title: The Design, Build, And Validation Of A Hybrid Tower Used To Conduct Helmet Impact Tests
Creators: name: Benn, Darren
Publisher: name: University of Nevada, Las Vegas
Year: 2015

description: The National Operating Committee on Standards for Athletic Equipment (NOCSAE) was established to enlist research directed towards the reduction of head injuries in organized sports. The function of the test methods developed by NOCSAE is to provide the blueprint for reliable and repeatable procedures to measure the evaluation of various types of protective sports headgear and projectiles. In addition, the methods also govern hardware such as testing apparatus and data acquisition instrumentation. In helmet testing, the method dictates whether the impact is induced by a projectile system or by a drop tower system with an anvil at the base. Altogether, the methods and procedures are used to determine a pass/fail for a Severity Index (SI) within specified tolerances. The SI is a measure of the severity of impact with respect to the instantaneous acceleration experienced by the headform (fitted with helmet) as it is impacted, and is defined as: SI=∫_0^T▒〖a(t)〗^2.5 dt  (Refer to PDF file for exact formulas.) where ‘a(t)' is the instantaneous acceleration expressed in g's. Also, NOCSAE standards for (drop) impact testing require the impact velocities to be measured during the last 1.5 in. (40mm) of free fall.
Although the NOCSAE standard uses the SI as a performance characteristic, the standard does not provide a means to measure the force of the impact to the headform (fitted with helmet) either by the helmet impacting an object or by the helmet being impacted by an object. Therefore, this analysis seeks to incorporate the measurement of the force of the impact as a viable test parameter without deviating from the protocols established by NOCSAE.
The objective of this research was to design, build, and validate a test structure for testing and measuring the effectiveness of baseball helmets in reducing shock to the head. Further, the design incorporated two test methods into one structure. The three primary components of the test structure were the Pendulum, the Pedestal, and the Linear Bearing Table (LBT). The design of the test structure and the test methods were guided by the following NOCSAE standards:
ND-001:‘Standard Test Method and Equipment Used in Evaluating the Performance Characteristics of Protective Headgear/Equipment'.
ND-021: ‘Standard Projectile Impact Testing Method and Equipment Used in Evaluating the Performance Characteristics of Protective Headgear, Faceguards or Projectiles'.
ND-022: ‘Standard Performance Specification for Newly Manufactured Baseball/Softball Batter's Helmets'.
ND-023:‘Laboratory Procedural Guide for Certifying Newly Manufactured Baseball/Softball Batter's Helmets'.
Congruent with ND-001, the NOCSAE medium headform was used for all tests. Of course, two major modifications to the preceding test methods were implemented. First, a single test structure was designed to conduct both the drop tower test and the projectile test. This is in contrast to ND-001 and ND-021, which employ a separate apparatus for each test. Second, a means to measure the force of the impact into the headform was developed.
Further, the applications of theoretical equations, in particular energy equations, were applied to the collected data with the hopes of forming a basis for comparison with established findings.
The results revealed that certain energy equations could be applied with a certain level of confidence to determine impact velocity, especially without the presence of impact attenuation. In addition, an unforeseen development suggested that an object in a stationary setting, such as a batter in baseball, may incur more damage from the rebound of an impact than the impact itself.
The results generated by the supplementary procedures will aid in developing a basis for comparison and creation of a means to reasonably measure the contributing biomechanical factors, such as linear acceleration, to the shock created by head impacts, which is the leading cause of sports related concussions.