Advanced Materials Research Vol. 837

Abstract: In the case of shaft-hub joints with cylindrical pins found in both macro and micro-devices, a longitudinal gutter with an almost half-circular cross section is practiced along the length of the shaft segment. The center of the circular arc is placed on the circular edge of the cross section. The present paper aims to model strain and stress states within such a shaft, when the material elastic properties are known along with shaft segment length and applied torque. Using the MathCad environment, 3D and constant stress level plots were obtained for the distribution of tangential stresses over the cross section. After application of torque, the transverse cross sections shift and become anti-symmetric as illustrated by the obtained 3D and constant strain plots.

Abstract: This paper presents the results of dilatometry and DTA analyses performed on a Ni base super alloy sample on which a ZrO₂/20%Y₂O₃ coating was deposited. The tests were done at similar temperatures as those present in a gas turbine engine at the inlet of the turbine. The purpose is to assess how a turbine blade with a ZrO₂/20%Y₂O₃ coating would behave to changes in volume due to temperature and structural changes. The differential thermal analyses and thermo gravimetric analyses were performed on the DTA PT 1600 Linseis installation. The thermal dilatometry was performed on the L75HX XXXX installation.

Abstract: This paper presents a concept of thermal barrier coating used to prevent exfoliation and increase the maximum working temperature of a turbine engine. The coating consist of a ZrO₂/20%Y₂O₃ ceramic layer and a NiCrAlY adherent layer, deposited by atmospheric plasma spraying (APS), on a Ni super alloy sample usually used for the manufacturing of turbine blades. The sample was subjected to thermal treatment and after that analyzed. SEM images of the samples were taken, to analyze their behaviour to thermal treatment. . Reference sample (without thermal treatment) and samples subjected to 5, 10 and 15 hours heat treatment were investigated using X-ray diffraction in 25-130o 2θ interval.

Abstract: The researches made in the last years have shown that lignin is a substance that gives wood strength. It can be found in the granular form that can be melted and injected. Lignin is used to obtain material with multiple uses such as electronics, food containers etc. This material is known as "liquid wood". Fibers with high specific resistance and high elasticity modules, such as aramid fibers, are used to create high performance composites. Here are the main physical-mechanical properties of aramid fibers: high tensile strength, high shock resistance, high stresses and fatigue, excellent characteristics of damping vibrations, exposure characteristics preservation at temperatures ranging from-700C to + 1800C, flame resistance (self-extinguishing, not melting), low smoke emission, corrosion stability, good electrical characteristics, low conductivity and low dielectric constant. The main areas of use of aramid wires are: special clothes resistance to cutting and high temperature components for materials composite, ropes, cables, lashing straps, safety equipment for the armed forces, police, aircraft, etc. This research used Arboform L, V3 Nature reinforced with aramid fiber. The experimental research plan observes the Taguchi methodology with 6 input factors, each with two levels of variation. The input parameters effects are analyzed on the mechanical properties of the specimens obtained. Micro-indentation tests and differential scanning calorimetry were conducted. The studied test samples showed the following mean recovery values: 31.219μm for the first sample, 31.059μm for the second sample and 25.996μm for the third sample. Three extreme points were detected on the DSC thermogram: an endothermic peak occurs up to 380 K (I) and an exothermic one of higher intensity (II); above 430 K the DSC thermogram shows a deviation from linearity of the flow heat, which suggests a melting phenomenon. The first variation of the heat flow can be attributed to the transformations that occur in solid form in the sample subjected to heating, the first adsorption heat exchanger (peak I) and the second heat releasing (peak II). Comparing the amount of heat absorbed by heat dissipation, one may notice that the exothermic conversion is increased. The initial transformation temperature (Ts 10) corresponds to 10% of the total peak area while the final transformation temperature (Tf 90) corresponds to 90% of the total surface area.

Abstract: The transport of aquatic organisms from one place to another by ships ballast water has created substantial environmental impact on discharging areas. In order to avoid that, the International Maritime Organization (IMO) recommends treating the ballast water by different methods. The paper presents four methods of managing ballast water, accepted by the Organization: treating by filtration and irradiation with ultraviolet light, treating by de-oxygenation, treating with biocide and treating by heating. The comparative analysis of the treating technologies allows the ship-owner to choose such equipment by analyzing the advantages and the disadvantages. Considering that not only the quality parameters are important but also the cost, the study is completed by a mathematical model for calculation of unit cost for treating ballast water onboard. The purpose of this study is to develop an instrument for selecting the optimum method of ballast water treatment suitable for each type of vessel or voyage, so the ship-owners would be able to choose a treatment method comparing the costs, based on the specific requirements.

Abstract: Rail-wheel contact problems have been analyzed by the use of the three-dimensional finite element models. Based on these models, the paper presents a study regarding the applicability of the Hertz contact to rail-wheel contact problems. Beside a standard rail, the study also considers a crane rail and a switching component. The bodies of the contact problem are the standard rail UIC60 and the standard wheel UICORE. The maximum contact pressure which the material can support in the elastic range in steady state conditions is known as the shakedown limit. With an operating contact pressure below the shakedown limit the rail would be expected to remain elastic a long period of its lifecycle. However, examination of rail cross-sections shows severe plastic deformation in a sub-surface layer of a few tens of microns thickness; the contact patch size is in tens of millimeters. Three-dimensional elastic-plastic rolling contact stress analysis was conducted incorporating elastic and plastic shakedown concepts. The Hertzian distribution was assumed for the normal surface contact load over a circular contact area. The tangential forces in both the rolling and lateral directions were considered and were assumed to be proportional to the Hertzian pressure. The elastic and plastic shakedown limits obtained for the three-dimensional contact problem revealed the role of both longitudinal and lateral shear traction on the shakedown results. An advanced cyclic plasticity model was implemented into a finite element code via the material subroutine. Finite element simulations were conducted in order to study the influences of the tangential surface forces in the two shear directions on residual stresses and residual strains. The Hertz theory is restricted to frictionless surfaces and perfectly elastic solids, but it is the best method for determining deformations and stress from pitch of contact. Form change due to wear and plastic deformation of a rail can reduce the service life of a track. The purpose of this investigation was to study the development of these damage mechanisms on new and three years old rails in a commuter track over a period of two years.

Abstract: The paper presents the effect of the discontinuity of the rails of a ferry boat and the presence of lower modulus insulation material at the gap to the variations of stresses in the insulated rail. The analysis consists of a three-dimensional wheel rail contact model based on the finite element method. One of the results shows that the maximum stress occurs in the subsurface of the railhead of the ferry boat. The ratio of the elastic modulus of the railhead and insulation material is found to alter the levels of stress concentration. Numerical result indicates that a higher elastic modulus insulating material can reduce the stress concentration in the railhead but will generate higher stresses in the insulation material, leading to earlier failure of the insulation material. A general subsurface crack propagation analysis methodology is used for the wheel and rail rolling contact. The fatigue damage in the wheel is calculated using a previously developed mixed-mode fatigue crack propagation model. The advantages of the proposed methodology are that it can accurately represent the contact stress of complex mechanical components and can consider the effect of loading non-proportionality. The effects of wheel diameter, vertical loading amplitude, initial crack size, location and orientation on stress intensity factor range are investigated using the proposed model. The prediction results of the proposed methodology are compared with in field observations. The contact elements were used to stimulate the interaction between a wheel and a railhead. Variations in contact stress fields at various locations of the rail are sensitive to the contact distance. The location of the maximum von Mises stress was shifted to the contact surface as the contact point moves close to the rail end. A higher stress, larger deflection and significant plastic deformation occurring at the rail from ferry boat may lead to deterioration at the rail end.

Abstract: Modeling of radio wave propagation onboard ship should take into account multipath effects, i.e., reflection and scattering on the ship conductive superstructure. Novel ultra-wide band communication technology consists of series of short pulses carrying information by changing the polarity as 0 or 1 bits are transmitted. Multipath effects actually impact on the interference free time-slots to be provided between carrier pulses. Narrow-band radio channels are presently modeled either deterministic or stochastic. Although accurate, deterministic models are rather complicated and difficult to use when the configuration of the propagation channel changes. Stochastic models are less sensitive with respect to the configuration of the channel if the distribution of the scatterers and their type do not change dramatically. This paper extends the stochastic, narrow-band log-distance model to ultra-wide band channels. The coefficients of the model are calculated from a set of real data measured onboard a maritime ship. The accuracy of our model is then investigated by comparing the real channel response to the calculated one. Finally, we investigate the channel response to a usual pulse waveform, i.e. the first time-derivative of the Gauss function. The figure of merit to be analyzed is the normalized correlation coefficient or fidelity factor. It should be noted that the dispersion of the measuring antennas was compensated by knowing the gain variation as a function of frequency. This study also leads to minimal values for the time slots between pulses.

Abstract: Vapour compression cycles are commonly used in household refrigerators and also in many commercial and industrial refrigeration systems. R-134a is a working fluid widespread in this kind of systems. A chlorine free refrigerant such as R-134a has a disadvantage in the sense of its relatively high Global Warming Potential (GWP), although the specific Ozone Depletion Potential (ODP) is null. International concern over the relatively high global warming potential of R-134a, and other refrigerants belonging to the same family, will lead in the near future to the stop of their production and use. For this reason, the interest in finding of an environmental more benign substitute for this refrigerant is growing. In the meantime, the alternatives for R-134a should be as thermodynamically attractive as this chemical. In this study it is theoretically assessed the opportunity of using R-600a (isobutane) in the future environment friendly vapour compression refrigeration systems. Choosing of isobutane is explained by the fact that it is a naturally occurring refrigerant. During the thermodynamic analysis, R-134a and R-600a are evaluated for a range of evaporating temperatures starting with 25°C and finishing with 0°C. There are considered three levels of the condensing temperature: 30°C, 40°C, 50°C. For these two refrigerants are compared results regarding saturated vapour pressure, Coefficient of Performance, volumetric cooling capacity, compressor discharge temperature, refrigerant mass flow rate. Also, in the scope of future improvement of systems adopting R-600a as a refrigerant, it is performed an exergy analysis, which is able to reveal the hierarchy of inefficiencies in the system. The results obtained indicate that adopting of R-600a instead of R-134a in vapour compression refrigeration systems is a decision motivated not only by environment reasons, but also by thermodynamic arguments. Values for the Coefficient of Performance when using R-600a are slightly lower than when in use is R-134a, but isobutane offers better environmental requirements like zero Ozone Depletion Potential and very low Global Warming Potential. Exergy analysis developed for R-600a as a working fluid revealed that the most inefficient is the compressor. Better exergy efficiency can be obtained for higher values of the evaporating temperature.

Abstract: We present data obtained after a 2 years period of monitoring the wave’s parameters in an off-shore location. We have used the location of a working petroleum platform situated at: N44⁰31’, E29⁰34’ at 50 km from land and 80 km NE from Constanta Harbor, in the Romanian Black Sea waters. We describe monitoring systems used.and their solution. The Advanced Doppler Velocymeter (ADV) for parameters of marine waves is based on Doppler effect and it is composed of a transmitter at a frequency of 10 MHz and of 3 receivers which are equidistant from 1200. Data storage on the HDD PC, with the possibility of take-over and normal review (ASCII file). We can get the values of the speed and current division marine tide amplitude and direction of the wave at each measurement, the number of measurements, date, hour, minute and second of measurement, as well as other parameters, both as numeric values and a graph having abscissa registration number. This monitoring, which comprises the period of one year including, reveals an amplitude an annual average of the wave of h_med=1.53 m, obtained by taking maximum envelope appeared in a measurement range of 120 seconds. We compare these off-shore values with the coastal ones and we conclude that the wave’s energetic off-shore potential is unexpectedly bigger that in the coastal region.