Fragments velocity distribution and estimating method of thin-walled cylindrical improvised explosive devices with different length-to-diameter ratios

The fragment velocity distribution of the improvised explosive device (IED) that is commonly made of thin-walled casings filled with explosives is an important parameter in the development of protection structures. In this study, the axial fragment velocity distributions of 10 thin-walled cylindrical casings with different L/D ratios filled with charges were measured and analyzed by orthogonal flash X-ray radiography. The results suggest that the axial rarefaction waves significantly affect the fragment velocity distribution at the L/D ratios less than 1.5. A bivariate 3D empirical model for calculating axial fragment velocity distribution was then constructed by fitting the experimental data with the coupled effect of the axial rarefaction waves included. The general applicability of the estimating method was verified with the experimental data of another set of 7 charges. The average relative error between the calculation results and experiment results is only 4.33%, suggesting that the model is reliable for estimating the fragment velocity distributions of the charges with different L/D ratios. Furthermore, the estimating method has also been verified based on numerical simulation. The numerical results show that the estimating method can be used for the casing with C/M of 0.2∼1.9, which means the potential of the estimating method in engineering applications. Our work can provide a practical guide in assessing the hazards of IEDs in the framework of anti-terrorism engineering.