg-0.1Sc-0.3Zr and Al-7Mg-0.3Sc-0.1Zr alloys. Thermally stable dispersed nano-sized Al3(Sc,Zr) particles strongly retard DDRX, accompanied by the retention of heterogeneous grain structure in Al-7Mg-0.1Sc-0.3Zr till fracture. The predominance of dislocation slip is proved by analyzing the evolution of texture and dislocations. In contrast, the bimodal grain structure evolves into a homogeneous fine one in Al-7Mg-0.4Sc with tensile deformation proceeding since coarsening Al3Sc precipitates play a weak role in restricting DDRX. The superplasticity in Al-7Mg-0.4Sc is achieved by cooperated mechanisms, i.e., grain boundary sliding (GBS) and dislocation slip as dominant mechanisms, which is accommodated by DDRX in the initial tensile deformation stage, followed by dislocation slip-accommodated GBS in the late stage.

Warm Aging of Pre-aged AA6013 Sheet and Its Relevance to Room Temperature and Warm Forming Applications—Experimental and Modeling Analyses

AbstractWarm forming has been shown to be an effective way to increase the formability of various aluminum sheet alloys. If applied to precipitation hardenable alloys, aging and/or coarsening may occur during heating and/or forming processes. As such, there is a potential to leverage the warm forming process to artificially age precipitation hardenable alloys. In this study, the aging characteristics of a pre-aged Al-Mg-Si-Cu alloy (designated AA6013-PA and comprising a 4 h, 100 °C pre-aging cycle following solutionization) were examined using: (i) room temperature tensile and (ii) bendability experiments, as well as (iii) elevated temperature tensile and formability experiments in the temperature range of 220-280 °C. In the pre-aged condition, the alloy exhibited very high work hardening, elongation and bendability. It was found that T6-like properties can be obtained with short duration secondary aging of the AA6013-PA starting temper (410 s at 235 °C), followed by a paint bake cycle (30 min at 177 °C). In such heavily aged conditions, the bendability is found to be moderate and consistent with a T6 temper. Bendability of the pre-aged alloy is shown to be enhanced by reducing the extent of aging, which may be beneficial for applications requiring energy absorption during crash, for example. In the pre-aged condition, AA6013 displayed a 55% improvement in room temperature formability, relative to the T6 condition, for near plane-strain loading using a Nakazima punch, although neither temper exhibited formability improvements through warm forming. The aging kinetics of AA6013-PA were determined from mechanical test data and used to calibrate an aging kinetics model. A strong obstacle model was used to relate precipitation state to yield strength, for artificial aging in the range 220-280 °C. The incremental strength increase due to exposure to an automotive paint cure cycle was also modeled and found to yield accurate results. Warm deformation, as well as room temperature deformation, were shown to enhance the paint bake response of the alloy, reducing the time to the peak aged condition by up to 14% for artificial aging at 177 °C.

High-strength, anti-freeze, transparent and recyclable composite organohydrogel for flexible strain sensor

Hydrogels have received widespread attention as flexible strain sensors in the fields of human motion detection and health monitoring. However, the presence of large amounts of water in traditional hydrogels leads to poor mechanical properties and low anti-freezing, which severely limits their applications. Herein, a novel PVA/DMSO/CMC/AlCl3/TA/LiCl (PDCATL) composite organo-hydrogel was developed by freeze-thaw and salt solution immersion methods, using polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), aluminum chloride hexahydrate (AlCl3·6H2O) and tannic acid (TA) dissolved in a dimethyl sulfoxide (DMSO)/water binary solvent. The PDCATL organohydrogel exhibited high tensile strength and elongation at break (up to 1.90 MPa and 587%), which can withstand >6000 times its own weight, good anti-freezing and excellent transparency (>90% light transmission). The PDCATL organohydrogel still maintained excellent transparency, flexibility, recyclability and signal sensing capability at low temperatures (−20 °C). The PDCATL organohydrogel also had good strain sensitivity (GF = 1.82) as a wearable strain sensor and can be used to detect motion and physiological activity signals in various parts of the human body. This study will provide a viable avenue for the application of hydrogel sensors in the fields of visual human-computer interaction, wearable sensors, visual optical detection and medical health detection.

Toughening of Bio-Based PA6.19 by Copolymerization with PA 6.6 - Synthesis and Production of Melt-Spun Monofilaments and Knitted Fabrics.

This work reports on the synthesis of statistical copolymers of bio-based PA6.19 and PA6.6 together with the production of melt-spun monofilaments for the production of sustainable textile fibers. The plant oil-based 1.19-nonadecanedioic acid is synthesized from bio-derived oleic acid via isomerizing methoxycarbonylation. The homopolymer PA6.19 with a carbon-based bio-content of 72% showsa good elongation at break of 166%, but lower tensile strength than commercial PA6 (43MPa versus 82MPa). Addition of adipic acid to form statistical PA 6.6/6.19 copolymers improves toughness while maintaining the high elongation at break. Two PA6.6/6.19 copolymers with a carbon-based bio-content of 26% and 33% are successfully synthesized and exhibited comparable toughness (94 ± 6MPa and 92 ± 2MPa) to the commercial PA6 (92 ± 15MPa). The bio-based copolymers also exhibit a much lower water uptake than PA 6 and PA 6.6, resulting in a higher dimensional stability. Melt spinning of the oleic acid-based polyamides is successfully carried out to produce monofilaments with sufficient properties for further processing in a knitting process, demonstrating the capabilities of the bio-based PA6.6/6.19 copolymers for use in the textile industry.

Silicone Elastomer with High Elongation at Break Used in Digital Light Processing 3D Printing

Silicone Elastomer with High Elongation at Break Used in Digital Light Processing 3D Printing

Transparent, thermoplastic, aliphatic polyesters through crystallization under molecular confinement

•We report segmented polyesters with nanoscale crystalline poly(L-lactic acid) domains •Polymers possess high modulus and elongation at break and can be melt processed •Solution processing yields transparent films that are degradable and cytocompatible •Films can be bonded by plasma activation and undergo infrared-activated shape change In semi-crystalline biodegradable polymers, uncontrolled evolution of crystallinity impacts processing and bulk properties, limiting their application. Through molecular confinement of low-molecular-weight poly(L-lactic acid) (PLLA) segments by polysiloxane blocks and processing at far-from-equilibrium conditions, PLLA crystallization into lamellae of a few nm in thickness with coherence lengths below 100 nm was achieved, thus giving access to films that are optically transparent for over 5 years, possess high Young’s modulus and elongation at break, undergo controlled degradation, and support functional endothelialization. The films possess a nanophase segregated bulk morphology with a hydrophobic siloxane-dominated surface that can be pressure bonded following cold oxygen plasma activation and low-temperature glassy PLLA domains interspersed by nanoscale crystalline physical crosslinks that enable glass transition temperature-triggered shape change. The segmented thermoplastic polyesters (STEPs) can additionally be processed using melt-extrusion printing into 3D objects, thus opening potential application opportunities in the fabrication of implantable/degradable electronics, smart textiles, and packaging. In semi-crystalline biodegradable polymers, uncontrolled evolution of crystallinity impacts processing and bulk properties, limiting their application. Through molecular confinement of low-molecular-weight poly(L-lactic acid) (PLLA) segments by polysiloxane blocks and processing at far-from-equilibrium conditions, PLLA crystallization into lamellae of a few nm in thickness with coherence lengths below 100 nm was achieved, thus giving access to films that are optically transparent for over 5 years, possess high Young’s modulus and elongation at break, undergo controlled degradation, and support functional endothelialization. The films possess a nanophase segregated bulk morphology with a hydrophobic siloxane-dominated surface that can be pressure bonded following cold oxygen plasma activation and low-temperature glassy PLLA domains interspersed by nanoscale crystalline physical crosslinks that enable glass transition temperature-triggered shape change. The segmented thermoplastic polyesters (STEPs) can additionally be processed using melt-extrusion printing into 3D objects, thus opening potential application opportunities in the fabrication of implantable/degradable electronics, smart textiles, and packaging.

Waste Management after the Injection Process by Manufacturing Polyamide Products Based on Regranulate

The aim of the work was to assess the possibility of utilizing the waste generated in the injection molding process for the production of new products based on polyamide 6 reinforced with glass fiber. The manufactured samples were prepared with the addition of 5, 10, 15, and 100 wt.% regrind from the runner system. The impact strength, tensile strength, and hardness of injection products were obtained directly and were assessed after conditioning in distilled water for 24 h. Moreover, the structure of the tested materials was assessed using the FTIR method and their thermal properties using the DSC method. The results of the tests confirm that the addition of regrind up to 15 wt.% to virgin polyamide does not adversely affect its impact strength, tensile strength, and hardness. The water-conditioned materials showed higher values of impact strength but lower values of tensile strength and Young’s modulus at a higher elongation at break. The obtained results are important due to the assumptions of the circular economy and the minimization of the amount of waste and material losses during the injection process.

Overcoming strength-ductility trade-off in CoCrNi medium entropy alloy by forming fine crescent grains in laser powder-bed fusion

This study investigated the influence of microstructure on the strengthening mechanism in CoCrNi medium entropy alloys (MEAs) fabricated by laser powder-bed fusion (L-PBF). An excellent combination of high strength and elongation was achieved in L-PBFed CoCrNi MEA. The yield strength of L-PBFed CoCrNi MEA was significantly improved because of the combined effect of grain boundary strengthening and dislocation strengthening. Due to the temperature gradient difference during L-PBF process, the crescent shape grain boundaries were evident in L-PBFed samples, which increased the mechanical properties.

Development of rapid die cooling technology using the Groove Pressing method in hot stamping process

The demand for hot stamping parts in the automobile industry is increasing due to the growth of eco-friendly vehicles with improved crash safety performance and lighter weight. However, the use of ultra-high-strength steel in cold stamping is challenging due to its high yield strength and low elongation. Hot stamping is a widely used process to overcome this challenge, but the long die quenching time reduces its productivity. In order to address this issue, a Groove Pressing method was applied to the sidewall of the die to improve cooling performance without requiring additional devices within the die. The study investigated the required contact pressure between the sheet and the die for the implementation of the groove shape on the sidewall. Computational analysis was performed to design optimal groove shape for the sidewall, and the results showed that Case 3 was the most suitable in terms of cooling performance and contact pressure. The groove shape was incorporated into the die making, and experiments were conducted on aluminized coated 22MnB5 1.2 mm sheet. The results showed that the implementation of the groove shape on the sidewall improved cooling performance, dimensional quality, and mechanical properties without affecting the corrosion resistance of the component. The study demonstrates the potential of the Groove Pressing method as a practical solution for improving the productivity of the hot stamping process in the automobile industry.

Load-bearing characteristics of 3D auxetic structures made with carbon fiber reinforced polymer composite

This paper presents a study of 3D novel hybrid auxetic structures made with carbon fiber reinforced polymer (CFRP) laminate composite based on the stretch-dominated mechanism. The homogenized mechanical characteristics of the designed structures, including Young's modulus, shear modulus, and Poisson's ratio, are evaluated via theoretical analysis and finite element simulation. The results exhibit that the structures have negative Poisson's ratio values in all the selected ranges of the design geometry parameters. The multi-objective optimization method is employed to achieve the optimized geometry parameters based on maximizing the stiffness and minimizing the relative density responses. Meanwhile, 2D fabricated auxetic sheets are assembled to build 3D structures through the interlocking method, and quasi-static compressive tests are performed to study their mechanical behaviors. The axial and lateral strains are evaluated by the strain gauge and video extensometer to measure the negative Poisson's ratio values through compressive tests. The results indicate that the proposed structures exhibit superior stiffness and high elongation percentage, suggesting them as a strong candidate for the next generation of load-bearing auxetic structures.

Improving mechanical properties of Mg-Sn alloys by co-addition of Li and Al

In this work, a novel low-alloyed Mg-Sn-Li-Al alloy with high-strength has been developed. The addition of ∼1 ​wt% Li into the Mg-2Sn wt.% binary alloy can change the type of strengthening phases in Mg-2Sn-1Li sample (TL21), involving the formation of both Li2MgSn and Mg2Sn phases. The co-addition of ∼1 ​wt% Al and ∼1 ​wt% Li can further induce the higher density of both micron-sized phases and nano-precipitations in the Mg-2Sn-1Li-1Al sample (TLA211). The nano-precipitations can inhibit the grain growth, which thus lead to the fine grain size of ∼1.38 ​μm in TLA211 sample, and ∼1.59 ​μm in the TL21 sample. Besides, the profuse nano-phases would improve the yield strength via Orowan hardening effect. Consequently, the TL21 sample can exhibit the high yield strength of ∼204 ​MPa, and elongation of ∼6.6%. The TLA211 sample exhibits the much higher yield strength of ∼250 ​MPa, ultimate tensile strength of ∼291 ​MPa, and also high elongation of ∼9.0%. The high strength-ductility synergy, together with the low-Sn content, make the present Mg-Sn based alloy to be potential for the wider industrial applications.

Physicochemical Properties and Tissue Structure of High Kernel Elongation Rice (Oryza sativa L.) Varieties as Affected by Heat Treatment.

Heat treatment could affect the structure and properties of rice varieties. The present study was conducted in order to determine the effects of heat treatment on the physicochemical properties and tissue structure of Mahsuri Mutan, Basmati 370 and MR219 rice varieties. The three rice varieties were subjected to heat treatment (ageing) at 90 °C, using an oven, for 3 h. After the heat treatment, the samples were cooled at room temperature (25 °C) for 1 h. Physicochemical properties, such as alkali digestion value, water uptake ratio, solids in cooking water, high kernel elongation ratio and amylose contents, were determined. The procedure used in determining both apparent and absolute amylose involved measuring the iodine affinity of defatted whole starch. Ahigh-performance anion-exchange chromatograph was used to analyse branch chain length distribution of amylopectin quantitatively. The starch structure of the rice samples was observed under a scanning electron microscope. Data collected on physicochemical traits, heat treatment and control (ageing and non-ageing) were subjected to an analysis of variance using SAS software version 9.4. In this study, Mahsuri Mutan and Basmati 370 showed superior high kernel elongation as compared to their respective rice progenies. This study also found that heat treatment directly affected the increasingly high kernel elongation for both populations. The phenotypic correlation co-efficient indicated that there was a high positive correlation between high kernel elongation and water uptake ratio, implying that selection for water uptake ratio would increase the high kernel elongation characteristic. The heat treatment showed significant difference in all the physicochemical traits of the varieties studied. Heat treatment also affected the very long branch chains of starch, such as amylose. Observation under an electron microscope showed that the samples subjected to heat treatment had more cracks on the tissue structure compared to normal rice samples. The hexagon structure in Mahsuri Mutan produced a greater elongation effect on its kernel. The findings from this study could be useful to breeders in the selection and development of a new high kernel elongation rice variety.

Discontinuous transformation-induced plasticity behaviour in governing the mechanical behaviour in medium-Mn steels

ABSTRACT Here, we address the continuing challenges and scientific gaps in obtaining high strength and high elongation in medium-Mn steels. Electron microscopy and X-ray diffraction studies clearly underscored that the discontinuous transformation-induced plasticity played a determining role in impacting high strength–toughness combination in conjunction with the microstructural constituents. The discontinuous TRIP effect during deformation involved stress relaxation, which was responsible for high ductility. An excellent combination of a high tensile strength in the range of 1238–1502 MPa and a total elongation of 25–33.6% was obtained when the steels were subjected to an intercritical hardening in the temperature range of 600–750°C and low tempering at 200°C. The intercritical hardening influenced the co-existence of austenite, ferrite and martensite in a manner such that the deformation behaviour varies with the Mn-content.

Enhanced ductility by delayed deformation-induced martensite transformation in multi-step hardened FeNiMnCoTiSi medium-entropy alloy

In the current study, a metastable Fe-15Ni-8Mn-8Co-3Ti-1Si ferrous medium entropy alloy is subjected to powder high-pressure torsion (HPT) followed by annealing. The body-centered cubic microstructure obtained from the HPT method largely changes into a metastable face-centered cubic phase decorated by Ti-Si-rich precipitates during the isothermal post-annealing process. The optimum heat treatment results in materials with high ultimate tensile strength and total elongation of 748 MPa and 68.81%, respectively. The material is strengthened by the numerous grain boundaries created during recrystallization, which effectively impede dislocation movement and postpone the deformation-induced martensitic transformation (DIMT) to the applied strain of over 20%. High ductility and high strength are combined by employing the simultaneous effects of controlled DIMT, grain boundary engineering, and precipitate strengthening, resulting in multistep strain hardening of the corresponding specimen.

Synthesis of Multiblock Copolymer Composed of Biodegradable Poly(butylene succinate) and Poly(2-pyrrolidone): Impact of Each Block Length on the Mechanical Properties.

A series of multiblock copolymers comprising a systematic combination of biomass-originated and biodegradable poly(butylene succinate) (PBS) and poly(2-pyrrolidone) (PA4) units is synthesized with various mean degrees of polymerization (mDP) of each unit. Despite the inherent immiscibility of PBS and PA4, multiblock structure allows to mix the two components in the solution-cast films from solution. The mechanical properties of the cast films are highly dependent on the mDP of each unit, as demonstrated by tensile tests. The film of the copolymer with the lowest mDP of each unit (PBS: 17, PA4: 10) is transparent and exhibits extremely high elongation at break (> 400%) and high tensile stress (39.5MPa) with strain hardening. The films with 50% or higher crystallinity are brittle and opaque, while a decrease in crystallinity can result in higher elongation, as revealed by wide-angle X-ray diffraction measurements.

Cryogenic mechanical behavior of a FeCrNi medium-entropy alloy fabricated by selected laser melting

A single-phase FeCrNi medium-entropy alloy (MEA) with a face-centered cubic structure was successfully fabricated by selected laser melting (SLM). The SLMed FeCrNi MEA exhibits hierarchical microstructures, including molten pools, coarse columnar grains, submicron cellular structures and high-density dislocations, and shows an excellent strength-ductility combination. Notably, the SLMed FeCrNi MEA has ultra-high yield strength and ultimate tensile strength of 1.1 GPa and 1.5 GPa, respectively, at 77 K, which are almost 1.5 times higher than those at room temperature, while still maintaining a high fracture elongation of 49%. It was also found that the SLMed FeCrNi MEA deformed at 77 K could produce more nanotwins compared with that deformed at room temperature. The twinning-prone matrix can produce more significant twinning-induced plasticity effects, which contributes to a high plasticity. Additionally, the high-density cellular substructure can effectively hinder dislocation motion, which is the main reason for the high strength.

Scalable-produced 3D elastic thermoelectric network for body heat harvesting

Flexible thermoelectric generators can power wearable electronics by harvesting body heat. However, existing thermoelectric materials rarely realize high flexibility and output properties simultaneously. Here we present a facile, cost-effective, and scalable two-step impregnation method for fabricating a three-dimensional thermoelectric network with excellent elasticity and superior thermoelectric performance. The reticular construction endows this material with ultra-light weight (0.28 g cm−3), ultra-low thermal conductivity (0.04 W m−1 K−1), moderate softness (0.03 MPa), and high elongation (>100%). The obtained network-based flexible thermoelectric generator achieves a pretty high output power of 4 μW cm−2, even comparable to state-of-the-art bulk-based flexible thermoelectric generators.

Rapid preparation of liquid‐free, antifreeze, stretchable, and ion‐conductive eutectic gels with good compression resistance and self‐healing properties by frontal polymerization

AbstractThe development of elastomers from renewable raw material resources, with excellent properties, has been a major and difficult area of research. In this work, ternary polymerizable deep eutectic monomers (DEMs) were synthesized from acrylamide, choline chloride, and glycerol (Gy). A series of mixed hydrogels were prepared in 15 min through thermal initiation in DEM using a frontal chemical change. The eutectic gel exhibited good mechanical and self‐healing properties, and the mechanical and self‐healing properties of the target gel could be regulated by adjusting the proportion of Gy, while the eutectic gel could maintain high elongation and self‐healing efficiency at low temperatures. Additional, eutectic gels could be compressed to a strain of more than 80% and could immediately recover to their original state when the compression force was released. In the cyclic compression test, the eutectic gel cyclic compression curves showed a high degree of overlap, and no significant hysteresis was observed, even at a set strain of 80% and 100 cyclic compression times. In addition, the eutectic gel showed fine ionic conductivity, and both the water content and Gy content could affect its conductivity, giving it the potential to be used in the application of manufacturing pressure‐sensitive sensors.

Enhanced antibacterial activity of composite fibers from polylactic acid and nanosilver‐coated ground tea leaves for sustainable green composite textiles

AbstractThis study aimed to create an environmentally friendly composite textile with enhanced antibacterial properties using polylactic acid (PLA) and nanosilver‐coated ground tea leaves (Ag/GTL). The green coating process was applied to produce the Ag/GTL, which was further used as an additive in the PLA matrix. Composite fiber showed a light green color and a slightly rough surface. The thermal properties tended to decrease with increasing masterbatch content, while the crystallinity was significantly increased. The mechanical test demonstrated the composite fibers trend toward decreased tenacity and higher elongation at break. PLA‐3, which has good spinnability and acceptable mechanical properties, was used to prepare the composite fabric. Moreover, the Ag/GTL additive also enhanced the antibacterial activity of composite fabric, especially Staphylococcus aureus as the gram‐positive bacteria and Escherichia coli as the gram‐negative bacteria, by up to 99%. In addition, composite fibers exhibiting engine oil sorption were expected to be applied in oil spill cleanup applications.

Effect of content and configuration of equiaxed α and lamellar α on deformation mechanism and tensile properties of a near-α titanium alloy

This work fabricated fully equiaxed, Widmanstätten, basketweave and bimodal microstructures to systematically investigate the influence of content of equiaxed α (αe) and configuration of α lamellas on the deformation mechanism and tensile properties of near-α titanium alloy. The bimodal microstructures (BMs) comprised of αe and parallel α lamellas (α colony) is denoted as BMC, while the BMs containing αe and basket-weave α lamellas (α basketweave) is denoted as BMB. With the decreasing content of αe, BMB has the higher increment of strength and lower reduction of elongation than BMC. Under the same content of αe, BMB has the higher strength and better elongation than BMC. Meanwhile, BMB with αe content of 15% could achieve a good combination of high strength and good elongation. The deformation mechanisms of fully equiaxed microstructure (FEM), BMC and BMB were investigated by in-situ tensile tests and TEM characterization. It is found that prismatic slip is the dominant slip system initiated in the three microstructures, while the dislocation multiplication of prismatic slip dominates all the αe grains. The αe could well coordinate deformation to benefit the elongation whereas the long slip length in αe grains could fairly degrade the strength. The calculation of geometry compatibility indicates α basketweave could better restrain slip transfer than α colony, which leads to the higher strength of BMB and basketweave microstructure. Moreover, the absence of continuous αGB in BMB and basketweave microstructure could promote a better elongation.