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You searched for +publisher:"Georgia Tech" +contributor:("Wegst, Ulrike G. K."). Showing records 1 – 2 of 2 total matches.

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1. Abba, Mohammed Tahir. Spherical nanoindentation protocols for extracting microscale mechanical properties in viscoelastic materials.

Degree: PhD, Mechanical Engineering, 2015, Georgia Tech

Nanoindentation has a high load resolution, depth sensing capabilities, and can be used to characterize the local mechanical behavior in material systems with heterogeneous microstructures. Recently nanoindentation has been used to extract useful stress-strain curves, primarily in hard materials such as metals and ceramics. To apply these indentation stress-strain methods to polymer composites, we have to first develop analysis techniques for materials that exhibit viscoelasticity. In a lot of current research the viscoelastic material properties are extracted after the material has been deformed enough to initiate plasticity and in some cases the time dependence of the deformation is ignored. This doesn’t give an accurate representation of the material properties of the undeformed sample or the local deformation behavior of the material. This dissertation develops analysis protocols to extract stress-strain curves and viscoelastic properties from the load-displacement data generated from spherical nanoindentation on materials exhibiting time-dependent response at room temperature. Once these protocols are developed they can then be applied, in the future, to study viscoelastic and viscoplastic properties of various mesoscale constituents of composite material systems. These new protocols were developed and tested on polymethyl methacrylate, polycarbonate, low-density polyethylene, and the bio-polymer chitosan. The properties extracted were consistent under different conditions and we were able to produce stress-strain curves for different loading rates and different indenter tip sizes. This dissertation demonstrates that a set of protocols can be used to reliably investigate the mechanical properties and deformation behavior of time-dependent materials using nanoindentation. Advisors/Committee Members: Kalidindi, Surya R. (advisor), Zhou, Min (committee member), Gall, Ken (committee member), Wegst, Ulrike G. K. (committee member), Jacob, Karl I. (committee member).

Subjects/Keywords: Nanoindentation; Viscoelastic; Polymers; Stress-strain; Mechanical properties

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Abba, M. T. (2015). Spherical nanoindentation protocols for extracting microscale mechanical properties in viscoelastic materials. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/54359

Chicago Manual of Style (16th Edition):

Abba, Mohammed Tahir. “Spherical nanoindentation protocols for extracting microscale mechanical properties in viscoelastic materials.” 2015. Doctoral Dissertation, Georgia Tech. Accessed March 20, 2019. http://hdl.handle.net/1853/54359.

MLA Handbook (7th Edition):

Abba, Mohammed Tahir. “Spherical nanoindentation protocols for extracting microscale mechanical properties in viscoelastic materials.” 2015. Web. 20 Mar 2019.

Vancouver:

Abba MT. Spherical nanoindentation protocols for extracting microscale mechanical properties in viscoelastic materials. [Internet] [Doctoral dissertation]. Georgia Tech; 2015. [cited 2019 Mar 20]. Available from: http://hdl.handle.net/1853/54359.

Council of Science Editors:

Abba MT. Spherical nanoindentation protocols for extracting microscale mechanical properties in viscoelastic materials. [Doctoral Dissertation]. Georgia Tech; 2015. Available from: http://hdl.handle.net/1853/54359

2. Weaver, Jordan S. Hierarchical and high throughput mechanical characterization of titanium alloys using spherical indentation stress-strain curves.

Degree: PhD, Mechanical Engineering, 2015, Georgia Tech

Recent work has shown the capability of spherical nanoindentation to capture local structure-property relationships in polycrystalline cubic metals by measuring indentation stiffness and yield strength from stress-strain curves as a function of the local microstructure in the indentation zone. However, these protocols capture structure-property relationships at only one level of the material hierarchy (e.g., single grains). Thus it is still very difficult to infer bulk structure-property relationships using these indentation protocols, which is mainly due to a lack of understanding indentation length scale effects and the important role played by structural hierarchy (i.e., unique structural features at different length scales). It is the goal of this work to extend these protocols to systematically study length scale effects of mechanical properties (e.g., indentation stiffness and yield strength) in titanium alloys. Alpha-beta titanium alloys were chosen because they display a rich variety of two phase microstructures and structural hierarchy and are well documented in literature. Firstly, nanoindentation protocols are extended to characterize the elastic and plastic anisotropy of a hexagonally close packed metal (alpha titanium in commercially pure and alloy Ti-6Al-4V) and a two phase microstructure (alpha-beta colony in Ti-6Al-4V). Secondly, spherical microindentation stress-strain protocols are developed and employed to characterize polycrystalline volumes in three titanium alloys (commercially pure, Ti-6Al-4V, and Ti18). The results of these major advances in indentation protocols and systematic study of length scale effects on the mechanical properties in Ti-6Al-4V will be presented and discussed along with applications demonstrating their high throughput nature to rapidly explore alloy development. Advisors/Committee Members: Kalidindi, Surya R. (advisor), Garmestani, Hamid (committee member), Pierron, Olivier (committee member), McDowell, David L. (committee member), Neu, Richard W. (committee member), Wegst, Ulrike G. K. (committee member).

Subjects/Keywords: Nanoindentation; Microindentation; Ti-6Al-4V

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Weaver, J. S. (2015). Hierarchical and high throughput mechanical characterization of titanium alloys using spherical indentation stress-strain curves. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/54398

Chicago Manual of Style (16th Edition):

Weaver, Jordan S. “Hierarchical and high throughput mechanical characterization of titanium alloys using spherical indentation stress-strain curves.” 2015. Doctoral Dissertation, Georgia Tech. Accessed March 20, 2019. http://hdl.handle.net/1853/54398.

MLA Handbook (7th Edition):

Weaver, Jordan S. “Hierarchical and high throughput mechanical characterization of titanium alloys using spherical indentation stress-strain curves.” 2015. Web. 20 Mar 2019.

Vancouver:

Weaver JS. Hierarchical and high throughput mechanical characterization of titanium alloys using spherical indentation stress-strain curves. [Internet] [Doctoral dissertation]. Georgia Tech; 2015. [cited 2019 Mar 20]. Available from: http://hdl.handle.net/1853/54398.

Council of Science Editors:

Weaver JS. Hierarchical and high throughput mechanical characterization of titanium alloys using spherical indentation stress-strain curves. [Doctoral Dissertation]. Georgia Tech; 2015. Available from: http://hdl.handle.net/1853/54398

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