PSI - Issue 57

Wilmer Velilla-Díaz et al. / Procedia Structural Integrity 57 (2024) 461–468

463

Velilla-D´ıaz & Zambrano / Structural Integrity Procedia 00 (2023) 000–000

3

Grain two

Grain two

GB

GB

Grain one

Grain one

z’ [0 0 1]

x' [1 0 0] z’ [0 0 1] y [0 1 0]

y' [0 1 0]

z [0 0 1]

z [0 0 1]

x [1 0 0]

y [0 1 0]

y [0 1 0]

x [1 0 0]

x [1 0 0]

y

y

z

z

x

x

(b)

(a)

Fig. 1. Atomistic system (a) Tilt GBs angle (b) Twist GBs angle.

Fig. 2. (a) Initial crack dimensions; (b) CTOD estimation.

employ the embedded atom method (EAM) potential proposed by Mendelev et al. Mendelev et al. (2008), which has been widely adopted by researchers investigating defect interactions with free surfaces and grain boundaries Velilla D´ıaz et al. (2021); Horstemeyer et al. (2010); Chandra et al. (2019); Ji et al. (2022). The primary objective of this research is to investigate the influence of grain misorientation on the mechanical behavior of nanocrystalline aluminum. To achieve this, eleven atomistic systems are analyzed. Firstly, a single crystal is subjected to both monotonic and cyclic deformations. Secondly, a bicrystal is examined under monotonic deforma tion, and eight bicrystal systems are considered, consisting of four tilt and four twist angles grain boundaries (GBs) with misorientations of θ = 5°, 10°, 20°, and 30°. The tilt GBs are defined by rotating the second grain along the y = [0 1 0] direction, while the twist GBs involve a rotation along the x = [1 0 0] direction, as illustrated in Figure 1. The dimensions of the atomistic systems are approximately 60 a × 20 a × 40 a , comprising around 200,000 particles. The initial edge crack is located at 20 a from the bottom of the atomistic system, with a height of 2 . 5 a and a length of 10 a , where the Al lattice parameter is a = 0 . 405 nm (See Figure 2). For all systems, the energy minimization of the atomistic structures is performed using the conjugate gradient method, and periodic boundary conditions are applied in the [0 1 0] and [0 0 1] directions. The isobaric-isothermal en semble is employed to equilibrate the systems at a temperature of 300K and a pressure of 1.01 bar for 20,000 timesteps of 0.001 ps, utilizing the Nose-Hoover barostat and thermostat Velilla-D´ıaz et al. (2019). Monotonic deformation is applied to the single crystal and bicrystal aluminum systems following the approach described in Velilla-D´ıaz et al. (2021). To simulate cyclic deformation in the remaining nine systems, the atomistic systems are deformed by ε = 0 . 02 in the [0 0 1] direction for 200,000 timesteps, followed by a deformation of ε = − 0 . 01 for 100,000 timesteps, as de picted in Figure 3. This cyclic deformation process is repeated until fracture occurs at a strain rate of 1 × 10 − 4 / ps.