Mismatch Plasticity Via Pressure Cycling

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9705558 Daehn This integrated program of experimentation, simulation, and analysis is aimed at a fundamental understanding of powder consolidation by pressure cycling. The FRG investigates mismatch plasticity in heterogeneous powder systems induced by cyclic pressure application which induces an equivalent effect via Eshelby mismatch, albeit at rates suitable for mass production. Recent experiments demonstrate the dramatic impact of cyclic pressure on consolidation densities and the even greater impact on green compact strengths. The former allows processing of powders with high reinforcement fractions while the latter introduces the possibility of secondary processing of highly reinforced green compacts, both of which are very challenging with traditional processing. A series of 2-D and 3-D experiments using real and idealized powders are compared with analysis and finite element modeling (FEM). A robust contact algorithm for large-strain FEM is developed for application to a wide range of micro-mechanical simulation. For each combination of experiment and simulation, compact densities and strengths are compared as functions of cyclic pressure application. An improved understanding of mismatch plasticity via pressure cycling and a robust numerical method for simulating micromechanical problems involving real contact properties should be developed. These advances eliminate the need for questionable assumptions inherent in today's theories and simulations. %%% The impact to the FRG is in several technological areas. Results from the project will demonstrate methods for producing powder-processed parts with greater consistency and shape accuracy, with or without secondary processing. New techniques for processing reinforced metal matrix composites via powder metallurgical routes will be identified. ***