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Research Papers

Understanding Effect of Grain Boundaries in the Fracture Behavior of Polycrystalline Tungsten under Mode-I Loading

[+] 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 134(3), 031010 (May 07, 2012) (9 pages) doi:10.1115/1.4006500 History: Received October 06, 2011; Revised February 24, 2012; Published May 04, 2012; Online May 07, 2012

Abstract

Polycrystalline tungsten is considered as an important material in aerospace, automobile, and energy industries due to its excellent thermal and mechanical properties. While grain boundaries (GBs) are perceived to play a major role in polycrystalline tungsten failure resistance, experimental data are scarce on explicit contribution of GBs to tungsten failure resistance. The present work focuses on understanding the effect of GB property variation on fracture resistance of polycrystalline tungsten. The cohesive finite element method is used for the simulation of crack propagation in polycrystalline tungsten microstructures. The results show a significant effect of GB property variation on change of crack propagation patterns during tungsten fracture. A variation of 10% in GB fracture energy resulted in distinctly different crack patterns with different primary crack propagation direction and the microcrack density. Based on the observed microstructural fracture attributes, a relation between cohesive energy dissipation and microcrack density in polycrystalline tungsten microstructures is proposed.

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Figures

Figure 1

Schematic showing finite element discretization from experimental tungsten microstructures with (a) experimental micrograph of polycrystalline tungsten, (b) extraction of GBs, and (c) completion of finite element discretization process by classifying grain types

Figure 2

Irreversible bilinear cohesive law

Figure 3

Convergence study showing (a) cohesive energy versus time plot and (b) crack length versus time plot as a function of finite element size. Element size of 1.6 μm was chosen.

Figure 4

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

Figure 5

Cohesive energy dissipation plots in the case of (a) high fracture strength GBs, (b) medium fracture strength GBs, and (c) low fracture strength GBs at t = 155 ns (ICOHE is the cohesive energy dissipation per element that was scaled down to have range of 0–1)

Figure 6

Damage plots in the case of (a) high fracture strength GBs, (b) medium fracture strength GBs, and (c) low fracture strength GBs at t = 155 nanosecond (IFAIL is the damage variable in Eq. 8 with range of 0–1)

Figure 7

Plot of cohesive energy as a function of crack length for (a) morphology 1 and (b) morphology 2

Figure 8

(a) Plot of crack length as a function of time for grains and interface where solid line indicates grains and dotted line indicates interface, (b) plot of cohesive energy dissipation as a function of time

Figure 9

Percentages of primary crack and microcracks for different cases of simulation which contain (a) high fracture strength GBs, (b) medium fracture strength GBs, and (c) low fracture strength GBs

Figure 10

Evaluated M values with distributed m values of three cases of study (a) on morphology 1 and (b) morphology 2

Figure 11

Schematic illustration that describes a relation between energy dissipation and crack density

Figure 12

Comparison of the analytical solution with simulation results for (a) morphology 1 and (b) morphology 2

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