Continuous roll forming(CRF) is a novel forming process for three-dimensional surface parts,in which a pair of bendable forming rolls is used as sheet metal forming tool.By controlling the gap between the upper and lo...Continuous roll forming(CRF) is a novel forming process for three-dimensional surface parts,in which a pair of bendable forming rolls is used as sheet metal forming tool.By controlling the gap between the upper and lower forming rolls,sheet metal is non-uniformly extended in the longitudinal direction while it is bent in the transverse direction during the rolling process.As a result,longitudinal bending is gained and a doubly curved surface is formed.With the rotations of the forming rolls,the sheet metal is deformed consecutively,and a three-dimensional surface part is shaped continuously.In this paper,the mechanism of the three-dimensional surface formation in CRF is set forth.Through theoretical analysis of the CRF process,the governing equations for the bending deformation in rolling process are presented.Based on the simplification on the deformation and material model,the formulation to calculate the longitudinal bending deformation is derived,and the methods to design the compression ratio and the roll gap are given,the effects of compression ratio of rolling and the width of blank sheet on the longitudinal bending curvature are analyzed.The forming experiments on typical surface parts and measured results show that forming results with good precision can be obtained by CRF process.展开更多
Covalent functionalization of graphene offers opportunities for tailoring its properties and is an unavoidable consequence of some graphene synthesis techniques. However, the changes induced by the functionalization a...Covalent functionalization of graphene offers opportunities for tailoring its properties and is an unavoidable consequence of some graphene synthesis techniques. However, the changes induced by the functionalization are not well understood. By using atomic sources to control the extent of the oxygen and nitrogen functionalization, we studied the evolution in the structure and properties at the atomic scale. Atomic oxygen reversibly introduces epoxide groups whilst, under similar conditions, atomic nitrogen irreversibly creates diverse functionalities including substitutional, pyridinic, and pyrrolic nitrogen. Atomic oxygen leaves the Fermi energy at the Dirac point （i.e., undoped）, whilst atomic nitrogen results in a net n-doping; however, the experimental results are consistent with the dominant electronic effect for both being a transition from delocalized to localized states, and hence the loss of the signature electronic structure of graphene.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51275202 and 51075186)
文摘Continuous roll forming(CRF) is a novel forming process for three-dimensional surface parts,in which a pair of bendable forming rolls is used as sheet metal forming tool.By controlling the gap between the upper and lower forming rolls,sheet metal is non-uniformly extended in the longitudinal direction while it is bent in the transverse direction during the rolling process.As a result,longitudinal bending is gained and a doubly curved surface is formed.With the rotations of the forming rolls,the sheet metal is deformed consecutively,and a three-dimensional surface part is shaped continuously.In this paper,the mechanism of the three-dimensional surface formation in CRF is set forth.Through theoretical analysis of the CRF process,the governing equations for the bending deformation in rolling process are presented.Based on the simplification on the deformation and material model,the formulation to calculate the longitudinal bending deformation is derived,and the methods to design the compression ratio and the roll gap are given,the effects of compression ratio of rolling and the width of blank sheet on the longitudinal bending curvature are analyzed.The forming experiments on typical surface parts and measured results show that forming results with good precision can be obtained by CRF process.
文摘Covalent functionalization of graphene offers opportunities for tailoring its properties and is an unavoidable consequence of some graphene synthesis techniques. However, the changes induced by the functionalization are not well understood. By using atomic sources to control the extent of the oxygen and nitrogen functionalization, we studied the evolution in the structure and properties at the atomic scale. Atomic oxygen reversibly introduces epoxide groups whilst, under similar conditions, atomic nitrogen irreversibly creates diverse functionalities including substitutional, pyridinic, and pyrrolic nitrogen. Atomic oxygen leaves the Fermi energy at the Dirac point （i.e., undoped）, whilst atomic nitrogen results in a net n-doping; however, the experimental results are consistent with the dominant electronic effect for both being a transition from delocalized to localized states, and hence the loss of the signature electronic structure of graphene.
