Toughness Enhancement Research Articles

Effects of Different Austenitizing Times on the Microstructure and Properties of Cr‐Ni‐Mo‐V Series High‐Strength Steels

Herein, the effects of varying austenitizing times on the microstructure and mechanical properties of Cr‐Ni‐Mo‐V series high‐strength steel are investigated, discussing the mechanisms that enhance strength and toughness. By controlling the austenitizing duration, the microstructure during subsequent heat treatments is improved, leading to enhanced overall mechanical properties. The experimental steel undergoes treatments at different austenitizing times, and the microstructure is characterized using optical microscopy, energy‐dispersive spectroscopy, field emission scanning electron microscopy, and X‐ray diffraction. Mechanical properties are assessed through tensile testing, impact testing, and microhardness measurements. The results indicate that, when comparing an austenitizing time of 1 to 1 h and 15 min, the ultimate tensile strength decreases by 10%, microhardness reduces by 78.2 HV, elongation increases by 1.39 times, and toughness improves by 80%. The enhancement in toughness is primarily attributed to the synergistic effect of tempered martensite and bainite within the microstructure. Fracture morphology analysis reveals that variations in austenitizing time affect carbide distribution, accelerate carbide dissolution, decrease the crack growth zone, and enhance toughness. This study provides valuable insights for designing Cr‐Ni‐Mo‐V series high‐strength steels with optimal strength‐toughness synergies.

Coherent Interface Migration Toughens Diamond

AbstractOvercoming the hardness‐toughness trade‐off in diamonds attracts much interest in physics, chemistry, materials science, and engineering. Recently synthesized nanotwinned diamond composite exhibits massive enhancement in fracture toughness without sacrificing its unprecedented Vickers hardness [Y. Yue et al., Nature 582, 370 (2020)]. Several mechanisms for the toughness enhancement are unveiled based on the edge‐cracked models while the mechanism from Vickers indentation has remained elusive. Here, the energy of nanotwinned diamonds, diamond polytypes, and diamond composites is systematically investigated from Vickers indentation simulation. The results show diamond structures dissipate energy by interface migration, accompanied by the phase transformation from diamond polytypes to the cubic diamond (3C diamond). By tuning the density and distribution of interfaces, the dissipated energy of the diamond is increased to more than twice that of a single‐crystal 3C diamond. This work complements the established mechanisms and provides a universal strategy for toughening diamonds and related materials.

Ultratough, Robustness, and Reprocessable Thermoset Epoxy Resins Synergistically Enhanced by Hierarchical Coordination Interactions and Dynamic Covalent Networks

AbstractEpoxy resins, ubiquitous and indispensable thermosetting material in various industries, suffer from the resistance to crack initiation, poor ductility, and irreparable permanent cross‐linked network, which hinder their utilization in high‐performance applications and are detrimental to the development of a sustainable economy. However, achieving the trade‐off between toughness, robustness, and reprocessability of epoxy resins remains a formidable challenge. Herein, an epoxy resin that combines ultratoughness, robustness, and reprocessability by incorporating a hierarchical crosslink structure embedded in a transesterification network is reported. The construction of hierarchical coordination structures facilitates formation of dense nano‐hard domains, enabling enhancement of both strength and toughness at multilength scales. As a result, the epoxy resin, integrating covalent adaptable networks with sacrificial non‐covalent networks, exhibits exceptional elongation at break (280%), modulus (1.8 GPa), stress at break (56.3 MPa), and tensile toughness (142 MJ m−3), showcasing its excellent endurance and ability to undergo multiple reprocessability. The application of this epoxy resin in carbon fiber‐reinforced polymer composites further underscores its potential as the resulting HCEV‐CFRPs exhibit unprecedented tensile properties and facilitate multiple non‐destructive recycling of high‐value carbon fiber under mild conditions. This research provides novel design principles for recyclable and high‐performance materials that combine strength and toughness.

Efficient sealing of cemented sheath: An oil-responsive self-healing latex with toughness enhancement for cement composites

The integrity of the cemented sheath is important to the safe exploration of oil and gas resources. Sealing failure of cement sheath will result in formation fluid channeling and pressure carryover in the annulus. The both toughening and oil-responsive self-healing latex (TOS) was prepared to achieve efficient sealing of cemented sheath, and prolong its service life. The structure and oil swelling behavior of TOS, its toughening and self-healing effects on hardened cement paste (HCP) were analyzed by comprehensive characterizations. Results demonstrated that TOS possessed excellent stability and an oil swelling rate of 1235 %. Cement specimens by curing 28d containing 8 % TOS exhibited a 27.8 % increase in flexural strength, a 48.7 % reduction in elasticity modulus and a 33.8 % reduction in brittleness coefficient. The addition of TOS can effectively improve the toughness of cement. The average pore size of specimens containing 8 % TOS admixture decreased to 9.17 nm. This indicates that TOS enhanced the structural density of cement materials. The crack about 103μm in the cracking specimens with 8 % TOS was almost healed, and the corresponding permeability was reduced 99.1 % after curing in oil. Adsorption and film formation of TOS can resist the cracking of cement sheath, and the oil swelling expansion of film in cement matrix can repair the cracked structure.

Indentation Fracture Toughness of Aluminium-Graphite Composites: Influence of Nano-particles

In the field of composite materials, extensive research has been undertaken on aluminum-graphite composites. However, a research gap has been identified regarding the specific influence of nano-sized graphite particles on their fracture toughness. Previous studies have predominantly focused on larger graphite particles or different reinforcement materials, resulting in relatively unexplored effects of nano-graphite particles. This research is deemed critical as it has the potential to generate lightweight, high-strength materials, aligning with the demands of aerospace, automotive, and structural engineering. The primary objective of this study is to investigate how the inclusion of nano-sized graphite particles affects the fracture toughness of aluminum-graphite composites. To achieve this objective, systematic dispersion and incorporation of nano-sized graphite particles into an aluminum matrix will be carried out. Mechanical testing, including fracture toughness assessments, will be conducted to evaluate the performance of the composite materials. Factors such as particle size, distribution, volume fraction, and interfacial bonding will also be characterized within the study. It is anticipated that the presence of nano-sized graphite particles will lead to a significant enhancement of the fracture toughness of the aluminum-graphite nanocomposites. This enhancement is expected to be attributed to crack deflection, tortuosity, altered stress distribution, and increased plastic deformation around cracks.

Fracture characteristics and microscopic mechanism of slag-based marine geopolymer mortar prepared with seawater and sea-sand

This study utilized seawater, sea sand, and ternary solid waste to produce marine geopolymer mortar (MGM). 23 groups of MGM samples with varying alkali content and basalt fiber (BF) and polypropylene fiber (PPF) volume fractions, as well as marine cement mortar (MCM), were tested for fracture characteristics. Three initial crack length ratios (a0/h) (0.2, 0.3, and 0.4) were designed. The analysis included load-crack mouth opening displacement (P-CMOD) curves for all specimens, focusing on critical crack length (ac), critical crack tip opening displacement (CTODc), fracture toughness (KSIC), fracture energy (GF), and facture brittleness index (FBI). Results indicated that increasing alkali content enhanced strength and elastic modulus, peak fracture load, critical crack extension length (Δac), and CTODc, while decreasing final CMOD. This was attributed to the increased alkali content, which enhanced the mortar’s density. However, excessive alkali content also led to increased shrinkage damage within the matrix, making it prone to stress concentrations and resulting in brittle failure. Based on the research, it is recommended that the alkali content be controlled within the range of 4–5 %. Hybrid fibers showed superior overall toughness enhancement, increasing KSIC, GF, and FBI by 54.3 %, 95.6 %, and 427.4 %, respectively. This improvement was due to the synergistic effect of BF and PPF, which increased the specimen’s elastic modulus, reduced crack propagation speed, and sustained load-bearing capacity during the later stages of crack development. The fracture toughness of conventional geopolymer mortar was positively correlated with the Ca/Si ratio and was lower than that of MGM. In contrast, MGM’s Ca/Si ratio showed an inverse correlation with KSIC, indicating that phase assemblage governs the fracture resistance of MGM. This is because Cl- in seawater intensified geopolymerization reactions. Interwoven gel structures in MGM, with surface depositions like magnesium aluminosilicate hydrate (M-A-S-H), magnesium silicate hydrate (M-S-H), and silica gel, filled pores, and improved homogeneity, resulting in its superior fracture toughness over conventional geopolymer mortar.

A novel water‐based mechanochemical approach for surface modification of graphene platelets and their epoxy nanocomposites

AbstractGraphene (nano) platelets (GPs) are cost‐effective and possess high structural integrity, but their limited surface functional groups hinder their compatibility with polymers. In this study, an eco‐friendly, water‐based mechanochemical approach was developed to modify GPs with polyacrylamide (PAM), creating PAM graphene platelets (PAM‐GPs) with a grafting ratio of approximately 15%. The platelet was measured to be a few nanometers in thickness, and the grafted PAM provides abundant functional groups, including amide groups, which enhance compatibility with polymers. A typical polymer, bisphenol‐A epoxy, was compounded with PAM‐GPs, resulting in a high degree of exfoliation and dispersion of PAM‐GPs within the matrix. The resulting epoxy/PAM‐GP composites exhibited significantly improved mechanical properties, including an 18% increase in Young's modulus and a substantial enhancement in fracture toughness, with a 71% increase at a low filler fraction of 0.5 wt%. These improvements are attributed to the effective interfacial interaction between the PAM‐GPs and the epoxy matrix, facilitated by the grafted functional groups. This study highlights the potential of PAM‐GPs as toughening fillers for epoxy composites, emphasizing their applicability in enhancing the durability and performance of structural components in industrial applications.Highlights Polyacrylamide (PAM)‐modified graphene platelets by a water‐based approach. A strong interface promoted exfoliation and dispersion of platelets. PAM‐modified platelets improved epoxy modulus and toughness. Fractographic analysis unveils toughening mechanisms.

The improvement strategy of fresh produce supply chain resilience based on extenics.

Nowadays, the world is in turmoil, climate and environmental problems are prominent, the import and export of fresh agricultural products are restricted, etc. The impact of the growing demand for fresh agricultural products and healthy lifestyle choices, and fresh agricultural products are essential for people's daily life, which are perishable, fragile, seasonal, and other unstable factors. Therefore, when the fresh produce supply chain faces various pressures and difficulties, how to enhance the resilience of the supply chain against various problems and risks with flexible and multi-dimensional strategies and methods has become the focus of extensive attention. This kind of problem is a typical contradictory problem, and previous studies have failed to achieve good results. In this paper, based on extenics, we are able to one-dimensionalise the multi-dimensional contradictory problems and multi-dimensionalise the one-dimensional contradictory problems to solve such problems in a scientific and effective way. Firstly, taking fresh agricultural products supply chain enterprise M as the research object, we constructed the fresh agricultural products supply chain enterprise toughness system and identified the toughness state of each index. Secondly, we found the low-evaluation toughness indexes that need to be solved and constructed a extension model of incompatible problems of enterprise toughness. Thirdly, we analysed the objectives and conditions of toughness incompatible problems of fresh agricultural products supply chain enterprises numerically and quantitatively, and then, with the objective of toughness improvement, we analyzed the correlation of the condition basic-elements of incompatible problems and carried out extension transformations. Again, the objectives and conditions of the incompatible problems of fresh produce supply chain enterprises are analysed numerically and quantitatively, and with toughness enhancement as the objective, the correlation analysis and extension transformation of the condition basic-elements of the incompatible problems are implemented to generate the set of toughness enhancement strategies that can solve the incompatible problems in a multidimensional and scientific way. Finally, the optimal toughness enhancement strategies are selected through the superiority evaluation and composed into a new strategy to enhance the toughness of the fresh produce supply chain. Combined with extenics calculations and screening, a new strategy for supply chain resilience enhancement of fresh agricultural products was finally formed. The existing problems are solved from six aspects: product supply type, product demand, product supply efficiency, human resource quantity, production and processing equipment, and logistics guarantee ability. It provides a certain reference significance for the fresh agricultural products supply chain toughness enhancement, and helps enterprises to strengthen their competitiveness and sustainability through the enhancement of toughness.

Toughness enhancement of low carbon steel through bainitic transformation

Toughness enhancement of low carbon steel through bainitic transformation

Enhanced Strengthening and Toughening of T6-Treated 7046 Aluminum Alloy through Severe Plastic Deformation

The 7046 aluminum alloy possesses a favorable fatigue property, corrosion resistance and weldability, but its moderate strength and plasticity limit its wider application and development. In the present study, severe plastic deformation (SPD) was applied prior to T6 treatment to significantly enhance the strength and toughness of the 7046 aluminum alloy. The results show that the alloy processed by four passes of equal channel angular pressing (ECAP) at 300 °C prior to T6 treatment exhibits an excellent mechanical performance, achieving an ultimate tensile strength (UTS) and elongation (EL) of 485 MPa and 19%, respectively, which are 18.6% and 375% higher than that of the T6 alloy. The mechanical properties of the alloy are further improved by an additional room temperature (RT) rolling process, resulting in a UTS of 508 MPa and EL of 23.4%, respectively. The increased presence of η′ and Al6Mn phases in the 300°C4P-R80%-T6 and 300°C4P-T6 alloys contributes to a strengthening and toughening enhancement in the SPD-processed T6 alloy. The findings from this work may shed new insights into enhancing the 7046 aluminum alloy.

Preparation of super toughened flame-retardant polylactic acid with an in situ hyperbranched structure by reactive blending with a phosphorus-containing copolyester and hexamethylene glycidyl cyclotriphosphazene

Achieving both super toughness and flame retardancy in polylactic acid (PLA) materials hinges on resolving the interface compatibility issues between flame retardants, toughening agents, and PLA, as well as overcoming potential antagonisms between these components. Here, we present an approach employing hyperbranched structures to simultaneously enhance the toughness and flame retardancy of PLA materials. Our strategy involved the reactive blending of PLA with a quaternary bio-based phosphorus-containing copolyester (PPE) featuring side hydroxyl groups and hexamethylene glycidyl cyclotriphosphazene (HGCP). The multi-epoxy groups of HGCP reacted with the hydroxyl and carboxyl groups present in PPE and PLA, resulting in the formation of hyperbranched PLA-PPE copolymers. The hyperbranched copolymers provided great interfacial compatibilization and low viscosity, synergistically promoting the melt-dripping flame-retardant mechanism facilitated by PPE, aiding in the rapid removal of heat and combustible material from the pyrolysis zone. Consequently, the PLA/PPE/HGCP blends exhibited super toughness, achieving a maximum notched impact strength of 70.2 kJ/m2. Additionally, the blends demonstrated a 27 % LOI and can pass the UL-94 V-0 rating. Moreover, all the blends are biodegradable in a Proteinase K solution. This research underscores the efficacy of utilizing hyperbranched structures as a promising strategy for the development of PLA materials with simultaneous enhancement of processability, toughness, and flame retardancy.

Effect of nitrogen-doped type on fracture toughness improvement and crack growth resistance of carbon nanotube/epoxy nanocomposites: Combined multiscale analysis approach

Recently, nitrogen-doped carbon nanotubes (N-doped CNTs) have received great attention in nanocomposite design. It has become highly necessary to develop predictive models to elucidate their toughning behavior. In this study, the effects of CNTs with three different types of N-doped functional groups (quaternary, pyrrolic, and pyridinic) on the fracture toughness (FT) and crack growth of polymer nanocomposites are predicted using a multiscale analysis approach. To scale up from the nanoscale to the macroscale, a multiscale analysis approach integrating molecular dynamics, micromechanics theory, linear fracture mechanics theory, and a phase-field fracture model (PFFM) is adopted. The toughness enhancement trends of the three different types of N-doped functional groups were quantified by considering four toughening mechanisms (CNT debonding, plastic nanovoid growth, CNT pull-out, and CNT rupture), and compared with experimental result. The results show that the excellent interphase and interfacial properties of quaternary and pyridinic functional groups significantly improve the FT and crack growth resistance of N-doped CNT/epoxy nanocomposites. Our study provides high-performance solutions for experimental studies pertaining to the FT and crack growth of N-doped CNT/epoxy nanocomposites.

Improving flexural response of rubberized RC beams with multi-dimensional sustainable approaches

This research presents a sustainable solution to waste tire disposal and raw material depletion by incorporating recycled rubber into concrete mixtures. To mitigate the reduction in mechanical properties, a novel slag pretreatment of rubber particles with controlled temperature is proposed. The study also investigates the effects of pouring concrete in layers with rubberized concrete (RuC) in tension side and normal concrete in compression side, as well as evaluating the use of GFRP compared to conventional steel, thereby introducing multiple innovative dimensions to enhance structural performance. The experimental study included a total of 27 specimens, consisting of normal concrete, untreated rubberized concrete, and treated rubberized concrete mixtures with 15 % rubber content. The study investigated both compression and tension mechanical properties of the concrete mixtures and assessed the flexural response of reinforced concrete (RC) beams. Parameters explored included rubber treatment, utilization of steel and GFRP as tensile reinforcement, and layered concrete pouring. Subsequently, a numerical study was conducted to address the impact of reinforcement ratio and layer depth on the behavior of slag-treated rubberized RC beams. The findings reveal a significant recovery of concrete compressive strength by 23 %, along with a 28 % enhancement in toughness and a 17 % increase in splitting tensile strength attributed to the application of slag treatment to rubberized concrete. The effect of rubber treatment was more pronounced in GFRP RC beams, as they showed similar load capacity as normal concrete. Furthermore, utilizing layered concrete beams with a 67 % depth of slag-treated RuC showed a comparable load capacity to normal RC beams, demonstrating only a 1 % reduction for steel-reinforced beams and a 2.4 % improvement for GFRP-reinforced beams. Notably, the numerical model emphasized this outcome and suggested that increasing the layer depth to 72 % of slag-treated depth displayed better performance.

A comparative study on nanoscale mechanical properties of CrMnFeCoNi high-entropy alloys fabricated by casting and additive manufacturing

Additive manufacturing (AM) has emerged as a pioneering method for fabricating high entropy alloys (HEAs), yet a comprehensive comparison of their nanoscale mechanical properties with those produced by the conventional casting method remains unexplored. In this study, the nanoindentation was utilized to investigate the nanoscale elastic and plastic characteristics in both additive-manufactured (AM-ed) and as-casted single-phase face-centered cubic (FCC) equiatomic CrMnFeCoNi HEAs. Herein, the hardness, reduced modulus, indentation size effect (ISE), yield strength, fracture toughness, and strain rate sensitivity were comprehensively investigated. The results indicated that the hardness of AM-ed HEA was higher than the as-casted HEA, and the reduced modulus values showed no notable distinction between the two samples. The AM-ed HEA demonstrated simultaneous enhancements in yield strength and fracture toughness compared to the as-casted HEA. The as-casted HEA possessed a more distinct indentation size effect (ISE) than the AM-ed HEA. It was observed that the AM-ed HEA exhibited relatively lower strain rate sensitivity and a larger activation volume. This direct comparison of the mechanical properties and deformation mechanisms from a nanoscale view offers unique insights for optimizing and advancing AM techniques in the fabrication of HEAs.

Enhanced mechanical properties and atomic-scale mechanisms of ferroelastic domain switching for GdNbO4-La2Zr2O7 materials

Optimization of mechanical properties in La2Zr2O7 (LZO) ceramics, composites and coatings is an on-going requirement for their practical application. Herein, the contribution of monoclinic (La, Gd)NbO4 (m-LGNO) enhancement of fracture toughness by ∼56% reveals its capability to be a prominent toughening agent. Due to the ferroelastic nature of LGNO, ferroelastic switching takes place within the stress concentrated regions, giving rise to significant strain energy relaxation. Atomic-scale evidence reveals that ferroelastic 94°/86° domain switching can occur, yielding merged 94° domains and newly formed 86° domains. The relevant strains induced by ferroelastic domain switching are quantified up to 8.06% and 6.20% in shear and normal strain, respectively. Such domain switching strains highlight their contribution to accommodate external mechanical loading for the 50 mol% GNO-LZO composite. The results indicate that the unique ferroelastic nature and 94°/86° ferroelastic domain switching in m-LGNO cooperatively provide a significant toughening effect.

Investigating mechanical properties of SIFCONs produced with waste PET fibers

It is known that slurry infiltrated fibers concrete (SIFCON) is a type of concrete that possesses superior properties. To reduce the initial cost of fibers and to overcome the detrimental effect of waste plastic this study has been attempted to use polyethylene terephthalate (PET) waste fibers to produce SIFCON mixtures and investigate their properties. Six SIFCON mixtures were produced in which three volumetric proportions of fibers (3 %, 5 %, and 7 %) and two aspect ratios (36.8 and 24.57) were used. Behavior of these mixtures was compared with a normal concrete mixture containing no fibers and having approximately the same compressive strength. Flexural testing was conducted for small prismatic specimens and also on large reinforced concrete beams. The behavior was evaluated in terms of flexural strength, toughness and ductility. The results showed better flexural strength in case of SIFCON mixtures compared to normal concrete mixtures for both investigated aspect ratios. In addition, toughness and ductility were significantly improved as PET fiber content increase. Moreover, enhancement in toughness and ductility is more obvious in case of first aspect ratio. SIFCON reinforced beams showed a ductile behavior and sustained more damage. The use of PET fibers can be considered a promising option to produce sustainable SIFCON mixtures with improved properties.

Analysis of the impact of exfoliated graphene oxide on the mechanical performance and in-plane fracture resistance of epoxy-based nanocomposite

Graphene oxide (GO) is a versatile material, derivative of graphene, and it has gained significant attention in the field of polymer nanocomposites due to its exceptional properties and unique structural features. These characteristics make it a successful secondary reinforcing agent for enhancing mechanical performance, fatigue resistance, and other various physical and thermal properties of nanocomposites. However, the low fracture toughness of nanocomposite has restricted the overall structural applications. In this research work, the epoxy nanocomposites were prepared with different weights of exfoliated graphene oxide (E-GO) nanoparticles by using a dual mixing probe ultra-sonication for homogeneous distribution and proper dispersion. A substantial enhancement in mechanical performance and fracture toughness of nanocomposite was observed. The good dispersion and interfacial adhesion among E-GO and epoxy matrix were investigated through the critical analysis of the fracture surfaces of the nanocomposite. The enhancement of mechanical performance of E-GO nanofiller-reinforced epoxy composite was observed superior at 1 wt. % of GO60 particle concentration. The maximum increment of mechanical properties such as tensile strength, flexural strength, and work of fracture were 40.763, 39.23, and 12.106 % respectively, whereas maximum tensile modulus and flexural modulus were 19.3724, 27.63 % at 1.5 wt. % of GO60 as compared to the neat composite. However, in the case of fracture toughness and energy, maximum improvement of 1.256 Mpa.m1/2 and 0.472 KJ/m2 respectively was observed at 1 wt. % of GO60. Such enhancement was primarily due to the bolstering of in-plane crack propagation resistance in the nanocomposites. Additionally, the highlight point in thermomechanical properties of the polymer nanocomposite is optimal storage modulus and damping factor such as 4066.75 MPa, and 0.46 respectively, for the GO60 at 1 wt.% nanocomposite. Moreover, GO60 at 1 wt.% demonstrates greater thermal stability, withstanding up to 50% material degradation at 413.65°C.

Enhancing mechanical performance of boronic ester based vitrimers via intermolecular boron–nitrogen coordination

Malleability and reprocessability of cross-linked polymers can be achieved via exchange reactions of the boronic ester crosslinking. Herein, we report a facile strategy to fabricate and modulate vitrimers by introducing intermolecular boron-nitrogen coordinated boronic ester crosslinking. Using a one-pot reaction, a series of boronic ester vitrimers based on polybutyl acrylate (PBA) was synthesized. The nitrogen containing monomer dimethylaminoethyl methacrylate (DMAEMA) was successfully copolymerized in the backbone to generate intermolecular boron-nitrogen (B–N) coordination. The presence of B–N coordination increases intermolecular interactions, leading to a denser crosslinked network structure and an elevated glass transition temperature. With the formation of B–N coordination, PBA-xB-yN samples at the same crosslinking density exhibit higher elongation at break and tensile strength. These samples dissipate more energy at the same strain and show a more pronounced strain rate dependency, highlighting the sacrificial role of the B–N coordination bonds. Stress relaxation experiments reveal that the intermolecular B–N coordination promotes faster relaxation of PBA-xB-yN compared to PBA-xB due to accelerated exchange dynamics of boronic ester. Mechanical reinforcement after recycling is observed in PBA-1B–2N, indicating that structural optimization of chemical and physical crosslinking occurs during thermal reprocessing. This study will provide a new strategy to fabricate boronic ester based vitrimeric materials with mechanical reinforcement and toughness enhancement.

Impact of specimen size on mixed mode I and II fracture behavior of asphalt mixture using MMTS criterion

This study investigates how the diameter of specimens impacts the cracking behavior of asphalt mixtures. Testing was conducted on SCB specimens with diameters of 64, 86, and 150 mm under different fracture modes and temperatures. Fracture toughness and fracture energy, crucial fracture parameters, were determined for the tested specimens. The findings revealed that an increase in Me (mode mixity) values led to a decrease in fracture toughness but an increase in fracture energy. By considering all specimen sizes and test temperatures, the fracture toughness for mixed mode I/II and pure mode II was, on average, 13 % and 29 % lower than that for pure mode I loading, respectively. Conversely, the fracture energy for mixed mode I/II and pure mode II was, on average, 19 % and 38 % higher than that for pure mode I loading, respectively. Larger specimens exhibited enhancements in both fracture toughness and fracture energy. Considering all loading modes and test temperatures, the fracture toughness for specimen diameters of 86 mm and 150 mm was, on average, 9 % and 26 % higher than that for a diameter of 64 mm, respectively. The corresponding improvements in fracture energy were 8 % and 14 %, respectively. Additionally, it was observed that fracture toughness increased with decreasing temperature until −20 °C, after which it declined. On the other hand, fracture energy rose with increasing test temperature for all specimen sizes and mode mixities, with a notable increase at 10 °C due to the brittle nature of asphalt concrete. Moreover, the size of the fracture zone (rc) was influenced by temperature and specimen size (R), with larger R resulting in an increase in rc. However, a decrease in temperature initially caused a slight decrease in rc followed by an increase. The study concluded that the MMTS (modified maximum tangential stress) criterion effectively predicted the fracture behavior of SCB specimens across various sizes and loading modes, providing accurate estimations for asphalt mixture fracture behavior. By considering all loading modes and test temperatures, the average error values were 5.9 %, 6.2 %, and 6.5 % for specimen diameters of 64 mm, 86 mm, and 150 mm, respectively.

3D printed multi-coupled bioinspired skin-electronic interfaces with enhanced adhesion for monitoring and treatment

Skin-electronic interfaces have broad applications in fields such as diagnostics, therapy, health monitoring, and smart wearables. However, they face various challenges in practical use. For instance, in wet environments, the cohesion of the material may be compromised, and under dynamic conditions, maintaining conformal adhesion becomes difficult, leading to reduced sensitivity and fidelity of electrical signal transmission. The key scientific issue lies in forming a stable and tight mechanical-electronic coupling at the tissue-electronic interface. Here, inspired by octopus sucker structures and snail mucus, we propose a strategy for hydrogel skin-electronic interfaces based on multi-coupled bioinspired adhesion and introduce an ultrasound (US)-mediated interfacial toughness enhancement mechanism. Ultimately, using digital light processing micro-nano additive manufacturing technology (DLP 3D), we have developed a multifunctional, diagnostic-therapeutic integrated patch (PAMS). This patch exhibits moderate water swelling properties, a maximum deformation of up to 460%, high sensitivity (GF = 4.73), and tough and controllable bioadhesion (shear strength increased by 109.29%). Apart from outstanding mechanical and electronic properties, the patch also demonstrates good biocompatibility, anti-bacterial properties, photothermal properties, and resistance to freezing at −20 °C. Experimental results show that this skin-electronic interface can sensitively monitor temperature, motion, and electrocardiogram signals. Utilizing a rat frostbite model, we have demonstrated that this skin-electronic interface can effectively accelerate the wound healing process as a wound patch. This research offers a promising strategy for improving the performance of bioelectronic devices, sensor-based educational reforms and personalized diagnostics and therapeutics in the future. Statement of significanceEstablishing stable and tight mechanical-electronic coupling at the tissue-electronic interface is essential for the diverse applications of bioelectronic devices. This study aims to develop a multifunctional, diagnostic-therapeutic integrated hydrogel skin-electronic interface patch with enhanced interfacial toughness. The patch is based on a multi-coupled bioinspired adhesive-enhanced mechanism, allowing for personalized 3D printing customization. It can be used as a high-performance diagnostic-therapeutic sensor and effectively promote frostbite wound healing. We anticipate that this research will provide new insights for constructing the next generation of multifunctional integrated high-performance bioelectronic interfaces.