Definition of Brittleness: Connections Between Mechanical
DEFINITION OF BRITTLENESS: CONNECTIONS BETWEEN MECHANICAL AND TRIBOLOGICAL PROPERTIES OF POLYMERS Haley E. Hagg Lobland, B.S., M.S. Dissertation Prepared for the Degree of DOCTOR OF PHILOSOPHY UNIVERSITY OF NORTH TEXAS August 2008 APPROVED: Witold Brostow, Major Professor Rick Reidy, Committee Member and Chair of the Department of Materials Science and Engineering Dorota Pietkewicz, Committee Member Nigel Shepherd, Committee Member Costas Tsatsoulis, Dean of the College of Engineering Sandra L. Terrell, Dean of the Robert B. Toulouse School of Graduate Studies Hagg Lobland, Haley E. Definition of brittleness: Connections between mechanical and tribological properties of polymers. Doctor of Philosophy (Materials Science and Engineering), August 2008, 51 pages, 5 tables, 13 illustrations, 106 references. The increasing use of polymer-based materials (PBMs) across all types of industry has not been matched by sufficient improvements in understanding of polymer tribology: friction, wear, and lubrication. Further, viscoelasticity of PBMs complicates characterization of their behavior. Using data from micro-scratch testing, it was determined that viscoelastic recovery (healing) in sliding wear is independent of the indenter force within a defined range of load values. Strain hardening in sliding wear was observed for all materials—including polymers and composites with a wide variety of chemical structures—with the exception of polystyrene (PS). The healing in sliding wear was connected to free volume in polymers by using pressure- volume-temperature (P-V-T) results and the Hartmann equation of state. A linear relationship was found for all polymers studied with again the exception of PS. The exceptional behavior of PS has been attributed qualitatively to brittleness.
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