Explicit Dynamics: Simulating Impact and Crash in SimScale

HIGH-SPEED PHYSICS

Master Explicit Dynamics in SimScale. Professional guide to drop tests, high-speed impacts, and crash simulations using nonlinear material models in the cloud.

Predicting Material Failure under High Strain Rates and Extreme Loading Conditions.

In the world of structural validation, not all loads are created equal. While static FEA handles "slow" forces, Explicit Dynamics is required for events that happen in milliseconds. Whether you are performing a Drop Test for a new smartphone or analyzing a vehicle Crumple Zone, SimScale’s explicit solver provides the computational muscle to handle extreme nonlinearities and material fragmentation.

1. Implicit vs. Explicit: When to Switch?

A frequent technical query is: "Why is my static simulation not converging for an impact?" The answer lies in the solver's mathematical approach. Implicit solvers (Standard FEA) struggle with high-speed contact and mass matrix inversions during sudden events.

The Fundamental Difference:

Implicit: Solves for global equilibrium ($Ku = F$). Best for slow, steady loads. High memory usage.

Explicit: Marches forward in tiny time steps ($Ma + Cv + Ku = F$). Best for impacts, explosions, and high-speed metal forming. Highly scalable in the cloud.

2. Physics of the Drop Test: Material Modeling

In a high-speed collision, materials behave differently than in a lab pull-test. You must account for Strain Rate Sensitivity. In SimScale, this often involves the Johnson-Cook or Plasticity models.

Inertial Effects

In explicit runs, mass and velocity dictate the result. Accurate density and "Point Mass" definitions for internal components (like batteries in a phone) are critical.

Energy Dissipation

Tracking Internal Energy vs. Kinetic Energy is the only way to validate a crash. Total energy must remain constant (Energy Balance).

3. The Courant-Friedrichs-Lewy (CFL) Condition

One of the most searched "unanswered" topics is: "Why is my SimScale explicit run taking forever?". It all comes down to the Stable Time Step. The solver cannot calculate faster than the time it takes for a sound wave to cross the smallest element in your mesh.

Critical Formula: Δt < L / c

Where:
- Δt: Time Step
- L: Smallest element edge length
- c: Speed of sound in the material

⚠️ MESHING TRAP: A single tiny, sliver element in your CAD geometry can force the solver to use a time step of 1e-9 seconds, exponentially increasing your Core Hour consumption. Always use "Geometry Clean-up" to remove tiny edges!

4. Key Metrics for Crashworthiness

When analyzing results in SimScale's post-processor, you should focus on these engineering metrics to meet international standards (like Euro NCAP or MIL-STD):

• Peak Deceleration (G-force) Impact Severity
• Equivalent Plastic Strain (PEEQ) Material Rupture Risk
• Absorbed Energy (Joules) Crumple Zone Efficiency
• Contact Force Evolution Structural Integrity

5. Business ROI: Virtual Prototyping

Physical crash testing is prohibitively expensive—a single vehicle test can cost $50,000 to $100,000. Cloud-native Explicit Dynamics allows startups and SMEs to perform 50 virtual drop tests for a fraction of the cost of one physical prototype. This "Democratization of CAE" is why SimScale is gaining massive traction in Consumer Electronics and Industrial Packaging.

Authored by: Nonlinear Dynamics Specialist
Expert in high-strain rate phenomena and structural impact. Consultant for defense contractors and automotive safety teams. Specialist in Cloud-HPC solver optimization.

Technical References:
• LS-DYNA Theory Manual (Explicit Integration Methods)
• SimScale Validation: Impact of a Steel Sphere on a Rigid Plate
• Johnson, G. R., and Cook, W. H., "A Constitutive Model and Data for Metals Subjected to Large Strains, High Strain Rates and High Temperatures."