A variable rate torsional oscillator for the rotational characterisation and comparison of advanced biofidelic headforms at impact relevant rates

Engineering of Sport 15 - Proceedings from the 15th International Conference on the Engineering of Sport (ISEA 2024)

In the UK, head injury is the leading cause of death or disability in under 40’s. This highlights the importance of work towards reducing the frequency and severity of head injury in sport. One main research theme towards this is the re-enactment of injury events in the laboratory, using impact apparatus such as drop towers, pneumatic rams, and projectile launchers. These all require a surrogate human headform from which measurements can be taken. Mechanical surrogates, referred to as anthropomorphic test devices (ATDs), are usual in this field due to their high experimental repeatability and ease of instrumentation (linear and rotational kinematics) compared to alternatives (e.g. cadavers). Current research shows that rotational kinematics are vital for understanding the risk of mild traumatic brain injury. ATD properties undoubtedly influence on the outcome of rotational kinematics due to impact. The human likeness of the ATD’s properties can be referred to as its biofidelity. The spectrum ranges from fully metal approximations such as the EN 960 to advanced research grade examples with increasingly more biofidelic properties. ATD rotational properties are commonly quantified by quasi-static moment of inertia (MOI). Is this representative of impact response? For a rigid body (EN 960) this is theoretically sufficient to characterise its rotational response to impact. However, it is possible that for a non-rigid body (humans and biofidelic ATDs), the loading rate might be a significant factor in response. MOI is usually measured using an oscillator setup where MOI is quantified using change in oscillation period relative to base oscillation period (unloaded). MOI is a property most often associated with rigid bodies where MOI is independent of base oscillation rate therefore, no commercial solution exists with capacity to vary the base test rate. This paper presents the development of a variable speed torsional oscillator and its use to characterise the rotational properties (MOI and dampening) of two headforms of differing biofidelity.