Anti-Buckling Device for Ultra-Thin Metallic Sheets Under Large and Reversed Shear Strain Paths

Abstract

The kinematic contribution to the hardening of ultra-thin metallic sheets characterized by monotonic and reversed simple shear tests is of high interest in the sheet metal forming industry, because of its influence on the accurate prediction of springback. However, ultra-thin sheets are very sensitive to buckling when submitted to shear stress because of the large gauge width to thickness ratio, the stress perturbations induced by the clamping and the alignment of sample, which thus limit the attainable strain levels using conventional simple shear devices. In this paper, a new simple shear test dedicated to ultra-thin metallic sheets is proposed through the development of a specific support. A transparent glass part enables the application of a normal tightening force to prevent the out-of-plane buckling of the sheets whilst also allowing full field strain measurements to be taken. Firstly, the capabilities of the device are shown by comparing the mechanical behavior in a simple shear test on an austenitic stainless steel with and without the support. A good reproducibility of the flow curves is observed with the support and large shear strains are reached without buckling. Secondly, the influence of friction due to the contact between the sample and the support is checked by finite elements simulations and shown to be negligible compared to the shearing force. Finally, monotonic and reversed shear tests on a pure copper sheet with a thickness of 0. were performed up to rupture without buckling, these were not previously conceivable on such a low thichness, and demonstrate the potential of the proposed device.

Estudo da conformabilidade do aço inoxidável AISI 409 sob rotas complexas de deformação

“…Observa-se ainda que para os dois valores de pré-deformação em cisalhamento direto, que a curva referente ao segundo cisalhamento direto exibiu uma queda (amaciamento) com posterior elevação (endurecimento), sinalizado a presença de transientes na taxa de encruamento normalizada e, consequentemente, uma maior desestruturação da subestrutura de discordâncias [17].…”

“…Em relação à evolução da taxa de encruamento normalizada do aço AISI 409 recozido/laminado, Figura 5, é possível observar, a presença de transientes na taxa de encruamento para os dois valores de pré-deformação em cisalhamento direto. Esse resultado, comparado com os dados exibidos na Figura 3, indica o efeito do modo e da quantidade de pré-deformação em laminação a frio na reestruturação da subestrutura de linhas de discordâncias, a qual pode ser relacionada com a presença desses transientes, associada ainda à provável modificação da orientação cristalográfica ao mudar o modo de deformação plástica (laminação para cisalhamento) [17]. Ainda referente à análise da Figura 5, nota-se um cruzamento entre as curvas da taxa de encruamento normalizada do aço AISI 409 pré-deformado de 3,88% e do carregamento monotônico, Figura 5a.…”

Low cycle fatigue performance of DP900 steel under cyclic shear paths

“…Strain is detected using an extensometer or via a digital image correlation (DIC) technique. The latter method also requires a transparent clamp to encase the experimental area to prevent the sheet from wrinkling 20,21 …”

“…The latter method also requires a transparent clamp to encase the experimental area to prevent the sheet from wrinkling. 20,21 The innovation of this paper is to study the mechanical properties and fatigue behavior of sheet metal under cyclic shear path. The clamping fixture is not used to prevent the plastic instability of the specimen, so as to avoid the interference of the clamping fixture on the stress state of the specimen.…”

Stress-Strain Response Determination during Incremental Step Tests and Variable Loadings on Flat Specimens

“…An anti-buckling support can, therefore, be attached to the test rig which prevents the buckling of the specimen [9][10][11][12]. In turn, friction between the specimen and the anti-buckling support occurs, which then affects the measured stress signal on the test rig.…”