Explicit Dynamics Hail Impact Simulation of an Aircraft Radome

An aircraft radome has to shield the radar inside it and stay transparent to radar signals at the same time, so its wall is thin and light. Hail is one of the harshest loads it meets in flight.

The client wanted to know how its composite sandwich radome would cope with repeated hail strikes at flight speed, and at what point damage would start. Shirsh Technosolutions simulated the impact sequence using explicit dynamics in ANSYS.

We used explicit dynamics, which takes very small time steps and is suited to short, violent events with contact, large deformation and material failure. The hailstone was modelled with particle hydrodynamics so that it breaks up and spreads on impact the way real ice does.

The skins were given orthotropic properties with progressive failure, so damage along the fibres and across them is tracked separately. The core was given a crushable foam model with a compressive stress-strain curve, so it can collapse locally and absorb energy. The layers were assumed perfectly bonded, and the panel was held at its real mounting points so it could flex locally.

Each strike was solved as its own transient event in sequence. After every impact we checked ply stresses along and across the fibres against the failure criteria, building a picture of how the damage grew from one hit to the next.

Common questions

Why model hail as particles instead of a solid sphere? At flight speed, ice shatters and spreads almost like a fluid. A solid sphere stays in one piece and puts an unrealistically concentrated load on the skin. A particle model lets the hailstone break up and spread the load the way real hail does.

Why use explicit dynamics for an impact? An impact is over in a very short time, with stress waves travelling through the layers. Explicit solvers march through it in very small time steps and cope well with contact and failing material, where an implicit solution would struggle.