Crash Physics Simulator: Impacts, Penetration and Car Crashes

Free impact and crash physics simulator: pick what flies (material, shape, size, speed, angle) and what it hits (material, thickness) to see whether it bounces, sticks, shatters or goes through, the exit speed, ballistic limit and thickness needed to stop it. Crash cars into walls or each other, or drop eggs and phones, with g-forces, crush and injury risk.

Pick what flies, how fast, and what it hits. The simulator works out whether it bounces, sticks, shatters or goes through, how deep it gets, how fast it comes out the other side, and how thick the plate would have to be to stop it. Then press Replay to watch it in slow motion.

What hits

Material Shape

Diameter

Length

Mass

Speed

Angle from straight on: °

What it hits

Material

Thickness

Panel width (how far apart its supports are)

Matters for thin sheets: it sets how far the sheet can bend and how much load it can take before it breaks or dents.

Tip: the bar chart below is clickable. Pick another material to hit.

What happens

Exit speed for every impact speed

Below the ballistic limit it stays on this side; above it the exit speed climbs towards the impact speed. Hover to read it.

How thick each material must be to stop it

Same object, same speed and angle. Log scale. Click a bar to hit that material.

The physics of impacts and crashes

Every collision is the same story: something moving has kinetic energy and momentum, and both have to go somewhere in a very short time. Where the energy goes (into crushing metal, cracking glass, heating the projectile, or bouncing back) decides what you see. How quickly the momentum is removed decides the force.

energy, momentum \(\displaystyle E = \tfrac12 m v^2, \qquad p = m v\)

stopping force \(\displaystyle \bar F = \frac{m v^2}{2 s} = \frac{m\,\Delta v}{\Delta t}, \qquad \bar a = \frac{v^2}{2 s}\)

Poncelet penetration \(\displaystyle m\frac{dv}{dt} = -A\left(R + B\rho_t v^2\right) \;\Rightarrow\; P = \frac{m}{2 B \rho_t A}\ln\!\left(1 + \frac{B\rho_t v^2}{R}\right)\)

shear plug \(\displaystyle W_{\text{plug}} \approx \tfrac12\,\tau\,\pi d\,t^2\)

exit speed \(\displaystyle v_r = \frac{m}{m + m_{\text{plug}}}\sqrt{v^2 - v_{\text{bl}}^2}\)

fast impacts \(\displaystyle P \approx L\sqrt{\rho_p/\rho_t}\ \ \text{(Newton)}, \qquad P \approx 0.3\,d\sqrt{\rho_p/\rho_t}\left(\rho_t v^2/Y_t\right)^{1/3}\)

head injury criterion \(\displaystyle \mathrm{HIC} = \max_{t_2-t_1\le 15\,\mathrm{ms}} \left[(t_2-t_1)\left(\frac{1}{t_2-t_1}\int_{t_1}^{t_2} a\,dt\right)^{2.5}\right]\)

Hitting a target: what the simulator does

First contact. The pressure at the nose is the target's resistance to being pushed aside, R, plus the inertia of the material it has to shove out of the way, Bρv² (at low speed the elastic Hertz contact pressure is used instead). If that pressure is less than the projectile can take, the projectile stays whole and pushes in. If not, a ductile one flattens (mushrooms) and a brittle one such as ice, glass or rock shatters. When even the projectile's own inertia, ½ρv², is bigger than the target's strength, both behave almost like fluids and the projectile erodes as it goes, which is how meteorites and space debris make craters.
Through a plate. The projectile pushes in to some depth and then shears out the rest of the plate as a plug (or pushes petals aside, if it is pointed). The simulator finds the first depth at which the remaining energy is enough to finish the job; a thin plate is mostly plug, a thick one mostly penetration. The slowest speed that gets through is the ballistic limit.
Thin sheets. A window breaks by bending, not by being punched: it can only store a little energy before its tensile strength gives way. A small pane breaks at a higher load, a wide one bends further before it goes. A thin metal sheet that is not punched through dents: the energy goes into bending and stretching it.
Very fast impacts. Above about 3 km/s (space debris, micrometeoroids) the crater depth grows with the cube root of the impact pressure over the target strength, and a plate is perforated if it is thinner than about 1.8 times that crater depth. The projectile melts or vaporises and comes out as a cloud of debris, which is why the ISS uses spaced Whipple shields.

Crashes and drops: what the simulator does

Each object is a spring (a car's crumple zone is about 1 MN/m; an egg's shell about 150 kN/m), in series with the surface it hits. Loading follows the spring; unloading is stiffer, so only a fraction e² of the energy comes back (e = restitution). The result is the classic half-sine crash pulse.
Two vehicles are worked out with their reduced mass and closing speed; momentum is conserved, and the lighter one gets the bigger change of speed (Δv). That is why a small car loses to an SUV.
The person inside is a second mass held by a belt and an airbag (springs with damping) or by nothing at all, in which case they fly forward until they hit the dashboard. From their acceleration the page gets the chest 3 ms clip and the head injury criterion, and NHTSA's NCAP risk curves turn those into a rough chance of a severe injury (AIS 4+).

How good are the numbers?

These are textbook engineering models, chosen because they show the right trends and the right orders of magnitude: expect roughly a factor of two against real tests. Real impacts depend on things a simulator like this leaves out: the exact alloy and heat treatment, strain rate, the shape of the nose, layered and laminated materials (a car windshield has plastic between two glass sheets), how the panel is held, and fragments. The crash pulse of a real car is not a perfect half sine, and the occupant model is a single mass, not a crash-test dummy. Use it to learn the physics, not to design or certify anything.

Everything runs on your device and nothing is uploaded. Mechanics of Materials · Tensile Test Simulator · Jump-Start a Car · Orbit Simulator · More MES tools

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