In Situ Testing Methods

In situ uniaxial testing with a novel sample design for self-alignment

I have developed a novel MEMS based uniaxial testing apparatus and a specimen design for measuring the mechanical response of material samples in situ in SEM. The stage adopts an assembly approach, where specimens are fabricated independently, allowing testing of a variety of materials. The assembly approach, however, involves intrinsic challenges in achieving pure uniaxial loading at the micro/nano scale due to off-axis loading (misalignment) errors. The effect of misalignment in stress evaluation increases with decreasing size scale of the sample -- an issue that has received limited attention in the literature. I have explored the source of intrinsic misalignment and its influence on the stress non-uniformity analytically and numerically. This work reveals substantial bending of the microspecimen due to small and often unavoidable off-axis loading. The proposed stage and the specimen ensure uniaxial loading by introducing hinge-like self-aligning mechanisms both in the stage as well as in the specimen. The analysis offers the parameter space to design and optimize uniaxial tests at the micro/nano scale. Also, I experimentally investigate the sources of misalignment during uniaxial test and their substantial influence on mechanical measurement of microspecimens. [3-5]In situ thermo-mechanical testing using a SiC based MEMS device

I have developed a SiC MEMS stage that allows, for the first time, to explore the effect of both size (100nm to 10s of micro meters) and temperature (room to 1000oC) on the thermo-mechanical properties of materials in situ in SEM and TEM. Such in situ experimental technique with both sample size and temperature control is essential for fundamental understanding of thermo-mechanical behaviors at the micro/nanoscale. During in situ uniaxial test, temperature, stress, and strain of a micro/nano material sample are simultaneously measured by built-in temperature and force sensors, and high resolution electron microscope images, respectively. [1-2]

Reference

1. W. Kang and T. Saif, A SiC MEMS Apparatus for In Situ Uniaxial Testing of Micro/Nanomaterials at High Temperature, Journal of Micromechanics and Microengineering, 21(10), 105017, 2011 (IOP Select Paper).
2. W. Kang and T. Saif, In Situ Thermo-Mechanical Testing for Micro/Nanomaterials, MRS Communications, 1(1), 13-16, 2011.
3. W. Kang, J. Han and T. Saif, A Novel Method for In Situ Uniaxial Tests at the Micro/Nano Scale–Part II: Experiment, Journal of Microelectromechanical Systems, 19(6), 1322-1330, 2010.
4. W. Kang and T. Saif, A Novel Method for In Situ Uniaxial Tests at the Micro/Nano Scale–Part I: Theory, Journal of Microelectromechanical Systems, 19(6), 1309-1321, 2010.
5. W. Kang, J. Rajagopalan, and T. Saif, In Situ Uniaxial Mechanical Testing of Small Scale Materials - a Review, Nanoscience and Nanotechnology Letters, 2(4), 282-287, 2010 (Invited Manuscript).