On the measurement of the plasticity length scale parameter in LIGA nickel foils

This paper presents measurements of the plasticity length scale for polycrystalline LIGA nickel foils produced by electroplating in a sulfamate bath. The micro-bend test method developed by Stolken and Evans [Acta Mater. 46 (1998) 5109] is used to obtain a composite length scale parameter. l(c). that is primarily associated with rotational gradients. The micro-bend test utilizes the measurement of the curvature change associated with elastic spring-back of bent micro-beams in the extraction of a composite length scale parameter. l(c). The length scale is measured to be similar to5.6 mum for foils between 25 and 175 pm thick. This is in the range (3-5 mum) reported from prior micro-bend experiments on nickel foils (loc. cit.). The measured length scale is also similar to values reported previously for polycrystalline copper wires using torsion tests in which rotation gradients dominate. (C) 2002 Published by Elsevier Science Ltd.