Crack Bridging Mechanisms Research Articles

Three-dimensional fracture mechanics model of conch shells with hierarchical crossed-lamellar structures

Conch shells, characterized by a highly mineralized hierarchical crossed-lamellar structure that represents the pinnacle of molluscan evolution, exhibit exceptional crack resistance to protect their soft bodies from predatorial attacks. In this paper, we present a three-dimensional fracture mechanics model to establish a correlation between fracture toughness and the crossed-lamellar structure, elucidating the hierarchical crack bridging mechanism of aragonite lamellae. We find that increased fracture toughness is achieved through the energy dissipation contributed by the interfacial debonding of both first-order and second-order lamellae. The conch shells demonstrate outstanding resistance to cracking in two principal directions, featuring a locally stacked structure of flat plates that effectively withstand complex loads. The vertically alternating stacking structure of macroscopic layers of equal thickness inspires a biomimetic design with more balanced mechanical properties, accompanied by enhanced crack resistance observed as the lamellae become thinner. The theoretical results are in good agreement with relevant experimental measurements. This work not only sheds light on the physical mechanisms responsible for the remarkable fracture toughness of crossed-lamellar structures but also provides guidelines for designing high-performance biomimetic structural materials.

High-strength TiO2/TPU composite fiber based textiles for organic pollutant removal

Effective integration of nanostructured photocatalysts into polymer matrices is crucial for the broad practical application of fiber-based photocatalytic composite textiles. Herein, highly durable TiO2/TPU composite fibers with high TiO2 content (>30 wt. %) were prepared through wet spinning using 1D electrospun TiO2 nanofibers (TNFs). Due to the fiber reinforcement principle, the TNF/TPU composite fibers exhibited superior mechanical properties compared with pure TPU fibers. Furthermore, the TNF/TPU composite fibers with a ratio of 1:2 process impressive degradation efficiency for rhodamine B (RhB). The orientation of 1D TNFs and stronger interface between TNF and TPU matrices not only enable the excellent load sharing and transfer effects following fiber pullout and crack bridging mechanisms, but also improve photogenerated charge transfer efficiency, resulting in high strength and high photocatalytic activity. In addition, enhanced TNF exposure on the fiber is due to the hollow and porous structures of composite fibers, which is advantageous for photocatalytic degradation. Notably, when the RhB concentration exceeded 15 ppm, the TNF/TPU composite fibers exhibited higher degradation efficiency than the TNF powder. Therefore, TNF/TPU composite fiber–based textiles with high photocatalytic activity and strength are promising for overcoming the separation and recovery issues of nanostructured catalysts in practical wastewater treatment applications.

Dispersion, solid solution, and covalent bond coupled to strengthen K4169/TiAl composite brazed joints: First-principles and experimental perspective

Ni/TiAl composite brazed joints could significantly reduce the aircraft's weight. However, low interfacial adhesion, coarse and brittle-hard intermetallic compounds (IMCs) seriously limited the application of Ni/TiAl composite joints in the next generation of aerospace applications. So enhanced K4169/TiAl composite joints were investigated by vacuum brazed with (Ni53.33Cr20B16.67Si10/Zr25Ti18.75Ta12.5Ni25Cu18.75) composite filler metal (CFM) designed based on cluster-plus-glue-atom model. The shear strength of the joint reached 485 MPa, comparable to the 491 MPa of TiAl substrate. The flat and brittle-hard diffusion reaction layer between Zones I and II was eliminated, simultaneously generating CrB4 dispersion strengthening due to the CFM developed with the interfacial solid-liquid space-time hysteresis effect. In Zones II and III, IMCs all transformed into Niss(Cr,Fe)[0–88], Niss(Ti, Al)[004], and Niss(Zr,Si)[11–2] of circular and oval shapes through isothermal solidification. Meanwhile, the residual stresses and hardness were distributed in reticulated cladding characteristics. Thereby, lattice distortion led to solid solution strengthening and increased plastic toughness through crack termination and bridging mechanisms, which inhibited dislocations from plugging and crack propagation. Various interfaces in Zone Ⅳ were regulated into semi- and coherent interfaces. Ni3(Ti,Al)/(Ni,Ti,Al) and (Ni,Ti,Al)/AlNi2Ti were composed of higher interfacial bonding energy (2.771 J/m2, 2.547 J/m2) and Ni-Ni covalent bonds. Interfacial covalent bonding and large interfacial bonding energy coupling strengthened Zone IV. Consequently, cracks initiated at the (Ni,Ti,Al)[013]/Ti3Al[010] and expanded rapidly into TiAl substrate. Therefore, applying this method to design CFMs and regulate the phase, grain morphology, and interface's fine structure could provide new pathways for dissimilar hard-to-join metals.

Natural Rubber Latex-Modified Concrete with Bottom Ash for Sustainable Rigid Pavements

This article investigates the viability of using natural rubber latex (NRL)-modified concrete with bottom ash (BA) as a partial replacement for river sand in sustainable rigid pavements. Concrete mixes with 10% and 20% BA replacement ratios and varying NRL dosages (0%, 1.0%, 1.5%, and 2.0% by weight of cement) were prepared and evaluated for their mechanical and microstructural characteristics. Results showed that BA substitution decreased the compressive strength of concrete. However, the addition of NRL at an optimal dosage of 1.0% significantly improved both the compressive and flexural strengths. The 10%BA+1.0%NRL and 20%BA+1.0%NRL mixes exhibited mechanical properties surpassing the control mix and meeting the minimum requirements for rigid pavement materials. However, excessive NRL content (1.5% and 2.0%) led to a reduction in mechanical strength. Scanning electron microscopy analysis exhibited a denser and more compact matrix in NRL-modified BA concrete, with NRL films enhancing the interfacial bonding and crack-bridging mechanism. Nonetheless, excessive NRL content resulted in the formation of abundant and thicker NRL films, which disrupted the continuity of the cement matrix and created weak zones. X-ray diffraction analysis confirmed the existence of crucial crystalline phases and their optimal balance in the 20%BA+1.0%NRL mix, contributing to its superior performance. Mixes with excessive NRL contents exhibited lower intensities of quartz, calcite, and portlandite peaks, indicating a disturbance in the proper formation and growth of essential crystalline phases. The findings demonstrated the potential of NRL-modified BA concrete as an eco-friendly and high-performance alternative for sustainable rigid pavements when using an optimal NRL dosage, promoting the employment of waste resources and reducing the environmental impact of the construction industry. Doi: 10.28991/CEJ-2024-010-08-05 Full Text: PDF

Mechanical and viscoelastic properties of novel resin-infused thermoplastic tri-block copolymer 3D glass fabric composites

The current study investigates the mechanical and viscoelastic properties of a novel acrylic resin-infused thermoplastic (Elium®) tri-block copolymer (Nanostrength®) 3D fibre-reinforced composites (FRCs). The toughened thermoplastic resins with three different concentrations of tri-block copolymer, i.e., 10 wt%, 15 wt%, and 20 wt%, were prepared and used to fabricate thermoplastic 3D-FRCs using a vacuum-assisted resin-infusion process at room temperature. The flexural, interlaminar, and viscoelastic properties and failure modes were evaluated and compared with those of pristine thermoplastic 3D-FRCs. The addition of tri-block copolymer significantly improves the flexural strength of 3D-FRC (up to 75 % and 34 % along the warp and fill directions, respectively, at 15 wt% of tri-block copolymer) and interlaminar shear strength (up to 80 % and 111 % along the warp and fill directions, respectively, at 20 wt% of tri-block copolymer). Additionally, the residual flexure and interlaminar shear strength improved up to 35 % and 109 % at 15 wt% of tri-block copolymer. Dynamic mechanical analysis (DMA) demonstrated that the glass transition temperature and storage modulus of thermoplastic 3D-FRCs were increased up to 11 °C and 24 %, respectively at 20 wt% of tri-block copolymer, which may be due to increased physical crosslinking and the agglomeration of tri-block copolymer particles. The improved mechanical and viscoelastic properties of resin-infused thermoplastic tri-block copolymer 3D-FRCs are attributed to better interface adhesion, improved matrix toughness, and crack-bridging mechanisms induced by the tri-block copolymer. The toughened thermoplastic 3D-FRCs can be utilized in the design and development of composite structures for improved damage tolerance applications.

Optimizing toughness and cost-effectiveness in one-part geopolymers via fiber reinforcement: A comprehensive investigation of PVA, PE, and glass fibers

This study explores developing and characterizing a one-part geopolymer, an innovative and sustainable construction material. The effects of incorporating polyvinyl alcohol (PVA), polyethylene (PE), and glass fibers (GF) on the toughness of slag and fly ash-based one-part geopolymer mortars were investigated through compressive, three-point flexural, and four-point bending tests. The findings demonstrate that fiber incorporation reduces fluidity and compressive strength due to increased porosity, lower elastic modulus of fibers, and weak interfacial bonding. However, fibers significantly enhance damage resistance and toughness via crack bridging and load transfer mechanisms. Formulations with 2 % PVA fibers and combinations of 1 % PVA with 1 % PE fibers and 1 % PVA mixed with 0.5 % PE and 0.5 % GF demonstrate excellent toughness. Notably, the latter two fiber blends achieve 14 % and 10 % cost reductions, respectively, compared to using only PVA fibers, making them economically viable for large-scale applications. Scanning electron microscopy and X-ray diffraction provided insights into the toughening mechanisms, including crack bridging, fiber pull-out, and enhanced stress distribution within the geopolymer matrix. Digital image correlation techniques further elucidated the fibers' role in improving the post-cracking behavior and structural resilience under load.

Effect of molybdenum disulfide functionalized multiwalled carbon nanotubes based hybrid on morphology, mechanical and thermal properties of epoxy nanocomposites

AbstractThree‐dimensional molybdenum disulfide (MoS2) functionalized MWCNTs hybrid nanoparticles were synthesized using in‐situ hydrothermal reaction. Two types of hybrids, MoS2/MWCNTs‐1 and MoS2/MWCNTs‐2 with MWCNTs to MoS2 precursor weight ratios 1:2 and 1:1 respectively were prepared with varying degrees of hybridization and the effects of their incorporation on tensile strength and fracture toughness properties of epoxies were investigated. Epoxy/MoS2/MWCNTs‐2 nanocomposites showed exceptional mechanical properties due to their improved dispersion, constrained chain mobility and excellent interfacial interactions. MoS2/MWCNTs‐2 nanocomposites showed maximum improvement of tensile strength by 28.52% at 0.5 wt% nanofiller concentration and the highest improvements in fracture toughness by 172% at 0.2 wt% nanofiller concentration. The excellent enhancement of fracture toughness properties was due to the synergic effect of MoS2/MWCNTs hybrid nanoparticles due to the crack pinning and bifurcation properties of MoS2 nanoparticles along with the pull‐out and crack bridging mechanisms of MWCNTs as observed in morphological analysis of fractures nanocomposites. The incorporation of 0.2 wt% of MoS2/MWCNTs‐2 increased the degradation temperatures of epoxy from 591 to 796°C at 95% weight loss due to the improved physical barrier effect.Highlights MoS2/MWCNTs nanoparticles were synthesized using in‐situ hydrothermal reaction 0.5 wt% MoS2/MWCNTs‐2 incorporated epoxies showed highest tensile strength 0.2 wt% MoS2/MWCNTs‐2 incorporated epoxy composites show improved K1c value Incorporation of MoS2/MWCNTs improved the thermal stability of epoxy Synergistic effect of nanocomposite due to crack pinning, bifurcation & bridging

Influence of cement and water content on the multifaceted capabilities of a self-sensing cement-based geocomposite: a comprehensive analysis

This study investigates the synergistic effects of cement, water, and hybrid carbon nanotubes/graphene nanoplatelets (CNT/GNP) concentrations on the mechanical, microstructural, durability, and piezoresistive properties of self-sensing cementitious geocomposites. Varied concentrations of cement (8% to 18%), water (8% to 16%), and CNT/GNP (0.1% to 0.34%, 1:1) were incorporated into cementitious stabilized sand (CSS). Mechanical characterization involved compression and flexural tests, while microstructural analysis utilized dry density, apparent porosity, water absorption, and non-destructive ultrasonic testing, alongside TGA, SEM, EDS, and x-ray diffraction analyses. The durability of the composite was also assessed against 180 Freeze-thaw cycles. Moreover, the piezoresistive behavior of the nano-reinforced CSS was analyzed during cyclic flexural and compressive loading using the four-probe method. The optimal carbon nanomaterials (CNM) content was found to depend on the water and cement ratios. Generally, elevating the water content led to a rise in the CNM optimal concentration, primarily attributed to improved dispersion and adequate water for the cement hydration process. The maximum increments in flexural and compressive strengths, compared to plain CSS, were significant, reaching up to approximately 30% for flexural strength and 41% for compressive strength, for the specimen containing 18% cement, 12% water, and 0.17% CNM. This improvement was attributed to the nanoparticles’ pore-filling function, acceleration of hydration, regulation of free water, and facilitation of crack-bridging mechanisms in the geocomposite. Further decreases in cement and water content adversely impacted the piezoresistive performance of the composite. Notably, specimens containing 8% cement (across all water content variations) and 10% cement (with 8% and 12% water content) showed a lack of piezoresistive responses. In contrast, specimens containing 14% and 18% cement displayed substantial sensitivity, evidenced by elevated gauge factors, under loading conditions.

The configuration design of cross-linked CNT networks to realize heterostructure in Cu matrix composite towards prominent mechanical-electrical property synergy

Developing reticular reinforcement and heterogeneous microstructure remains persistent challenges in one-dimensional carbon nanotube (CNT)-Cu system. We herein fabricated dual-heterostructured Cu composite by diazotizing CNT into cross-linked (CL) networks and achieving bimodal grain distribution. The CL-CNT networks uniformly dispersed in Cu matrix, forming strong C–N/O–Cu covalent bonds at the interfaces and effectively retarding grain growth to create ultra-fine grain (UFG) regions around them. The CL-CNT networks/UFG regions, along with the surrounding coarse grain (CG) regions, resulted in a remarkable synergy between mechanical and electrical properties within the composite. Systematic analysis indicates that CL-CNT network acts as a whole to bear loading, remarkably enhances the load-transfer strengthening and promotes the dislocation accumulation around the interface. Meanwhile, hetero-deformation between “hard” CL-CNT networks/UFG regions and “soft” CG regions lead to extra-strengthening and hardening associated with strain partitioning, generation of geometrically necessary dislocation (GND) and strain delocalization. In-situ tensile test further reveals that CL-CNT/Cu with dual-heterostructure introduces the extra-toughening via crack bridging and deflection mechanisms. Besides, CL-CNT network with the robust interface is considered to reduce the interfacial inelastic scattering and provide additional paths for electron transport, accounting for the high electrical conductivity. This work highlights the importance of configuration design of reinforcement in tailoring heterostructured metal matrix composites (MMCs) with outstanding comprehensive performance.

Fabrication of cemented carbides with bidirectional gradient structure via graphene deposition to simultaneously enhance surface hardness and toughness

The adoption of a continuous gradient in Co content stands as the foremost strategy for attaining heightened surface hardness and improved core toughness in cemented carbides. Nevertheless, the reduction in surface toughness stemming from a decreased Co content often precipitates premature surface failure of components. In this paper, WC-11Co powders was utilized as the precursor materials for fabricating a bidirectional gradient cemented carbide using the combined approach of low-temperature presintering and ultrasonic treatment techniques. The resultant cemented carbide exhibited a distinct gradient distribution, characterized by a forward gradient of graphene content, a reverse gradient of Co content, a forward gradient of WC grain size, and a forward gradient of residual compressive stress. The hardening and toughening mechanisms of the fabricated bidirectional gradient cemented carbides were comprehensively characterized and quantitatively discussed. The results provide compelling evidence that the gradient distribution of Co content plays a crucial role in attaining an impressive surface hardness of 1820 kgf/mm2. By utilizing the crack bridging mechanism of graphene, which efficiently exploits its strain transfer capabilities across a semi-coherent interface, in conjunction with the toughening effects of crack deflection and residual compressive stress, an exceptional surface fracture toughness of 17.62 MPa m1/2 is achieved. Additionally, the gradient layer exhibited a higher critical load for cracking. The present findings presents a novel strategy for the fabrication of high-performance ceramic-based composites.

Influences of hybrid fiber-reinforcement using wollastonite and cellulose nanofibers on strength and microstructure characterization of ultra-high-performance mortar

This paper presents the effect of incorporating wollastonite microfibers and cellulose nanofibers on mechanical properties and microstructure of ultra-high-performance mortar (UHPM). Cellulose nanofibers of 0.005%, 0.015%, and 0.030% are combined with 4.8% wollastonite microfiber by weight of binder, which consists of 10% silica fume and 90% cement. Compressive and flexural strengths of the UHPM specimens are measured at 7 days. The microstructure is characterized in terms of SEM/EDX, XRD, FTIR, and nanoindentation. The results show the effectiveness of the fiber hybridization in enhancing the compressive and flexural strength of ultra-high-performance mortar with the improvement in flexural toughness and fracture energy by as much as 10% than control mortar. Moreover, hybrid fiber-reinforcement based on the microstructural analysis provided more synergic effect and uniform distribution of the fibers, thus developing an efficient micro crack bridging mechanism as well as resulting in enhanced toughening properties and an increased load carrying capacity. Additionally, the combination of wollastonite microfibers and cellulose nanofibers promoted the hydration reaction products and contributed a denser matrix between the fibers and cement matrix, resulting in an increase of the microstructure and interface area between the fibers and cement matrix. Nano indentation analysis also confirmed the increase of UHD C-S-H from 65% to 84% and lower percentage of anhydrous phase in ultra-high-performance matrix after combining wollastonite microfibers and cellulose nanofibers.

Shear behavior of low-cost and sustainable bio-fiber based engineered cementitious composite beams –experimental and theoretical studies

The design of reinforced concrete (RC) members subjected to shear dominant loading is complex due to their quasi-brittle failure nature. Hence, a highly ductile material as a replacement for conventional concrete is essential to perform well under shear loading. Engineered Cementitious Composite (ECC) is one such material designed based on micromechanical theory for achieving a high strain capacity of about 3%. The objective of the proposed research work is to develop a cost-effective ECC using bio-based natural fibers such as flax, hemp, kenaf, and pineapple for achieving a large strain levels under shear dominant loading. The test program consists of different ECC specimens with (a) 2.0% flax fiber, (b) 2.0% hemp fiber, (c) 2.0% kenaf fiber, and (d) 2.0% pineapple fiber. In addition, the ultimate shear capacity of natural fiber-based ECC beams are estimated theoretically using the AIJ method and the results are compared with the tests and FE predictions. Test results revealed that the use of flax fibers in ECC beams was highly effective in enhancing the ultimate load through an excellent crack-bridging mechanism when compared to the other natural fiber types. Also, the ultimate load predictions from analytical calculations matched well with the test results.

Izod impact resistance of 3D printed discontinuous fibrous composites with Bouligand structure

The Bouligand structure found in the dactyl club of mantis shrimps is known for its impact resistance. However, Bouligand-inspired reinforced composites with 3D shapes and impact resistance characteristics have not yet been demonstrated. Herein, direct ink writing was used to 3D print composites reinforced with glass microfibers assembled into Bouligand structures with controllable pitch angles. The energy absorption levels of the Bouligand composites under impact were found to surpass those of composites with unidirectional microfiber alignment. Additionally, the Bouligand composites with a pitch angle of 40° exhibited a maximum energy absorption of 2.4 kJ/m2, which was 140% higher than that of the unidirectional composites. Furthermore, the characterization of the topography of the fractured surface, supplemented with numerical simulations, revealed a combination of crack twisting and crack bridging mechanisms. Flexural tests conducted on the composites with a pitch angle of 40° revealed that these composites had the strongest properties, including a flexural strength of 36.9 MPa, a stiffness of 2.26 GPa, and energy absorption of 8 kJ/m2. These findings are promising for the microstructural design of engineered composites using direct ink writing for applications in aerospace, transportation, and defense.

Mechanical and fracture properties of sugar beetroot-based nanosheets (SNS) doped cementitious composites

This paper examines the mechanical and fracture properties of cementitious composites doped with a new type of 2D bio-nanoplatelets sheets, synthesized from sugar beet pulp waste. The sugar beetroot nanosheets (SNS) were added to the cement pastes at different concentrations. The influence of SNS treatment and water-to-cement (w/c) ratio on the performance of the cementitious composites was elucidated. The experimental results showed that 0.2- wt% and 0.35 were the optimal SNS concentration and w/c ratio for increasing the compressive, splitting tensile and flexural strength, flexural modulus, fracture energy and fracture toughness. These properties were enhanced by as much as 12.15%, 36.87%, 39.91%, 32.69%, 69.01% and 49.06%, respectively. This enhancement was due to crack deflection and crack bridging mechanisms in the cementitious composites as a result of the high specific surface area of SNS and the strong chemical and physical bonding of SNS with the hydration phases. The SNS materials offers strong advantages over graphene-based materials on improving the engineering properties of cementitious materials and reducing their cost and CO2 emissions.

Mechanical properties and oxidation behavior of (Mo,W)AlB, (Mo,Cr)AlB, and (Mo,W,Cr)AlB MAB solid solutions synthesized with spark plasma sintering

This study reports the effects of solid solution on the mechanical and oxidation behavior of MoAlB ceramics. (Mo,W)AlB, (Mo,Cr)AlB, and (Mo,W,C)rAlB were synthesized under 30 MPa at 1200 °C by Spark Plasma Sintering (SPS). Composition and microstructure were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS). Although it was determined that the main phase was MoAlB solid solution, it was observed that binary borides such as WB were also present in the (Mo,W)AlB and (Mo,W,Cr,)AlB. Hardness was measured by the Vickers indentation test. The hardnesses of MoAlB solid solutions improved considerably compared to pure MoAlB and were obtained as 13.65, 12.72, and 13.37 GPa, respectively, for (Mo,W)AlB, (Mo,Cr)AlB, and (Mo,W,Cr)AlB. The reasons for the improvement in hardness are estimated to be grain refinement and solid solution hardening mechanism. Fracture toughnesses calculated from radial cracks formed during Vickers indentation are 6.52, 5.88, and 6.40 MPam1/2, respectively. Although crack bridging and deflection mechanisms work with solid solutions, as in pure MoAlB, the brittle binary borides in the structure did not improve fracture toughness. The oxidation test was carried out at 1200 °C for 12 h. A dense and continuous protective oxide layer was formed in all samples. The scale thicknesses of (Mo,W)AlB, (Mo,Cr)AlB, and (Mo,W,Cr)AlB are 3.2, 2.1, and 2.6 μm, respectively.

Effect of carbon nanotubes on microstructure and mechanical properties of TiZrVMnCu–Er high entropy alloy composites

Abstract To improve the ductility and toughness of refractory high entropy alloy (Ti, Zr, V), Mn and Cu were added to form TiZrVMnCu high entropy alloy with soft and hard phases. Carbon nanotubes (CNTs) and Er were introduced to fabricated composites with high strength and ductility. The relative density, microhardness, and compressive strength of TiZrVMnCu–Er–CNTs composites were in direct proportional to CNTs content from 0 to 0.5 wt%. The composite with 0.5 wt% CNTs has the highest hardness (634.4 HV) and strength (1720.7 MPa), and the strain variable is 14.3 %. The fracture toughness of the composites was improved by the crack bridging mechanism and crack deflection mechanism induced by adding CNTs. The fine grain, second phase strengthening mechanism, and the load transfer mechanism induced by CNTs improved the strength and hardness of the composites. Er can achieve solid solution strengthening or play a role in the second phase and fine grain strengthening.

Wetting-drying durability performance of cement-stabilized recycled materials and lateritic soil using natural rubber latex

This research was conducted to assess the role of natural rubber latex (NRL) in improving the durability of cement stabilized lateritic soil and recycled materials blends against wetting–drying (w-d) cycles. 70% and 50% by weight of recycled materials, including steel slag (SS) and recycled concrete aggregate (RCA) were replaced for Lateritic soil (LS) and 5% cement by weight of dry aggregate was used in this research. The dry NRL to cement (r/c) ratios of 0%, 3%, 5%, and 10% were the influence factor that were investigated. The unconfined compressive strength (UCS), physical and weight loss, water absorption, and microstructural analysis were performed to evaluate the influence of NRL on the durability of cement-NRL stabilized SS:LS and RCA:LS by comparison with those of control cement-stabilized mixtures (without NRL). The results indicated that the UCS development of all mixtures was found to be similar in that the UCS value increased up to the third w-d cycle and gradually decreased thereafter. The microstructural analysis result indicated that the increase of UCS during the w-d cycles can be attributed to the high temperature, which promotes the moisture diffusivity of cementitious materials and thus increases chemical reaction and strength development. However, with further increase of w-d cycles, the strength reduction was attributed to the Ca2+ leaching from the cement-stabilized materials during the soaking stages and the dissolution of cementitious products. In addition, the crack propagation and extension gradually caused the crumbling of samples and microcracks, resulting in the deterioration and strength loss of samples. It was evident that the formation of the NRL films filled up the pore spaces and microcrack, acting as NRL film crack-bridging mechanism, resulting in the enhanced interparticle bonding strength and durability.

Simultaneous hardening and toughening of a high‐entropy (NbTaZrW)C ceramic carbide using SiC particle

AbstractPreviously, we have found that (NbTaZrW)C exhibits a good combination of nanohardness and toughness. In this report, we explore the possibility to further increase the overall properties of this high‐entropy carbide ceramic (HECC) through introducing SiC particle (SiCP). To this end, a series of (NbTaZrW)C–xSiC ceramic composites (x = 0/5/15/30/50 vol.%) were fabricated using spark plasma sintering (SPS), their microstructure and mechanical properties were characterized. Our results reveal a grain refinement effects of SiCP, an agglomeration of SiCP with (1 0 0) plane preferentially perpendicular to the SPS‐pressing direction and the formation of a transition region with various stoichiometric ratio of (NbTaZrW)xC1−x in the (NbTaZrW)C–SiCP vicinity. The elastic modulus, microhardness, and flexural strength of the HECCs show tight positive relations with the SiCP content and the beneficial effect of SiCP to the fracture toughness of (NbTaZrW)C becomes evident once the content of SiCP reaches 30 vol.%. Altogether, (NbTaZrW)C–50%SiC, which has a microhardness of 22 GPa, a flexural strength of 455 MPa, and an indentation fracture toughness of 6.54 MPa m1/2, presents the optimal combination of mechanical properties among the investigated composites. Mechanistically, the strengthening effect of SiCP introduction arises from the intrinsic high hardness of SiCP and the SiCP‐induced grain refinement and the toughening effect is mainly associated with crack bridging mechanism.

The synergistic effect of hybrid nano-silica and GNP additives on the flexural strength and toughening mechanisms of adhesively bonded joints

This study intended to research the effects of nanoparticle hybridization (nano-silica and GNP) on the bending performance of adhesively bonded joints of Al-2024 sheets. For this purpose, nano-silica/GNP hybrid nanofiller reinforced single lap joints (SLJ) with total additive ratios of 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% by weight were manufactured and subjected to three-point bending tests. Among hybrid nanoparticle-doped joints with a ratio of nano-silica to GNP of 1:2,1:1, 2:1, 3:1, and 3:2, the best performance was obtained in a 1.5% nano-silica +0.5% GNP doped sample with 3:1 particle ratio. The enhancement in flexural strength was 51.3% in this sample compared to the sample containing pure Araldite 2014 adhesive. In addition, it exhibited 3.1% and 30.8% better strength, respectively, compared to the samples containing single GNP and single nano-silica particles. In the SEM views which were taken from fracture surfaces of the damaged samples, it was observed that the hybridization of nano-silica and GNPs improved the particle dispersion. Nano-silica particles were attached between the GNP lamellae, forming a new three-dimensional hybrid structure. This structure improved the interfacial interaction of nanoparticles with the adhesive, and also increased the resistance of crack deviation, crack stopping, crack bridging and pull-out mechanisms against peeling and shear stresses caused by three-point bending loads.

Preparing and Investigating the Structural Properties of Porous Ceramic Nano-Ferrite Composites

Highly porous kaolin ceramics composites were produced by adding space-holder materials during dry pressing. To increase the strength of porous kaolin ceramic composites different ratios of cobalt-nickel ferrite nanoparticles (5, 10, 15, and 20%) were added. The sol-gel auto-combustion method prepared the nano cobalt-nickel ferrite particles (CNF). Space-holder materials were removed by preheating, and solid specimens were produced by sintering. X-ray diffraction (X-RD) and Fourier transform infrared spectroscopy (FT-IR) was used to examine the structural characteristics. Up to 47.05% porosity was achieved when 20% CNF was added to the porous kaolin ceramics composites. The results indicated that the higher percentages of nano CNF 20% decreased linear shrinkage and the loss of ignition by 4.4% and 30.4%, respectively. While increased apparent density and diametrical strength of 1.42 g/cm3, and 9.03MPa respectively. Diametrical strength nanoparticles increased the strength attributed to the formation of a secondary phase in the porous ceramics, improving the crack bridging mechanism.