Advanced Materials Research Vols. 383-390

Abstract: Recently, the fiber reinforced composite embedded with visco-elastic layer has received great attention because of its good damping capability. Damping is an important feature for dynamic behaviour of composite structures, which alleviates the resonant vibrations and thus prolongs the service life of structures under fatigue loading or impact. The present paper deals with the dynamic response of a 3D composite structure embedded with visco-elastic layer. The modal analysis, harmonic analysis and transient analysis are carried out respectively. The amplitude of z-displacement of a specific node on the bottom reduces quickly due to the high damping of the visco-elastic layer.

Abstract: Recently intensive research has been carried out on carbon nanotube (CNT) based polymer composites. However, in this work the macro scale IM700 carbon fiber (CF) has been integrated with amino modified multi-wall carbon nanotubes (MWCNT-NH2) within LY-556 epoxy matrix to produce three-phase, multi-scale composites, with the applications in missiles. The fictionalization of CNTs has been carried out for improved and consistent mechanical and physical properties. High frequency probe sonication method was used for homogenous dispersion of CNTs. Mechanical characterization of the multiscale composites fabricated by hand layup process included tensile, flexure and inter-laminar shear stress tests. The addition of small amounts of MWCNTs (upto 1.5 weight %) for the fabrication of multiscale composites resulted in a maximum enhancement in tensile strength by 23% , flexural modulus by 35%, flexural strength by 5% and ILSS by 7%. CF/epoxy composites (without CNTs) have also been characterized for comparison with MWCNT-NH₂ /CF/ epoxy composites. For a more accurate prediction of the Young’s moduli of multi-scale composites several micromechanical models (Voigt-Reuss, Halpin-Tsai, and modified mixture Law) compared with the experimental work. These models have been tested for upto 1.5 weight % of CNTs. The difference of approximate 28% of the values in Young’s modulus has been reported in the classical micromechanical models and experimental results and it comes out 11% for CF/epoxy composites as they do not have reinforcement of CNT’s within it. In all the classical models, the Young’s moduli of the carbon nanotube composites were used as matrix properties.

Abstract: In this study, aluminum alloy (Al-2wt. % Cu) matrix composites reinforced with 1, 2 and 4 wt. % boron carbide nanoparticles with average size of 80 nm were fabricated via stir casting method at 850 °C. The microstructures of composites were studied by scanning electron microscope (SEM). Density measurement, tensile and compressive tests were carried out to identify the mechanical properties of composites and effect of B4C nanoparticles amount. In all fabricated composites, severe agglomeration was observed in the micrographs. With increasing the amount of B4C nanoparticles up to 2 wt. %, yield and tensile strength increased but with more increasing B4C content they were decreased. Also, the compressive strength of samples was increased with increasing weight percentage of B4C nanoparticles.

Abstract: Mechanical milling was used to synthesize Al nanostructured powder in a planetary ball-mill under argon atmosphere up to 20 h. The same process was conducted for Al-4 wt. % B4C nanocomposite powders to explore the role of nanosize reinforcements on mechanical milling stages. The results show that the addition of boron carbide particles accelerate the milling process, leading to a faster work hardening rate and fracture of aluminum matrix. Tensile of a nanostructured matrix of Al prepared via hot extrusion were investigated before and after incorporation of B4C nanoparticles. The results revealed a, higher yield strength and tensile strength for nanostructured Al matrix in contrast to the commercial coarse grained Al matrix. The same trend was also found to be valid for the nanocomposite samples with respect to the base matrix.

Abstract: Using polypropylene (PP) as matrix and kenaf mat as reinforcement, composite test samples were fabricated by compression molding. Thereafter, the effect of fibre loading and the alkaline fibre surface treatment on the mechanical properties were studied. The kenaf/PP composites were found to have better mechanical properties than the polymer matrix. As expected, the interfacial bonding between the matrix and the fibres improved considerably when the fibres were subjected to alkaline treatment.

Abstract: Hybrid tubes made by metal and composite combine the benefits of the high strength to weight ratio of the fiber/resin composite and the stable, ductile plastic collapse mechanism of the metal, to form a composite tube with high strength and energy absorption capability. The improvement of energy absorption parameters of circular steel tube as crash energy absorber that usually is used in automobile and train structures is studied in this paper. In order to improving energy absorption characteristics, circular steel tube wrapped by glass fiber reinforced polyester with different fiber orientation and various number of layers tested under axial quasi-static loading to achieve the optimum structure.

Abstract: In this research, a new application of friction stir processing (FSP) in producing surface composite on circular billets was introduced. Al/Cu composite was fabricated by FSP on the surface of a 1050 aluminium cylinder with the diameter of 60 mm. Then this cylinder with surface composite was extruded with the extrusion ratio of 1.7. Finally, microstructure and microhardness were investigated before and after the extrusion. H13 hot work steel was used as the material of the tool whose pin diameter and length were 6 mm and shoulder diameter was 18 mm. The rotation and traverse speed of the tool were 1000 rpm and 25 mm/min respectively. The microstructural investigations show that the thickness of the composite layer decreases and a uniform layer of the composite remains on the surface after the extrusion. Also the microhardness measurements demonstrated that the hardness of the composite layer was higher than the base metal and the microhardness of all zones increased after the extrusion.

Abstract: Friction stir processing (FSP) was used to fabricate Al/Cu metal matrix composite (MMC). The effects of two different tool pin profiles (straight cylindrical and square) and the number of FSP passes on microstructure, tensile properties and microhardness were studied. The results indicated that good dispersion of micro-sized Cu particles, finer grains, higher tensile properties and higher microhardness, can be achieved by the square tool pin profile compared to the samples produced by the other tool. Also it was observed that the ultimate tensile strength of the samples produced by two FSP passes, as a result of Cu particles shattering, increased intensively compared to the samples fabricated with first FSP pass. Further FSP passes increased the elongation of the composites without any considerable changes in yield and ultimate tensile strength.

Abstract: Pure Aluminium mixed with SiC powder (size 70 micron) in 5, 10 , 15 and 20 percentage weight fractions have been stir cast and test samples have been made. The samples have been machined to produce 8 mm diameter pins for testing in Pin on Disc wear monitor under water lubricated condition. The wear behaviour of these samples has been studied by plotting the wear rates against sliding distance and velocity. The co efficient of friction has been found out under varying load and varying time. The results were compared with that of pure aluminium under similar test conditions. It has been found that the sample having 20% weight fraction of SiC with highest hardness has maximum wear resistance under such conditions.

Abstract: Composite soils have been widely used in civil engineering applications, especially in slopes, embankment dam and landfills. This paper aims to investigate effect of fiber inclusion on shear stress of composite soil (i.e. sand composite). A series of laboratory direct shear tests carried out to evaluate fiber effect on strength behavior of composite sand. Clayey sand was selected as soil part of the composite and glass fiber was used as reinforcement. The fiber parameters differed from one test to another, as fiber length were changed from 10 mm to 35 mm and fiber content were varied from 0.6% and 3%.Normal stress kept constant at 150 kpa. For each test, stress_ displacement graph derived and the results were compared. The results proved that inclusion of fiber affected strength behaviour of sand composite so that increasing in fiber content and length caused increasing in shear stress.