Surface Contact Features, Impact Obliquity, and Preimpact Rotational Motion in Concussive Helmet-to-Ground Impacts: Asse
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Annals of Biomedical Engineering (Ó 2020) https://doi.org/10.1007/s10439-020-02621-x
Concussion Biomechanics in Football
Surface Contact Features, Impact Obliquity, and Preimpact Rotational Motion in Concussive Helmet-to-Ground Impacts: Assessment via a New Impact Test Device RICHARD KENT,1,2 JASON FORMAN,2 ANN BAILEY,1 JOSEPH CORMIER,1 GWANSIK PARK,1 JEFF CRANDALL,1 KRISTY B. ARBOGAST,3 and BARRY MYERS4 1
Biomechanics Consulting and Research, Charlottesville, VA, USA; 2Center for Applied Biomechanics, University of Virginia, Charlottesville, VA, USA; 3Children’s Hospital of Philadelphia, Philadelphia, PA, USA; and 4Duke University, Durham, NC, USA (Received 21 August 2020; accepted 12 September 2020) Associate Editor Dan Elson oversaw the review of this article.
Abstract—This paper reports the development of a test device for replicating unique features of concussion-causing helmet-to-ground impacts. Helmet-to-ground impacts are characterized by an oblique impact velocity vector, preimpact rotational motion of the helmeted head, and an impact into a compliant frictional surface of unknown effective mass. No helmet assessment testing program replicates these impact characteristics, yet they influence brain injury risk and therefore may influence helmet design priorities. To replicate these mechanics, the carriage of a drop tower was modified by the addition of a curvilinear bearing track and a hinged torso-neck fixture to which a helmeted head of a Hybrid III anthropomorphic test device was mounted. Preimpact rotational motion of the head was imparted by forcing a link arm to follow the curvilinear path as the carriage fell under gravity. At impact, the rotating helmeted head struck a vertically mounted surface. The ground impact features of head kinematics are illustrated by comparing rear impacts into a rigid, low-friction surface against those into a compliant frictional surface simulating turf. With the rigid, low-friction surface, the head experienced a change in rotational rate of approximately 40 rad/s, which corresponded to a peak rotational acceleration of approximately ay = 2 4000 rad/s2. In contrast, peak rotational acceleration with the compliant frictional surface was approximately ay = 2 1000 rad/s2 while the helmet was in contact with the surface. Neck loads were significantly greater with the compliant frictional surface. Translational head acceleration was less sensitive to the surface characteristics, with the peak of the anterior-posterior component essentially unchanged.
Keywords—Concussion, American Ground impact, Test devices.
Helmets,
INTRODUCTION Current methods for assessing the impact performance of American football helmets include linear impactor tests and drop tests performed over a range of velocities at different locations with different impactor stiffnesses, shapes, effective masses, and eccentricity of the closing velocity vector relative to the head’s center of gravity.3,9,18,21,22,28 While some characteristics of helmet-to-ground impacts have informed the historical development of t
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