Constitutive Modeling of the Densification Process of Ceramic Powders Subjected to Cold, Quasi-Static Pressing

The consistent, uniform pressing of green bodies is a necessary part of producing high-quality, high-performance ceramics with predictable qualities and behavior. Undesirable density variation in the compacted ceramic powder causes variability in performance, failure to meet quality control standards, and, possibly, complete piece failure during successive processing. These issues contribute directly to a decrease in production efficiency through lost time and an increase in energy and material use. The careful control of the green body density field is of the utmost importance to consistently producing high-performance ceramics. Current methods for minimizing heterogeneity of the density field are often based on trial-and-error to optimize mold geometry and forming pressure, which is both expensive and prolongs development. The present research presents a continuum-level constitutive model for accurately modeling the densification of ceramic powders into green bodies and outlines the numerical implimentation of said model. The constitutive model incorporates nonlinear elasticity, elatic-plastic coupling, cap evolution, pressure- and Lode angle-dependent plasticity, and hardening. To evaluate the constitutive model, a new method for measuring density in green bodies has been developed. This method utilizes readily-available laboratory equipment to produce density projection data for the sample and subsequently processes that data to produce a 3D density field using well-developed tomographic reconstruction techniques. Finally, a green body is produced from alumina powder (Martoxid KMS-96) and the density field is evaluated and compared to that of a numerical simulation. They are shown to agree within the error of the density measurements. These comparisons demonstrate the performance of the developed constitutive model and the potential utility for companies and research institutions that are in the ceramics production field.