Molecular dynamics simulations have been performed to investigate the mechanical properties of hydrogen functionalized graphene for H-coverages spanning the entire range from graphene (H-0) to graphane (H-100). We find that the Young's modulus, tensile strength, and fracture strain of the functionalized graphene deteriorate drastically with increasing H-coverage up to about 30. Beyond this limit the mechanical properties remain insensitive to H-coverage. While the Young's modulus of graphane is smaller than that of graphene by 30, the tensile strength and fracture strain show a much larger drop of about 65. We show that this drastic deterioration in mechanical strength arises both from the conversion of sp2 to sp3 bonding and due to easy-rotation of unsupported sp3 bonds. Our results suggest that the coverage-dependent deterioration of the mechanical properties must be taken into account when analyzing the performance characteristics of nanode-vices fabricated from functionalized graphene sheets.
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