Many mathematical models based on the advanced theory of bending to predict bending characteristics for monolithic sheet materials are available in the literature. In this work, a similar approach is utilized to develop bending models for a bilayer laminated sheet material. The principal stresses and strains through the thickness and change in relative thickness, at specified bend curvatures, are obtained as a function of increasing curvature during bending. Additionally, three-dimensional (3D) finite element (FE) based models for bilayer laminate bending are developed to overcome simplifications of the analytical models. In order to experimentally validate the two models, a new experimental bend test-jig is developed and experiments are performed on bilayer steel–aluminum laminate for different clad to matrix thickness ratios. These experiments have enabled continuous measurements of strain along the width at the bend line and through the laminate thickness at one of the specimen edges using an online strain mapping system based on digital image correlation (DIC) method. Analytical model results indicate how the through-thickness strain distribution and relative thickness of the specimen in bending are influenced by the location and thickness of the soft clad material. The FE model and experimental results exhibit similar trends in the relative thickness change for different geometric arrangements of steel–aluminum layers. The tangential and radial stresses decrease in magnitude with increasing aluminum clad thickness ratios. The 3D FE model of laminate bending provided strain predictions across the specimen width at the bend line on the tension and compression sides that increased with increasing clad thickness ratios. Also, relative thickness data from the 3D FE model showed uniaxial and plane strain stress states at the edge and midwidth sections of the test specimen. The results from analytical and FE models and from DIC and microscopic thickness measurements indicate that thickness at the bend line increases with increasing clad thickness for the case of clad layer on the compressive side of the laminate (i.e., C-C case) and vice versa for clad layer on the tensile side (C-T).

Bending of sheet materials is a common forming mode for shaping sheet components. Although many numerical models of bending, both analytical and numerical simulations based, are available in the literature, extensive experimental validations have been rather limited. A new bend test method and complementary three-dimensional finite element (FE) simulation of the experiments are employed to assess the predictions from an advanced analytical and FE model of pure bending of aluminium sheet materials. The experimental set-up developed and utilised is an open concept design that allows access to the tensile surface and through-thickness region in the vicinity of the specimen bend line to continuously record images of the deforming specimen with two cameras. The specimen images are analysed for strains using an online strain mapping system based on digital image correction method. Tangential strain distribution results from the models in terms of material thinning in the bend region are compared with those from the experiments on AA2024 aluminium sheet material by considering the responses from the specimen edges and mid-width regions at the bend line. Furthermore, the tangential and radial stress distributions on the through-thickness section of the specimen from the analytical model are compared with those from the FE model. The results from experiments, FE model and analytical model are compared and discussed in the light of the experimental data and the assumptions involved in the development of the models.

No abstract