CAREER: Material Removal Mechanism of Ceramic Materials in Ultra-Precision Machining

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This Faculty Early Career Development (CAREER) Program research will create a fundamental understanding of ceramic material removal during nanoscale machining. Ceramics, such as sapphire, zirconia, calcium fluoride, etc., have many superior mechanical, chemical, biomedical and optical properties, but fabricating ceramic components is very difficult due to their high hardness and brittleness. However, at a microscopic scale, ceramics can be machined like metals, although the mechanism explaining this phenomenon is not yet known. General machining creates cracks on ceramic surfaces because the crystal structure of the material is prone to fracture. Each crystal structure has multiple fracture systems; each fracture system can be initiated under some conditions, especially high pressure. This study will explore how the force generated by cutting action initiates fracture and will use this understanding so that cutting can be done without generating cracks. The research will allow the use of ceramics in various industries, including consumer electronics, biomedical and defense applications, and optical elements. Thus, the research directly and favorably affects economic welfare and national security. The knowledge generated from this project will be distributed through the advanced CNC (Computer Numerical Control) machine training program, online expert system, and public media in addition to journal publication and integration into undergraduate and graduate courses. The project goal is to understand how the microscopic crystal structure of ceramics influences material behavior during machining. The research will identify the activation mechanisms of ductile shear and brittle fracture of ceramics. This knowledge will lead to the development of machining strategies to suppress brittle fracture and to enable ductile mode machining on ceramics for a wide range of applications. The research will initially test the role of three potential parameters (resolved shear stress, fracture energy, and stress intensity factor) in activating plastic deformation or crack initiation. Specific contributions will include: (1) data generation on critical depth of cut where ductile to brittle transition occurs for all orientations for each distinctive crystal plane of sapphire and zirconia; (2) identification of triggering parameter(s) on activation of slip system or fracture system; and (3) modeling of ceramic machining.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.