PSI - Issue 57

Wilmer Velilla-Díaz et al. / Procedia Structural Integrity 57 (2024) 461–468 Velilla-D´ıaz & Zambrano / Structural Integrity Procedia 00 (2023) 000–000

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as a significant factor that influences various nanoscale phenomena, such as crack propagation, mechanical property enhancement, surface integrity improvement, and enhanced electrical properties Velilla-D´ıaz et al. (2019); Chandra et al. (2017); Zhang et al. (2016); Shu et al. (2017); Wang et al. (2016); Chatterjee et al. (2017); Velilla-D´ıaz and Zam brano (2021); Ovid (2007); Jeong et al. (2018); Kaliyaperumal et al. (2020); Berman and Krim (2013); Tritremmel et al. (2017). Several simulation methods have been developed to accurately represent atomistic systems with mini mal uncertainty in the results Hahn and Meyers (2015); Haouala et al. (2018). However, molecular dynamics (MD) simulations are the most used for investigating the fracture behavior and deformation mechanisms of nanocrystalline materials at the nanoscale Hahn and Meyers (2015); Horstemeyer et al. (2010). To determine the primary deformation mechanism in crystalline materials, researchers have explored the influence of GB morphology Hahn and Meyers (2015). For instance, Sato et al. investigated the cutting mechanism of single crystal aluminum and its relationship with crystal orientation, slip systems, specific cutting force, and cutting direction SATO et al. (1981, 1983). Through MD simulations, White demonstrated that the accumulation of dislocations at the crack tip reduces crack propagation White (2012). Pal et al. studied the e ff ect of amorphous intergranular films (AIF) and their thickness in nanocrystalline copper using MD simulations Pal et al. (2019). They observed resistance to crack propagation due to crack tip blunting with increasing AIF thickness, and the presence of twins / stacking faults as the AIF thickness decreased. Li and Jiang proposed that nanocrack nucleation occurs at triple junctions to release strain energy, as evidenced by the configuration of GBs in their study Li and Jiang (2019). Consequently, grain boundary motion and void nucleation could lead to nanocrack nucleation at specific GB angles. Usually, extensive studies are conducted on the fracture behavior of nanocrystalline materials at the nanoscale under monotonic deformation to estimate fracture mechanics parameters Velilla-D´ıaz et al. (2021); Ding et al. (2020); Liu et al. (2019); Skogsrud and Thaulow (2015), the same parameters are typically determined at the macroscale through tests under increasing cyclic loading ASTM International (2017). Therefore, this research employs MD simulations of nanocracked crystals under cyclic loading to investigate the mechanical behavior of bicrystalline Al with di ff erent misorientations, computing the crack tip opening displacement (CTOD) to assess crack propagation, as previously done in studies by Horstemeyer et al. (2010); Skogsrud and Thaulow (2017); Velilla-D´ıaz et al. (2021). Initial findings reveal that Al crystals without GBs exhibit similar mechanical behavior under both monotonic and cyclic loading. In contrast, Al crystals with GBs exhibit di ff erent deformation mechanisms that significantly a ff ect the mechanical response. Specifically, low-angle GBs reach the maximum stress after the first tearing, while high-angle GBs reach maximum stress at the first tearing. Consequently, it is now feasible to fabricate materials with improved properties based on a comprehensive understanding of the role of misoriented GBs. Therefore, the present study focuses on the e ff ect of misoriented GBs on the deformation mechanisms and fracture behavior of nanocrystalline Al. Specifically, the study considers twist and tilt GBs, as well as cyclic loading under deformation control. The objective is to elucidate the deformation mechanisms and fracture behavior associated with each misoriented GB in the nanocrystalline Al system. To achieve this, MD simulations are conducted on bicrystals withdi ff erent high and low tilt and twist GBs, all containing an initial edge nanocrack. The remainder of this paper is structured as follows: Section 2 provides an overview of the modeling considerations employed in the MD simulations. It discusses the selection of the MD simulation code, LAMMPS Plimpton (1995), and the embedded atom method (EAM) potential of Mendelev et al. Mendelev et al. (2008). Section 3 presents the re sults of the MD simulations, including the analysis of the di ff erent atomistic systems with various misorientations and the examination of the deformation mechanisms and fracture behavior. Section 4 o ff ers a comprehensive discussion of the findings, compares them with previous studies, and provides insights into the underlying mechanisms. Finally, Section 5 summarizes the main conclusions drawn from the study and outlines future research directions in this field.

2. Materials and Methods

2.1. Molecular Modeling

In recent years, numerous methods have been developed to e ff ectively model the mechanical behavior of nanoma terials. Among these methods, molecular dynamics (MD) simulations have emerged as a powerful tool for studying deformation mechanisms and fracture behavior. In this study, MD simulations are conducted using the open-source code Large-scale Atomic Molecular Massively Parallel Simulator (LAMMPS) Plimpton (1995). The MD simulations