Headform Acceleration Research Articles

Radial and Oblique Impact Testing of Alpine Helmets onto Snow Surfaces

Recent studies have found that alpine helmets reduce the risk of focal injuries associated with radial impacts, which is likely due to current alpine helmet standards requiring helmets to be drop-tested on flat anvils with only linear acceleration pass criteria. There is a need to evaluate the performance of alpine helmets in more realistic impacts. The current study developed a method to assess the performance of alpine helmets for radial and oblique impacts on snow surfaces in a laboratory setting. Snow samples were collected from a groomed area of a ski slope. Radial impacts were performed as drop tests onto a stationary snow sample. Oblique impacts were performed as drop tests onto a snow sample moving horizontally. For radial impacts, snow sample collection time was found to significantly (p = 0.005) influence mean peak linear headform acceleration with an increase in ambient temperature softening the snow samples. For oblique tests, the recreational alpine sports helmet with a rotation-damping system (RDS) significantly (p = 0.002) reduced mean peak angular acceleration compared to the same helmets with no RDS by approximately 44%. The ski racing helmet also significantly (p = 0.006) reduced mean peak angular acceleration compared to the recreational alpine sports helmet with no RDS by approximately 33%, which was attributed to the smooth outer shell of the ski racing helmet. The current study helps to bridge the knowledge gap between real helmet impacts on alpine snow slopes and laboratory helmet impacts on rigid surfaces.

Efficacy of Softball Face Masks at Reducing Linear and Rotational Head Acceleration

This research study looked at the efficacy of infield softball face masks at reducing concussion risk. The primary goal of this research was to contrast head accelerations experienced during softball impacts for different brands of softball face masks. In order to achieve this goal, a surrogate headform equipped with different brands of face masks was impacted at a constant impact location and ball speed. The resulting headform accelerations (linear and rotational) were collected with a Vernier accelerometer upon each impact and analyzed. The results of the study showed that all tested brands of face masks were successful at reducing head acceleration severity. Moreover, significant differences in performance were observed between the different brands of face masks. One can conclude from this research that particular brands of face masks can more effectively reduce concussion risk because they better reduce head acceleration values. Due to the study results, softball players may have a better understanding of face mask performance, which could lead to higher mask implementation in the sport and an overall reduction in softball-related concussion occurrence.

Erratum: Mattacola et al. (2019).

In the article Mattacola CG, Quintana C, Crots J, Tumlin KI, and Bonin S, Repeated Impacts Diminish the Impact Performance of Equestrian Helmets, J Sport Rehabil, 2019;28(4):368–372, https://doi.org/10.1123/jsr.2018-0355, the Troxel helmet was not identified as a prototype. In each occurrence, it has been corrected to read Troxel-prototype. In addition, two sentences were added to the text: (1) “The Troxel helmet, according to the manufacturer, was a prototype with a lower density liner.” (see third sentence of Methods section); (2) “We did not quantify liner densities of the tested helmets and therefore did not explore the relationship between liner density and peak headform acceleration.” (see paragraph 2, sentence 10 of the Discussion section). These corrections have been made in the online version of the article. The authors regret this error.

Density Variation in the Expanded Polystyrene Foam of Bicycle Helmets and Its Influence on Impact Performance.

Bicycle helmets attenuate head impacts using expanded polystyrene (EPS) foam liners. The EPS density plays a key role in determining the helmet and head response during an impact. Prior pilot work in our lab showed that EPS density varied by up to 18 kg/m3 within a single helmet, and thus the purpose of this study was to quantify the regional density variations within and between helmets and to establish how these variations influence helmet impact performance. We evaluated 10-12 samples of two traditional and two bicycle motocross (BMX) bicycle helmets with EPS liners. The bulk liner density and density of 16-19 cores extracted from specific locations on each sample were measured. Additional samples of two of these helmet models were then impacted at 3.0, 6.3, and 7.8 m/s to determine the relationship between local EPS density and helmet impact performance. We found that density varied significantly within each sample in all helmet models and also varied significantly between samples in three helmet models. The density variations were not symmetric across the midline in two of the four helmet models. The observed density variations influenced the helmets' impact performance. Our data suggest that variations in peak headform acceleration during impacts to the same location on different samples of the same helmet model can be partially explained by density differences between helmet samples. These density variations and resulting impact performance differences may play a role in a helmet's ability to mitigate head injury.

Parametric study of impact parameters on peak head acceleration and strain for collision impacts in sport

Collisions are a common cause of concussions. The nature of a collision impact is governed by the velocity of the striking players and the body parts involved. The purpose of this study was to describe the effects of velocity, mass, surface stiffness and location on peak linear and angular acceleration and strain.A variable-mass pendulum fitted with simplified impact surfaces representing the stiffness of an unprotected head, a protected (helmet) and a well-padded (i.e. shoulder pad) condition were used to impact a Hybrid III headform at four locations and velocities. Headform accelerations were input into a finite-element model to approximate peak strain in the cerebrum.Stiffness was most influential on peak linear and angular acceleration, and strain was most influenced by velocity. Interaction effects demonstrated that the 9 kg mass had consistently higher peak linear and angular acceleration and strain than the 15 kg mass between 3.0 and 4.5 m/s. Mass and velocity interactions may have important implications for age and size related concussion risk.

Repeated Impacts Diminish the Impact Performance of Equestrian Helmets.

Context: During thoroughbred races, jockeys are placed in potentially injurious situations, often with inadequate safety equipment. Jockeys frequently sustain head injuries; therefore, it is important that they wear appropriately certified helmets. Objective: The goals of this study are (1)to perform impact attenuation testing according to ASTM F1163-15 on a sample of equestrian helmets commonly used by jockeys in the United States and (2)to quantify headform acceleration and residual crush after repeat impacts at the same location. Participants and Design: Seven helmet models underwent impact attenuation testing according to ASTM F1163-15. A second sample of each helmet model underwent repeat impacts at the crown location for a total of 4 impacts. Setting: Laboratory. Intervention: Each helmet was impacted against a flat and equestrian hazard anvil. Main Outcome Measures: Headform acceleration was recorded during all impact and computed tomography scans were performed preimpact and after impacts 1 and 4 on the crown to quantify liner thickness. Results: Four helmets had 1 impact that exceeded the limit of 300g. During the repeated crown impacts, acceleration remained below 300g for the first and second impacts for all helmets, while only one helmet remained below 300g for all impacts. Foam liner thickness was reduced between 5% and 39% after the first crown impact and between 33% and 70% after the fourth crown impact. Conclusions: All riders should wear a certified helmet and replace it after sustaining a head impact. Following an impact, expanded polystyrene liners compress, and their ability to attenuate head acceleration during subsequent impacts to the same location is reduced. Replacing an impacted helmet may reduce a rider's head injury risk.

Interaction of external head impact parameters on region and volume of strain for collisions in sport

Collisions with the head are the primary cause of concussion in contact sports. Head impacts can be further characterized by velocity, striking mass, compliance, and location (direction). The purpose of this study was to describe the interaction effects of these parameters on peak strain in four brain regions and the volume of strain for collision impacts. A pendulum test set-up was used to deliver impacts to an adult Hybrid III headform according to four levels of mass (3, 9, 15, and 21 kg), four velocities (1.5, 3.0, 4.5, and 6.0 m/s), two impact locations (through the centre of gravity and a non-centre of gravity), and three levels of compliance simulating unprotected, helmeted, and well-padded conditions in sport. Headform accelerations were input into a brain finite element model to obtain peak strain in the frontal, temporal, parietal, and occipital lobes and the volume of the brain experiencing 0.10, 0.15, 0.20, and 0.25 strains. Centre-of-gravity impacts created the highest strains (peak and volume) under low compliance and non-centre-of-gravity impacts produced greater strain responses under medium and high compliance conditions. The temporal lobe was the region that consistently displayed the highest peak strains, which may be due to the proximity of the impact locations to this region. Interactions between mass and velocity displayed effects where the 9-kg mass had higher peak and volumes of strain than the 15-kg mass at velocities of 3.0 and 4.5 m/s. This study demonstrates the important role of interacting impact parameters on increasing strain responses that are relevant to the spectrum of diffuse brain injuries, including concussion.

A review of laboratory methods and results used to evaluate protective headgear in American football

As head trauma becomes more firmly associated with American football, research has focused on improving the impact performance of protective headgear. Since helmet use became mandatory in 1939–1940, both helmet design and laboratory methods used to evaluate helmet impact performance have evolved. Through a comprehensive review of the literature, this article analyzes the impact results from laboratory evaluations of helmet performance, including a look at the evolution of protective headgear performance in football. In total, 35 separate studies conducted between 1975 and 2017 were used to examine current testing methodologies and reported impact results from headgear performance laboratory assessments. This review showed that the evolution in helmet design over the last 50 years has resulted in a decrease in linear and rotational acceleration of an impacted headform. The most common laboratory methods used to reconstruct football-specific head impacts included (1) linear drop methods, (2) pendulum methods, and (3) pneumatic ram methods. Each method provided greater understanding of helmet impact performance, helmet design, and use in football, with each method having specific limitations in the evaluation of protective headgear performance.

Combat Helmet Suspension System Stiffness Influences Linear Head Acceleration and White Matter Tissue Strains: Implications for Future Helmet Design.

Combat helmets are expected to protect the warfighter from a variety of blunt, blast, and ballistic threats. Their blunt impact performance is evaluated by measuring linear headform acceleration in drop tower tests, which may be indicative of skull fracture, but not necessarily brain injury. The current study leverages a blunt impact biomechanics model consisting of a head, neck, and helmet with a suspension system to predict how pad stiffness affects both (1) linear acceleration alone and (2) brain tissue response induced by both linear and rotational acceleration. The approach leverages diffusion tensor imaging information to estimate how pad stiffness influences white matter tissue strains, which may be representative of diffuse axonal injury. Simulation results demonstrate that a softer pad material reduces linear head accelerations for mild and moderate impact velocities, but a stiffer pad design minimizes linear head accelerations at high velocities. Conversely, white matter tract-oriented strains were found to be smallest with the softer pads at the severe impact velocity. The results demonstrate that the current helmet blunt impact testing standards' standalone measurement of linear acceleration does not always convey how the brain tissue responds to changes in helmet design. Consequently, future helmet testing should consider the brain's mechanical response when evaluating new designs.

A Test Bed to Examine Helmet Fit and Retention and Biomechanical Measures of Head and Neck Injury in Simulated Impact

Conventional wisdom and the language in international helmet testing and certification standards suggest that appropriate helmet fit and retention during an impact are important factors in protecting the helmet wearer from impact-induced injury. This manuscript aims to investigate impact-induced injury mechanisms in different helmet fit scenarios through analysis of simulated helmeted impacts with an anthropometric test device (ATD), an array of headform acceleration transducers and neck force/moment transducers, a dual high speed camera system, and helmet-fit force sensors developed in our research group based on Bragg gratings in optical fiber. To simulate impacts, an instrumented headform and flexible neck fall along a linear guide rail onto an anvil. The test bed allows simulation of head impact at speeds up to 8.3 m/s, onto impact surfaces that are both flat and angled. The headform is fit with a crash helmet and several fit scenarios can be simulated by making context specific adjustments to the helmet position index and/or helmet size. To quantify helmet retention, the movement of the helmet on the head is quantified using post-hoc image analysis. To quantify head and neck injury potential, biomechanical measures based on headform acceleration and neck force/moment are measured. These biomechanical measures, through comparison with established human tolerance curves, can estimate the risk of severe life threatening and/or mild diffuse brain injury and osteoligamentous neck injury. To our knowledge, the presented test-bed is the first developed specifically to assess biomechanical effects on head and neck injury relative to helmet fit and retention.

A Test Bed to Examine Helmet Fit and Retention and Biomechanical Measures of Head and Neck Injury in Simulated Impact.

Conventional wisdom and the language in international helmet testing and certification standards suggest that appropriate helmet fit and retention during an impact are important factors in protecting the helmet wearer from impact-induced injury. This manuscript aims to investigate impact-induced injury mechanisms in different helmet fit scenarios through analysis of simulated helmeted impacts with an anthropometric test device (ATD), an array of headform acceleration transducers and neck force/moment transducers, a dual high speed camera system, and helmet-fit force sensors developed in our research group based on Bragg gratings in optical fiber. To simulate impacts, an instrumented headform and flexible neck fall along a linear guide rail onto an anvil. The test bed allows simulation of head impact at speeds up to 8.3 m/s, onto impact surfaces that are both flat and angled. The headform is fit with a crash helmet and several fit scenarios can be simulated by making context specific adjustments to the helmet position index and/or helmet size. To quantify helmet retention, the movement of the helmet on the head is quantified using post-hoc image analysis. To quantify head and neck injury potential, biomechanical measures based on headform acceleration and neck force/moment are measured. These biomechanical measures, through comparison with established human tolerance curves, can estimate the risk of severe life threatening and/or mild diffuse brain injury and osteoligamentous neck injury. To our knowledge, the presented test-bed is the first developed specifically to assess biomechanical effects on head and neck injury relative to helmet fit and retention.

Analysis of a bicyclist’s head injury in lateral and frontal impact using the human full-body model

Helmets reduce the frequency and severity of head and brain injuries resulting from bicycle crashes. To ensure that all bicycle helmets provide a certain level of effectiveness, helmets are required to satisfy certain standards of construction and material design before they can be sold in the market. Impact protection is the primary consideration of nearly every helmet standard. The general terms for a test for assessing impact protection involve shock absorption. A helmeted headform is dropped onto an anvil and the headform acceleration is measured. However, the test procedures of the existing standards do not properly assess the protection level of helmets against oblique impacts. To investigate bicycle helmets in a real accident scenario, this study simulated the full body of a bicyclist when free falling onto a road. This study considered the normal velocity (VN) of 5.66 m/s and tangential velocity (VT) values of 0, 5, and 10 m/s. Finite element analyses of helmet impact tests were conducted using LS-DYNA software. Moreover, the impact responses obtained using full-body and detached-headform models were compared under identical impact conditions. The analysis results obtained herein can be useful for evaluating helmet quality and guiding future developments in helmet innovation.

The effect of motorcycle helmet fit on estimating head impact kinematics from residual liner crush

Proper helmet fit is important for optimizing head protection during an impact, yet many motorcyclists wear helmets that do not properly fit their heads. The goals of this study are i) to quantify how a mismatch in headform size and motorcycle helmet size affects headform peak acceleration and head injury criteria (HIC), and ii) to determine if peak acceleration, HIC, and impact speed can be estimated from the foam liner’s maximum residual crush depth or residual crush volume. Shorty-style helmets (4 sizes of a single model) were tested on instrumented headforms (4 sizes) during linear impacts between 2.0 and 10.5m/s to the forehead region. Helmets were CT scanned to quantify residual crush depth and volume. Separate linear regression models were used to quantify how the response variables (peak acceleration (g), HIC, and impact speed (m/s)) were related to the predictor variables (maximum crush depth (mm), crush volume (cm3), and the difference in circumference between the helmet and headform (cm)). Overall, we found that increasingly oversized helmets reduced peak headform acceleration and HIC for a given impact speed for maximum residual crush depths less than 7.9mm and residual crush volume less than 40cm3. Below these levels of residual crush, we found that peak headform acceleration, HIC, and impact speed can be estimated from a helmet’s residual crush. Above these crush thresholds, large variations in headform kinematics are present, possibly related to densification of the foam liner during the impact.

A Finite Element Investigation into the Impact Performance of an Open-Face Motorcycle Helmet with Ventilation Slots

Motorcycle helmets are essential for reducing the risk of head injuries in the event of an impact. However, during the design of helmets, a compromise must be made between user safety and user comfort. Accordingly, the present study proposes a novel open-face helmet design, in which the helmet features three ventilation slots in the upper-head region. Finite element analysis (FEA) models were constructed for both a prototype helmet design, and three traditional helmet designs (full-face, open-face, and half-face helmets). In simulating the proposed open-face helmet, this study considered three different ventilation slot widths, namely 8, 14, and 18 mm. The simulation results showed that of all the helmet designs, the half-face helmet resulted in the greatest headform acceleration (303 G). The internal ventilation helmet achieved a lower peak acceleration than that of the full-face helmet. By contrast, the proposed open-face helmet with ventilation slots resulted in the lowest acceleration, irrespective of the ventilation slot width. The 8-mm ventilation slot width resulted in the optimal impact performance level (i.e., a peak headform acceleration of 160 G). Overall, the results suggest that the proposed open-face helmet design with ventilation slots provides a promising solution for ensuring both user protection and user comfort in warm climates.

Response of a full-face motorcycle helmet FE model to the UNECE 22.05 chin bar impact test

ABSTRACTThis study investigates the role of full-face motorcycle helmet components in reducing the severity of chin bar impacts to a motorcyclist. A finite element helmet model was created for chin bar impacts by carrying out component tests on the chin bar padding, helmet shell and the chinstrap. Addition of two composite layers to the chin bar, stiffening the shell, reduced the peak headform centre of gravity acceleration from 168.3 g to 122.6 g in the UNECE 22.05 chin bar impact test configuration. The presence of chin bar foam was necessary to avoid excessive headform responses but optimal foam stiffness was dependent on shell stiffness. The lowest peak headform acceleration of 113.1 g was achieved by stiffening the helmet shell and softening the chin bar foam padding in comparison to the validated helmet model. The chinstrap was also critical, causing peak acceleration increases of 27.3 g and 118 g when slightly loose and absent, respectively. The significance of the shell and chinstrap in chin bar impacts is in contrast to cranial helmet impacts which are predominantly controlled by the crushable foam liner. The fact that chinstrap pre-test tightness influences the headform acceleration response is important for the helmet test technician.

The impact response of traditional and BMX-style bicycle helmets at different impact severities

Bicycle helmets reduce the frequency and severity of severe to fatal head and brain injuries in bicycle crashes. Our goal here was to measure the impact attenuation performance of common bicycle helmets over a range of impact speeds. We performed 127 drop tests using 13 different bicycle helmet models (6 traditional style helmets and 7 BMX-style helmets) at impact speeds ranging from 1 to 10m/s onto a flat anvil. Helmets were struck on their left front and/or right front areas, a common impact location that was at or just below the test line of most bicycle helmet standards. All but one of the 10 certified helmet models remained below the 300g level at an impact speed of 6m/s, whereas none of the 3 uncertified helmets met this criterion. We found that the helmets with expanded polystyrene liners performed similarly and universally well. The single certified helmet with a polyurethane liner performed below the level expected by the Consumer Product Safety Commission (CPSC) standard at our impact location and the helmet structure failed during one of two supplemental tests of this helmet above the test line. Overall, we found that increased liner thickness generally reduced peak headform acceleration, particularly at higher impact speeds.

Headform Mounting Performance in Cricket Standard Testing

The current British Standard for head protectors for cricketers specifies a projectile test to ensure that a helmet can prevent the ball penetrating the peak-grille gap and deformation of the grille onto the face. For practical reasons, it is specified that the headform is mounted onto a grounded frame. This study aims to determine whether this “Fixed” mounting technique influences the response of the headform relative to a theoretically preferable “Free” suspension. A pressurised air cannon was used to project a “BOLA”TM ball at three nominal speeds (22, 25 and 28 m/s) and at three target impact locations (136 (Top), 108 (Middle) and 80 (Bottom) mm from the base). High speed video was used to identify the contact duration and accelerometer data were used to assess the peak resultant headform acceleration and velocity during this period.Generally, good agreement between the two scenarios was found in regard to peak resultant headform acceleration, particularly at the 25 and 28 m/s impact speeds. In terms of headform velocity, the two scenarios showed greater variation when the full contact duration was considered, with root mean square deviations ranging from 1.77 – 5.6 in all testing conditions. However, some portions of the impact were considerably more consistent than others. These initial results indicate that the result of the penetration test, as specified in BS 7928:2013, would be independent of the suspension technique particularly given the convergence of results at the specified standard velocity (28 m/s). Future work should look to identify the loading and unloading phases of an impact, and use this to compare headform response. Thus allowing a more in-depth investigation of headform mounting performance and provide more clarity on the use of the Fixed technique in cricket standard tests.

The impact performance of headguards for combat sports

Background/aim To assess the impact energy attenuation performance of a range of headguards for combat sports. Methods Seven headguards worn during combat sport training or competition, including two Association Internationale...

Boxing headguard performance in punch machine tests

Background The paper presents a novel laboratory method for assessing boxing headguard impact performance. The method is applied to examine the effects of headguards on head impact dynamics and injury...

Resultant linear acceleration of an instrumented head form does not differ between junior and collegiate taekwondo athletes' kicks

ObjectiveThe purpose of this study was to compare the effects of various taekwondo kicks and age (school level) in absolute terms and relative body mass on the resultant linear acceleration (RLA) of an instrumented head form. MethodsForty-eight male (middle school: 16; high school: 16; university: 16) taekwondo athletes were recruited for this study. Subjects performed 10 turning, 10 jump spinning hook, and 10 jump back kicks on a Hybrid II head mounted on a height-adjustable frame. ResultsA 2-way (School × Kick) MANOVA was used to determine the differences in RLA between schools (age groups) by type of kick. There was no univariate School main effect for absolute RLA (η2 = 0.06) and RLA relative to body mass (η2 = 0.06). No univariate Kick main effects were found for absolute (η2 = 0.06) and relative RLA (η2 = 0.06). ConclusionIt is of concern that RLA did not significantly differ between school levels, implying that young taekwondo athletes generate similar forces to their adult counterparts, possibly exposing young athletes to an increased risk for head injuries.