Main properties of ultra-high performance fiber reinforced cement composites under couple effect of load and environment

This study aims to reveal the mechanism that how the content of steel fibers and strength grades affect the macro performance of the ultra-high performance fiber reinforced cementitious composite （UHPFRCC） and to study the UHPFRCC durability under the combined effect of loads and environments. Three types of high and ultra-high performance fiber reinforced cement composites with different strength grades （100, 150, 200 MPa） and different steel fiber volume fractions （0%, 1%, 2%, 3%） are prepared. The main properties of mechanical performance and short-term durability are studied. A preloading frame is designed to apply a four- point load external flexural stress with a stress selection ratio of 0.5 for UHPFRCC150 specimens. The results show that the growth in strength grade with a proper content of steel fiber greatly increases the strength and toughness of the HPFRCC and the UHPFRCC while decreasing the dry-shrinkage ratio. For the loaded specimens, the existence of steel fiber can reduce the negative influence of tensile stress on the Cl- penetration resistance of the UHPFRCC in addition to improving its ability to resist the freeze-thaw damage.

OBSERVATIONS ON DEFORMATION BEHAVIOR OF HIGH PERFORMANCE FIBERS BY POLARIZING OPTICAL MICROSCOPY

By means of polarizing optical microscopy (POM), deformation behavior of four kinds of fibers, i.e, ultra high molecular weight polyethylene (UHMW-PE) fiber, polyvinyl alcohol (PVA) fiber, polyethylene terephthalate (PET) fiber, and wholly aromatic (rho-hydroxybenzoic acid/2-hydroxy-6-naphthoic acid) copolyester [P(HBA/HNA)]/PET (ACPET blend) fiber, in axial compression, axial impacting, and bending was observed. In compression, kink bands formed at an angle of 55-60 degrees ro the fiber axis in 10-times-drawn UHMW-PE fiber, 75-80 degrees in 40-times-drawn sample, 80 degrees in PVA fiber, and 90 degrees in the ACPET blend fiber. In impacting and bending, band angles of UHMW-PE, PVA and PET fibers are nearly the same as those formed in compression, indicating that slip systems do not change. For any of the four kinds of fiber, band spacing exhibits great differences in compression, in impacting, and in bending, which may be attributed to the differences in the degrees of strain or stress concentration.

Dynamic Mechanical Behaviour of Ultra-high Performance Fiber Reinforced Concretes

Ultra-high performance fiber reinforced concretes （UHPFRC） were prepared by replacing 60% of cement with ultra-fine industrial waste powder. The dynamic mechanical behaviour of UHPFRC with different fiber volume fraction was researched on repeated compressive impact in four kinds of impact modes through split Hopkinson pressure bar （SHPB）. The experimental results show that the peak stress and elastic modulus decrease and the strain rate and peak strain increase gradually with the increasing of impact times. The initial material damage increases and the peak stress of the specimen decreases from the second impact with the increasing of the initial incident wave. Standard strength on repeated impact is defined to compare the ability of resistance against repeated impact among different materials. The rate of reduction of standard strength is decreased by fiber reinforcement under repeated impact. The material damage is reduced and the ability of repeated impact resistance of UHPFRC is improved with the increasing of fiber volume fraction.

Transfer of β-hydroxy-β-methylbutyrate from sows to their offspring and its impact on muscle fiber type transformation and performance in pigs

Background： Previous studies suggested that supplementation of lactating sows with β-hydroxy-β-methylbutyrate（HMB） could improve the performance of weaning pigs, but there were little information in the muscle fiber type transformation of the offspring and the subsequent performance in pigs from weaning through finishing in response to maternal HMB consumption. The purpose of this study was to determine the effect of supplementing lactating sows with HMB on skeletal muscle fiber type transformation and growth of the offspring during d 28 and180 after birth. A total of 20 sows according to their body weight were divided into the control（CON, n = 10） or HMB groups（HMB, n = 10）. Sows in the HMB group were supplemented with β-hydroxy-β-methylbutyrate calcium（HMB-Ca） 2 g/kg feed during d 1 to 27 of lactation. After weaning, 48 mixed sex piglets were blocked by sow treatment and fed standard diets for post-weaning, growing, finishing periods. Growth performance was recorded during d 28 to 180 after birth. Pigs were slaughtered on d 28（n = 6/treatment） and 180（n = 6/treatment） postnatal and the longissimus dorsi（LD） was collected, respectively.Results： The HMB-fed sows during lactation showed increased HMB concentration（P ＆lt; 0.05） in milk and LD of weaning piglets（P ＆lt; 0.05）. In addition, offsprings in HMB group had a higher finishing BW and lean percentage than did pigs in CON group（P ＆lt; 0.05）, meanwhile, compared with pigs from sows fed the CON diet, pigs from sows fed HMB diet showed higher type Ⅱ muscle fiber cross-sectional area（CSA）, elevated myosin heavy chain（MyHC） Ⅱb and Sox6 mRNA, and fast-MyHC protein levels in LD（P ＆lt; 0.05）.Conclusions： HMB supplemented to sow diets throughout lactation increases the levels of HMB in maternal milk and skeletal muscle of pigs during d 28 after birth and promotes subsequent performance of pigs between d 28 and 180 of age by enhancing glycolytic muscle fiber transformation.

Performance improvement of continuous carbon nanotube fibers by acid treatment

Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers＇ properties.After HCISO_3 treatment for 2 h,the fibers＇ strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G＇ band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.

The influence of Fe extracting as a filler of fiber concrete performance

This research is showing the effect of increasing an Fe extracting from the compression strength, tension and bending moment. The variations in this experiment are the increasing of Fe extracting 0.5%, 1% and 1.5% of concrete volume. Water Cement Ratio （WCR） variation of 0.48, 0.56 and 0.60. The result of increasing 1.5% Fe extracting causes the increasing of tension strength 44.028 kN/cm2, the increasing of slit tension strength 2.226 kN/cm2, the increasing of bending moment 14.81 kN/cm2 from normal concrete. 0.48 WCR produces tension strength, slit tension strength and bending moment more than 0.56 and 0.60 WCR. The increasing of Fe extracting with the distribution variation area and the spread concrete in the tension concrete area produce 3.705 kN/cm2 bending moment higher than the spread fiber in all of concrete area. The 4 cm fiber length produces the higher bending moment than the 2 cm fiber length. The difference is equally 5.185 kN/cm2. The combination result of the examined acting varieties by continuation statistic test gives the result to get the maximum tension and split tensile. It is a concrete combination of increasing 1.5% fiber percentage, 0.48 WCR, full spreading area and the 4 cm fiber length. The maximum bending moment is the increasing of 0.5% fiber percentage, 0.48 WCR, full spreading area and the 4 cm fiber length.

Influence of different curing regimes on the microstructure and macro performance of UHPFRCC

This study investigates the influence of different curing regimes on the microstructure and macro properties of ultra-high performance fiber reinforced cementitious composite （UHPFRCC）, and aims to discover whether it is possible to produce qualified UHPFRCC using different curing regimes. A control mix of UHPFRCC is prepared. The mechanical performance and the short-term durability of the UHPFRCC matrix under three curing regimes are studied. In addition, the microstructures of the UHPFRCC matrix with different curing conditions are analyzed by combining scanning electron microscopy （SEM） and mercury intrusion porosimetry （MIP）. The results explore how different UHPFRCC curing regimes affect its microstructure and how the microstructure affects its macro behavior. Heat and steam curing for 3 d is succeeded to produce the UHPFRCC with nearly the same mechanical properties and durability as those of the 90 d standard curing. However, the heat cured UHPFRCC does not show great resistance to chloride-ion penetration.

Structural Design and Analysis of a Booster Arm Made of a Carbon Fiber Reinforced Epoxy Composite Material

An analysis of a booster arm made of a carbon fiber reinforced epoxy composite material is conducted by means of a finite element analysis method.The mechanical properties are also determined through stretching and compression performance tests.It is found that the surface treatment of the fibers causes the silane coupling agent to undergo a chemical reaction on the surface of the glass fiber.The used material succeeds in producing significant vibrations damping(vibration attenuation effect is superior to that obtained with conventional alloy materials).

Behavior of High Performance PVA Fiber Reinforced Cement Composites in Triaxial Compression

Based on an extensive experimental program,the paper studies the behavior of HPFRCC under triaxial compression. The experimental parameters are lateral confining pressure and PVA fiber content by volume. The test results indicate that ultimate strength and peak strain are significantly improved with the increases of confining pressure. The confining effect introduced by the fibers becomes minor in triaxial compression tests,where there is relatively high external confining pressure. The axial stress-strain curves with different confining pressure and different PVA fiber content by volume are obtained. Lateral confining pressure constraints the lateral expansion of HPFRCC,so there is a big plastic deformation with its ultimate strength improved. At lower confining pressure,PVA fiber content by volume has some effect on the decreased section of stress-strain curve. According to test results,the paper establishes formula of confining pressure with ultimate strength and axial peak strain respectively.

Investigations on the Interactions between Li-TFSI and Glass Fibers in the Ternary PP/GF/Li-TFSI Composites

The polypropylene/glass fiber（PP/GF） composites with excellent antistatic performance and improved mechanical properties have been reported by incorporation of a very small amount of the organic salt, lithium bis（trifluoromethanesulfonyl）imide（Li-TFSI）, into the PP/GF composites. It was considered that GF could play the role as the pathways for the movements of ions in the ternary composites. In this work, the interactions between Li-TFSI and glass fiber and the effects of such interactions on the physical properties of the composites have been systematically investigated. Three types of glass fibers with different ―OH group concentrations have been prepared in order to compare the interactions between GF and Li-TFSI. It was found that the ―OH group concentrations on the surface of glass fiber have significant effects on interactions between glass fibers and Li-TFSI. Such interactions are crucial for both the antistatic and mechanical performances of the final PP/GF/Li-TFSI composites. The investigation indicated that the GF with high ―OH group concentrations confined the movement of TFSI-, which decreased the antistatic properties of PP/GF/Li-TFSI composites. On the other hand, the GF with low ―OH group concentrations inhibited the absorption of Li-TFSI onto the GF, which also hindered the formation of Li-TFSI conductive pathway. The best antistatic performance of the ternary composites can be achieved at the intermediate ―OH concentrations on the GF.

Electrospinning of GeO_2–C fibers and electrochemical application in lithium-ion batteries

GeO2–C fibers were successfully synthesized using electrospinning homogeneous sol and subsequent calcination in an inert atmosphere. The spinnable sol was prepared by adding polyacrylonitrile（PAN）and polyvinylpyrrolidone（PVP） in a weight ratio of 1：1 into a mixture with white precipitate produced by dropping GeCl4 into DMF. X-ray diffraction（XRD）, X-ray photoelectron spectroscopy（XPS）,thermogravimetric analysis（TGA）, scanning electron microscopy（SEM） and transmission electron microscopy（TEM） were employed to characterize the as-obtained fibers, and electrochemical tests were conducted to measure electrochemical performance of the electrode. The electrospun fibers have uniform diameters of 300 nm. After being calcined at 600 8C for 2 h in Ar, they transform to amorphous GeO2–C fibers with the same morphologies. The Ge O2–C fibers exhibit excellent cycling stability with a high reversible capacity of 838.93 m A h g^-1after 100 cycles at a current density of 50 m A g^-1, indicating the composite fibers could be promising anode candidates for lithium-ion batteries.