Applied Mechanics and Materials Vols. 110-116

Abstract: Al alloy/SiC composites possess better mechanical and physical properties thus finding applications in automotive, sports, and aerospace. In some cases, these components require nanolevel finished surface. But, traditional abrasive finishing processes are labor intensive, time consuming and confined to only simple geometries. Abrasive flow finishing (AFF) is one of the advanced finishing processes that can be used to finish complex surfaces by flowing polymer based abrasive medium but its finishing rate is low. In the present work, Rotational-AFF (R-AFF) process is developed where in workpiece rotates about its axis. This rotation provides the dynamic motion (additional force and velocity components) to the workpiece. By cumulative effect of workpiece rotation and medium reciprocation, the active abrasive particles try to abrade the workpiece in a helical path. Thus, finishing length and finishing rate both increase. In AFF process, because of more finishing time medium undergoes chemical change or degradation (loses its viscosity) because of continuous shearing and rise in temperature. Therefore the effect of medium shear viscosity variation with the temperature is studied to understand how the viscosity reduces with the temperature. Later complete experiments are conducted on R-AFF process by varying plasticizer to polymer volume ratio and polymer to abrasive ratio. The finishing from micron surface topography to nanosurface topography is studied using atomic force microscopy.

Abstract: This work presents a comprehensive investigation of the piezoresistive response of a metal-polymer composite for robotic tactile sensor application. Composite samples, based on nickel nanostructured conductive filler in a polydimetihylsiloxane (PDMS) insulating elastomeric matrix, were prepared changing several process parameters like thickness, composition of the polymer and nickel filler content. A variation of electric resistance up to nine orders of magnitude under applied uniaxial load was measured in the fabricated samples. Cost efficient materials, simplicity of the process, large sensibility, and harsh environment compatibility make this quantum tunnelling composite adapted to be integrated as sensing coating in space robotic applications.

Abstract: The superposition-finite element method is developed to analyze the mixed-mode delamination in laminated composites. Both a coarse global mesh and an overlaying fine local mesh are integrated into the finite element analysis model. The whole design domain is discretized by a uniform global mesh, while the high stress regions are discretized by fine local meshes. Local mesh is built independently from the global mesh, which greatly simplifies the model generation procedures. Strain energy release rate is calculated based on the modified virtual crack closure-integral method, which is used to describe the propagation of delamination in laminated composites. Mixed-mode bending tests are performed for unidirectional and cross-ply carbon fiber reinforced laminated composites to characterize the interlaminar fracture behavior under mixed-mode I/II loading conditions. The interlaminar fracture toughness is also given for different mixed-mode ratio. It is seen that fracture resistance for laminated composites exhibit R-curve behavior (increase as delamination propagation). However, once the delamination is sufficiently long, the interfacial fracture toughness changes slightly as the delamination extended and become almost independent of the delamination length. The results of finite element method are in good agreement with the experimental results and provides a basis for establishing failure criterion used in damage tolerance analysis of composite structures.

Abstract: In this paper an energy-based model for predicting fatigue life and evaluation of progressive damage using plane-stress assumption is proposed. This model allows us to predict fatigue durability taking into account principal directions of the stress tensor relative to planes of elastic symmetry of material. First, the unknown parameters of this model will be calculated for three different composites with various lays-up. Method for determining these parameters is based on the minimum necessary set of experimental data. Afterwards the model was used to predict fatigue life and estimate accumulated fatigue damage in a unidirectional composite under different angles of loading. The analysis of conclusions of the theory for various loading conditions was carried out and performed comparison between the experimental data and predicted results. The predicted fatigue lives obtained by the proposed energy model were in good agreement with the experimental data.

Abstract: — Using Composite materials are growing more and more today and we have to use them in possible situation. One of the Composite materials applications is on the Airplane and aero space. Reduction of Airplane weight and more adaptability with nature are examples of benefit of using composite materials in aerospace industries. In this article process of manufacturing of composite materials and specially carbon fiber composite are explained. Advance composite materials are common today and are characterized by the use of expensive, high-performance resin systems and high-strength, high-stiffness fiber reinforcement. The aerospace industry, including military and commercial aircraft of all types, is the major customer for advanced composites. Product range now includes materials for low pressure and low temperature. Some using composite materials in aero space are as follow: Satellite Components, Thin Walled Tubing for Aircraft and Satellites, launch vehicle components and honeycomb structures.

Abstract: The heterogeneous catalyst are environment friendly and render the process simplified. A wide variety of solid bases have been examined for this process. The present work reports the use of hydrotalcite catalyst for the synthesis of Biodiesel from jatropha oil. An experimental investigation has been carried out to analyze the performance and emission characteristics of a compression ignition engine fuelled with Jatropha oil and its blends (10%, 20%, 40%, 50%, and 60 % ) with mineral diesel. The effect of temperature on the viscosity of Jatropha oil has also been investigated. A series of engine tests, have been conducted using each of the above fuel blends for comparative performance evaluation. The performance parameters evaluated include thermal efficiency, brake specific fuel consumption (BSFC), brake specific energy consumption (BSEC), and exhaust gas temperature whereas exhaust emissions include mass emissions of CO, HC, NO. These parameters were evaluated in a single cylinder compression ignition diesel engine. The results of the experiment in each case were compared with baseline data of mineral diesel. Significant improvements have been observed in the performance parameters of the engine as well as exhaust emissions. The gaseous emissions of oxide of nitrogen from all blends are lower than mineral diesel at all engine loads. Jatropha oil blends with diesel (up to 50% v/v) can replace diesel for operating the CI engines giving lower emissions and improved engine performance. More over results indicated that B20 have closer performance to diesel and B100 have lower brake thermal efficiency mainly due to its high viscosity compared to diesel.

Abstract: — Aluminum alloy based metal matrix composites are becoming very popular because of their outstanding properties such as high strength to weight ratio, excellent mechanical properties and improved wear properties. From literature survey it was observed that very limited report available on Aluminum alloy-beryl composites, particularly on the effect of beryl content, quenching media and heat treatment on the mechanical and wear properties of Aluminum-beryl composites. Accordingly, the aims of the present study are (i) preparation of Al6061-beryl particles by liquid metallurgy method (stir cast) with possible standardization of the beryl addition to liquid Aluminum alloy, (ii) Study the effect of different quenching media and the beryl content (2-12 wt. %) on the mechanical and wear properties of these composites in both as cast and heat treated conditions. Heat treatment procedure of solutionising at temperature of 5300C for 1hour and quenching in different media (air, water and ice) followed by natural and artificial ageing for different times was adopted. It was observed that the addition of beryl particles to Al6061 alloy improves its hardness, tensile strength and wear resistance with increasing beryl content while the heat treatment had significantly improved these properties compared to that of base alloy and as cast composites.

Abstract: In this paper, experimental investigation of pressure exponent in burning rate of composite propellant was conducted. Four sets of different propellant compositions had been prepared with the combination of Ammonium Perchlorate (AP) as an oxidizer, Aluminum (Al) as fuel and Hydroxy-Terminated Polybutadiene (HTPB) as fuel and binder. For each mixture, HTPB binder was fixed at 15% and cured with isophorone diisocyanate (IPDI). By varying AP and Al, the effect of oxidizer-fuel mixture ratio (O/F) on the whole propellant can be determined. The propellant strands were manufactured using compression molded method and burnt in a strand burner using wire technique over a range of pressure from 1atm to 31atm. The results obtained shows that the pressure exponent n, increases with increasing O/F. The highest pressure exponent achieved was 0.561 for propellant p80 which has O/F ratio of 80/20.

Abstract: After sulfur-plus-gold sensitization on silver bromoiodide (AgBr/I) microcrystal emulsions prepared by the emulsifying process in the double-jet apparatus controlled by a microcomputer, a certain amount of oxalate salt (1×10-1、1×10-2、1×10-3and 1×10-4mol/molAg) was respectively added at a specific time and pAg to a reactor to prepare a series of tabular silver bromoiodide (AgBr/I) microcrystal at whose surface oxalate ions and Ag2S or AuAgS were doped. The sensitometric results from these crystal emulsions showed: 1) that the sensitivities of oxalate-doped AgBr/I emulsion, relative to that of the undoped emulsion as the controlled one, were remarkably increased; 2) that a cooperative sensitization by oxalate dopant, sulfur-plus-gold was observed without any significant increase in fog level when 10-3—10-4 mol/molAg oxalate was doped；3） that sensitivity gain (SG) was maximal, when 10-3mol/molAg oxalate (in 10-1—10-4 mol/molAg ) was doped at the surface of AgBr/I grains.

Abstract: In this paper, the silicone rubber composed of carbon fibers was prepared. The influence of different concentration of carbon fibers on the conductivity, electromagnetic shielding interference effectiveness property of the silicone rubber was discussed from the point of view of condition of carbon fiber and silicone rubber. The results showed that there existed the extreme conductivity and shielding effectiveness (SE) across the tested frequency range from 2.6 GHz to 3.95 GHz of silicone rubber composites filled with carbon fibers. When the content of the carbon fibbers was 50 parts per hundred of rubber (phr), the SE values of composites were typically above 63 dB and close to the extremum. The compact packing structure of carbon fibers does not play an important role in improved the conductivity of composite. The SE of the composite depends on the conductivity of composite.