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Ferroelectric materials are widely used in actuators, exciters, and memory devices due to their excellent electromechanical properties. However, the instinctive brittleness of ferroelectric materials makes them easy to fracture under external load. Since giant strain gradient can be easily generated near the crack tip, the flexoelectric effect is indispensable in the research of fracture properties of ferroelectric materials. With the combination of time-dependent Ginzburg–Landau theory and phase-field model, the electromechanical behavior of PbTiO 3 in the vicinity of the crack tip is determined in this work. The simulation results demonstrate that the domain structure near the crack tip becomes asymmetric with the flexoelectric effect. The polarization switching-induced toughening, which is characterized by the J -integral, depends on the direction of the crack relative to the original polarization orientation. Furthermore, the longitude flexoelectric coefficient f 11 has more significant impact on the fracture toughness than that of the transverse flexoelectric coefficient f 12 and the shear flexoelectric coefficient f 44. The results of the present work suggest that the flexoelectric effect must be considered in the reliable design of ferroelectric devices. [ABSTRACT FROM AUTHOR]

Amorphous intergranular films (AIFs) have been proven in experiments to improve the damage tolerance of nanocrystalline materials. However, a quantitative study is still lacking. Molecular dynamics simulations were performed here to investigate the effect of CuNb AIFs on the fracture toughness of nanocrystalline Nb. In order to clarify the role of AIFs, a bicrystal Nb model with one straight symmetrical tilt grain boundary and a mode-I crack in one of the grains was constructed, in which the AIF effect was introduced by replacing the normal grain boundary with a CuNb AIF. Then, AIF thickness-dependent tensile deformation of the bicrystal Nb samples was simulated. The work-of-fracture, which is defined as the released strain energy due to the newly generated unit area in the crack during stretching, was employed to quantify the fracture toughness of the bicrystal systems. The results show that the fracture toughness of the AIF sample can be tripled due to the blunted crack tip and the relieved stress concentration at the crack tip as compared to the AIF-free one that exhibits a brittle crack propagation behavior. Also, the thicker the AIFs, the more pronounced this reinforcing effect. More importantly, it is found that there exists a critical AIF width of 1.7 nm, below which the crack will eventually break through the AIF, and above which the crack failed to do this. It is revealed that the enhanced fracture toughness originated from the transformation of brittle crack propagation to abundant dislocation emission from AIFs. [ABSTRACT FROM AUTHOR]

Fine-grained nuclear graphite is one of the key structural materials for high temperature gas-cooled reactors as well as several Generation IV nuclear fission reactor designs. However, its deformation and fracture behaviours at elevated temperatures are not well understood. In light of this, the current study focused on investigating the flexural strength and fracture toughness of two fine-grained graphite (SNG623 and T220) using real-time X-ray computed micro-tomography imaging at room temperature, 750 °C and 1100 °C. Specifically, nonlinear-elastic fracture mechanics-based JR(Δa) R-curves at these temperatures were presented with evolution of damage and failure micro-mechanisms, local strain distributions and J-integral fracture analysis, purveying notable findings. Compared to the coarser-grained Gilsocarbon nuclear graphites used in the current UK Advanced Gas-cooled Reactors (AGRs), these modern fine-grained graphites display deficient fracture resistance in the form of far less stable crack growth prior to catastrophic fracture and reduced failure strain at 1100 °C. Moreover, their elevation in strength and toughness at high temperatures is remarkably lower than that of Gilsocarbon graphite. Based on in situ high-temperature Raman spectroscopy mapping, we believe that one of the major causes of this behaviour can be attributed to the smaller magnitude of ‘frozen-in’ residual stress relaxed at elevated temperatures compared with Gilsocarbon graphite.

Amorphous solids are known to fail catastrophically via fracture, and cavitation at nano-metric scales is known to play a significant role in such a failure process. Micro-alloying via inclusions is often used as a means to increase the fracture toughness of amorphous solids. Modeling such inclusions as randomly pinned particles that only move affinely and do not participate in plastic relaxations, we study how the pinning influences the process of cavitation-driven fracture in an amorphous solid. Using extensive numerical simulations and probing in the athermal quasistatic limit, we show that just by pinning a very small fraction of particles, the tensile strength is increased, and also the cavitation is delayed. Furthermore, the cavitation that is expected to be spatially heterogeneous becomes spatially homogeneous by forming a large number of small cavities instead of a dominant cavity. The observed behavior is rationalized in terms of screening of plastic activity via the pinning centers, characterized by a screening length extracted from the plastic-eigenmodes. [ABSTRACT FROM AUTHOR]

In this study, functionally graded composite (FGC) was prepared using a high-energy ball mill by fabricating five layers of alumina (Al 2 O 3), titania (TiO 2), hydroxyapatite (HA), and iron oxide (Fe 3 O 4), which were sintered at 1100 °C to create an FGC sample. Scanning electron microscopy (SEM), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and weight loss measurements were used to assess bioactivity and biodegradation after immersing samples in simulated body fluid (SBF). Also, the antimicrobial activity and biocompatibility of these layers were evaluated. Furthermore, their electrical, dielectric, and mechanical properties were examined. The results revealed that all sintered layers were bioactive, and adding HA and Fe 3 O 4 enhanced this desired property. Also, S. aureus bacterial growth was inhibited by TiO 2 and Fe 3 O 4. Fortunately, the sintered layers showed no cytotoxic effect, validating the ICP findings that demonstrated acceptable biodegradation. Adding HA and Fe 3 O 4 enhanced fracture toughness in another hopeful outcome, which is crucial for biomaterial efficacy and long-term therapeutic success. Moreover, the compressive strength of all the layers and the FGC sample was 191.7, 182.2, 171.18, 159.8, 142.5, and 171.1 MPa. Layers 3, 4, and 5 notably had a compressive strength similar to cortical bone. This means that implanting these layers into human bone will protect the bone around them from stress-shielding action. Finally, the successive increase in HA/Fe 3 O 4 contents increased the electrical conductivity. Accordingly, the prepared FGC sample and its layers are attractive bone substitute materials. [ABSTRACT FROM AUTHOR]

The effects of carbon content on microstructure and mechanical properties of the (TiTaNbZrMo)C-Co cermets were investigated in details. Uniform high-entropy carbide powders with different carbon contents were obtained through carbothermal reduction and mixed with a Co binder phase via ball milling for fabricating cermets at the elevated temperature. The increased carbon content makes the hardness of cermets initially rose and then decreased, while the fracture toughness demonstrates an overall decline. Among all high-entropy ceramic based cermets, (TiTaNbZrMo)C 0.9 -Co cermet (C1) exhibited the optimal combination of hardness and fracture toughness properties, with a Vickers hardness (HV 30) of 15.83 GPa and a fracture toughness of 7.74 MPa m1/2. Furthermore, the presence of graphite phases accompanied by the excess carbon content could enhance the wear resistance of cermets. (Ti,Ta,Nb,Zr,Mo)C-Co high-entropy ceramic based cermets have potential applications in the fields of cutting tools and wear-resistant components. [ABSTRACT FROM AUTHOR]

Interface structure of ceramic matrix composite is crucial for flexural strength, fracture toughness, electromagnetic wave (EMW) absorbing properties, and oxidation resistance. This work prepared the multi-layer C-SiC interfaces in SiC f /mullite composites via a precursor infiltration-pyrolysis process (PIP) combining ball-milling dispersion. The effects of the interface thickness on the flexural strength, toughness, and EMW absorbing performance were investigated. The result shows that the SiC f /mullite with a thickness (t) of 0.32 μm C-SiC interface exhibits excellent flexural strength (154.66 MPa) and strong absorbing performance with a broad effective absorption bandwidth (EAB, RL ≤ -10 dB) covering the whole X-band. The composite with a 1.35 μm C-SiC interface significantly improves up to 32.01 MPa m1/2 in fracture toughness. The oxidation behaviors of SiC f /C-SiC/mullite under 1000 °C were also investigated by analyzing the cross-section morphology and fracture models. The C-SiC interface isolated the SiO 2 generated on the fiber from the Al 2 O 3 in the matrix. The flexural strength retention rate of the oxidized composite is 82 % when the thickness of C-SiC interface is 0.32 μm. [ABSTRACT FROM AUTHOR]

Ceramics or refractories prepared in the Al 2 O 3 -rich corner of the Al 2 O 3 -MgO-CaO system show excellent high-temperature mechanical properties and chemical stability because of the presence of spinel (MgAl 2 O 4) and calcium hexaluminate (CaAl 12 O 19). However, the densification of these two crystals usually requires high firing temperatures due to their poor sinterability. To address this issue, La 2 O 3 -doped MgAl 2 O 4 -CaAl 4 O 7 -CaAl 12 O 19 refractory composites were designed, and the influence of the doping level on the densification, microstructure, and mechanical properties of the composite was investigated. It was found that the doped La3+ was predominantly dissolved in the CA 6 grains by replacing Ca2+, forming uniform solid solutions regardless of doping concentration. This reaction significantly accelerates ion diffusion and CA 2 grain growth. Besides, it reduces the aspect ratio of CA 6 crystals, weakening the negative effect of the elongated grains on mass transfer and sintering. As a result, the relative density increases from 79.5 % to 95.1 % after sintering at 1600 °C with doping only 0.5 wt% La 2 O 3 into the composite, producing a uniform and dense microstructure with regular angular grains. The above effects result in a significant improvement in flexural strength and fracture toughness (increasing by 61 % and 57 %, respectively). Moreover, the La 2 O 3 -doped refractory composite achieves a decline of the high-temperature creep rate by one order of magnitude at 1600 °C. [ABSTRACT FROM AUTHOR]

A novel α/β SiC-(Ti, Nb)B 2 toughened (Ti, Nb)C-based composites was fabricated by reactive hot pressing with TiC, NbB 2 and Si powders at 1500 °C and 1600 °C, respectively. The influence of NbB 2 , Si content, and sintering temperature on the microstructure and mechanical properties of the composite was investigated. The intermediate product NbC reacts with Si to form NbSi 2 and β-SiC phases. With addition of 10 mol% NbB 2 , a toughening phase α-SiC was formed. During the reaction process, insufficient diffusion of Nb atoms in TiC leads to the formation of a specific "core-shell" microstructure, which improves the flexural strength of the composite ceramics. The (Ti, Nb)C has a specific crystallographic orientation relationship with NbSi 2 and α-SiC. The high-density stacking faults and ordered structures in β-SiC crystals enhances its hardness. The rod-shaped α-SiC and plate-like (Ti, Nb)B 2 by in situ reactions effectively improve the fracture toughness of the composites. TiC-32 mol% Si-10 mol% NbB 2 (raw powder composition) sintered at 1600 °C has excellent comprehensive mechanical properties, with fracture toughness, flexural strength, and Vickers hardness of 5.45 MPa·m1/2, 665 MPa, and 22 GPa, respectively, which provide a new insight into the optimization strength and toughness of TiC-based composites. In addition, under high temperature oxidation of 1000∼1200 °C, the 30NB (54 mol% TiC-16 mol% Si-30 mol% NbB 2) sample has better high-temperature oxidation resistance than the 30ZB (54 mol% TiC-16 mol% Si-30 mol% ZrB 2) sample. [ABSTRACT FROM AUTHOR]

Achieving well-balanced light weight with simultaneous improvement in mechanical and antioxidant properties of SiC-based composite polymer-derived ceramics (PDCs) for hypersonic vehicle components is still a huge challenge. Herein, lightweight SiC(rGO, x ZrB 2) composite PDCs were prepared via re-pyrolyzing ball-milling-induced ZrB 2 -SiC(rGO) p /polycarbosilane-vinyltriethoxysilane-graphene (PCS-VTES-GO, PVG) blends. Main reinforcements consist of ZrB 2 , ZrO 2 (ZrC), ZrOSi and SiO 2 /β-SiC phases, among which favorable compatibility enables enhanced bear loading performances and high-temperature oxidation resistance. Rigid SiC(rGO) p tightly links with flexible PVG pyrolysis products, and co-assembles into robust SiO x C y /C free (rGO) matrix in framework owing to plentiful Si-dangling bonds at their interfaces. More interestingly, interfacial ZrOSi/ZrC transition zone can augment structural disorder of ceramic network, give bridging effects, strengthen interfacial compatibility, and even hinder further crack propagation for self-densification. Particularly, SiC(rGO, 30% ZrB 2) composite PDCs possess optimal hardness (6.49 GPa) and outstanding fracture toughness (5.77 MPa⋅m1/2). Porous SiC(rGO, 30% ZrB 2) composite PDCs own stable structure integrity within 60-min testing under butane torch flame at 1300 °C. Self-healing protective SiO 2 -ZrO 2 glass layer avoids destructive structure and timely covers defects, thus retains good mechanical performances. Such good synergistic reinforcement and multiscale design of porosity-controlled composite, realizes integration of lightweight/good load-bearing characteristics with improved oxidation resistance for thermal protection system (TPS) of hypersonic vehicles. [Display omitted] • Lightweight SiC(rGO, x ZrB 2) composite were in-situ constructed by multiscale design. • ZrB 2 , ZrO 2 (ZrC), ZrOSi and SiO 2 /β-SiC phases synergistically reinforce ceramic network. • ZrOSi/ZrC transition zone strengthens interfacial compatibility to improve toughness. • Porous products with good anti-oxidation/thermal insulation capacities were developed. • Self-healing protective SiO 2 -ZrO 2 glass layer timely prevents further oxidation. [ABSTRACT FROM AUTHOR]

Samples of alumina – 3 % yttria-stabilized zirconia (YSZ) composites were sintered in rapid processing regimes using 24 GHz microwave heating at rates of up to 200 °C/min and zero hold time. The final relative density was 96–99 % for the samples containing 1.5 and 7.5 wt % YSZ and 98–99 % for the samples containing 13 wt % YSZ. The microwave sintering kinetics were compared for the processes carried out by direct and susceptor-assisted microwave heating. Under direct microwave heating, the effect of an intense microwave electromagnetic field with an estimated absorbed power density of up to 130 W/cm3 resulted in a shift of the shrinkage curves by about 100 °C towards lower temperatures compared to the case of susceptor-assisted heating. The grain size of the samples sintered by direct microwave heating decreased with an increasing heating rate. The mechanical properties were slightly higher for the materials sintered under susceptor-assisted microwave heating. The samples containing 13 wt % YSZ exhibited a microhardness of about 20 GPa and a fracture toughness of about 7 MPa m1/2. [ABSTRACT FROM AUTHOR]

The study addresses the limited fracture toughness of Al 2 O 3 ceramics by developing graphene-TiO 2 reinforced alumina nanocomposites through pressing. Mechanical properties, including hardness, fracture toughness, and elasticity, were examined, alongside the structural characterization via XRD analysis and microstructure evaluation using SEM. Cytotoxicity and cell adhesion tests were conducted for in vitro biological evaluation. The inclusion of a graphene additive led to a nearly threefold increase in fracture toughness, reaching up to 8.161 MPa m1/2. Graphene doping induced a discernible shift to lower angles in the XRD pattern, revealing the presence of Al 2 O 3 , Al 2 TiO 5 , and TiO 2 phases. Samples immersed in artificial body fluid for 14 days exhibited minimal ion release, with Titanium ion below 0.001 mg/L and aluminum ion below 0.05 mg/L, indicating a lack of significant ion release. The cytotoxic activity of the samples against NIH/3T3 cells was assessed through Alamar Blue analysis, revealing no significant change in cell viability after 48 h of exposure. [ABSTRACT FROM AUTHOR]

The brittleness and limited plastic deformation of ceramics restrict their applications. In this work, the effects of pristine (CNT P), functionalized (CNT OH , CNT COOH) and silanized MWCNTs on the mechanical properties of Silicon Carbide obtained by pyrolyzing polycarbosilane SMP-10 were studied. Functionalization with 3-glycidoxypropyltrimethoxy was analyzed through dispersion stability, zeta potential, and EDS analyses, revealing increased silicon content and colloidal stability in silanized MWCNTs. However, silanized MWCNTs led to reduced mechanical properties in composites, while untreated MWCNTs (CNT P , CNT OH , CNT COOH), showed a substantial increase in modulus by 74.2 %, 86.9 %, and 30.5 %, respectively. The observed enhancement in mechanical properties exceeded the outcomes predicted by the rule of mixtures, suggesting notable morphological changes induced by MWCNTs. Potential underlying factors including toughening mechanisms and changes in porosity were evaluated and discussed in depth. Composites with untreated MWCNTs showed nearly a two-fold increase in fracture toughness. This work shows a streamlined approach for the development of ceramic nanocomposites (CNCs), achieving significant improvement in mechanical properties through pyrolysis, surpassing traditional methods reliant on densification processes. These findings demonstrate the substantial potential of CNCs, enhancing their suitability for advanced engineering applications. [ABSTRACT FROM AUTHOR]

High fracture toughness and low erosion wear play key roles in improving the working reliability and service life of erosion-resistant ZTA ceramic parts (ZTA-CPs). To reconcile the hardness, fracture toughness and erosion wear resistance, the Y 2 O 3 content of ZTA-ceramics with 20 wt% ZrO 2 (Z20TA) was successfully controlled by adjusting the mass ratio of commercially available m -ZrO 2 and 3Y–ZrO 2 powders in the initial compositions in this paper. Significantly, the fracture toughness and Vickers hardness of Z20TA bulk ceramics with different Y 2 O 3 content can reach up to 5.35 MPa m1/2 and 15.82 GPa, and the erosion wear volume can be reduced to as low as 0.019 cm3, higher than those of Z20TA-ceramic parts by 5∼22 %, 12–19 % and 24–47 %, respectively. This novel Y 2 O 3 content adjustment method is feasible for the industrial level mass production of anti-erosion wear high-performance ZTA parts, promoting the industrial development and wider application of erosion-resistant ceramic parts. [ABSTRACT FROM AUTHOR]

In-situ consolidation of thermoplastic composites using Automated Fibre Placement (AFP) technology is an emerging manufacturing technique, offering tailored composite properties through customised processing parameters. Multiple competing parameters during AFP manufacturing influence the quality and mechanical performance of the laminates. These lay-up parameters are interrelated, and often require comprehensive experimental characterisation which is costly and time-intensive. This study aims to optimise the fracture toughness of in-situ consolidated thermoplastic composite (AS4/APC-2) and investigate the mechanisms that contribute to it. Taguchi's method is employed to efficiently analyse the effect of various process parameters at multiple levels. Based on the obtained results, a considerable effect of process parameters on Mode I and II fracture toughness is observed. The statistical analysis reveals that the Hot Gas Torch (HGT) temperature required for AFP processing significantly affects the Mode I fracture toughness, contributing to 33.8%. Whereas, the consolidation force, another key processing parameter in AFP notably affects Mode II fracture toughness, with the contribution of 81.8%. The analysis of variance (ANOVA) reveals interdependent processing parameter relations for both fracture modes. A validation test showed good agreement between the predicted fracture toughness and the experimental test. [ABSTRACT FROM AUTHOR]

Functionally Gradient cemented carbides (FGCCs) are promising substrates for polycrystalline diamond composite (PDC). Carburization is the mainstream method for preparing FGCCs, but limited carburizing depth often leads to excessive retention of brittle low-carbon phase (η phase) in the core. This study used Powder Extrusion 3D Printing (PEP) to create dual-layered cemented carbide parts with varying thicknesses of low-carbon outer layers. After pre-sintering and carburization, three new FGCCs were produced. Results showed the η phase was confined to the interface region before carburization. With 3.84 mm carbon-depleted layer, the maximum η phase thickness was 1/10 compared to homogeneous FGCCs, with Co gradient of about 4.5 wt%. The two FGCCs with thinner low-carbon layers had smaller Co gradient with no detected η phase. Additionally, the novel FGCCs displayed enhanced fracture toughness in the core. This study achieved controlled η phase distribution, offering new insights for fabricating high-toughness carburized FGCCs without the η phase. [ABSTRACT FROM AUTHOR]

Material extrusion (ME) 3D printing is an emerging technology to fabricate short carbon fiber reinforced SiC ceramic matrix composites (C sf /SiC CMCs) with highly oriented short carbon fibers. In this study, the C sf /SiC CMCs were fabricated by ME 3D printing combined with the following precursor infiltration and pyrolysis (PIP). The short carbon fibers could be well kept after the PIP process. The effects of solid loading and fiber content on the microstructure and mechanical properties of the C sf /SiC CMCs were also investigated. Higher solid loading was beneficial for obtaining the denser C sf /SiC CMCs with more oriented fibers. The introduction of short carbon fibers brought more pores. The bending strength and fracture toughness of C sf /SiC CMCs first increased and then decreased with the increase in fiber content. The pulling-out and breakage of short carbon fibers contributed to the improvement of mechanical properties. High performance C sf /SiC CMCs with a bending strength of 212.74 MPa and fracture toughness of 5.84 MPa m1/2 were simultaneously achieved when the solid content was 50 vol% and the fiber content was 20 vol%. It is believed that this study can provide some understanding of the 3D printing of fiber reinforced CMCs. [ABSTRACT FROM AUTHOR]

Borides are promising wear-resistant materials. The mechanical and tribological properties of ZrB 2 , (Ta, Zr)B 2 , (Ta, Zr, Ti)B 2 , (Ta, Zr, Ti, V)B 2 and (Ta, Zr, Ti, V, Hf)B 2 synthesized by spark plasma sintering were compared to examine the elemental dependence. The results indicated that the hardness and fracture toughness of borides increased with the increase of entropy. (Ta, Zr, Ti, V, Hf)B 2 obtained the highest hardness and fracture toughness of 23.14 GPa and 5.13 Mpa·m1/2 due to the pores and second phases that change the path of crack propagation. In terms of wear, all the Ta-contained borides have a lower wear rate than that of ZrB 2. It is almost one order of magnitude lower for (Ta, Zr, Ti, V, Hf)B 2 than that of ZrB 2. This is mainly due to the formation and action of tribofilm rich of amorphous Ta 2 O 5. Thermodynamic calculation indicates that the Ta atoms in borides are more prone to being oxidized resulting in the formation of a layer of Ta 2 O 5 on the surface, which is beneficial to wear resistance improvement. This work provides guidelines for the composition-design of high-entropy borides for wear-resistant material applications. [ABSTRACT FROM AUTHOR]

Direct ink writing (DIW) offers significant advantages for efficient manufacturing of complex ceramic composite components. However, the mechanical properties of short carbon fiber-reinforced ceramic composites fabricated by DIW technology were not ideal, mainly be ascribed to the absence of a suitable coating on the fiber as an interface. In this work, C sf /ZrB 2 green bodies were printed by an optimized extrusion process using pyrolytic carbon-coated short carbon fibers (C sf). High-performance C sf /ZrB 2 –SiC composites were obtained through the infiltration and pyrolysis of SiC precursor six times. With increasing C sf content, the dimensional deviations decreased and the mechanical properties increased. When the C sf content was 30 vol%, the dimensional deviation of the C sf /ZrB 2 –SiC composite was less than −0.5 % in the X and Y directions and about −2 % in the Z direction. A marked increase in the flexural strength and fracture toughness of the composite was also obtained, reaching 275.0 MPa and 5.26 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

Hafnium-based ceramic with low thermal expansion is suitable for thermal and environmental barrier coating materials. However, the fracture toughness is relatively low. In this work, GdAlO 3 is doped into Gd 2 Hf 2 O 7 , increasing the fracture toughness by 31 %. The increase originates from crack deflecting, crack branching and more tortuous crack route. Meanwhile, GdAlO 3 -Gd 2 Hf 2 O 7 has lower thermal expansion, making it more compatible with environmental barrier coating systems. The thermal conductivity increases from Gd 2 Hf 2 O 7 to GdAlO 3 -Gd 2 Hf 2 O 7 , which can be expected to reduce by controlling the content of GdAlO 3. [ABSTRACT FROM AUTHOR]

Highlights Carbon fiber‐reinforced cyanate ester resin matrix composites (CF/CE) are widely used in aerospace for their high‐temperature resistance and wave‐absorbing properties. However, CF/CE is prone to interlaminar delamination during the curing molding process or practical applications due to the brittleness of CE resin. In this study, we use polyether sulfone (PES) as a toughening layer through the inter‐tow toughening method to prepare PES inter‐tow toughened CF/CE (CF/CE‐P) and to investigate their thermal, mechanical, and microscopic morphology. We find that CF/CE‐P has a higher glass transition temperature (Tg) and a lower coefficient of thermal expansion (CTE) than those of CF/CE composites. The flexural strength, flexural modulus, interlaminar shear strength (ILSS), and impact toughness of CF/CE‐P with 15 wt% PES is increased by 34%, 15%, 34%, and 45%, respectively, compared to CF/CE. In addition, the mode I interlaminar fracture toughness (GIC) of CF/CE‐P with 15 wt% PES is 1.86 times that of CF/CE. The inter‐tow toughening technique on a three‐dimensional scale is proposed. Model I interlaminar fracture toughness increased by 86% after inter‐tow toughness modification carbon fiber‐reinforced cyanate ester resin matrix composites. The composite material exhibits improved toughness and thermal performance. The prepreg preparation process is suitable for continuous industrial production. [ABSTRACT FROM AUTHOR]

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Human skin is essential for perception, encompassing haptic, thermal, proprioceptive, and pain-sensing functions through ion movement. Additionally, it is mechanically resilient and self-healing for protection. Inspired by these unique properties, researchers have attempted to develop stretchable, self-healing sensors based on ion dynamics. However, most self-healing sensors reported to date suffer from low fracture strength and toughness. In this work, we present an ion-based self-healing electronic skin with exceptionally high fracture strength and toughness. We enhanced self-healing polymers and ionic conductors by introducing two types of orthogonal dynamic crosslinking bonds: dynamic aromatic disulfide bonds and 2-ureido-4-pyrimidone moieties. These dynamic bonds provide autonomous self-healing and high mechanical toughness even in the presence of ionic liquids. As a result, our self-healing polymer and self-healing ionic conductor exhibit remarkable stretchability (700%, 850%), fracture strength (34 MPa, 30 MPa), and toughness (78.5 MJ/m3, 87.3 MJ/m3), the highest values reported among self-healing ionic conductors to date. Using our materials, we developed various fully self-healing sensors and a soft gripper capable of autonomously recovering from mechanical damage. By integrating these components, we created a comprehensive self-healing electronic skin suitable for soft robotics applications. Stretchable and self-healing sensors based on ion dynamics usually suffer from low fracture strength and toughness. Here, the authors describe an ion-based self-healing electronic skin with autonomous self-healing, high mechanical toughness and fracture strength. [ABSTRACT FROM AUTHOR]

The aim of this investigation is to assess the impact of using nano‐silica (Na) at varying weight percentages of 0%, 1.5%, 3%, 4.5%, and 6% as partial cement substitute on fracture parameters of recycled aggregate concrete (RAC). A servo‐controlled testing system was employed to carry out three‐point flexure tests on 90 notched beams. Boundary effect method was used in order to interpret the fracture features. The results illustrate that adding Na increases the size‐independent fracture energy, fracture toughness and initial fracture energy of RAC by 29%, 32%, and 24% compared to that without Na, respectively. The maximum values of these parameters occur at 4.5% Na. The reference crack length (α∞*$$ {\alpha}_{\infty}^{\ast } $$) decreases from 6% to 22% by adding 1.5% to 6% Na. This shows that the RAC gets more brittle by the addition of Na. Moreover, the RAC behavior moves towards linear elastic fracture mechanics criteria by adding Na. Finally, according to the mechanical properties and test variables, multivariable models were suggested for prediction of the fracture parameters of the RAC containing Na. The models predictions were compared with experimental findings of the previous research. [ABSTRACT FROM AUTHOR]

Highlights Composite materials provide an alternative to conventional structural materials. Sandwich composites show high bending strength and superior strength‐to‐weight ratio. The major drawback in sandwich composites is debonding of skin from core, that causes failure of a component during the usage at different loads. To overcome this issue, the current work identifies a solution of introducing nylon screws (M6 × 32) to adhere firmly the skins consisting of glass fibers with PET (Polyethylene Terephthalate) core. The sandwich composites were fabricated by vacuum infusion process. Two flat sandwich composites were fabricated; one with nylon screws placed perpendicular to the skin and the other a plain sandwich composite. Mechanical characteristics of the specimens such as fracture toughness, flexural strength and shear strength were studied. Specimens with nylon screws showed 21.78% more fracture toughness compared to plain specimen. The presence of screws acts as hindrance to the propagation of cracks in the interfacial region resulting in the enhancement of debonding resistance of the specimens. Also, sandwich specimens with nylon screws exhibited 136% and 142% improvement in flexural and shear strength respectively when compared to plain sandwich specimens. The investigation of scanning electron microscope (SEM) images of tested specimens indicates strong interfacial bonding between skin and the core of specimens with nylon screws. Introduction of light‐weight nylon screws in z‐direction enhanced the bonding between face sheets and foam core. Sandwich composites with nylon screws exhibited superior bending and shear strength compared to plain specimens. Crack propagation in the interfacial region is restricted by the presence of nylon screws. Investigation of fractured specimens indicated a strong interfacial bonding in the specimens with screws. [ABSTRACT FROM AUTHOR]

ABSTRACT Rock masses in alpine regions inevitably undergo freeze–thaw (F–T) cycles, which affects the safety of infrastructure such as slopes, with shear failure being a significant concern. This study investigates the Mode II fracture behavior of F–T treated granite via the short core in compression (SCC) test, analyzing the related physical properties and mechanical properties while also discussing F–T damage mechanism at a microscopic level. Results reveal that as F–T cycles increase, the dynamic elastic modulus and P‐wave velocity decrease, whereas porosity and backbone fractal dimension of pore scale increase, indicating a transition towards a large‐scale pore. Mode II fracture toughness decreased by 31.19% and fracture process zone width increased by 248.49% with F–T cycles rising from 0 to 80, and related fractal dimension of surface morphology also increased by 11.17%. Microscopic observation reveals the microstructure deterioration induced by F–T treatment, indicating the correlation between microscopic damage and macroscopic fracture properties. [ABSTRACT FROM AUTHOR]

Highlights In this study, to improve the interlayer fracture toughness of carbon fiber reinforced polymer (CFRP) composites, polyethersulfone (PES)/carbon nanotubes (CNTs)/graphene oxide (GO) hybrid films were prepared by wet phase transition method based on a total of seven different ratios of CNTs and GO, 0:5, 1:4, 2:3, 1:1, 3:2, 4:1, and 0:5 (with a total concentration of 1 wt%). The optimal toughening system of hybrid particles mixed with thermoplastic resin films for CFRP composites was investigated by the double cantilever beam test and end notched flexure test. The results showed that when 20 wt% of PES was added to the film and the ratios of CNTs to GO were 3:2 and 2:3, respectively, the Mode I and II fracture toughness of the laminates were significantly enhanced. Compared with the original specimens, the increases were 123.66% and 204.55%, respectively. In addition, CNTs/GO = 3:2 had the best enhancement effect on the Mode I test, increasing by 111.84%, filling the gap in the effect of low temperature environment on the interlayer fracture performance of high‐performance composites. Finally, a scanning electron microscope was used to observe the microstructure of the fracture surface and analyze the toughening mechanism. Seven hybrid films with different ratios were prepared. The superiority of film for enhancing the fracture toughness was verified. Fills the gap in the interlayer toughness of samples at low temperature. [ABSTRACT FROM AUTHOR]

Porosity is a critical microstructural factor in ceramic materials, influencing their mechanical and thermal properties. However, the detailed mechanisms through which porosity, grain size, and grain boundary fracture energy affect the thermal shock resistance of porous ceramics are still not fully understood. This study introduces a dual‐scale model that integrates these microstructural parameters to predict fracture toughness and thermal shock resistance. Using the single‐edge V‐notch fracture toughness testing principle, we calculate the thermal stress intensity factor and establish its relationship with temperature differentials. The critical temperature differential, which marks the onset of thermal shock damage, is determined when the thermal stress intensity factor reaches the fracture toughness threshold. The model reveals a significant interplay between porosity, grain size, and grain boundary fracture energy, with fine‐grained ceramics (grain size < 10 µm) showing a sharp decrease in fracture toughness as porosity increases, while coarser‐grained ceramics are less affected by porosity. These findings provide a deeper understanding of the microstructural optimization needed to enhance the thermal shock resistance of high‐performance porous ceramics. [ABSTRACT FROM AUTHOR]

The development of vat photopolymerization (VPP) 3D printing technology has created the conditions for the fabrication of complex structured Si3N4 ceramics. However, Si3N4 ceramics produced through VPP often lack sufficient mechanical properties, which limiting their applications. This study introduces short carbon fibers (Cf) into the VPP‐Si3N4 ceramics, combined with the polymer infiltration and pyrolysis (PIP) process, to prepare Cf/Si3N4 composites. The effect of Cf content on slurry preparation, green part printing, and mechanical properties of the Cf/Si3N4 composites was systematically investigated. The results indicate that Cf significantly enhances the mechanical properties of Cf/Si3N4 composites. At 6 wt.% Cf content, the samples exhibit the highest strength and fracture toughness, reaching 183.2 MPa and 6.2 MPa·m1/2, respectively, representing increases of 29.7% and 92.3% compared to samples without Cf. The improvement in mechanical properties is partly due to the ‘pinning effect’ of Cf, which enhances interlayer bonding strength in the printed green parts, positively impacting the overall mechanical properties of the composites. Additionally, inherent toughening mechanisms of Cf, such as fiber pull‐out, crack deflection, and crack bridging, further enhance the composite's mechanical properties. This study confirms the feasibility of using Cf to enhance the mechanical properties of VPP‐Si3N4 ceramic. [ABSTRACT FROM AUTHOR]

The influence of hydrogen on the fracture of X65 was studied. The fracture toughness in air was 369 MPa√m. The ASTM-valid fracture toughness with cathodic hydrogen charging was lower but was similar for these charging conditions 189 MPa√m and 181 MPa√m at 9 mA/cm2; 192 MPa√m and 179 MPa√m at 16 mA/cm2; and 177 MPa√m at 25 mA/cm2; even though the fractography changed from (i) ductile fracture by microvoid coalescence in air and at 9 mA/cm2 to (ii) more brittle fracture for hydrogen charging at 16 mA/cm2 and 25 mA/cm2, with flat facets and secondary cracks, which increased with increasing current density. • The influence of hydrogen on the fracture of X65 was studied. • The fracture toughness in air was 369 MPa√m. • The ASTM-valid fracture toughness with cathodic hydrogen charging was lower. • The fracture toughness with hydrogen was 152–186 MPa√m. • The fractography changed from ductile fracture to more brittle fracture with increasing hydrogen. [ABSTRACT FROM AUTHOR]

ZrB 2 –SiC–Si 3 N 4w ceramics (ZSN w) were prepared via the hot-pressing sintering method. The bending strength and fracture toughness of ZSN w at room temperature reached to 520 ± 24 MPa and 5.2 ± 0.16 MPa m1/2, respectively. The enhancement in mechanical properties is attributed to the grain refinement and attenuation of grain boundary induced by the homogeneous distribution of Si 3 N 4 whiskers. The oxidation resistance of ZSN w were conducted at 1500 °C in an air atmosphere. Remarkably, after 10 h of oxidation, ZSN w remained excellent strength and toughness reaching at 589 ± 26 MPa and 4.8 ± 0.12 MPa m1/2, respectively. This oxidation resistance of ZSN w was mainly attributed to the gain refinement induced by Si 3 N 4 whiskers, which effectively reduced the voids within the ceramic matrix. Therefore, this process promoted the densification and homogenization of the SiO 2 protective barriers, accompanied with hindering the inward permeation of oxygen and the outward release of oxides. [ABSTRACT FROM AUTHOR]

Hydrothermal degradation deteriorates the fracture toughness and strength of tetragonal stabilised zirconia. The phase transformation to the monoclinic phase is particularly critical for materials with lower stabiliser content such as 2 mol% and 3 mol% yttria stabilised zirconia (2YSZ and 3YSZ). In this work, two routes in two-step sintering and co-doping with calcium oxide are analysed to mitigate the degradation. Both strategies show a reduction in average grain size of the 2YSZ while maintaining a comparable densification. The achieved smaller grains suppress the hydrothermal degradation rates. In addition, a mitigating effect beyond the reduction in grain size of YSZ is found for CaO doping. 1.6 mol% CaO co-doped 2YSZ shows less than 4% of monoclinic phase after 50 h in an autoclave with H 2 O at 134 °C. Pure 2YSZ contrarily reaches 100% monoclinic phase after 20 h at the same conditions. A suppression of degradation by CaO doping was also observed for the composite of nickel oxide and 3 mol% yttria stabilised zirconia. Hence, CaO co-doping can be an interesting strategy to increase resistivity against hydrothermal degradation for both biomedical and renewable energy applications. The findings further outline a route to achieve tetragonal YSZ with lower yttria contents than 2 mol%. • Two approaches were analysed to mitigate hydrothermal degradation in 2YSZ and 3YSZ. • Co-doping with CaO and two-step sintering reduced the grain growth and degradation. • CaO co-doping mitigated the degradation beyond the effect of the grain size. • A complete suppression of degradation was achieved by the addition of 1.6 mol% CaO. • The results show a route to ageing-resistant tetragonal YSZ with lower yttria contents. [ABSTRACT FROM AUTHOR]

To enhance the density of SiC and improve the purity of the SiC, carbon is frequently used as a sintering additive. SiC ceramics were prepared in this study by using various carbon sources (graphitic carbon microsphere, carbon black, and flake graphite) combined with B 4 C through spark plasma sintering (SPS) at temperatures ranging from 1800 °C to 1900 °C. Among the above carbon sources, the graphitic carbon microspheres were created by hydrothermal carbonization combined with catalytic graphitization. The influence of the carbon sources on the phase compositions, microstructure, physical properties, and oxidation resistance of the SiC specimens was investigated. The findings revealed that the SiC specimens prepared with graphitic carbon microsphere had a smaller crystallite size than those prepared with other kinds of carbon. The SiC specimens prepared with graphitic carbon microsphere displayed high relative density, hardness, fracture toughness, and remarkable oxidation resistance. This was attributed to the lower oxygen content, better dispersion, and higher chemical reactivity of graphitic carbon spheres. In terms of the oxidation resistance of SiC specimens, factors such as purity (residual carbon) and porosity were found to have a more significant impact than grain size. In general, the use of carbon sources with high reactivity and good dispersion is an effective method in preparing SiC ceramics. [ABSTRACT FROM AUTHOR]

Nowdays, the demand for high-power laser lighting applications is on the rise, however, phosphor in glass (PiG) prepared using conventional glass systems often experience damage under intense laser irradiation. To tackle this issue, we introduce a novel LAS glass system for phosphor encapsulation to create PiG, and by utilizing a spray coating technique, we blend PiG with high thermal conductivity sapphire to obtain phosphor in glass film (PiF), effectively improving laser irradiation resilience and optical characteristics. In this study, a novel LAS glass system (SiO 2 –Li 2 CO 3 –MgO–Al 2 O 3 –CaO–P 2 O 5 –K 2 O–ZrO 2 –Na 2 O) was utilized to encapsulate Ce:GdYAG phosphors to prepare a series of PiG and PiF. The glass system exhibits multi-directional interlocking lithium disilicate crystals, significantly enhancing the glass's strength and fracture toughness. There is no apparent interface reaction between the glass system and the phosphors, indicating effective protection of the phosphor particles. The PiF sample demonstrates a minor decrease of 5.2 % in internal quantum efficiency compared to the original phosphor, while boasting a high thermal conductivity of 7.4 W m−1 K−1. Notably, the optimized PiF shows remarkable enhancements with a saturation threshold of 4.37 W mm−2, surpassing PiG (1.668 W mm−2), and achieving LF max of 424.41 lm and LE max of 147.16 lm W−1. It features a high color rendering index (CRI) of 68.7 and low color correlated temperature (CCT) of 3646 K, significantly improving laser irradiation resistance and optical quality, making it a promising warm yellow laser illumination converter for diverse lighting applications. [ABSTRACT FROM AUTHOR]

SiC whiskers (SiC w)-reinforced α/β-SiAlON ceramic tool materials were synthesized via spark plasma sintering (SPS). A comprehensive study was conducted on densification mechanism, phase composition, microstructure, mechanical properties, and wear resistance of the SiC w /α/β-SiAlON composites. The results indicated that SiC w constrained the densification process and impeded the growth of SiAlON grains, and the introduction of SiC w significantly enhanced mechanical properties of the α/β-SiAlON ceramic. The composite containing 28 wt% SiC w synthesized at 1700 °C showed well mechanical properties, with a density of 3.35 g/cm³, Vickers hardness of 19.38 ± 0.33 GPa, and fracture toughness of 7.35 ± 0.27 MPa m1/2.The principal toughening mechanisms of SiC w /α/β-SiAlON included crack deflection, branching, bridging, as well as transgranular fracture and whisker pullout. The addition of SiC w improved the wear resistance of α/β-SiAlON ceramic. Compared to those without whiskers, the wear volume and wear rate were decreased by 38.8 %. [ABSTRACT FROM AUTHOR]

Understanding the damage evolution of thermal barrier coatings (TBCs) is crucial for optimizing TBCs systems and predicting service lifetime. This study investigates the correlation between mechanical properties and the thermal cycle lifetime of TBCs with conventional air plasma sprayed (APS) and micro-agglomerated particles embedded (EMAP) plasma sprayed structures, utilizing the Gd 2 Zr 2 O 7 (GZO) and GSc 0.075 Ce 0.3 Z (GSCZ) material systems. The damage evolution and cracking behavior of TBCs with varying material compositions and coating structures are evaluated using a combination of three-point bending tests and digital image correlation (DIC) techniques. Experimental results demonstrate that the thermal cycling lifetime of conventional APS TBCs correlates positively with the fracture toughness of the ceramic layer. Specifically, the conventional APS GSCZ coating with a fracture toughness of 1.12 MPa/m1/2 and the APS GZO coating with a fracture toughness of 0.97 MPa/m1/2 exhibit lifetimes of 34 cycles and 31 cycles, respectively. Moreover, the EMAP structural design exhibits notable advantages in enhancing the thermal cycle lifetime of TBCs across all material systems. DIC results confirm that strain accumulation during interface cracking of EMAP TBCs is effectively mitigated compared to conventional APS TBCs. The loose and porous characteristics of this structure significantly improve the compliance and interface fracture toughness of the TBC system, thereby alleviating TBC failure dominated by interface cracking. [ABSTRACT FROM AUTHOR]

High entropy (Y 0.2 Gd 0.2 Lu 0.2 Sc 0.2 Tm 0.2) 2 O 3 transparent ceramics with a single phase of cubic structure were prepared for the first time via vacuum sintering using ZrO 2 as sintering aid. In addition, the content of ZrO 2 was optimized and the investigated systematically. The Zr4+ ions in sintering aid replaced RE3+ sites and produced interstitial oxygen, promoted densification of the ceramics, and inhibited growth of grains. The relative density was increased to 99.79 % from 96.91 %. The grain size reduced from 34.25 μm to 5.68 μm. Due to the higher relative density and smaller grain size, (Y 0.2 Gd 0.2 Lu 0.2 Sc 0.2 Tm 0.2) 2 O 3 transparent ceramics with 1 wt% ZrO 2 had better optical and mechanical properties. The transmittance is better than 75 % at the region of 2–7 μm and reached 80.9 % at 5.43 μm, and the hardness and fracture toughness were 9.179 ± 0.062 GPa and 0.805 ± 0.024 MPa m1/2, respectively. This high-entropy transparent ceramics has potential applications in medium wave atmospheric windows (3–5 μm). [ABSTRACT FROM AUTHOR]

In this study, high entropy (Ti 0.6 ,W 0.1 ,Mo 0.1 ,Nb 0.1 ,Ta 0.1)(C 0.78 ,N 0.22) ceramics (HECN) powders were synthesized by carbothermal reduction nitridation. (100-x) HECN-(x/2) Co-(x/2) Ni (x = 5–25 wt%) cermet was prepared by vacuum sintering. The relationship between microstructure and mechanical properties of HECN-based cermet sintered at 1450 °C and 1500 °C was studied. The results show that the second phase (W,Mo,Ti) 3+x (Co, Ni) 3−x C appears at both sintering temperatures, and its content decreases with the increase of binder Co, Ni content and sintering temperature; At the same time, the grain size of the hard phase of the cermet grows with the increase of Co and Ni content. In terms of mechanical properties, at both sintering temperatures, the cermet showed a decrease in hardness and an increase in fracture toughness with the increase of Co and Ni content, while the bending strength increased and then decreased. Among them, when the content of Co and Ni is 20 wt%, the bending strength of HECN-based cermet sintered at 1450 °C is the best, and the bending strength reaches 1640 MPa. This is attributed to the combined influence of many elements in high entropy cermet, which on the one hand leads to serious lattice distortion; On the other hand, improving the wettability and density of the cermet has a strengthening effect on the cermet. In addition, with the increase in Co and Ni content, the plastic deformation of the bond phase will inhibit crack propagation. The main paths are crack deflection and crack bridging, which increase the energy required for crack propagation and lead to a gradual increase in fracture toughness. [ABSTRACT FROM AUTHOR]

Poor fracture toughness and calcium–magnesium–aluminum–silicate (CMAS) corrosion resistance adversely affect environmental barrier coatings (EBCs) during prolonged service. Herein, an in-situ nanostructured Lu 2 O 3 /Lu 2 SiO 5 composite EBC was successfully prepared using nanostructured Lu 2 SiO 5 feedstocks. The morphologies and phase structures of the Lu 2 SiO 5 feedstocks and the corresponding coating were thoroughly characterized. Additionally, the mechanism of the in suit reaction of the Lu 2 O 3 /Lu 2 SiO 5 composite EBC was examined. The results indicate that the nanostructured as-deposited EBC exhibits a bimodal and dual-phase structure. The nanostructured Lu 2 SiO 5 coating comprises melted lamellae and unmelted or partially melted particles. The phase structure of these unmelted or partially melted particles includes Lu 2 O 3 and X2-Lu 2 SiO 5. The Lu 2 O 3 nanoparticles are formed by the decomposition of Lu 2 SiO 5 during spraying, and their content can be controlled to <15 %, which can enhance the fracture toughness and CMAS corrosion resistance of the EBCs to some extent. [ABSTRACT FROM AUTHOR]

The current study investigates the effects of powder homogenization on the characteristics of polycrystalline diamond (PCD) sintered with molybdenum (Mo) at high pressure-high temperature (HPHT). PCD combines excellent properties, such as high hardness, wear resistance, and good thermal conductivity. Furthermore, it has greater fracture toughness when compared to a single-crystal diamond, which makes it suitable as a cutting tool. The properties of PCD, however, are sensitive to the preparation conditions, which include the particle size of the initial powders, contaminants, and dispersion of the binder phase. Bearing this in mind, in order to study the effects of the preparation conditions on the properties of PCD, the blends were homogenized by a manual method, such as High-Energy Ball Mills (HEBM), at different times: 30s, 60s, and 90s. Data regarding micromorphology, phase transformations, resulting residual stresses, and thermostability were determined. According to the results, the blends prepared by HEBM showed superior phase dispersion, greater effectiveness in the formation of molybdenum carbides, and good densification. The thermoanalytical data showed that composites with superior thermal performance to commercial PCD were obtained, with thermostability between 802 °C and 837 °C. [ABSTRACT FROM AUTHOR]

Highly robust ceramics materials are promising materials for applications in the automobile, aerospace, and ceramic cutting tool industries. However, conventional ceramics are typically brittle, which limits their suitability for advanced applications. In this study, with zeolite imidazolium salt skeleton-8 (ZIF-8) as a carbon source, discharge plasma sintering is used to create carbon nanonetworks derived from metal-organic frameworks (MOFs) in situ on the grain boundaries of zirconia-toughened alumina (ZTA) ceramic. ZTA exhibits maximum bending strength (719 ± 20.5 MPa) and fracture toughness (7.91 ± 0.7 MPa m1/2) at MOF concentrations of 1.0 wt% and 2.0 wt%, respectively, which are 1.37 and 1.88 times higher than that of the unmodified sample. This demonstrates that the MOF-derived carbon nanonetworks significantly improve the mechanical properties of the ceramic. The finite element analysis results indicate that the carbon nanonetworks can effectively disperse the stress inside the material and transfer the concentrated stress from the internal defects to the two-phase grain boundary on the surface of the sample, thereby contributing to strengthening and toughening. Overall, this work validates that the in situ production of carbon nanonetworks from MOFs is an effective strategy to enhance the mechanical properties of ZTA ceramics. Moreover, it offers new approaches for reinforcing and toughening other ceramic materials. [ABSTRACT FROM AUTHOR]

Materials scientists have taken a learn-from-nature approach to study the structure-property relationships of natural materials. Here we introduce a nature-inspired composite architecture showing a hierarchical assembly of granular-like building blocks with specific topological textures. The structural complexity of the resulting architecture is advanced by applying the concept of grain orientation internally to each building block to induce a tailored crack resistance. Hexagonal grain-shaped building blocks are filled with parallel-oriented filament bundles, and these function as stiff-blocks with high anisotropy due to the embedded fiber reinforcements. Process-induced interfacial voids, which provide preferential crack paths, are strategically integrated with cracks to improve fracture toughness at the macroscopic scale. This study discusses the structural effects of the local/global orientations, stacking sequences, feature sizes, and gradient assemblies of granular blocks on crack tolerance behavior. Alternating stacking sequences induce cracks propagating in the arrestor direction, which boost the fracture energy up to 2.4 times higher than the same layup stacking sequence. Gradient arrangements of feature sizes from coarse to fine or fine to coarse result in the coexistence of stiffness and toughness. Our approach to applying crystallographic concepts to complex composite architectures inspires for original models of fracture mechanics. Authors demonstrate crack control of 3D printed composite architectures by leveraging crystallographic concepts of filament orientation in macroscale 'grains', enhancing structural complexity. [ABSTRACT FROM AUTHOR]

This paper utilizes the Wohler curve and the J-integral principle to predict the service life of purposely-damaged acrylonitrile butadiene styrene (ABS) specimens. The hardness of single- and double-notched specimens was measured using the J-integral, facilitating a comparison between two different types of defects. By analyzing the Wohler curve, we were able to examine the decline in the service life of the ABS specimens over various time intervals. According to the comparison, a hole with a single internal notch flaw is not as detrimental as one with two notch defects. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effects of incorporating the 0–20 wt% tetrapod-shaped zinc oxide (tZnO) whiskers on the mechanical, antibacterial, and cytotoxic properties exhibited by experimental dual-cure resin composites. Commercially obtained tZnO whiskers underwent surface modification using 3-methacryloxypropyltrimethoxysilane (γ-MPS). Subsequently, four groups of resin composites containing 0, 5, 10, and 20 wt% silanized tZnO along with barium borosilicate glass (BaBSG) fillers were fabricated while maintaining total filler loading at 60 wt%. Mechanical properties were examined utilizing specimens produced adhering to ISO 4049:2019 guidelines where applicable. Depth of cure was quantified immediately, while three-point flexural strength, flexural modulus, fracture toughness, Vickers hardness, compressive strength, and diametral tensile strength were assessed after 24 h of storage in 37 °C distilled water. Planktonic bacteria of Streptococcus mutans (S. mutans) were cultured and tested for antibacterial activity using disk diffusion and microbial anti-adhesion assays. Cytotoxicity was examined by preparing extracts from specimens in a cell culture medium and exposing stem cells from human exfoliated deciduous teeth (SHED) to serial dilutions of these extracts, then assessing cell viability and survival using CCK-8 assay and live/dead staining. Elevating tZnO loading yielded significant reductions in depth of cure, compressive (from 296.4 to 254.6 MPa), and diametral tensile strength (from 42.7 to 31.0 MPa), while flexural strength (91.3–94.1 MPa), flexural modulus (6.4–6.6 GPa), fracture toughness (0.96–1.04 MPa·m0.5), and Vickers hardness (36.5–37.4 kgf·mm−2) remained the same. Composites integrating tZnO displayed markedly enhanced antibacterial activity against S. mutans , based on anti-adhesion tests and live/dead staining. No cytotoxicity was observed for SHED treated with extracts from resin composites possessing up to 20 wt% tZnO whiskers. This study demonstrates that incorporating up to 20 wt% silanized tZnO in place of traditional barium glass particles appreciably enhances dual-cure resin composite antibacterial function against S. mutans without compromising mechanical properties. [ABSTRACT FROM AUTHOR]

The anisotropic fracture characteristics of oil shale are crucial in determining reservoir modification parameters and pyrolysis efficiency during in situ oil shale pyrolysis. Therefore, understanding the mechanisms through which temperature and bedding planes influence the fracture behavior of oil shale is vital for advancing the industrialization of in situ pyrolysis technology. In this study, scanning electron microscopy (SEM), CT scanning, and a real-time high-temperature rock fracture toughness testing system were utilized to investigate the spatiotemporal evolution of pores and fractures in oil shale across a temperature range of 20–600 °C, as well as the corresponding evolution of fracture behavior. The results revealed the following: (1) At ambient temperature, oil shale primarily contains inorganic pores and fractures, with sizes ranging from 50 to 140 nm. In the low-temperature range (20–200 °C), heating primarily causes the inward closure of inorganic pores and the expansion of inorganic fractures along bedding planes. In the medium-temperature range (200–400 °C), organic pores and fractures begin to form at around 300 °C, and after 400 °C, the number of organic fractures increases significantly, predominantly along bedding planes. In the high-temperature range (400–600 °C), the number, size, and connectivity of matrix pores and fractures increase markedly with rising temperature, and clay minerals exhibit adhesion, forming vesicle-like structures. (2) At room temperature, fracture toughness is highest in the Arrester direction (KIC-Arr), followed by the Divider direction (KIC-Div), and lowest in the Short-Transverse direction (KIC-Shor). As the temperature increases from 20 °C to 600 °C, both KIC-Arr and KIC-Div initially decrease before increasing, reaching their minimum values at 400 °C and 500 °C, respectively, while KIC-Shor decreases continuously as the temperature increases. (3) The energy required for prefabricated cracks to propagate to failure in all three directions reaches a minimum at 100 °C. Beyond 100 °C, the absorbed energy for crack propagation along the Divider and Short-Transverse directions continues to increase, whereas for cracks propagating in the Arrester direction, the absorbed energy exhibits a 'W-shaped' pattern, with troughs at 100 °C and 400 °C. These findings provide essential data for reservoir modification during in situ oil shale pyrolysis. [ABSTRACT FROM AUTHOR]

Fracture tests are a necessary means to obtain the fracture properties of concrete, which are crucial material parameters for the fracture analysis of concrete structures. This study aims to fill the gap of insufficient test results on the fracture toughness of widely used ordinary C40~C60 concrete. A three-point bending fracture test was conducted on 28 plain concrete and 6 reinforced concrete single-edge notched beam specimens with various depths of prefabricated notches. The results are reported, including the failure pattern, crack initiation load, peak load, and complete load versus crack mouth opening displacement curves. The cracking load showed significant variation due to differences in notch prefabrication and aggregate distribution, while the peak load decreased nonlinearly with an increase in the notch-to-height ratio. The reinforced concrete beams showed a significantly higher peak load than the plain concrete beams, attributed to the restraint of steel reinforcement, but the measured cracking load was comparable. A compliance versus notch-to-height ratio curve was derived for future applications, such as estimating crack length in crack growth rate tests. Finally, fracture toughness was determined based on the double-K fracture model and the boundary effect model. The average fracture toughness value for C50 concrete from this study was 2.0 M P a · m , slightly smaller than that of lower-strength concrete, indicating the strength and ductility dependency of concrete fracture toughness. The fracture toughness calculated from the two models is consistent, and both methods employ a closed-form solution and are practical to use. The derived fracture toughness was insensitive to the discrete parameters in the boundary effect model. The insights gained from this study significantly contribute to our understanding of the fracture toughness properties of ordinary structural concrete, highlighting its potential to shape future studies and applications in the field. [ABSTRACT FROM AUTHOR]

The development of dental materials needs to be supported with sound evidence. This in vitro study aimed to measure the fracture toughness of a short fibre-reinforced composite (sFRC), at differing thicknesses. In this study, 2 mm, 3 mm and 4 mm depths of sFRC were prepared. Using ISO4049, each preparation was tested to failure. A total of 60 samples were tested: 10 samples for each combination of sFRC and depth. Fractured samples were viewed, and outcomes were analysed. EXF showed greater toughness than EXP, with a mean of 2.49 (95%CI: 2.25, 2.73) MPa.m1/2 compared to a mean of 2.13 (95%CI: 1.95, 2.31) MPa.m1/2, (F(1,54) = 21.28; p < 0.001). This difference was particularly pronounced at 2 mm depths where the mean (95%CI) values were 2.72 (2.49, 2.95) for EXF and 1.90 (1.78, 2.02) for EXP (Interaction F(2,54) = 7.93; p < 0.001). Both materials performed similarly at the depths of 3 mm and 4 mm. The results for both materials were within the accepted fracture toughness values of dentine of 1.79–3.08 MPa.m1/2. Analysis showed crack deflection and bridging fibre behaviour. The optimal thickness at the cavity base for EXF was 2 mm and for EXP 4 mm. Crack deflection and bridging behaviour indicated that restorations incorporating sFRCs are not prone to catastrophic failure and confirmed that sFRCs have similar fracture toughness to dentine. sFRCs could be a suitable biomimetic material to replace dentine. [ABSTRACT FROM AUTHOR]

A dense monolithic SiC/(Hf0.25Ta0.25Zr0.25Nb0.25)C/C high-entropy ceramic nanocomposite was prepared using a polymer-derived ceramic (PDC) method combined with spark plasma sintering (SPS). The microstructural evolution and mechanical properties of the obtained nanocomposites were characterized by X-ray diffractometer (XRD), transmission electron microscope (TEM), scanning-electron microscope (SEM), and nanoindentation. The results indicate that the phase composition of SiC/(Hf0.25Ta0.25Zr0.25Nb0.25)C/C can be adjusted by modifying the metal content of the single-source precursor (SSP) through molecular design. The resulting precursor exhibits an exceptionally high ceramic yield, with mass retention of over 90% at 1100 °C, which guarantees the densification of the final SiC/(Hf0.25Ta0.25Zr0.25Nb0.25)C/C composites. The PDC route facilitates the in situ formation of a high-entropy phase within the ceramic matrix under low temperature pyrolysis conditions. Combined with SPS, a dense monolithic SiC/(Hf0.25Ta0.25Zr0.25Nb0.25)C/C nanocomposite was obtained, exhibiting an open porosity of 0.41 vol%, nano-hardness of 27.47 ± 0.46 GPa, elastic modulus of 324.00 ± 13.60 GPa, and fracture toughness of 3.59 ± 0.24 MPa·m0.5, demonstrating excellent mechanical properties. [ABSTRACT FROM AUTHOR]

A novel TiB2-CeO2-modified (Nb,Mo,Cr,W)Si2 coating was prepared on a Nb-5W-2Mo-1Zr alloy substrate using two-step slurry sintering and halide-activated pack cementation to address the limitations of a single NbSi2 coating in meeting the service requirements of niobium alloys at elevated temperatures. At 1700 °C, the static oxidation life of the coating exceeded 20 h, thus indicating excellent high-temperature oxidation resistance. This was due to the formation of a TiO2-SiO2-Cr2O3 composite oxide film on the coating surface, which, due to low oxygen permeability, effectively prevented the inward infiltration of oxygen. Additionally, the dense structure of the composite coating further enhanced this protective effect. The composite coating was able to withstand over 1600 thermal shock cycles from room temperature to 1700 °C, and its excellent thermal shock performance could be attributed to the formation of MoSi2, CrSi2, and WSi2 from elements such as Mo, Cr, and W, which were added during modification. In addition to adjusting the difference in thermal expansion coefficients between the layers of composite coatings to reduce the thermal stress generated by thermal shock cycles, the formation of silicide compounds also improved the overall fracture toughness of the coating and thereby improved its thermal shock resistance. [ABSTRACT FROM AUTHOR]