Advanced Materials Research Vol. 716

Abstract: Carbon nanotube/expanded graphite composite material was prepared by expanding the mixture of multi-walled carbon nanotubes and expansible graphite under the condition of high temperature. The microstructure and composition was studied by using SEM and XRD. The study shows that the tubular structure of carbon nanotubes in the composite material is changed by high temperature expanding process, and the microstructure is different with different expanding temperature. When the expanding temperature was 900°C, carbon nanotubes transformed, then attached to the surface of expanded graphite flake, so carbon nanotubes and expanding graphite combined strongly; globular carbon nanotubes attached to the surface of expanded graphite flake at the temperature of 700°C, both were combined much more strongly; carbon nanotubes retained the tube structure at the temperature of 500°C, combination was looser due to the simple physical adsorption. The result shows that the choice of expanding temperature has an important effect on microstructure of carbon nanotube/expanded graphite composite material.

Abstract: Epoxy asphalt is a thermoset material used in paving industry with good properties in hot environments. However, it is still a brittle pavement in cold environments. Hyperbranched polyester (HBP), which has the characteristics of highly branched structures, massive functional end groups and low viscosity, was used as an active modifier for epoxy asphalt to improve its toughness and processability. It can be found that lower viscosity, higher tensile strength and elongation at break of HBP modified epoxy asphalt than those of epoxy asphalt can be obtained. Modulus of HBP modified epoxy asphalt higher than that of neat epoxy asphalt also indicate the improved stiffness of epoxy asphalt with the introduction of HBP.

Abstract: This paper reports a study of self-healing epoxy composites. The healing agent was a two-component one synthesized in the authors laboratory, which consisted of epoxy-loaded urea-formaldehyde microcapsules as the polymerizable binder and CuBr₂(2-MeIm)₄ (the complex of CuBr₂ and 2-methylimidazole) as the latent hardener. Both the microcapsules and the matching catalyst were pre-embedded and pre-dissolved in the composites matrix cured by 2-ethyl-4-methylimidazole (2E4MIm), respectively. The data of curing kinetics show that the latent hardener CuBr₂(2-MeIm)₄ is not affected during the curing process of 2 h at 80°C, 2 h at 120°C and 2 h at 140°C, and heat deformation temperature of composites consisting of 2 wt% CuBr₂(2-MeIm)₄ and 5 wt% mcirocapsules cured at the same curing process is 180.2°C.

Abstract: Epoxy composites were provided with healing capability by pre-dispersing a novel repair system in the composites matrix cured by 2-ethyl-4-methylimidazole (2E4MIm). The healing agent consisted of ureaformaldehyde microcapsules containing epoxy and latent hardener CuBr₂(2-MeIm)₄ (the complex of CuBr2 and 2-methylimidazole). Single-edge notched bending (SENB) test were conducted to evaluate fracture toughness of the composites before and after healing. Moreover, healing efficiency was studied as a function of the content of the two-component healing agents. It was found that a healing efficiency of 173% relative to the fracture toughness of virgin composites was obtained in the case of 15 wt% epoxy-loaded microcapsules and 3 wt% CuBr₂(2-MeIm)₄.

Abstract: The property and microstructure of pure Al prepared by the cryogenic ECAP after annealing at different temperatures and times with and without the application of 12T high magnetic field were investigated by hardness test and optical microscopy observation. The results show that with the application of high magnetic field, the hardness of cryo-ECAPed pure Al is lower than that of material annealing without high magnetic field. The high magnetic field accelerates crystallization of cryo-ECAPed pure Al during annealing.

Abstract: The quality of two synthetic quartz crystals, Z lump and Y bar, was researched by the infrared spectrophotometer technology and chemical spectral analysis in this study. The relationships between typical impurity OH and other impurities such as Fe, CO and Mg were discussed which impacted the quality of artificial rock crystal; the defects in artificial rock crystal and crystals, such as lattice dislocation and distortion with a close relation appear at the same time and impact the quality of synthetic quartz. The work in future should begin from the following two aspects in order to improve synthetic quartz crystal quality: the one is to further study the crystal structure characteristics and to explore the cutting type of crystal with convenient cultivation and processing process, high use ratio and high Q value. For example, the research is to make the Z area of Y bar crystals bigger and the other areas smaller or disappear. The other one is to improve the existing technological level and to reduce defects.

Abstract: This paper studies the fracture mechanics of a thermoelastic material layer with an internal crack subjecting to a prescribed temperature. The hyperbolic heat conduction theory is used and the transient thermal stress intensity factor is obtained. Comparisons of the results from the non-Fourier model and the Fourier model are made. The results demonstrate that the non-Fourier effect has a strong effect on the transient thermal stress around the crack tip. Thermal stress intensity factor predicted by the hyperbolic heat conduction model is considerably high then that predicted by the classical Fourier.

Abstract: The effect of the nanoscale fractal tree-shaped network on the fluid permeation in wool fiber driven by capillary force was investigated in this paper. The fluid permeation obeys murrays law, and the permeation efficiency highly depends on the fractal dimension of the channel length. A better understanding of the mechanism of structural effect on the tree-shaped flow in the nanoscale fractal network of wool fiber could help the further design of bio-mimetic artificial fiber and functional fabric.

Abstract: In order to solve the deep profile control problem and improve oil recovery of the oilfield, a novel profile control agent pore-scale polymer elastic microspheres (PSPEMs) was synthesized. The swelling property of PSPEMs in aqueous solution was analyzed. Core flow test and double-tube sand pack models were used for studying profile control and flooding performance of PSPEMs in oil formation. The results show that PSPEMs have good swelling property in aqueous solution with high salinity, high temperature and high pressure. Fig 5 and Fig 6 show that PSPEMs are better than polyacrylamide polymer on profile control. Table 1 indicates PSPEMs can improve water injection profile of heterogeneous formation effectively and plug the high permeable layer first. The higher the concentration of PSPEMs, the shorter the time it spends to realize profile control. The results also confirm that use proper concentration of PSPEMs, the profile control efficiency can increase enormously.

Abstract: The fatigue life of S135 drill pipe steel was investigated by means of tension-compression loading and torsion loading under uniaxial loading during the fatigue test. The quantitative formulas of fatigue life were obtained by regression analysis method, and the fatigue fracture mechanism was analyzed. The results show that a linear correlation was found between fatigue life and effective stress in the double logarithmic plots. Cracks initiated from the specimens surfaces under tension-compression loading as well as torsion loading. For the tension-compression fatigue and the torsion fatigue specimens, the main characteristics for cracks propagation were striations and sheares ripple marks, respectively.