Dependence of stress intensity factor (SIF) on crack velocity (KK_! - aa dependence) in Homalite-100 specimens subjected to pulse loading was numerically studied. The numerical scheme is based on finite element method and incubation time fracture criterion. Experimental results from works by Ravi-Chandar and Knauss (1984a,b,c) were used. Experimentally obtained KK_! - aa dependence is characterized by considerable scatter of the SIF values. Application of the incubation time based approach made it possible to qualitatively describe scattering of the SIF values since the used fracture condition does not rely neither on critical SIF value, nor on a a priori given KK_! - aa dependence.