Investigation and Analysis of Attack Angle and Rear Flow Condition of Contra-Rotating Small Hydro-Turbine

At present, there is strong impetus for renewable energy to replace the traditional energy sources because of the environmental pollution. Small hydropower is a promising renewable energy source; however, small hydro-turbines easily become blocked and impacted, and the efficiency of such devices is lower. Therefore, we examined contra-rotating rotors to overcome these disadvantages. We have made modifications to the blade thickness and to the front hub of the original model. In this paper, we focus on the attack angle and rear flow condition of the original model and the modified one. The axial and circumferential velocities are given as outputs, from which the attack angle is then calculated. The results show that the attack angle of new model is smaller at the hub area. The stagnation point of the rear rotor was moved slightly to the pressure surface of the rear blade, and the separation at leading edge area was suppressed. The crowed flow at the tip clearance area is also reduced. The high turbulent kinetic energy area is moved forward to the middle of the blade. The rear rotor’s torque is bigger and changes more smoothly. Therefore, the rear flow conditions of the new model are improved

Experimental Investigation on the Joining of Aluminum Alloy Sheets Using Improved Clinching Process

Aluminum alloy sheets have been widely used to build the thin-walled structures by mechanical clinching technology in recent years. However, there is an exterior protrusion located on the lower sheet and a pit on the upper sheet, which may restrict the application of the clinching technology in visible areas. In the present study, an improved clinched joint used to join aluminum alloy sheets was investigated by experimental method. The improved clinching process used for joining aluminum alloy evolves through four phases: (a) localized deformation; (b) drawing; (c) backward extrusion; and (d) mechanical interlock forming. A flat surface can be produced using the improved clinching process. Shearing strength, tensile strength, material flow, main geometrical parameters, and failure mode of the improved clinched joint were investigated. The sheet material was compressed to flow radially and upward using a punch, which generated a mechanical interlock by producing severe localized plastic deformation. The neck thickness and interlock of the improved clinched joint were increased by increasing the forming force, which also contributed to increase the strength of the clinched joint. The improved clinched joint can get high shearing strength and tensile strength. Three main failure modes were observed in the failure process, which were neck fracture mode, button separation mode, and mixed failure mode. The improved clinched joint has better joining quality to join aluminum alloy sheets on the thin-walled structures

Improved Analysis of Manganese in Steel Samples Using Collinear Long–Short Double Pulse Laser-Induced Breakdown Spectroscopy (LIBS)

A long-short double pulse laser-induced breakdown spectroscopy (long-short DP-LIBS) method was employed to improve the performance of LIBS for the measurement of manganese in steel samples. The long pulse was generated by a Nd:YAG laser which was operated at free runing (FR) mode. To investigate the detection ability without sample preparation, the steel washers were tested using SP-LIBS and long-short DP-LIBS, respectively. The measurement results show that the long-short DP-LIBS method was able to record clear spectra from the rusty steel washers. The steel washers were also measured after the polishing process. The measurement results show that the signal intensity was enhanced by long-short DP-LIBS. Through the observation with scanning electron microscope (SEM) on the laser craters, the results suggest that the improvement of detection ability can be attributed to the pre-radiation effect of long-pulse laser beam. Next, the analytical performance for quantitative measurement of manganese was evaluated by employing ten standard steel samples. The results show that the linearty fit (R2) of calibration curve is 0.988 for long-short DP-LIBS, whereas, R2 is only 0.810 for SP-LIBS under the same measurement conditions. The five times repeated measurement results show that the average Relative Standard Deviation (RSD) of the tested samples is 29.3% for SP-LIBS and is 10.5% for long-short DP-LIBS. The prediction results also show that the average Relative Error of Prediction (REP) is 94.9% for SP-LIBS and it 4.9% for long-short DP-LIBS. The experimental results in current work demonstrate that long-short DP-LIBS is promising for the on line measurement of steel in the steelmaking plant

Microstructure of Semi-Solid 6063 Alloy Fabricated by Radial Forging Combined with Unidirectional Compression Recrystallization and Partial Melting Process

Radial forging combined with unidirectional compression (RFCUM) is introduced in recrystallization and partial melting (RAP) to fabricate semi-solid 6063 aluminum alloy, which can be defined as a process of RFCUM-RAP. In this study, the microstructures of semi-solid 6063 alloy prepared by semi-solid isothermal treatment (SSIT) and RFCUM-RAP processes are investigated. The results show that, the solid grains of semi-solid alloy prepared by SSIT are large and irregular. However, solid grains of semi-solid billet prepared by RFCUC-RAP are fine and spherical. Additionally, during RFCUC-RAP process, with the increase of isothermal holding time, the shape of solid grain is more and more spherical, but the size of solid grain is gradually increased. To obtain ideal semi-solid microstructure, the optimal isothermal holding temperature and time are 630 °C and 5~10 min, respectively

Microstructure of Semi-Solid 6063 Alloy Fabricated by Radial Forging Combined with Unidirectional Compression Recrystallization and Partial Melting Process

Radial forging combined with unidirectional compression (RFCUM) is introduced in recrystallization and partial melting (RAP) to fabricate semi-solid 6063 aluminum alloy, which can be defined as a process of RFCUM-RAP. In this study, the microstructures of semi-solid 6063 alloy prepared by semi-solid isothermal treatment (SSIT) and RFCUM-RAP processes are investigated. The results show that, the solid grains of semi-solid alloy prepared by SSIT are large and irregular. However, solid grains of semi-solid billet prepared by RFCUC-RAP are fine and spherical. Additionally, during RFCUC-RAP process, with the increase of isothermal holding time, the shape of solid grain is more and more spherical, but the size of solid grain is gradually increased. To obtain ideal semi-solid microstructure, the optimal isothermal holding temperature and time are 630 °C and 5~10 min, respectively

Research on Radial Motion Characteristic of the Cropping Hammer in Radial-Forging Cropping Method

The radial loading form applied to the bar is very important for reducing or avoiding the impact and vibration of the radial-forging cropping system and obtaining the high-quality cross section. A new radial stroke loading curve of the cropping hammer based on the cycloid form is proposed and the dynamic model of radial stroke loading mechanism is built. With the aim of obtaining the equivalent stiffness of the bar with V-shaped notch, which is a key parameter affecting the dynamic characteristic of radial stroke loading mechanism, the analytic model of the bar is built and the simulation experiments are designed by means of the orthogonal test method. The analytical results show that the diameter of the bar has the significant influence on the equivalent stiffness of the bar. Furthermore, the equivalent stiffness of the bar with V-shaped notch can be directly calculated according to the equivalent stiffness of smooth bar when h/d<0.05 and r>0.15. By using the cycloid stroke curve, the cropping experimental results for 45 steel bars and 20 steel bars show that the radial impact and vibration of the cropping system are decreased and the bar cross-section qualities have been significantly improved

Investigation on the Crack Initiation of V-Shaped Notch Tip in Precision Cropping

The crack initiation of V-shaped notch tip has a very important influence on the cross-section quality and the cropping time for every segment of metal bar in course of low stress precision cropping. By the finite element method, the influence of machining precision of V-shaped notch bottom corner on the crack initiation location is analyzed and it is pointed out that the crack initiation point locates in the place at the maximal equivalent stress change rate on V-shaped notch surface. The judgment criterion of the crack initiation direction is presented and the corresponding crack initiation angle can be calculated by means of the displacement extrapolation method. The factual crack initiation angle of the metal bar has been measured by using the microscopic measurement system. The formula of the crack initiation life of V-shaped notch tip is built, which mainly includes the stress concentration factor of V-shaped notch, the tensile properties of metal material, and the cyclic loading conditions. The experimental results show that the obtained theoretical analyses about the crack initiation location, the crack initiation direction, and the crack initiation time in this paper are correct. It is also shown that the crack initiation time accounts for about 80% of the cropping time for every segment of the metal bar

Investigation and Analysis of Attack Angle and Rear Flow Condition of Contra-Rotating Small Hydro-Turbine

At present, there is strong impetus for renewable energy to replace the traditional energy sources because of the environmental pollution. Small hydropower is a promising renewable energy source; however, small hydro-turbines easily become blocked and impacted, and the efficiency of such devices is lower. Therefore, we examined contra-rotating rotors to overcome these disadvantages. We have made modifications to the blade thickness and to the front hub of the original model. In this paper, we focus on the attack angle and rear flow condition of the original model and the modified one. The axial and circumferential velocities are given as outputs, from which the attack angle is then calculated. The results show that the attack angle of new model is smaller at the hub area. The stagnation point of the rear rotor was moved slightly to the pressure surface of the rear blade, and the separation at leading edge area was suppressed. The crowed flow at the tip clearance area is also reduced. The high turbulent kinetic energy area is moved forward to the middle of the blade. The rear rotor&rsquo;s torque is bigger and changes more smoothly. Therefore, the rear flow conditions of the new model are improved