Researchers from Rice University and Georgia Tech measured the fracture toughness of imperfect graphene for the first time and found it to be somewhat brittle. It turns out that graphene is really only as strong as its weakest link, and this can make a defected graphene substantially less strong than a perfect graphene.
According to the researchers, graphene follows the century-old Griffith theory that quantifies the useful strength of brittle materials. Imperfections in graphene drastically lessen its strength (which has an upper limit of about 100 gigapascals for a perfect graphene).
In a previous research from Rice University and Tsinghua University, that team discovered (using theoretical calculations) that defects in graphene can cause it to become weak - if they occur at the grain boundaries of graphene sheets. On the other hand, in 2011 it was reported that some defects might actually allow graphene a little flexibility, making it even more resilient to tearing or fracturing.