The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformati...The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformation behaviors of the steel,back propagation-artificial neural network(BP-ANN)with 16×8×8 hidden layer neurons was proposed.The predictability of the ANN model is evaluated according to the distribution of mean absolute error(MAE)and relative error.The relative error of 85%data for the BP-ANN model is among±5%while only 42.5%data predicted by the Arrhenius constitutive equation is in this range.Especially,at high strain rate and low temperature,the MAE of the ANN model is 2.49%,which has decreases for 18.78%,compared with conventional Arrhenius constitutive equation.展开更多
Powder mixture of pure Al and oxidized Si C was consolidated into 10%（mass fraction） Si Cp/Al composites at 250 °C by equal channel angular pressing and torsion（ECAP-T）. The valence states of Si for Si C part...Powder mixture of pure Al and oxidized Si C was consolidated into 10%（mass fraction） Si Cp/Al composites at 250 °C by equal channel angular pressing and torsion（ECAP-T）. The valence states of Si for Si C particulates and Al for the as-consolidated composites were detected by X-ray photoelectron spectroscopy（XPS）. The interfacial bondings of the composites were characterized by scanning electron microscopy（SEM）. The elements at the interface were linearly scanned by energy dispersive spectroscopy（EDS） and the EDS mappings of Si and Al were also obtained. The values of the nanohardness at different positions within 2 μm from the boundary of Si C particulate were measured. The results show that after ECAP-T, interfacial reaction which inhibits injurious interfacial phase occurs between Al and the oxide layer of Si C, and the element interdiffusion which can enhance interfacial bonding exists between Al and Si C. As ECAP-T passes increase, the reaction degree is intensified and the element interdiffusion layer is thickened, leading to the more smooth transition of the hardness from Si C to Al.展开更多
To gain a thorough understanding of the load state of parallel kinematic machines(PKMs), a methodology of elastodynamic modeling and joint reaction prediction is proposed. For this purpose, a Sprint Z3 model is used a...To gain a thorough understanding of the load state of parallel kinematic machines(PKMs), a methodology of elastodynamic modeling and joint reaction prediction is proposed. For this purpose, a Sprint Z3 model is used as a case study to illustrate the process of joint reaction analysis. The substructure synthesis method is applied to deriving an analytical elastodynamic model for the 3-PRS PKM device, in which the compliances of limbs and joints are considered. Each limb assembly is modeled as a spatial beam with non-uniform cross-section supported by lumped virtual springs at the centers of revolute and spherical joints. By introducing the deformation compatibility conditions between the limbs and the platform, the governing equations of motion of the system are obtained. After degenerating the governing equations into quasi-static equations, the effects of the gravity on system deflections and joint reactions are investigated with the purpose of providing useful information for the kinematic calibration and component strength calculations as well as structural optimizations of the 3-PRS PKM module. The simulation results indicate that the elastic deformation of the moving platform in the direction of gravity caused by gravity is quite large and cannot be ignored. Meanwhile, the distributions of joint reactions are axisymmetric and position-dependent. It is worthy to note that the proposed elastodynamic modeling method combines the benefits of accuracy of finite element method and concision of analytical method so that it can be used to predict the stiffness characteristics and joint reactions of a PKM throughout its entire workspace in a quick and accurate manner. Moreover, the present model can also be easily applied to evaluating the overall rigidity performance as well as statics of other PKMs with high efficiency after minor modifications.展开更多
The universal creep equation is successful in relating the creep （ε） to the aging time （t） , coefficient of retardation time （β） , and intrinsic time （ to ）. This relation was used to treat the creep experim...The universal creep equation is successful in relating the creep （ε） to the aging time （t） , coefficient of retardation time （β） , and intrinsic time （ to ）. This relation was used to treat the creep experimental data for polyvinyl chloride （ PVC ） specimens at a given stress and different aging times. The βgs found by the “polynomial fitting” method in this work instead of the “middle - point” method reported in the literature. The unified master line was constructed with the treated data and curves according to the universal equation. The master line can be used to predict the long- term creed behavior and lifetime by extrapolating.展开更多
It is considered thai the damage of the underground structures caused by earthquakes is minor for a long time. However, the catastrophic damages induced by several recent earthquakes （e. g. Kobe earthquake in 1995 ）...It is considered thai the damage of the underground structures caused by earthquakes is minor for a long time. However, the catastrophic damages induced by several recent earthquakes （e. g. Kobe earthquake in 1995 ） revealed that the study on the dynamic properties of the underground structures is indispensable. The dynamic behavior and damage mechanism of underground structure are analyzed by using shaking table tests （ both shallow-and deep-buried） and numerical simulation （3D FEM） including horizontal and vertical input motions, individually and simultaneously. From the results, the underground structure collapsed due to strong horizontal forces although vertical deformation is not negligible. The vertical excitation increases the response of structure, especially the stress and shear stress at the upper section; the soil influenced the property of soilstructure system. In the same excitation, the response in shallow-buried test is larger than deep case. Both overburden and vertical earthquake play important roles in the response of structure and those are two critical aspects in the design of the large-span underground structures, such as subway stations.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
ZnO micro/nanostructures with various morphologies were grown via hydrothermal etching of Zn foil.Controlling the reaction temperature and time,rod-like,pencil-like,tube-like and flowerlike ZnO micro/nanostructures co...ZnO micro/nanostructures with various morphologies were grown via hydrothermal etching of Zn foil.Controlling the reaction temperature and time,rod-like,pencil-like,tube-like and flowerlike ZnO micro/nanostructures could be prepared directly on the Zn foil surface at temperatures 100-180℃ with excellent reproducibility.X-ray diffraction patterns indicated that these ZnO micro/nanostructures were hexagonal.Possible mechanisms for the variation of morphology are discussed.Moreover,photoluminescence spectra of the as-grown samples revealed that all of them consist of UV emission band at around 392 nm.展开更多
文摘The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformation behaviors of the steel,back propagation-artificial neural network(BP-ANN)with 16×8×8 hidden layer neurons was proposed.The predictability of the ANN model is evaluated according to the distribution of mean absolute error(MAE)and relative error.The relative error of 85%data for the BP-ANN model is among±5%while only 42.5%data predicted by the Arrhenius constitutive equation is in this range.Especially,at high strain rate and low temperature,the MAE of the ANN model is 2.49%,which has decreases for 18.78%,compared with conventional Arrhenius constitutive equation.
基金Project(51175138)supported by the National Natural Science Foundation of ChinaProjects(2012HGZX0030,2013HGCH0011)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(20100111110003)supported by the Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘Powder mixture of pure Al and oxidized Si C was consolidated into 10%（mass fraction） Si Cp/Al composites at 250 °C by equal channel angular pressing and torsion（ECAP-T）. The valence states of Si for Si C particulates and Al for the as-consolidated composites were detected by X-ray photoelectron spectroscopy（XPS）. The interfacial bondings of the composites were characterized by scanning electron microscopy（SEM）. The elements at the interface were linearly scanned by energy dispersive spectroscopy（EDS） and the EDS mappings of Si and Al were also obtained. The values of the nanohardness at different positions within 2 μm from the boundary of Si C particulate were measured. The results show that after ECAP-T, interfacial reaction which inhibits injurious interfacial phase occurs between Al and the oxide layer of Si C, and the element interdiffusion which can enhance interfacial bonding exists between Al and Si C. As ECAP-T passes increase, the reaction degree is intensified and the element interdiffusion layer is thickened, leading to the more smooth transition of the hardness from Si C to Al.
基金Project(Kfkt2013-12)supported by Open Research Fund of Key Laboratory of High Performance Complex Manufacturing of Central South University,ChinaProject(2014002)supported by the Open Fund of Shanghai Key Laboratory of Digital Manufacture for Thin-walled Structures,ChinaProject(51375013)supported by the National Natural Science Foundation of China
文摘To gain a thorough understanding of the load state of parallel kinematic machines(PKMs), a methodology of elastodynamic modeling and joint reaction prediction is proposed. For this purpose, a Sprint Z3 model is used as a case study to illustrate the process of joint reaction analysis. The substructure synthesis method is applied to deriving an analytical elastodynamic model for the 3-PRS PKM device, in which the compliances of limbs and joints are considered. Each limb assembly is modeled as a spatial beam with non-uniform cross-section supported by lumped virtual springs at the centers of revolute and spherical joints. By introducing the deformation compatibility conditions between the limbs and the platform, the governing equations of motion of the system are obtained. After degenerating the governing equations into quasi-static equations, the effects of the gravity on system deflections and joint reactions are investigated with the purpose of providing useful information for the kinematic calibration and component strength calculations as well as structural optimizations of the 3-PRS PKM module. The simulation results indicate that the elastic deformation of the moving platform in the direction of gravity caused by gravity is quite large and cannot be ignored. Meanwhile, the distributions of joint reactions are axisymmetric and position-dependent. It is worthy to note that the proposed elastodynamic modeling method combines the benefits of accuracy of finite element method and concision of analytical method so that it can be used to predict the stiffness characteristics and joint reactions of a PKM throughout its entire workspace in a quick and accurate manner. Moreover, the present model can also be easily applied to evaluating the overall rigidity performance as well as statics of other PKMs with high efficiency after minor modifications.
基金Sponsored by the Departmet of Science ad Technology, Government of Heilongjiang Province(Grant No.GC04A407).
文摘The universal creep equation is successful in relating the creep （ε） to the aging time （t） , coefficient of retardation time （β） , and intrinsic time （ to ）. This relation was used to treat the creep experimental data for polyvinyl chloride （ PVC ） specimens at a given stress and different aging times. The βgs found by the “polynomial fitting” method in this work instead of the “middle - point” method reported in the literature. The unified master line was constructed with the treated data and curves according to the universal equation. The master line can be used to predict the long- term creed behavior and lifetime by extrapolating.
文摘It is considered thai the damage of the underground structures caused by earthquakes is minor for a long time. However, the catastrophic damages induced by several recent earthquakes （e. g. Kobe earthquake in 1995 ） revealed that the study on the dynamic properties of the underground structures is indispensable. The dynamic behavior and damage mechanism of underground structure are analyzed by using shaking table tests （ both shallow-and deep-buried） and numerical simulation （3D FEM） including horizontal and vertical input motions, individually and simultaneously. From the results, the underground structure collapsed due to strong horizontal forces although vertical deformation is not negligible. The vertical excitation increases the response of structure, especially the stress and shear stress at the upper section; the soil influenced the property of soilstructure system. In the same excitation, the response in shallow-buried test is larger than deep case. Both overburden and vertical earthquake play important roles in the response of structure and those are two critical aspects in the design of the large-span underground structures, such as subway stations.
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.
基金financed by the 211 project of Anhui UniversityNational Natural Science Foundation of China (50901074, 50672001)+1 种基金Anhui Provincial Natural Science Fund (11040606M49)Higher Educational Natural Science Foundation of Anhui Province (KJ2010A012)
文摘ZnO micro/nanostructures with various morphologies were grown via hydrothermal etching of Zn foil.Controlling the reaction temperature and time,rod-like,pencil-like,tube-like and flowerlike ZnO micro/nanostructures could be prepared directly on the Zn foil surface at temperatures 100-180℃ with excellent reproducibility.X-ray diffraction patterns indicated that these ZnO micro/nanostructures were hexagonal.Possible mechanisms for the variation of morphology are discussed.Moreover,photoluminescence spectra of the as-grown samples revealed that all of them consist of UV emission band at around 392 nm.
