Constructing high-toughness polyimide binder with robust polarity and ion-conductive mechanisms ensuring long-term operational stability of silicon-based anodes

Silicon-based materials have demonstrated remarkable potential in high-energy-density batteries owing to their high theoretical capacity.However,the significant volume expansion of silicon seriously hinders its utilization as a lithium-ion anode.Herein,a functionalized high-toughness polyimide(PDMI) is synthesized by copolymerizing the 4,4'-Oxydiphthalic anhydride(ODPA) with 4,4'-oxydianiline(ODA),2,3-diaminobenzoic acid(DABA),and 1,3-bis(3-aminopropyl)-tetramethyl disiloxane(DMS).The combination of rigid benzene rings and flexible oxygen groups(-O-) in the PDMI molecular chain via a rigidness/softness coupling mechanism contributes to high toughness.The plentiful polar carboxyl(-COOH) groups establish robust bonding strength.Rapid ionic transport is achieved by incorporating the flexible siloxane segment(Si-O-Si),which imparts high molecular chain motility and augments free volume holes to facilitate lithium-ion transport(9.8 × 10^(-10) cm^(2) s^(-1) vs.16 × 10^(-10) cm^(2) s~(-1)).As expected,the SiO_x@PDMI-1.5 electrode delivers brilliant long-term cycle performance with a remarkable capacity retention of 85% over 500 cycles at 1.3 A g^(-1).The well-designed functionalized polyimide also significantly enhances the electrochemical properties of Si nanoparticles electrode.Meanwhile,the assembled SiO_x@PDMI-1.5/NCM811 full cell delivers a high retention of 80% after 100 cycles.The perspective of the binder design strategy based on polyimide modification delivers a novel path toward high-capacity electrodes for high-energy-density batteries.

Product Development of High Strength and Toughness Spring Flat Steel

With the continuous development of mechanical industry,higher requirements are put forward for the comprehensive properties of spring steel.The chemical composition and production process of spring flat steel are designed to meet the requirements of high strength and high toughness of spring flat steel,through the test,the product surface quality and internal quality all meet the national standards,the performance indicators to meet user requirements.

Effect of microstructure on the low temperature toughness of high strength pipeline steels

Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.

Mechanics Behavior of Ultra High Toughness Cementitious Composites after Freezing and Thawing

Mechanical behaviors of UHTCC after freezing and thawing were investigated,and compared with those of steel fiber reinforced concrete（SFRC）,air-entrained concrete（AEC） and ordinary concrete（OC）.Four point bending tests had been applied after different freezing-thawing cycles（0,50,100,150,200 and 300 cycles,respectively）.The results showed that residual flexural strength of UHTCC after 300 freezing-thawing cycles was 10.62 MPa（70% of no freezing thawing ones）,while 1.58 MPa（17% of no freezing thawing ones） for SFRC.Flexural toughness of UHTCC decreased by 17%,while 70% for SFRC comparatively.It has been demonstrated experimentally that UHTCC without any air-entraining agent could resist freezing-thawing and retain its high toughness characteristic in cold environment.Consequently,UHTCC could be put into practice for new-built or retrofit of infrastructures in cold regions.

Uniaxial Compressive Properties of Ultra High Toughness Cementitious Composite

Uniaxial compression tests were conducted to characterize the main compressive performance of ultra high toughness cementitious composite （UHTCC） in terms of strength and toughness and to obtain its stress-strain relationships. The compressive strength investigated ranges from 30 MPa to 60 MPa. Complete stress-strain curves were directly obtained, and the strength indexes, including uniaxial compressive strength, compressive strain at peak stress, elastic modulus and Poisson＇s ratio, were calculated. The comparisons between UHTCC and matrix were also carried out to understand the fiber effect on the compressive strength indexes. Three dimensionless toughness indexes were calculated, which either represent its relative improvement in energy absorption capacity because of fiber addition or provide an indication of its behavior relative to a rigid-plastic material. Moreover, two new toughness indexes, which were named as post-crack deformation energy and equivalent compressive strength, were proposed and calculated with the aim at linking up the compressive toughness of UHTCC with the existing design concept of concrete. The failure mode was also given. The study production provides material characteristics for the practical engineering application of UHTCC.

Flexural response of reinforced concrete beams strengthened with post-poured ultra high toughness cementitious composites layer

Four-point bending tests were conducted up to failure on eleven reinforced concrete (RC) beams and strengthening beams to study the effectiveness of externally pouring ultra high toughness cementitious composites (UHTCC) on improving the flexural behavior of existing RC beams.The strengthening materials included UHTCC and high strength grade concrete.The parameters,such as thickness and length of strengthening layer and reinforcement in post-poured layer,were analyzed.The flexural behavior,failure mode and crack propagation of composite beams were investigated.The test results show that the strengthening layer improves the cracking and ultimate load by increasing the cross section area.Introducing UHTCC material into strengthening not only improves the bearing capacity of the original specimens,but also disperses larger cracks in upper concrete into multiple tightly-spaced fine cracks,thus prolonging the appearance of harm surface cracks and increasing the durability of existing structures.Compared with post-poured concrete,UHTCC is more suitable for working together with reinforcement.The load?deflection plots obtained from three-dimensional finite-element model (FEM) analyses are compared with those obtained from the experimental results,and show close correlation.

Mechanical properties and grain refinement by acicular ferrite in high strength high toughness weld metal

The volume fraction and morphology of acicular ferrite evolution in a high strength high toughness weld metal were studied and the mechanical properties of weld metal under heat input of 21 kJ/cm with and without fast cooling were tested. The results show the weld metal can obtain a large proportion of acicular ferrite during a wide range of cooling rate and the sizes of acicular ferrite in length and thickness decrease with cooling rate increasing. The weld metal exhibited high tensile strength （895 MPa and 870 MPa） and good low temperature toughness （average AKv-30℃ 104 J and 79. 2 J）. The higher tensile strength and better low temperature toughness of the weld metal under fast cooling are due to the more refined grain of acicular ferrite.

EFFECT OF WELDING THERMAL CYCLE ON THE MICROSTRUCTURE AND TOUGHNESS OF LOW ALLOY HIGH STRENGTH STEEL

Weldingthermalcyclicsimulated techniquesisemployed in thestudy. By meansof analysismetalloscope, fracture morphology and impact toughness test of the sample, the effect ofweldingthermalcycle peak temperature and dualthermal cycle on the micro structure and toughnessoflow alloy high strength steel HQ100 isinvestigated.Inner fine martensitic andbainitic microstrctureisobservedby TEM.Theresultsshow that withtheincreaseof peaktem perature, grain sizesbecomelarger,theimpacttoughness drop down .Ifthermalcycleisim posed twiceand dualthermalcyclicpeaktemperatureis1275 ℃+ 750 ℃,theimpacttoughnessisatthelowest value.Alsotheimpacttoughnessagrees withthefracture morphology.

Dynamic fracture toughness of high strength metals under impact loading:increase or decrease

An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1. For the purpose of verification, variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry, 30CrMnSiA and 40Cr, is studied in this work. Results of the experiments are compared, which were conducted on the modified split Hopkinson pressure bar （SHPB） apparatus, with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr, respectively. It is observed that for 30CrMnSiA, the crack tip loading rate increases with the increase of the striker velocity, while the fracture initiation time and the DFT simultaneously decrease. However, in the tests of 40Cr, there is also an increasing tendency of DFT, similar to other reports. Through an in-depth investigation on the relationship between the dynamic stress intensity factor （DSIF） and the loading rate, it is concluded that the generally increasing tendency in previous studies could be false, which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes. To disclose the real dependency of DFT on the loading rate, experimentsneed to be performed in a comparatively large striker velocity range.

Effect of Plastic Deformation and H_2S on Dynamic Fracture Toughness of High Strength Casing Steel

The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel（C110 steel） were investigated. The studied casing specimens are as follows： original casing, plastic deformation（PD） casing and PD casing after being immersed in NACE A solution saturated with H2S（PD＋H2S）. Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness（JId） was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2 S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows： the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.

Effect of Zr-Ti combined deoxidation on impact toughness of coarse-grained heat-affected zone with high heat input welding

In this study, the effects of Zr-Ti combined deoxidation and AI deoxidation on the impact toughness of coarse- grained heat-affected zone in high-strength low-alloy steels were investigated. More fine oxides were formed in the Zr-Ti-killed steel than in Al-killed steel. It was also found that more acicular ferrite grains were formed in the coarse-grained heat-affected zone in the Zr-Ti-killed steel than in Al-killed steel. The impact toughness of coarse-grained heat-affected zone of Zr-Ti-kiUed steel was higher than that of Al-killed steel. The good impact toughness was attributable to the pinning effect of fine oxides and the formation of acicular ferrite grains on fine oxides.

Low temperature impact toughness of laser hybrid welded joint of high strength low alloy steel

High strength low alloy steel with 16 mm thickness was welded by using high power laser hybrid welding. Microstrueture was characterized by using optical microscopy, scanning electron microscopy （ SEM ） , transmission electron microscopy （TEM） and selected area electron diffraction （SAED）. Low temperature impact toughness was estimated by using Charpy V-notch impact samples selected from the upper part and the lower part at the same heterogeneous joint. Results show that the low temperature impact absorbed energies of weld metal are （202,180,165 J） of upper samples and （178,145,160 J） of lower samples, respectively. All of them increase compared to base metal. The embrittlement of HAZ does not occur. Weld metal primarily consists of refined carbide free bainite and a little granular bainite since laser hybrid welding owns the character of low heat input. Retained austenite constituent film ＂locates among the lath structure of bainitie ferrite. Refined bainitic ferrite lath and retained austenite constituent film provide better low temperature impact toughness compared to base metal.

Fabrication of High Toughness Silk Fibroin/Tungsten Disulfide Nanoparticles Hybrid Fiber and Self-Heating Textile by Wet Spinning|

Traditionally,silkworm silk has been used to make high-quality textiles.Nevertheless,various wastes from silk-worm silk textiles that are no longer used are increasing.which is also causing considerable waste and contam-ination.This issue is causing widespread concern in countries that use more silk.Regenerated silk fibroin(RSF)fibers have been shown to be fragile and tender,which prohibits RSF from being widely used as a structural com-ponent.Therefore,enriching the function of silk and enhancing the RSF mechanial properties are important directions to expand the comprehensive utilization of silk products.In the present research,wet spinning was used to create a series of RSF/tungsten disulfide(WS_(2))nanoparticles(NPs)hybrid fiber having distinct WS_(2) nanoparticles concentrations.It was discovered that the temperature of hybrid fibers containing 0.8 wt%RSF/WS_(2) nanoparticles might climb from 20.4℃ to 85.6℃in 1 min and 108.3℃ in 10 min after being exposed to simulated sunlight for a period of one minute and ten minutes.It also had certain antibacterial activity and thermal stability.Fabrics created by hand mixing had outst anding photothermal characteristics under natural sunlight.Further-more,adding WS_(2) nanoparticles might increase the tensile properties of hybrid fibers,which could be caused by the reality that the blending of WS_(2) nanoparticles inhibited the self-assembly of sheets in RSF reaction mixture in a dosage dependent way,as evidenced by the fact that RSF/WSz nanoparticles hybrid fibers had lesser β-sheets material,crystalline nature,and arystalline size.The above performance makes the RSF/WS_(2) nanoparticles hybrid fbers promising candidates for application in photothermal fabrics as well as military dothing.

Development of the High Toughness Spirally Submerged Arc Welded Pipe Line

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A New Method for Determining J_(IC) of High StrengthHigh Fracture Toughness Steels by SingleThree Point Bend Specimen

A single three point bend specimen compliance method for determining JIC of high strength high fracture toughness steels is presented and a formula for calculatinff J-integral is proposed as follows.It is simple and valid for high strength high fracture toughness steels. The values of JIC and KIC measured by this method are in good agreement with those measured by standard test method.

Preparation of Self-compacting Ultra-high Toughness Cementitious Composite

A self-compacting ultra-high toughness cementitious composite （UHTCC） reinforced by discontinuous short polyvinyl alcohol （PVA） fibers, which exhibits self-compacting performance in the fresh state and strain-hardening and multiple cracking behavior in the hardened state, was developed through controlling flow properties of fresh mortar matrix at constant ingredients concentrations determined by micromechanical design and ensuring uniform fibers dispersion. The superplasticizer was utilized to adjust its flow properties in the fresh state. A series of flow tests, including deformability test, flow rate test, and self-placing test, were conducted to characterize and quantify the fluidity performance of fresh mortar matrix and self-compactability of fresh UHTCC. It is revealed that the utilization of superplasticizer is efficient in producing the fresh mortar matrix with desirable fluidity and the resulting self-compacting UHTCC. In addition, results of four point bending tests on the developed self-compacting UHTCC confirm the insensitivity of mechanical performance of self-compacting UHTCC to the presence of external vibrations as well as the flexural characteristics of deformation hardening and multiple cracking.

Progress in the technological development of oxide metallurgy for manufacturing steel plates with excellent HAZ toughness

In the present study, the market needs for the （HAZ） toughness are analyzed, and the mechanism of the development of steel plates with excellent heat affected zone decrease in the HAZ toughness during high-heat input welding is discussed.The important countermeasure for improving the HAZ toughness is to employ the technology of oxide metallurgy ,namely,to make use of fine inclusion particles for improving the microstructure of HAZ. The progress and theories of oxide metallurgy technologies developed in the Nippon Steel Corporation （ NSC）, the JFE Steel Corporation and the Kobe Steel Group are illustrated. Steel plates developed by these three companies with excellent HAZ toughness are introduced.

Excellent heat affected zone toughness technology improved by strong deoxidizers

Excellent heat affected zone(HAZ)toughness technology improved by strong deoxidizers(ETISI)technology has been developed by Baosteel.In the deoxidation process of molten steel by adding strong deoxidizers,the formation of micrometer inclusions and nano-meter precipitates in steel plates can be effectively controlled by a precise control of oxygen concentration.In the welding process with a high-heat input,the formation of acicular ferrite can be selectively promoted with the aid of the micrometer inclusions;the growth of γ grains can also be selectively restrained by the pinning effect of the nano-meter precipitates.After welding with a high-heat input of 400 kJ/cm,excellent HAZ toughness can be obtained in the steel plates with both of the above microstructures,and the average absorbed energy is greater than 200 J for the V-notch Charpy impact test at-20℃.

Improvement of Toughness of UHMWPE/PP Blends

Ultra-high molecular weight polyethylene (UHMWPE) was blended with polypropylene (PP) in order to ensure good processing. Inorganic rigid particles were also used to toughen UHMWPE/PP blends. CaCO3 and a compound additive containing heat mixed polyethylene glycol 2000 and white diatomite were added to the blends. The crystalline, surface morphology and mechanical properties of the blends were investigated comprehensively. The toughness of the material is effectively improved. By contrast, the compound additive had a better result. When the content of additive was 15%, the elongation at the break increased by 279.2% and the fracture energy increased by 343.8% compared to the original samples.

基于热障涂层的La_(2)Zr_(2)O_(7)材料改性研究进展

随着航空发动机不断向高推重比、高性能方向发展,传统、单一的热障涂层(Thermal barrier coating,TBC)已经不能满足热端部件严苛的服役要求。锆酸镧(La_(2)Zr_(2)O_(7))具有熔点高、高温下结构稳定、低热导率等优点,具有极好的隔热性能,有望成为新一代热障涂层候选材料,但在实际应用中仍存在两大关键问题,即热膨胀系数低和断裂韧性差。因此,La_(2)Zr_(2)O_(7)材料在服役过程中会因热失配而造成局部热应力集中,导致涂层过早剥落失效,严重影响涂层的服役寿命。国内外研究表明,对La_(2)Zr_(2)O_(7)材料进行改性可以有效解决上述问题。为此,系统分析了关于La_(2)Zr_(2)O_(7)材料改性的研究工作,将La_(2)Zr_(2)O_(7)材料改性总结为4类:第二相复合、稀土掺杂、纳米化和高熵化。重点介绍了4种不同改性方式对La_(2)Zr_(2)O_(7)材料热导率、热膨胀系数的影响及增韧机理,并对La_(2)Zr_(2)O_(7)材料改性研究工作进行总结和展望,以为La_(2)Zr_(2)O_(7)材料在热障涂层领域的应用提供理论支撑。