Features of ultrasonic wave propagation to identify defects in composite materials modelled by finite element method

A two-dimensional plane strain finite element model with absorbing boundary condition has been developed to investigate the ultrasonic wave propagation in isotropic and orthotropic media. It is capable of simulating the experimental pulse echo technique to obtain A-scan data, when a short duration pulse is transmitted into a domain with or without a flaw. The flaw can either be a crack or an inclusion of different material such as a Teflon insert or a resin rich zone. After performing FFT on the A-scan data, frequency domain feature analysis is done. The study provides a guideline regarding the suitability of certain harmonics sensitive to certain types of flaw. The simulation shows other important artifacts of wave propagation such as mode conversion and scattering due to the presence of flaws.     

Electrical Insulation Characteristics of Silicone and EPDM Polymeric Blends. I

The typical parts of a polymeric insulator are core, metal end fittings and polymeric housing material. The housing is intended to protect the fibre glass rod from the environment and electrical surface discharges. Since the housing materials are made of organic polymeric material, its insulation characteristics need to be studied. Amongst the many different polymers available, this work focuses on silicone rubber and ethylene propylene diene monomer (EPDM). Blends of EPDM and silicone rubber are prepared in a two roll mixing mill. Dicumyl peroxide is used as vulcanizing agent. The blends consisting of various proportions of component polymers are prepared, compression moulded into sheets, and post cured. The blends are tested for their insulation characteristics as per IEC and ASTM standards. Volume and surface resistivity, dielectric strength, dielectric constant, tan delta, tracking resistance, arc resistance, comparative tracking index, tensile strength, and percentage elongation at break of the blends are studied and discussed. The test results show that the increasing proportion of silicone enhances the electrical insulation properties whereas increasing weight percentage of EPDM improves the mechanical strength of the blends.     

Product mix determination in the presence of alternate process plans and stochastic demand

The product mix problem in the presence of alternate process plans under uncertain demand is formulated as a non-linear programming model. A heuristic solution procedure based on lagrangean relaxation technique is also presented.     

APPLICATION OF RESPONSE SURFACE METHODOLOGY FOR THE MAXIMIZATION OF CONCORA CRUSH RESISTANCE OF PAPERBOARD

Response surface methodology is often used by researchers in different fields to determine the optimum values for controlled variables to maximize or minimize the response variables. Either maximization or minimization might be necessary depending on the response property. For example, if the response variable represents the yield of a process, maximization could be necessary; on the other hand, if the response variable is the biological oxygen demand (BOD) of an effluent the aim would definitely be minimization

Response surface methodology can be used two ways. It can be applied to the full-scale production or it can be scaled to a laboratory or the pilot plant. When applied to the full-scale production, the method is known as evolutionary operation (EVOP). EVOP is the continuous optimization of a process. The optimum conditions in a production plant can change depending on many factors such as raw material, ambient temperature, and equipment wear. Therefore, controlled variables should be optimized continuously to keep the response variable as close as possible to the maximum or minimum value. Hence, controlled variables are systematically changed around a center point to depict any shift of the response variable from the extreme. A thorough discussion of EVOP is given by Box, Evolutionary Operation: A Method for Increasing Industrial Productivity, Appl. Statist., 6, 81-101 (1957).     

Dyes from the leaves of deciduous plants with a high tannin content for wool

The aqueous leaf extracts of five different deciduous plants, namely, silver oak, flame of the forest, tanner’s senna, wattle and serviceberry, were used on their own and in combination with aluminium sulphate, stannous chloride and ferrous sulphate to dye wool by a simultaneous mordanting technique. The washing and light fastness properties of the developed shades were moderate to good. Based on the CIE 2000 spectral colour coordinate values (K/S, ΔL, Δa, Δb and ΔE), the developed shades were classified into four groups: yellow/brown, yellow, orange and dark grey. The use of aluminium sulphate gave medium shades (K/S = 8.24), while the stannous chloride and ferrous sulphate mordants provided deep shades (K/S = 30.5). Statistical analyses have shown that only the type of mordant and not the dye source significantly influenced the development of colour on wool. Hence, it was theoretically possible to use five selected leaves as a single mixture to produce four different colours on wool.     

Structural and electrical measurements of CdZnSe composite

TheI—Vcharacterization and the electrical resistivity of selenium rich Se₈₅Cd_15-xZn_x (x = 0, 3, 7, 11 and 15) system at room temperature have been studied. Samples were obtained using melt cooling technique. So prepared samples were then characterized in terms of their crystal structure and lattice parameter using X-ray diffraction method. The materials were found to be poly crystalline in nature, having zinc blend structure over the whole range of zinc concentration. The measurements ofI—V bdcharacteristics have been carried out at different temperatures from room to 140°C. The electrical resistivity of the samples with composition at room temperature has been found to vary between maximum 2.7 x 10⁸ Ωm and minimum 7.3 x 10⁵ Ωm and shows a maximum at 3 at. wt.% of Zn. The carrier activation energy of the samples with composition has also been determined and found to vary from 0.026 eV to 0.111 eV.     

Deceleration of a porous rotating disk in a viscous fluid

The flow due to a rotating disk decelerating with an angular velocity inversely proportional to time with either surface suction (or injection) which again varies with time is investigated. The unsteady Navier-Stokes equations are transformed to non-linear ordinary differential equations using similarity transformations. The resulting equations are solved numerically using a globally convergent homotopy method. The flow depends on two non-dimensional parameters, namely an unsteadiness parameter $\text{S}$ and a suction (or injection) parameter $\text{A}$. Some interesting numerical results are presented graphically and discussed.     

Soil–conduit interaction: an artificial intelligence application for reinforced concrete and corrugated steel conduits

Neural Computing and Applications - Marston’s load theory is commonly used for understanding the soil–conduit interaction. However, there are no practical methods available which can...