Applied Mechanics and Materials Vols. 110-116

Abstract: The vibration properties of multi-layer beam structure comprising axially non-homogeneous magneto-rheological (MR) fluids layer are investigated. The governing equations of a non-homogeneous MR fluids multi-layered beam are formulated using finite element method and Ritz formulation. The validity of the proposed finite element formulations is demonstrated by comparing the results with those obtained from the Ritz formulation. The properties of different configurations of a non-homogeneous MR-fluid beam are evaluated to investigate the influences of the location of the different MR-fluids for various boundary conditions. The properties in terms of natural frequencies and loss factors corresponding to various modes are evaluated under different magnetic field intensities. The effect of location of the fluid treatment on deflection mode shapes is also investigated. The results suggest that the natural frequencies and loss factors of the non-homogeneous MR fluid beams are strongly influenced not only by the intensity of the applied magnetic field, but also by the location of the MR fluids. It is also concluded that the application of non-homogeneous MR fluids could also alter the deflection pattern of the beam, particularly the location of the peak deflection.

Abstract: The aim of this paper is to find out the randomness in the material properties on the buckling of laminated composite plate needed for the economy, safety and reliability of the structures and components in their operational life especially for sensitive Aerospace Engineering applications in hygrothermal environments. Micromechanical model has been taken for the analysis .The used methodology is a C0 finite element method based on higher-order shear deformation plate theory for deriving the standard eigenvalue problem. A Taylor series based mean-centered first order perturbation technique is used to find out the second order statistics of the hygrothermal buckling loads under different sets of environmental conditions..The numerical results for deterministic parameters are compared and validated with available literature and random parameters with independent Monte Carlo Simulation. The result shows that the plate is significantly affected by the hygrothermal buckling load.

Abstract: Desiccant systems have been proposed as energy saving alternatives to vapor compression air conditioning for handling the latent load. Desiccants are classified as either liquid or solid. The main components for a liquid desiccant system are the dehumidification and regeneration towers. This paper presents the results from a study of the performance of a packed tower absorber for lithium chloride desiccant dehumidification system. A finite difference model was developed to determine the packing height of the dehumidification towers. The finite difference model was written in MATLAB language which is a suitable model to measure the optimum height of a tower. The paper also examines the effects of different design parameters on the height of a packed tower using a mathematical model. The effects of air and liquid flow rates, air humidity, desiccant temperature and concentration were reported on the packing height and humidity effectiveness of the column. In conclusion the results of the present study are compared with previous experimental studies.

Abstract: The accuracy of measurement of opening mode stress intensity factor using strain gage techniques mainly depends on location of the strain gages. The present work proposes a finite element based simple procedure for accurate determination of three parameter zone and optimum strain gage location for various eccentric cracked configurations. In this paper, the effect of specimen size and crack length to width of the eccentric cracked plate on optimum location of strain gage is also studied. The results of the present investigation show that specimen size and ratio of crack length to width of the plate strongly influence the optimum location of strain gage.

Abstract: Thermal interface material is one of the many tools often used as part of the thermal control scheme for space-based applications. An experimental investigation was conducted to better understand the effect of graphite based thermal interface material under vacuum condition. The heat transfer ability of different interface materials was evaluated. Theoretical and experimental studies have yielded valuable data which provide an insight into the complexity of the problem and a better understanding for future development.

Abstract: Fossil fuel resources are decreasing daily and attracted researchers to focus on alternative fuels. Biofuels (renewable fuels) are attracting attention worldwide as blending components or direct replacements for petroleum based fuel in vehicle engines. Moreover, Biofuel will also provide rich biomass and nutrients to the soil. This paper presents the results of performance and emission analysis carried out in a naturally aspirated unmodified diesel engine fuelled with preheated crude palm oil (PCPO) and its blends with diesel. It was observed that preheated CPO reduces exhaust emissions such as CO and HC as compared to ordinary diesel (OD). This is mainly attributed to the fact that preheating of crude palm oil reduces its viscosity to the level of ordinary diesel fuel, which improves the fuel spray and atomization characteristics and produces better combustion.

Abstract: In this paper, mechanical and thermal stresses of rotating hollow disks composed of functionally graded materials (FGMs) is presented. The material properties for FG are expressed as nonlinear exponential functions through the radius of disk and Poisson’s ratio is taken to be constant. The temperature distribution is derived from first law thermodynamics by solving energy equation, general thermal and mechanical boundary conditions are assumed on the inside and outside surfaces of the disk. Heat conduction and Navier equations of a FGM disk are expressed in elliptic cylinder coordinates system and solved analytically. The results are shown for displacement and stresses components along the radial direction.

Abstract: Effects of various grain sizes (10~390 µm) under heating rate of 40 °C/min on ammonium perchlorate (AP) decomposition characteristic parameters, the decomposition thermal behavior and kinetic parameters (activation energy and pre-exponential factor), were investigated by simultaneous DSC/TGA in a dynamic nitrogen atmosphere. In addition, the specific surface areas were measured by the BET-method. Moreover, the kinetic parameters were determined by a simplified approach based on the isoconversional method. The results showed that, the higher the AP particle size the lower the determined decomposition kinetic parameters. In addition, the results were in acceptable agreements with some important literatures. Moreover, it was highly recommended to apply the higher agreeable heating rates for AP samples to determine that parameters more accurately.

Abstract: When deformations are carried out with fine grained microstructure and within a narrow range of strain rates and temperature, metals and ceramics have been shown to exhibit superplastic behavior. Under these conditions the material demonstrates unusually high elongation with a relatively stable microstructure. But when the above mentioned parameters lie beyond a limit, near superplastic behavior is observed. The microstructure changes actively during the process of deformation and the response of the material becomes dependant on the history of loading. A model to describe the dependence on loading history by taking into account the change in microstructure is proposed. The model predicts the general trends observed and also provides possible explanation to some of the effects observed in the experimental data.

Abstract: Dielectric constant and ac conductivity of Polyester doped with carbon black are investigated in the frequency range (0.5-103) KHz and within the temperature range (26-80) oC. Dielectric permittivity and loss tangent reduced with increasing frequency and increase with increasing temperature. The ac conductivity σac for all samples were found to be weak frequency dependent at low frequency, however vary with frequency as a power law ωs at higher frequency range. The variation of frequency exponential factor s between 0.63 and 0.77, indicates a dominant hopping process at low temperatures. From the temperature dependence of dc conductivity, the increase of activation energy was observed with carbon black concentrations.