Solid State Phenomena Vol. 188

Abstract: Polymer adhesives offer a viable method for mounting silicon dies for high temperature applications. Here a test vehicle for comparing the thermal conductivity of different die attach materials is presented. The setup can be used to determine the degree of degradation of polymers. It consists of a mock die that has an integrated thick film heater, which is mounted onto a substrate. In operation, the substrate is placed on a heatsink and the die is heated. When the temperature reaches equilibrium the heater is switched off and the temperature of the die is measured as it cools. The time constant of the temperature decay is calculated to give the thermal conductivity. In this paper the thermal conductivity of an epoxy die attach adhesive is compared to its shear strength.

Abstract: An innovative multifunctional LTCC module has been designed for miniature atomic clock packaging. Efficient packaging and interconnection of the atomic clock packaging is a critical issue and a precise temperature control is required for some components, such as mini-cell and light source. The great advantage of using LTCC technology for this application is that it allows the integration of different functions, such as heaters and PTCs resistors for temperature measurement and control, and optionally other active elements. In this research, a platform for measuring the thermal conductivity of materials has been developed in order to perform precise thermal studies on the packaging. The relationship between achieved temperature and power dissipated for the heating of the LTCC module has been calculated in different experimental configurations, in order to determine the effects of conduction and convection on the heating and estimate the thermal losses that they introduce into the system.

Abstract: Demand for high-strength alloys in aerospace, marine and off-shore industries has grown significantly over last decades, primarily thanks to their high strength, light weight as well as good fatigue and corrosion-resistance properties. However, these materials are extremely difficult to machine with conventional machining methods. Hot machining is an alternative technique used by many researchers for cutting of hard-to-cut materials in turning and milling operations. In this assisted machining technique, an external heat source is used to reduce shear strength of the machined workpiece, enhancing material removal of such alloys. Drilling is one of the most important and basic operations for producing cylindrical holes in machined components. In this work, a three-dimensional finite-element (FE) model of drilling process is developed in a commercial FE software DEFORM 3D. A nonlinear temperature-dependent material behaviour is incorporated in numerical simulations. The effect of an external heat source on thrust forces and torque on a drill-bit was investigated with the developed FE model. Advantages of hot drilling in reducing thrust force and torque reduction are demonstrated.

Abstract: This paper presents the durability analysis of a machine shaft subjected to bending with torsion, based upon the stress analysis at a notch which joins segments of different cross-sections (circular and square respectively) of the shaft. During the specific operating conditions of the equipment which’s part the shaft is, this notch has proven to be critical, causing premature failure. The durability analysis is carried out based on the real loading conditions, allowing the stress state evaluation at the base of the notch for different radii, using ABAQUS 6.9-3 finite element analysis program. The experimental studies carried out on the shaft’s material, 41Cr4 steel, resulted in the determination of material properties and of torsion fatigue curves in case of two different heat treatments. The cycles composing the equivalent stress spectrum are counted using the rainflow algorithm. The number of loading blocks to failure (number of load spectrum repetitions), considering the real operating conditions, is obtained using Miner’s rule, based on the rotating bending fatigue curve, corrected corresponding to the shaft’s specific characteristics. The proposed calculation method, based on the variation in time of the stress tensor during operating conditions, leads to the determination of the optimal notch radius for which the shaft’s durability falls between prescribed limits.

Abstract: In this paper we present two studies in order to evaluate the residual stresses in two materials. The first one, the residual stresses regenerated in shot peened aluminium plate by neutron diffraction on the strain imaging instrument SALSA at the Institut Laue Langevin, Grenoble, France, also the validation of a model of finite element analysis permitting to predict the final deformation. The second example of this work we use the cobalt-alloys coating deposited on stainless steel forging tools via Plasma Transfer Arc (PTA) process, the evaluation of the residual stresses and characterization of phases close to substrate/coating interface were done by Synchrotron X-ray diffraction.

Abstract: The article emphasizes the improvement of compatibility in a polymer blend composed of two normally incompatible constituents as LDPE and PA6. The effect of amount and type of compatibilizing agents is evaluated using electronic microscopy and dielectric spectroscopy, to obtain the optimum materials structure.

Abstract: A demand for high-strength alloys in aerospace, marine and off-shore industries has stimulated development of new and efficient machining techniques. In the recent past, a novel machining technique known as ultrasonically assisted turning (UAT) has been introduced; in it low-energy ultrasonic vibration is superimposed on movement of a cutting tool. In the present work, a comparative study of machining of two advanced alloys - Ti15V3Cr3Al3Sn and Inconel 718 - is carried out numerically by developing a two-dimensional finite-element model of the turning process. A non-linear material description is used in the FE model to incorporate plastic deformation behaviour of the high-strength alloys. The model is employed to investigate the effect of tool geometry and contact conditions on cutting forces, temperature of the cutting region and the chip shape in orthogonal turning of modern alloys.

Abstract: Continuous casting of steel has gradually replaced traditional casting, due to many advantages such as: casting to a close form to the finished product, low steel losses, the possibility of sequential casting of steel, high productivity, quality of continuously cast product. To benefit of all these advantages, the continuous casting machine must be flexible relative to the demands of customers. This paper presents a comparative analysis relative to main parameters of steel continuous casting for more type of semi-finished product, by processing of data collected from a continuous casting plant with five casting wires. From this study, can be pointed reliable conclusions relatively to the correlation of casting factors and the operating parameters for casting machine and with quality indicators for semi-finished continuous casting product.

Abstract: Within the researches made, the establishment of the processing with synthetic slag decreasing possibilities, of the sulphur and oxygen contents, from the steel made in electric arc ovens, of 100 ton ladle capacity oven (LF) - (EBT) type, was taken into account. For the formation of the synthetic slag, reducing mixing made of lime, fluorine, bauxite and aluminum slag from the aluminum electrolysis were used. On average 1950 kg reducing mix/charge added on three stages were used. The processing period in LF was 40-60 min., and the pressure of Argon used at splashing was in the range of 3.5 - 5.5 at. Within the experiments, for the desulphurisation degree, respectively deoxidation, medium values of: ηSmed = 38,75 (35- 44), ηOmed = 54,821 (47 - 61) were obtained. On the Matlab program data processing, correlation equations between: ηO and ηS and the chemical composition of reducing slag and the parameters of splashing with Argon were obtained.

Abstract: NiTi welded joints in the form of wires or thin blades are used in orthodontic appliances. Problems arise due to welding heat transfer sections specifically reduced. The research is focused on the welding flame, laser and ultrasound. The main objective is to define the characteristics of use of welded joints based on mechanical testing of tensile, hardness determination, metallographic examination. The study was enjoyed on a statistical interpretation of results. The results highlight the comparative strengths, weaknesses of the processes used respectively. It highlights opportunities offered by laser welding process is related to the flame, i.e. ultrasound.