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Research Papers

Effect of Meso to Micro Transition in Morphology Dependent Fracture of SiC Ceramics

[+] Author and Article Information
Hongsuk Lee

 School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN 47907lee761@purdue.edu

Vikas Tomar

 School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN 47907

J. Eng. Mater. Technol 133(4), 041001 (Oct 13, 2011) (10 pages) doi:10.1115/1.4004686 History: Received March 04, 2011; Revised July 14, 2011; Accepted July 22, 2011; Published October 13, 2011; Online October 13, 2011

Silicon carbide (SiC) is an important ceramic material usually found in polycrystalline form with grain boundary thickness ranging from a few nanometers to a few hundred nanometers and grains with multiple orientations with sizes of the order of few micrometers. The present work focuses on analyzing how the interplay between different orientations of SiC grains and different grain boundary thicknesses can be exploited for targeted improvement in the fracture resistance properties of SiC. Crack propagation simulations using the cohesive finite element method (CFEM) are performed on the finite element meshes developed on experimentally processed SiC morphologies. Analyses were performed at two different length scales: 300 μm × 60 μm (scale-1:Microscale) and 75 μm × 15 μm (scale-2:Mesoscale). Lower resolution microstructure at scale-1 does not explicitly consider the presence of grain boundaries (GBs). Higher resolution microstructure at scale-2 explicitly models GBs. Results indicate that the effect of change in grain orientation is on crack path only. The fracture resistance is not significantly affected. The presence of GBs may directly aid in strengthening a microstructure’s fracture resistance. However, indirectly it may weaken a microstructure by favoring the formation of microcracks. Significantly higher crack formation in grain interior while lower interfacial energy dissipation in comparison to interfaces indicates overall lower fracture strength of grain interiors in comparison to interfaces. If GBs are not accounted for, the second most influencing factor affecting fracture strength is the average grains size. Overall, it is mainly the GBs not the grain orientation distribution and grain size that significantly affects fracture strength.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic showing procedure (a) of obtaining picture from digital silicon carbide micrograph and (b) of digitizing picture to obtain finite element mesh at two different resolutions considered in the present work (300 μm × 60 μm-scale-1 and 75 μm × 15 μm-scale-2)

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Figure 2

Finite element meshes of three different SiC orientation sets: (a) without grain boundary at scale-1 and (b) with grain boundary at scale-2. SiC1 , SiC2 , and SiC3 are the three different orientations specified in Tables  12.

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Figure 3

Irreversible bilinear cohesive law

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Figure 4

Dynamic fracture simulation setup with FEM discretization for carrying out the CFEM simulations

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Figure 5

Total crack length as a function of time and finite element size at (a) scale-1 and at (b) scale-2

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Figure 6

Damage distribution at scale-1 at the loading rate of 0.1 m/s as a function of time in the case of (a) orientation set1 (b) orientation set2 and (c) orientation set3. SiC1 , SiC2 , and SiC3 are the three different orientations specified in Table 1

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Figure 7

Damage distribution at scale-2 at the loading rate of 0.1 m/s as a function of time in the case of (a) orientation set1 (b) orientation set2 and (c) orientation set3. SiC1 , SiC2 , and SiC3 are the three different orientations specified in Table 2

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Figure 8

Cohesive energy average as a function of crack length at (a) scale-1 and at (b) scale-2

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Figure 9

Average crack length and variations as function of time at 0.1 m/s loading rate in the case of microstructures at (a) scale-1 and at (b) scale-2

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Figure 10

Average mean energy release rate and variations as a function of crack length at 0.1 m/s loading rate in the case of microstructures at (a) scale-1 and at (b) scale-2

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Figure 11

Value of parameter m as function of time in the case of (a) scale-1 and in the case of (b) scale-2 simulations

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