Helmet Damage Research Articles

Energy-absorbing limitations of hard hat safety helmets in mitigating trauma from falling objects

The aim of the study was to analyze the effectiveness of hard hat helmets in mitigating head injuries from high-energy falling objects through a real-world case study, advanced numerical simulations and an uncertainty study. The study aims to answer the following research questions: (a) to what extent would the use of the protective helmet limit the kinetic energy of the falling construction prop, (b) whether the hard hat helmet would be damaged, and if so, to what extent, according to the helmet standards? A fatal construction accident involving a falling prop impact on the victim’s head was reconstructed using multi-body dynamics simulations and finite element analysis (FEA) based on uncertainty-based determination of initial conditions. The study quantified the impact energy, helmet damage and its energy-absorbing capabilities, and potential injury reduction compared to scenarios without a helmet. While the helmet absorbed significant energy (245% of the standard requirement) and reduced the Head Injury Criterion by 8–11%, the high impact energy ultimately proved fatal. This study highlights the limitations of hard hat helmets in extreme scenarios with high kinetic energy impacts. While helmets offer valuable protection, unrealistic expectations should not be placed on their ability to prevent all head injuries. The study not only enhances our understanding of the biomechanics of head injuries in such incidents but also provides practical implications for safety protocols and regulations.

Modeling the mechanical behavior of a helmeted headform impacted with a laminated windshield with consideration of composite failure

In a bicycle–vehicle or a motorcycle–vehicle accident, the head of an adult rider with a helmet is very likely to impact the windshield laminated glass. Such a complex impact phenomenon normally involves head injury, windshield failure, and helmet damage. The main purpose of this work is to present a computational framework for modeling the impact interaction between a helmeted headform and a windshield glazing. To achieve this, a finite element helmet model is established, where a crushable foam model and a continuum damage mechanics based fracture model are used to describe helmet composite failure. The accuracy of the model is validated by comparing the numerical results with the corresponding experimental data. For the windshield failure, we adopt the commonly used intrinsic cohesive zone model to account for two main failure patterns, i.e., glass fracture and glass–PVB debonding. The mechanical responses of a helmeted headform are compared with those of a pure headform to investigate the protective performance of the helmet. Finally, parametric studies are carried out to numerically investigate the effects of impact velocity, helmet posture, and impact location on the windshield on headform response.

Laboratory Reconstructions of Real-world Bicycle Helmet Impacts.

The best way to prevent severe head injury when cycling is to wear a bike helmet. To reduce the rate of head injury in cycling, knowing the nature of real-world head impacts is crucial. Reverse engineering real-world bike helmet impacts in a laboratory setting is an alternative to measuring head impacts directly. This study aims to quantify bike helmet damage using computed tomography (CT) and reconstruct real-world damage with a custom, oblique test rig to recreate real-world impacts. Damaged helmets were borrowed from a helmet manufacturer who runs a helmet warranty program. Each helmet was CT-scanned and the damage metrics were quantified. Helmets of the same model and size were used for in-lab reconstructions of the damaged helmets where normal velocity, tangential velocity, peak linear acceleration (PLA) and peak rotational velocity (PRV) could be measured. The damage metrics of the in-lab dropped helmets were quantified using the same CT scanning process. For each case, a multiple linear regression (MLR) equation was created to define a relationship between the quantified damage metrics of the in-lab tested helmets and the associated measured impact velocities and kinematics. These equations were used to predict the impact kinematics and velocities from the corresponding real-world damaged helmet based on the damage metrics from the original damaged helmet. Average normal velocity (3.5 m/s), tangential velocity (2.5 m/s), PLA (108.0 g), PRV (15.7 rad/s) were calculated based on a sample of 23 helmets. Within these head impact cases, five notes reported a concussion. The difference between the average PLA and PRV for concussive cases versus other impacts were not significantly different, although the average impact kinematics for the concussive cases (PLA = 111.4 g, PRV = 18.5 rad/s) were slightly higher than the remaining cases (PLA = 107.1 g, PRV = 15.0 rad/s). The concussive cases were not indicative of high magnitude impact kinematics.

Analysis of bicycle helmet damage visibility for concussion-threshold impacts

ABSTRACT Any helmet involved in an accident should be replaced, regardless of appearance after impact. However, consumer compliance and interpretation of this recommendation is unclear, for which there is additional ambiguity for lesser impacts. This study aims to investigate the relation between helmet damage visibility and lesser impacts in line with concussion. As a preliminary model, a commercially available road-style helmet was chosen. Twelve helmets underwent impact attenuation testing; four were dropped from the standard testing height of 2 m, and eight from lower drop heights (0.34 and 0.42 m) associated with the production of linear accelerations (90 and 100 g, respectively) consistent with the production of concussion. Expanded polystyrene damage was assessed via flat punch penetration testing. American adults were then polled on helmet damage visibility based upon before and after photos. All helmets demonstrated damage to the expanded polystyrene liner in the form of altered material properties. Helmets dropped from 2 m displayed significant changes in elastic buckling (p < .01) and densification behavior (p < .01) as compared with lower drop height results. Adverse change in elastic buckling behavior was found to increase linearly with drop height (p < .001). Damage visibility was significant for helmets dropped from a 2-meter height, however, such a relation among the helmets impacted at the threshold for concussion was lacking. These findings suggest that for the chosen helmet model, consumers may be unable to distinguish between new helmets and helmets with diminished protective abilities.

Laboratory Reconstructions of Bicycle Helmet Damage: Investigation of Cyclist Head Impacts Using Oblique Impacts and Computed Tomography

Although head injuries are common in cycling, exact conditions associated with cyclist head impacts are difficult to determine. Previous studies have attempted to reverse engineer cyclist head impacts by reconstructing bicycle helmet residual damage, but they have been limited by simplified damage assessment and testing. The present study seeks to enhance knowledge of cyclist head impact conditions by reconstructing helmet damage using advanced impact testing and damage quantification techniques. Damage to 18 helmets from cyclists treated in emergency departments was quantified using computed tomography and reconstructed using oblique impacts. Damage metrics were related to normal and tangential velocities from impact tests as well as peak linear accelerations (PLA) and peak rotational velocities (PRV) using case-specific regression models. Models then allowed original impact conditions and kinematics to be estimated for each case. Helmets were most frequently damaged at the front and sides, often near the rim. Concussion was the most common, non-superficial head injury. Normal velocity and PLA distributions were similar to previous studies, with median values of 3.4 m/s and 102.5 g. Associated tangential velocity and PRV medians were 3.8 m/s and 22.3 rad/s. Results can inform future oblique impact testing conditions, enabling improved helmet evaluation and design.

Analysis of Helmet Damage and Associated Head Injuries Arising from Real-World Equestrian Fall Accidents

Abstract There is significant difference between the loading conditions used to certify equestrian helmets and the environment in which they are commonly used. This may affect their ability to provide adequate protection against head injury during a riding accident. The efficacy of helmet performance under real-world riding conditions can be judged by examining physical damage to the helmet during an impact, along with details of any head injury that may have been sustained by the rider. The present study considered the influence of different impact events on helmet damage sustained during real-world equestrian racing and eventing accidents. Video analysis of the accidents and assessment of the corresponding helmets allowed helmet damage to be matched to impacts. From a total of 1,119 accident videos and 218 inspected helmets, there was a total of 18 cases for which both the helmet and unobstructed video views of the accident sequence were available, along with details of any injuries sustained by the rider. All 18 cases involved the riders falling from their horses and impacting their heads against the turf. For 7 of the 18 cases, head impacts occurred in which a rider’s head was also either kicked, crushed, or stomped on by a horse: those subsequent impacts led to significant helmet damage, suggesting that the helmets provided protection for the riders during those secondary and tertiary impacts. Surprisingly, 11 of the 18 cases involved only a fall for which none of the helmets had any evident damage, despite 6 of those cases involving diagnosed concussions and 1 hematoma. This indicates that traumatic brain injury can occur in equestrian sports even while the rider wears a helmet, which suggests that there is scope to further improve the ability of equestrian helmets to protect against concussion when riders fall and impact their head against turf.

Reporting of Concussion-Like Symptoms After Cycling Crashes: A Survey of Competitive and Recreational Cyclists.

Cycling crashes are common among recreational and competitive riders and may result in head and bodily trauma. Information is limited regarding the signs and symptoms of head injury (HI) after cycling crashes, medical treatment, and recovery. To evaluate concussion-like symptom reporting after cycling crashes with or without HI in recreational and competitive cyclists and to assess crash characteristics and follow-up medical care. Cross-sectional study. Voluntary online survey. A convenience sample of 780 cyclists residing in the United States: 528 males, 249 females, 2 gender queer/nonbinary, and 1 transgender female. Survey-based, self-reported signs and symptoms of HI, including the third edition of the Sport Concussion Assessment Tool (SCAT3) symptom checklist, loss of consciousness, posttraumatic amnesia, and helmet damage. Of the participants, 403 reported crashes in the previous 2 years. Cyclists who self-reported no significant injury after their crash were excluded, leaving 77 HI reporters (HI group) and 260 trauma controls (TC group). The HI group more frequently reported experiencing 17 of the 22 symptoms on the SCAT3 symptom checklist. The HI group described a 4-fold higher incidence of loss of consciousness (HI = 13/77 [16.9%] versus TC = 11/2600 [4.2%]) and memory loss immediately after the crash (HI = 44/77 [57.1%] versus TC = 37/260 [14.2%]). The HI group reported major, noncosmetic helmet damage 2.5 times more frequently than the TC group (HI = 49/77 [63.6%] versus TC = 67/260 [25.8%]). The findings suggest that a standardized concussion assessment is needed for cyclists who experience major trauma.

Do equestrian helmets prevent concussion? A retrospective analysis of head injuries and helmet damage from real-world equestrian accidents

ObjectivesTo collect and analyse helmets from real-world equestrian accidents. To record reported head injuries associated with those accidents. To compare damage to helmets certified to different standards and the injuries associated with them.MethodsTwo hundred sixteen equestrian helmets were collected in total. One hundred seventy-six helmets from amateur jockeys were collected via accident helmet return schemes in the UK and USA, while 40 helmets from professional jockeys were collected by The Irish Turf Club. All helmet damage was measured, and associated head injury was recorded.ResultsEighty-eight percent (189) of equestrian fall accidents returned an injury report of which 70% (139) reported a head injury. Fifty-four percent (75) of head injury cases had associated helmet damage while 46% had no helmet damage. Reported head injuries consisted of 91% (126) concussion, 4% (6) skull fractures, 1 (0.7%) subdural hematoma, 1 (0.7%) cerebral edema and 5 (3.6%) diffuse axonal injury (DAI). It is also shown that helmets certified to the most severe standard are overrepresented in this undamaged group (p <0.001).ConclusionsIt is clear that despite jockeys wearing a helmet, large proportions of concussion injuries still occur in the event of a jockey sustaining a fall. However, the data suggest it is likely that helmets reduce the severity of head injury as the occurrence of skull fracture is low. The proportion of undamaged helmets with an associated head injury suggests that many helmets may be too stiff relative to the surface they are impacting to reduce the risk of traumatic brain injury (TBI). It may be possible to improve helmet designs and certification tests to reduce the risk of head injury in low-severity impacts.

279 Association of Personal Protective Equipment Use and Maintenance with Burn Injury: A Pilot Survey of Firefighters

Thermal injury remains a persistent occupational hazard for both volunteer and career firefighters. While advances in personal protective equipment (PPE) offer improved safety and reported rates of compliance are high, injuries still occur. The purpose of this pilot project was to investigate the correlation between PPE use and damage with injury characteristics. A structured questionnaire was distributed to a convenience sample of firefighters undergoing initial outpatient evaluation in a burn clinic. Data were collected regarding fire experience, incident circumstances and extent of injury sustained, as well as PPE use and post-injury damage and PPE integrity monitoring history. Chi-square tests were used to evaluate the relationship between PPE use, damage and monitoring with injury. There were 45 respondents included in this analysis. Firefighters were on average 31.8 ± 7.5 years with 10.8 ± 8.9 mean years of experience (range 1-32 years). The majority of respondents identified as career firefighters (72.4%). Injuries were sustained primarily in structure fires (93.3%), and 22.0% were in a training setting. Ears were the most commonly burned area (n=25) followed by arms, hands, and wrists. Nearly all injuries were small (< 5% TBSA) and managed in an outpatient setting. Only one patient requiring grafting, though 60.0% reported missing at least one shift. The majority reported use of most PPE elements at the time of injury, although more than 25% indicated not using suspenders. Eight individuals had not been sized for PPE in the last two years, two of whom indicated never having been properly sized. Although ear burns were not significantly associated with use of helmets or earflaps, there was a significant association with helmet damage (p = 0.04), with a trend toward significance for visible gear damage (p = 0.05) and hood damage (p = 0.09). Arm burns were significantly associated with visibly damaged gear (p = 0.003), damaged gloves (p = 0.012), and damaged coats (p < 0.001). Given the association of PPE damage and injury identified in this pilot study, further training directed towards improved frequency of resizing and inspection of PPE post-injury may be warranted. These findings necessitate further investigation, which is planned via more extensive questionnaire distribution within the firefighting community. Further significant associations may be revealed within a larger sample size. Thermal injury will continue to be an occupational hazard for firefighters. Better understanding of associated factors can help target training and prevention strategies to mitigate risk.

A Computationally Efficient Computer-Aided Design Strategy for Iterative Combat Helmet Design and Analysis

Assessing combat helmet ballistic performance is a costly endeavor using either an experimental or a computational process. Experimental assessment requires many iterations and helmets to acquire a sufficient data set. To circumvent this, computational simulation is incorporated into the design process to supplement a few experiments. However, due to the complex constitutive response of the helmet (anisotropic elasticity, plasticity, damage initiation and evolution, and failure), it is computationally costly to run many ballistic impact simulations. The goal of this work is to develop a computer-aided design (cad) software to rapidly analyze combat helmets undergoing a ballistic impact. The software considers a representative mix of potential threats, helmet geometry modifications and additions, brain functional anatomy, and injury considerations. The resulting software demonstrates that a given helmet can be analyzed in a matter of minutes on a standard desktop computer and parametric studies can be completed in a matter of hours. The results of the cad software show how helmet design parameters such as helmet shell materials, geometry, and ceramic appliques all affect helmet ballistic performance.

3D assessment of damaged bicycle helmets and corresponding craniomaxillo-mandibular skull injuries: A feasibility study

ObjectivesIn the Netherlands, cyclists continue to outnumber other road users in injuries and deaths. The wearing of bicycle helmets is not mandatory in the Netherlands even though research has shown that wearing bicycle helmets can reduce head and brain injuries by up to 88%. Therefore, the aim of this study was to assess the feasibility of using 3D technology to evaluate bicycle-related head injuries and helmet protection. MethodsThree patients who had been involved in a bicycle accident while wearing a helmet were subjected to multi-detector row computed tomography (MDCT) imaging after trauma. The helmets were separately scanned using the same MDCT scanner with tube voltages ranging from 80kVp to 140kVp and tube currents ranging from 10mAs to 300mAs in order to determine the best image acquisition parameters for helmets. The acquired helmet images were converted into virtual 3D surface hence Standard Tessellation Language (STL) models and merged with MDCT-derived STL models of the patients’ skulls. Finally, all skull fractures and corresponding helmet damage were visualized and related. ResultsImaging bicycle helmets on an MDCT scanner proved to be feasible using a tube voltage of 120kVp and a tube current of 120mAs. Merging the resulting STL models of the patients’ skull and helmet allowed the overall damage sustained by both skull and helmet to be related. ConclusionOur proposed 3D method of assessing bicycle helmet damage and corresponding head injuries could offer valuable information for the development and design of safer bicycle helmets.

Photo-oxidative degradation of motorcycle helmets in Hanoi, Vietnam: A prospective preliminary study

ABSTRACTObjective: Vietnamese spend hours travelling on the road using their motorcycles. Their helmets are exposed continuously to sunlight and rain. The objectives of this study were to determine the association between the effect of photo-oxidative degradation (POD) of the outer shells and helmet age on helmet damage. The micro-structural change of the outer shell was also investigated.Methods: This was a prospective, cross sectional study recruiting injured motorcyclists from Hanoi, Vietnam hospital. The participants were interviewed by a trained researcher. The participants' helmets were collected post-crash. Initially, the helmets were examined for their type and external characteristics. A 3 cm × 3 cm cut was made on the helmet in the impacted and non-impacted areas (control). These areas were investigated for evidence of POD and presence of micro-cracks and material disintegration.50 participants were enrolled. Sources of information included questionnaire and laboratory analyses. The helmet factors of interest were age of the helmet, exposure of helmet to sunlight and rain (duration/day) and history of previous impact. Laboratory analyses included Fourier Transform Infra Red (FTIR) for degradation and scanning electron microscopy (SEM) for micro-structural examination.Results: Majority of the helmets was the open-face type, 40 (80.0%). 31 (62.0%) helmets aged less than three years (LTY) and 19 (38.0%) were three years old or more (MTY). 19 (61.3%) of the LTY helmets and 12 (63.2%) MTY helmets showed evidence of POD. The duration of helmet exposure to sunlight was between 93 to 6570 hours (mean 2347.74 hours; SD 1733.39). The SEM showed 15 helmets (30%) with micro-fractures, 21 helmets (42.0%) with material disintegration.Prolonged uv exposure to the ABS helmets resulted in changes in the helmet material in the form of material disintegration and microcracks and this association was statistically significant (p = 0.03).Conclusion: POD occurs due to routine exposure to the ultraviolet light. Prolonged uv exposure affects outer shell surface material integrity.

Simulation, fabrication and impact testing of a novel football helmet padding system that decreases rotational acceleration

Recent studies suggest that concussion may be associated with long-term neurological sequelae. Both linear impact and rotational acceleration have been identified as contributors to concussion and traumatic brain injury (TBI). Modern football helmets are designed according to the National Operating Committee on Standards for Athletic Equipment (NOCSAE) standard for protection from linear impact, without consideration of protection from rotational injury. A multidisciplinary team was assembled with expertise in brain injury, computational modeling, and materials engineering to design, fabricate and impact test a novel helmet padding system. A rotational fixture with magnesium headform and linear impactor was constructed using a rotary encoder to enable measurement of z axis rotational angle, velocity and acceleration. Helmet padding material designs were evaluated using finite element (FE) computational modeling, fabricated to specification and then impact tested. Models from two different manufacturers were retrofit with prototype pads and then compared with unmodified versions for attenuation of rotational acceleration. The helmets were then tested using a standard NOCSAE drop apparatus and headform for linear acceleration performance. Large-size Riddell Revolution and Schutt ION4D helmets retrofit with prototype padding demonstrated 21.6 and 33.6 % decreased peak z axis rotational acceleration following a 3.2 m/s side impact compared with their respective unmodified commercial models (717.7 vs. 914.0 rad/s2 and 768.4 vs. 1,158.6 rad/s2, p < 0.0001, respectively). The improved performance effect appeared consistent over at least 50 impacts without evidence of early material degradation or helmet damage. Compared with unmodified versions, drop test performance for hybridized helmets, measured by Peak G and severity index (SI), were comparable for most, but were worse for rear (Riddell Revolution) and side (Schutt ION4D) impact conditions. Rotational acceleration from side impacts may be attenuated by directed helmet design while maintaining acceptable linear impact performance. Future work will focus on optimization and durability testing of prototype padding for larger impacts.

Performance of an advanced combat helmet with different interior cushioning systems in ballistic impact: Experiments and finite element simulations

This paper presents results from both experiments and numerical simulations of frontal and lateral ballistic impacts on a Hybrid III headform equipped with Advanced Combat Helmets (ACH) of two different interior cushioning designs, namely the strap-netting system and the Oregon Aero (OA) foam padding. It aims to study the differences between two different impact orientations for these two different interior cushioning systems. The experiments involve frontal and lateral ballistic impacts of a 11.9g spherical steel projectile traveling at speeds of approximately 200m/s, striking on the helmet-cushion-headform assemblies. The dynamic interaction between various components of the helmet-cushion-headform assemblies are investigated with the use of high-speed photography while post-test evaluation of the damaged helmets are performed using visual observation, optical microscopy and computed tomography (CT) scan. A series of ballistic impact simulations with finite element (FE) models of the two assemblies reconstructed from CT images, are performed to correlate with experimental results. The commercial software, Abaqus™, is used for the FE analyses. In general, there is reasonable correlation between numerical and experimental observations and on quantitative parameters, such as head accelerations, helmet damage and deflections. It is also found that softer foams with low stiffness are more effective as shock absorbing cushion against ballistic impacts under certain condition. Additionally, results of the two interior cushioning systems are compared with various injury criteria to assess their acceleration levels. It is found that, for frontal impact, the helmet with strap-netting system fails both the Wayne State Tolerance Curve (WSTC) and Federal Motor Vehicles Safety Standards (FMVSS) 218 criteria while the one with OA foam-padding passes both.

Impact reconstruction from damage to pedal and motorcycle helmets

Pedal and motorcycle helmets offer a high level of protection to the wearer’s head. There is a need to review and assess the performance offered by helmets, so that helmet design and test standards can be optimized. One input into this process is crash reconstruction. Helmeted crash cases can be collected and examined, leading to insights into impact severity, helmet performance and injury outcomes. However, it is unclear to what extent residual helmet damage reflects the impact characteristics. This paper addresses this issue using controlled laboratory impact tests. Two pedal cycle and three motorcycle helmet models were tested with an ‘M’ size headform in impact energy attenuation tests from 1 m, 2 m and 2.5 m. Headform acceleration, impact force and post-impact deformation were measured. The dynamic deformations were measured with three methods: video, kinetic energy and an analytical approach using impact force and liner yield stress. All five models offered highly repeatable performance in terms of impact energy attenuation and acceleration management in radial impacts across the impact severities. The results showed that the Standards Australia certified helmets provided impact protection to the head in impacts that greatly exceeded the impact energy attenuation performance requirements of those standards. The residual and dynamic deformation measurements were correlated with drop height and headform acceleration for pedal cycle helmets. The results indicate that the residual deformation observed in a pedal cycle helmet collected from a crash can be used to estimate the impact severity and, after undertaking exemplar impact tests on the same model helmet, the head impact acceleration. However, the residual deformation measured on the three motorcycle helmets was not correlated with the drop height, which indicated that, within the limits of this study, estimating crash severity from motorcycle helmet damage is not reliable.

Motorcycle Helmet Protection and Basilar Skull Fracture

The CASR Head Injury Database contains in-depth investigations of 174 mainly fatal motorcycle accident cases collected in South Australia between 1983 and 1994. The data collected includes the autopsy with investigation of injury to the neck of the wearer, the helmet damage and a detailed crash report. The CASR data was found to be high severity crashes representative of fatal crash studies in the literature. In 70% of the cases full face helmets were worn. BSF was seen in 59% of these cases. Almost 50% of the severe impacts to the head were in the facial region and 42% of these impacts were to the chin bar. The prevalence of BSF was found to be due mainly to the migration of the skull fracture to the base of the skull due to the severity of the impact to the face (and other regions of the head).

Human head tolerance limits to specific injury mechanisms inferred from real world accident numerical reconstruction

This study presents an original numerical human head model which is validated in both modal and temporal domain against vibration analysis in vivo and cadaver impact tests. The head finite element model developed presents two particularities : one at the interface between the brain and the skull were fluid structure interaction is taken into account, the other at the skull modelling level by integrating the bone fracture prediction. Validation shows that the model correlated well with a number of experimental cadaver tests. This improved numerical head surrogate is then used for numerical real world accident reconstruction. Helmet damage from thirteen motorcycle accidents is replicated in drop tests in order to define the head's loading conditions. A total of twenty two well documented American football players head trauma is reconstructed as well as twenty nine pedestrian head impacts on car windscreens. By correlating head injury type and location with calculated mechanical parameters, it is possible to...

Head and Neck Injuries in Fatal Motorcycle Collisions as Determined by Detailed Autopsy

Detailed layer-by-layer autopsy of the head and neck was performed on a prospective series of 73 fatally injured motorcyclists in order to identify occult injuries, particularly soft tissue neck injuries such as hemorrhage of vertebral and carotid arteries. The fatal cases were gathered as part of a larger study of 1,082 on-scene in-depth motorcycle crash investigations in Thailand. Detailed neck dissection was done on nearly all fatal cases. Injuries were coded using the 1990 revision of the Abbreviated Injury Scale (AIS 90) and an Injury Severity Score (ISS) was determined for each case. Additional AIS codes are proposed for neck injuries that were often identified during the detailed autopsy procedures, but which are not listed explicitly among existing AIS codes. Helmet use was determined based on analysis of injury patterns and helmet damage with consideration also given to witness statements. Both helmeted and unhelmeted motorcyclists showed a high frequency of occult neck injuries such as hemorrhages in the carotid sheath or surrounding the vertebral arteries, phrenic nerve, or brachial plexus. These soft tissue neck injuries sometimes accompanied more obvious injuries to cervical vertebrae or spinal cord, but about one-third of riders had no obvious injury to suggest the presence of occult neck injury. Twenty-eight motorcyclists had been wearing a helmet at the start of the collision sequence, but only nine helmets remained in place through the entire collision event. Helmeted riders showed more severe somatic (below-the-neck) injuries than unhelmeted riders, suggesting helmeted riders are less likely to die in low-threat accidents with somatic injuries below AIS-3. The most significant finding of this study was the identification of serious internal neck injuries despite the absence of external physical evidence of trauma to the neck. Virtually all riders with significant head injuries showed some of these soft tissue neck injuries. Approximately one-third of the critically injured riders who survived at least a few hours before death showed serious occult soft tissue neck injuries.

Numerical and physical modelling of the human head under impact - towards new injury criteria

This paper presents original physical and numerical human head models followed by their modal and temporal validation against human head vibration analysis in vivo and cadaver impact tests. The human head FE model developed by ULP presents two particularities: one at the brain-skull interface level where fluid-structure interaction is taken into account, the other at the skull modelling level by integrating the bone fracture simulation. Validation shows that the model correlated well with a number of experimental cadaver tests and predicted intracranial pressure accurately. However, for long duration impacts the model reaches its limits. The skull stiffness and fracture force were very accurately predicted when compared with values from the literature. In a second step, a new dummy head prototype, named Bimass, is presented. It has been constructed using a Hybrid III headform and comprises two masses: a skull and a mass to represent the brain attached to the skull with a damped spring system. The novel feature of this device is that it can simulate the brain-skull relative displacement at a frequency close to 150 Hz as recorded under vibration analysis in vivo. Helmet damage from thirteen motorcycle accidents was replicated in drop tests conducted in collaboration with Transport Research Laboratory (UK). Simulation of these accidents using both FE model and Bimass dummy head led to the first tentative proposals for tolerance limits and injury criteria relative to specific injury mechanisms.

Human head tolerance limits to specific injury mechanisms

This study presents an original numerical human head model followed by there modal and temporal validation against human head vibration analysis in vivo and cadaver impact tests. The human head FE model developed by ULP presents two particularities : one at the brain-skull interface level were fluid-structure interaction is taken into account, the other at the skull modelling level by integrating the bone fracture simulation. Validation shows that the model correlated well with a number of experimental cadaver tests and predicted intra-cranial pressure accurately. However, for long duration impacts the model reaches its limits. The skull stiffness and fracture force were accurately predicted when compared with experimental values from the literature. This improved numerical human head surrogates has then be used for numerical real world accident reconstruction. Helmet damage from thirteen motorcycle accidents was replicated in drop tests in order to define the head's loading conditions. A total of twenty two well documented American football head trauma have been reconstructed as well as twenty eight pedestrian head impacts. By correlating head injury type and location with intra-cerebral mechanical field parameters, it was possible to derive new injury risk curves relative to specific injury mechanisms.