Theta-like specimens for measuring mechanical properties at the small-scale: effects of non-ideal loading

As material structures, and devices fabricated from them, shrink to the nano-scale, it is ever more difficult to measure accurately the mechanical properties needed for designing small-scale devices and for assessing reliability. A promising test configuration for localized, small-scale uniaxial tensile measurements is the theta specimen. Stress distributions in this test configuration are examined via finite element analysis. When loaded uniformly with a double-articulating loading platen, a uniform uniaxial stress state is realized in the test gauge. When alternative, more easily realized experimentally, loading configurations are used (i. e., line or point contact), large secondary stresses develop. For each loading configuration, influences of non-ideal load application are elucidated. Two design modifications are considered to mitigate undesirable stresses: a compliant layer and an extended upper loading tab. The latter yields the most favorable stress state and is the most tolerant to non-ideal loading.