MEMS Device for Fatigue Testing of 25 μm Thick Aluminum Specimens

Abstract

We report the development and demonstration of a MEMS (micro-electro-mechanical system) test instrument to perform fatigue testing on 25 μm thick aluminum 1145 H19 foil. Both the foil material and the specimen fabrication were obtained from commercial sources, while the MEMS device was fabricated in-house. The loading was in bending with a ratio R of minimum to maximum force equal to zero. The gauge section of the specimens had a minimum width of about 120 μm. The bending force was applied at a distance of about 3 mm from the gage section, through a lever arm fabricated as part of the specimen. The forces used were on the order of 5 mN, while the displacements at the load point were up to 50 μm. The loading waveform was a 70 Hz square wave. The S-N (stress versus number of cycles to failure) curve exhibits the expected behavior, with the shortest lives occurring at stresses near the tensile strength and the longest at stresses near half that value. The cracks exhibited a very abrupt transition from the incubation stage, marked by increasing surface deformations and other evidence of local microstructural damage, to the rapid growth stage. The failure criterion used for the S-N curve was the beginning of the rapid-growth stage.

Contribution of the U.S. National Institute of Standards and Technology. Not subject to copyright in the U.S.A.