Dynamic friction is a critical process of crustal earthquake ruptures. Recent experimenta1 and theoretica1 progress in rock friction have demonstrated that most continental earthquakes are associated with stick-slip i...Dynamic friction is a critical process of crustal earthquake ruptures. Recent experimenta1 and theoretica1 progress in rock friction have demonstrated that most continental earthquakes are associated with stick-slip in the brittle field of the crust and that only dynamic instability with fast slip is related to seismicity. Dynamic stability will be influenced by frictional parameters a-b, a, stiffness K, characteristic displacement L, slip rate history (velocity weakening), normal stress history (pressure strengthening), and temperature, which is described by the frictional constitutive laws. Velocity-weakening (a-b<0) can cause dynamic instability if the medium stiffness is below the critical stiffness (X/Kc<1), while velocity-strengthening enhances the frictional stability.The most recent experimental evidence of rock friction will be systematically reviewed in this paper.展开更多
Friction stir welding experiments were conducted to study the effects of the process parameters on the weld quality of 2A12 aluminium alloys. Through appropriate selection of the shoulder press amount （axial force）,...Friction stir welding experiments were conducted to study the effects of the process parameters on the weld quality of 2A12 aluminium alloys. Through appropriate selection of the shoulder press amount （axial force）, tool rotation speed and welding speed, good joints were obtained for the test pieces with thickness of 6 ram. The microstructures in weld nugget zone, thermo-mechanical affected zone and heat-affected zone were analyzed. It is found that the ratio of the tool rotation speed to the welding speed should be optimized for a suitable shoulder press amount.展开更多
This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention （NIED）, Tsuk...This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention （NIED）, Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 kN, the main frame for holding two large rectangular prismatic specimens with a sliding area of 0.75 m^2 and for applying normal stresses an up to 1.33 MPa, and a reaction force unit holding the stationary specimen to the ground. The shaking table can produce loading rates v up to 1.0 m/s, accelerations up to 9.4 m/s^2, and displacements d up to 0.44 m, using four servocontrolled actuators. We report results from eight preliminary experiments conducted with room humidity on the same gabbro specimens at v = 0.1-100 mm/s and an = 0.66-1.33 MPa, and with d of about 0.39 m. The peak and steady-state friction coefficients were about 0.8 and 0.6, respectively, consistent with the Byerlee friction. The axial force drop or shear stress drop during an abrupt slip is linearly proportional to the amount of displacement, and the slope of this rela- tionship determines the stiffness of the apparatus as 1.15 × 10^8 N/m or 153 MPa/m for the specimens we used. This low stiffness makes fault motion very unstable and the overshooting of shear stress to a negative value was recognized in some violent stick-slip events. An abrupt slip occurred in a constant rise time of 16-18 ms despite wide variation of the stress drop, and an average velocity during an abrupt slip is linearly proportional to the stress drop. The use of a large-scale shaking table has a great potential in increasing the slip rate and total displacement in biaxial friction experiments with large specimens.展开更多
Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch an...Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.展开更多
文摘Dynamic friction is a critical process of crustal earthquake ruptures. Recent experimenta1 and theoretica1 progress in rock friction have demonstrated that most continental earthquakes are associated with stick-slip in the brittle field of the crust and that only dynamic instability with fast slip is related to seismicity. Dynamic stability will be influenced by frictional parameters a-b, a, stiffness K, characteristic displacement L, slip rate history (velocity weakening), normal stress history (pressure strengthening), and temperature, which is described by the frictional constitutive laws. Velocity-weakening (a-b<0) can cause dynamic instability if the medium stiffness is below the critical stiffness (X/Kc<1), while velocity-strengthening enhances the frictional stability.The most recent experimental evidence of rock friction will be systematically reviewed in this paper.
文摘Friction stir welding experiments were conducted to study the effects of the process parameters on the weld quality of 2A12 aluminium alloys. Through appropriate selection of the shoulder press amount （axial force）, tool rotation speed and welding speed, good joints were obtained for the test pieces with thickness of 6 ram. The microstructures in weld nugget zone, thermo-mechanical affected zone and heat-affected zone were analyzed. It is found that the ratio of the tool rotation speed to the welding speed should be optimized for a suitable shoulder press amount.
基金supported by the NIED research project titled‘‘Development of the Earthquake Activity Monitoring and Forecasting,’’the JSPS KAKENHI Grant No.23340131the State Key Laboratory of Earthquake Dynamics,Institute of Geology,CEA(LED2014A06)
文摘This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention （NIED）, Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 kN, the main frame for holding two large rectangular prismatic specimens with a sliding area of 0.75 m^2 and for applying normal stresses an up to 1.33 MPa, and a reaction force unit holding the stationary specimen to the ground. The shaking table can produce loading rates v up to 1.0 m/s, accelerations up to 9.4 m/s^2, and displacements d up to 0.44 m, using four servocontrolled actuators. We report results from eight preliminary experiments conducted with room humidity on the same gabbro specimens at v = 0.1-100 mm/s and an = 0.66-1.33 MPa, and with d of about 0.39 m. The peak and steady-state friction coefficients were about 0.8 and 0.6, respectively, consistent with the Byerlee friction. The axial force drop or shear stress drop during an abrupt slip is linearly proportional to the amount of displacement, and the slope of this rela- tionship determines the stiffness of the apparatus as 1.15 × 10^8 N/m or 153 MPa/m for the specimens we used. This low stiffness makes fault motion very unstable and the overshooting of shear stress to a negative value was recognized in some violent stick-slip events. An abrupt slip occurred in a constant rise time of 16-18 ms despite wide variation of the stress drop, and an average velocity during an abrupt slip is linearly proportional to the stress drop. The use of a large-scale shaking table has a great potential in increasing the slip rate and total displacement in biaxial friction experiments with large specimens.
基金Supported by the National Natural Science Foundation of China(11472093 and21276056)
文摘Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.
