Dissertations / Theses on the topic 'Head impact biomechanics'

The research presented in this thesis aims to improve the knowledge of head impact biomechanics in youth football players by analyzing head impact exposure of youth football players and the performance of youth football helmets. The results of the studies presented provide a foundation for researchers, football leagues, and helmet manufactures to implement changes and modifications that aim to reduce concussion risk in youth athletes. The first study presented in this thesis aims to quantify the head impact exposure of 7 to 8 year old football players and determine the cause of variation in player exposure. To conduct this study, 19 players were instrumented with helmet mounted accelerometers that measured real-time acceleration data on the field. This data was analyzed to determine the magnitude, frequency, and location of each impact sustained by players in the 2011 and 2012 football season. From these data, it was determined that the average 7 to 8 year old player experienced 161 impacts per season, 60% of which were in practice and 40% were in games. The median impact for 7 to 8 year old players was 16 g and 686 rad/s². The magnitude of the 95th percentile impact was 38 g and 2052 rad/s². A total of 125 impacts above 40 g were recorded, 67% of which occurred in practices and 33% occurred in games. It was determined that returning players experienced significantly more impacts per season than first time players and practices had significantly higher magnitude impacts than games. These data can be used to further develop practice modifications that aim to reduce total impacts and high magnitude impacts experienced by youth football players. The second study presented in this thesis aims to quantify differences in youth football helmet performance before and after a football season. Currently, the only requirement regarding helmet recertification and reconditioning states that no helmet older than 10 years will be recertified or reconditioned. Quantitative data is needed to either support or refute this guideline and provide data describing how often youth football helmets should be recertified and reconditioned. To conduct this study, 6 youth Riddell Revolution football helmets, 3 that were new and 3 that had been used for one season, were tested on a drop tower from various heights and impact locations before and after the 2013 football season. It was determined that there was no significant difference in helmet performance before and after a season for new helmets or helmets that had been used for one season. In addition, there was no significant correlation between the frequency of impacts, the 95th percentile impact magnitude, or the product of the frequency and 95th percentile impact magnitude with the change in helmet performance. Future studies should be conducted that analyze the performance of youth football helmets over the course of multiple seasons.
Master of Science

The research presented in the thesis explores the biomechanics of the head and neck during impacts in football. The research related to the head is geared towards advancing the current understanding of the mechanisms of mild traumatic brain injury, specifically by investigating head accelerations experienced by football players during impacts. To do this, a six degree of freedom sensor that could be integrated into existing football helmets and is capable of measuring linear and angular acceleration about each axis of the head was developed and validated. This sensor was then installed in the helmets of 10 Virginia Tech football players and data was recorded for every game and practice during the 2007 football season. A total 1712 impacts were recorded, creating a large and unbiased dataset. No instrumented player sustained a concussion during the 2007 season. From 2007 head acceleration dataset, 24 of the most severe impacts were modeled using a finite element head model, SIMon (Simulated Injury Monitor). Besides looking at head acceleration, the force transmitted to the mandible by chin straps in football helmets was investigated through impact testing. Little research has been conducted looking at the mandible-chin strap interface in the helmet, and this may be an area of helmet design that can be improved. The research presented in this thesis related to the neck is based on stingers. Football players wear neck collars to prevent stingers; however, their designs are largely based on empirical data, with little biomechanical testing. The load limiting capabilities of various neck collars were investigated through dynamic impact testing with anthropomorphic test devices. It was found that reductions in loads correlate with the degree to which each collar restricted motion of the head and neck. To investigate the differences in results that using different anthropomorphic test devices may present, the matched neck collar tests were performed with the Hybrid III and THOR-NT 50th percentile male dummies. The dummies exhibited the same trends, in that either a load was reduced or increased; however, each load was affected to a different degree.
Master of Science

Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury.
Master of Science
Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury.

Although cycling offers many health and environmental benefits, it is not an activity free of injury risk. Increases in cycling popularity in the United States over the past 15 years have been paralleled by a 120% growth in cycling-related hospital admissions, with injuries to the head among the most common and debilitating injuries. Bicycle helmets can reduce head injury risk and are presently required to meet safety standard certification criteria specifying a minimal level of acceptable impact protection. However, the conditions surrounding cyclist head impacts are thought to be much more complex than the test conditions prescribed in standards and have important implications related to mechanisms of injury. The overarching aim of this dissertation was thus to investigate the protective capabilities of bicycle helmets in the context of real-world impact conditions and relevant head injury mechanisms. This aim was achieved through a series of studies, the objectives of which were to: compare helmet impact performance across standards impact testing and more realistic, oblique impact testing; to probe how changing boundary conditions of oblique impact testing may influence helmet test outcomes; to use this knowledge to inform the development of an objective helmet evaluation protocol reflective of realistic impact conditions and related head injury risks; and finally, to enhance the body of knowledge pertaining to cyclist head impact conditions via advanced helmet damage reconstruction techniques. The compilation of results across these studies serves to enhance cyclist safety by stimulating improved helmet evaluation and design while simultaneously providing objective, biomechanical data to consumers, enabling them to make safety-based purchasing decisions.
Doctor of Philosophy
Although cycling offers many health and environmental benefits and is increasing in popularity in the United States, it is not always a perfectly safe activity. The number of cycling-related hospital admissions in the US has been increasing over the past 15 years. Cyclists often sustain head injuries from crashes, which can be particularly debilitating. Fortunately, wearing a helmet can protect against head injuries during a crash. Bicycle helmets are presently designed around safety standards that drop a helmeted dummy head onto a horizontal anvil and require the helmet to limit the force on the head to acceptable levels. However, standards tests overly simplify how cyclists actually hit their head during a crash and are consequently unable to assess how well helmets protect against common brain injuries like concussion. The overarching goal of this research was to evaluate how effectively bicycle helmets protect cyclists from concussion in realistic impact scenarios. Several studies were conducted to achieve this goal. Their individual objectives were to: compare how bicycle helmets reduce impact forces associated with standards tests versus more realistic, angled impact tests; to understand how changing constraints of an angled impact setup influences helmet effectiveness; to develop an unbiased evaluation protocol for bicycle helmets based on realistic cyclist crash scenarios and concussion risk assessment; and finally, to further explore how cyclists impact their head in real-world crashes using advanced techniques for reconstructing bicycle helmet damage from actual accidents. All of these studies lead to improved cyclist safety by stimulating improved helmet evaluation and design, while also providing consumers with information on how protective their helmets are.

Concussions are diffuse injuries that affect areas of the brain responsible for a person's physical, cognitive, and emotional health. Although concussions were once thought only to present transient symptoms, mounting evidence suggests potential for long-term neurological impairments. The deleterious effects of concussion can be from a single, high severity impact event or the accumulation of lower severity impacts. Clinical changes that can result from concussion include an elevated symptom presentation and changes in gait, or an individual's walking pattern. It is not well understood if similar deficits result after an accumulation of subconcussive impacts. The majority of research on human tolerance to head injury has been based on American football, using helmet-mounted sensors in male athletes. Limited studies have attempted to quantify biomechanical tolerance in women, despite the sex-specific nature of presentation and outcome of concussion. Biomechanical, physiologic, and psychosocial factors differ between males and females, likely contributing to this difference. The research presented in this dissertation was aimed at describing sex-specific outcomes of subconcussion in a matched cohort of male and female athletes to gain a better sense of unhelmeted, sex-specific tolerance to head impacts. On-field data were collected from collegiate rugby players using instrumented mouthguards. Rugby involves high energy, frequent head impacts, does not require protective headgear, and is played the same for both men and women. The females in our study sustained fewer impacts per session than the males, but their impacts had similar linear acceleration magnitudes. The kinematics of the concussive male impacts were higher than the kinematics of the concussive female impacts. Both sexes reported concussion-like symptoms in the absence of diagnosed concussion during a season. Females reported more symptoms with a higher severity in-season compared to males after subconcussive and concussive impacts. Female athletes saw deficits in cadence, double support time, gait speed, and stride length post-concussion. The majority of athletes improved in their dual-task gait assessment by the end of the season, suggesting there may not be a negative effect on gait after an accumulation of subconcussive impacts. This work assessed the biomechanics of head impacts and concussions of this population, and evaluated changes in symptom presentation through weekly graded symptom surveys and dual-task gait assessments both after a concussion and as an effect of subconcussive impacts. Understanding the sex-specific clinical effects of head impacts is critical, and can provide insight into concussion diagnostic, management, and prevention tools that are appropriate and effective.
Doctor of Philosophy
Concussions are injuries that affect many areas of the brain, including those responsible for a person's physical, cognitive, and emotional health. Although concussions were once thought only to present transient symptoms, mounting evidence suggests potential for long-term neurological impairments. The harmful effects of concussion can be from a single, high intensity impact event or the build-up of lower intensity impacts. Clinical changes that can result from concussion include an elevated symptom presentation and changes in gait, or an individual's walking pattern. It is not well understood if similar side effects result after an accumulation of subconcussive impacts. The majority of research on human tolerance to head injury has been based on American football, using helmet-mounted sensors in male athletes. Limited studies have attempted to quantify concussion tolerance in women, despite the differences in men and women's symptoms and recovery time after a concussion. Female's neck strength, hormones, and increased honesty in reporting concussion differ from males, likely contributing to this difference. The research presented in this dissertation was aimed at describing how sex affects the results of subconcussion in a group of male and female athletes to gain a better sense of unhelmeted, sex-specific tolerance to head impacts. On-field data were collected from collegiate rugby players using sensor-embedded mouthguards. Rugby involves high energy, frequent head impacts, does not require protective headgear, and is played the same by both men and women. The females in our study sustained fewer impacts per session than the males, but their impacts were similar in magnitude. The impact energies of the concussive male impacts were higher than those of the concussive female impacts. Both sexes reported concussion-like symptoms in the absence of diagnosed concussion during a season. Females reported more symptoms with a higher severity in-season compared to males after subconcussive and concussive impacts. Female athletes had a slower walking pace and walking speed, a shorter stride length, and spent more time with both feet on the ground post-concussion. The majority of athletes improved in their dual-task gait assessment by the end of the season, suggesting there may not be a negative effect on gait after an accumulation of subconcussive impacts. This work assessed the biomechanics of head impacts and concussions of this population, and evaluated changes in symptom presentation through weekly graded symptom surveys and dual-task gait assessments both after a concussion and as an effect of subconcussive impacts. Understanding the sex-specific clinical effects of head impacts is critical, and can provide insight into concussion diagnostic, management, and prevention tools that are appropriate and effective.

The incidence of concussive injury has continued to arise annually with up to 3.8 million concussions reported per year (Thurman 1999) and 15% of these injuries occurring with persistent symptoms (Kraus and Chu, 2005). Few studies have examined the differences between youth and adult concussion (Yeates et al, 2012; Gosselin et al, 2010) therefore it is unknown whether youth and adults pose a similar risk of sustaining a concussion following impact. For this reason, the purpose of this study is to determine if differences exist in the dynamic response of the head and brain tissue deformation characteristics between children and adolescents for falls in comparison to adult data which have resulted in concussive injuries. Patient data was collected from emergency room hospitals across Canada. After exclusion criterion was applied, 11 child and 10 adolescent falls were reconstructed using mathematical (MADYMO) model, physical model (Hybrid III Headforms) and finite element modelling. Both groups were compared to each other as well as an adult group collected by Post et al (2014b) using a one-way ANOVA and Welsh test. The results of this study show that the children produced the lowest values for all variables when compared to the adolescents and adults whereas the adolescents produced the largest (with the exception of MPS where the adolescent and adult MPS was the same). Although all results were above the suggested thresholds for risk of concussive injury, the youth produced the lowest brain tissue strain yet still suffered a concussion. This is important to note as it may suggest that children are at an increased risk of injury at a lower brain tissue strain level. Understanding the differences in parameters influencing concussive injury may aid researchers in comprehending the unique risk for youth at difference ages. This information would be useful in terms of protective equipment design, promoting safe play in games and management of patients following injury.

Injury to the human neck is a frequent consequence of automobile accidents and has been a significant public health problem for many years. The term `whiplash' has been used to describe these injuries in which the sudden differential movement between the head and torso leads to abnormal motions within the neck causing damage to its soft tissue components. Although many different theories have been proposed, no definitive answer on the cause of `whiplash' injury has yet been established and the exact mechanisms of injury remain unclear. Biomechanical research is ongoing in the field of impact analysis with many different experimental and computational methods being used to try and determine the mechanisms of injury. Experimental research and mathematically based computer modelling are continually used to study the behaviour of the head and neck, particularly its response to trauma during automobile impacts. The rationale behind the research described in this thesis is that a computational model of the human head and neck, capable of simulating the dynamic response to automobile impacts, could help explain neck injury mechanisms. The objective of the research has been to develop a model that_,, can accurately predict the resulting head-neck motion in response to acceleration impacts of various directions and severities. This thesis presents the development and validation of a three-dimensional computational model of the human head and cervical spine. The novelty of the work is in the detailed representation of the various components of the neck. The model comprises nine rigid bodies with detailed geometry representing the head, seven vertebrae of the neck and the first thoracic vertebra. The rigid bodies are interconnected by spring and damper constraints representing the soft-tissues of the neck. 19 muscle groups are included in the model with the ability to curve around the cervical vertebrae during neck bending. Muscle mechanics are handled by an external application providing both passive and active muscle behaviour. The major findings of the research are: From the analysis of frontal and lateral impacts it is shown that the inclusion of active muscle behaviour is essential in predicting the head-neck response to impact. With passive properties the response of the head-neck model is analogous to the response of cadaveric specimens where the influence of active musculature is absent. Analysis of the local loads in the soft-tissue components of the model during the frontal impact with active musculature revealed a clear peak in force in the majority of ligaments and in the intervertebral discs very early in the impact before any forward rotation of the head had occurred. For the case of rear-end impact simulations it has been shown for the first time that the inclusion of active musculature has little effect on the rotation of the head and neck but significantly alters the internal loading of the soft-tissue components of the neck.

American-style football participation is associated with high risks to a spectrum of sports-related brain injury involving acute reactions and chronic manifestations. Traditional methods of identifying injury have proven ineffective at protecting athletes and mitigating risk as they rely on the presence and recognition of inconsistent symptom expression. This is, in part, due to the lack of an objective measure of quantifying exposure. Brain trauma profiling was defined to capture a spectrum of exposure by incorporating the primary characteristics that associate with risk of neurological injury. This profile includes strain magnitude associated with impact, frequency at which impacts are experienced, time interval between impacts, over the duration of exposure. Trauma profiling methods differentiated player field position in professional American-style football where three unique trauma profiles were identified based on similarities among the characteristics of trauma. Regional strain from common head impacts showed that distribution was independent of field position regardless of variation in impact conditions. Rather, brain regions vulnerable to strains were dictated by the frequency and magnitude that govern the position profile. The extent of tissue volume involved in common head impacts was field position dependent. Skill positions tended to experience impacts involving greater tissue volumes reaching deeper white matter structures, but were infrequent. Impacts common to line positions typically involved less brain tissue of predominately superficial cortical gray matter, but were experienced at high frequency counts. The primary findings from this research show that brain trauma profiling may be used as an objective measurement tool to define exposure. The results indicate that exposure is not uniform and that brain trauma and injury risk can be described using unique combinations of these characteristics. Regional areas vulnerable to strain are dictated by the frequency and magnitude of impact and therefore in order to effectively protect against brain injury, both characteristics need to be managed. Lastly, this research demonstrates that either few impacts involving high brain volume or frequent impacts with little brain volume involvement may both result in brain dysfunction. Brain trauma profiling methods has broad application in future research. This measurement tool will be useful in identifying how injury occurs in various sports, military units, and particularly important for vulnerable populations and the developing brain. This knowledge is instrumental in establishing risk prevention strategies and public health policies for specific environments.

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.

Les piétons comptent parmi les usagers de la route les plus vulnérables dans la mesure où ils ne bénéficient d'aucune protection en cas d'impact avec un véhicule automobile. Plus de 1,17 millions de personnes sont tués sur la route de part le monde dont environ 65% ce piétons. Les blessures de la tête, souvent fatales, concernent environ 30 % des blessures enregistrées. Ces blessures conduisent à des incapacités de longue durée avec un coût sociétal et économique immense. Il est par conséquent essentiel de comprendre aussi bien les mécanismes d'accidents que les mécanismes de blessure de la tête afin d'intervenir sur la conception de la face avant des véhicules automobile. Dans ce contexte l'objet de la présente thèse est d'analyser la répons dynamique du piton en cas d'accident et ce contribuer au développement de critères de blessure de la tête. Dans le but d'étudier l'influence de la position du piéton, de la géométrie de la face avant du véhicule et de sa vitesse initiale sur la cinématique du piéton et les conditions d'impact de la tête, une simulation multi-corps a été mise en place. Les résultats de ces simulations donnent la vitesse et l'angle d'impact de la tête et la position de l'impact sur le véhicule. Cette analyse paramètrique a été conduite sur cinq types de véhicules et pour un modèle humain adulte et enfant de 6 ans et a permis de consolider les connaissances sur la conditions d'impact de la tête en comparaison avec les tests normatifs en vigueur.[...]
Pedestrians are regarded as an extremely vulnerable and high-risk group of road users since they are unprotected in vehicle impacts. More than 1.17 million people throughout the world are killed in road traffic accidents each year. Where, about 65% of deaths involve pedestrians. The head injuries in vehicle-pedestrian collisions accounted for about 30% of all reported injuries on different body regions, which often resulted in a fatal consequence. Such injuries can result in disabilities and long-term sequence, which lead to significant social costs. It is therefore important to study the characteristics of pedestrian accidents and understand the head injury mechanism of the pedestrian so as to improve vehicle design for pedestrian protection. The aim of this study is to investigate pedestrian dynamic response and develop head injury risk functions.In order to investigate the effect of pedestrian gait, vehicle front geometry and impact velocity on the dynamic responses of the head, the multi-body dynamic (MBD) models were used to simulate the head responses in vehicle to pedestrian collisions with different vehicle types in terms of head impact point measured with Wrap Around Distance (WAD), head relative velocity and impact angle. A simulation matrix is established using five vehicle types, and two mathematical models of the pedestrians represented a 50th male adult and a 6 year old child as well as seven pedestrian gaits based on typical postures in pedestrian accidents. In order to simulate a large range of impact conditions, four vehicle velocities (30 km/h, 40 km/h, 50 km/h and 60 km/h) are considered for each pedestrian position and vehicle type.A total of 43 passenger car versus pedestrian accidents were selected from In-depth Investigation of Vehicle Accidents in Changsha, China (IVAC) and German In-Depth Accident Study (GIDAS) database for simulation study. According to real-world accident investigation, accident reconstructions were conducted using multi-body system (MBS) pedestrian and car models under MADYMO simulation environment to calculate head impact conditions, in terms of head impact velocity, head position and head orientation. In order to study kinematics of adult pedestrian, relationship curves: head impact time, throw distance, head impact velocity and vehicle impact velocity, were computed and logistic regression models: head impact velocity, resultant angular velocity, HIC value, head contact force and head injuries, were developed based on the results from accident reconstructions.The automobile windshield, with which pedestrians come into frequent contact, has been identified as one of the main contact sources for pedestrian head injuries. In order to investigate the mechanical behavior of windshield laminated glass in the caseof pedestrian head impact, windshield FE models were set up using different combination for the modeling of glass and PVB, with various connection types and two mesh sizes (5 mm and 10 mm). Each windshield model was impacted with a standard adult headform impactor in an LS-DYNA simulation environment, and the results were compared with the experimental data reported in the literatures.In order to assess head injury risks of adult pedestrians, accident reconstructions were carried out by using Hybrid III head model based on the real-world pedestrian accidents. The impact conditions were obtained from the MBS simulation, including head impact velocity, head position and head orientation. They were used to set the initial conditions in a simulation of a Hybrid III FE head model striking a windshield FE model. Logistic regression models, Skull Fracture Correlate (SFC), head linear acceleration, Head Impact Power (HIP), HIC value, resultant angular acceleration and head injuries, were developed to study brain injury risk.{...]

An estimated 3.8 million sports-related concussions occur every year. Little research has been collected on soccer players, despite women's soccer having the third highest rate of concussion among all popular collegiate sports. The objective of this work was to evaluate multiple interventions that have been introduced to address the high rate of concussions in this population. Wearable head impact sensors were evaluated on their ability to accurately count and measure head impacts during a collegiate women's soccer season. Head impact exposure was quantified using video analysis of this season as well. Sensors were unable to accurately count impacts and reported nonsensical head acceleration measurements, indicating that data reported from head impact sensors should be interpreted with caution. The ability of soccer headgear to reduce linear and rotational head accelerations during common soccer impacts was examined in the laboratory. Ball-to-head and head-to-head impacts were performed at a range of speeds and impact orientations. Headgear resulted in small reductions during ball-to-head tests, which are not likely to be clinically relevant. In head-to-head tests, use of headgear on the struck head provided an overall 35% reduction in linear head acceleration, and a 53% reduction when another headgear was added to the striking head. The ten headgear tested varied greatly in performance. These data suggest that the use of protective headgear could reduce concussion incidence significantly in this population. Research presented in this thesis will inform soccer organizations on best practices for player safety with regard to head impacts.
Master of Science

More than 19 million children participate in youth baseball and softball annually. Although baseball and softball are not commonly depicted as contact sports in the, according to the U.S. CPSC baseball and softball were responsible for 11.6% of all head injuries treated in emergency rooms in 2009; third most behind only cycling and football. Ball impact has been identified as the leading cause of injury in baseball and softball, with the most frequent injury resulting from a ball impacting the head. Reduced injury factor balls, infield softball masks, batter's helmets, and catcher's masks have all been integrated into baseball and softball as a means for preventing serious head injury from ball impact. The research in this thesis had four objectives: to compare the responses of the Hybrid III and NOCSAE headforms during high velocity projectile impacts, to compare head injury risk across a range of baseball stiffness designed for different age groups, to evaluate the effectiveness of infielder softball masks' ability to attenuate facial fracture risk, and to describe a novel methodology to evaluate the performance of batter's helmets and catcher's masks. Results of these research objectives determined the most suitable ATD headform to evaluate head injury risk for high velocity projectile impacts, provided a framework for determining the optimal age-specific ball stiffness and optimal infield mask design, and disseminated STAR ratings for batter's helmets and catcher's masks to the public. The research presented in this thesis can be used to further improve safety in baseball and softball.
MS

Doutoramento em Engenharia Mecânica
A cortiça é um material celular natural capaz de suster quantidades consideráveis de energia. Estas características tornam este material ideal para determinadas aplicações como a proteção de impactos. Considerando equipamentos de segurança passiva pessoal, os materiais sintéticos são hoje em dia os mais utilizados, em particular o poliestireno expandido. Este também é capaz de absorver razoáveis quantidades de energia via deformação permanentemente. Por outro lado, a cortiça além de ser um material natural, é capaz de recuperar grande parte da sua forma após deformada, uma característica desejada em aplicações com multi-impacto. Neste trabalho é efetuada uma avaliação da aplicabilidade da cortiça em equipamentos de segurança pessoal, especificamente capacetes. Vários tipos de cortiça aglomerada foram caracterizados experimentalmente. Impactos foram simulados numericamente para avaliar a validade dos modelos constitutivos e as propriedades utilizadas para simular o comportamento da cortiça. Capacetes foram selecionados como caso de estudo, dado as energias de impacto e repetibilidade de impactos a que estes podem ser sujeitos. Para avaliar os capacetes de um ponto de vista biomecânico, um modelo de cabeça humana em elementos finitos foi desenvolvido. Este foi validado de acordo com testes em cadáveres existentes na literatura. Dois modelos de capacete foram modelados. Um modelo de um capacete rodoviário feito de materiais sintéticos, o qual se encontra disponível no mercado e aprovado pelas principais normas de segurança de capacetes, que serve de referência. Este foi validado de acordo com os impactos da norma. Após validado, este foi avaliado com o modelo de cabeça humana em elementos finitos e uma análise ao risco de existência de lesões foi efetuado. Com este mesmo capacete, foi concluído que para incorporar cortiça aglomerada, a espessura teria de ser reduzida. Então um novo modelo de capacete foi desenvolvido, sendo este uma espécie de modelo genérico com espessuras constantes. Um estudo paramétrico foi realizado, variando a espessura do capacete e submetendo o mesmo a duplos impactos. Os resultados destes impactos e da análise com o modelo de cabeça indicaram uma espessura ótima de 40 mm de cortiça aglomerada, com a qual o capacete tem uma melhor resposta a vários impactos do que se feito de poliestireno expandido.
Cork is a natural cellular material capable of withstanding considerable amounts of energy. These features make it an ideal material for some applications, such as impact protection. Regarding personal safety gear, synthetic materials, particularly expanded polystyrene, are typically used. These are also able to absorb reasonable amounts of energy by deforming permanently. On the other hand, in addition to cork being a natural material, it recovers almost entirely after deformation, which is a desired characteristic in multi-impact applications. In this work, the applicability of agglomerated cork in personal safety gear, specifically helmets, is analysed. Different types of agglomerated cork were experimentally characterized. These experiments were simulated in order to assess the validity of the constitutive models used to replicate cork's mechanical behaviour. In order to assess the helmets from a biomechanical point of view, a finite element human head model was developed. This head model was validated by simulating the experiments performed on cadavers available in the literature. Two helmet models were developed. One of a motorcycle helmet made of synthetic materials, which is available on the market and certified by the main motorcycle helmets safety standards, being used as reference. This helmet model was validated against the impacts performed by the European standard. After validated, this helmet model was analysed with the human head model, by assessing its head injury risk. With this helmet, it was concluded that a thinner helmet made of agglomerated cork might perform better. Thus, a new helmet model with a generic geometry and a constant thickness was developed. Several versions of it were created by varying the thickness and subjecting them to double impacts. The results from these impacts and the analyses carried out with the finite element head model indicated an optimal thickness of 40 mm, with which the agglomerated cork helmet performed better than the one made of expanded polystyrene.

The research presented in this thesis focuses on head impact exposure in youth football. The on-field portion of this research investigated high magnitude head impacts that youth football players experience in games and practices. With previously validated data collection methods, linear and rotational head accelerations from head impacts were collected. Over the course of two seasons, 79 total player-seasons resulted in over 13,000 impacts. A small subset of these, 979 impacts exceeding 40 g, represented the focus of this research as these impacts pose the greatest risk of injury to individuals. Some tackling drills in practice were found to have higher acceleration severities than those observed in games. How practice activities are conducted also contributes towards the overall high magnitude head impact exposure for practice, not just the practice drill itself. Within games, players who are running backs and linebackers played most frequently and experienced higher magnitude impacts more often than their teammates. Data were also collected from all players off the field. Each player completed balance assessments at the beginning and end of the season to allow for comparison, even in absence of a clinically-diagnosed concussion. Current balance assessments were observed to fall short for detecting postural control differences in this youth population. Modifications to these assessments were recommended that might allow for further insights. Research presented in this thesis will inform youth football organizations as they continue to develop strategies to enhance player safety and mitigate head impact exposure.
Master of Science

The research presented herein is an analysis of acceleration measurements of the head during helmet-helmet impacts, where a playerâ s helmet impacts another playerâ s helmet, and with a youth population in football. This research is aimed at advancing current understanding of impact biomechanics for two specialized groups. The first study is an observational analysis focusing on helmet-helmet impacts, and the difference in effective mass and head acceleration measurements between the striking player and the struck player. The study involved working with football players outfitted with a sensor integrated into their helmets containing a 6 accelerometer array, capable of measuring linear accelerations and estimating angular accelerations. To evaluate helmet-helmet impacts, video analysis of past NCAA football competitions between Virginia Tech and University of North Carolina (UNC) were utilized to identify these impacts between instrumented players. A force balance was then carried out for the observed impacts and their respective acceleration measurements to compute the effective mass of the players. It was determined that the total mass recruited by the striking player was 28% to 77% more than that of the struck player. The second study focused on documenting the head impact biomechanics of a youth population. To accomplish this objective, unique accelerometer arrays, capable of measuring linear and angular accelerations, were integrated into existing youth football helmets for 7 players on a local team. Acceleration data were collected for every practice and game during the 2011 season to amass a total of 748 impacts. No instrumented player sustained a concussion during the 2011 season. Results of the study indicated impacts of greater magnitudes were more likely to occur in practices, and can be minimized by augmenting practice activities.
Master of Science

La biomécanique des chocs vise à étudier les lésions, établir des limites de tolérance et de proposer des mesures de protections adéquates. La méthode des éléments-finis permet l’étude approfondie des mécanismes de lésions, évitant des problèmes liés à l’expérimentation et d’éthique. La biomécanique de la tête humaine chez l’adulte a pris ce virage très tôt, et des modèles de la tête de l’adulte existent, dont celui développé à l’Université de Strasbourg : le SUFEHM (Strasbourg University Finite Element Head Model). Le présent projet a pour but d’ouvrir cette thématique à la modélisation des traumatismes crâniens du nourrisson. Deux axes de travail ont été conduits successivement pour étudier des situations d’accidents et de maltraitances. Le premier axe consiste à développer un modèle de l’œil du nourrisson pour l’étude des hémorragies rétiniennes. Le deuxième consiste à améliorer le modèle de tête en intégrant d’une part les données de l’imagerie médicale comme l’orientation et la densité des fibres axonales, et d’autre part en validant la formulation du crâne pour prédire les fractures crâniennes
Impact biomechanics aim at studying injuries, establishing tolerance limit and propose efficient protective systems. The finite-element method permits to study precisely injury mechanisms by avoiding questions linked to experimentation and ethics. For the human adult head biomechanics, this methodology was taken earlier and several stable and validated models exist worldwide, among which one can find the Strasbourg University Finite Element Head Model (SUFEHM). This thesis aims at widening the human head biomechanics by studying infant head trauma. The research work has been conducted in two steps. In the first one, an infant eye numerical model was developed in order to study retinal hemorrhages. The second one consisted in improving the infant head model by integrating medical images data such as axonal fiber density and orientations into the infant brain and by validating the mechanical formulation of the infant skull in order to predict skull fractures

The research presented herein is a combination of work done in two distinct subcategories of sport related head injury research. The body of work is aimed at increasing the understanding of head impact biomechanics across a broad spectrum of impact scenarios as well as the ability of helmets to affect head impact biomechanics over time. The first study utilizes in situ testing of controlled impacts of an instrumented head form to more fully characterize head accelerations resulting from impacts to the ice, board, and glass surfaces present in an ice hockey rink. The full characterization of head impacts across a spectrum of loading conditions and impact surfaces gives researchers insight into head impact tolerance and head protection capabilities and limitations in ice hockey. The second study details the development of a method to impact helmet pads for repeated loading studies based on published head impact exposure data. The third study uses this newly developed methodology to test the effects of a season of impacts on the energy absorbing properties of three different helmet padding technologies. The body of work is aimed at increasing understanding of head impact and concussion and the ability of existing helmet technologies to prevent these injuries with a goal of reducing the occurrence of injury.
Master of Science

Accumulation of head impacts may contribute to acute and long-term brain trauma. Wearable sensors can measure impact exposure, yet current sensors do not have validated impact detection methods for accurate exposure monitoring. Here we demonstrate a head impact detection method that can be implemented on a wearable sensor for detecting field football head impacts. Our method incorporates a support vector machine classifier that uses biomechanical features from the time domain and frequency domain, as well as model predictions of head-neck motions. The classifier was trained and validated using instrumented mouthguard data from collegiate football games and practices, with ground truth data labels established from video review. We found that low frequency power spectral density and wavelet transform features (10 similar to 30 Hz) were the best performing features. From forward feature selection, fewer than ten features optimized classifier performance, achieving 87.2% sensitivity and 93.2% precision in cross-validation on the collegiate dataset (n = 387), and over 90% sensitivity and precision on an independent youth dataset (n = 32). Accurate head impact detection is essential for studying and monitoring head impact exposure on the field, and the approach in the current paper may help to improve impact detection performance on wearable sensors.

Dans les accidents de la circulation, les blessures de la tête sont réputées fréquentes et graves. En raison des diverses formes de la lésion (osseuse, vasculaire ou neurologique) et des limitations des connaissances biomécaniques de la tête, de vieux et simples critères de protection (comme le hic ou le pic d'accélération linéaire de la tête) sont encore utilises dans les tests normalises. Contrairement aux autres segments corporels, il n'est pas possible d'utiliser une méthode directe (consistant à réaliser des impacts sur des modèles biologiques du corps humain) pour déterminer la tolérance et le seuil de blessure. Afin de s'affranchir de ces contraintes, une méthodologie de recherche originale qui repose sur la reconstruction d'accidents de la circulation est développée. Les premiers travaux ont porté sur la définition d'un nouveau modèle de tête défini par la méthode des éléments finis. Les particularités de ce modèle concernent le liquide céphalo-rachidien décrit par un comportement hyperélastique et la définition d'une interface de glissement entre ce dernier et l'encéphale pour reproduire le mouvement relatif encéphale/crane. La confrontation de simulations représentatives d'essais expérimentaux menés sur têtes de sujets cadavériques atteste la représentativité du modèle. Une méthodologie de reconstruction d'accidents a été développée. Elle s'articule autour d'une reconstruction cinématique de l'accident, d'une reconstitution de la collision, d'une simulation de la seconde collision et d'une analyse du comportement intracrânien à l'aide du modèle de tête. Cette démarche de reconstruction est illustrée par un cas réel d'accident automobile. Le développement d'un modèle générique pour des applications d'accidents de motocyclettes est étudié. A partir des résultats de la reconstruction de l'accident automobile, un parallèle entre la contusion intracérébrale et la durée d'application d'un certain niveau de contraintes de von Mises est émis
In traffic accidents, head injuries are considered to be frequent and serious. Because of the various kind of injuries (bone, vascular and neurology) and limitations of the biomechanical representation of the head, old and simple protection criteria (such as the HIC or the peak linear acceleration of the head ) are still used in standard tests. Contrary to the others body segments, it’s not possible to use a direct approach (consisting in impacting biological human body models) to determine the tolerance and the threshold. In order to better represent the physical phenomena, an original research methodology that is based on traffic accidents reconstruction is developed. The first batch of works deals with the definition of a new finite element model of the head. The features concern the cerebro-spinal fluid described by an hyperelastic material defined by a sliding without separation interface with the brain in order to represent its relative movement with respect to the skull. The confrontations with experimental tests made on cadaver’s head confirm the model prediction. An accident reconstruction methodology has been developed. It is based on kinematics reconstruction, experimental reconstruction of the vehicle’s collision, multibody simulation of the second collision and study of the internal head response with the head model. This reconstruction approach is then validated on a real automotive accident. Furthermore, the development of a generic model applied to motorcycle accidents is also analysed. From the results of the automotive accident reconstruction, the intercerebral contusion observed has been bridged to a particular time duration of a certain level of von Mises stresses

Athletes competing in the unarmed combat sport of mixed martial arts (MMA) are at an increased risk for long-term neurological consequences due to repetitive head trauma. Mass differentials as well as reported differences in fight styles between Lightweight and Heavyweight fighters in MMA may affect head impact kinematics creating different levels of head injury risk. Factors that influence the risk for head injury include the frequency, magnitude and interval of head impacts. The purpose of this study was to compare differences in frequency, frequency distribution of impact magnitudes, and time interval between head impacts per match between Lightweight and Heavyweight fighters in the Ultimate Fighting Championship (UFC). Head impacts of 60 fighters were documented from 15 Lightweight and 15 Heavyweight MMA fight videos. Impact type, frequency, and interval were recorded for each fighter, followed by the reconstruction of 345 exemplar impacts in the laboratory using a Hybrid III headform and finite element modeling to determine impact magnitudes. Next, head impacts (punches, kicks, knees and elbows) from fight videos were visually estimated to determine their corresponding magnitude range and establish the frequency distribution of impact magnitudes. The study revealed no significant differences in overall impact frequency and interval between Lightweight and Heavyweight fighters. The frequency distribution of different impact magnitudes was significantly different, with Lightweights sustaining significantly more Very Low, and High magnitude impacts. Overall, both Lightweight and Heavyweight MMA fighters sustain similar impact characteristics as other high-risk athletes including professional boxers and football players. Understanding the different factors that create brain trauma allows for the monitoring, identification, and protection of higher-risk athletes within these two weight classes.

Unintentional injuries present a major threat to the health and welfare of humans. Over 120,000 deaths and over 30,000,000 non-fatal injuries are estimated annually in the United States. The leading causes of nonfatal injuries vary with age, but falls, motor vehicle collisions (occupants), and being struck by or against are among the top 4 leading causes of unintentional injury for all ages. The loading mechanism that cause forces to be transmitted to the body during these events can cause a wide assortment of injury types with a range of severities. Understanding the biomechanical response to loading in these environments can facilitate efforts in injury mitigation. Biomechanical responses can be quantified by performing controlled laboratory experiments with human volunteers and surrogates, such as anthropomorphic test devices (ATDs) and post mortem human surrogates (PMHSs). The overall objective of this dissertation is to quantify the biomechanical response to loading regimes present in motor vehicle collisions, falls, and when being struck by or against an object using human volunteers and surrogates. Specifically, the research will achieve the following: quantify the dynamic responses of human volunteers, Hybrid III ATD, and PMHSs in low-speed frontal sled tests; quantify the neck response of human volunteers and PMHSs in low-speed frontal sled tests; quantify the kinetic and kinematic responses of PMHSs and the Hybrid III ATD in high-speed frontal sled tests; characterize thoracic loading as a result of same level falls using a Hybrid III ATD; and quantify the ability of children to swing sword-like toys and the human kinematic response that could be anticipated as a result of forceful impact using a Hybrid III 6-year old head and neck.
Ph. D.

Les études statistiques d'accidents montrent que la tête est le segment corporel le plus vulnérable lors d'un accident (chocs piétons, chocs deux-roues et chocs latéraux). Pour enrichir les modèles virtuels d'être humain et développer de nouveaux outils de prédictions lésionnelles, ce travail propose une série d'expérimentations afin d'obtenir les propriétés mécaniques homogénéisées de l'os du crâne humain (pas de distinction entre l'os cortical et spongieux).
Des essais ont été réalisés sur 20 SHPM (Sujet Humain Post Mortem) « frais ». Un protocole spécifique a été développé afin de prélever 19 éprouvettes par crâne. Au total, 380 échantillons ont été testés en flexion trois points. Les courbes effort/déplacement ont servi de référence pour l'identification du comportement élastique. De nombreuses relations par zones et orientations osseuses ont été obtenues.
Des essais de cyclage dans la zone élastique ont été réalisés sur 105 échantillons prélevés sur 7 SHPM congelés. L'effet de la vitesse de sollicitation a été étudié. Cette seconde campagne permet de comparer les éprouvettes en fonction de leur mode de conservation. Une corrélation a été mise en évidence et a permis d'extrapoler le module d'élasticité à l'état « frais » d'un SHPM testé congelé.
Ces deux campagnes d'essais ont permis d'aboutir à une corrélation entre le module d'élasticité équivalent et les propriétés géométriques (épaisseur et densité) d'un SHPM « frais ».
Les derniers travaux ont porté sur le développement d'un nouveau prototype de tête. Pour cela, 7 calottes, provenant de SHPM congelés, ont été testées en compression. Les propriétés élastiques du prototype sont issues des campagnes expérimentales précédentes et présentent une distinction entre chaque zone. Ce prototype a été validé par des essais statiques et dynamiques en compression dans différentes zones osseuses.

Every year in the United States, an estimated 1.6 to 3.8 million people sustain sports-related traumatic brain injuries (TBIs), with an appreciable number of these injuries coming from the sport of softball. Several studies have analyzed the impact performance of catcher’s masks within the context of baseball; however, virtually no studies have been performed on fielder’s masks within the context of softball. Thus, the main objective of the present work was to evaluate the protective capabilities of softball fielder’s masks. To better understand the injury mechanisms and frequency associated with softball head/facial injuries, epidemiological data from a national database was reviewed first. Results displayed “struck-by-ball” as the most frequent injury mechanism (74.3%) for all head/facial injuries with a large majority occurring to defensive players (83.7%). With further motivation, the present work focused on testing the impact attenuation and facial protection capabilities of fielder’s masks from softball impacts. Testing with an instrumented Hybrid III headform was conducted at two speeds and four impact locations for several protective conditions: six fielder’s masks, one catcher’s mask, and unprotected (no mask). The results showed that most fielder’s masks reduced head accelerations, but not to the standard of catcher’s masks. On average, they reduced peak linear and angular acceleration from 40-mph impacts by 36-49% and 14-45%, respectively, while for 60-mph impacts they were reduced by 25-42% and 13-46%, respectively. Plastic-frame fielder’s masks were observed to allow facial contact when struck at the nose region at high speed. Observed differences in impact attenuation across fielder’s mask designs further suggested influence from specific design features such as foam padding and frame properties. Overall, the results clearly demonstrate that head/facial injuries may be mitigated through the broader use of masks, while further optimization of impact attenuation for fielder’s masks is pursued.

Le perçage de l’os est couramment pratiqué dans de nombreux types de chirurgie comme lors de la pose de vis d’ostéosynthèse et d’implants dentaires et cochléaires. Lors de l'opération de perçage, le chargement thermomécanique dû à l'interaction outil-os peut endommager les tissus osseux au voisinage de la zone de perçage. Ainsi, une augmentation significative de la température peut provoquer une ostéonécrose thermique. Il est donc important d'optimiser les conditions opératoires (vitesses de rotation et d'avance, géométrie du foret, stratégie de perçage...) afin de réduire les risques d'endommagement de l'os. Pour ce faire, il faut analyser et comprendre les effets des conditions de coupe sur les mécanismes contrôlant l'interaction foret-os. Les travaux de cette thèse ont pour objectif de contribuer à la compréhension de ces mécanismes en combinant une approche expérimentale avec de la modélisation numérique et analytique. L'étude expérimentale porte sur l’effet de la vitesse de coupe, de l’avance du foret et de la microstructure de la zone percée sur l’évolution des efforts de coupe (l'effort d'avance et le moment axial) et de l’augmentation de la température pendant le perçage d’un échantillon d’os porcin et de matériaux de tests biomécaniques (Sawbones). Ces derniers présentent l'avantage d'une microstructure uniforme par échantillon donné contrairement à l'os. Les modèles numériques de la coupe orthogonale et du perçage de l’os cortical sont développés en utilisant le code Eléments Finis ABAQUS/Explicit. L’objectif est d'analyser l’influence des lois de comportement et d’endommagement sur les prédictions du modèle (mécanisme de coupe, température et efforts de coupe). Afin de proposer une approche simplifiée, une modélisation analytique basée sur la théorie de la source mobile a également été proposée. La validation expérimentale a montré la pertinence des approches proposées ainsi que leurs limites
Bone drilling is commonly practised in various surgical operations for orthosynthesis screws insertion or placement of dental and cochlear implants. During bone drilling procedure, the thermomechanical constraints resulting from the tool-bone interaction can damage the bone tissues in the vicinity of the drilling area. Thus, a significant increase in temperature can cause thermal osteonecrosis. It is therefore important to optimize the operating conditions (spindle speed and feed rate, geometry of the drill, drilling operation strategy ...) in order to reduce the risk of damage to bone tissues. To do this, it is necessary to analyse and understand the effects of cutting conditions on the mechanisms controlling the drill-bone interaction. The present work aims to contribute to the understanding of these mechanisms by combining an experimental approach with numerical and analytical modelling. The experimental study investigates the effect of the cutting speed, feed rate of the drill and the microstructure of the drilled area on the resulting cutting forces (thrust force and axial torque) and temperature rise during the drilling of porcine bone specimens and biomechanical test materials (Sawbones). These materials have the advantage of a uniform microstructure per given sample unlike bone. Numerical models of orthogonal cutting and bone drilling are implemented using the Finite Element code ABAQUS / Explicit. The purpose of this development is to analyse the influence of bone constitutive and damage laws on the model predictions (cutting mechanism, temperature and cutting forces). In order to propose a simplified approach, an analytical modelling based on moving heat source theory is developed for predicting bone thermal response. The relevance and limits of the approach proposed is shown through experimental validation

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.

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.

[ES] Las cargas de impacto son la fuente primaria de lesiones en la cabeza y pueden resultar en un rango de traumatismo desde leve hasta severo. Debido a la existencia de múltiples entornos en los que se pueden desencadenar lesiones por impacto (accidentes automovilísticos, deportes, caídas accidentales, violencia), éstas pueden afectar potencialmente a toda la población independientemente de su estado de salud. Pese al creciente esfuerzo en investigación para comprender la biomecánica de las lesiones por traumatismo en la cabeza, todavía no es del todo posible realizar predicciones precisas ni prevenir estos eventos. En esta Tesis, se han estudiado algunos aspectos del comportamiento ante impacto de los diferentes tejidos biológicos involucrados mediante el desarrollo de un modelo numérico de cabeza humana a partir de imágenes de tomografía computerizada (TAC). Se han realizado simulaciones en elementos finitos (EF) de ensayos experimentales de la literatura con el fin de validar el modelo numérico desarrollado, estableciendo unas propiedades mecánicas adecuadas para cada uno de sus constituyentes. De esta manera se puede adquirir una predicción adecuada del riesgo de sufrir daños. Parte de esta Tesis se centra en el entorno balístico, específicamente en cascos de combate antibalas, los cuales son susceptibles de causar traumatismo craneoencefálico debido a la elevada deformación que sufren durante el impacto. Previamente al estudio de estos fenómenos de alta velocidad, se han realizado ensayos experimentales y numéricos para caracterizar la respuesta mecánica de algunos materiales compuestos ante impacto de baja velocidad. Al principio de esta Tesis se ha realizado una revisión del estado del arte acerca de los criterios existentes para cuantificar el trauma craneoencefálico.Este es un aspecto clave para las simulaciones numéricas, ya que la idoneidad de algunos de estos criterios para la predicción de lesiones cerebrales todavía es un debate abierto. Mediante EF se han realizado simulaciones de impactos balísticos en una cabeza protegida con un casco de combate. Mediante la posterior aplicación de diferentes criterios de daño sobre los resultados obtenidos se ha evaluado el nivel de protección que aseguran los protocolos de aceptación de cascos de combate, así como las estrategias para determinar su tallaje. Se ha demostrado que las normativas existentes para cascos de combate son capaces de mitigar algunos mecanismos de trauma pero no logran prevenir otros como los gradientes de presión intracraneales. Además, se ha demostrado que algunas de las estrategias de tallaje más comúnmente adoptadas por los fabricantes, como producir un solo tamaño de calota, deberían ser reconsideradas ya que existe un mayor riesgo de traumatismo cuando la distancia entre la cabeza y la calota del casco no es suficiente. Siguiendo la línea de protecciones personales, algunos de los materiales compuestos comúnmente empleados en la industria armamentística se han combinado para crear distintas configuraciones de calota para optimizar la relación entre peso del casco y protección para la cabeza. Materiales ligeros como el UHMWPE han resultado en un comportamiento menos eficiente que el de los apilados de tejido de aramida a la hora de limitar la BFD (deformación máxima en la calota del casco en la zona de impacto). Hacia el final de la Tesis se presenta un modelo numérico de cabeza humana detallado, que incluye treinta y tres de las estructuras anatómicas principales. Dicho modelo se ha desarrollado para la simulación de un accidente ecuestre en el que aparecen múltiples lesiones craneoencefálicas. Principalmente, se pretende establecer un criterio mecánico para predecir el hematoma subdural (HS) basado en la ruptura de los vasos sanguíneos intracraneales. Se ha propuesto un valor umbral de ruptura en tensiones de 3.5 MPa, pero tanto este límite como la localización del vaso dañado son altamen
[CAT] Les càrregues d'impacte son la font primària de lesions al cap i poden resultar en un rang de severitat des de lleu a greu. Degut als múltiples entorns en que poden desencadenar-se lesions per impacte (accidents automobilístics, esports, caigudes accidentals, violència), aquestes poden afectar potencialment a tota la població independentment del seu estat de salut. Malgrat el creixent esforç en investigació per comprendre la biomecànica de les lesions per traumatisme al cap, encara no és del tot possible realitzar prediccions precises ni prevenir aquestos esdeveniments. En aquesta Tesi, s'han estudiat alguns aspectes del comportament a impacte dels diferents teixits biològics involucrats mitjançant el desenvolupament d'un model numèric de cap humà a partir d'imatges de tomografia computeritzada (TAC). S'han realitzat simulacions en elements finits (EF) d'assajos experimentals de la literatura amb la finalitat de validar el model numèric desenvolupat, establint unes propietats mecàniques adequades per a cadascun dels seus constituents. D'aquesta manera es pot aconseguir una predicció del risc de sofrir danys traumàtics. Part d'aquesta Tesi es centra en l'entorn balístic, específicament en cascs de combat antibales, els quals són susceptibles de causar traumatisme degut a l'elevada deformació que sofrixen durant l'impacte. Previament a l'estudi d'aquests fenòmens d'alta velocitat, s'han realitzat assajos experimentals i numèrics per a caracteritzar la resposta mecànica d'alguns materials compostos en condicions d'impacte a baixa velocitat. Al començament d'aquesta Tesi s'ha realitzat una revisió de l'estat de l'art sobre els criteris existents per quantificar el trauma cranioencefàlic. Aquest és un aspecte clau per a les simulacions numèriques, ja que l'utilitat d'alguns d'aquestos criteris per a la predicció de lesions cerebrals és encara un debat obert. Mitjançant EF s'han realitzat simulacions numèriques d'impactes balístics en un cap protegit amb un casc de combat. Gràcies a la posterior aplicació de diferents criteris de dany sobre els resultats obtinguts s'ha evaluat el nivell de protecció que asseguren els protocols d'acceptació de cascs de combat, així com les estratègies per a determinar les seues talles. S'ha demostrat que les normatives existents són capaces de mitigar alguns mecanismes de trauma però no aconseguixen prevenir altres com els gradients de pressions intracranials. A més, s'ha demostrat que algunes estratègies per determinar les talles més comunament adoptades pels fabricants (com produir només un tamany de calota i adaptar el gruix de les escumes interiors a les diferents dimensions dels subjectes) haurien de ser reconsiderades ja que existeix un major risc de traumatisme quan la distància entre el cap i la calota del casc no és suficient. Seguint la línia de proteccions personals, alguns dels materials compostos comunament utilitzats en la indústria de l'armament s'han combinat per a crear distintes possibles configuracions de calota amb la finalitat d'optimitzar la relació entre pes i protecció. Materials lleugers com l'UHMWPE han resultat en un comportament menys eficient que el d'apilats de teixit d'aramida a l'hora de limitar la BFD (deformació màxima a la calota del casc a la zona d'impacte). Cap al final de la Tesi es presenta un model numèric detallat de cap humà, que inclou trenta-tres de les estructures anatòmiques principals. Aquest model s'ha desenvolupat per a la simulació d'un accident eqüestre en el qual apareixen múltiples lesions cranioencefàliques. Principalment, es pretén establir un criteri mecànic per a la predicció de l'hematoma subdural (HS) basat en la ruptura dels vasos sanguinis intracranials. S'ha proposat un valor umbral de ruptura en tensions de 3.5 MPa, pero tant aquest límit com la ubicació del vas danyat són altament dependents de l'anatomia específica de cada subjecte.
[EN] Impact loading is the primary source of head injuries and can result in a range of trauma from mild to severe. Because of the multiple environments in which impact-related injuries can take place (automotive accidents, sports, accidental falls, violence), they can potentially affect the entire population regardless of their health conditions. Despite the increasing research effort on the understanding of head impact biomechanics, accurate prediction and prevention of traumatic injuries has not been completely achieved. In this Thesis, some aspects of the impact behaviour of the different biological tissues involved have been analysed through the development of a numerical human head model from Computed Tomography (CT) images. FE simulations of experimental tests from the literature have been performed and enhanced the validation of the head model through the establishment of proper material laws for its constituents, which enable adequate prediction of injury risks. Part of this Thesis focuses on the ballistic environment, especifically in bulletproof composite helmets, which are susceptible to cause blunt injuries to the head because of their large deformation during impact. Prior to the study of these high-speed impacts, experimental tests and finite element (FE) models have been performed to characterise the mechanical response of composite materials subjected to low velocity impact. The implementation of a continuum damage mechanics approach coupled to a Hashin failure criterion and surface-to-surface cohesive relations to the numerical model provided a good matching with the impact behaviour obtained experimentally, capturing the principal damage mechanisms. A review of the head injury criteria currently available in the literature has been performed at the beginning of this Thesis. This is a key issue for the numerical simulations, as the suitability of some criteria to predict head injuries is still an open question. Numerical simulation of ballistic impacts on a human head protected with a combat helmet has been conducted employing explicit FE analysis. The level of protection ensured by helmet acceptance protocols as well as their sizing strategies have been studied and discussed by means of the application of different mechanical-based head injury criteria. It has been demonstrated that current helmet testing standards do mitigate some specific forms of head trauma but fail to prevent other injury mechanisms such as the intracranial pressure gradients within the skull. Furthermore, it has been demonstrated that some well-established helmet sizing policies like manufacturing one single composite shell and adapting the thickness of the interior pads to the different head dimensions should be reconsidered, as there is a great risk of head injury when the distance between the head and the helmet shell (stand-off distance) is not sufficient. Following the line of personal protections, some composite materials commonly employed in the soft body armour industry have been combined into different helmet shells configurations to optimise the ratio of weight-to-head protection. Light materials like UHMWPE appear to be less efficient than integral woven-aramid lay-ups in the limitation of the backface deformation (BFD), the maximum deformation sustained by the helmet at the impact site. A detailed head numerical model including thirty-three of its main anatomical structures has been developed for the simulation of an equestrian accident that resulted in many head injuries. Above all, the establishment of a mechanical criterion for the prediction of subdural hematona (SDH) based on the rupture of the head blood vessels is intended. A stress threshold for vein rupture has been set on 3.5 MPa, but both this limit and the location of vessel failure are highly dependent on the specific anatomy of the subject's vascularity.
Palomar Toledano, M. (2019). Assessment of head injury risk caused by impact using finite element models [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135254
TESIS

The overall goal of my research was to advance our understanding of the potential for novel compliant flooring systems to reduce the risk for fall-related injuries in older adults, including fall-related traumatic brain injury (TBI). This entailed an assessment of how these floors affect the competing demands of fall-related TBI – impact severity attenuation in concert with minimal concomitant impairments to balance control and postural stability. Two studies are included as part of this thesis. The first study used a mechanical drop tower to assess the effects of four traditional flooring systems and six novel compliant flooring conditions on the impact dynamics of a surrogate headform during the impact phase of simulated ‘worst- case’ head impacts. The second study entailed an assessment of the effect of two traditional and three novel compliant floors on the initial phase of the compensatory balance reactions of older adult men and women living in a residential-care facility environment following an externally induced perturbation using a tether-release paradigm. Overall, this thesis demonstrates that novel compliant floors substantially attenuate the forces and accelerations applied to the head during simulated worst- case impacts when compared to traditional flooring surfaces such as vinyl and carpet with underpadding. These benefits are achieved without compromising indices of balance control, supported by the finding that parameters characterizing early compensatory balance reactions were unaffected by the novel compliant floors tested. This work supports the introduction of pilot installations of novel compliant flooring systems into environments with high incidences of falls to test their effectiveness at reducing fall-related injuries in clinical settings.

碩士
國立中興大學
生物產業機電工程學系
93
Among all the car accidents, the rear-end impact commonly happens and the whiplash injuries to head or neck tends to be the most frequent cases. However, there is still much clinical controversy over such whiplash injuries caused by whiplash effect. In this study, the software ADAMS and LifeMOD are used to establish the model of human head, neck and up-torso. By using this model, it was to simulate rear-end impact and observed the biomechanics analysis in the whiplash effect to cervical spine and the soft tissues of human neck. The result showed that in the initial stage, the flexion occurred in the upper cervical spine and extension in the lower cervical spine. Meanwhile, the cervical spine first formed an S-shaped curve and then bended back totally to forms a C-shaped curve. The maximum horizontal acceleration of head was 1.5 times of the impacted one and arose later during the whiplash effect. Besides, the results in analysis of facet joint showed that when the impact acceleration reached over 7g, the cervical spine might hurt itself because the rotation angle surpassed the physiological value. In the intervertebral disk research, the human head activities which caused cervical spine transformation have contributed to main factor of neck injuries. Apparently, all these testified the accuracy of the established human models by comparing to relative experiments. Upcoming, it will present the whiplash effect more clearly through the establishment of muscles on the model and benefit a lot to clinical diagnosis and injury prevention.

Mechanical trauma to the brain, both big and small, and the method to protect the brain in its presence is a crucial field of research given the large population exposed to neuronal trauma daily and the benefit available through better understanding and injury prevention. A population of particular interest and risk are youth athletes in contact sports due to large accelerations they expose themselves to and their developing brains. To better monitor the risk these athletes are exposed to, their accumulation of head acceleration events (HAEs), a measure correlated with harmful neurological changes, was tracked over sport seasons. It was observed that few significant differences in HAEs accumulated existed between players of ages from middle school to high school, but there did exist a difference between sports with girls' soccer players accumulating fewer HAEs than football players. This highlights to risk youth athletes are exposed to and the importance of improved technique and individual player size. To better monitor HAEs for each individual, a novel head segmentation program was developed that extracts player specific geometries from a single T1 MRI scan that can improve the accuracy of HAE monitoring. Acceleration measures processed with individualized head model versus those using a standardized head model typically displayed higher accelerations, highlighting the need for individualized measure for accurate monitoring of HAEs and risk of neurological changes. In addition to the large accelerations present in contact sports, the small but constant strains produced by neural implants embedded in the brain is also an important field of neuro-mechanical research as the physical properties of neural implants have been found to contribute to the chronic immune response, a major factor preventing the widespread implementation of neural implants. To reduce the severity of the immune response and provide improved chronic functionality, researchers have varied neural implant design and materials, finding general trends but not precise relationships between the design factors and how they contribute the mechanical strain in the brain. Performing a large series of mechanical simulations and Cotter's sensitivity analyses, the relationships between neural design factors and the stain they produce in the brain was examined. It was found that the direction which neural implants are loaded contributes the most to the strain produced in the brain followed by the degree of bonding between the brain and the electrode. Directly related to the design of electrodes themselves, it was found that in most cases reducing the cross-sectional area of the probe resulted in a larger decrease of mechanical strain compared to softening the implant. Finally, a study was performed quantifying the resting micromotion of the brain utilizing a novel method of soft tissue micromotion measurement via microCT, applicable within the skull and the throughout the rest of the body.