Atomistic investigation of crack growth resistance in a single-crystal Al-nanoplate
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The fracture behavior of a single-crystal Al-nanoplate with an edge crack under tensile loading was simulated using a molecular statics technique to evaluate crack growth resistance in Al. The crack length was determined using a stiffness method. A parabolic function fitted from simulation results was used to predict the crack length from the stiffness value extracted from unloading curves. Based on energy considerations, crack growth resistance was calculated. Crack growth resistance rose sharply in the initial stages of crack growth, and with an additional crack extension, it increased gradually to converge to a constant far exceeding the fracture toughness predicted by the Griffith criterion. This trend in the crack growth resistance curve was closely related to the amorphous zone formed at the crack tip after the onset of crack propagation.
I. INTRODUCTION
Nanomaterials are attracting increasing interest among worldwide research groups and various industries, due to their extraordinary thermal, electrical, magnetic, mechanical, and optical properties, which are different from their bulk counterparts.1–5 Over the past several decades, we have witnessed their broad application in nanodevices such as nanosensors, nanoresonators, nanoactuators, nanooscillators, and nanogenerators.6–10 Cracks may nucleate in nanomaterials during the fabrication of nanodevices. Moreover, mechanical or thermal loadings applied to nanodevices may induce crack nucleation in nanomaterials. Once nucleated, cracks may arrest or propagate in a solid material, depending on the loading condition as well as on the crack growth resistance (R), which represents the material’s resistance to crack growth. Hence, for maintaining the reliability of nanodevices, a comprehensive knowledge of the R-curve of nanomaterials is essential. Many techniques are used in experiment to evaluate the R-curve of engineering materials, including compact tension, single-edged-notched tension, and three-point bending. However, it is a very challenging task to carry out such experiments on nanomaterials because of their extremely small size. In addition, R is calculated by equations derived on the base of continuum mechanics, which assumes that materials are continuous. This theory is valid on the macroscopic scale. However, when material size comes to nanoscale, its validity is debatable because of the significant role of lattice discreteness. Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.155 J. Mater. Res., Vol. 31, No. 9, May 14, 2016
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Atomistic simulation is a useful method for investigating mechanical responses of materials. Many breakthrough observations have been made using this technique.11,12 In particular, atomistic simulations can capture the discreteness of nanomaterials and the essential process of bond rupturing associated with a crack extension. Consequently, they have been broadly utilized in the examination of fractu
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