Elastic-plastic Properties of Meso-scale Electrodeposited Liga Nickel Alloy Films: Analysis of Measurement Uncertainties

Abstract

It is well documented that the microstructure and properties of electrodeposited films, such as LIGA Ni and its alloys, are highly sensitive to processing conditions hence the literature shows large discrepancies in mechanical properties, even for similar alloys. Given this expected material variability as well as the experimental challenges with small-scale mechanical testing, measurement uncertainties are needed for property values to be applied appropriately, and yet are uncommon in micro- and meso-scale tensile testing studies. In a separate paper we reported the elastic-plastic properties of 200 μm -thick freestanding films of LIGA-fabricated nanocrystalline Ni-10 %Fe and microcrystalline Ni-10 %Co, with specimen gauge widths ranging from 75 μm to 700 μm, and tensile tested at strain rates 0.001 s-1 and 1 s-1. The loads were applied by commercial miniature and benchtop load frames, and strain was measured by digital image correlation. In this paper we examine the measurement uncertainties in the ultimate tensile strength, apparent Young's modulus, 0.2 % offset yield strength, and strain hardening parameters. For several of these properties, the standard deviation cannot be interpreted as the statistical scatter because the measurement uncertainty was larger. Microplasticity affects the modulus measurement, thus we recommended measuring the modulus after cyclic loading. These measurement uncertainty issues might be relevant to similar works on small-scale tensile testing and might help the reader to interpret the discrepancies in literature values of mechanical properties for LIGA and electrodeposited films.