A novel intracranial strain measurement for helmet performance evaluation

At present, methods for evaluating helmet performance focus primarily on head kinematics as a means of quantifying risk of brain injury. Head kinematics are used as inputs in computational models of injury, as well as a range of impact severity measures, in an effort to approximate strain response and predict injury outcomes. While the mild Traumatic Brain Injury (mTBI) is thought to be caused by intracranial strain, our current helmet testing approaches are not able to directly resolve these parameters. The focus of the present work is to detail ongoing efforts to introduce intracranial strain measurements within a tissue-simulating head surrogate. In the present work, we will demonstrate our current progress in measuring intracranial strains within a polymeric surrogate headform developed by Defence Research and Development Canada Valcartier, that enables us to make direct measurements of displacement and strain, in addition to measuring its kinematic response. The headform was subjected to a series impacts using a pneumatically-driven linear impactor. Impact tests were conducted with the bare and helmeted headform and monitored using an in situ high speed X-ray cineradiography system, developed at Carleton University. The impacts were captured at a cineradiography speed of 5,000 fps and the internal strain fields were computed using digital image correlation.