Strain gradient plasticity length scale parameters for LIGA Ni MEMs thin films

摘要

This paper presents a recent study of the effects of plasticity strain gradient length scale parameters on plastic deformation. The plasticity length scale parameters are obtained for LIGA Ni MEMS structures plated from sulfamate baths. Micro-tensile experiments were explored in current study to evaluate the basic tensile properties for LIGA Ni MEMS structures at micron scale. The composite length scale parameter [J.S. Stoelken, A.G. Evans, Acta Mater. 6 (1998) 5109-5115] was obtained from the micro-bend techniques, and the stretch gradient length scale parameter [J.S. Stoelken, A.G. Evans, Acta Mater. 46 (1998) 5109-5115; N.A. Fleck, J.W. Hutchinson, Adv. Appl. Mech. 33 (1997) 295-361; W.D. Nix, H. Gao, J. Mech. Phys. Solids 46 (1998) 411-425; M.R. Begley, J.W. Hutchinson, J. Mech. Phys. Solids 46 (1998) 2049-2068] was extracted from the nano-indentation experiments. A constitutive expression, which is an extension of the traditional J_2 theory, was obtained for the LIGA Ni MEMS structures. This constitutive equation can be used for the further modeling of plasticity of LIGA Ni MEMS structures plated under similar conditions. The implications of plasticity length scale parameters are discussed for multi-scale modeling between the micron- and nano-scales.