The electronic packaging box with high silicon aluminum-base alloy was prepared by semi-solid thixoforming technique.The flow characteristic of the Si phase was analyzed.The microstructures of different parts of the b...The electronic packaging box with high silicon aluminum-base alloy was prepared by semi-solid thixoforming technique.The flow characteristic of the Si phase was analyzed.The microstructures of different parts of the box were observed by optical microscopy and scanning electron microscopy,and the thermophysical and mechanical properties of the box were tested.The results show that there exists the segregation phenomenon between the primary Si phase and the liquid phase during thixoforming,the liquid phase flows from the box,and the primary Si phase accumulates at the bottom of the box.The volume fraction of primary Si phase decreases gradually from the bottom to the walls.Accordingly,the thermal conductivities of bottom center and walls are 107.6 and 131.5 W/（m·K）,the coefficients of thermal expansion（CTE） are 7.9×10-6 and 10.6×10-6 K-1,respectively.The flexural strength increases slightly from 167 to 180 MPa.The microstructures and properties of the box show gradient distribution overall.展开更多
Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability wer...Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250℃, but uniform elongation and maximum expansion ratio get the highest value at 175℃. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.展开更多
With diminishing population divident, rising labor costs＇ will become a medium- to long-term trend and this change will significantly affect price formation and the direction of development in China. This paper uses ...With diminishing population divident, rising labor costs＇ will become a medium- to long-term trend and this change will significantly affect price formation and the direction of development in China. This paper uses a New Keynesian Phillips Curve （NKPC） model to conduct empirical analysis on all possible drivers of inflation in China. The authors conclude that while monetary expansion and expectation on inflation both have significant, driving impacts on China＇s inflation, rising labor costs have also become an important driver of China＇s rising prices. They argue that the solution to China＇s inflation problem lies not in currency policy and currency controls alone; it must be complemented by other policies that address the root causes of inflation.展开更多
A chemo-damage model for cracking analysis of concrete dams affected by alkali-aggregate reaction (AAR) is proposed, which combines the plastic-damage model for concrete with the AAR kinetics law. The chemo-damage mod...A chemo-damage model for cracking analysis of concrete dams affected by alkali-aggregate reaction (AAR) is proposed, which combines the plastic-damage model for concrete with the AAR kinetics law. The chemo-damage model is first verified by a stress-free AAR expansion test. The expansion deformation obtained from the simulation is in good agreement with the measurement, demonstrating that the proposed model has a sufficient accuracy to predict the expansion of AAR-affected concrete. Subsequently, the expansion deformation and cracking process of the AAR-affected Fontana gravity dam is analyzed. It shows that permanent displacements in the upstream direction and the vertical direction are gradually increased during the long-term operation period, and that their maximal values reach 1.6 and 3.6 cm, respectively. A crack is observed on the wall in the foundation drainage gallery, and extends towards the downstream face of the dam. With the further development of AAR, another crack forms on the downstream face, and then intersects with the gallery crack to penetrate the downstream side profile of the dam. The third crack occurs in the upstream side wall of the gallery and propagates a short distance towards the upstream face of the dam. The simulated cracking pattern in the dam due to AAR is similar to the in situ observation.展开更多
文摘The electronic packaging box with high silicon aluminum-base alloy was prepared by semi-solid thixoforming technique.The flow characteristic of the Si phase was analyzed.The microstructures of different parts of the box were observed by optical microscopy and scanning electron microscopy,and the thermophysical and mechanical properties of the box were tested.The results show that there exists the segregation phenomenon between the primary Si phase and the liquid phase during thixoforming,the liquid phase flows from the box,and the primary Si phase accumulates at the bottom of the box.The volume fraction of primary Si phase decreases gradually from the bottom to the walls.Accordingly,the thermal conductivities of bottom center and walls are 107.6 and 131.5 W/（m·K）,the coefficients of thermal expansion（CTE） are 7.9×10-6 and 10.6×10-6 K-1,respectively.The flexural strength increases slightly from 167 to 180 MPa.The microstructures and properties of the box show gradient distribution overall.
基金Project(NCET-07-0237) supported by New Century Excellent Talents Program in Chinese University
文摘Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250℃, but uniform elongation and maximum expansion ratio get the highest value at 175℃. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.
基金This paper was made possible by grants from the National Social Science Foundation, the Ministry of Education, the 985 Project, and the School of Humanities and Social Sciences at Nanjing University.
文摘With diminishing population divident, rising labor costs＇ will become a medium- to long-term trend and this change will significantly affect price formation and the direction of development in China. This paper uses a New Keynesian Phillips Curve （NKPC） model to conduct empirical analysis on all possible drivers of inflation in China. The authors conclude that while monetary expansion and expectation on inflation both have significant, driving impacts on China＇s inflation, rising labor costs have also become an important driver of China＇s rising prices. They argue that the solution to China＇s inflation problem lies not in currency policy and currency controls alone; it must be complemented by other policies that address the root causes of inflation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51209120, 41274106 and 40974063)
文摘A chemo-damage model for cracking analysis of concrete dams affected by alkali-aggregate reaction (AAR) is proposed, which combines the plastic-damage model for concrete with the AAR kinetics law. The chemo-damage model is first verified by a stress-free AAR expansion test. The expansion deformation obtained from the simulation is in good agreement with the measurement, demonstrating that the proposed model has a sufficient accuracy to predict the expansion of AAR-affected concrete. Subsequently, the expansion deformation and cracking process of the AAR-affected Fontana gravity dam is analyzed. It shows that permanent displacements in the upstream direction and the vertical direction are gradually increased during the long-term operation period, and that their maximal values reach 1.6 and 3.6 cm, respectively. A crack is observed on the wall in the foundation drainage gallery, and extends towards the downstream face of the dam. With the further development of AAR, another crack forms on the downstream face, and then intersects with the gallery crack to penetrate the downstream side profile of the dam. The third crack occurs in the upstream side wall of the gallery and propagates a short distance towards the upstream face of the dam. The simulated cracking pattern in the dam due to AAR is similar to the in situ observation.
