Improving the formability of the material is a key issue in the deep drawing process. Heating the material above its recrystallization temperature drastically increases formability, but in the case of dual phase (DP) steels, it results in a loss of their mechanical properties. To improve the drawing ratio, only the heating of the flange region in the warm temperature range up to 573 K was studied on DP600 sheet steel by numerical simulation. A thermo-elastic-plastic finite element method (FEM) analysis of deep drawing at several drawing ratios was performed and compared with experimental results. During the experiments, the flange area of the blank was heated by induction heating, and the central part over the punch was cooled with spray water. Experimental results showed that limiting drawing ratio could be increased by 25.58%. The microstructure of the DP 600 steel was analyzed before and after the warm forming process. No significant changes were observed, and the high strength properties of the DP 600 steel remained intact. There was good agreement between numerical and experimental results.
COBISS.SI-ID: 15859227
The discharging method is most well-known for its central role in the proof of the Four Color Theorem. This proof technique was extensively applied to study various graph coloring problems, in particular on planar graphs. In this paper, we show that suitably altered discharging technique can also be used on domination type problems. The general discharging approach for domination type problems is illustrated on a specific domination type problem, the double Roman domination on some generalized Petersen graphs. By applying this approach, we first prove that ? dR (G) ? 3n ?(G)+1 for any connected graph G with n ? 2 vertices. As examples we also determine the exact values of the double Roman domination numbers of the generalized Petersen graphs P (n, 1) and the double generalized Petersen graphs DP (n, 1). The obtained results imply that P (n, 1) is double Roman if and only if n ? 2 (mod 4) and DP (n, 1) is double Roman if and only if n ? 0 (mod 4).
COBISS.SI-ID: 16501787
In this paper, a closed-loop volume flow PWM control algorithm of fast switching pneumatic solenoid valves is studied on the basis of experimental results of fluid flow valve characteristics. Dynamic nonlinear behavior of fast switching valves is analyzed using state-of-the-art mass flow sensors. Minimal Pulse Width Modulation (PWM) pulse width and nonlinear flow characteristics depending on pulse width and pressure difference are observed. Based on experimental data, different approaches to mathematically describe correlation of volume flow, pressure difference and pulse width are given. Bilinear interpolation is found out to have the best correlation and is used to develop a closed-loop control algorithm. The algorithm was tested with controlling of Pneumatic Artificial Muscle (PAM) contraction/position with two fast switching valves and minimal PLC / microcontroller requirements were determined.
COBISS.SI-ID: 15981083
The modified Hosoya polynomial of double weighted graphs, i.e. edge and vertex weighted graphs, is introduced that enables derivation of closed expressions for Hosoya polynomial of some special graphs including unicyclic graphs. Furthermore, the Hosoya polynomial is given as a sum of edge contributions generalizing well known analogous results for the Wiener number. A linear algorithm for computing the Hosoya polynomial on cactus graphs is provided. Hosoya polynomial is extensively studied in chemical graph theory, and in particular its weighted versions have interesting applications in theory of communication networks. Double-weighted graphs and Hosoya polynomials are therefore and important tool in understanding models for optimizing traffic or flow in the production networks.
COBISS.SI-ID: 16257563
Flow boiling of degassed double-distilled water in a single 50 × 50 µm and 100 × 50 µm microchannel was investigated on the basis of experimental measurements and high-speed visualization. The visualized events during boiling were analyzed in terms of the bubble frequencies and boiling front oscillations in microchannels. A digital image sequence analysis algorithm was composed to determine the time dependence of bubble and meniscus locations. The results show (i) the dynamic characteristics of boiling in microchannels, (ii) the increase of fundamental oscillation frequencies with increasing heat flux and temperature of the microchannel bottom, (iii) the amplitudes of the flow boiling oscillations are inversely proportional to the fundamental frequencies. The outcomes of the study are important as the oscillations during boiling in single microchannels are experimentally confirmed to be predictable in terms of oscillation frequencies and amplitudes trends and dependencies. This knowledge is especially significant at constructing efficient two-phase micro heat exchangers, micro mixers or micro reactors, as the cross section and the length of the channel become exceedingly important design parameters in micro devices with boiling.
COBISS.SI-ID: 16407579