Increase In Fracture Toughness Research Articles

Contribution of cellulose nanofibrils on the strengthening and toughening of neat and blended polylactide specimens; and the differences after 3D-printing

The main purpose of this study was to use “green materials” approach by investigating effects of only 1 wt% Cellulose Nanofibrils (CNF) on the strengthening and toughening of neat and blended polylactide (PLA) biopolymer matrix. For this purpose, first of all effects of CNF were investigated in PLA/CNF biocomposite specimens. After blending of PLA with 10 phr bio-based thermoplastic polyester (b-TPE) elastomer, effects of CNF were investigated also for this PLA/b-TPE/CNF ternary biocomposite specimens. Mechanical tests revealed that due to the efficient strengthening and toughening mechanisms, CNF increased flexural strength of PLA by 33%, while b-TPE increased fracture toughness of PLA by 104%. When CNF and b-TPE were incorporated together, synergism in the strength and toughness values were occurred. All bioblend and biocomposite specimens were produced by using the same “melt mixing” technique in a laboratory size twin-screw extruder, and their test specimens were shaped by conventional “compression molding”. Since shaping by “3D-printing” is frequently used in the biomedical sectors, another distinctive aim of this study was to reveal whether there were any differences in the strength and toughness values of specimens after their 3D-printing. It was observed that due to the “textured” structure of 3D-printed specimens, their flexural strength values were approximately 20% lower, while fracture toughness values were approximately 20% higher.

High-entropy carbide (ZrNbTiCrV)C ceramic composite coating possessing good mechanical properties and wear resistance

High entropy carbide ceramics possess high hardness but suffer from low toughness and densification challenges. A dense (ZrNbTiCrV)C composite coating was fabricated through spraying ZrO2-Nb2O5-TiO2-Cr2O3-V2O5-Al-SiC powders, which was subsequently compared to a (ZrNbTiCrV)C coating produced from binary carbides. Incorporating the V element facilitated the densification and element diffusion. The coating obtained via spraying ZrO2-Nb2O5-TiO2-Cr2O3-V2O5-Al-SiC powders exhibited superior mechanical properties and wear resistance, particularly achieving a 17.2 % increase in fracture toughness and a 73.3 % reduction in wear rate compared to the coating derived from binary carbides. These improved properties were attributed to fine-grained particles and a low porosity of 1.56 %. Wear resistance was also enhanced through rolling friction and the formation of a protective oxide film.

Study on Microstructure and Tribological Mechanism of Mo Incorporated (AlCrTiZr)N High-Entropy Ceramics Coatings Prepared by Magnetron Sputtering.

(AlCrTiZrMox)N coatings with varying Mo content were successfully prepared using a multi-target co-deposition magnetron sputtering system. The results reveal that the Mo content significantly affects the microstructure, hardness, fracture toughness, and tribological behavior of the coatings. As the Mo content in the coatings increases gradually, the preferred orientation changes from (200) to (111). The coatings consistently exhibit a distinct columnar structure. Additionally, the hardness of the coatings increases from 24.39 to 30.24 GPa, along with an increase in fracture toughness. The friction coefficient is reduced from 0.72 to 0.26, and the wear rate is reduced by 10 times. During the friction process, the inter-column regions of the coatings are initially damaged, causing the wear track to exhibit a wavy pattern. Greater frictional heat is generated at the crest of the wave, resulting in the formation of a MoO2 lubricating layer. The friction reaction helps to reduce the shear force during friction, demonstrating the lower friction coefficient of the (AlCrTiZrMox)N coatings. Both the hardness and fracture toughness work together to reduce the wear rate, and the (AlCrTiZrMox)N coatings show excellent wear resistance. Most notably, although the columnar structure plays a negative role in the hardness, it contributes greatly to the wear resistance.

SiC whisker toughened WC-Al2O3-ZrO2 binderless cemented carbides via fast-hot-pressed sintering and DFT calculations

Binderless cemented carbide has garnered attention for its exceptional hardness and suitability in extreme service conditions. The absence of a metal binder, however, leads to inadequate fracture toughness, which limits its broader application. This study explores the influence of SiC whisker on the microstructure and mechanical properties of WC-Al2O3-ZrO2 binderless cemented carbide, utilizing a combination of experimental method and Density Functional Theory (DFT) calculations. The inclusion of 1 wt.% SiC whisker resulted in a notable increase in fracture toughness, reaching an impressive toughness of , while maintaining a high Vickers hardness of 19.4 GPa. DFT calculations provided insights into the interface energy, cohesive energy, and charge density differences at the WC/SiC interface. This work also presents two models depicting the behavior of whiskers during fracture, based on the observed microstructure and computational findings. Overall, the present work offers significant insights and practical guidance for advancing binderless cemented carbide technologies.

Microstructure, mechanical, and thermal properties of (MoTaTiVW)CX high entropy ceramics with different carbon stoichiometries

In present work, high entropy (MoTaTiVW)CX ceramics with different carbon stoichiometries (X = 3–6) were produced using spark plasma sintering. The microstructure, mechanical properties, and thermal properties of (MoTaTiVW)CX with different carbon stoichiometries were studied. At X = 3, the carbon deficiency resulted in a multiphase structure of the sample, (MoTaTiVW)C3 with a Mo-rich carbide phase. At X = 3.5, the single-phase rock salt structure was formed despite carbon vacancies of up to 30 %. The relative density of (MoTaTiVW)CX gradually decreases as the carbon stoichiometry increases from X = 3 to X = 6. The concentration of carbon vacancies affects the sintering activation energy, which can enhance mass transfer and promote the densification process. The Vickers hardness of (MoTaTiVW)CX shows an overall decreasing trend as the carbon stoichiometry increases from X = 3.5 to X = 6, peaking at 20.4 ± 0.4 GPa at X = 3.5. The fracture toughness increases and then decreases, peaking at 4.4 ± 0.2 MPa m1/2 at X = 4. The thermal conductivity of (MoTaTiVW)CX gradually increases, then decreases and finally increases with the increase of carbon stoichiometry. At room temperature, the maximum value of thermal conductivity is 6.35 ± 0.29 W/m·K of (MoTaTiVW)C5 and the minimum value is 5.32 ± 0.35 W/m·K of (MoTaTiVW)C5.5. At 1000 °C, the thermal conductivity of (MoTaTiVW)CX ranges from 15.94 ± 0.37 W/m·K to 19.56 ± 0.45 W/m·K. As the concentration of carbon vacancies decreases, the decrease in point defect concentration will reduce the degree of lattice distortion, thereby reducing phonon scattering and affecting thermal conductivity. The study suggests that carbon stoichiometry can be used to adjust the microstructure, mechanical properties, and thermal properties of high entropy carbide ceramics.

Seamlessly embedded microcapsules in self-repairing coatings: Improved compatibility and enhanced corrosion resistance recovery

Microcapsules, with polyether amine as the core repairing agent and polyether amine-cured epoxy as the shell, were prepared via the multiple emulsion polymerization and applied in an epoxy/polyether amine coating system on carbon steel surfaces. The microcapsules and the coating substrate have the same composition and are seamlessly connected by chemical bonds, akin to the direct injection of liquid healing agents into the substrate. When the repairing agent flows out, it will crosslink and cure with the epoxy groups in the substrate to achieve no difference self-repair. The characteristics of microcapsules were studied by scanning electron microscope (SEM), Fourier transform infrared (FTIR) and Thermal gravimetric (TG). The mechanical properties and corrosion resistance recovery of coatings loaded of coatings with different weight percentages of loaded microcapsules were investigated using tensile testing, electrochemical impedance spectroscopy (EIS) and neutral salt spray test (NSS). Results indicate that the 7 wt% microcapsules composite coating shows a 37.7 % increase in tensile strength and a 71.4 % increase in fracture toughness over pure epoxy coating. After immersing in saltwater for 7 days, the scratch sealing efficiency can reach 99.85 %. The coating system not only improved the compatibility between microcapsules and the substrate, but also enhanced the toughness of thermosetting brittle epoxy materials, giving it long-lasting anti-corrosion capability.

Chemical short-range order enhances fracture toughness of medium entropy alloy CoCrNi

Using hybrid molecular dynamics and Monte Carlo simulations, we examine the role of lattice distortion (LD) and chemical short-range ordering (CSRO) on the development of defects ahead of a mode I crack in medium entropy alloy CoCrNi. We show that CSRO noticeably increases fracture toughness. The result can be explained by the effect of CSRO on lowering LD and increasing intrinsic stacking fault energy and the direct impact CSRO has on the energetic barriers for emitting partial dislocations and forming nanotwins from CoCr clusters on the crack tip. CSRO allows the nanotwin domains to further support inelastic deformation, such as dislocation glide and amorphization, leading to stable crack-tip plasticity and postponement of softening. These findings imply that the superior fracture toughness in CoCrNi can be attributed to the non-negligible CSRO that naturally exists.

Damage identification and fracture behavior of 2.5D SiCf/SiC composites under coupled stress states

Continuous fiber-reinforced silicon carbide composites have received significant attention due to their high-temperature mechanical stability. However, their widespread implementation has been hindered by intricate fracture mechanisms and limited toughness. This study presents a real-time approach for identifying damage type in 2.5D SiCf/SiC composites and highlights the significant impact of minor eccentric loading angle on the fracture behavior and mechanical properties using acoustic emission (AE). Even a slight degree of eccentric loading angle can significantly alter the fracture behaviors, leading to a significant increase in fracture toughness. The fracture damage evolution law of 2.5D SiCf/SiC under varying eccentric loading angles was investigated with the help of the AE damage identification, fracture morphology and finite element analysis. These findings provide valuable insights for multi-axis stress analysis of 2.5D high-performance composites.

Mechanical behavior of carbon nanotubes reinforced polymer

Abstract Carbon nanotubes (CNTs) have garnered significant attention due to their extraordinary mechanical and other physical characteristics. This study demonstrates that incorporating a small number of carbon nanotubes, ranging from 0.1 to 0.9 wt.%, into a polymer, can effectively enhance its mechanical properties. In comparison to the pure polymer, the addition of −0.3 % carbon nanotubes resulted in a notable 24.1 % increase in tensile strength, a 4.4 % increase in compressive strength, a significant 319.5 % increase in the fatigue life cycle at 0.1 % carbon nanotubes, and a remarkable 43.0 % increase in fracture toughness at 0.3 wt.% carbon nanotubes.

In-situ hybridization of an epoxy resin using polyurethane and MXene nanoplatelets for thermally stable nanocomposites with improved strength and toughness

A novel ternary composite system has been developed by combining MXene nanoplatelets with pre-polyurethane (PU) and an epoxy (EP) resin through in-situ polymerization and solution blending. Our approach aims to enhance the strength and toughness of the EP matrix while maintaining its thermal stability. The strong compatibility between isocyanate-terminated PU and hydroxyl-terminated MXene with the resin was demonstrated through chemical grafting and hydrogen bonding processes. In this ternary composite, significant improvements were observed, including a 32 % increase in tensile strength, a 46.4 % increase in flexural strength, and a 13.4 % increase in fracture toughness, even at very low filler contents of 0.05 wt% for MXene and 1 wt% for PU. A thorough examination of the fractured surfaces revealed the underlying mechanisms responsible for the improved strength and toughness. These mechanisms involve a transition from a brittle to a ductile fracture mode, which can be attributed to the combined effects of thermoplastic toughness, strong chemical bonding between PU and EP, and crack-anchoring and bridging effects facilitated by MXene nanoplatelets. The results presented herein are relevant to a wide range of applications in aerospace, automotive, electronics and various other industries where durability and thermomechanical performance of materials are critical.

The influence of Co and SiC on the sintering, microstructure and tribological properties of (Ti1/3Zr1/3V1/3)B2 medium-entropy diboride-based ceramics

The (Ti1/3Zr1/3V1/3)B2(MEB) composite ceramics with various Co and SiC additions were prepared by spark plasma sintering technology at 1600 °C. The influence of Co and SiC on the microstructure and mechanical properties were studied. Reciprocating sliding wear experiments of boride ceramics sliding against GCr15 ceramic were also performed at 1 N, 5 N and 10 N (Temperature: 25 °C, frequency: 3 Hz, stroke: 1 mm). The result suggest that the sintering additives not only significantly reduces the sintering temperature of boride ceramic, but also refines the microstructure and improves its mechanical properties. The hardness and fracture toughness of MEB-20SiC–10Co ceramics are 27.76 GPa and 3.9 MPa m1/2, 30.6 % and 60 % higher than that of MEB, respectively. The increase in fracture toughness results from crack deflection and branching of the SiC particles. Tribological results indicates that MEB-20SiC–10Co also show the best tribological performance. The wear rate of MEB and MEB-20SiC–10Co at 10 N load are 2.17 × 10−6 mm3N−1m−1, 1.29 × 10−6 mm3N−1m−1, oxidative wear and adhesive wear are the main wear mechanisms. Analyzing of the wear tracks revealed a significant transfer of material from the counterpart to the tribo-interface. A friction film consisting mainly of titanium oxide and part of boron oxide was generated on the worn surface, which contributes to the improvement of tribological performance.

Low temperature and high efficiency synthesis of boron nitride nanosheets (BNNSs) and its application in SiO2 microwave-transparent composites

In this study, Zn8B3H3O14 nanosheets were synthesized through a one-step coprecipitation process and employed as both a boron source and substrate templates for the fabrication of boron nitride nanosheets (BNNSs), which were synthesized efficiently at low temperatures by the borate nitration method using ammonia as the nitrogen source. The thickness of the synthesized BNNSs ranged from 3 to 10 nm with a flake dimension of about 2.56 μm. The prepared BNNSs using this method realized 98.8% boron source utilization and single batch yields up to gram level. In addition, BNNSs/SiO2 microwave-transparent composites were prepared to investigate the potential for large-scale applications of the BNNSs produced by using this method. The composites demonstrated a remarkable increase in bending strength and fracture toughness, reaching 122.02 MPa and 2.31 MPa·m1/2, respectively, with the addition of only 0.5 wt% BNNSs. Compared with SiO2 without BNNSs, the fracture toughness of the composites is increased by 106%. A novel crack plugging strong toughening mechanism of BNNSs is proposed. Simultaneously, the composites exhibit exceptional microwave-transparent properties, with dielectric constants below 4 in the real part and below 0.03 in the imaginary part. Therefore, this study has successfully achieved the low-temperature and efficient synthesis of micron-scale BNNSs, laying the groundwork for their large-scale application.

Influence of Interfacial Interaction and Composition on Fracture Toughness and Impact Properties of Carbon Fiber-Reinforced Polyethersulfone.

In this study, the interlaminar fracture toughness and impact strength of polyethersulfone reinforced with continuous carbon fibers were studied. Interlaminar fracture toughness tests were performed using the double cantilever beam method. It was shown that surface modification using the thermal oxidation method of the carbon fibers can strongly increase the interlaminar fracture toughness of the obtained composites. Thus, the maximum value reached 1.72 kJ/m2, which was 40% higher than the fracture toughness of the composites reinforced with initial carbon fibers. Moreover, fractographic analysis using a scanning electron microscope allowed us to highlight the main reasons for the dependence of fracture toughness on fiber content and surface modification conditions of the carbon fibers. It was shown that the main factor that allowed for an increase in fracture toughness was the enhanced interfacial interaction between the fibers and polymer matrix. Additionally, it was found that expectedly, there was a good correlation between interlaminar fracture toughness and interlaminar shear strength results. However, a negative influence of surface modification on the impact properties of composites was found. Such behavior occurred because of higher structural stability and lower exposure to delamination in multiple layers of the composites reinforced with the modified carbon fibers. It was found that impact energy reached ~150 kJ/m2 for the polyethersulfone-based composites reinforced with initial fibers, while the composites reinforced with modified carbon fibers showed impact energy values of only ~80 kJ/m2. Nevertheless, surface modification of carbon fibers using the thermal oxidation method can be an effective method for improving the performance properties of polyethersulfone-based composite materials.

Enhancing Bone Implants: Magnesium-Doped Hydroxyapatite for Stronger, Bioactive, and Biocompatible Applications.

Hydroxyapatite (HAp) with the chemical formula Ca10(PO4)6(OH)2 is an inorganic material that exhibits morphology and composition similar to those of human bone tissues, making it highly desirable for bone regeneration applications. As one of the most biocompatible materials currently in use, HAp has undergone numerous attempts to enhance its mechanical strength. This research focuses on investigating the influence of magnesium (Mg) incorporation on the structural and mechanical properties of synthesized magnesium-doped hydroxyapatite (MgHAp) samples. Apart from its biocompatibility, Mg possesses a density and elasticity comparable to those of human bone. Therefore, incorporating Mg into HAp can be pivotal for improving bone formation. Previous studies have not extensively explored the structural changes induced by Mg substitution in HAp, which motivated us to revisit this issue. Hydrothermal synthesis technique was used to synthesize MgHAp samples with varying molar concentrations (x = 0, 0.5, 1.0, and 1.5). Theoretical simulation of HAp and MgHAp for obtaining 3D structures has been done, and theoretical X-ray diffraction (XRD) data have been compared with the experimental XRD data. Rietveld analysis revealed the alteration and deviation of lattice parameters with an increase in the Mg content, which ultimately affect the structure as well the mechanical properties of prepared samples. The findings revealed an increase in compressive stress and fracture toughness as the Mg concentration in the composition increased. Furthermore, using a finite-element analysis technique and modeling of the mechanical testing data, the von Mises stress distribution and Young's modulus values were calculated, demonstrating the similarity of the prepared samples to human cortical bone. Biocompatibility assessments using NIH-3T3 fibroblast cells confirmed the biocompatible and bioactive nature of the synthesized samples. MgHAp exhibits great potential for biomedical applications in the dental, orthopedic, and tissue engineering research fields.

Viable route to the manufacture of short carbon fiber-rich UHTC complex shapes with enhanced toughness

ZrB2 - based pasted, containing 5, 20, 45, 60 vol% short carbon fibers (Cf), were prepared in order to obtain complex shapes via direct ink writing, which were then sintered by hot pressing. The rheological behavior of the pastes indicated that at low Cf concentrations, the fibers act as a lubricant decreasing the paste viscosity. Above 20 vol% Cf, they act also as a binder creating an interconnected network that dominates over the lubrication effect, resulting in a viscosity increase. Complex shapes in the form of a hollow cylinder and a winglet with a functionally graded composition were then extruded and hot pressed, using a versatile powder bed method that enabled full densification with no need to use ad-hoc machined graphite inserts. Bars obtained from the direct ink writing process resulted in high alignment of the short fiber and displayed fracture toughness increase of 54% over that of the unreinforced matrix, while demonstrating a 42% increase with respect to conventionally hot pressed dry mixtures of ZrB2 and short fibers.This work shows the great potential of manufacturing complex shapes in ultra-high temperature ceramics matrices reinforced with short fibers for a plethora of design possibilities, including functional grading with control over layer composition, thickness and even alignment of short fiber.

Rare-earth high-entropy magnetoplumbite structure hexaluminates (La1/5Nd1/5Sm1/5Eu1/5Gd1/5)MAl11O19 (M = Mg, Zn) for thermal barrier coating applications with enhanced mechanical and thermal properties

By applying the high-entropy strategy, one can develop stable mixed oxide by populating a single sublattice with many distinct cations. Two kinds of rare-earth high-entropy hexaaluminates (La1/5Nd1/5Sm1/5Eu1/5Gd1/5)MAl11O19 (M = Mg and Zn) were successfully synthesized, and their mechanical and thermal properties were analyzed. We highlight that the Zn-containing sample displays a significant increase in fracture toughness (2.48 MPa m1/2) and a decrease in thermal conductivity (1500 °C, 1.2 W m−1 K−1) as compared to the Mg-containing sample. The diffusion of fine grains in platelet-like grains observed only in the Zn-containing sample is considered to be responsible for its outstanding mechanical properties. This work demonstrates the excellent thermal-mechanical properties of the Zn-containing sample and indicates the promising use of high-entropy hexaaluminate in the aerospace field acting as thermal barrier coating materials.

Experimental study of fracture behaviors of granite at ultra-low temperatures

A good understanding of fracture characteristics of rocks at ultra-low temperatures is essential in selecting and designing cavernous liquefied natural gas (LNG) storage facilities. In this study, three-point bending tests on Notched Semi-Circular Bend (NSCB) granite specimens with various grain sizes and saturation levels were conducted at temperatures of 25°C, −90°C, −120°C, and −165°C, respectively. The test results show that the fracture characteristics of granite are significantly weakened at −165°C under saturated conditions. As the temperature goes low, granite’s peak strength, fracture toughness, and fracture energy increase under dry conditions. A robust linear relationship between the mode-I fracture toughness (KIC) and the fracture energy of granite at ultra-low temperatures is established in this study. This relationship demonstrates that specimens with higher fracture toughness require more energy to reach their fractures. In addition, the relationship, along with its test constraints, forms a theoretical basis that can be used to explain the fracture damage modes and the characteristics of granite at different temperatures. Furthermore, granite at ultra-low temperatures was also investigated from the view of pores with frozen water and the change of particle sizes. The data obtained from our experiments can serve as valuable parameters for simulating underground LNG storage. The research findings from this study provide a valuable foundation that can be used for designing and installing cavernous LNG storage tank facilities.

Higher order structures and toughening mechanisms for simultaneously polymerized polymethacrylate/polyurethane

AbstractAmorphous polymer/crystalline polymer blends can be prepared via the simultaneous polymerization of polymethacrylate/polyurethane combinations. The relationship between higher order structures and fracture mechanisms in these blends must be uncovered to elucidate the source of the increased fracture toughness of such materials. The present work involves the production of blended polymethacrylate/polyurethane and assess the internal structures of these specimens using optical and electron microscopy. These observations reveal the presence of both spherulites and elastomeric phases. The spherulites consisting of the polyurethane and are several micrometers in diameter whereas the phase‐separated polyurethane elastomeric domains are approximately 100 nm in size. Multiple cracks, crack bridging and plastic deformation around the precrack tips of loaded specimens are evidently responsible for the increased toughness of these blends. The former two phenomena are attributed to the presence of spherulites while the plastic deformation of the methacrylate matrix is ascribed to cavitation of the polyurethane elastomeric phases in response to loading.

Microstructure, mechanical properties, and bone cell interactions of ZTA composites reinforced with BN

Due to their remarkable mechanical properties and biocompatibility, zirconia toughened alumina (ZTA) based composites are preferred materials for dental and orthopedic uses. This study focuses on the production and characterization of hexagonal boron nitride (BN) containing ZTA ceramics. To achieve this, we formulated composite systems with a composition of 70Al2O3-(30-x)YSZ-(x)BN (in vol%, where x ranges from 1 to 5). These mixtures were densified via spark plasma sintering (SPS) at a temperature of 1350 °C under a pressure of 40 MPa, with a dwell time of 5 min. The densification, resulting microstructure, and mechanical properties, including Vickers hardness and indentation fracture toughness, were thoroughly examined. All ZTA-BN composites achieved sintering densities exceeding 98.5% of their theoretical values. Incorporating BNs into ZTA composites increased fracture toughness by ∼55% while maintaining Vickers hardness values. Notably, crack deflection mechanism played a dominant role in toughening, particularly for the composite containing 3 vol% BNs. Furthermore, in vitro biocompatibility assessment of the YZTAB3 sample demonstrated that the composite had no cytotoxic effects towards human bone cells, indicating its potential for biomedical applications.

Fracture Performance Study of Carbon-Fiber-Reinforced Resin Matrix Composite Winding Layers under UV Aging Effect.

There is limited research on the fracture toughness of carbon-fiber-reinforced polymer (CFRP) materials under accelerated UV aging conditions. In this study, the primary focus was on investigating the influence of varying durations of ultraviolet (UV) irradiation at different temperatures on the Mode I, Mode II, and mixed-mode fracture toughness of CFRP laminates. The results indicate that with increasing UV aging duration, the material's Mode I fracture toughness increases, while Mode II fracture toughness significantly decreases. The mixed-mode fracture toughness exhibits an initial increase followed by a subsequent decrease. Furthermore, as the aging temperature increases, the change in the fracture toughness of the material is more obvious and the rate of change is faster. In addition, the crack expansion of the composite layer of crack-containing Type IV hydrogen storage cylinders was analyzed based on the extended finite element method in conjunction with the performance data after UV aging. The results reveal that cracks in the aged composite material winding layers become more sensitive, with lower initiation loads and longer crack propagation lengths under the same load. UV aging diminishes the overall load-bearing capacity and crack resistance of the hydrogen storage cylinder, posing increased safety risks during its operational service.