Materials often exhibit a trade-off between stiffness and extensibility; for example, strengthening elastomers by increasing their cross-link density leads to embrittlement and decreased toughness. ...Inspired by cuticles of marine mussel byssi, we circumvent this inherent trade-off by incorporating sacrificial, reversible iron-catechol cross-links into a dry, loosely cross-linked epoxy network. The iron-containing network exhibits two to three orders of magnitude increases in stiffness, tensile strength, and tensile toughness compared to its iron-free precursor while gaining recoverable hysteretic energy dissipation and maintaining its original extensibility. Compared to previous realizations of this chemistry in hydrogels, the dry nature of the network enables larger property enhancement owing to the cooperative effects of both the increased cross-link density given by the reversible iron-catecholate complexes and the chain-restricting ionomeric nanodomains that they form.
The overall performance of rubber is largely governed by its internal cross-linked network structure. However, it remains a major challenge to probe into cross-linked networks associated with their ...fascinating hierarchy and dynamic characteristics. Herein, we propose a strategy for developing “hierarchical dynamic cross-linked networks (HDCs)” in rubber composites to circumvent the inherent trade-off between stiffness and toughness while accelerating the dynamic properties of the networks. The robust HDCs enabled by networks union enhances the stiffness, and at the same time improves the toughness by dissipating energy in motion and dissociation of multiple interactions. Moreover, the strong diffusivity of the polymer chains and the dynamic reversibility of the cross-linking sites ensure that the rubber composites can be readily healed and recycled, restoring the original mechanical properties under heating. By means of a model system of carboxylate nitrile rubber (XNBR) material, a healable, recyclable and intelligent responsive rubber composite with simultaneously enhanced stiffness (modulus = 3.20 ± 0.12 MPa) and toughness (40.9 MJ m−3) is fabricated. The clever design of the HDCs in rubber composites conciliates the stubborn contradiction between reinforcement, self-healing/recycling and functional application, which is expected to impact many fields in elastomer science and engineering.
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The microstructure of wire arc additive manufactured (WAAMed) titanium alloy was characterized by brittle martensitic, which was significantly different from that of wrought alloy. It was generally ...believed that brittle martensitic was detrimental to the toughness of titanium alloys. In order to obtain WAAMed titanium alloy with excellent combination of strength and toughness, Ti5111 alloy, which is a newly developed deformation twinning induced plasticity(TWIP) alloy with an excellent combination of impact toughness and strength, was prepared by arc additive manufacturing(WAAM) technology and then annealed at 900 °C + air cooling(AC) and 950 °C+ air cooling. Microstructure, tensile properties and impact toughness of WAAMed Ti5111 alloy were investigated. Electron backscatter diffraction (EBSD) observation was adopted to identify the deformation twins activated in impact samples. Results showed that as-built WAAMed Ti5111 with excellent toughness was obtained, which was 42.8% higher than that of WAAMed Ti–6Al–4V alloy. After annealing, more deformation twins and secondary twins were activated during impact loading, which could effectively improve the toughness of WAAMed Ti5111.
Erosive wear characteristics of (18 and 27) wt.% Cr based multicomponent (3 wt% V, Mo, W, and Co) white cast iron have been systematically investigated with three conditions: as-cast (AC), ...as-quenched (Q), and as-quenched tempered (QT).
The result shows that Q specimens has the better erosive wear resistance compared to AC due to the transforming of the austenite matrix to be martensite and precipitation of secondary carbide. However, the erosive wear resistance of Q specimens was slightly reduced by the tempering process due to a significant increment of M7C3 carbide fracture toughness. Therefore, it can be concluded that the excessive Cr addition can be a negative factor on erosive wear-resistance in heat-treated condition and the tempering process should be ignored.
•Erosive resistance of as-cast was increased as increasing the Cr addition and after applying heat treatment process.•Erosive wear resistance slightly decreased when conducting the tempering compared to as-quenched.•Secondary carbide can negatively influence erosive wear resistance when its volume fraction over the threshold.•Microstructure and fracture toughness of the main carbide played as important factors in the erosion performance.
We present a phase-field formulation to model fatigue crack growth over large numbers of cycles. Building upon a recently introduced phase-field formulation by the authors, fatigue is modeled ...phenomenologically by degradation of the fracture toughness, treated as a spatiotemporally evolving material property, inside a region around the crack tip with size Rfatigue. The present formulation, however, treats cycle number N as a continuous variable, allowing for crack growth prediction over large numbers of cycles of experimental relevance in arbitrary geometries containing one or several cracks, as well as under various loading conditions. The phenomenological form of the degradation law is analytically motivated by first deriving a relationship between the crack growth rate per cycle da/dN and the stress intensity factor (SIF) variation amplitude ΔK in the sharp-interface limit where Rfatigue is much larger than the phase-field regularization length ξ. This relationship reproduces salient features of experimentally measured fatigue growth curves, including the existence of a minimum ΔK for growth, a power law over an intermediate range of ΔK, and a sharp increase of growth rate when the peak SIF value approaches the Griffith threshold Kc. Phase-field simulations are shown to reproduce similar growth curves with quantitative differences depending on the ratio Rfatigue/ξ. The ability of the model to predict realistic crack paths is demonstrated by various examples in two and three dimensions including crack kinking under mode I+II loading, “en-passant” interacting cracks, and crack twisting in a three-point bending geometry with mode I+II+III loading.
•Phase-field models to efficiently simulate high-cycle fatigue crack growth are proposed.•The models quantitatively reproduce fatigue growth curves of ductile materials.•Example applications are presented for interacting cracks and mixed mode fracture.
Gradient-structured (GS) materials are capable of displaying high strength without compromising ductility, which can result in damage-tolerant structures. However, due to the difficulties in ...fabricating bulk GS materials, there has been only limited studies on the fracture behavior in GS metals. In the present work, the impact toughness of the macroscale GS pure Ni plates was investigated using instrumented Charpy impact testing. The gradient orientation was found to have a significant influence on the impact toughness of GS Ni. For gradient structures that transition from coarse grains (CG) to nano-grains (NG), termed CG→NG gradients (in the present study from ∼8 μm to ∼30 nm), the absorbed energy and the tensile strength were increased, respectively, by 1.6 and 2.3 times from those exhibited by uniform coarse-grained structures, demonstrating a simultaneous enhancement in strength and impact toughness. Analysis of load-displacement curves revealed that the resistance to both crack initiation and propagation were significantly enhanced as the crack penetrated through the CG→NG gradient structure, leading to markedly rising dynamic R-curve behavior estimated from nonlinear-elastic fracture mechanics J-based measurements. The superior fracture resistance in the CG→NG gradient structure was found to originate from sustained ductile fracture by microvoid coalescence, taking place not only in the initial CG zone, but also within the latter NG regions where adiabatic shear bands form during impact; in these latter regions, plasticity becomes enhanced due to grain coarsening induced by recrystallization under the dynamic loading. The present work not only reveals how the dynamic fracture resistance can be significantly enhanced in GS metals, but also provides structure-design strategies for developing superior metallic materials for impact engineering applications.
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•Multifunctional vanillin-based porphyrin (VPR) was designed and synthesized.•PLA/VPR biocomposites exhibited highly enhanced toughness.•PLA/VPR biocomposites showed excellent ...UV-resistance properties.•PLA/VPR biocomposites presented great self-extinguishing performance.
To achieve high-performance polylactic acid (PLA) composites, the exploitation of multifunctional biomass additives derived from renewable resources are highly demanded. Herein, a vanillin-based porphyrin (VPR) was designed and synthesized to impart PLA with enhanced mechanical, anti-UV, and flame retardant properties. Multiple intermolecular interactions between VPR and PLA enabled significant toughening of the PLA/VPR biocomposites compared to PLA itself. The elongation at break and impact strength for PLA/3VPR were improved by 88.2 % and 104.2 %, respectively, without influence on their tensile strength. Furthermore, the PLA/VPR biocomposites exhibited improved anti-UV performance with only 1.5 % and 8.6 % decrease of the strength and elongation at break respectively after UV aging. More importantly, incorporation of only 3 wt% VPR loading within the PLA/3VPR composite allowed for excellent self-extinguishing with a UL-94 V-0 level, greatly improving the versatility of PLA composites. We envision that such bio-based PLA/VPR materials with multifunctional features will extensively broaden the usable range of PLA composites.
Hydrogels possess unique polymer networks that offer flexibility/stretchability, high ionic conductivity, and resistance to electrolyte leakage, making them suitable for deformable energy storage ...devices. Endowing the mechanical functionality of the hydrogel electrolytes focus on either enhancing the stretchability or the toughness. However, the stretchability and the toughness are generally a trade‐off that the stretchable gels are intrinsically prone to damage and sensitive to notches and cracks. Here, the regulating strategies on the hydrogel's mechanical properties are provided to develop the designated hydrogel electrolyte, where different polymeric network structures are constructed, including single network structures, semi‐interpenetrating network structures, and interpenetrating dual‐network structures. A comprehensive comparison of these polymer network structures is conducted to evaluate their mechanical stretchability and toughness. Designing super‐tough and super‐stretchable hydrogels based on specific application requirements can be realized by striking a balance by regulating the hydrogel structure. In specific, incorporating semi‐interpenetrating networks significantly can enhance stretchability to achieve a break elongation up to 1300%, while the interpenetrating dual‐networks can largely improve the toughness to realize the extraordinary fracture toughness of 6.843 kJ m−2. These findings offer valuable designing guidance for designated hydrogel electrolytes and the deformable zinc‐silver battery is demonstrated with high mechanical stability and electrochemical performance.
This research proposes three universal strategies based on polymer network designs for strengthening hydrogel network structure, including single network reinforcement, construction of semi‐interpenetrating network, and interpenetrating network, which have significantly enhanced the mechanical toughness and tensile properties of hydrogels, hoping to expand the application scope of hydrogels in flexible sensing and energy storage fields.
The microstructural and mechanical properties of creep enhanced ferritic (CSEF) steels are affected by various parameters, solutionizing temperature is one of them. In the present investigation, the ...effect of normalizing temperature on the microstructural and mechanical properties of cast and forged (C&F) P92 steel were carried out. Grade P92 steel is considered as a candidate material for Thermal and Nuclear power plants at temperatures of up to 650°C. In this study, C&F P92 steel was subjected to various normalizing temperatures (from 950°C to 1150°C). For microscopic characterization, Optical microscope and Field emission scanning electron microscope (SEM) were used. The grain size, precipitate size, area fraction of precipitates and Cr/Fe were calculated from micrographs. The normalized specimens were tested for tensile strength, hardness, and toughness. Considering observation for the optimum combination of strength, ductility, and toughness, the normalizing at 1000°C and tempering at 760°C has been suggested for C&F P92 steel.
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