The present invention provides methods of strengthening composites. In some embodiments, such methods generally comprise a step of applying a dynamic stress to the composite in order to increase at least one of the stiffness or strength of the composite. In some embodiments, the composite comprises: a polymer matrix; nanomaterial fillers; and an interphase between the polymer matrix and the nanomaterial fillers. In some embodiments, the stiffness or strength of the composite increases permanently in response to the applied stress. In some embodiments, the increase in the stiffness or strength of the composite may be associated with an increase in the storage modulus of the composite, a decrease in the loss modulus of the composite, and a decrease in the loss tangent of the composite. In some embodiments, the applied stress results in a rearrangement of the interphase.