Strain-rate sensitivity of strength in macro-to micro-to nano crystalline nickel

dc.contributor.committeeChairJankowski, Alan F.
dc.contributor.committeeMemberRasty, Jahan
dc.contributor.committeeMemberRivero, Iris V.
dc.creatorHumphrey, Ryan T. Engineering
dc.description.abstractThe strain-rate sensitivity of strength is a key parameter to evaluate the deformation mechanism in crystalline materials. It is widely reported that many metals strengthen with increasing strain rate, wherein an increase in the strain-rate exponent occurs as the grain size decreases. The strain-rate sensitivity exponent as evaluated from a power-law relationship between yield strength and strain rate is thought to increase when the deformation mechanisms change. As increase in the strain-rate occurs, strengthening is attributable to alloy content, then to dislocation activity, and finally to an increase in effective mass – also known as the phonon drag regime. We will evaluate the behavior of nickel over eight-orders of magnitude change in strain rate to see if the change in strain-rate exponent is affected by the scale of the grain size from the macro- to micro- to nano- scale range as the strain rate increases. In this study, tensile testing is used to measure the strain-rate dependence of the tensile strength on the grain size in crystalline nickel foils. Similarly, micro-scratch testing is used to determine the strain-rate dependence of the scratch hardness variation with scratch velocity. Results for these two tests methods are compiled for strain rates that range from 0.00001 to 1000 sec-1. It is found that these mechanical test results can be directly compared, and the increase in strain rate sensitivity exponent with increasing strain rate is slower for nanocrystalline than for microcrystalline nickel.
dc.subjectStrain-rate sensitivity
dc.subjectNanomaterials behavior
dc.subjectStrength of materials
dc.titleStrain-rate sensitivity of strength in macro-to micro-to nano crystalline nickel