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Author: David Bruneau
Publisher:
ISBN:
Category : Biomechanics
Languages : en
Pages : 159
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Book Description
Among high school and college athletes, ~50% of American football players report a concussion each year, and at least 30% of players sustain more than one concussion per year, which may be reduced in part through improvements in head protection. Football helmets are commonly assessed experimentally using a linear impactor test, where a helmet is donned on a Hybrid III Anthropometric Testing Device (ATD) head and neck affixed to a sliding carriage, and is struck by a deformable impactor. The biofidelity of the Hybrid III ATD is known to have some limitations: the ATD was developed to predict anterior-posterior response while the current test includes multi-directional loading, and the passive neck structure does not simulate active muscle. Additionally, the linear impactor test does not include the body of the player, which may influence the head response. The current study used an advanced Human Body Model (HBM) combined with a validated finite element model of a modern football helmet to assess the importance of the aforementioned limitations, and was then extended to investigate the response of the brain to impact scenarios. A virtual evaluation tool provides the advantage of assessing changes to current helmet designs, and new helmet designs prior to the construction of a physical prototype. An existing ATD head and neck model validated in the linear impact configuration, and a validated football helmet model previously assessed with 60 impact cases, were used as a baseline for the assessment of head response in football impact scenarios. The Global Human Body Models Consortium (GHBMC) head and neck model (HNM) and Full Human Body Model (FBM) were integrated with the helmet and linear impactor, and assessed using the same boundary conditions as the ATD. The HNM allowed for the investigation of muscle activation, using a muscle activation scheme representing a player braced for impact, and a baseline case with no activation. The models were used in three studies to assess: (1) the kinematic response of the ATD and HNM, (2) the effect of ATD and HNM boundary conditions on brain response, and (3) the role of the whole body mass and inertia on head and brain response. The first study compared the head kinematics of the HNM to those of the ATD simulation using the boundary conditions of the linear impactor test. It was found that the HNM and ATD had similar head acceleration and angular velocity in the primary direction of impact, and exhibited similar responses regardless of muscle activation. Differences between the ATD and HNM were identified in the axial head acceleration, attributed to axial neck stiffness, and longer term metrics measured at the base of the neck differed but did not have a large effect on the short-term head response assessed using existing head response metrics (HIC, BrIC, HIP). In the second study, two boundary conditions were investigated for a head FE model: (1) a commonly-used simplified boundary condition where head model kinematics are prescribed from experimentally measured ATD kinematics and (2) a full simulation of the HNM, helmet and linear impactor. The second approach enables the opportunity to assess the effect of modifications to the helmet. While the lateral and rear impacts exhibited similar levels of Maximum Principal Strain (MPS) in the brain tissue using both the prescribed kinematics and simulated HNM boundary condition, differences were noted in the frontal orientation (MPS varied by
Author: David Bruneau
Publisher:
ISBN:
Category : Biomechanics
Languages : en
Pages : 159
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Book Description
Among high school and college athletes, ~50% of American football players report a concussion each year, and at least 30% of players sustain more than one concussion per year, which may be reduced in part through improvements in head protection. Football helmets are commonly assessed experimentally using a linear impactor test, where a helmet is donned on a Hybrid III Anthropometric Testing Device (ATD) head and neck affixed to a sliding carriage, and is struck by a deformable impactor. The biofidelity of the Hybrid III ATD is known to have some limitations: the ATD was developed to predict anterior-posterior response while the current test includes multi-directional loading, and the passive neck structure does not simulate active muscle. Additionally, the linear impactor test does not include the body of the player, which may influence the head response. The current study used an advanced Human Body Model (HBM) combined with a validated finite element model of a modern football helmet to assess the importance of the aforementioned limitations, and was then extended to investigate the response of the brain to impact scenarios. A virtual evaluation tool provides the advantage of assessing changes to current helmet designs, and new helmet designs prior to the construction of a physical prototype. An existing ATD head and neck model validated in the linear impact configuration, and a validated football helmet model previously assessed with 60 impact cases, were used as a baseline for the assessment of head response in football impact scenarios. The Global Human Body Models Consortium (GHBMC) head and neck model (HNM) and Full Human Body Model (FBM) were integrated with the helmet and linear impactor, and assessed using the same boundary conditions as the ATD. The HNM allowed for the investigation of muscle activation, using a muscle activation scheme representing a player braced for impact, and a baseline case with no activation. The models were used in three studies to assess: (1) the kinematic response of the ATD and HNM, (2) the effect of ATD and HNM boundary conditions on brain response, and (3) the role of the whole body mass and inertia on head and brain response. The first study compared the head kinematics of the HNM to those of the ATD simulation using the boundary conditions of the linear impactor test. It was found that the HNM and ATD had similar head acceleration and angular velocity in the primary direction of impact, and exhibited similar responses regardless of muscle activation. Differences between the ATD and HNM were identified in the axial head acceleration, attributed to axial neck stiffness, and longer term metrics measured at the base of the neck differed but did not have a large effect on the short-term head response assessed using existing head response metrics (HIC, BrIC, HIP). In the second study, two boundary conditions were investigated for a head FE model: (1) a commonly-used simplified boundary condition where head model kinematics are prescribed from experimentally measured ATD kinematics and (2) a full simulation of the HNM, helmet and linear impactor. The second approach enables the opportunity to assess the effect of modifications to the helmet. While the lateral and rear impacts exhibited similar levels of Maximum Principal Strain (MPS) in the brain tissue using both the prescribed kinematics and simulated HNM boundary condition, differences were noted in the frontal orientation (MPS varied by
Author: Timothy Darling
Publisher:
ISBN:
Category : Brain
Languages : en
Pages : 63
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Book Description
The football helmet is a device used to help mitigate the occurrence of impact-related traumatic (TBI) and minor traumatic brain injuries (mTBI) in the game of American football. The current design methodology of using a hard shell with an energy absorbing liner may be adequate for minimizing TBI, however it has had less effect in minimizing mTBI. The latest research in brain injury mechanisms has established that the current design methodology has produced a helmet to reduce linear acceleration of the head. However, angular accelerations also have an adverse effect on the brain response, and must be investigated as a contributor of brain injury. To help better understand how the football helmet design features effect the brain response during impact, this research develops a validated football helmet model and couples it with a full LS-DYNA human body model developed by the Global Human Body Modeling Consortium (v4.1.1). The human body model is a conglomeration of several validated models of different sections of the body. Of particular interest for this research is the Wayne State University Head Injury Model for modeling the brain. These human body models were validated using a combination of cadaveric and animal studies. In this study, the football helmet was validated by laboratory testing using drop tests on the crown of the helmet. By coupling the two models into one finite element model, the brain response to impact loads caused by helmet design features can be investigated. In the present research, LS-DYNA is used to study a helmet crown impact with a rigid steel plate so as to obtain the strain-rate, strain, and stress experienced in the corpus callosum, midbrain, and brain stem as these anatomical regions are areas of concern with respect to mTBI.
Author: Tate Russell Fonville
Publisher:
ISBN:
Category : Brain
Languages : en
Pages : 0
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Book Description
The objective of this research was to present a model for brain damage to investigate the head’s response to mechanical loadings. A Finite Element (FE) head and brain mesh used throughout this dissertation was constructed from Magnetic Resonance Imaging (MRI) scan data of one of the authors and validated in previous research. A computational modal analysis was first conducted on the whole head and an isolated brain to identify the resonant frequencies, mode shapes, and locations. A physics-based Internal State Variable (ISV) constitutive model for polymers was modified to include damage in the form of pore growth. The brain damage model was developed to capture pore growth influenced by both tensile pressure and shear strains. The damage model constants were calibrated to match intermediate strain rate (50 s-1) compression tests done on fresh porcine brain samples. The calibrated brain damage model was then used to evaluate the relationship between impact, brain pressure, brain strain, and damage using a 2D model of a helmeted head. The same boundary conditions were then applied to a 3D model of a helmeted head to study the differences in responses between 2D and 3D. Finally, a sensitivity analysis was conducted to study the influence of impact location, impact velocity, helmet shell material, helmet facemask material, helmet foam liner classification, and helmet foam liner general stiffness level. Both impact studies were carried out at low and high velocities intending to replicate a range of common impact magnitudes experienced by both linemen and skill positions. Based on the findings presented in this dissertation, a deeper understanding of brain damage resulting from head impacts is useful to help designers engineer safer helmet equipment.
Author: David Koncan
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Concussions are injuries that can result in debilitating symptoms, suffered by people of all ages, with children being at elevated risk for injury. Falls account for over 20% of head injuries worldwide, and up to 50% of concussive injuries in children. Following a concussion, children typically take longer for symptoms to resolve compared to adults. It is unknown whether or not children are more, less, or equally susceptible to concussive injury based on the mechanical response, with researchers divided on the subject. There is currently a paucity of published data for concussive injuries in children, with few studies investigating impact biomechanics and strain response in the brain using FE models. Those that exist typically rely on scaled adult models that do not capture age-dependent geometric properties, material properties of tissues, and the developmental stage of the brain reflected by the patterns of grey and white matter within the brain. Newer child models are being developed, however at present they are focused on car crash investigations that do not offer an accurate reflection of sports-related impacts, and those that could be experienced from day-to-day activities since impact characteristics (e.g. magnitude, duration, surface compliance) differ largely between these types of events. Strain magnitudes differ between events causing concussion in adults (falls, collisions, punches, and projectiles), so it follows that the unique impact characteristics of car crash events do not typically coincide with those associated with sports impacts. Car crash events can result in much longer impact durations compared to sporting impacts (100 ms duration in car crashes vs. 5-30 ms in sports impacts). The purpose of this thesis was to assess how the mechanical response of the brain in young children near 6 years old differs from an adult brain in cases resulting in concussive injury for sports impacts. Study one created a novel FE model of a 6-year-old brain, using medical images to extract an accurate representation of the geometry and tissues inside the head of a 6-year-old child. The developmental stage of the younger brain was captured using a highly-refined mesh to accurately represent the folds of white matter within the cerebrum. With no intracranial data for child cadavers available, published data of adult cadavers was used to validate the brain motion from impacts. Comparisons were made to a scaled adult model to highlight how the different model constructions influence brain motion and resulting strains. The new model showed higher correlation to the cadaver data compared to the scaled model, and yielded "good biofidelity" measures when assessed using a modified version of the normalized integral square error method. For young children, the new model was proposed to be more appropriate for concussion investigations as it captures age-appropriate geometry, material properties, and developmental stage of the brain, reflected in the patterns and volumes of grey and white matter within the brain. Study two tested the model for sensitivity across three levels of surface compliance and impact velocity consistent with sport impact events, and compared strain responses to a scaled adult model. The 6-year-old model showed unique strain responses compared to the scaled adult model with peak strains being lower across most impact events. Strain patterns also differed between models, with less strain being transmitted into the white matter in the 6-year-old model. Low compliance impacts yielded highest differences in strains (3̃0%), moderate compliance impacts yielded more similar strains (9̃% lower), with high compliance impacts showing a location dependent response with frontal impacts being 14% lower, and side impacts being 9% higher than the scaled model. The sensitivity study characterized the model responses, allowing for better comparisons between the two different model constructions. Study three then compared the strain responses of reconstructed real-world concussive events for both children and adults. Forty cases of concussion from falls in children and adults (20 children aged 5-7, 20 adults) were reconstructed using physical models, with the measured impact kinematics used to load the FE models. Concussive cases of children showed lower strains than adults, finding a velocity driven relationship since the child concussions occurred at lower impact velocities compared to the adults. Lower peak strains, as well as cumulative strains in the child cases suggest that children are vulnerable to concussion at lower strain compared to adults. Protective strategies for children should address this vulnerability, no longer relying on product scaling to create head protection for youth.
Author: Derek Wallin
Publisher:
ISBN:
Category :
Languages : en
Pages : 63
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Book Description
Football helmets worn today are primarily designed to prevent skull fracture and irreversible brain injury. In that limited respect, today’s helmets are a success with the frequency of reported football-related skull fracture a rare occurrence. In recent decades, however, concussion, mild traumatic brain injury (mTBI), and chronic traumatic encephalopathy (CTE) are being reported with increasing incidence. Helmet manufacturing companies are limited in their performance analysis of helmets, with no standard helmet testing procedures incorporating anatomical data or physiological weaknesses of the brain. Finite Element Modeling of the brain has allowed for analysis of the mechanics of brain injury and can provide injury metrics based on simulated brain injury. In this study the background on current helmet testing procedures is provided as well as a finite element study of brain injury to determine helmet performance. In addition, this modeling will be used to identify what types of impacts are most dangerous.
Author: Anna Marie Dulaney
Publisher:
ISBN:
Category :
Languages : en
Pages : 89
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Book Description
A finite element model was developed for a range of human head-sUAS impacts to provide multiple case scenarios of impact severity at two response regions of interest: global and local. The hypothesis was that for certain impact scenarios, local response injuries of the brain (frontal, parietal, occipital, temporal lobes, and cerebellum) have a higher severity level compared to global response injury, the response at the Center of Gravity (CG) of the head. This study is the first one to predict and quantify the influence of impact parameters such as impact velocity, location, offset, and angle of impact to severity of injury. The findings show that an sUAS has the potential of causing minimal harm under certain impact scenarios, while other scenarios cause fatal injuries. Additionally, results indicate that the human head’s global response as a less viable response region of interest when measuring injury severity for clinical diagnosis. It is hoped that the results from this research can be useful to assist decision making for treatments and may offer different perspectives in sUAS designs or operation environments.
Author: Janie Cournoyer
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The severity of injury associated with sport concussions that present with a loss of consciousness or impact seizures is ambiguous. A disconnect between the clinical and biomechanical aspect can be observed throughout the literature pertaining to loss of consciousness and impact seizures. Clinicians have dismissed a loss of consciousness or the presence of impact seizures as an indicator of severity. However, early biomechanical research suggests that loss of consciousness is caused by greater magnitudes of impacts and damage to more vulnerable brain regions. However, this research was conducted on animal and cadaver models and may not adequately represent sport-related concussions. Recent methodologies such as laboratory reconstructions of head impacts and finite element modeling can provide new information on the severity of impact associated with these signs of concussions. Study One compared the magnitudes of head dynamic response and brain tissue deformation between impact representations of punches that lead or do not lead to LOC in boxing. The main findings of this study revealed knockout punches were the result of by unprotected hooks to the mandibular angle resulting in greater brain tissue trauma. Study Two compared cases of concussions with and without LOC in American football. Head dynamic response and brain tissue deformation was also greater in the LOC group in this sport, consistent with boxing impacts. The main predictor of LOC was found to be impact velocity which has implications in terms of prevention. Study Three compared the magnitudes of head dynamic response and brain tissue deformation between cases of concussions with a loss of consciousness and cases of concussion with impact seizures in American football. The two types of clinical presentations had similar severities of brain tissue deformation with the exception of strain rate in the white matter being smaller in cases of impact seizures. The findings of this thesis support the notion that concussions with loss of consciousness or impact seizure represent a more severe injury than concussions without these signs. It may be appropriate to address these signs of injury differently in return to sport protocols to reflect their severity. The findings also suggests that prevention of loss of consciousness should be sport specific. Hooks to the side of the jaw were the primary cause in boxing, whereas LOC could be caused by different event types in American football. However, in both sports, impact velocity and impact location played an important role in the risk for loss of consciousness.
Author: David Bradford Stark
Publisher:
ISBN:
Category : Brain
Languages : en
Pages : 323
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Book Description
While concussions are a mild brain injury with a large prevalence, drone, or UAS head impacts pose a risk for more traumatic head injuries but currently have a low prevalence. However, the rate of drone impacts is likely to increase as the industry is expanding at a rapid rate and benefits associated with drone use are driving new federal regulations which would allow for more widespread UAS flights over people. Before UAS flight over people is made legal, the risk of human injury due to UAS impacts must be quantified and understood. For this work, UAS head impacts were carried out on post-mortem human surrogates (PMHS) (i.e. cadavers) and the Hybrid III ATD. PMHS impacts were used to assess the likelihood of injury resulting from UAS impacts, while ATD tests were compared to matched PMHS data to assess how well the ATD replicates human response in this new impact scenario. The study’s main conclusions were that serious head injuries are possible as a result of UAS impacts and additional investigation is required to determine appropriate injury criteria for use in predicting the severity of head injuries in UAS impact cases. Additionally, the ATD response did not replicate that of the PMHS, specifically in angled or vertical impacts; thus, caution should be exercised when using the Hybrid III ATD to assess the risk of injury in UAS impact scenarios.
Author: Society of Automotive Engineers
Publisher: SAE International
ISBN:
Category : Science
Languages : en
Pages : 158
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Book Description
Thirteen papers from the biomechanics technical sessions of the 2002 SAE congress use laboratory experiments, computer models, and field data to evaluate the human body's kinematics, kinetics, and injury potential in response to impact loads caused by automobile accidents. Topics include finite elem
Author: Danielle N. George
Publisher:
ISBN: 9781423525363
Category :
Languages : en
Pages : 106
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Book Description
The objective of this study is to develop a finite element model of the human head and neck to investigate the biomechanics of head injury. The finite element model is a two-dimensional, plane strain representation of the cervical spine, skull, and major components of the brain including the cerebrum, cerebellum, brain stem, tentorium and the surrounding cerebral spinal fluid. The dynamic response of the model is validated by comparison with the results of human volunteer sled acceleration experiments conducted by Ewing et al. 10 . To validate the head model, one of the head impact experiments performed on cadavers by Nahum et al. 24, is simulated. The model responses are compared with the measured cadaveric test data in terms of head acceleration, and intracranial pressures measured at four locations including the coup and contrecoup sites. The validated model is used to demonstrate that the Head Injury Criterion (HIC), which is based on resultant translational acceleration of the center of gravity of the head, does not relate to the various mechanisms of brain injury and is therefore insufficient in predicting brain injury.
