Improving Energy Dissipation to Lower Concussion Risk in Football Helmets MASC HUSETTS 1NS rKf9 by OFTECHNOLOGY JUN 0 42014 Christine Elizabeth Labaza LIBRARIES Submitted to the Department of Materials Science and Engineering in Partial Fulfillment of the Requirements for the Degree of Bachelor of Science in Materials Science and Engineering at the Massachusetts Institute of Technology June 2014 @ 2014 Massachusetts Institute of Technology. All rights reserved. Signature redacted Signature of Author: Department of MateLals Science and Engineering 2 May 2014 Signature redacted Certified by: Lorna J. Gibson Professor of Materials Science and Engineering Thesis Supervisor Signature redacted Accepted by: V /Yf Jeffrey C. Grossman Chairman of the DMSE Undergraduate Committee 1 2 Improving Energy Dissipation to Lower Concussion Risk in Football Helmets by Christine Elizabeth Labaza Submitted to the Department of Materials Science and Engineering in Partial Fulfillment of the Requirements for the Degree of Bachelor of Science in Materials Science and Engineering Abstract American football is notorious for being a high impact sport. There exists an especially high amount of danger to each player's brain, created in part by gameplay, but also from the helmets worn by the athletes. Football helmet pads were comparatively investigated, in order to find a better alternative that can lower the amount of acceleration on the brain. A new pad system was introduced that allows for the force to be dissipated horizontally, through use of a dashpot-like center, also employing a foam shell to assist in the vertical energy dissipation. The pad currently used, along with the new dashpot system were further tested inside helmet shells on a head form drop test, and compared to the national standards that regulate athletic equipment. Thesis Supervisor: Lorna Gibson Professor of Materials Science and Engineering 3 4 Acknowledgements I would like to thank Christopher di Perna, Mike Tarkanian, Geetha Berera, and Daniel Newman for their constant help with anything that I could ask for. I would also like to thank Scott Stephens, Emily McDonald, and James Balchunas for starting this project and laying the foundation for the ideas within. Furthermore, Joseph Crisco and Ryan Rich provided excellent help and feedback in the testing of the full helmets at Brown University. Lastly, I would like to thank Professor Lorna Gibson for her advice and support. 5 6 Table of Contents 1.Introduction ............................. 11 2. Background ......................... .... 14 2.1 Traumatic Brain Injury in Football ............... 14 2.2 Medical impacts of Traumatic Brain Injuries.....15 2.3 Previous Research................................................. 16 2.4 Overview of Foams and Energy Absorption..... 20 3. Materials and Methods.................................. 21 3 .1 Pad M aterials ....................................................... 2 1 3.1.1 Vacuum Grease Sandwich Structure..... 21 3.1.2 Asics Shoe and Gel Sandwich Structure 22 3 .2 D rop Tow er............................................................ 23 3.2.1 ISN Drop Tow er.........................................26 3 .3 H ead Form ............................................................. 29 3.4 Instron M achine................................................... 32 3.5 D SC M achine........................................................ 33 4. Results................................. .. MEE.......... me..m.m 35 4.1 ISN Drop Tower Results..................................... 35 4.2 MIT Drop Tower Results..................................... 37 4 .3 Instron Testing...................................................... 39 4 .4 D S C D ata............................................................... 40 7 4.5 Brown University Head Form.............................. 41 5. Discussion............................. 4 3 6. Conclusion.............................. 5 0 8 Figure 1: Riddell Revolution Speed helmet with vinyl nitrile pads.................................12 Figure 2: Linear acceleration of im pacts.................................................................................... 16 Figure 3: Linear acceleration of vinyl nitrile. .............................................................................. 17 Figure 4: Linear impacts of sandwich structures. ..................................................................... 18 Figure 5: V iscous fluids choices.................................................................................................. 19 Figure 6: A final comparison of the results for the vinyl nitrile control pad and the vacuum grease filled sandw ich structure pad......................................................................................... 19 Figure 7: The four 'pad' choices - Asics shoe heel, vinyl nitrile, gel sandwich structure, and vacuum grease sandw ich structure ........................................................................................... 22 Figure 8: Unwrapped vacuum grease sandwich structure........................................................ 23 Figure 9: MIT drop tower used for linear impact tests to compare pad choices..................... 25 Figure 10 : ISN D ro p Tow er ............................................................................................................ 27 Figure 11: Drop Tower pushes grease horizontally outward .................................................... 28 Figure 12: Positions of strikes for Head Form testing................................................................ 30 Figure 13: Head Form in action.................................................................................................. 31 Figure 14: Vacuum grease pad helm et. ..................................................................................... 32 Figure 15: M axim um Load At Im pact......................................................................................... 35 Figure 16: M axim um Failure At Im pact .................................................................................... 36 Figure 17: Deflection vs. Energy - Vinyl Nitrile .......................................................................... 37 Figure 18: Deflectin vs. Energy - Vacuum Grease ...................................................................... 37 Figure 19: Force at Im pact - Vinyl Nitrile ................................................................................. 38 Figure 20: Force at Im pact - Asics Shoe .................................................................................... 39 Figure 21: Stress Strain Curve - Asics Foam ............................................................................... 40 Figure 22: Stress Strain Curve - Vinyl Nitrile ............................................................................. 40 Figure 23: Severity Index - Low Drop ......................................................................................... 42 Figure 24: Severity Index - High Drop ........................................................................................ 42 Figure 25: Energy Dissipation directions. .................................................................................. 44 Figure 26: Polydim ethylsiloxane structure ............................................................................... 45 Figure 27: Dim ethyl Siloxane structure ...................................................................................... 46 9 10 1. Introduction Concussions and brain trauma are an extremely dangerous reality of playing football, from the professional level to young children's leagues. Recently, the danger of concussions in players has swept the country, from media reports to lawsuits. Take, for example, Mike Webster, a retired football player. He was found dead, at the early age of 50, and the autopsy showed a brain that had signs of repeated hits to the head. Webster had a history of depression, amnesia, and depression in the years before his death.8 Medical studies have linked concussive injuries to both short and long term health effects. Short term concussive effects are well known, and those in the athletic training field who work with athletes, monitor those cases closely, and do what they can to help the athlete return to play after all symptoms have subsided. In fact, the football helmet manufacturer Riddell has included impact sensors inside some of the helmets used, so that dangerous circumstances can be watched closely, and if necessary, a player removed from them. However, that doesn't do enough for the long-term consequences that can be found after even low intensity impacts, if they are 11 repeated often enough. "Seven years after concussion, participants displayed disrupted higher-order neurocognition in the form of chronically impaired attention, working memory, inhibition, and interference control". 4 As it is not much of an option to remove helmets altogether, simply because of the way football is played, the next step is to look at the helmets themselves and find solutions for bettering their components. A Riddell helmet is the most commonly used helmet, especially in the NFL. These helmets have a set of vinyl nitrile foam pads. Figure 1: Riddell Revolution Speed helmet with vinyl nitrile pads 12 The purpose of this thesis work is to build off the research done by Scott Stephens, Emily McDonald, James Balchunas, and Christine Labaza while working at MIT. Testing more thoroughly a dashpot system pad, and looking at other possible