Addition Of Short Carbon Fibers Research Articles

Joints of carbon fiber-reinforced SiC composites to Ti-alloy brazed by Ag–Cu–Ti short carbon fibers

Ag–Cu–Ti short carbon fibers were used as brazing material to join carbon fiber-reinforced SiC composite and Ti-alloy. The effects of the content of short carbon fibers, brazing temperature and holding time on the shear strength and microstructure of the brazed joints were investigated. The fibers uniformly distribute in the brazing layer of the performed joint and are preferentially oriented in the plane parallel to the brazed surface of the Ti-alloy or the composite. The fibers react with Ti in the brazing layers, forming TiC x thin layers on the fibers themselves and TiC x small particles in the brazing layer. When the brazing temperature is low and the holding time is short, such as 950 °C × 5 min, the addition of short carbon fibers lowers interfacial bonding strength between brazing layer and composite due to the reaction of the carbon fibers. High brazing temperature and long holding time, such as 950 °C × 15 min, bring about pores in the brazing layer. Only the joint brazed at optimal brazing temperature and time and with suitable content of short carbon fibers has maximum shear strength, which is up to 30% higher than maximal strength for the case with pure Ag–Cu–Ti, due to the reduction of the joint thermal stress and the reinforcing effect provided by the carbon fibers.

Simulation of Electrical and Thermal Behavior of Poly(propylene) / Carbon Filler Conductive Polymer Composites

AbstractPP‐carbon CPC show interesting thermo‐electrical properties, smooth resistivity increase with temperature up to 150°C and consequently high power dissipation on a wide temperature range. The addition of short carbon fibers to PP already formulated with carbon black increases sharply the electrical conductivity of the CPC but does not have much influence on thermal conductivity as it could have been expected from the favorable aspect ratio of the fibers. The simulations of the thermo‐electrical behavior of the CPC under tension put into evidence a temperature gradient at high heat flux due to the low thermal conductivity, which may damage the material itself.

Morphology, crystallization and melting behaviors of isotactic polypropylene/high density polyethylene blend: effect of the addition of short carbon fiber

The effect of vapor grown carbon fiber (VGCF) on the morphology, crystallization and melting behaviors of isotactic polypropylene (iPP)/high density polyethylene (HDPE) blend have been studied by means of Scanning Electron Microscopy (SEM) and Differential Scanning Calorimeter (DSC). It is found that the addition of VGCF results in a dramatic change in the morphology of iPP/HDPE blends. The crystallization peak temperature and melting point of iPP are not altered significantly by the blending. However, the degrees of crystallinity of iPP in the blends are reduced. Compared with the unfilled blends, the crystallization peak temperatures of iPP increase dramatically for the composites. The isothermal crystallization behavior of iPP is further investigated. The analysis of the crystallization half time shows that the crystallization rate of iPP is reduced by the presence of HDPE melt, and is enhanced by carbon fibers. For the unfilled blends in which iPP is the major component, the Avrami exponent closes to 3, independent of the HDPE content. However, for the composites, the Avrami exponent varies with the composition in a rather complex manner. An explanation based on heterogeneous and homogeneous nucleation is supposed. The sharp changes in the crystallization and melting behaviors for the composites containing 30–35wt% HDPE correspond to the sudden change in the morphology of the two phases. It is supported by the observation of SEM and the electrical measurement.

Effect of carbon fibers on the vibration-reduction ability of cement

The addition of short carbon fibers (0.5% by weight of cement) to cement paste containing silica fume (15% by weight of cement) and methylcellulose (0.4% by weight of cement) causes the loss tangent under flexure at a loading frequency of ⩽1 Hz to decrease by up to 25% and the storage modulus (⩽2 Hz) to increase by up to 67%, such that both effects increase in the order: as-received fibers, ozone-treated fibers, dichromate-treated fibers, and silane-treated fibers. The addition of methylcellulose to cement paste containing silica fume causes the loss tangent to increase by up to 50% and the storage modulus to decrease by up to 14%. Silane treatment of silica fume has little effect on the loss tangent, but increases the storage modulus by up to 38%.

Improving brick-to-mortar bond strength by the addition of carbon fibers to the mortar

The addition of short carbon fibers in the optimum amount of 0.5% of the cement weight to mortar increased the brick-to-mortar bond strength by 150% under tension and 110% under shear when the gap between the adjoining bricks was fixed, and by 50% under tension and 44% under shear when this gap was allowed to freely decrease due to the weight of the brick above the joint. This effect is attributed to a decrease of the drying shrinkage by the fiber addition. The drying shrinkage decrease was particularly large at 2 to 24 h of curing. At 24 h, the shrinkage was decreased by 50% by the addition of fibers in the amount of 0.5% of the cement weight. Fibers in excess of the optimum amount gave less bond strengthening due to increased porosity in the mortar.

Improving the abrasion resistance of mortar by adding latex and carbon fibers

The abrasion resistance of mortar was found to be significantly improved by the addition of latex (20% by weight of cement), and further improved by the further addition of short carbon fibers (0.27 vol.%). Both effects relate to the increase in tensile strength. The abrasion resistance was also improved by the addition of silica fume (15% by weight of cement), due to the increase in tensile modulus. The abrasion resistance was better for mortar with silica fume than mortar with latex, but was worse for mortar with silica fume than mortar with latex and carbon fibers.

Brick Structure Improved by Using Cement Mortar Containing Short Carbon Fibers

AbstractThe addition of short carbon fibers in the optimum amount of 0.5% of the cement weight to mortar increased the brick-to-mortar bond strength by 150% under tension and 110% under shear when the gap between the adjoining bricks was fixed, and by 50% under tension and 44% under shear when the gap between the adjoining bricks was allowed to freely decrease due to the weight of the brick above the joint. This effect is attributed to the decrease of the drying shrinkage by the fiber addition. The drying shrinkage decrease was particularly large at 2 to 24 h of curing. At 24 h, the shrinkage was decreased by 50% by the addition of fibers in the amount of 0.5% of the cement weight. Fibers in excess of the optimum amount gave less bond strengthening due to increased porosity in the mortar.

Improving the bonding between old and new concrete by adding carbon fibers to the new concrete

The addition of short carbon fibers in the amount of 0.35 vol.% resulted in mortars that bonded more strongly to old mortars. The increase in shear bond strength was up to 89%. This effect is attributed to the lowering of the drying shrinkage by the fiber addition. The effect is largest when the fibers were used with latex, which was in the amount of 20% of the cement weight.