We know that carbon nanotubes are about hundred times stronger than steel and several times lighter but it is not known that nanotubes often break without warning, making their production difficult. Rice University news release explains how. Nanotubes break in one of two ways: the bonds either snap in a brittle fashion or they stretch and deform. The breaking mechanism for a particular nanotube depends to a great extent on its intrinsic twist called chirality and temperature which still influences the outcome. By combining detailed quantum mechanical computations of failure nucleation and transition-state barriers with the probabilistic approach of the rate theory the failure phenomenon has been modeled. It is proposed that a competition between two alternative routes of brittle bond breaking and plastic relaxation determine the domains of their dominance.