Poster D4 - 3D Printed Auxetic Materials for Concussion Prevention in Youth Football Helmets

Thursday, October 24, 2024

10:00 AM – 11:00 AM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Saiabhinav Devulapalli (he/him/his)

Undergraduate Research Assistant
Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, United States

Co-Author(s)

SA

Stephen Arce

Teaching Faculty III
Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, United States

Primary Investigator(s)

Tristan Driscoll, PhD (he/him/his)

Assistant Professor
Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University
Tallahassee, Florida, United States

Introduction: Concussions are a major concern in youth football, commonly occurring with impacts that cause linear accelerations of 70-120 g and/or rotational accelerations of 5,582 to 9,515 rad/s². Research indicates that concussions occur irrespective of the point of impact [1]. The highest predictive occurrence of concussions has been observed at 96.1 g and 5,582 rad/s² [2]. Protective equipment can reduce the likelihood of a concussion by absorbing energy and reducing these accelerations [2]. Here we developed 3D printed porous materials to test and model their auxetic behavior which can increase impact energy absorption [4].

Materials and

Methods: Multiple 3D printed geometries utilizing various porous structures were developed, focusing on optimizing their mechanical and structural properties for enhanced energy absorption and impact mitigation. As a control, samples of football helmet foam from a youth Riddell Speed Icon youth helmet were tested. The new geometries were printed using Formlabs Flexible 80A Resin (E = 4.0 MPa; ν = 0.13) and the Formlabs 3B+ SLA Resin Printer. The geometries were then subjected to compression tests using a mechanical clamp, which applied controlled, uniform displacement to test the material strain response and Poisson’s ratio. A camera recorded images of fiducial surface markers, capturing displacements during deformation of the foams. For the analysis of these deformation patterns, we employed MATLAB. Custom scripts were developed to process the images and calculate key mechanical parameters. First, image segmentation and tracking of surface markers was used to calculate displacements. These displacements were used to calculate the deformation gradient tensor (F), which was used to calculate the Lagrangian strain tensor (E=1/2(FTF-I), the components of which are the normal strains in X and Y directions and the XY shear strain). From these strains (X & Y Direction), the Poisson's ratio was calculated. Additionally, finite element models (FEM) of the materials were created using Autodesk Fusion which achieved similar Poisson’s Ratios to the MATLAB Analysis. These simulations replicated the experimental conditions and provided insights into the internal stress distribution and deformation mechanisms. Key performance indicators included Poisson’s ratio and the propagation of the deformation across the material.

Results, Conclusions, and Discussions: The Hourglass geometry (Vertical Direction) consistently demonstrated the lowest shear strains and most auxetic Poisson's ratio among all materials tested (Fig. 1), indicating potential for high energy absorption. In the horizontal direction, this material showed a low but positive Poisson’s ratio, likely due to the geometry at the perimeter of the print. The Hexagonal Hourglass (compressed along the Y) demonstrated a low Poisson’s ratio (Fig. 1B-C) indicating that different print perimeter can influence the deformation field and auxetic response. The Cube structure had a positive but low Poisson’s ratio, similar to the Football foam, indicating a comparable energy absorption with a 3D-printed design (Fig. 1B-C). Simulation of compression tests showed a very similar Poisson’s ratio for the hourglass geometry when compressed in the x direction (Figure 2).

These results emphasize the potential efficiency of auxetic materials in reducing concussion risks in youth football. Additionally, this study also suggests that structurally auxetic materials, especially the Hourglass geometry could advance the design of safer sports equipment. The 3D printed design would also allow for integration into commercially available helmets for enhanced protection.

References: [1] Brennan+, Sports Medicine (2017); [2] Clark+, Sports Medicine (2017); [3] Foster+, Sports Materials (2018); [4] Najafi+, Materials Today (2021); [5] Lovell+, Journal of Sports Sciences (2016); [6] Oeur+, Journal of Neurosurgery (2015);

Acknowledgements (Optional):