Back to Search
Start Over
Multiresolution atomistic simulations of dynamic fracture in nanostructured ceramics and glasses.
- Source :
- International Journal of Fracture; May2003, Vol. 121 Issue 1/2, p71-79, 9p
- Publication Year :
- 2003
-
Abstract
- Multimillion atom molecular-dynamics (MD) simulations are performed to investigate dynamic fracture in glasses and nanostructured ceramics. Using multiresolution algorithms, simulations are carried out for up to 70 ps on massively parallel computers. MD results in amorphous silica (a-SiO<subscript>2</subscript>) reveal the formation of nanoscale cavities ahead of the crack tip. With an increase in applied strain, these cavities grow and coalesce and their coalescence with the advancing crack causes fracture in the system. Recent AFM studies of glasses confirm this behavior. The MD value for the critical stress intensity factor of a-SiO<subscript>2</subscript> is in good agreement with experiments. Molecular dynamics simulations are also performed for nanostructured silicon nitride (n-Si<subscript>3</subscript>N<subscript>4</subscript>). Structural correlations in n-Si<subscript>3</subscript>N<subscript>4</subscript> reveal that interfacial regions between nanoparticles are amorphous. Under an external strain, nanoscale cavities nucleate and grow in interfacial regions while the crack meanders through these regions. The fracture toughness of n-Si<subscript>3</subscript>N<subscript>4</subscript> is found to be six times larger than that of crystalline α-Si<subscript>3</subscript>N<subscript>4</subscript>. We also investigate the morphology of fracture surfaces. MD results reveal that fracture surfaces of n-Si<subscript>3</subscript>N<subscript>4</subscript> are characterized by roughness exponents 0.58 below and 0.84 above a certain crossover length, which is of the order of the size of Si<subscript>3</subscript>N<subscript>4</subscript> nanoparticles. Experiments on a variety of materials reveal this behavior. The final set of simulations deals with the interaction of water with a crack in strained silicon. These simulations couple MD with a quantum-mechanical (QM) method based on the density functional theory (DFT) so that chemical processes are included. For stress intensity factor K=0.4 MPa m<superscript>1/2</superscript>, we find that a decomposed water molecule becomes attached to dangling bonds at the crack or forms a Si-O-Si structure. At K=0.5 MPa m<superscript>1/2</superscript>, water molecules decompose to oxidize Si or break Si-Si bonds. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 03769429
- Volume :
- 121
- Issue :
- 1/2
- Database :
- Complementary Index
- Journal :
- International Journal of Fracture
- Publication Type :
- Academic Journal
- Accession number :
- 16866907
- Full Text :
- https://doi.org/10.1023/A:1026216101073