Cycling is an increasingly popular mode of transportation and a preferred form of exercise worldwide. From 1990 to 2015, commuting via bicycle increased as much as four-fold in cities across North America and Europe. However, this increase in cycling is associated with an increase in cycling related fatalities and head injuries. The best way to prevent severe head injury while cycling is to wear a bike helmet. Bike helmets are designed to decrease the linear acceleration of the head, decreasing the rider's risk of severe head injuries, such as skull fracture. In order to sell a bike helmet, it must meet a minimum standard of protection based on linear acceleration of the head upon impact. However, bike helmet impacts are not completely linear in nature and experience a tangential component through angled impacts of the helmet, resulting in rotational accelerations and shear-strain at the skull-brain interface. This strain cause brain injuries such as concussion. Therefore, recent helmet advancements have aimed to decrease rotational acceleration of the head. To continue the advancement of helmet technology and the subsequent decrease of brain injury risk to riders, investigating the impact conditions of real-world impacts is pertinent. This thesis aimed to increase the current body of knowledge of cycling related head impacts. The first aim was to quantify real-world impact locations and analyze how impact location may influence helmet performance. The second aim of this thesis was to investigate the impact velocities and resulting kinematics of real-world crashes based on the magnitude of corresponding damage conditions. Additionally, this aim analyzed the impact conditions from cases which resulted in concussion. Together these studies aim to provide valuable real-world data to be used for the advancement of helmet technologies and design. / Master of Science / Cycling is an increasingly popular mode of transportation and a preferred form of exercise worldwide. From 1990 to 2015, commuting via bicycle increased as much as four-fold in cities across North America and Europe. However, this increase in cycling is associated with an increase in cycling related fatalities and head injuries. The best way to prevent severe head injury while cycling is to wear a bike helmet. Bike helmets are designed to decrease the linear acceleration of the head, decreasing the rider's risk of severe head injuries, such as skull fracture. In order to sell a bike helmet, it must meet a minimum standard of protection based on linear acceleration of the head upon impact. However, bike helmet impacts are not completely linear in nature and experience a tangential component through angled impacts of the helmet, resulting in rotational accelerations and shear-strain at the skull-brain interface. This strain cause brain injuries such as concussion. Therefore, recent helmet advancements have aimed to decrease rotational acceleration of the head. To continue the advancement of helmet technology and the subsequent decrease of brain injury risk to riders, investigating the impact conditions of real-world impacts is pertinent. This thesis aimed to increase the current body of knowledge of cycling related head impacts. The first aim was to quantify real-world impact locations and analyze how impact location may influence helmet performance. The second aim of this thesis was to investigate the impact velocities and resulting kinematics of real-world crashes based on the magnitude of corresponding damage conditions. Additionally, this aim analyzed the impact conditions from cases which resulted in concussion. Together these studies aim to provide valuable real-world data to be used for the advancement of helmet technologies and design.

The recent emergence of electric scooter (e-scooter) ride share companies has greatly increased the use of e-scooters in cities around the world. In this thesis, firstly, e-scooter injuries reported in the current literature as well as an overview of current e-scooter company policies, state laws, and local laws are reviewed. The most injured regions of the body were the head and extremities. These injuries are generally minor to moderate in severity and commonly include fractures and lacerations. A primary cause of e-scooter accidents is front wheel collisions with a vertical surface such as a curb or object, generically referred to as a "stopper." Therefore, various e-scooter-stopper crashes were simulated numerically across different impact speeds, approach angles, and stopper heights to characterize their influence on rider injury risk during falls. A finite element (FE) model of a standing Hybrid III anthropomorphic test device was used as the rider model after being calibrated against certification test data. The angle of approach was found to have the greatest effect on injury risk to the rider, and it was shown to be positively correlated with injury risk. Smaller approach angles were shown to cause the rider to land on their side, while larger approach angles caused the rider to land on their head and chest. Additionally, arm bracing was shown to reduce the risk of serious injury in two thirds of the impact scenarios. The majority of e-scooter rider fatalities (about 80%) are recorded in collisions between a car and an e-scooter. Therefore, crashes between an e-scooter and a sedan (FCR) and a sports utility vehicle (SUV) were simulated using finite element models. The vehicles impacted the e-scooter at a speed of 30 km/hr in a perpendicular collision and at 15 degrees towards the vehicle, to simulate a rider being struck by a turning vehicle. The risks of serious injury to the rider were low for the head, brain, and neck, but femur/tibia fractures were observed in all simulations. The primary cause of head and brain injuries was found to be the head-ground impact if such an impact occurred. / Master of Science / The recent emergence of electric scooter (e-scooter) ride share companies has greatly increased the use of e-scooters in cities around the world. In this thesis, firstly, e-scooter injuries reported in the current literature as well as an overview of current e-scooter company policies, state laws, and local laws are reviewed. The most injured regions of the body were the head and extremities. These injuries are generally minor to moderate in severity and commonly include fractures and lacerations. A primary cause of e-scooter accidents is front wheel collisions with a vertical surface such as a curb or object, generically referred to as a "stopper." Therefore, various e-scooter-stopper crashes were simulated numerically across different impact speeds, approach angles, and stopper heights to characterize their influence on rider injury risk during falls. A finite element (FE) model of a standing Hybrid III anthropomorphic test device was used as the rider model after being calibrated against certification test data. The angle of approach was found to have the greatest effect on injury risk to the rider, and it was shown to be positively correlated with injury risk. Smaller approach angles were shown to cause the rider to land on their side, while larger approach angles caused the rider to land on their head and chest. Additionally, arm bracing was shown to reduce the risk of serious injury in two thirds of the impact scenarios. The majority of e-scooter rider fatalities (about 80%) are recorded in collisions between a car and an e-scooter. Therefore, crashes between an e-scooter and a sedan (FCR) and a sports utility vehicle (SUV) were simulated using finite element models. The vehicles impacted the e-scooter at a speed of 30 km/hr in a perpendicular collision and at 15 degrees towards the vehicle, to simulate a rider being struck by a turning vehicle. The risks of serious injury to the rider were low for the head, brain, and neck, but femur/tibia fractures were observed in all simulations. The primary cause of head and brain injuries was found to be the head-ground impact if such an impact occurred.

Ballistic shields are supported by a user’s arm, placing the upper extremity at close proximity to the back-face of the shield. Although ballistic shields must pass a protective standard that outlines projectile (bullet) penetration; there is no standard that stipulates the amount of acceptable deformation when ballistic shields stop or deflect projectiles. There are no injury criteria developed for the high-rate, short duration and focal loading that is typical of shield back-face deformation from these events. In this research, an anthropomorphic test device (ATD) was modified to allow for additional instrumentation capable of measuring these loads. It was then used in a ballistic testing facility to quantify loading at the hand, wrist, forearm, and elbow. A lightweight projectile was created that matched the shape and stiffness of the deforming ballistic shield and impacts within 5% of the peak force measured in the ballistic testing facility were applied with it to post-mortem human subjects (PMHS) until failure. Eight 50th percentile male PMHS pairs were segmented at the mid-humerus and impacted to failure to determine the fracture threshold of the hand, wrist, forearm, and elbow, confirmed by x-ray imaging. The peak force required to generate fracture varied significantly among anatomical location, indicating boundary conditions influence failure threshold. Further, these injury criteria were substantially different than previously reported criteria for other loading events (e.g., automotive), highlighting the importance of developing injury criteria specific for the intended application. An existing finite element human body model designed for automotive impacts was also assessed for its applicability to predict injury in these high-rate loading scenarios, and performed well for peak force, but not for the force-time curve shape. This is the first study of its kind to assess injury risk resulting from shield behind armour blunt trauma, and results from this work will inform a protective standard to assess ballistic shields. / Thesis / Doctor of Philosophy (PhD) / Ballistic shields used by defence personnel are designed to stop incoming bullets by deflecting or absorbing them. In the process, the back-face of the shield undergoes a rapid deformation that can potentially cause an upper extremity injury to users, an injury mechanism termed behind shield blunt trauma. This work aimed to quantify the injury risk that this mechanism poses at four locations along the upper extremity: the hand, wrist, forearm, and elbow. This was conducted by modifying and employing a crash test dummy upper extremity and measuring loads applied to the upper extremity in a ballistic testing range. Assessment of whether these loads caused injury was conducted using cadaveric specimens and testing them to failure. An existing finite element human body model was also assessed for its applicability to predict injury in these high-rate loading scenarios. Results from this work will inform a protective standard to assess ballistic shields.

In the current study, mechanoporation-related neuronal injury as a result of mechanical loading has been studied using a multiscale approach. Injurious mechanical loads to the head induce strains in the brain tissue at the macroscale. As each length scale has its own unique morphology and heterogeneities, the strains have been scaled down from the macroscale brain tissue to the nanoscale neuronal components that result in mechanoporation of the neuronal membrane, while relevant neuronal membrane mechanoporation-related damage criteria have been scaled up to the macroscale. To achieve this, first, damage evolution equations has been developed and calibrated to molecular dynamics simulations of a representative neuronal membrane at the nanoscale. These damage evolution equations are strain rate and strain state dependent. The resulting damage evolution model has been combined with Nernst-Planck diffusion equations to analytically compare to intracellular ion concentration disruption through mechanical loading of in vitro neuron cell culture and found to agree well. Then, these damage evolution equations have been scaled up to the microscale for dynamic simulations of 3-dimensional reconstructed neurons of similar mechanical loads. It was found that the neuronal orientation significantly affects average damage accumulation on the neuron, while the morphology of neurons, for a given neuron type, had little effect on the average damage accumulation. At the mesoscale, finite element simulations of geometrical complexities of sulci and gyri, and the structural complexities of the gray and white matter and CSF on stress localization were studied. It was found that the brain convolutions, sulci, and gyri, along with the effects of impedance mismatch between the cerebrospinal fluid (CSF) and brain tissue localized shear stresses, at the depths of the sulcus end (near field effects) and in-between sulci (far field effects), that correlated well with the regions of tau protein accumulation that is observed in chronic traumatic encephalopathy (CTE). Further, sulcus length and orientation, with respect to impending stress waves, had a significant impact on the magnitude of stress localization in the brain tissue. Lastly, gray-white matter differentiation, pia matter, and brain-CSF interface interaction properties had minimal impact of the shear stress localization trends observed in these simulations.

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Impact induced injury to the human head is a major cause of death and disability; this has driven considerable research in this field. Despite this, the methods by which the brain is damaged following non-penetrative (blunt) impact, where the skull remains intact, are not well understood. The mechanisms which give rise to brain trauma as a result of blunt head impact are frequently explored using indirect methods, such as finite element simulation. Finite element models are often created manually, but the complex anatomy of the head and its internal structures makes the manual creation of a model with a high level of geometric accuracy intractable. Generally, approximate models are created, thereby introducing large simplifications and user subjectivity. Previous work purports that blunt head impacts of short duration give rise to large dynamic transients of both positive and negative pressure in the brain. Here, three finite element models of the human head, of increasing biofidelity, were employed to investigate this phenomenon. A novel approach to generating finite element models of arbitrary complexity directly from three-dimensional image data was exploited in the development of these models, and eventually a highly realistic model of the whole head and neck was constructed and validated against a widely used experimental benchmark. The head models were subjected to a variety of simulated impacts, ranging from comparatively long duration to very short duration collisions. The dynamic intracranial pressure response, characterised by large transients of both positive and negative pressure in the brain, was observed following short duration impacts in all three of the models used in this study. The dynamic intracranial response was also recorded following short duration impacts of high energy, involving large impact forces, which were deemed to be realistic representations of actual impact scenarios. With the aid of an approximate analytical solution, analysis of the simulations revealed that the dynamic response is caused by localised skull deflection, which induces flexural waves in the skull. The implications of these magnified pressures are discussed, with particular regard to the potential for intracranial cavitation.

<p>Between October 2001 and May 2012 approximately 70% of U.S. military personnel killed in action and 75% wounded in action were the direct result of exposure to an explosion. As of 2008, it was estimated that close to 20% of all Operation Iraqi Freedom and Operation Enduring Freedom (OIF/OEF) veterans had sustained some form of traumatic brain injury (TBI). Further, blast exposure is also a civilian problem due to the increased usage of explosives in terrorist attacks. Blast injury research has historically focused on the pulmonary system and the other air-containing organs which have been shown through extensive experimentation to be susceptible to blast overpressure injury. A shift in injury pattern during recent conflicts is characterized by decreased incidence of pulmonary injuries with an increase in TBI thought to be associated with blast exposure. This increase in observation of blast TBI has resulted in a large research effort to understand mechanisms and thresholds. However, due to the relatively sudden shift, much of this research is being conducted without a proper understanding and consideration of blast mechanics and interspecies scaling effects.</p><p>This dissertation used experimental and computational finite element (FE) analysis to investigate some large questions surrounding blast TBI research. An experimental investigation was conducted to determine the effects of modern thoracic body armor usage on blast pressure exposure seen by the body. To improve FE modeling capabilities, brain tissue mechanics in common blast TBI animal model species were investigated experimentally and computationally to determine viscoelastic constitutive behavior and measure interspecies variation. Meta-analysis of blast pulmonary literature was conducted to update interspecies scaling and injury risk models. To derive interspecies scaling and injury risk models for blast neurotrauma endpoints a meta-analysis of existing experimental data was used.</p><p>This dissertation makes major contributions to the field of injury biomechanics and blast injury research. Research presented in this dissertation showed that modern thoracic body armor has the ability to lower the risk of pulmonary injury from blast exposure by attenuating and altering blast overpressure. The study shows that the use of soft body armor results in the pulmonary injury threshold being similar to that for neurotrauma. The use of hard body armor results in the threshold for pulmonary injury occurring at higher levels than that of neurotrauma. This finding is important, as it helps to explain the recent shift in injury types observed and highlights the importance of continued widespread usage of body armor not only for ballistic protection but for protection from blast as well.</p><p>This dissertation also shows the importance of interspecies scaling for investigation of blast neurotrauma. This work looks at existing in vivo animal model data to derive appropriate scaling across a wide range of brain size. Appropriate scaling for apnea occurrence and fatality for blast isolated to the head was found to be approximately equal to a characteristic length scaling of brain size, assuming similar brain geometry. By combining the interspecies scaling developed and existing tests data, injury risk models were derived for short duration blast exposures.</p><p>The contributions and conclusions of this dissertation serve to inform the injury biomechanics field and to improve future research efforts. The consideration by researchers of the recommendations presented in this dissertation for in vivo animal model testing will serve to maximize the value gained from experimentation and improve our understanding of blast injury mechanisms and thresholds. The injury risk models presented in this work help to improve our ability to prevent, diagnose, and treat blast neurotrauma.</p> / Dissertation

The current focus of research efforts in the area of the biomechanics of traumatic brain injury is the development of numerical (finite element) models of the human head. A validated numerical model of the human head may lead to better head injury criteria than those used currently in crashworthiness studies. A critical step in constructing a validated finite element model of the head is determining the mechanical threshold, should it exist, for various types of injury to brain tissue. This thesis describes a biomechanical study of axonal injury in the anaesthetised sheep. The study used the measurements of the mechanics of an impact to the living sheep, and a finite element model of the sheep skull and brain, to investigate the mechanics of the resulting axonal injury. Sheep were subjected to an impact to the left lateral region of the skull and were allowed to survive for four hours after the impact. The experiments were designed specifically with the numerical model in mind; sufficient data were collected to allow the mechanics of the impact to be faithfully reproduced in the numerical model. The axonal injury was identified using immunohistological methods and the injury was mapped and quantified. Axonal injury was produced consistently in all animals. Commonly injured regions included the sub-cortical and deep white matter, the hippocampi and the margins of the lateral ventricles. The degree of injury was closely related to the peak impact force and to kinematic measurements, particularly the peak change in linear and angular velocity. There was significantly more injury in animals receiving fractures. A three-dimensional finite element model of the sheep skull and brain was constructed to simulate the dynamics of the brain during the impact. The model was used to investigate different regimes of material properties and boundary conditions, in an effort to produce a realistic model of the skull and brain. Model validation was attempted by comparing pressure measurements in the experiment with those calculated by the model. The distribution of axonal injury was then compared with the output of the finite element model. The finite element model was able to account for approximately thirty per cent of the variation in the distribution and extent of axonal injury, using von Mises stress as the predictive variable. Logistic regression techniques were used to construct sets of curves which related the extent of injury, to the predictions of the finite element model, on a regional basis. The amount of observable axonal injury in the brains of the sheep was clearly related to the severity of the impact, and was related to the predictions of a finite element model of the impact. Future improvements to the fidelity of the finite element model may improve the degree to which the model can explain the variation in injury throughout the brain of the animal and variations between animals. This thesis presents results, and a methodological framework, that may be used to further our understanding of the limits of human endurance, in the tolerance of the brain to head impact. All experiments reported herein conformed with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes. / Thesis (Ph.D.)--Mechanical Engineering, 2000.

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