We present the results of thermal-activation analysis of fracture of uni-directional fiberglass plastics both for constant stresses and stresses increasing in time under the conditions of tension and buckling. We obtain experimental dependencies of the activation volume including into the equation of rate of fracture on temperature and time. We reveal two processes of relaxation that result in increase of durability of fiberglass plastics under buckling. The relationships for the activation energy of fracture and forces reveal distinction of kind between rheological properties of specimens under tension and specimens under buckling.