Discipline: Technology and Engineering
Subcategory: Civil/Mechanical/Manufacturing Engineering
Michael Conward - Rensselaer Polytechnic Institute
Co-Author(s): Johnson Samuel, Rensselaer Polytechnic Institute, Troy, NY
It is well known that the microstructure of cortical bone and its material properties vary from patient to patient based on their age and health-history. However, today’s state-of-the-art bone surgeries do not account for these variations. This approach can result in damage to the bone, which in turn contributes to an increase in patient recovery times. In order to make the vision of patient-specific bone surgery protocols a reality, there is an imperative need to examine the machining responses of the microstructural constituents of bone especially considering surgical tools take depth of cuts in the micro-scale range. For the most part, past bone machining studies have been conducted on a macro-scale level and were insensitive to microstructural variations/constituents. Additionally, machining researchers have not paid much attention to the bone microstructure while interpreting their results. For example, cortical bovine bone is primarily made up of two load-carrying components viz., haversian bone and plexiform bone, both of which have distinctly different microstructure and properties. However, to-date the machining studies have not isolated the effects of these individual components on the machining responses of interest. The objective of this research is to investigate the characteristic differences observed while machining the haversian and plexiform components of bovine cortical femoral bone. To this end micro-milling slotting experiments are performed on both the components by varying both the cutting velocity and the feed-per-tooth values. The scale of machining is chosen specifically to ensure sensitivity to the microstructural variations in the bone. The material properties of the microstructural components obtained by nanoindentation along with their size-scale relative to the feed-per- tooth values are seen to dictate the failure mechanisms encountered during machining. The cutting force, surface roughness, and tool wear are all uniquely affected by the plexiform and haversian components of the cortical bone. In general, plexiform bone requires a higher cutting force than the haversian bone. While a higher cutting velocity can lower the surface roughness of haversian bone, it typically results in the most surface damage. The cutting force and surface roughness values for both the components show strain rate sensitivity. The tool wear is seen to be the highest while cutting parallel to the lamellar structures seen in the plexiform bone. Future studies will examine how the microstructural constituents of bone and their material properties change with age and subsequently have an effect on machining responses.
Funder Acknowledgement(s): The authors acknowledge funding support from the United States National Science Foundation CAREER award (CMMI 13- 51275).
Faculty Advisor: Johnson Samuel, firstname.lastname@example.org
Role: I performed all of the research.