Crack Bridging Research Articles

Microstructure and mechanical properties of cellular (Ti,M)(C,N)-based cermets fabricated by pre-granulation and subsequent vacuum sintering

Cellular (Ti,M)(C,N)-based cermets were fabricated through pre-granulation followed by vacuum sintering. In this study, (Ti,Mo)(C,N) and (Ti,W,Ta)(C,N) solid solutions were utilized as hard phase components in agglomerates. The effects of the (Ti,M)(C,N) powders on the microstructure and mechanical properties of cellular cermets were studied. Cermet A, incorporating (Ti,Mo)(C,N) in the agglomerates, exhibited a cellular microstructure with double-layered agglomerates distributed in the matrix. By contrast, cermet B, which included (Ti,W,Ta)(C,N) in the agglomerates, exhibited a notable contrast between the agglomerates containing irregular elongated grains and the matrix. The mechanical properties of the cellular cermets were analyzed comprehensively in conjunction with the fractal dimension. Compared with cermet A, cermet B exhibited more transgranular fractures within the matrix, with dimples and tearing ridges visible in the agglomerates. Additionally, increased crack deflection, bridging, and bifurcation were observed near the interface, considerably impeding crack propagation. Overall, cermet A with significantly refined grains demonstrated higher hardness and TRS. The fracture morphology and crack propagation in cermet B were more complex and layered, resulting in the enhanced fracture toughness.

Bond behavior between highly ductile fiber-reinforced concrete (HDC) and deformed rebar under repeated and post-repeated monotonic loading

This paper tested nine groups of six specimens each to investigate the bond behavior between deformed steel reinforcing bars and highly ductile fiber-reinforced concrete (HDC) under repeated and post-repeated monotonic loading considering different compressive strengths, flexural toughnesses, fiber volume contents and cover thicknesses. The results indicate that fiber bridging of cracks allowed the bonds in the HDC specimens to exhibit more ductile failure mode and greater energy dissipation capacity than those in conventional concrete. Furthermore, an increase in compressive strength or cover thickness improved the bond strength, whereas excessive flexural toughness was detrimental to further improvement in the bond strength and energy dissipation capacity. Finally, the residual bond strength increased by 95.03 % as the fiber volume content increased from 1 % to 2 %. Specimens with insufficient flexural toughness and cover thickness exhibited the deterioration in their bond strength and residual bond strength, with the former degrading more than the latter. After repeated loading, the stiffness of the primary ascending branch of the monotonic bond stress–slip curve significantly increased, whereas that of descending branch generally decreased. These results were applied to derive an equation for the bond strength between deformed bars and the HDC in which they are embedded under post-repeated monotonic loading.

Delamination bridging response of Z‐pins under mixed mode loading: The influence of carbon and Kevlar Z‐pins

AbstractThis paper presents the effect of varying the type of Z‐pin on the delamination bridging performance of unidirectional composite laminates. Carbon and Kevlar Z‐pins were inserted in thick composite laminates using the pre‐hole insertion Z‐pinning process and their bridging performance characterized across the different mode‐mixity range. The bridging response indicated that Kevlar Z‐pin experienced load reduction driven by interfacial friction (Stage III), which was absent in the Carbon Z‐pin. When Mode II dominated the bridging crack, Kevlar Z‐pin showed partial pullout and fiber shear cracking, while the Carbon Z‐pin exhibited clean transverse fracture. Although the bridging load obtained by the Carbon Z‐pin was twice that of Kevlar Z‐pin, the Kevlar Z‐pin provided a higher interlaminar fracture energy. The superior bridging performance of Kevlar Z‐pin is correlated with the enhanced ductility. Moreover, the resin‐rich area was involved in deformation and provided the extra axial load of Z‐pin.Highlights The comparison of mixed‐mode bridging mechanism between Kevlar Z‐pin and Carbon Z‐pin. Reveal the variation of multi‐directional load and energy consumption with mixed‐mode angle in thick laminates. Detailed scanning electron microscope observation to understand failure characteristics of ductile Z‐pin. Evidence that the extra axial load of Z‐pin provided by resin‐rich area.

The effect of fibers addition on the microstructure and mechanical properties of ZrO2 fibers toughened Al2O3/ZrO2 (Y2O3) solidified ceramics

Fiber toughening is considered an effective way to strengthen the toughness of traditional sintered ceramics. Herein, ZrO2 fibers toughened Al2O3/ZrO2 (Y2O3) directionally solidified eutectic ceramics (DSECs) were prepared with the high-frequency induction heating zone melting (IHZM). The effects of ZrO2 fibers content on the phase composition, microstructure, and mechanical properties of the eutectic ceramics were studied. The findings revealed that DSEC consists of α-Al2O3 and ZrO2 phases, presents a typical colony microstructure. The phase spacing in the colony decreased with the addition of fibers, reaching a minimum value of 1.99 ± 0.25 μm at 20 wt%, which was nearly 40 % lower than that without the fiber’s addition. The hardness of DSEC increased gradually with the addition of fibers. Its highest value reaches 18.42 ± 0.55 GPa when the fiber content is 20 %. The fracture toughness of DSEC first increased and then decreased, reaching a maximum of 5.43 ± 0.22 MPa·m1/2 at 10 wt%, which was 1.5 times higher than that of the fibers-free eutectic ceramic. The improvement of fracture toughness was primarily due to the fibers toughening. In addition, the crack deflection, pinning, bridging, and branching had a significant inhibitory effect on the crack propagation.

Fracture Resistance and Failure Mode of Polyethylene Fiber-reinforced Resin-based Restorations in Structurally Compromised Premolars: an in Vitro Study.

To evaluate the effect of polyethylene fiber-reinforcement on the fracture resistance and fracture mode of extensive resin-based composite (RBC) restorations in structurally compromised maxillary premolars. Maxillary premolars (54) with specific dimensions and extracted for orthodontic reasons were used. Following mesio-occluso-distal (MOD) cavity preparation and endodontic access, teeth were randomly assigned to one of three restorative protocols (n=18): RBC applied incrementally (I) or reinforced with woven polyethylene fibers (Ribbond) placed horizontally (H) or U-shaped (U). Restored teeth were stored for 45 days in distilled water at 37°C and then loaded monotonically until fracture. Half of the specimens in each group received axial loading (A) and the other half was loaded paraxially (PA). Fracture load data was assessed using two-way analysis of variance and Tukey's post hoc test for multiple comparisons (α=0.05). The fracture initiation and propagation path were analyzed using stereomicroscopy and scanning-electron microscopy. No significant differences were observed for the fracture strength among loading configurations, except for groups IA (825 N) and HA (553 N). Fracture initiated and propagated mainly at and through the RBC restoration in the I group, whereas a shift to the interface was observed in both polyethylene fiber-reinforced groups. Blocking and bridging of cracks were identified around the fibers, especially in specimens of group U. Incorporation of woven polyethylene fibers to reinforce extensive MOD resin-based composite restorations on endodontically treated premolars reduced the occurrence of cohesive fractures in the restorative material but was unable to increase the fracture resistance of the affected teeth.

Mechanical Properties of Silicon Carbide Composites Reinforced with Reduced Graphene Oxide.

This article presents research on the influence of reduced graphene oxide on the mechanical properties of silicon carbide matrix composites sintered with the use of the Spark Plasma Sintering method. The produced sinters were subjected to a three-point bending test. An increase in flexural strength was observed, which reaches a maximum value of 503.8 MPa for SiC-2 wt.% rGO composite in comparison to 323 MPa for the reference SiC sample. The hardness of composites decreases with the increase in rGO content down to 1475 HV10, which is correlated with density results. Measured fracture toughness values are burdened with a high standard deviation due to the presence of rGO agglomerates. The KIC reaches values in the range of 3.22-3.82 MPa*m1/2. Three main mechanisms responsible for the increase in the fracture toughness of composites were identified: bridging, deflecting, and branching of cracks. Obtained results show that reduced graphene oxide can be used as a reinforcing phase to the SiC matrix, with an especially visible impact on flexural strength.

Enhancing Flexural Behavior of Reinforced Concrete Beams Strengthened with Basalt Fiber-Reinforced Polymer Sheets Using Carbon Nanotube-Modified Epoxy.

The external bonding (EB) of fiber-reinforced polymer (FRP) is a usual flexural reinforcement method. When using the technique, premature debonding failure still remains a factor of concern. The effect of incorporating multi-wall carbon nanotubes (MWCNTs) in epoxy resin on the flexural behavior of reinforced concrete (RC) beams strengthened with basalt fiber-reinforced polymer (BFRP) sheets was investigated through four-point bending beam tests. Experimental results indicated that the flexural behavior was significantly improved by the MWCNT-modified epoxy. The BFRP sheets bonded by the MWCNT-modified epoxy more effectively mitigated the debonding failure of BFRP sheets and constrained crack development as well as enhanced the ductility and flexural stiffness of strengthened beams. When the beam was reinforced with two-layer BFRP sheets, the yielding load, ultimate load, ultimate deflection, post-yielded flexural stiffness, energy absorption capacity and deflection ductility of beams strengthened using MWCNT-modified epoxy increased by 7.4%, 8.3%, 18.2%, 22.6%, 29.1% and 14.3%, respectively, in comparison to the beam strengthened using pure epoxy. It could be seen in scanning electron microscopy (SEM) images that the MWCNTs could penetrate into concrete and their pull-out and crack bridging consumed more energy, which remarkably enhanced the flexural behavior of the strengthened beams. Finally, an analytical model was proposed for calculating characteristic loads and characteristic deflections of RC beams strengthened with FRP sheets, which indicated a reasonably good correlation with the experimental results.

Enhanced fracture toughness of high entropy boride by adding SiC

The effect of SiC content (10 vol%, 20 vol% and 30 vol%) and sintering temperature (1800 °C, 1900 °C and 2000 °C) on the microstructure and mechanical properties of high entropy boride-silicon carbide (HEB-SiC) composites were systematically investigated in this work. The densification was gradually increased with the increase of SiC content and sintering temperature. More specially, the densification of HEB-30 vol% SiC composite obtained at 2000 °C was as high as 99.1 %. As for the mechanical properties, the dense HEB-30S-2000 composite possessed the highest fracture toughness (5.24 MPa m1/2) and Vickers hardness (28.5 GPa). The above significantly enhanced fracture toughness was closely pertained to the fracture modes adjusting. In details, after the addition of SiC, the branching and bridging of crack, the rupture of large SiC grain, and the deflection of crack existing near the HBE matrix and SiC particles jointly promote the improvement of fracture toughness. Besides, the Vickers hardness increased linearly with the relative density increasing. A simplified equation was established, which could effectually reflect the linear connection between the Vicker hardness and relative density (SiC content) of HEB-SiC composites. It will certainly play an important guiding role in the further development of HEB-SiC composites.

Hot-pressing-oriented graphene in Si3N4 composites for enhanced electromagnetic wave absorption in X and Ku bands

In this study, the oriented graphene within graphene/Si3N4 composites was successfully achieved by two-step hot-press sintering. Microstructure analysis revealed that the graphene sheets were well dispersed in the Si3N4 matrix and oriented perpendicular to the applied stress. The composites exhibited effective electromagnetic wave (EMW) absorption capabilities and good mechanical properties. The effective absorption bandwidth (EAB) was 9.63 GHz, nearly covering the entire X and Ku bands (8.2–18 GHz), and the minimum reflect loss (RL) was −24.23 dB when the graphene content reached 7 wt% at a thickness of 2.02 mm. Meanwhile, the oriented graphene/Si3N4 composites demonstrated a bending strength of 576.66 MPa and a fracture toughness of 8.40 MPa·m1/2. The EMW absorption in these composites should be primarily due to polarization relaxation loss and conductivity loss, and the toughening mechanism should involve the graphene pull-out, crack bridging, and crack deflection. The graphene/Si3N4 composites have a promising application in structurally integrated functional materials.

Study of damage evolution in 316L stainless steel composite enamel coatings by in situ scanning electron microscopy and acoustic emissions analyses

Ceramics and glass ceramics are used in many demanding applications due to their exceptional properties including wear resistance, thermal stability, and corrosion resistance. However, sizable efforts are spent to improve their low fracture toughness, by, for example, modification of microstructure, and fiber-reinforcement. The addition of metallic particles also represents a well-known approach to solve this issue. Metal-reinforced glass-ceramics also emerge as a potential solution providing the desirable ability of crack bridging and absorption of energy by ductile deformation. This concept was in this study applied to the production of novel composite enamel coatings with different amount of 316L stainless steel flakes. This study aims to evaluate the steel-enamel composite coatings’ mechanical properties, using flexural tests and in-situ techniques. Acoustic Emission is introduced as a valuable method to monitor damage evolution and the quantitative results are compared to combined SEM in-situ flexural tests carried out on the same samples. The addition of stainless-steel flakes resulted to effectively counteract the nucleation and propagation of cracks and the AE technique was demonstrated to be a first-choice method for assessing the mechanical properties of composite enamel coatings.

Morphology Control and Mechanism of Different Bath Systems in Cu/SiCw Composite Electroplating.

With the rapid development of electronic technology and large-scale integrated circuit devices, it is very important to develop thermal management materials with high thermal conductivity. Silicon carbide whisker-reinforced copper matrix (Cu/SiCw) composites are considered to be one of the best candidates for future electronic device radiators. However, at present, most of these materials are produced by high-temperature and high-pressure processes, which are expensive and prone to interfacial reactions. To explore the plating solution system suitable for SiCw and Cu composite electroplating, we tried two different Cu-based plating solutions, namely a Systek UVF 100 plating solution of the copper sulfate (CuSO4) system and a Through Silicon Via (TSV) plating solution of the copper methanesulfonate (Cu(CH3SO3)2) system. In this paper, Cu/SiCw composites were prepared by composite electrodeposition. The morphology of the coating under two different plating liquid systems was compared, and the mechanism of formation of the different morphologies was analyzed. The results show that when the concentration of SiCw in the bath is 1.2 g/L, the surface of the Cu/SiCw composite coating prepared by the CuSO4 bath has more whiskers with irregular distribution and the coating is very smooth, but there are pores at the junction of the whiskers and Cu. There are a large number of irregularly distributed whiskers on the surface of the Cu/SiCw composite coating prepared with the copper methanesulfonate (Cu(CH3SO3)2) system. The surface of the composite is flat, and Cu grows along the whisker structure. The whisker and Cu form a good combination, and there is no pore in the cross-section of the coating. The observation at the cross-section also reveals some characteristics of the toughening mechanism of SiCw, including crack deflection, bridging and whisker pull-out. The existence of these mechanisms indicates that SiCw plays a toughening role in the composites. A suitable plating solution system was selected for the preparation of high-performance Cu/SiCw thermal management materials with the composite electrodeposition process.

The anomalous crack growth behaviour of an elastic-brittle octet-truss architected solid

Strongly rising R-curves are observed for octet-truss architected material specimens comprising ∼1 million unit cells and made from an elastic-brittle parent material. The measurements are supported by finite element (FE) calculations where the octet-truss is modelled discretely and show that the pseudo-ductility is not related to the usual toughening mechanisms such as crack bridging or crack-tip plasticity. Rather, the toughening is attributed to the three-dimensional (3D) structure of the octet-truss specimen: remarkably, no R-curve effect is observed in a quasi two-dimensional (2D) octet-truss specimen. This anomalous behaviour is clarified via FE calculations of the indentation stiffness of the octet-truss which reveal a strong indentation size effect in 3D with the stiffness decreasing with decreasing indenter size relative to the cell size of the octet-truss. In the 3D octet-truss, the size independent continuum stiffness is only attained for indenter sizes greater than about 20 unit cells while the size effect is almost absent in the quasi-2D octet-truss. The strong elastic softening in the 3D octet-truss in the presence of strain gradients gives rise to a large elastic crack-tip process zone. This in turn implies that a specimen geometry independent fracture toughness (i.e., a material property) can only be measured in specimens with large numbers of unit cells. We report a fracture mechanism map that reveals that measurements of specimen geometry independent fracture toughness can only be made in specimens with more than ∼10 million unit cells. This map is also used to rationalise the measured rising R-curves in the 3D specimens with ∼ 1 million unit cells. We end with a discussion on the implication of these findings for the laboratory measurement of the fracture toughness of both architected materials as well as biological cellular materials such as bone.

Effect of densification technology on the microstructure and mechanical properties of high-entropy (Ti, Zr, Hf, Nb, Ta)C ceramic-based cermets

High-entropy ceramic-based cermets represent a new and promising direction in improving the mechanical properties of conventional hardmetals through the formation of complex microstructures during synthesis. This has been systematically studied in two Co-free, high-entropy (Ti,Zr,Hf,Nb,Ta)C ceramic-based cermets using 10 wt% Ni and 10 wt% FeCrAl metallic binders during hot-press and spark plasma sintering. Fully densified microstructures were achieved in the temperature range of 1400–1500 °C, which is below the melting points of the pure Ni and FeCrAl alloy, owing to the liquid-phase assisted sintering. The optimal densification routes resulted in Vickers hardness (HV30) of 16.77 ± 0.72 and 18.32 ± 0.99 GPa, and fracture toughness (KIc_SENB) of 5.31 ± 0.41 and 4.83 ± 0.50 MPa m0.5, respectively for the Ni and FeCrAl bonded cermets. The improved damage tolerance of these cermets compared to the base (Ti,Zr,Hf,Nb,Ta)C high-entropy carbide is related to the reduced grain size and microstructural toughening mechanisms (e.g. crack deflection and bridging).

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

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

Pixel-level concrete bridge crack detection using Convolutional Neural Networks, gabor filters, and attention mechanisms

Cracks are prominent defects that significantly impact concrete bridges' structural safety and serviceability assessments. The conventional manual bridge inspection is often limited by multiple challenges related to the heavy workload of data processing and the subjective judgment of inspectors. Several vision-based methods, from traditional image processing techniques to segmentation deep learning models, have been employed for pixel-level crack detection to detect cracks in various scenes and surfaces automatically. The present paper proposes an end-to-end framework for crack segmentation combining UNet, Gabor filters, and Convolutional Block Attention Modules leveraging the complementary strengths of both spatial and frequency domains to enhance crack feature extraction and mitigate the impact of image disturbances. The designed network is trained and evaluated on a multi-source annotated crack dataset established by the authors to expose the model to multiple instances of crack appearance and background complexity and enhance its generalization ability. The proposed model achieves an Intersection over Union (IoU) of 60.62 % and an F1-score of 74.49 %, outperforming benchmark segmentation networks. Experimental results demonstrate the effectiveness of cross-domain feature fusion and multi-source data utilization in segmenting cracks with diverse patterns and background interference scenarios.

Design of an explicit crack bridging constitutive model for engineered cementitious composites using polyvinyl alcohol (PVA) or polyethylene (PE) fiber

This paper aims to establish an explicit crack bridging model that can link engineered cementitious composites (ECC) behavior from single fiber to single crack scale, which is great of designing ECC featuring pseudo tensile strain hardening and multiple cracks expanding by tailoring microstructure and materials selection. In this study, fiber bridging stress was divided into three parts including fiber bridging stress with no rupture, fiber debonding fracture stress, and fiber pullout fracture stress. Subsequently, the fundamental crack bridging model was emerged when fiber bridging stress with no rupture subtracted from the fiber rupture stress in debonding and pullout stage. Moreover, two-way pullout and Cook-Gordon effect were also considered to establish the complete model. It was found that the two-way pullout situation of polyvinyl alcohol (PVA) fiber has a significant influence on the crack opening width due to its slip hardening property, while the Cook-Gordon effect presents a faint crack width increment for PVA-ECC. However, the Cook-Gordon effect makes a significant contribution to the crack opening width of the composite produced by polyethylene (PE). This building intelligible model presents a better prediction for ECC through the comparison of experimental data or real average crack width in previous models, thus confirming the validity of this model.

Tough and Ductile Architected Nacre‐Like Cementitious Composites

AbstractEnhancing fracture toughness and ductility of brittle materials such as concrete remains a challenge. Nature offers numerous mechanisms to enhance fracture toughness using purposeful designs of materials’ architecture. Natural nacre exhibits high fracture toughness by promoting inelastic deformation and hierarchical toughening mechanisms. Here, “nacre‐like‐separated” and “nacre‐like‐grooved” cementitious composites inspired by brick‐and‐mortar arrangement of mollusk shells are proposed. These nacre‐like composites are engineered by laser processing cement paste into individual tablets and grooved patterns (as intentional defects) and laminating them with limited amounts of suitable elastomeric (polyvinyl siloxane) interlayers. It is found that interlayer deformation, tortuous crack propagation guided by the defects, and crack bridging are the main toughening mechanisms in these composites that lead to rising resistance curves. The study hypothesizes tablet sliding as an additional toughening mechanism in “nacre‐like‐separated”, preventing tablet failure and leading to the postponed onset of bulk composite failure. These mechanisms significantly enhance both fracture toughness and ductility by 17.1 and 19 folds, compared to constituent hardened cement paste, respectively. By engineering laser‐induced defects into tabulated cementitious‐elastomeric material at meso‐scale, a class of tough and ductile cementitious composites is introduced, resulting in significantly high fracture toughness values (73.68 MPa.mm1/2), comparable to Ultra‐high‐performance‐concrete without sacrificing the strength.

Effect of glass beads on the tensile and impact properties of polyurethane bark glue

ABSTRACT This study investigates the mechanical properties of Polyurethane Bark Gum (PBG) reinforced with Solid Glass Beads (SGBs) of varying diameters and content. The tensile analysis demonstrates that a 1% SGB volume fraction maximizes tensile stress and fracture elongation due to synergic composite effects, with smaller SGBs enhancing interfacial adhesion and reducing microcrack formation. The impact analysis revealed that the addition of SGB reduced the impact strength due to interface delamination and energy dissipation mechanisms, with optimal impact resistance observed at a particle size of 0.4–0.6 mm and a content of 5%. Morphological characterization was conducted using optical microscopy, scanning electron microscopy, and synchrotron radiation CT scanning techniques, highlighting the role of SGB in toughening, crack bridging, and stress shielding. This study provides insights into the performance of PBG/SGB composite materials and guides the material design for specific applications.

Fracture Behavior and Mechanism of Nb-Si-Based Alloys with Heterogeneous Layered Structure.

Novel Nb-Si-based alloys with heterogeneous layers that have the same composition (Nb-16 at.%Si) but different phase morphologies were designed in this work. Heterogeneous layered structure (HLS) was successfully fabricated in Nb-16Si alloys by layering composite powders after various degrees of mechanical alloying (6 h, 12 h, 18 h, and 24 h) alternately and subsequent spark plasma sintering (SPS). The influence of HLS on the fracture behavior at both room and elevated temperature was investigated via single-edge notched bending (SENB) and high-temperature compression, respectively. The results show that the diversified HLS is obtained by combining hard layers containing fine equiaxed crystals and/or soft ones with coarse lamellar niobium solid solution (Nbss). By affecting the crack propagation in SENB, HLS is favorable for improving the fracture toughness and exhibits a significant increase compared with the corresponding homogenous microstructure. Moreover, for the same HLS, a more excellent performance is achieved when the initial crack is located in the soft layer and extended across the interface to the hard one through crack bridging, crack deflection, crack branching, and shielding effect. Fracture starts in the soft layer (from powders of ball-milled for 12 h) of a 12-24 alloy, and a maximum KQ value (14.89 MPa·mm1/2) is consequently obtained, which is 33.8% higher than that of the homogeneous Nb-16Si alloy. Furthermore, the heterogeneous layered alloys display superior high-temperature compression strength, which is attributable to the dislocation multiplication and fine-grained structure. The proposed strategy in this study offers a promising route for fabricating Nb-Si-based alloys with optimized and improved mechanical properties to meet practical applications.

Enhanced fracture toughness of Ti2AlNb/Ti6Al4V layered metal composite

Drawing inspiration from the intricacies of nacre structure, Ti2AlNb/Ti6Al4V layered metal composite was fabricated by vacuum hot pressing and achieved high fracture toughness. The fracture toughness of the composite registers at 48.5 MPa∙m1/2, surpassing the theoretical fracture toughness calculated based on the rule of mixture (ROM) and exhibiting 54 % improvement compared toTi2AlNb alloy. The introduction of a layered configuration imparts complex crack propagation pathways to the composite. The occurrences of crack deflection, crack bridging, crack passivation, and interface delamination serve to increase the resistance to crack propagation. Moreover, the plastic deformation of the ductile Ti6Al4V layer and the large plastic zone size of the crack tip can release the stress concentration and delay the fracture of the composite. This understanding not only advances our comprehension of the toughening mechanisms but also has practical implications for the application and development of layered Ti2AlNb alloys.