Extreme Physics: Ballistics and Blast Simulation in Ansys LS-DYNA

Professional guide to high-velocity impact and blast simulation using Ansys LS-DYNA and Autodyn. Explore SPH, ALE, and Lagrangian solvers for defense applications.

Analyzing Structural Survivability and Armor Penetration under High-Velocity Impact.

In defense and aerospace engineering, the physics of impact happens at velocities where materials behave like fluids. Ansys LS-DYNA and Autodyn are the premier solvers for capturing these transient, non-linear events. From bird strikes on turbine blades to kinetic energy penetrators, understanding Shock Wave Propagation is the key to survivability.

1. Solver Selection: Lagrangian vs. SPH vs. ALE

A frequent unanswered question is: "When should I use SPH instead of a standard mesh?" In high-velocity impacts where material fragmentation occurs, traditional meshes suffer from Element Distortion, leading to solver termination.

Lagrangian

Best for solid structures with moderate deformation. High accuracy for stress wave propagation.

SPH (Smooth Particle Hydrodynamics)

Meshless method. Ideal for fluids, brittle fragmentation, and high-velocity debris.

ALE (Arbitrary Lagrangian-Eulerian)

The gold standard for blast simulations where air-structure interaction is critical.

2. Material Laws: The Johnson-Cook Model

Standard elastic-plastic models fail at ballistic speeds. You must account for Strain-Rate Hardening and Thermal Softening. The Johnson-Cook Failure Criterion is essential here, as it predicts when an element should be "deleted" from the simulation to represent a crack or penetration.

Technical Warning: Explicit simulations are sensitive to "Mass Scaling." While it speeds up the solver, excessive mass scaling can artificially increase the kinetic energy, leading to invalid penetration results. Always monitor the Global Energy Balance.

3. Blast Analysis: FSI and Detonation

Using the Jones-Wilkins-Lee (JWL) equation of state, Autodyn can simulate the chemical energy release of high explosives. Coupling this with structural FEA allow engineers to design blast-resistant vehicles (MRAPs) by optimizing the hull's V-shape to deflect shock fronts.