Helmet Foam Drop Tower with Auxetic Lattices Science Fair

ISEF Category: Biomedical Engineering

Subcategory: Biomechanics  ·  Difficulty: Advanced  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

Helmet liners haven't changed much since the 1980s. New options include cornstarch goo, sorbothane scraps, and 3D-printed auxetic lattices that pull inward when squeezed. A PVC drop tower with a $5 accelerometer can put each one through real impacts. Free FEA software predicts how the protected brain would deform.

What Is It?

A drop tower is a vertical guide that releases a weight onto a sample. The peak acceleration measured at the weight tells you how much the sample absorbed.

Cornstarch oobleck is a non-Newtonian fluid that stiffens under fast loads. Sorbothane is a viscoelastic polymer that dissipates energy as heat. Auxetic lattices use a geometry that pulls inward when compressed, distributing load over more area.

CalculiX is free FEA software. The Holbourn rotational model treats the brain as a spinning mass inside the skull. By feeding measured drop-tower kinematics into a surrogate FEA model, you predict brain strain without imaging an actual head.

Why This Is a Good Topic

Helmet design connects materials science, mechanics, and simulation. The drop tower is buildable for under a hundred dollars and the FEA is free. You will learn impact testing, viscoelastic materials, and surrogate-model interpretation.

Research Questions

• How does drop height change peak acceleration across liners?
• What is the effect of auxetic cell size on energy absorption?
• Does oobleck outperform foam at high impact velocity?
• To what extent does layer stacking change attenuation?
• Which liner predicts lowest brain strain in the FEA surrogate?
• How does temperature affect sorbothane performance?
• What is the effect of repeated impacts on liner degradation?

Basic Materials

• PVC pipe and joints for drop tower.
• Standard weight (steel puck or similar).
• ADXL345 or MPU-6050 accelerometer.
• Microcontroller (ESP32 or Arduino).
• Cornstarch and water for oobleck.
• Sorbothane sample sheet.
• 3D-printed auxetic lattice samples.
• Safety eyewear and shielding.

Advanced Materials

• Calibrated load cell at drop base.
• High-speed camera.
• Industry-standard impact test rig.
• Calibrated brain-injury surrogate head form.

Software & Tools

• CalculiX: Runs the FEA surrogate brain-strain model.
• Python (NumPy): Processes accelerometer time series.
• OpenSCAD: Designs auxetic lattices.
• Cura: Slices 3D-printed liners.

Experiment Steps

1. Build and calibrate the drop tower against a known free fall.
2. Print a single liner geometry so only material varies.
3. Decide drop heights, replicate counts, and the order of conditions.
4. Plan controls (no liner, rigid block) that bracket performance.
5. Run drops in randomized order and log every trial.
6. Compare measured kinematics to predicted brain strain in CalculiX.

Common Pitfalls

• Using an accelerometer that saturates at the highest drop.
• Reusing oobleck across drops, which dehydrates the mix.
• Running too few replicates and missing high variance.
• Skipping calibration of drop height between sessions.
• Treating raw acceleration as injury risk without a strain surrogate.

What Makes This Competitive

Calibrate the accelerometer against a known free-fall reference. Run multiple drop heights, replicate each at least five times, and use a standard liner geometry across foams. Compare your predicted brain strain to published thresholds and use ANOVA across designs.

Project Variations

• Replace 3D-printed auxetic lattices with origami patterns and compare.
• Add a temperature sweep on sorbothane.
• Test multiple ball-shape impactors to vary contact area.

Learn More

• CalculiX documentation: Free FEA tutorials.
• PubMed: Search auxetic helmet liner review.
• NIH PubMed Central: Open-access head-injury biomechanics papers.
• NIST Material Measurement Lab: Impact-test references.
• MIT OpenCourseWare: Course 3.054 Cellular Solids.