Showing papers on "Ultimate tensile strength published in 2021"

A Comprehensive Review on Recycled Aggregate and Recycled Aggregate Concrete

Abstract: Using recycled aggregate s from construction and demolition waste can preserve natural aggregate resources, reduce demand of landfill, and contribute to sustainable built environment. This study provides a comprehensive review on recycled aggregate (RA) and recycled aggregate concrete (RAC) regarding their history, recycling, reuse and manufacture process, inherent defects (e.g. existing of additional interfacial transition zones in RAC), and materials properties. Specifically, these properties of RAC include fresh concrete workability, physical and chemical properties (i.e. density, carbonation depth, and chloride ion penetration), mechanical properties (i.e. compressive, flexural, and splitting tensile strength as well as elastic modulus), and long-term performance (i.e. freezing-thawing resistance, alkali-silica reaction resistance, creep, and dry shrinkage). On top of that, methods for improving RAC mechanical properties and long-term performance are summarized and categorized into three groups, i.e. (1) reduction of recycled aggregate porosity, (2) reduction of old mortar layer on recycled aggregate surface, and (3) property improvement without recycled aggregate modification (i.e. different concrete mixing design and addition of fibre reinforcement). Next, current regression-based models and artificial intelligence models on the prediction of compressive strength, modulus, and compressive stress-strain curves of RAC are reviewed and the ir limitations of those models are discussed. Furthermore, the state-of-the-art RAC applications are presented. Additionally, challenges of RAC application are reviewed taking China as an example. The link between material from CDW and EU green policy are discussed by analysing the previous research projects funded by European Commission. Finally, future perspectives of RAC research focus are discussed, i.e. development of “green” treatment methods on recycled aggregate s , further direction on nanoparticle application in RAC, and the establishment of database for RAC strength prediction.

Packaging and degradability properties of polyvinyl alcohol/gelatin nanocomposite films filled water hyacinth cellulose nanocrystals

Abstract: Cellulose nanocrystals isolated from water hyacinth fiber (WHF) have been studied as a reinforcement for polyvinyl alcohol (PVA)-gelatin nanocomposite. Central composite design was used to study and optimize effects of the PVA, gelatin and cellulose nanocrystal (CNC) concentration on tensile strength and elongation of formed films. The results of this study showed that WHF CNC had a diameter range of 20–50 nm produced films reaching 13.8 MPa tensile strength. Thermal stability of the films was improved from 380 ℃ to 385 ℃ in addition of CNCs and maximum storage modulus of 3 GPa were observed when 5 wt% CNC was incorporated. However, water absorption, water vapour permeability (WVP) and moisture uptake of the films decreased in addition of CNC to the PVA-gelatin blends. Moisture uptake decreased from 22.50% to 19.05% while the least WVP when 10 wt% CNC added was 1.64 × 10–6 g/(m•h•Pa). These results show possibility for industrial application of WHF CNC and PVA-gelatin blends in biodegradable films for on-the-go food wrappers.

Renewable Castor-Oil-based Waterborne Polyurethane Networks: Simultaneously Showing High Strength, Self-Healing, Processability and Tunable Multishape Memory.

Abstract: Materials with multifunctionality or multiresponsiveness, especially polymers derived from green, renewable precursors, have recently attracted significant attention resulting from their technological impact. Nowadays, vegetable-oil-based waterborne polyurethanes (WPUs) are widely used in various fields, while strategies for simultaneous realization of their self-healing, reprocessing, shape memory as well as high mechanical properties are still highly anticipated. We report development of a multifunctional castor-oil-based waterborne polyurethane with high strength using controlled amounts of dithiodiphenylamine. The polymer networks possessed high tensile strength up to 38 MPa as well as excellent self-healing efficiency. Moreover, the WPU film exhibited a maximum recovery of 100 % of the original mechanical properties after reprocessing four times. The broad glass-transition temperature of the samples endowed the films with a versatile shape-memory effect, including a dual-to-quadruple shape-memory effect.

A self-reinforcing and self-healing elastomer with high strength, unprecedented toughness and room-temperature reparability

Abstract: The development of intrinsic self-healing elastomers with simultaneous high mechanical strength, toughness and room-temperature reparability remains a formidable challenge. Herein, we report a mechano-responsive strategy, known as strain induced crystallization, to address the above issue, whereby synthesized elastomers with unprecedented high mechanical performances are bestowed with room-temperature self-healing materials, achieving tensile strength, toughness and fracture energy values of 29.0 MPa, 121.8 MJ m-3 and 104.1 kJ m-2, respectively.

Bifunctional nanoprecipitates strengthen and ductilize a medium-entropy alloy.

Abstract: Single-phase high- and medium-entropy alloys with face-centred cubic (fcc) structure can exhibit high tensile ductility1,2 and excellent toughness2,3, but their room-temperature strengths are low1–3. Dislocation obstacles such as grain boundaries4, twin boundaries5, solute atoms6 and precipitates7–9 can increase strength. However, with few exceptions8–11, such obstacles tend to decrease ductility. Interestingly, precipitates can also hinder phase transformations12,13. Here, using a model, precipitate-strengthened, Fe–Ni–Al–Ti medium-entropy alloy, we demonstrate a strategy that combines these dual functions in a single alloy. The nanoprecipitates in our alloy, in addition to providing conventional strengthening of the matrix, also modulate its transformation from fcc-austenite to body-centred cubic (bcc) martensite, constraining it to remain as metastable fcc after quenching through the transformation temperature. During subsequent tensile testing, the matrix progressively transforms to bcc-martensite, enabling substantial increases in strength, work hardening and ductility. This use of nanoprecipitates exploits synergies between precipitation strengthening and transformation-induced plasticity, resulting in simultaneous enhancement of tensile strength and uniform elongation. Our findings demonstrate how synergistic deformation mechanisms can be deliberately activated, exactly when needed, by altering precipitate characteristics (such as size, spacing, and so on), along with the chemical driving force for phase transformation, to optimize strength and ductility. Increased strength and ductility in a medium-entropy alloy of Fe, Ni, Al and Ti is demonstrated using nanoprecipitates that simultaneously hinder phase transformation and block dislocation motion.

Microstructure evolution and mechanical properties of in-situ Ti6Al4V–TiB composites manufactured by selective laser melting

Abstract: In-situ TiB reinforced titanium matrix composites (TMCs) were fabricated by selective laser melting (SLM) of ball-milled Ti6Al4V–TiB2 powders. Optimized SLM processing and stress relief annealing were applied to obtain crack-free and fully dense composites. TiB reinforcement is mainly present in the form of whisker clusters and exhibits a quasi-continuous distribution in TMC1 (2 vol%TiB) while a full-continuous distribution in TMC2 (5 vol%TiB). The distribution of TiB whisker clusters in primary β-Ti grain is not consistent with the complete dissolution mechanism proposed previously. As a result, a dual mechanism of direct reaction and precipitation has been put forward to describe the formation of TiB phase. The microhardness, compressive strength and tensile strength of TMC1 are improved by 14%, 36%, 25% respectively, compared with those of Ti6Al4V alloy. These enhancements can be mainly attributed to Hall-Petch strengthening and load-bearing transformation strengthening. The fracture surface of TMC1 after tensile testing shows a mixture of regions of cleavage facets with regions of small dimples.

Microstructure evolution of wire-arc additively manufactured 2319 aluminum alloy with interlayer hammering

Abstract: The cold metal transfer (CMT) based wire-arc additive manufacturing (WAAM) technology has been widely recognized as a suitable method for fabricating large-sized aluminum alloy components. However, the poor mechanical properties of the as-deposited aluminum alloys prevent their wide application in the aerospace industry. In this paper, three categories of samples with different interlayer deformation strains were fabricated by WAAM. These samples were further investigated to evaluate the effects of interlayer deformation on the mechanical properties, microstructural evolution, and the underlying strengthening mechanism. The grain size distribution and internal sub-microstructure were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). As compared to the as-deposited samples, the yield strength and ultimate tensile strength of the 50.8% deformed sample increased from 148.4 to 240.9 MPa and from 288.6 to 334.6 MPa, respectively. The microstructure of the samples with interlayer hammering exhibited highly refined grain, which is a combined result of deformation and subsequent intrinsic in-situ heat treatment induced by the next deposition layer. The recrystallized grains can be further deformed with subsequent hammering, which leads to an increase in dislocation density and contributes to an increase in ultimate tensile strength of the additively manufactured 2319 aluminum alloys with interlayer hammering.

Highly thermally conductive liquid metal-based composites with superior thermostability for thermal management

Abstract: Thermally conductive polymer composites (TCPCs) are highly desirable for thermal management in modern electrical systems and next-generation flexible electronic devices. However, the integration of superior thermal conductivity, good mechanical performance, and high thermostability in TCPCs remains a daunting challenge, due to the utilization of abundant rigid fillers (such as graphene, boron nitride and aluminum nitride) and the low thermal stability of polymer matrices. Herein, a highly thermally conductive film with excellent mechanical strength and toughness is developed based on soft liquid metal (LM) and rigid aramid nanofibers (ANFs), via a vacuum infiltration technique. The LM/ANF composite films possess superior in-plane and through-plane thermal conductivity (7.14 @ 1.68 W m−1 K−1) because of the formation of a tightly packed structure, in which LM droplets are randomly distributed among the well-ordered ANFs to construct efficient heat conduction networks. Meanwhile, an outstanding tensile strength of 108.5 MPa and a high toughness of 10.3 MJ m−3 are achieved in the LM/ANF composite films. Furthermore, the LM/ANF composite films also have remarkable thermostability, flexibility, and mechanical reliability, without an obvious change in the thermal conductivity even at an elevated temperature of 250 °C and after repeated folding for 1000 cycles, respectively. These admirable features shed light on the application of the LM/ANF composite films for thermal management of high-power integrated electronic devices.

CT scanning of internal crack mechanism and strength behavior of cement-fiber-tailings matrix composites

Abstract: This paper deals the relationship between compressive strength and internal crack formation (e.g., crack width and volume) of cement-fiber-tailings matrix composites (CFTMC) using an industrial computed tomography system and scanning electron microscopy. Two types of fibers (polypropylene PP and polyacrylonitrile PAN) were used to manufacture CFTMC with a constant cement-to-tailings ratio, solid content and curing time of 1:6, 75 wt% and 14 days, respectively. The results showed that strength gaining of CFTMC increased remarkably with fiber additions which effectively improve its toughness. When compared to samples without fibers, the compressive strength of CFTMC was the highest because of the reduced interconnection between pores and high particle packing density. The internal structure analysis showed that the maximum crack widths of CFTMC increased when the fiber content increased from 0.3 to 0.6 wt%, regardless of fiber type, growing the crack volumes of samples. The failure pattern of all CFTMC samples was mainly tensile, shear and mixed failure (tensile/shear), and a high strength value accompanies with a big volume of crack. At last, the findings of this study may offer a key reference for fiber-reinforced backfills, which can lift their strength, stability and integrity behavior under extreme conditions, such as rock burst, squeezing ground, blast or seismic event.

A novel crack-free Ti-modified Al-Cu-Mg alloy designed for selective laser melting

Abstract: A novel crack-free Ti-modified Al-Cu-Mg alloy for SLM was developed here, based on the thermodynamic calculations of the crack susceptibility index and growth-restriction factor. We found that the introduction of Ti into the Al-Cu-Mg alloy effectively promoted the grain refinement and columnar-to-equiaxed grain transition as a result of the heterogeneous nucleation provided by Al3Ti precipitates. The hot tearing cracks were eliminated after Ti modification due to the formation of the homogeneous and fine equiaxed microstructure. We created a new high-strength Al-Cu-Mg-Ti alloy with a tensile strength of 426.4 MPa, yield strength of 293.2 MPa and ductility of 9.1%. This novel Ti-modified Al alloy with fine equiaxed grains and highly-enhanced mechanical properties offers a new compositional space for the printable lightweight material categories specifically for the SLM technique.

The Interfacial Shear Strength of Carbon Nanotube Sheet Modified Carbon Fiber Composites

Abstract: Carbon fiber reinforced polymer composites have low density and high tensile strengths. However, their compressive strengths are much lower than their corresponding tensile strengths due to fiber micro-buckling and interface failure between fiber and matrix. To address this issue, we report a method for fabricating carbon nanotube (CNT) sheet scrolled carbon fibers or fiber tows to improve the interfacial shear strengths. A CNT sheet is drawn from a drawable carbon nanotube forest grown on a silicon substrate, it is used to wrap around individual carbon fibers. The CNT wrapped carbon fiber is subsequently impregnated into a polymer to form a composite. Scanning electron micrograph shows that the wettability of CNT wrapped carbon fiber composite increases drastically in comparison with the composite without CNT, indicating significantly increased bonding between carbon fiber and polymer due to the addition of aligned CNT at the interphase. Fiber push-out and push-in nanoindentation characterization indicates increased interfacial shear strengths, consistently at over 80% with the use of wrapped aligned CNT sheet. The results from scrolling CNT sheet around individual carbon fibers to enhance compressive strengths indicate the potential performance enhancement of composites when this approach is scaled up.