Nanoindentation of Polymers Wyoming NSF/EPSCoR Undergraduate Research Fellowship Ashley Bucsek Nano- and Micro-Mechanics Laboratory members: Chung-Souk Han, Ph.D. Nitin Garg Farid Alisafaei Seyed Hamid Reza Sanei Rajib Krishna Shasa Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Small-scale polymers Coatings and adhesives Micromechanical devices Biomedical microdevices Composites Engineers use mechanical properties to safely predict the behavior of objects under applied loads. It is important to understand the properties of polymers at very small scales. Boisen, A. et al. (2011). [Figure 8] “Cantilever-like micromechanical sensors,” Reports on Progress in Physics, 74. Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Hardness: the resistance of a material to permanent penetration by another significantly harder material On the macroscale, material properties like hardness are constant. Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Indentation Size Effects (ISE): the apparent increase in material-specific properties at very small scales Metals ISE well documented, well understood Polymers ISE not well document, not well understood Research Study ISE in polymers, using polydimethylsiloxane (PDMS) Improve the understanding of ISE in polymers Help develop physically based theories to model and explain ISE in polymers ISE can be observed in PDMS. These ISE vary with different cross-link densities. cross links Callister, W. (2010). [Figure 14.7] “Materials Science and Engineering: An Introduction, 8th ed.” Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research G200 Nano Indenter™ Nanoindenter tip under a load, F, displacing a material to an indentation depth, h Berkovich indenter tip Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Parameters Surface Approach Sensitivity, Ktol Time to Load Hold Time Maximum Load, Fmax Results Maximum Indentation Depth, hmax Permanent Indentation Depth, hf Hold Time Time to Load Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Cross-Link Densities 2.5% 5% 10% Parameters Time to Load: 5 seconds Hold Time: 0 seconds Surface Approach Sensitivity, Ktol: 50 N/m Maximum Load, Fmax: 0.3 mN to 45 mN Berkovich Tip Sizes 0.3 mN to 10 mN: “Berkovich ISO Tip” 8 mN to 45 mN: “Berkovich MACRO Tip” Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research 1 2 ISO 14577-1 Metallic materials – Instrumented indentation test for hardness and materials parameters – Part 1: test method. International Organization for Standardization (2002). Sneddon, I. "The relation between load and penetration in the axisymmetric boussinesq problem for a punch of arbitrary profile." Int. J. Eng. Sci. 3. (1965): 47-57. Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Two important characteristics: Drastic increase with decreasing indentation depths below 90 µm Reach transient quantity as indentation depths increase above 90 µm Indentation Size Effects Two important characteristics: There is a clear increase in universal hardness, HU, and elastic modulus, E, with decreasing indentation depths below 90 µm. The hardness and elastic modulus reach a transient quantity as indentation depths increase above 90 µm. Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Two important characteristics: There is a clear increase in universal hardness, HU, and elastic modulus, E, with decreasing indentation depths below 90 µm. The hardness and elastic modulus reach a transient quantity as indentation depths increase above 90 µm. Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Two important characteristics: There is a clear increase in universal hardness, HU, and elastic modulus, E, with decreasing indentation depths below 90 µm. The hardness and elastic modulus reach a transient quantity as indentation depths increase above 90 µm. Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Elastic Modulus The material property, elastic modulus, does not actually increase. Has been shown to be constant by lab member, Seyed Hamid Reza Sanei. The problem is how the test results are used to calculate elastic modulus. Classical continuum theories do not account for strain gradients. This research will help shed light on the shortcomings of classical continuum theory. spherical indenter tip Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Current Project Goals: Determine appropriate surface approach sensitivity criteria, Ktol. Repeat testing for 2.5%, 5%, and 10% with new Ktol. Repeat experimental procedure for epoxy. Interpret for a manuscript to be submitted for publication in an international scientific journal. Unanswered Question: How does ISE vary with cross-link density? Determine an appropriate surface approach sensitivity criteria, Ktol, at each cross-link density Repeat testing for 2.5%, 5%, and 10% with new Ktol values. Repeat experimental procedure for epoxy. Assemble and interpret collection of ISE data in polymers for a manuscript to be submitted for publication in an international scientific journal. Background│ Hypotheses │Instrumentation │ Procedure │ Results │ Discussion │ Current Research Thank you for your attention. Special Thanks to Dr. Han and EPSCoR. Questions?