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This paper focuses on the twist defects and the control strategy in the process of four-roll bending for aluminum alloy Z-section profiles with large cross-section. A 3D finite element model (3D-FEM) of roll bending process has been developed, on the premise of the curvature radius of the profile, the particularly pronounced twist defects characteristic of 7075-O aluminum alloy Z-section profiles were studied by FE method. The simulation results showed that the effective control of the twist defects of the profile could be realized by adjusting the side roller so that the exit guide roll was higher than the entrance one (the side rolls presented an asymmetric loading mode with respect to the main rolls) and increasing the radius of upper roll. Corresponding experimental tests were carried out to verify the accuracy of the numerical analysis. The experimental results indicated that control strategies based on finite element analysis (FEA) had a significant inhibitory function on twist defects in the actual roll bending process.

Abstract: The insertion of a structurally chiral layer defect between two identical chiral mirrors, made of periodic structurally chiral materials such as chiral liquid crystals and chiral sculptured thin films, generates two different types of spectral holes, depending on the thicknesses of the chiral mirrors and the central layer defect. [Copyright &y& Elsevier]

Abstract: The introduction of either a central layer defect or a central twist defect in a periodic structurally chiral material generates circular-polarization-sensitive spectral holes in the remittance spectrums for normally incident plane waves. We propose and theoretically establish here the third method to generate such spectral holes using two-section chiral sculptured thin films (STFs). Both sections of the proposed device have the same periodicity and handedness, but their dielectric properties are different and related in a specific way. The concept of pseudoisotropy is highly relevant for the production of the proposed device. [Copyright &y& Elsevier]

This paper focuses on the twist defects and the control strategy in the process of four-roll bending for aluminum alloy Z-section profiles with large cross-section. A 3D finite element model (3D-FEM) of roll bending process has been developed, on the premise of the curvature radius of the profile, the particularly pronounced twist defects characteristic of 7075-O aluminum alloy Z-section profiles were studied by FE method. The simulation results showed that the effective control of the twist defects of the profile could be realized by adjusting the side roller so that the exit guide roll was higher than the entrance one (the side rolls presented an asymmetric loading mode with respect to the main rolls) and increasing the radius of upper roll. Corresponding experimental tests were carried out to verify the accuracy of the numerical analysis. The experimental results indicated that control strategies based on finite element analysis (FEA) had a significant inhibitory function on twist defects in the actual roll bending process. [ABSTRACT FROM AUTHOR]