Apparatus for measurement of pitch and yaw damping derivatives in high Reynolds number blowdown wind tunnel

The pitch/yaw apparatus designed for the measurement of the moment derivative due to an aircraft or missile model angular oscillatory motion in a wind tunnel test section is presented. A model is forced to oscillate with the primary angular oscillation around its transversal axis (pitch or yaw). Damping derivatives are obtained as a difference between total damping measured in the presence of aerodynamic load and mechanical damping measured in the absence of aerodynamic load. The main requirements for a new apparatus were: high load capacity, high structural rigidity, high range of the experimental frequencies and high sensors sensitivity. The choice of the hydraulic drive is made considering these requirements. Amplitude of the excitation moment is measured either by internal wind tunnel balance or by a specially designed excitation moment sensor. The T-38 wind tunnel data for the Modified Basic Finner Model and Basic Finner Model obtained using the pitch/yaw apparatus are shown.     

Microcontroller based system for electrical breakdown time delay measurement in gas-filled devices

This paper presents realization of a digital embedded system for measuring electrical breakdown time delay. The proposed system consists of three major parts: dc voltage supply, analog subsystem, and a digital subsystem. Any dc power source with the range from 100 to 1000 V can be used in this application. The analog subsystem should provide fast and accurate voltage switching on the testing device as well as transform the signals that represent the voltage pulse on the device and the device breakdown into the form suitable for detection by a digital subsystem. The insulated gate bipolar transistor IRG4PH40KD driven by TC429 MOSFET driver is used for high voltage switching on the device. The aim of a digital subsystem is to detect the signals from the analog subsystem and to measure the elapsed time between their occurrences. Moreover, the digital subsystem controls various parameters that influence time delay and provides fast data storage for a large number of measured data. For this propose, we used the PIC18F4550 microcontroller with a full-speed compatible universal serial bus (USB) engine. Operation of this system is verified on different commercial and custom made gas devices with different structure and breakdown mechanisms. The electrical breakdown time delay measurements have been carried out as a function of several parameters, which dominantly influence electrical breakdown time delay. The obtained results have been verified using statistical methods, and they show good agreement with the theory. The proposed system shows good repeatability, sensitivity, and stability for measuring the electrical breakdown time delay.     

Multi-output fuzzy inference system for modeling cutting temperature and tool life in face milling

This paper proposes a method for cutting parameters identification using the multi-inputs-multi-outputs fuzzy inference system (MIMO-FIS). The fuzzy inference system (FIS) was used to identify the initial values for cutting parameters (cutting speed, feed rate and depth of cut) and flank wear using cutting temperature and tool life as outputs. The objective was to determine the influence of cutting parameters on cutting temperature and tool life. The model for determining the cutting temperature and tool life of steel AISI 1060 was trained (design rules) and tested by using the experimental data. The average deviation of the testing data for tool life was 11.6 %, while that of the cutting temperature was 3.28 %. The parameters used in these testing data were different from the data collected for the design rules. The test results showed that the proposed MIMO-FIS model can be used successfully for machinability data selection. The effect of parameters and their interactions in machining is analyzed in detail and presented in this study.     

Compositional Inhomogeneity in Li- and Ta-Modified (K, Na)NbO3 Ceramics

Compositional inhomogeneity is examined in Li- and Ta-modified potassium sodium niobate (K,Na)NbO₃ perovskite ceramics. The inhomogeneous distribution of the A-site (K and Na) and B-site (Nb and Ta) cations is found to be correlative. The inhomogeneity could not be eliminated by prolonged high-temperature annealing in samples prepared by direct mixing of alkaline carbonates and Ta and Nb oxides. In contrast, the precursor method, where a (Nb _x Ta_{1− x} )₂O₅ solid solution was first formed, led to a considerably improved compositional homogeneity and appreciably enhanced dielectric, ferroelectric, and piezoelectric properties. Our results suggest that more attention needs to be paid toward controlling the compositional fluctuation of this complex solid solution system.