Auxetic 3D-Printed Helmet Liners

ISEF Category: Materials Science

Subcategory: Composite Materials  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

A helmet liner can look the same on the outside and still behave very differently on impact. Some structures squeeze inward when you stretch them, or spread when you press them. That odd behavior can help absorb force in new ways. You can test that with a phone, a printer, and careful video analysis.

What Is It?

Auxetic materials do something most materials do not. When you stretch them, they get wider instead of thinner. When you compress them, they can expand sideways. That strange response comes from the internal structure, not just the plastic itself.

Think of it like a chain of linked shapes that open and close together. A regular foam crushes in one direction. An auxetic foam or lattice can spread stress across more of the structure. That can matter in helmet liners, padding, and other impact-absorbing parts.

In this project, you are not just asking whether a printed liner survives a drop. You are comparing how different internal shapes move, deform, and slow down the impact. Slow-motion phone video lets you turn those motions into numbers.

Why This Is a Good Topic

This is a strong science fair topic because you can change one design feature at a time, then measure a real performance outcome like peak bounce, rebound height, or deformation pattern. It connects to safety gear, sports protection, and lightweight packaging. You can also learn real research skills, like experimental design, video tracking, and comparing groups with statistics.

Research Questions

• How does auxetic lattice geometry affect peak deformation during a drop test?
• What is the effect of PLA to TPU ratio on impact rebound and energy absorption?
• Does layer orientation change the way a printed helmet liner spreads force on impact?
• To what extent does cell size change the acceleration profile recorded in slow-motion video?
• Which auxetic pattern produces the lowest rebound height after the same drop height?
• How does print infill direction affect crack growth or permanent set after repeated impacts?

Basic Materials

• 3D printer with PLA and TPU filament.
• CAD software for designing lattice patterns.
• Smartphone with slow-motion video mode.
• Tripod or stable phone mount.
• Rigid drop-test frame or guided release setup.
• Standardized test mass to simulate an impact load.
• Measuring tape or ruler with clear markings.
• Digital kitchen scale with 0.1 g accuracy.
• Graph paper or printed scale marker for video calibration.
• Safety glasses.

Advanced Materials

• Access to a universal testing machine for compression testing.
• High-speed camera or higher frame-rate phone setup.
• Force sensor or load cell with data logger.
• 3D printer with dual-material or multi-material capability.
• Digital calipers for precise geometry checks.
• ImageJ for frame-by-frame motion analysis.
• Test fixtures for repeated impact alignment.
• Microscope or loupe for crack and surface damage checks.

Software & Tools

• ImageJ: Tracks motion frame by frame and measures deformation, rebound, and displacement from video.
• Tracker: Lets you mark points in slow-motion clips and extract position, velocity, and acceleration data.
• Tinkercad: Helps you sketch simple lattice concepts before moving to more detailed CAD work.
• Fusion 360: Supports parametric design so you can change cell size, angle, and wall thickness in a controlled way.
• Google Sheets: Organizes trial data, calculates averages, and makes graphs for comparing designs.

Experiment Steps

1. Define one impact metric you will compare, such as rebound height, peak compression, or deformation recovery.
2. Choose a single lattice family and change only one geometry variable at a time.
3. Plan a control group with a non-auxetic structure so you can compare performance against a baseline.
4. Design a repeatable drop setup that keeps release height, alignment, and landing surface consistent.
5. Build a video analysis plan before you print, including a calibration scale and the exact frames you will measure.
6. Decide how you will compare trials with averages, variation, and a statistical test that matches your sample size.

Common Pitfalls

• Printing lattices with inconsistent wall thickness, which changes stiffness from sample to sample.
• Using a drop setup that shifts the sample position, which makes impact angles vary across trials.
• Comparing designs with different mass, which can hide the effect of geometry.
• Recording video without a fixed scale in the frame, which makes motion measurements hard to trust.
• Testing one sample too many times without checking damage, which mixes first-impact behavior with fatigue.

What Makes This Competitive

A stronger project will do more than say one design looks better. You can compare multiple auxetic geometries, include a non-auxetic control, and analyze the data with the same metric across all samples. Careful video tracking, repeat trials, and a clear statistic will make your results much more convincing. A design that links structure, motion, and energy absorption will feel much more like real engineering research.

Project Variations

• Test auxetic liners made from all-PLA prints versus PLA-TPU blends to see how material softness changes impact response.
• Compare different auxetic unit cells, such as re-entrant honeycombs, rotating squares, or chiral patterns, under the same drop test.
• Analyze repeated-impact damage instead of single-drop rebound to see which design keeps its shape longer.

Learn More

• PubMed: Search review articles on auxetic materials, impact absorption, and protective padding to find biomedical and materials background.
• NASA Technical Reports Server: Search for open reports on lightweight structures, impact testing, and lattice design.
• NIH 3D Print Exchange: Explore printable lattice and scaffold concepts, then adapt the geometry ideas for a materials project.
• MIT OpenCourseWare: Look for free materials science and mechanics courses that cover stress, strain, and deformation basics.
• Journal of Materials Science: Search the journal for peer-reviewed studies on auxetic polymers, foams, and composite impact performance.