Title: The effect of statistical variability in material properties on springback

Authors: D. Gary Harlow

Addresses: Mechanical Engineering and Mechanics, Lehigh University, 19 Memorial Drive West, Bethlehem, PA 18015-3085, USA

Abstract: A major concern with manufacturing processes using metals is the accurate prediction of the response of the material to complex forming operations that shape a blank into a component. One of the more difficult problems is springback, which is the tendency of a metal to not maintain the desired shape after the forming process is terminated. Springback is more pronounced in high-strength steel and aluminium alloys than other metals. Unless springback is accurately estimated, manufactured parts may deviate excessively from the design specifications. The purpose of this paper is to use mechanistically based probability modelling to accurately estimate variability in the dimensions of a component and the adherence to design tolerances. It is assumed that the variability in the component dimensions is due to randomness in the material properties that directly affect the magnitude of the springback. The yield stress is the primary source of randomness and is most critical in the springback prediction. In order to assess the effects of variability, a simple model for elastic springback in a straight rectangular bar bent around a circular mandrel is considered. Explicit computations are made for a commercially available aluminium alloy for which material properties are readily available. The stress–strain behaviour of the alloy is assumed to be bilinear. The effects of the stress–strain behaviour, the model parameters, and the statistical variability in material properties on springback are assessed.

Keywords: design tolerances; mechanistically based probability modelling; springback; stress–strain behaviour; variability in material properties; yield stress.

DOI: 10.1504/IJMPT.2004.003921

International Journal of Materials and Product Technology, 2004 Vol.20 No.1/2/3, pp.180 - 192

Published online: 10 May 2004 *

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