▎ 摘　　要

We use molecular dynamics simulations to delineate crack propagation speed as a function of the crack length and the axial prestrain in a single layer graphene sheet. A covalent bond between two carbon atoms is assumed to break when the bond length has been stretched by 100%. For a pristine single layer graphene sheet the maximum axial force is attained at a nominal axial strain of 15.5%. A pristine graphene sheet is first deformed in tension in the armchair direction to the desired value of the axial strain, and then one or two cracks are simultaneously inserted in it at central locations by breaking the bonds. Five such problems have been studied with four different values of the axial prestrain up to 15.3%. For each problem, crack-tip speeds are found to reach steady state values as the crack elongates. The steady state crack speed increases with an increase in the axial nominal prestrain. The crack propagation is found to be stable in the sense that the value of the J-integral increases with an increase in the crack length. For the same normalized crack length the value of the J-integral increases with an increase in the nominal axial prestrain. (C) 2013 Elsevier B. V. All rights reserved.