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Introducing a Numerical Method for Estimating Median Crack Depth during Machining on Optical Glasses

Asqari, Mohammad Amin | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52026 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Akbari, Javad
  7. Abstract:
  8. In present research, a cohesive based finite element model has been introduced to estimate median crack depth during mechanical machining on optical glasses. Development of the machining numerical model has been initiated by investigating the indentation process. Experimental results of this step have been calibrated primary numerical model which has been used in the scratch process. Due to differences between the scratch mechanism and indentation one, mathematical bases fracture formulas and cohesive relations have been developed. After extracting primary result, using them in the scratch model and developing the primary model, ultimately numerical model has been evolved to an abstract numerical model which demonstrated the cutting process in mechanical machining. The abstract machining model has been structured around scratch final parameters. To research validity expansion, the research empirical test has been conducted on eight types of optical glasses: BK7, Pyrex, SF6, Quartz, SF19, Fused Silica, F2 and Q5. The scratch experimental results illustrated that the model output accuracy is 99 percent for glasses with brittle toughness between 600 kPa.m1/2 to 900 kPa.m1/2 such as BK7, F6, and Pyrex. As a result, these three types of glasses have been selected as targeted materials for the machining process. The machining model results proved that the cohesive model estimates the median depth with 98 percent accuracy for selected materials. Moreover, the model results demonstrated the linear relation between median crack depth and lateral crack length in the machining process. Current findings have been compared with other studies to solidify deductions. According to research outputs, the cohesive numerical model is accurate to devise a reliable estimation method for median crack depth
  9. Keywords:
  10. Numerical Model ; Brittle Machining ; BK7 Optical Glass ; Indentation ; Scratch ; Cohesive Zone Model

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