A microbend test method for measuring the plasticity length scale

A versatile microbend test method for determining the plasticity length scale has been developed and described. It involves the bending of a thin annealed foil around a small diameter cylindrical mandril, followed by measurement of the unloaded and loaded radii of curvature. This lest fully characterizes the moment-curvature relation, subject to independent knowledge of the elastic modulus of the foil material. By using mandrils having different radii as well as foils with different thicknesses, the plasticity length scale can be established, upon comparison with tensile stress-strain measurements made on the same foils. The analysis relating the length scale to the measured moments is described and used to interpret results obtained for high purity Ni. This length scale is in the range 3-5 mu m. It is dominated by rotation (rather than stretch) gradient and similar to that found previously for Cu using wire torsion tests. It is larger than the length scale determined from nanohardness tests. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.