Sabin Rizescu

Thermal study of a shape memory alloy (SMA) spring actuator designed to insure the motion of a barrier structure

The study concerns an experimental model using a SMA spring actuator for improving the whole performance of a barrier structure. The study is, specifically, focused on the thermal analysis of the SMA spring material and on determination of the SMA spring working time periods at different values of the activating electric current inducing different phase changing speeds.

Condition monitoring of transformer oil using thermal analysis and other techniques

Any transformer oil undergoes continuous degradation because of all electric, thermal, mechanical, and climatic stresses it suffers while operating in the transformer. Therefore, the oil has to be checked on regular basis in order to decide whether it is necessary to regenerate or replace it, avoiding thus a sudden failure of the transformer. This article presents results of in-the-laboratory-performed experiments on transformer mineral oil samples. Those samples came from a power transformer that works in the Romanian power network. There were three monitoring stages conducted over four-and-a-half years. We used two measuring techniques: (i) measurement of the state parameters of transformer oil (breakdown voltage, loss factor, water contents, acidity index, interfacial tension, number of particles larger than 5 microns, and gas contents) in order to describe the oil condition during the monitoring period and to anticipate any severe fault. This enables the user to take preventive action before a severe fault might eventually occur; (ii) thermal analysis (TA) and Fourier transform infrared spectroscopy (FTIR), in order to determine the stability of oil samples. By using TA and FTIR, and by evaluating each and every significant parameter, it has been proven that the tested oil is still adequate for further employment in the power transformer.

Active solar panel tracking system actuated by shape memory alloy springs

The unique properties (e.g. Shape memory effects) exhibited by shape memory alloys (SMAs) offer the possibility of producing Smart Sun Tracking Mechanisms (SSTMs) for photovoltaic panels. The paper presents an experimental model of an active solar panel tracking system, conceived by authors. This model uses SMA springs as actuators. The SMA springs work as linear actuators by contracting with great strength and speed when heated. The SMA springs attached to this structure can be activated to accurately change the position of the solar panel, following, this way, the motion of the sun throughout the day (appropriately tilted to directly face the sun during the day time). The active shape-change control of SMA spring, the possibilities for miniaturization, easy integration in system structure can effectively increase the efficiency of such SSTM.

Shape memory alloy-based smart module structure working under intense thermo-mechanical stress

The paper presents a complete model for a modular mechatronic structure actuated by a one-way memory effect shape memory alloy actuator. In order to claim the complete attribute of the model, the austenite transformation temperature evolution of actuator was evaluated in relation with the precision and repeatability related capabilities of the mechatronic structure. The evolution of austenite transformation temperature was obtained through determinations based on DSC method. Those determinations were performed on the shape memory alloy wire used as actuator in the modular mechatronic structure. The wire is subject of intense and repetitive operating mode. All determinations are performed on the SMA wire used as actuator system after 5,000, and 1,003,600 cycles, respectively. The results indicate a shift in both As and Af temperatures, a trend that is heavily dependent on the operating history of the system. Using experimental results, authors built a graph (surface) that is based on heating time schedule, heating current, and austenite finish temperature. Also, the results lead to the conclusion that for any desired heating time, it can be identified (in a restricted but relatively wide range), at least a pair of both austenite finish temperature and heating current. If the control algorithm modifies the electrical current in accordance with the number of working cycles and austenite transformation temperature evolution, the time response and, by default, the structure repeatability are assured even after over 1 million working cycles.

Modal Parameters Identification for some Sandwich Bars Reinforced with Fiber-Glass

In this paper, there are built new composite bars with different core: with the core made of polypropylene honeycomb and polystyrene reinforced with fiber-glass. Starting from the theoretical background the modal parameters identification, there will be established an experimental method used to determine the eigenparameters of the sandwich bars. In the end, some comparisons between the eigenparameters will be made.