Analysis of ball carrier head motion during a rugby union tackle without direct head contact: A case study

Rugby union players can be involved in many tackles per game. However, little is known of the regular head loading environment associated with tackling in rugby union. In particular, the magnitude and influencing factors for head kinematics during the tackle are poorly understood. Accordingly, the goal of this study was to measure head motion of a visually unaware ball carrier during a real game tackle to the upper trunk with no direct head contact, and compare the kinematics with previously reported concussive events. Model-Based Image-Matching was utilised to measure ball carrier head linear and angular velocities. Ball carrier componential maximum change in head angular velocities of 38.1, 20.6 and 13.5 rad/s were measured for the head local X (coronal plane), Y (sagittal plane) and Z (transverse plane) axes respectively. The combination of a high legal tackle height configuration and visually unaware ball carrier can lead to kinematics similar to average values previously reported for concussive direct head impacts

Relevant factors in the design of composite ballistic helmets

[EN] In this paper, the design methodology of composite ballistic helmets has been enhanced considering biomechanical requirements by means of finite element analysis. Modern combat helmets lead to a new type of non-penetrating injury, the Behind Helmet Blunt Trauma (BHBT), generated by the deformation of the inner face of the helmet, the so-called backface deformation (BFD). Current standard testing methodologies use BFD as the main measure in ballistic testing. Nonetheless, this work discusses the relationship between this mechanical parameter and the head trauma (BHBT) by studying different head injury criteria. A numerical model consisting of a helmet and a human head is developed and validated with experimental data from literature. The consequences of non-penetrating high-speed ballistic impacts upon the human head protected by an aramid combat helmet are analysed, concluding that the existing testing methodologies fail to predict many types of head injuries. The influence of other parameters like bullet velocity or head dimensions is analysed. Usually, a single-sized helmet shell is manufactured and the different sizes are adjusted by varying the foam pad thickness. However, one of the conclusions of this work is that pad thickness is critical to avoid BHBT and must be considered in the design process.The authors thank the financial support received from the Spanish Ministry of Economy and Competitiveness (MINECO) and the European Regional Development Fund (ERDF-FEDER) through the project RTC-2015-3887-8, and from the Conselleria d'Educació, Investigació, Cultura i Esport of the Generalitat Valenciana through the program PROMETEO 2016/007.Palomar-Toledano, M.; Lozano-Mínguez, E.; Rodriguez-Millán, M.; Miguélez, MH.; Giner Maravilla, E. (2018). Relevant factors in the design of composite ballistic helmets. Composite Structures. 201:49-61. https://doi.org/10.1016/j.compstruct.2018.05.076S496120

On the characterization of the heterogeneous mechanical response of human brain tissue

The mechanical characterization of brain tissue is a complex task that scientists have tried to accomplish for over 50 years. The results in the literature often differ by orders of magnitude because of the lack of a standard testing protocol. Different testing conditions (including humidity, temperature, strain rate), the methodology adopted, and the variety of the species analysed are all potential sources of discrepancies in the measurements. In this work, we present a rigorous experimental investigation on the mechanical properties of human brain, covering both grey and white matter. The influence of testing conditions is also shown and thoroughly discussed. The material characterization performed is finally adopted to provide inputs to a mathematical formulation suitable for numerical simulations of brain deformation during surgical procedures.</p