skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Prediction of crack initiation in single-crystal sapphire during ultra-precision machining using MD simulation-based slip/fracture activation model
Title: Prediction of crack initiation in single-crystal sapphire during ultra-precision machining using MD simulation-based slip/fracture activation model
In this paper, material deformation during ultra-precision machining (UPM) on the C-, R-, and A-planes of sapphire was investigated using the slip/fracture activation model where the likelihood of activation of individual plastic deformation and fracture systems on different crystallographic planes was calculated. The stress data obtained from molecular dynamics (MD) simulations were utilized, and the slip/fracture activation model was developed by incorporating the principal stresses in calculating the plastic deformation and fracture cleavage parameters. The analysis methodology was applied to study material deformation along various cutting orientations in sapphire. The stress field at crack initiation during UPM on C-, R-, and A-planes of sapphire was calculated using molecular dynamics (MD) simulations. An equation describing the relationship between crack initiation and its triggering parameters was formulated considering the systems’ plastic deformation and cleavage fractures. The model can qualitatively predict the crack initiations for various cutting orientations. The proposed model was verified through ultra-precision orthogonal plunge cut experiments along the same cutting orientations as in the MD simulations.  more » « less
Award ID(s):
1844821 2009150
PAR ID:
10493922
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
Elsevier
Date Published:
Journal Name:
Precision Engineering
Volume:
86
Issue:
C
ISSN:
0141-6359
Page Range / eLocation ID:
265 to 275
Subject(s) / Keyword(s):
Ductile-to-brittle transition Molecular dynamics Single-crystal sapphire Slip/fracture activation model Ultra-precision machining
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Nanotechnology and Precision Engineering)
    Duan, Xuexin; Fu, Richard; Guan, Weihua; Guan, Yingchun; Sun, Shuhui (Ed.)
    With the growing demand for the fabrication of microminiaturized components, a comprehensive understanding of material removal behavior during ultra-precision cutting has become increasingly significant. Single-crystal sapphire stands out as a promising material for microelectronic components, ultra-precision lenses, and semiconductor structures owing to its exceptional characteristics, such as high hardness, chemical stability, and optical properties. This paper focuses on understanding the mechanism responsible for generating anisotropic crack morphologies along various cutting orientations on four crystal planes (C-, R-, A-, and M-planes) of sapphire during ultra-precision orthogonal cutting. By employing a scanning electric microscope to examine the machined surfaces, the crack morphologies can be categorized into three distinct types on the basis of their distinctive features: layered, sculptured, and lateral. To understand the mechanism determining crack morphology, visualized parameters related to the plastic deformation and cleavage fracture parameters are utilized. These parameters provide insight into both the likelihood and direction of plastic deformation and fracture system activations. Analysis of the results shows that the formation of crack morphology is predominantly influenced by the directionality of crystallographic fracture system activation and by the interplay between fracture and plastic deformation system activations. 
    more » « less
  2. ; ; ; (, Nanotechnology and Precision Engineering)
    In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed. 
    more » « less
  3. ; ; ; ; ; ; (, Computational Materials Science)
    Sinnott, Susan (Ed.)
    Single crystalline sapphire (-) possesses superior mechanical, thermal, chemical, and optical properties over a wide range of temperatures and pressure conditions, allowing it for a broad spectrum of industrial applications. For the past few decades, research has aimed at comprehensive understanding of its plastic deformation mechanisms under mechanical loading. In this study, we have employed molecular dynamics (MD) simulations to study rhombohedral twinning of sapphire, which is of critical importance in understanding the plastic deformation of sapphire as one of most commonly observed deformation modes. Since the critical resolved shear stress (CRSS) plays a pivotal role in describing the activation of slip systems, it is adopted in this study as the key parameter for analysis. The CRSS is calculated during the uniaxial compression test of a cubic sapphire crystal, oriented to exclusively activate rhombohedral twinning deformation, under simulation conditions such as temperature, strain rate, and system size. Furthermore, a theoretical model of CRSS is constructed based on theories of thermal activation processes, then empirically fitted to CRSS data gathered from the MD simulations. This model accurately captures the relationships between CRSS and external parameters including temperature, strain rate, and system size and shows excellent agreements with the simulation results. 
    more » « less
  4. ; (, 19th International Conference on Precision Engineering)
    The Japan Society for Precision Engineering (Ed.)
    Machining is in general conducted in multiple paths and thus residual stress and subsurface damage formed by previous cut may influence subsequent cutting. Ceramics materials are extremely brittle and prone to cracks. Ultra-precision machining with very small depth of cut enables ductile mode cutting. There have been various reports that critical depth of cut (CDC) for single crystal sapphire exists, where the ductile to brittle transition occurs. However, the CDC of subsequent cutting changes due to the influence of residual stress and subsurface damage by previous cut. This study investigates the indirect effect of residual stress and subsurface damage on the critical depth of cut of the second cut by analyzing the plastic deformation mechanisms activated during 2-step machining on A-plane of sapphire. It was found that the [1#100] machining orientation was most suitable since the critical depth of cut remained fairly constant due to dominant rhombohedral twinning activation during subsequent machining operations. 
    more » « less
  5. ; ; (, American Society of Mechanical Engineers)
    Using direct high-speed imaging, we study the transition between different chip formation modes, and the underlying mechanics, in machining of ductile metals. Three distinct chip formation modes — continuous chip, shear-localized chip, and fragmented chip — are effected in a same material system by varying the cutting speed. It is shown using direct observations that shear-localized chip formation is characterized by shear band nucleation at the tool tip and its propagation towards the free surface, which is then followed by plastic slip along the band without fracture. The transition from shear-localized chip to fragmented chip with increasing cutting speed is triggered by crack initiation at the free surface and propagation towards the tool tip. The extent to which crack travels towards the tool determines whether the chip is partially fragmented or fully fragmented (discontinuous). It is shown that shear localization precedes fracture and controls the crack path in fragmented chip formation. Dynamic strain and strain-rate fields underlying the each chip formation mode are quantified through image correlation analysis of high-speed images. Implications for using machining as an experimental tool for fundamental studies of localization and shear fracture in ductile metals are also discussed. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email