Length scale effects in epoxy: The dependence of elastic moduli measurements on spherical indenter tip radius |
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Affiliation: | 1. School of Control Science and Engineering, Dalian University of Technology, Dalian 116024, China;2. Department of Engineering Mechanics, Dalian University of Technology, Dalian 116024, China;3. Department of Electrical and Computer Engineering, University of Alberta, Edmonton T6R 2V4 AB, Canada;4. Department of Electrical and Computer Engineering, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia;5. Systems Research Institute, Polish Academy of Sciences, Warsaw, Polandn;1. Université Rennes 1, LGCGM-INSA Rennes, 20 avenue des buttes de Coësmes, CS 14315, F-35043 Rennes, France;2. Université Lille Nord de France, Lille 1, LML, UMR 8107, F-59650 Villeneuve d''Ascq, France;1. School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China;2. School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, PR China |
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Abstract: | Significant increases in the measured elastic moduli with decreasing indentation depth have been previously found in various polymers by indentation tests with a Berkovich tip at micro-to nanometer length scales. These increases in the determined elastic moduli were related to second order displacement gradients which increase with decreasing depth when a conical tip is applied. When a spherical tip is applied, such depth dependence should not be present as the second order displacement gradients remain essentially unchanged with indentation depth. However, these gradients should be proportional to the radius of the spherical tip. To examine the notion of second order displacement gradient dependence in measurements of elastic moduli, indentation experiments are conducted on epoxy with spherical tips of different nominal radii. Accounting for tip imperfections, an increase in the determined elastic moduli is found with decreasing tip radius, which corroborates the notion of second order displacement gradient dependence. |
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Keywords: | Indentation Elastic moduli Spherical tip Tip radius Second order displacement gradients |
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