Clemson University TigerPrints All Theses Theses 5-2010 Characterization and Modification of Helmet Padding System to Improve Shockwave Dissipation Katelyn Howay Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_theses Part of the Materials Science and Engineering Commons Recommended Citation Howay, Katelyn, "Characterization and Modification of Helmet Padding System to Improve Shockwave Dissipation" (2010). All Theses. 849. https://tigerprints.clemson.edu/all_theses/849 This Thesis is brought to you for free and open access by the Theses at TigerPrints. It has been accepted for inclusion in All Theses by an authorized administrator of TigerPrints. For more information, please contact [email protected]. CHARACTERIZATION AND MODIFICATION OF HELMET PADDING SYSTEM TO IMPROVE SHOCKWAVE DISSIPATION A Thesis Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements of the Degree Master of Science Polymer and Fiber Science by Katelyn Breanne Howay May 2010 Accepted by: Dr. Philip Brown, Committee Chair Dr. Vincent Blouin Dr. Christine Cole ABSTRACT Currently soldiers are being exposed a much higher number of improvised explosive devices (IEDs) and the resulting shockwaves. These shockwaves can cause traumatic brain injuries (TBIs) even without the occurrence of ballistic impact. The focus of this research was to reduce the amount of shockwaves soldiers are exposed to by inserting fibers and woven fabrics into a foam padding system. These fibers and fabrics facilitate the dissipation of the shockwave energy before it is able to penetrate the padding and cause TBIs. The sound velocity of high-performance fibers, commodity fibers and woven fabric was measured using a Dynamic Modulus Tester. There was a significant difference between the sound velocities of the high-performance and commodity fibers. The instrument was also used to investigate the effect of crimping, denier, twist and multiple fiber system on the sound velocity. Tensile testing was conducted to find mechanical properties and predict the sound velocity theoretically. The comparison of the theoretical and experimental sound velocities showed small error. The acoustic impedance of the fibers was also calculated. The sound velocity of various viscoelastic foams was also measured which showed certain foams would be more appropriate for the application at hand. Tensile testing of reticulated foam was performed to find the Poisson’s ratio of the foams to predict their behavior. The energy absorption of various foams (viscoelastic and ii reticulated) was observed by using an Indentation/Rebound Drop Test and damping information. Optical images were obtained to visually evaluate the various foams. Thermal and infrared spectroscopy analysis was done to help characterize the foams. Two tests were developed to investigate the energy absorption properties of fiber/foam composite padding systems. Various samples of foam with layers of woven Kevlar® fabric were evaluated using a Helmet Drop Test and Rebound Drop Test. In these tests rebound heights were related to the energy absorption of the samples. Using this method differentiation between the energy absorption of foams was seen and the behavior of viscoelastic and reticulated foams were observed. The effect of ball size and shape was also observed. iii DEDICATION This work is dedicated to the unwavering support from my parents throughout the years. To my mom who has always believed in me and my dad who has never failed to be there when I need him. Also, to my friends for encouraging me in both my professional and personal life. Your constant presence in my life has proven the great things that can be achieved when surrounded by wonderful people. The experiences we’ve had together have helped shape me and I think the world of all of you. iv ACKNOWLEDGEMENTS I would like to thank Dr. Christine Cole for her help and guidance throughout the duration of this project. Her knowledge of various topics has inspired me to push the envelope of my own comprehension. I would also like to thank Dr. Philip J. Brown and Dr. Vincent Blouin for being a part of my research experience at Clemson. I would like to give special thanks to Bob Bennett for his help creating prototypes and testing methods and a fresh perspective of the research task. Also thanks to Jeff Moreland for his help with dynamic modulus testing and Ansell Healthcare for allowing me to use their instrument. I appreciate the help of Robbie Nicholson for teaching me how to do various types of tensile testing and Kimberly Ivey for help conducting thermal and infrared analysis. I am also grateful to Dr. Gary Lickfield for being available and willing to help with any questions I have had. I also thank Oregon Aero, Inc and SKYDEX® Technologies, Inc for providing us with samples of their respective padding systems. Thanks to FoamPartner –Swisstex Inc for allowing us to tour your facilities and supply foam samples and to Innegrity, LLC for providing me with fiber samples. I would especially like to thank the Brown research group for being a constant help and creating a great environment: Dr. Kate Stevens, Joel Barden, Julien Boyon, v Jessica Domino, Brett Ellerbrock, Lisa Fuller, Kyle Gipson, Stephen Hipp, Cody Reynolds, and Liz Skomra. Clemson would not have been the same without you all. I would finally like to thank the Army Research Laboratory for funding this project. vi TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii DEDICATION .............................................................................................................................. iv ACKNOWLEDGEMENTS .......................................................................................................... v LIST OF TABLES .......................................................................................................................... x LIST OF FIGURES ..................................................................................................................... xiii LIST OF EQUATIONS ............................................................................................................. xvii INTRODUCTION ......................................................................................................................... 1 1.1 - Significance of the Research Problem ............................................................................ 1 1.2 - Description of Improvised Explosive Devices and Shockwaves ............................... 3 1.2.1 - Improvised Explosive Devices (IEDs) .................................................................... 3 1.2.2 - Shockwaves Caused by Improvised Explosive Devices ...................................... 6 1.3 - Traumatic Brain Injuries .................................................................................................. 7 1.3.1 - Description of TBI ..................................................................................................... 8 1.3.2 - Proposed Mechanism of TBI .................................................................................... 9 1.3.3 - Diagnosis, Symptoms and Treatment .................................................................. 11 1.4 - Helmet and Padding System Description................................................................... 12 1.4.1 - Brief History of Helmet Models ............................................................................ 12 1.4.2 - Structural and Performance Specifications for Padding Suspension Systems 15 1.4.3 - Helmet Padding Systems Currently on the Market ........................................... 17 1.5 - Fiber-Reinforced Composites ....................................................................................... 26 1.5.1 - Characteristics that Affect the Relevant Properties of Composites .................. 28 1.5.2 - Energy Absorption of Fiber-Reinforced Composites ......................................... 29 1.5.3 - Examples of Uses of Fiber-Reinforced Composites for Energy Absorption ... 31 EXPERIMENTAL PROCEDURE .............................................................................................. 32 2.1 - Tensile Testing of Materials .......................................................................................... 32 2.1.1 - Tensile Testing of Foams for Poisson’s Ratio ...................................................... 32 2.1.2 - Tensile Testing of Fibers ......................................................................................... 33 2.2 - Indentation/Rebound Drop Test .................................................................................. 34 vii 2.3 - Helmet Drop Test ........................................................................................................... 37 2.4 - Dynamic Modulus Testing ........................................................................................... 39 2.4.1 - Dynamic Modulus Testing of Fibers .................................................................... 39 2.4.2 - Dynamic Modulus Testing of Foams ................................................................... 41 2.4.3 - Dynamic Modulus Testing of Woven Fabrics ..................................................... 42 2.4.4 - Dynamic Modulus Testing of Fiber/Foam Composite ....................................... 43 2.5 - Optical Microscopy .......................................................................................................