TY - JOUR
T1 - Experimental investigation of strain rate dependence of nanocrystalline Pt films
AU - Jonnalagadda, K. N.
AU - Chasiotis, I.
AU - Yagnamurthy, S.
AU - Lambros, J.
AU - Pulskamp, J.
AU - Polcawich, R.
AU - Dubey, M.
N1 - Funding Information:
Acknowledgements The authors acknowledge the support by the Army Research Office (ARO) under the Grant W911NF-05-1-0063 with Dr. Bruce LaMattina as the program manager, and by the National Science Foundation under Grant CMS 0555787. Furthermore, the authors would like thank Mr. William Wheeler for assisting with the speckle pattern apparatus. The authors also wish to thank Mr. Joel Martin (ARL) and Prashant Ranade (General Technical Services) for their assistance in the fabrication of the tensile specimens.
PY - 2010/1
Y1 - 2010/1
N2 - A new microscale uniaxial tension experimental method was developed to investigate the strain rate dependent mechanical behavior of freestanding metallic thin films for MEMS. The method allows for highly repeatable mechanical testing of thin films for over eight orders of magnitude of strain rate. Its repeatability stems from the direct and full-field displacement measurements obtained from optical images with at least 25nm displacement resolution. The method is demonstrated with micron-scale, 400-nm thick, freestanding nanocrystalline Pt specimens, with 25nm grain size. The experiments were conducted in situ under an optical microscope, equipped with a digital high-speed camera, in the nominal strain rate range 10 -6-10 1s -1. Full field displacements were computed by digital image correlation using a random speckle pattern generated onto the freestanding specimens. The elastic modulus of Pt, E=182±8 GPa, derived from uniaxial stress vs. strain curves, was independent of strain rate, while its Poisson's ratio was v=0.41±0.01. Although the nanocrystalline Pt films had the elastic properties of bulk Pt, their inelastic property values were much higher than bulk and were rate-sensitive over the range of loading rates. For example, the elastic limit increased by more than 110% with increasing strain rate, and was 2-5 times higher than bulk Pt reaching 1.37GPa at 10 1s -1.
AB - A new microscale uniaxial tension experimental method was developed to investigate the strain rate dependent mechanical behavior of freestanding metallic thin films for MEMS. The method allows for highly repeatable mechanical testing of thin films for over eight orders of magnitude of strain rate. Its repeatability stems from the direct and full-field displacement measurements obtained from optical images with at least 25nm displacement resolution. The method is demonstrated with micron-scale, 400-nm thick, freestanding nanocrystalline Pt specimens, with 25nm grain size. The experiments were conducted in situ under an optical microscope, equipped with a digital high-speed camera, in the nominal strain rate range 10 -6-10 1s -1. Full field displacements were computed by digital image correlation using a random speckle pattern generated onto the freestanding specimens. The elastic modulus of Pt, E=182±8 GPa, derived from uniaxial stress vs. strain curves, was independent of strain rate, while its Poisson's ratio was v=0.41±0.01. Although the nanocrystalline Pt films had the elastic properties of bulk Pt, their inelastic property values were much higher than bulk and were rate-sensitive over the range of loading rates. For example, the elastic limit increased by more than 110% with increasing strain rate, and was 2-5 times higher than bulk Pt reaching 1.37GPa at 10 1s -1.
KW - Digital image correlation
KW - Mechanical properties
KW - Nanocrystalline platinum
KW - Strain rate
KW - Thin films
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U2 - 10.1007/s11340-008-9212-7
DO - 10.1007/s11340-008-9212-7
M3 - Article
AN - SCOPUS:77949293429
SN - 0014-4851
VL - 50
SP - 25
EP - 35
JO - Experimental Mechanics
JF - Experimental Mechanics
IS - 1
ER -