Please consider attending the following: MATERIALS ENGINEERING SEMINAR "Characterization of Molecular Crystals and Identification of Mechanical Mocks Using Nanoindentation" By Alexandra C. Burch Purdue MSE Ph.D. Preliminary Exam Advisor: Professor David F. Bahr ABSTRACT Due to limitations such as the safety and cost of testing energetic materials, particularly explosives, mock materials that are inert and can simulate the mechanical properties of an energetic material may be desired. These mock materials, often found in pharmaceuticals and foods, are often used and tested in the form of small submillimeter sized crystals, with which typical crystal size and geometry make many mechanical tests difficult or impossible. Therefore nanoindentation can be useful in measuring the mechanical properties of these crystals without the need to grow large single crystals or do additional processing on existing crystals. In investigating materials as potential mocks, results of an indentation test that may be useful are hardness, elastic modulus, elastic-plastic response, and indentation fracture. Fracture in particular is not a direct measurement made by nanoindentation, but rather can be deduced by superimposability or lack thereof of indentation unloading traces. Previously, sucrose has been used as a mock material for some energetic materials, notably HMX and RDX, but may not be the most suitable simulate due to its relatively low density and poor thermal stability. Recently, three new materials have been proposed as potential mocks for HMX based on density, crystal structure, and thermal stability: 5-iodo-2'-deoxyuridininine 2, 3, 4, 5, 6 - pentafluorobenzamide, and N,N'- bis (2, 3, 4, 5, 6 -pentafluorophenyl)oxamide. These materials were chosen based on crystal structure, density, and thermal properties, but mechanical similarities to HMX were not tested. It is proposed that minimum mechanical similarity thresholds can be established for declaring a material as a mock; that nanoindentation can be used to identify which of the previously named three materials is the most appropriate mechanical mock for HMX by comparing hardness and elastic modulus values, elastic-plastic behavior, and critical stress to fracture, as well as that the same methods can be applied to other potential explosive-mock systems; that minimum similarity thresholds can be established for what degree of superimposability of indentation unloading curves is indicative of indentation fracture; and that mechanical mocks can be found in molecular crystals that do not share identical crystal structures. Date: Monday, January 8, 2017 Time: 11:00 A.M. Place: ARMS 3115