Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming,the stress concentration and defects such as wrinkling and fracture may easily occur.It is a key to reveal the defo...Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming,the stress concentration and defects such as wrinkling and fracture may easily occur.It is a key to reveal the deformation behaviors in order to obtain a sound product.Based on the ABAQUS platform,a 3 D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment.The stress and strain distributions,wall thickness variations and bellow profiles of each layer in the whole process,including bulging,folding and springback stages,are studied.Then deformation behaviors of bellows under different forming conditions are discussed.It is found that the wall thinning degrees of different layer vary after hydroforming,and is the largest for the inner layer and smallest for the outer layer.At folding stage,the wall thinning degree of the crown point increases lineally,and the difference among layers increases as the process going.The displacements of the crown point decrease from the inner layer to the outer layer.After springback,the U-shaped cross section changes to a tongue shape,the change of convolution pitch is much larger than the change of convolution height,and the springback values of the inner layer are smaller than the outer layer.An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase.With changing of process parameters,bellows with deep convolution are easily encountered wall thinning during hydroforming and convolution distortion after springback.This research is helpful for precision forming of multi-layered bellows.展开更多
The Ge_(2)Sb_(2)Te_(5)alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature.However widely used,this composition is not suitable...The Ge_(2)Sb_(2)Te_(5)alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature.However widely used,this composition is not suitable for embedded memories—for example,for automotive applications,which require very high working temperatures above 300℃.Ge–Sb–Te alloys with higher Ge content,most prominently Ge2Sb1Te2(‘212’),have been studied as suitable alternatives,but their atomic structures and structure–property relationships have remained widely unexplored.Here,we report comprehensive first-principles simulations that give insight into those emerging materials,located on the compositional tie-line between Ge_(2)Sb_(1)Te_(2) and elemental Ge,allowing for a direct comparison with the established Ge_(2)Sb_(2)Te_(5)material.Electronic-structure computations and smooth overlap of atomic positions(SOAP)similarity analyses explain the role of excess Ge content in the amorphous phases.Together with energetic analyses,a compositional threshold is identified for the viability of a homogeneous amorphous phase(‘zero bit’),which is required for memory applications.Based on the acquired knowledge at the atomic scale,we provide a materials design strategy for high-performance embedded phase-change memories with balanced speed and stability,as well as potentially good cycling capability.展开更多
基金the funds of the National Natural Science Foundation of China(No.51875456)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2019JM-450)+3 种基金the Young Talent fund of University Association for Science and Technology in Shaanxi,China(No.20170518)the Key Laboratory of Advanced Manufacture Technology for Automobile Parts(Chongqing University of Technology),Ministry of Education(No.2018KLMT03)Materials Science and Engineering provincial-level superior discipline funding project of Xi'an Shiyou Universitythe Program for Young Innovative Research Team in Xi'an Shiyou University(No.2015QNKYCXTD02)。
文摘Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming,the stress concentration and defects such as wrinkling and fracture may easily occur.It is a key to reveal the deformation behaviors in order to obtain a sound product.Based on the ABAQUS platform,a 3 D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment.The stress and strain distributions,wall thickness variations and bellow profiles of each layer in the whole process,including bulging,folding and springback stages,are studied.Then deformation behaviors of bellows under different forming conditions are discussed.It is found that the wall thinning degrees of different layer vary after hydroforming,and is the largest for the inner layer and smallest for the outer layer.At folding stage,the wall thinning degree of the crown point increases lineally,and the difference among layers increases as the process going.The displacements of the crown point decrease from the inner layer to the outer layer.After springback,the U-shaped cross section changes to a tongue shape,the change of convolution pitch is much larger than the change of convolution height,and the springback values of the inner layer are smaller than the outer layer.An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase.With changing of process parameters,bellows with deep convolution are easily encountered wall thinning during hydroforming and convolution distortion after springback.This research is helpful for precision forming of multi-layered bellows.
基金W.Z.thanks the support of National Natural Science Foundation of China(61774123)111 Project 2.0(BP2018008)R.M.acknowledges funding from Deutsche Forschungsgemeinschaft(DFG)within SFB 917(‘Nanoswitches’).V.L.D.acknowledges a Leverhulme Early Career Fellowship.The authors acknowledge the support by the HPC platform of Xi’an Jiaotong University,and the International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies of Xi’an Jiaotong University.
文摘The Ge_(2)Sb_(2)Te_(5)alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature.However widely used,this composition is not suitable for embedded memories—for example,for automotive applications,which require very high working temperatures above 300℃.Ge–Sb–Te alloys with higher Ge content,most prominently Ge2Sb1Te2(‘212’),have been studied as suitable alternatives,but their atomic structures and structure–property relationships have remained widely unexplored.Here,we report comprehensive first-principles simulations that give insight into those emerging materials,located on the compositional tie-line between Ge_(2)Sb_(1)Te_(2) and elemental Ge,allowing for a direct comparison with the established Ge_(2)Sb_(2)Te_(5)material.Electronic-structure computations and smooth overlap of atomic positions(SOAP)similarity analyses explain the role of excess Ge content in the amorphous phases.Together with energetic analyses,a compositional threshold is identified for the viability of a homogeneous amorphous phase(‘zero bit’),which is required for memory applications.Based on the acquired knowledge at the atomic scale,we provide a materials design strategy for high-performance embedded phase-change memories with balanced speed and stability,as well as potentially good cycling capability.
