Advanced Materials Research Vol. 852

Abstract: In this paper, a kind of variable frequency and multi-pressure water supply control system based on STM32 processor is designed. It can adjust the water pressure dynamically, according to the changes of water flow. Therefore, it can economize the energy consumption significantly. In order to improve real-time performance, the system adopts STs STM32F407 series processor which is based on ARM® CortexTM-M4 32-bit RISC core. It is used to collect the water flow, pressure and other data in real time, and automatically adjust the output frequency to control the motor speed, according to the set pressure value, and ultimately control the flow and pressure of the water supply system. According to the test, this variable frequency and multi-pressure water supply control system based on STM32 processor can meet the design requirements.

Abstract: In order to achieve high efficiency of photovoltaic grid-connected system, the constant frequency hysteresis control is introduced into the Z-source grid-connected control, and realized by the fuzzy control technology. Because of the particularity of Z-source shoot-through working state, analyses shoot-through boosting characteristic of Z-source inverter and voltage control performance of DC-link, get the control signal of shoot-through vector. Add the shoot-through vector into hysteresis grid-connected control by using the logical analysis. This method has the advantages of fast dynamic response, high tracking accuracy and stability, and to overcome the traditional hysteresis control filter design is difficult. The simulation results prove the correctness of the theoretical analysis.

Abstract: In orthogonal turn-milling process, both of the workpiece and the cutter rotate at the same time, which causes cutting depth and cutting thickness to change instantaneously. In this paper, a new 2D stability model of orthogonal turn-milling is established, in which the effect of variable cutting depth and cutting thickness is considered. The stability lobe diagrams are obtained by using Full-discretization Method. By analyzing the stability of orthogonal turn-milling, it is found that it is better than that of ordinary milling in same machining conditions. It means that in orthogonal turn-milling process deep cutting depth can be chosen and high machining efficiency can be obtained compared to that in ordinary milling process.

Abstract: When mixed with the admixture MgO, the volume contraction deformation of mass concrete could be compensated, which is an effective way to solve the temperature cracking problems in construction of concrete projects. Taking an arch dam in China as an example, the thermal stress compensation characteristics of MgO concrete in cold areas are studied using the finite element method. Results indicate that the stress compensation of MgO concrete is significant inside the dam, and with a better effect along with a larger mixing amount of MgO in a certain range. But on the surface of the dam, the stress compensation of MgO concrete is not significant.

Abstract: A compensation algorithm, based on the steady-state fluid force of spool, was proposed to reduce the error between the actual and theoretical spool displacement obtained from indirect measurement method and equilibrium of the pilot pressure and spring force, respectively. The steady-state fluid force of spool was calculated and the force analysis was carried out on the spool. Study on the influence of the steady-state fluid force on spool displacement during the spool movement. Finally, the relationship curve between the compensated flow area of valve port and the spool displacement was established. The error of spool displacement was effectively reduced and the accuracy of the test was improved by the proposed compensation method, thus it can provide certain reference value for the design of multi-way valves.

Abstract: Domestic CNC machine tool and NC machine tools abroad's main gap is accuracy stabilization rather than accuracy. Accuracy stabilization test is done on some three-axis vertical machining center aiming at the status. Laser interferometer is used to test X, Y, Z axis's positioning accuracy, repeat positioning accuracy and reverse gap. The test is done taking 80 days as the period. The accuracy test results is analyzed. From the positioning accuracy, repeat positioning accuracy and reverse gap curves we can see that, because of the factors of machine's use and temperature's change, X, Y, Z axis's positioning accuracy changes violently, repeat positioning accuracy and reverse gap change a little.

Abstract: The mechanical properties of rock mass under unloading conditions are essentially different from that under loading conditions. Triaxial compression tests and unloading confining pressure tests are conducted, and test results show that unloading failure is more brittle, and rock samples suffer more damage under unloading failure. The larger the initial confining pressure is, the easier of unloading failure is occurred. The increasing or decreasing values of rock deformation modulus under unloading conditions are within 10% of rock triaxial compressive strength. Unloading failure leads to deterioration of rock deformation modulus, which decreases gradually with confining pressure decreasing, and the decrease rates get bigger and bigger with unloading ratio of confining pressure increasing. Deformation modulus is only 24-34% of that under loading condition when rock strength goes down to residual strength.

Abstract: The finite element method was applied in the construction design of the welding column of CNC boring machine for dynamic analysis and modal analysis. The laws of deformation and stress of a loaded column were obtained, and the natural frequency of each step and modes of column were also given according to this method. The results implied that the strength and the stiffness of welding column were met the machining requirements. Machine working frequency far less than inherent frequency, thus resonance is not easy to occur. Through the way, the optimization proposals of structure were given.

Abstract: The performance of high strength steels is sensitive to the surface quality of machined surfaces. The effect of cutting condition on the variation of surface roughness in turning of 30CrMnSiA steel has been investigated through a serial of dry and oil-lubricant cutting tests. The characters of an amplitude characteristics set, Ra, Ry and tp, which are associated with the general shape of the machined surface profiles, are investigated in this study. It is concluded that, in the aspect of Ra and Ry values, dry cutting condition provides a similar surface roughness as in wet cutting condition under the experimental conditions of the present research; the bearing capacity of both kinds of machined surfaces, characterized by the bearing length rate tp, could be different according to the cutting parameters combinations.

Abstract: This paper proposes an approach to predict cutting force of trochoidal milling based on radial depth of cut in order to study the mechanics of trochoidal milling. The tool entry angle and exit angle can be easily achieved to get the cutting force infinitesimals via the radial depth of cut. Through coordinate transformation, a time domain analytical model of cutting force is introduced. Subsequently, a corresponding experiment was done to measure the actual cutting force. Compared with the actual measurement data, the theoretical model is verified to be valid.