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Metallic materials play important roles in providing electrical, thermal, and mechanical functions in electronic devices and systems. The understanding of the electrical-thermal-mechanical interaction caused by the passage of electric current with high density is important to improve the performance and reliability of electronic assembly and packaging. The electromechanical interaction on the deformation behavior of copper and tin is studied in this work. The electromechanical response of Cu strips was studied by passing a DC electric current. The electric resistance linearly increased with time before the occurrence of electric fusing. The electrothermal interaction led to the buckling of the Cu strips with the maximum deflection increasing with the increase of the electric current density. The total strain was found to be proportional to the square of the electric current density. A power law relation was used to describe the dependence of the time-to-fusing on the electric current density. Using the nanoindentation technique, the effect of electric current on the indentation deformation of copper and tin was studied. The reduced contact modulus of copper and tin decreased with increasing the electric current density. With the passage of a DC electric current, the indentation hardness of copper increased slightly with increasing electric current density. With the passage of an AC electric current, the indentation hardness of copper decreased with increasing the indentation deformation. With the passage of a DC electric current, the indentation hardness of tin decreased with increasing the indentation load, showing the normal indentation size effect. Both the limit of infinite depth and the characteristic length were dependent on the electric current density. Using the tensile creep technique, the creep deformation of pure tin was studied with the passage of a DC electric current. The steady state creep rate increased with the increase in temperature, tensile stress and electrical current density. For the same tensile stress and the same chamber temperature, the steady state creep rate increased linearly with the square of the electric current density. The electric current density has no significant effect on the stress exponent and activation energy of the tensile creep of tin for the experimental conditions.

Abstract Dynamic electrical resistance during resistance spot welding has been quantitatively modeled and analyzed in this work. A determination of dynamic resistance is necessary for predicting the transport processes and monitoring the weld quality during resistance spot welding. In this study, dynamic resistance is obtained by taking the sum of temperature dependent bulk resistance of the workpieces and contact resistances at the faying surface and electrode-workpiece interface within an effective area corresponding to the electrode tip where welding current primarily flows. A contact resistance is composed of constriction and film resistances, which are functions of hardness, temperature, electrode force, electrical resistivity and surface condition. Unsteady, axisymmetric transport of mass, momentum, energy, species, and magnetic field intensity with a mushy-zone phase change in workpieces and temperature, and magnetic fields in electrodes during resistance spot welding, are systematically investigated. Electromagnetic force, joule heat, heat generation at the electrode-workpiece interface and faying surface between workpieces, different properties between phase, and geometries of electrodes are taken into account. The predicted nugget thickness and dynamic resistance versus time show quite good agreement with available experimental data. Excluding expulsion, the dynamic resistance curve can be divided into four stages. A rapid decrease of dynamic resistance in stage 1 is attributed to decreases in film resistances at the faying surface and electrode-workpiece interface. In stage 2, the increase in dynamic resistance results from the primary increase of bulk resistance in the workpieces and an increase of the sum of contact resistances at the faying surface and electrode-workpiece interface. Dynamic resistance in stage 3 decreases, because increasing rate of bulk resistance in the workpieces and contact resistances decrease. In stage 4 decrease of dynamic resistance is mainly due to the formation of the molten nugget at the faying surface. The molten nugget is found to occur in stage 4 rather than stage 2 or 3 as qualitatively proposed in the literature. The effects of different parameters on the dynamic resistence curve are also presented. Besides, electromagnetic force effect on velocity field of molten nugget was proven to be crucial. Higher current, smaller magnetic diffusivity and decreasing the radius of electrode tip will lead to high current density around the corner between electrode and workpiece. Sometimes the corner of electrode and surface of workpieces will be melted due to local high current density.

Lead-acid battery is one of the most widely used electrochemical cells. These batteries have been associated with supplying energy to start the car. Currently used for propulsion and the overall operation of hybrid electric vehicles. When operating lead-acid batteries are made inside cell the thermal happens. The thermal going generate heat caused by chemical reactions during charging and discharging of the electrochemical system, the heat generated by ohmic and polarization losses and heat mediated contact with the environment. In this diploma thesis shows the principle of lead-acid battery and thermal processes that take places in the accumulator during its operation.

This master's thesis deals with the issue of lead-acid batteries, their charging methods and issue of thermal processes in lead-acid batteries. The thesis is divided into three main parts. The first section describes the theoretical knowledge of lead-acid batteries, such as history of lead-acid battery, structure, principle of operation, methods of charging and thermal processes taking place in the lead-acid battery. The second part describes in detail the production of experimental electrodes. The last section describes the automatic data logger for measuring and experiments, which were focused on pulse charging method with variable duty cycle pulses.

The aim of this thesis is the analysis of thermal processes in lead accumulators with oxygen cycle. The work is explaining the structure and principle of operation of the standard lead-acid battery and lead-acid battery with oxygen cycle. Generally are described thermal action inside a lead battery with oxygen cycle and the different types of heat generated during operation of the battery are discussed in detail. One chapter describes the practical experiments and their results.

Securing of electrical devices is important not only to protect against destruction under the effects of electric current, but also for protection of people or animals against electric shock. With increasing of living standards goes hand in hand increasing of the electricity consumption. Therefore In the grid of low voltage, there are increasing short-circuit currents. With improving technology is posed considerable demand on the performance, security and switching capacity of circuit breakers. This thesis is oriented on development of thermal and electromagnetic switch of circuit breaker on which is put a big demand in development of new types of circuit breakers. The thesis is interesting because of comprehensive use of circuits’ breakers since it can be used in AC and DC networks with frequency of 50 Hz and 400 Hz.