Lithium‐metal batteries (LMBs) with high energy densities are highly desirable for energy storage, but generally suffer from dendrite growth and side reactions in liquid electrolytes; thus the need ...for solid electrolytes with high mechanical strength, ionic conductivity, and compatible interface arises. Herein, a thiol‐branched solid polymer electrolyte (SPE) is introduced featuring high Li+ conductivity (2.26 × 10−4 S cm−1 at room temperature) and good mechanical strength (9.4 MPa)/toughness (≈500%), thus unblocking the tradeoff between ionic conductivity and mechanical robustness in polymer electrolytes. The SPE (denoted as M‐S‐PEGDA) is fabricated by covalently cross‐linking metal–organic frameworks (MOFs), tetrakis (3‐mercaptopropionic acid) pentaerythritol (PETMP), and poly(ethylene glycol) diacrylate (PEGDA) via multiple CSC bonds. The SPE also exhibits a high electrochemical window (>5.4 V), low interfacial impedance (<550 Ω), and impressive Li+ transference number (tLi+ = 0.44). As a result, Li||Li symmetrical cells with the thiol‐branched SPE displayed a high stability in a >1300 h cycling test. Moreover, a Li|M‐S‐PEGDA|LiFePO4 full cell demonstrates discharge capacity of 143.7 mAh g−1 and maintains 85.6% after 500 cycles at 0.5 C, displaying one of the most outstanding performances for SPEs to date.
A thiol‐branched SPE is synthesized to decouple ionic conductivity and mechanical strength, and it features high mechanical strength, toughness, and ionic conductivity. Meanwhile, the SPE is also endowed with the functions of both enabling fast Li+ transport and blocking Li dendrite growth, thereby guaranteeing a high stability in battery cycling.
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•A new flame retardant DOPONH2-S was synthesized.•It solved the problems of epoxy resin (EP) including flammability and brittleness.•DOPONH2-S achieved high efficiency in reducing ...THR, P-HRR and EHC of EP.•DOPONH2-S increased the impact strength and thermal stability of EP.
Epoxy resin (EP) has two shortcomings: flammability and brittleness. Previous studies have improved brittleness or flame retardancy but they will compromise the glass transition temperature (Tg) and thermal stability. Herein, a novel DOPO based phosphorus-, nitrogen- and sulfur-co-contained macromolecular flame retardant (DOPONH2-S) was synthesized and incorporated into EP to improve its flame retardancy and toughness with not damaging Tg and thermal stability. After curing, both Tg and the tensile strength of EP-2 improved at the addition of DOPONH2-S is 6.75 wt%. Simultaneously, the thermogravimetric analysis (TGA) results showed DOPONH2-S is helpful increasing the thermal stability of EP composites and protecting the polymer from further decomposition. In the fire safety test, EP-2 achieved V-0 rating in the vertical burning test and obtained a limiting oxygen index value of 30.5%. In comparison with pure EP, the peak heat release rate, total heat release and effective heat of combustion of EP-4 incorporated with 10.0 wt% DOPONH2-S were reduced by 59.1%, 58.5% and 46.3%, respectively. A two-phase mechanism was discussed to explain the combination effect in DOPONH2-S. In condensed-phase, rich char residue prevents the exchange of mass and heat during combustion. It also obstructs the release of combustible gases into the combustion zone. In gas-phase, the produced phosphorus- and sulfur-containing free radicals can capture active free radicals (H· and OH·), thus ending the chain reaction of combustion. Moreover, the addition of DOPONH2-S apparently improved the impact strength (62.5%). This work provided ideas for the development of multifunctional EP.
•The fracture toughness and tensile strength show anisotropy ratios of 2.27 and 2.61.•The DIC results confirm the development of a semi-elliptical fracture process zone.•The FPZ in anisotropic rocks ...is isotropic in shape but anisotropic in size.•The FPZ length obtained from DIC tests are compared to theoretical models.•The FPZ length is proportional to the square of fracture toughness over strength.
This paper presents experimental results on the anisotropy of the fracture toughness, Brazilian tensile strength, and the fracture process zone (FPZ) in granodiorite samples. The fracture toughness is measured using semi-circular bending tests, while Brazilian disk tests were conducted to measure the tensile strength indirectly. Digital image correlation (DIC) was employed to obtain full-field surface deformation associated with the fracture propagation and identify the FPZ. An averaging scheme is proposed to determine the length and width of the FPZ from the strain field. The DIC results confirm a semi-elliptical FPZ developing ahead of the crack tip, with an average length-to-width ratio of approximately two. The results also indicate that the theoretical models such as Irwin and strip-yield with uniform traction, which are based on plastic deformation near the crack tip, underestimate the extent of the inelastic zone, while the strip-yield model with a linear cohesion stress distribution overestimate the length of the process zone. The anisotropy ratio of the FPZ length obtained from the models, however, agrees very well with the ratio obtained from the DIC measurements. This evidence supports the basis of the theoretical models that predict the FPZ length to be proportional to the square of fracture toughness over tensile strength.
•A multiscale framework is proposed to predict the fracture toughness enhancement of polymer nanocomposites.•The effect of strain rate and interfacial characteristic on fracture toughness is ...studied.•Interfacial debonding and subsequent plastic void growth are considered as toughening mechanisms.•The toughening mechanisms are described progressively in the fracture process.•The fracture toughness is dependent on interfacial characteristics and decreases with increasing strain rate.
We propose a multiscale framework to predict the fracture toughness enhancement in polymer nanocomposites at various strain rates considering the interfacial debonding and subsequent plastic yielding of the matrix mechanisms. The elasto-plastic behavior of pure polymer and polymer nanocomposite is characterized at different strain rates via molecular dynamics simulation, and the fracture toughness enhancement are computed using a multiscale bridging approach via the finite element simulation and linear elastic fracture mechanics. The predicted results show that the toughness enhancement is affected by the strain rate and interfacial characteristics, and that it agrees well with the experimental results. These findings is expected to provide guidelines for predicting the fracture toughness of nanocomposites under various strain rate conditions, as well as insights into the customization of interfacial characteristics for the target toughness.
Duplex Stainless Steels (DSSs) are biphasic austenite-ferrite stainless steels, with higher mechanical properties and corrosion resistance than the other stainless steels grades. Impact toughness is ...a very important mechanical property and even though DSSs have a lower impact toughness as compared to the austenitic grades, the transition to ductile to brittle behavior is more gradual and it occurs at lower temperature than ferritic grades. On the other hand, DSSs suffer from embrittlement due to secondary phase precipitation, which affects all mechanical and corrosion properties, in particular impact toughness, even in low amount.
In this research paper, the influence of a small amount (< 2%) and different morphologies of secondary phases (coarse and finely dispersed) on the ductile to brittle transition of standard Duplex Stainless Steel UNS S32205 was studied. Two isothermal heat treatments were conducted on the solubilized DSS in order to precipitate the same amount but different morphologies of secondary phases. Charpy tests were conducted on a temperature range between 20 °C and − 196 °C.
The wrought material retained a very good impact toughness even at − 90 °C (100 J), but a small volume fraction of secondary phases affected the impact toughness even at room temperature. Coarser secondary phases affect the impact toughness largely as compared to small and finely dispersed particles.
•321-type metastable austenitic stainless steel was studied.•The steel was cold swaged and annealed at 500 °C.•Cold swaging with annealing resulted in the gradient structure formation.•Annealing ...dramatically increased strength and toughness of steel.
The effect of cold swaging and subsequent annealing on the structure and mechanical properties of a 321-type metastable austenitic stainless steel was studied. Cold swaging to a strain of 90% produced a gradient structure with a gradual decrease in the α-phase content from the edge to the center of the bar. Globular and lamellar regions of both strain-induced martensite and retained austenite were found in the center, meanwhile, a completely globular austenite–martensite dual-phase structure was formed at the edge. After annealing at 500 °C, (~30° below the reverse martensite-to-austenite phase transformation temperature) microstructure refinement due to simultaneous development of recrystallization and reverse martensite-to-austenite transformation was observed. Both ultimate tensile strength and yield strength increased noticeably after the annealing. Besides, notch toughness of the annealed specimen doubled in comparison to that of the cold-swaged condition and almost reached the level of a coarse-grained condition.
Abstract Objective The objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear ...resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials. Methods Test methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method. Results The properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear—abrasion (third body) and Wear—attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush. Significance The following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance.
In this study, the effects of interleaved nanofibre veils on the Mode I and Mode II interlaminar fracture toughness (ILFT) of autoclave cured unidirectional carbon/epoxy composite laminates were ...investigated. Various electrospun nanofibre veils consisting of a range of different polymer types, fibre diameters and veil architectures were placed in the laminate mid-planes, which were subsequently subjected to double cantilever beam and end-notch flexure tests. It was found that the polymer type and veil areal weight were the most important factors contributing to laminate performance. A 4.5g/m2 PA66 veil provided the best all-round performance with fracture toughness improvements of 156% and 69% for Mode I and Mode II, respectively.
AbstractTwo kinds of asphalt binders and four kinds of aggregate gradations were selected. Cylinder specimens of six types of asphalt mixtures were molded by the superpave gyratory compactor (SGC) ...rotary compaction method, and semicircular bending (SCB) tests were conducted with different temperatures and notch depths. The effects of notch depth, gradation, asphalt properties, and temperature on the crack resistance of the asphalt mixture were analyzed based on essential fracture energy and fracture toughness. The analysis results show that the greater the notch depth leads to lower fracture energy and weaker crack resistance. The effect of gradation is slight when the nominal maximum particle size is relatively large, and smaller nominal maximum particle size leads to greater effect of gradation on crack resistance of the asphalt mixture. Asphalt properties have a positive influence, which means higher quality bitumen would give higher crack resistance. The effects of gradation and asphalt properties on crack resistance are limited by temperature.
The development of a hierarchically engineered micro-nano hybrid composite system is described. A spray coating technique has been utilized as an effective way to deposit carbon nanotubes (CNTs) onto ...carbon fibre prepregs with good control of network formation and the potential for localization. Compared to more traditional approaches of introducing CNTs into epoxy matrices for enhancing composite properties, this technique has benefits in terms of its simplicity and versatility, as well as the potential for industrial scale-up. The effectiveness of the technique is demonstrated by the extremely low CNT loading (0.047wt.%) needed to significantly increase the Mode-I fracture toughness of the carbon fibre laminates by about 50%, which is so far the largest reported improvement for such extremely low concentrations of non-functionalized CNTs. In-situ damage sensing has also been presented for the monitoring of structural health of these nano-engineered composite laminates upon loading, and a systematic analysis of sensing signals is performed.
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