In order to characterize the plastic state of a deformed material, an indentation method to determine the plastic equation of state(PES) was developed. The work-hardening coefficient and the strain rate sensitivity co...In order to characterize the plastic state of a deformed material, an indentation method to determine the plastic equation of state(PES) was developed. The work-hardening coefficient and the strain rate sensitivity coefficient of the plastic mechanic equation of state were determined by two kinds of indentation tests respectively. Therefore, the PES of materials under deformation can be obtained, and the plastic state of materials can be determined.展开更多
An indentation method for determining the plastic mechanical equation of state (PES) was studied. The constant loading rate and constant loading rate/load indentation tests were carried out. The method for determinin...An indentation method for determining the plastic mechanical equation of state (PES) was studied. The constant loading rate and constant loading rate/load indentation tests were carried out. The method for determining the work-hardening coefficient and the strain rate sensitivity coefficient of PES were discussed in detail. 304 stainless steel hot-treated at 1100°C was used to verify the method. The work-hardening coefficient and strain rate sensitivity coefficient of 304 stainless steel were respectively determined as 0.30 and 0.015. These values are very close to those achieved by tensile tests. From the establishment of the PES of 304 stainless steel it is shown that the PES obtained by the indentation method is easier than that by the tensile test.展开更多
A thermo-mechanical constitutive model for unsaturated clays is constructed based on the existingmodel for saturated clays originally proposed by the authors. The saturated clays model was formulatedin the framework o...A thermo-mechanical constitutive model for unsaturated clays is constructed based on the existingmodel for saturated clays originally proposed by the authors. The saturated clays model was formulatedin the framework of critical state soil mechanics and modified Cam-clay model. The existing model hasbeen generalized to simulate the experimentally observed behavior of unsaturated clays by introducingBishop＇s stress and suction as independent stress parameters and modifying the hardening rule and yieldcriterion to take into account the role of suction. Also, according to previous studies, an increase intemperature causes a reduction in specific volume. A reduction in suction （wetting） for a given confiningstress may induce an irreversible volumetric compression （collapse）. Thus an increase in suction （drying）raises a specific volume i.e. the movement of normal consolidation line （NCL） to higher values of voidratio. However, some experimental data confirm the assumption that this reduction is dependent on thestress level of soil element. A generalized approach considering the effect of stress level on themagnitude of clays thermal dependency in compression plane is proposed in this study. The number ofmodeling parameters is kept to a minimum, and they all have clear physical interpretations, to facilitatethe usefulness of model for practical applications. A step-by-step procedure used for parameter calibrationis also described. The model is finally evaluated using a comprehensive set of experimental datafor the thermo-mechanical behavior of unsaturated soils.2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
Under the hypothesis of the rigid-plastic material, specific efforts are placed on the developments of the key simulation techniques of the meshless Galerkin method because of the complexity of the deformation process...Under the hypothesis of the rigid-plastic material, specific efforts are placed on the developments of the key simulation techniques of the meshless Galerkin method because of the complexity of the deformation process as well as the generality and atomization of the simulation procedures for non-steady state large deformation plastic processes, therefore, an adaptive rigid meshless Galerkin method is developed. The influence domain control method is used in the least square approximation by dynamic evaluation of the magnitude of the influence domain and the effective control of the amount and the positions of the points in the least square approximation in order to improve approximation precision. The amount of the Gauss integration points in the discrete domain is maintained in a considerable magnitude in order to ensure the integration precision in the discrete domain. The length of the frictional boundary of the plastic deformation process may be getting longer when its deforma- tion is getting severe. Thus, the densities of the boundary points of some places get lower. The adaptive boundary points setting method is employed to improve the approximation precision of the boundary points and enhance the constraint of the boundary condition by adaptive control of boundary point density. Some typical extrusion processes are analyzed, detail simulation results such as the deformation field, velocity field, effective strain field, effective strain rate field, the volume loss curve and load-stroke curve are obtained. The effectiveness of the method developed is demonstrated and the precision of the meshless simulation is proved by overall comparison with the results obtained by using the commercial software deform.展开更多
目的:基于静息态功能磁共振成像(functional magnetic resonance imaging,fMRI)研究慢性期左侧皮层下脑卒中后轻中度手功能障碍(部分偏瘫手)患者运动功能网络的重组模式。方法:招募32例脑卒中后部分偏瘫手患者和40例匹配的健康老年对照...目的:基于静息态功能磁共振成像(functional magnetic resonance imaging,fMRI)研究慢性期左侧皮层下脑卒中后轻中度手功能障碍(部分偏瘫手)患者运动功能网络的重组模式。方法:招募32例脑卒中后部分偏瘫手患者和40例匹配的健康老年对照。采集两组受试者的静息态fMRI数据,并采用Fugl-Meyer腕手运动功能量表评定患者的手功能障碍程度。采用RESTplus软件分析双侧初级运动皮层(primary motor cortex,M1)与全脑功能连接(functional connectivity,FC)的组间差异,并采用Pearson相关分析探究患者的FC模式与手功能评分之间的关系。结果:与健康老年对照相比,部分偏瘫手患者的患侧M1区与健侧感觉运动区、患侧海马和患侧颞中回的FC减弱,并且健侧M1区与患侧中央后回、健侧顶下小叶、患侧颞上回和患侧脑岛的FC也减弱。相关性分析发现,部分偏瘫手患者的健侧M1区与辅助运动区的FC强度与手功能评分正相关(r=0.67,P<0.001)。结论:慢性期左侧皮层下脑卒中后部分偏瘫手患者的运动功能网络发生了广泛的失连接重组,其中,健侧M1区与辅助运动区之间增强的FC可能是提示良好手功能结局的神经影像标记物。展开更多
以丙烯腈(AN)为单体,聚丙二醇双甲基丙烯酸酯(PPGDMA)为交联剂制备了丁二腈(SN)增塑的塑性PAN-co-PPGDMA交联聚合物-双三氟甲基磺酰亚胺锂(Li TFSI)复合电解质poly-SN40。研究表明,poly-SN40具有较宽的电化学窗口(0-5.2 V vs Li/Li^(+)...以丙烯腈(AN)为单体,聚丙二醇双甲基丙烯酸酯(PPGDMA)为交联剂制备了丁二腈(SN)增塑的塑性PAN-co-PPGDMA交联聚合物-双三氟甲基磺酰亚胺锂(Li TFSI)复合电解质poly-SN40。研究表明,poly-SN40具有较宽的电化学窗口(0-5.2 V vs Li/Li^(+))和较高的室温离子电导率(1.27 mS/cm);组装的锂电池Li/ploy-SN40/LiFePO4的充放电实验表明,在0.5 m A/cm^(2)的电流密度下,电池能够正常、安全地循环使用;电池在0.2 C倍率下室温循环比容量超过133.5 m Ah/g,在200次循环后容量保持率为92%,表现出98.3%的优异平均库仑效率。展开更多
文摘In order to characterize the plastic state of a deformed material, an indentation method to determine the plastic equation of state(PES) was developed. The work-hardening coefficient and the strain rate sensitivity coefficient of the plastic mechanic equation of state were determined by two kinds of indentation tests respectively. Therefore, the PES of materials under deformation can be obtained, and the plastic state of materials can be determined.
文摘An indentation method for determining the plastic mechanical equation of state (PES) was studied. The constant loading rate and constant loading rate/load indentation tests were carried out. The method for determining the work-hardening coefficient and the strain rate sensitivity coefficient of PES were discussed in detail. 304 stainless steel hot-treated at 1100°C was used to verify the method. The work-hardening coefficient and strain rate sensitivity coefficient of 304 stainless steel were respectively determined as 0.30 and 0.015. These values are very close to those achieved by tensile tests. From the establishment of the PES of 304 stainless steel it is shown that the PES obtained by the indentation method is easier than that by the tensile test.
文摘A thermo-mechanical constitutive model for unsaturated clays is constructed based on the existingmodel for saturated clays originally proposed by the authors. The saturated clays model was formulatedin the framework of critical state soil mechanics and modified Cam-clay model. The existing model hasbeen generalized to simulate the experimentally observed behavior of unsaturated clays by introducingBishop＇s stress and suction as independent stress parameters and modifying the hardening rule and yieldcriterion to take into account the role of suction. Also, according to previous studies, an increase intemperature causes a reduction in specific volume. A reduction in suction （wetting） for a given confiningstress may induce an irreversible volumetric compression （collapse）. Thus an increase in suction （drying）raises a specific volume i.e. the movement of normal consolidation line （NCL） to higher values of voidratio. However, some experimental data confirm the assumption that this reduction is dependent on thestress level of soil element. A generalized approach considering the effect of stress level on themagnitude of clays thermal dependency in compression plane is proposed in this study. The number ofmodeling parameters is kept to a minimum, and they all have clear physical interpretations, to facilitatethe usefulness of model for practical applications. A step-by-step procedure used for parameter calibrationis also described. The model is finally evaluated using a comprehensive set of experimental datafor the thermo-mechanical behavior of unsaturated soils.2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
基金This project is supported by National Natural Science Foundation for Dis-tiguished Young Scholars of China (No. 50425517).
文摘Under the hypothesis of the rigid-plastic material, specific efforts are placed on the developments of the key simulation techniques of the meshless Galerkin method because of the complexity of the deformation process as well as the generality and atomization of the simulation procedures for non-steady state large deformation plastic processes, therefore, an adaptive rigid meshless Galerkin method is developed. The influence domain control method is used in the least square approximation by dynamic evaluation of the magnitude of the influence domain and the effective control of the amount and the positions of the points in the least square approximation in order to improve approximation precision. The amount of the Gauss integration points in the discrete domain is maintained in a considerable magnitude in order to ensure the integration precision in the discrete domain. The length of the frictional boundary of the plastic deformation process may be getting longer when its deforma- tion is getting severe. Thus, the densities of the boundary points of some places get lower. The adaptive boundary points setting method is employed to improve the approximation precision of the boundary points and enhance the constraint of the boundary condition by adaptive control of boundary point density. Some typical extrusion processes are analyzed, detail simulation results such as the deformation field, velocity field, effective strain field, effective strain rate field, the volume loss curve and load-stroke curve are obtained. The effectiveness of the method developed is demonstrated and the precision of the meshless simulation is proved by overall comparison with the results obtained by using the commercial software deform.
文摘目的:基于静息态功能磁共振成像(functional magnetic resonance imaging,fMRI)研究慢性期左侧皮层下脑卒中后轻中度手功能障碍(部分偏瘫手)患者运动功能网络的重组模式。方法:招募32例脑卒中后部分偏瘫手患者和40例匹配的健康老年对照。采集两组受试者的静息态fMRI数据,并采用Fugl-Meyer腕手运动功能量表评定患者的手功能障碍程度。采用RESTplus软件分析双侧初级运动皮层(primary motor cortex,M1)与全脑功能连接(functional connectivity,FC)的组间差异,并采用Pearson相关分析探究患者的FC模式与手功能评分之间的关系。结果:与健康老年对照相比,部分偏瘫手患者的患侧M1区与健侧感觉运动区、患侧海马和患侧颞中回的FC减弱,并且健侧M1区与患侧中央后回、健侧顶下小叶、患侧颞上回和患侧脑岛的FC也减弱。相关性分析发现,部分偏瘫手患者的健侧M1区与辅助运动区的FC强度与手功能评分正相关(r=0.67,P<0.001)。结论:慢性期左侧皮层下脑卒中后部分偏瘫手患者的运动功能网络发生了广泛的失连接重组,其中,健侧M1区与辅助运动区之间增强的FC可能是提示良好手功能结局的神经影像标记物。
文摘以丙烯腈(AN)为单体,聚丙二醇双甲基丙烯酸酯(PPGDMA)为交联剂制备了丁二腈(SN)增塑的塑性PAN-co-PPGDMA交联聚合物-双三氟甲基磺酰亚胺锂(Li TFSI)复合电解质poly-SN40。研究表明,poly-SN40具有较宽的电化学窗口(0-5.2 V vs Li/Li^(+))和较高的室温离子电导率(1.27 mS/cm);组装的锂电池Li/ploy-SN40/LiFePO4的充放电实验表明,在0.5 m A/cm^(2)的电流密度下,电池能够正常、安全地循环使用;电池在0.2 C倍率下室温循环比容量超过133.5 m Ah/g,在200次循环后容量保持率为92%,表现出98.3%的优异平均库仑效率。
