Journal
CERAMICS INTERNATIONAL
Volume 43, Issue 14, Pages 10726-10736Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ceramint.2017.05.054
Keywords
Single grit scratching; Isotropic brittle materials; Elastic stress field; Micro-crack evolution; Optical glass; Ductile to brittle transition
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Funding
- National Natural Science Foundation of China [51305237]
- Key Laboratory for Precision & Non-traditional Machining of Ministry of Education, Dalian University of Technology [JMTZ201504]
- Key Laboratory of Optical System Advanced Manufacturing Technology [Y4GX1SJ141]
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An analytical model for the elastic stress field in isotropic hard and brittle materials during scratching is presented. The model considers the entire elastic stress field and the effect of material densification that was ignored in past studies, and is developed under a cylindrical coordinate system to make the modeling process simpler. Based on the model's predictions, the location and sequence of crack nucleation are estimated and the associated mechanisms are discussed. A single grit scratching experiment with an increasing scratch depth up to 2 mu m is conducted for two types of optical glasses representing isotropic brittle materials: fused silica and BK7 glasses. It is found that the model's predictions correlate well with experimental data. Median cracks are found to be formed first during scratching, and the corresponding depth of the scratch sets the basis for determining the critical depth for brittle to ductile machining. Lateral cracks are initiated in the plastic yielding region and deflect to the work surface to cause material removal, while Hertzian cracks interact with lateral cracks to help remove lateral-cracked material. Furthermore, it is found that, owing to its open network molecular structure, fused silica has a much worse ductile machinability than the BK7 glass.
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