Numerical investigation of fragmentation initiation threshold for sphere impacting on thin wall at hypervelocity

The sphere impacting on the thin wall is simulated with node-separation finite element method, and investigations of the projectile fragmentation initiation threshold are processed based on the numerical results. The bumper-thickness-to-projectile-diameter ratio (t/D) is found to be the main determinant of the velocity threshold. The simulation cases contain the t/D ranging from 0.008 to 0.424 and impact velocity ranging from 2 km/s to 7 km/s. The numerical results are in good agreement with the tests in sphere fragmentation initiation threshold, inner spall of the sphere, debris cloud pattern. The simulations reproduce the fragmentation initiation threshold curve that is obtained by the tests. That shows the feasibility of node-separation finite element method for hypervelocity impact simulation. The shock wave analyses show that the propagation/reflection process of shock wave in the thin wall cases is very different from that in thick wall cases. That inherently results in the different variations of the threshold in the low and high intervals of t/D. The extreme thin plate case shows that when t/D is further reduced, a thick layer of debris cloud would form at the rear of the plate. Compared to the projectile residual, the debris cloud from the plate would induce wider destruction in the inner structure.