The cellulose graft copolymer bearing a highly branched poly(ε-caprolactone) structure, upon blending with PLA induces an more ordered crystal phase resulted in significantly enhanced toughness of ...PLA bio-blends.
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•A series of PLA/cellulose graft copolymer (CghbP) bio-blends were fabricated.•The prepared PLA/CghbP blend series were found to be miscible at scale of 10–30 nm.•An optimal loading of CghbP induced a structurally robust PLA-based bio-blend.•The enhanced toughness was related to a hard/soft multi-phase system of PLA blend.•The prepared PLA/CghbP exhibited excellent migration stability and bio-degradability.
In this research, a series of PLA bio-blends with a highly-branched polycaprolactone (PCL)-grafted cellulose bio-toughener (CghbP) (i.e., PLA/CghbP series) were facilely fabricated and characterized to improve the tensile toughness of neat PLA. The prepared PLA/CghbP bio-blends were examined by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and differential scanning calorimetry (DSC) analysis to be physically intact and partially miscible at the scale of ca.10∼30 nm. It was confirmed by the DSC and wide-angle X-ray diffraction (WXRD) analyses that the incorporation of CghbP into PLA matrix can induce a more disordered α′ crystalline phase of PLA in the prepared PLA/CghbP blends. The tensile properties of PLA/CghbP bio-blends investigated by universal testing machine (UTM) suggested that the mechanical behavior of highly-tough hard/soft multiphase polymeric system was realized with the incorporation of 5 wt% CghbP to PLA (i.e., PLA/CghbP5), resulting in a ∼215% increase in the tensile toughness (56.1 MJ m−3) compared to pristine PLA (17.8 MJ m−3). This research empirically identified that the improved tensile toughness of PLA/CghbP bearing 5 wt% CghbP are conjunctly correlated with the concurrent formation of more ordered hard PLA α crystalline and highly-branched soft phase induced by the loading of an appropriate CghbP into PLA. Furthermore, the PLA/CghbP5 bio-blend showed remarkably higher migration stability with the weight loss ∼0.1% CghbP after additive spillage test than those of other PLA/CghbP blends and PLA blends with conventional low molar mass plasticizers.
Silicon (Si), as one of the most promising anode candidates, is expected to improve the energy density of Li−ion batteries due to its high specific capacity (≈4200 mAh g−1). However, the cyclic ...performance of Si anode is unsatisfactory for practical usage due to its inadequate toughness when exceeding the mass loading beyond 2 mg cm−2, which triggers unceasing electrode breakage. Here, a biomimetic Si electrode is created by interconnecting vertically aligned graphene oxide sheets with conductive carbon nanotubes (AGO−Si/C). Unlike reported structures, the AGO−Si/C electrode exhibits superior interlaminar toughness owing to its unique crumpling architecture of reversible interlayer slipping. The elastic structure releases the accumulative lithiation stress of Si nanoparticles to address the degraded inactivation. Thus, the AGO−Si/C electrode shows long−lived cycles by toughening the structure, allowing the fabrication of very thick loading (4.1 mg cm−2) with an impressive areal capacity of 10.0 mAh cm−2. This discovery offers an easily scalable method for graphite/Si anode with high areal capacity that exceeds the commercial−level of 5 mAh cm−2.
Alloy‐type anodes usually have a non‐ideal critical cracking thickness due to their negative relationship between mass loading and intrinsic toughness. Here this issue is addressed by tailoring a biomimetics‐like structure, which achieves rapid ionic/electronic conductivity, high strength, and robust toughness, co‐contribution to boost the maximize the areal‐capacity and long‐life cycle stability.
The present study focuses on further extensions of the more general three-parameter Weibull distribution to describe the statistical scatter of fracture toughness values and to evaluate the ...characteristic toughness of structural steels using a statistical description of toughness data in comparison with the minimum of three equivalent (MOTE) method. Fracture toughness tests conducted on several types of structural steels, including an ultra high strength steel and pressure vessel steels, provide the experimental data upon which the Weibull statistical analyses are conducted. These analyses compare descriptions of fracture toughness values based on a standard three-parameter Weibull function with fixed values for parameters α and Kmin, and a general three-parameter Weibull distribution with unknown parameters (α,K0,Kmin) in connection with a goodness-of-fit method to assess how well the experimental data fits the assumed distribution. Further, the study also shows that use of a fixed percentile of the distribution describing the toughness data set provides more consistent values of characteristic toughness compared to the MOTE procedure.
•Implications on the use of a 2P and 3P Weibull model for the scatter of toughness.•Use of Kolmogorov–Smirnov goodness-of-fit test to fracture toughness distributions.•Relatively weak dependence of T0 on the fitted Weibull distribution.•The MOTE method may provide unreliable evaluation of the characteristic toughness.•A 3P Weibull distribution gives a more consistent characteristic toughness value.
•Presenting the relationship between fracture toughness and the number of freeze–thaw cycles.•Presenting the relationship between fracture toughness and freezing temperature.•Analysis of X-ray CT to ...investigate the damage caused by the freeze–thaw cycles.
The freeze–thaw process is one of the natural phenomena significantly affecting the characteristics of rocks and their properties. This study aimed at investigating the effects of freeze–thaw cycles and freezing temperature on mode I and mode II fracture toughness of Lushan sandstone. To this end, specimens were exposed to 0, 5, 10, 20 and 30 freeze–thaw cycles, and mode I and mode II fracture toughness were evaluated in different cycles. The effect of freezing temperature in a freeze–thaw cycle on mode I and mode II fracture toughness was also investigated. X-ray computerized tomography (CT) was used to determine specimen damages caused by freeze–thaw cycles. According to the results, mode I and mode II fracture toughness nonlinearly decreased with increasing the number of freeze–thaw cycles. The CT photographs showed an increase in the damage factor caused by freeze–thaw cycles. The mode I and mode II fracture toughness of Lushan sandstone nonlinearly decreased with increasing the freezing temperature in the freeze–thaw process.
The design and synthesis of supramolecular self‐healing polymers with high healing efficiency and excellent integrated mechanical properties is challenging due to conflicting attributes of dynamic ...self‐healing and mechanical properties. Herein, this study introduces a design concept, that is, “dynamic hard domains,” to balance self‐healing performance, mechanical strength, elastic recovery, and at the same time obtain extreme toughness. The essential features of the dynamic hard domains include: (i) a noncrystallized and loose structure, (ii) low binding energy and high mobility, and (iii) sequential dissociation and rapid rearrangement. Based on this strategy, a simple one‐step polycondensation route is reported to synthesize a transparent polyurethane‐urea supramolecular elastomer (PPGTD‐IDA), which successfully combines decent mechanical strength, extreme toughness, outstanding notch‐sensitiveness, self‐recoverability, and room‐temperature self‐healing. Upon rupture, the PPGTD‐IDA completely restores the mechanical properties within 48 h. Furthermore, the results demonstrate repeatable healing of mechanical properties and prominent antiaging healability. Taking advantages of merits of PPGTD‐IDA, it can be utilized for fabricating impact‐resistant materials for protection of aluminum alloys as well as stretchable and self‐healing conductors, which exhibits unique characteristics such as stable conductivity during stretching (even after healing or with notch), and automatic elimination of the notch during stretching/releasing cycles.
A transparent supramolecular elastomer, combining relatively high mechanical strength, extreme toughness, outstanding notch‐insensitiveness, self‐recoverability, and room‐temperature self‐healing properties with complete recovery of mechanical properties is facilely synthesized via the design conception of dynamic hard domains. These well‐balanced properties enable its immediate use in impact‐resistant and energy‐absorbing protective materials as well as stretchable and self‐healing conductors.
Aiming at the problem of the “inverse relationship” between the hardness (wear resistance) and toughness of the traditional single homogeneous structure coating on the surface of titanium alloy, the ...design and development of a high hardness, high toughness and wear-resistant coating with high reliability and long life is great significance for expanding the application of titanium alloy. Inspired by the microstructure of high-performance organisms in nature, the design ideas of multi-phase, multi-level and multi-scale hybrid reinforcement are used to give full play to the synergy, coupling and multi-functional response mechanism between different phases in the coating to obtain the wear-resistant coating with high hardness and high toughness. This article mainly reviews the research progress of several typical wear-resistant coatings with high hardness and high toughness on the surface of titanium alloy from the aspects of preparation process, microstructure, mechanical properties, and strengthening-toughening mechanisms, such as gradient structure coating, multi-scale structure coating and layered structure coating. On this basis, it is pointed out that in the future, the wear-resistant coating with high hardness and high toughness on the surface of titanium alloy should develop in the direction of developing intelligent manufacturing technology, optimal design and precise tailoring of microstructural architectures, and constructing the numerical simulation technology of composition-structure-performance. Furthermore, the authors propose the technology route for the controllable preparation of wear-resistant coating with high hardness and high toughness on the surface of titanium alloy, namely, through the coordination of theoretical calculations, numerical simulations, and intelligent manufacturing technologies to achieve the controllable preparation of the optimal structural coatings on the surface of titanium alloy, establish the functional relationship between composition-structure-performance, and accurately reveal the mechanism of strengthening and toughening, which provides a new idea for alleviating and balancing the bottleneck of the “inverse relationship” between hardness (wear resistance) and toughness, and achieving the preparation of titanium-based surface composite with excellent comprehensive properties.
•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.
Epoxies are widely used in many engineering applications, however, their fracture energy remains less than desired and conventional toughening agents usually lead to compromised tensile strength. In ...this study, a simple one-pot blending method was used, in which both graphene oxide and a block ionomer were blended with epoxy resin. Herein, we reported that increases of ∼200% in fracture energy (GIC), 48% in uniaxial tensile strength (σt) and 340% in tensile strain could be achieved by incorporating 1.0 wt% graphene oxide into an epoxy matrix with 20 wt% sulfonated polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SSEBS). In addition, the glass transition temperature (Tg) of the nanocomposite increased with increasing graphene oxide (GO) content and the storage modulus (E′) decreased when the GO content was less than 0.50 wt% owing to the introduction of the block ionomer SSEBS. Careful examination of the nano-morphology of SSEBS revealed that it improved the dispersion of the graphene oxide in and enhanced its interaction with the epoxy matrix, hence simultaneously strengthening and toughening the epoxy resin.
Intergranular and intragranular Si and Mn rich oxide inclusions are present in laser additive manufactured austenitic stainless steel. The uniform oxide dispersions in additive manufactured material ...promoted early initiation of microvoids and reduced its impact toughness relative to powder metallurgy (hot isostatic pressing) and wrought materials. For stress corrosion cracking in high temperature water, the silica inclusions along the grain boundaries preferentially dissolved and appeared to accelerate oxidation and caused extensive crack branching.
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