Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a cry...Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.展开更多
To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based ...To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based on the minimum phase method,and the time-domain SE can be derived from frequency-domain SE.The SE of an energy selective surface(ESS) made of a novel material is investigated,and the relationship between SE and radiation field intensity are analyzed.The results show that not only material,but also the intensity of radiation electric field shows influence on SE in its frequency; for some materials,the dependence of SE on radiation electric field intensity needs to be considered.Therefore,it is necessary to research on the SE of shielding material in high-intensity electromagnetic environment.展开更多
以2195铝锂合金搅拌摩擦焊接头为研究对象,开展基于相场法的脆性断裂数值模拟研究.相场法以Francfort-Marigo变分原理为理论基础,在系统总势能中考虑断裂能,并考虑应变能的拉伸和压缩分解.引入弥散裂纹模型近似非光滑的裂纹拓扑关系,以...以2195铝锂合金搅拌摩擦焊接头为研究对象,开展基于相场法的脆性断裂数值模拟研究.相场法以Francfort-Marigo变分原理为理论基础,在系统总势能中考虑断裂能,并考虑应变能的拉伸和压缩分解.引入弥散裂纹模型近似非光滑的裂纹拓扑关系,以序参量表征材料损伤.基于Abaqus软件联合用户自定义元素子程序(user element subroutine,UEL),采用交替解法实现位移场和相场的耦合,进而求解脆性断裂问题.通过与试验结果对比,基于相场法的紧凑拉伸试件焊接区脆性断裂的裂纹扩展路径模拟吻合较好,且最大载荷值误差仅为0.46%.文中进一步研究增量步步长△u、相场特征宽度L_(c)与网格尺寸h对相场法模拟结果的影响,并将相场法与扩展有限元法(extended finite element method,XFEM)和内聚力模型(cohesive zone model,CZM)进行对比.研究表明,当分析增量步为1×10^(-4)时,分析结果收敛. L_(c)与裂纹h存在2倍的关系时,模拟结果较为准确.相场法可以准确模拟2195铝锂合金搅拌摩擦焊接头脆性断裂演化过程.展开更多
基金Project(11102164)supported by the National Natural Science Foundation of ChinaProject(G9KY101502)supported by NPU Foundation for Fundamental Research,China
文摘Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.
基金Project supported by National Basic Research Program of China（973 Program） （6131380301） National Natural Science Foundation of China （61001050）.
文摘To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based on the minimum phase method,and the time-domain SE can be derived from frequency-domain SE.The SE of an energy selective surface(ESS) made of a novel material is investigated,and the relationship between SE and radiation field intensity are analyzed.The results show that not only material,but also the intensity of radiation electric field shows influence on SE in its frequency; for some materials,the dependence of SE on radiation electric field intensity needs to be considered.Therefore,it is necessary to research on the SE of shielding material in high-intensity electromagnetic environment.
文摘以2195铝锂合金搅拌摩擦焊接头为研究对象,开展基于相场法的脆性断裂数值模拟研究.相场法以Francfort-Marigo变分原理为理论基础,在系统总势能中考虑断裂能,并考虑应变能的拉伸和压缩分解.引入弥散裂纹模型近似非光滑的裂纹拓扑关系,以序参量表征材料损伤.基于Abaqus软件联合用户自定义元素子程序(user element subroutine,UEL),采用交替解法实现位移场和相场的耦合,进而求解脆性断裂问题.通过与试验结果对比,基于相场法的紧凑拉伸试件焊接区脆性断裂的裂纹扩展路径模拟吻合较好,且最大载荷值误差仅为0.46%.文中进一步研究增量步步长△u、相场特征宽度L_(c)与网格尺寸h对相场法模拟结果的影响,并将相场法与扩展有限元法(extended finite element method,XFEM)和内聚力模型(cohesive zone model,CZM)进行对比.研究表明,当分析增量步为1×10^(-4)时,分析结果收敛. L_(c)与裂纹h存在2倍的关系时,模拟结果较为准确.相场法可以准确模拟2195铝锂合金搅拌摩擦焊接头脆性断裂演化过程.
