Modeling of Bending and Bend-Stretching of Laminated Aluminum Sheets

Bending and subsequent stretching of sheet materials is typical of many sheet forming operations. Bending and bend-stretching characteristics and limit strain of monolithic AA2024 and laminated tri-layer Alclad 2024 aluminum sheet materials are studied by modeling and experimentation. A computationally efficient analytical model based on advanced bending theory is developed for the laminated sheet materials and utilized to predict the bending characteristics of the above sheet materials. The effects of cladding thickness ratio on the bending characteristics of laminated sheet are compared with the monolithic constituent. Also, predictions from the above analytical bending model are compared with 2D and 3D FE-based bending models. In addition, bend-stretching experiments are conducted using a specialized test jig while continuously recording images using dual-camera set-up from tensile surface and edge of the specimen. A stochastic pattern is applied to the specimen prior to the test and the images are later processed to analyze the development and localization of strains based on digital image correlation (or DIC) method. Strain maps from DIC analysis are utilized to determine the limit strain in the vicinity of the bend line, as well as from FE modeling of bend-stretching tests, using maximum major strain acceleration criterion for localized necking proposed by one of the authors. The results from experimental and modeling work indicate higher limit strains in bend-stretching for Alclad 2024 compared to monolithic AA2024 sheet.