Head Injury Criterion Research Articles

Modeling and validation of a detailed FE viscoelastic lumbar spine model for vehicle occupant dummies

The dummies currently used for predicting vehicle occupant response during frontal crashes or whole-body vibration provide insufficient information about spinal loads. Although they aptly approximate upper-body rotations in different loading scenarios, they overlook spinal loads, which are crucial to injury assessment. This paper aims to develop a modified dummy finite element (FE) model with a detailed viscoelastic lumbar spine. This model has been developed and validated against in-vitro and in-silico data under different loading conditions, and its predicted ranges of motion (RoM) and intradiscal pressure (IDP) maintain close correspondence with the in-vitro data. The dominant frequency of the model was f = 8.92 Hz, which was close to previous results. In the relaxation test, a force reduction of up to 21% was obtained, showing high agreement in force relaxation during the in-vitro test. The FE lumbar spine model was placed in the HYBRID III test dummy and aligned in a seated position based on available MRI data. Under two impulsive acceleration loadings in flexion and lateral directions with a peak acceleration of 60 m/s2, flexion responses of the modified and original dummies were close (RoMs of 29.1° and 29.6°, respectively), though not in lateral bending (RoMs of 34.1° and 15.6°, respectively), where the modified dummy was more flexible than the original. By reconstructing a real frontal crash, it was found that the modified dummy provided a 10% reduction in the Head Injury Criterion (HIC). Other than the more realistic behavior of this modified dummy, its capability of approximating lumbar loads and risk of lumbar spine injuries in vehicle crashes or whole-body vibration is of great importance.

Introducing composite lattice core sandwich structure as an alternative proposal for engine hood

Pedestrian protection capability is critical for lightweight design of automotive engine hood. Here, a novel and lightweight composite sandwich hood including two fiber reinforced composite panels and a lattice core was proposed and the corresponding pedestrian protection performance was evaluated via Head Injury Criterion (HIC). The novel double-curvature composite sandwich hood with a pyramidal lattice core was designed based on a commercialized product with a weight reduction by 25%, and fabricated using interlocking approach. A homogenized constitutive model was developed for the pyramidal lattice core and utilized in the following headform-to-hood impact simulations with LS-DYNA. The stiffer sandwich hood revealed better pedestrian safety performance compared with the corresponding baseline hood without lattice core where secondary collision happened. Also, effects of geometrical variables, material selection and core types were discussed. The variation of panel thickness played a more important role in the average HIC values compared with that of core geometries. Among various material selections, hoods designed with carbon fiber reinforced composite (CFRC) panels and a flax fiber reinforced composite (FFRC) lattice core achieved the minimum head injury. Additionally, lattice core outperformed traditional honeycomb and foam in sandwich hood design. The present study demonstrates the feasibility of employing lattice materials in lightweight design of hood and other car body coverage.

Weight threshold estimation of falling UAVs (Unmanned Aerial Vehicles) based on impact energy

Different weight thresholds for drone operations have been specified by regulatory agencies in different countries, without detailed backgrounds of guidelines. Therefore, this paper aims to study weight thresholds by focusing different levels of injuries caused by the impact of the drones on human head of different weights dropped at various heights. The work covers drone free drop modelling, FEM (finite element method) based impact modeling, and comparable drop impact experiments. The analyses and experiments were conducted accordingly to two individual commercially-available groups: small and large drones in weights. Two well-established indicators defining head injuries due to impact, which are known as Head Injury Criterion (HIC) and Abbreviated Injury Scale (AIS), are used in the present weight threshold study. The proposed AIS level for the weight threshold estimation has been set at AIS level 3, which indicates major skull fracture, in the further analysis through the probability of fatality. The main focus of the present work is to perform a parametric study and to present a reliable model to estimate the weight thresholds of the drone operations based on HIC and AIS. In conclusion, the results obtained and presented in this paper have demonstrated and provided a comprehensive analysis of possible direct injuries of a falling drone impacting a human head, with relevant data of impact or injury levels associated with HIC and AIS obtained for a drone with different weights falling from various heights.

Improved child-resistant system for better side impact protection

The article presents a new solution of child-resistant systems to improve the safety of children transported in motor vehicles subjected to a side impact during a vehicle crash. The proposed concept works by means of implementation of an energy dissipation mechanism acting between a child restraint system anchorage and a restraint system seat. The effectiveness of the proposed system is evaluated using numerical analyses of a simplified basic model as well as more complex mechanical design of the mechanism. The latter is analyzed as a part of the child restraint system (CRS) together with a deformable model of an anthropomorphic test device of Q3 series. Tests outcomes clearly show a positive effect of application of the proposed energy dissipation system resulting in reduction of head and thorax acceleration and influencing a lower factor (index) of the head injury criteria. The presented solution shows that there is still a room for improvement of young passengers safety.

Foul tip impact attenuation of baseball catcher masks using head impact metrics.

Currently, no scientific consensus exists on the relative safety of catcher mask styles and materials. Due to differences in mass and material properties, the style and material of a catcher mask influences the impact metrics observed during simulated foul ball impacts. The catcher surrogate was a Hybrid III head and neck equipped with a six degree of freedom sensor package to obtain linear accelerations and angular rates. Four mask styles were impacted using an air cannon for six 30 m/s and six 35 m/s impacts to the nasion. To quantify impact severity, the metrics peak linear acceleration, peak angular acceleration, Head Injury Criterion, Head Impact Power, and Gadd Severity Index were used. An Analysis of Covariance and a Tukey’s HSD Test were conducted to compare the least squares mean between masks for each head injury metric. For each injury metric a P-Value less than 0.05 was found indicating a significant difference in mask performance. Tukey’s HSD test found for each metric, the traditional style titanium mask fell in the lowest performance category while the hockey style mask was in the highest performance category. Limitations of this study prevented a direct correlation from mask testing performance to mild traumatic brain injury.

Relevant factors in the design of composite ballistic helmets

In this paper, the design methodology of composite ballistic helmets has been enhanced considering biomechanical requirements by means of finite element analysis. Modern combat helmets lead to a new type of non-penetrating injury, the Behind Helmet Blunt Trauma (BHBT), generated by the deformation of the inner face of the helmet, the so-called backface deformation (BFD). Current standard testing methodologies use BFD as the main measure in ballistic testing. Nonetheless, this work discusses the relationship between this mechanical parameter and the head trauma (BHBT) by studying different head injury criteria. A numerical model consisting of a helmet and a human head is developed and validated with experimental data from literature. The consequences of non-penetrating high-speed ballistic impacts upon the human head protected by an aramid combat helmet are analysed, concluding that the existing testing methodologies fail to predict many types of head injuries. The influence of other parameters like bullet velocity or head dimensions is analysed. Usually, a single-sized helmet shell is manufactured and the different sizes are adjusted by varying the foam pad thickness. However, one of the conclusions of this work is that pad thickness is critical to avoid BHBT and must be considered in the design process.

Low-Speed Go-Kart Crash Tests and a Comparison to Activities of Daily Living

Abstract Go-karts are a common amusement park feature enjoyed by people of all ages. While intended for racing, contact between go-karts does occur. To investigate and quantify the accelerations and forces which result from contact, 44 low-speed impacts were conducted between a stationary (target) and a moving (bullet) go-kart. The occupant of the bullet go-kart was one of two human volunteers. The occupant of the target go-kart was a Hybrid III 50th percentile male anthropomorphic test device (ATD). Impact configurations consisted of rear-end impacts, frontal impacts, side impacts, and oblique impacts. Results demonstrated high repeatability for the vehicle performance and occupant response. Go-kart accelerations and speed changes increased with increased impact speed. Impact duration and restitution generally decreased with increased impact speed. All ATD acceleration, force, and moment values increased with increased impact speed. Common injury metrics such as the head injury criterion (HIC), Nij, and Nkm were calculated and were found to be below injury thresholds. Occupant response was also compared to published activities of daily living data.

Survivability assessment of a soldier wearing a ballistic helmet collided by a non-penetrating high speed projectile

Since combat capability depends on the survivability of a soldier, it is important to estimate the survivability properly. Head and neck injuries are major incidents that affect the survivability in battle field. Although a soldier usually wears a ballistic helmet, he can be injured by a ballistic impact which results in the deformation and energy propagation of the helmet. Previous research activities focused on the head injury only. In this study, a finite element model including the neck as well as head was developed using LS-DYNA. It consists of a skull, brain, cerebrospinal fluid, cervical vertebrae, neck muscle, helmet, and bullet. The helmet consists of a shell and interior cushion system. The bullet speeds of 250, 360, 410 and 460 m/s were used for the simulation. The pressure of the brain and von Mises stress/ strain of the skull and brain were calculated. Head and neck injury criteria were used to assess the survivability of a soldier. Effects of firearm type on head and neck injuries were also investigated. Generally, the head injury turned out to be more dangerous than the neck injury under the same condition. Among firearms, the riffle type turned out to be generally much more dangerous than the pistol type.

Application of resampling techniques to improve the quality of survival analysis risk curves for human frontal bone fracture

BackgroundIn automotive events, head injuries (skull fractures and/or brain injuries) are associated with head contact loading. While the widely-used head injury criterion is based on frontal bone fracture and linear accelerations, injury risk curves were not developed from original datasets. ObjectivesDevelop skull fracture-based risk curves for using previously published data and apply resampling techniques to assess their qualities. MethodsForce, deflection, energy, and stiffness data from thirteen human cadaver head impact tests were used to develop risk curves using parametric survival analysis. Injuries occurred to all specimens. Data points were treated as uncensored. Variables were ranked, and the variable best explaining the underlying fracture response was determined using the Brier Score Metric (BSM). The qualities of the risk curves were determined using normalized confidence interval sizes. Statistical resampling methods were used to assess the quality of the risk curves and the impact of the sample size by conducting 2000 simulations. Sample sizes ranged from 13 to 26. FindingsThe Weibull distribution was optimal for all the response variables, except deflection (log-logistic). The quality of the risk curves was the highest for deflection. This variable best explained the underlying head injury response, based on BSM. Improvements in the quality of the risk curves were achieved with additional samples of force and deflection (<13), while energy and stiffness variables required more size. Individual risk curves are given. InterpretationThese probability curves from head contact loading add to the understanding skull fractures and can be used to improve safety in injury producing environments.

Development of Headform Impactor Finite Element Model Considering the Hyperelastic and Viscoelastic Responses of Rubber

To evaluate and analyze the pedestrian injury risk of automobiles, the finite element models of headform impactors are used. In this study, a modeling method that can accurately estimate the peak of the headform impactor impact pulse and head injury criterion (HIC) was developed. The headform impactor skin has the characteristics of both hyperelasticity and viscoelasticity. Therefore, compression tests, stress relaxation tests, and rheometer tests were conducted, and the hyperelastic and viscoelastic models were developed. The models were combined and used in the finite element analysis. The new headform impactor model was verified to accurately estimate the peak of impact pulse and HIC at the certification test of the headform impactor.

Correlation of Occupant Evaluation Index on Vehicle-occupant-guardrail Impact System

Aiming at the occupant safety risk assessment of vehicle guardrail impact, a finite element model of vehicle-occupant-guardrail impact system was established and the validation of the model was verified based on the test result. Different impact speed such as 60 km/h, 80 km/h, 100 km/h, 120 km/h and different impact angle such as 25°, 30°, 35°were selected and combined to conduct 12 groups of vehicle guardrail impact simulation test by Hyper Mesh and LS-DYNA. The Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV), Post-impact Head Deceleration (PHD) and Head Injury Criterion (HIC) were analyzed by obtaining the longitudinal, transverse and vertical acceleration data of vehicle centroid and occupant head in the impact process. Quantitative corresponding relations between other occupant risk assessment index and Head Injury Criterion (HIC) was analyzed by SPSS, and the results showed that ASI and HIC had good correlation. Fitting degree between ASI and HIC is 0.93 with the exponential function. The study results of occupant would have guiding significance for related standards’ development and revision of related standard, experimental study and product development.

Designing safer composite helmets to reduce rotational accelerations during oblique impacts.

Oblique impact is the most common accident situation that occupants in traffic accidents or athletes in professional sports experience. During oblique impact, the human head is subjected to a combination of linear and rotational accelerations. Rotational movement is known to be responsible for traumatic brain injuries. In this article, composite foam with a column/matrix composite configuration is proposed for head protection applications to replace single-layer uniform foam, to better attenuate rotational movement of the head during oblique impacts. The ability of composite foam in the mitigation of rotational head movement is studied by performing finite element (FE) simulations of oblique impact on flat and helmet shape specimens. The performance of composite foam with respect to parameters such as compliance of the matrix foam and the number, size and cross-sectional shape of the foam columns is explored in detail, and subsequently an optimized structure is proposed. The simulation results show that using composite foam instead of single-layer foam, the rotational acceleration and velocity of the headform can be significantly reduced. The parametric study indicates that using a more compliant matrix foam and by increasing the number of columns in the composite foam configuration, the rotation can be further mitigated. This was confirmed by experimental results. The simulation results were also analyzed based on global head injury criteria such as head injury criterion, rotational injury criterion, brain injury criterion and generalized acceleration model for brain injury threshold which further confirmed the superior performance of composite foam versus single-layer homogeneous expanded polystyrene foam. The findings of simulations give invaluable information for design of protective helmets or, for instance, headliners for the automotive industry.

Top tether effectiveness during side impacts

ABSTRACTObjective: Few studies have looked at the effectiveness of the top tether during side impacts. In these studies, limited anthropomorphic test device (ATD) data were collected and/or few side impact scenarios were observed. The goal of this study was to further understand the effects of the top tether on ATD responses and child restraint system (CRS) kinematics during various side impact conditions.Methods: A series of high-speed near-side and far-side sled tests were performed using the FMVSS213 side impact sled buck and Q3s ATD. Tests were performed at both 10° and 30° impacts with respect to the pure lateral direction. Two child restraints, CRS A and CRS B, were attached to the bench using flexible lower anchors. Each test scenario was performed with the presence and absence of a top tether. Instrumentation recorded Q3s responses and CRS kinematics, and the identical test scenarios with and without a top tether attachment were compared.Results: For the far-side lateral (10°) and oblique (30°) impacts, top tether attachment increased resultant head accelerations by 8–38% and head injury criterion (HIC15) values by 20–140%. However, the top tether was effective in reducing lateral head excursion by 5–25%. For near-side impacts, the top tether resulted in less than 10% increases in both resultant head acceleration and HIC15 in the lateral impact direction. For near-side oblique impacts, the top tether increased HIC15 by 17.3% for CRS A and decreased it by 19.5% for CRS B. However, the injury values determined from both impact conditions were below current injury assessment reference values (IARVs). Additionally, the top tether proved beneficial in preventing forward and lateral CRS rotations.Conclusions: The results show that the effects of the top tether on Q3s responses were dependent on impact type, impact angle, and CRS. Tether attachments that increased head accelerations and HIC15 values were generally counterbalanced by a reduction in head excursion and CRS rotation compared to nontethered scenarios.

Differences in the protective capabilities of bicycle helmets in real-world and standard-specified impact scenarios

ABSTRACTObjective: The purpose of this study was to investigate relative differences in impact attenuation capabilities of bicycle helmets under real-world impact conditions and safety standard-specified conditions using a standard rig.Methods: A Consumer Product Safety Commission (CPSC) test rig was used to impact 10 helmet models of varied design. Impact configurations included 2 locations and 2 velocities. A frontal rim location (inferior to the standard-defined test area) and a temporal location were selected to reflect common cyclist impacts. An impact velocity of 3.4 m/s, an average normal impact velocity in cyclist accidents, was selected, as well as the CPSC standard velocity of 6.2 m/s. Four samples per helmet model were subjected to each of the 4 impact configurations once (randomized test order per sample), resulting in 160 drop tests. Peak linear acceleration (PLA) and head injury criterion (HIC)-based Abbreviated Injury Scale (AIS) ≥ 4 brain injury risk were determined and compared across helmets and impact configurations using analysis of variance. Other impact characteristics such as duration, effective liner stiffness, and energy dissipated were also calculated from acceleration data.Results: Helmet performance varied significantly between models. PLA ranged from 78 to 169 g at 3.4 m/s (0–2% AIS ≥ 4 brain injury risk) and 165–432 g (10–100% risk) at 6.2 m/s. Temporal impacts resulted in higher PLAs than frontal impacts, likely due to increased effective liner stiffness. However, 2 helmets exceeded the CPSC pass–fail threshold (300 g) at the frontal rim location, producing >70% risk. Force–displacement curves suggest that bottoming-out occurred in these impacts. Aside from bottoming-out cases, helmets that performed worse in one impact configuration tended to perform worse in others, with non-road-style helmets among the worst.Conclusions: The 10 bicycle helmets tested produced considerable differences in their protective capabilities under both real-world and standard-specified conditions on the CPSC rig. Risk of severe brain injury varied widely between helmets at the standard impact velocity, whereas the common, lower severity impacts produced PLAs associated with concussion. Helmets of a nonroad style generally performed worse across configuration. The temporal location produced higher risks for most helmets, although some helmets were found to offer inadequate protection at the helmet rim. Because this is a commonly impacted location in cyclist accidents, there may be benefit to expanding the testable area in standards to include the rim. Results from this study demonstrate the value in testing nonstandard conditions and can be used to inform standards testing and helmet design.

Head, chest and femur injury in teenage pedestrian–SUV crash; mass influence on the speeds

This work studies the teenage pedestrian–sport utility vehicle (SUV) crash; injury to the vital parts of the body, such as the head and chest, and to the femur is evaluated. More advanced injury criteria are applied, as provided in the rules. The multibody technique is applied by making use of SimWise software and of the teenager anthropomorphic model, the use of which is now consolidated. Head injury criterion (HIC) is used for the head, thoracic trauma index (TTI) criterion for the thorax in the case of side impact and 3 ms criterion in the case of frontal impact, while the force criterion is used for the femur. Both the TTI and femur load evaluation require non-substantial modifications of the dummy, by insertion of sensors for the measurement of the acceleration of the 4th rib and the 12th vertebra and two very thin plates at the knees for the correct individuation of the contact point with the vehicle bumper. Particular attention is paid to the front shape of the vehicle, concluding that the SUV examined in this paper is less dangerous than the sedan studied in a previous work, since its frontal dimensions (bonnet angle, bumper height and bonnet height) are more advantageous. However the teenage pedestrian in a lateral position is less prone to injuries in the head and chest, with respect to the frontal position; the pedestrian’s position has little influence on femur damage. Furthermore, the braking of the vehicle reduces the possibility of crash fatality. In conclusion, a theoretical approach is shown, to highlight the influence of the vehicle mass on the pedestrian speed after the impact.

Development of a multibody system for crashworthiness certification of aircraft seat

This work proposes a multibody approach in the simulation of 16-g aircraft seats, referred to the front-row of seats located behind bulkheads compliance with the Head Injury Criteria (HIC) requirement. The multibody model of the seat structure has been developed and analysed by using a home-made algorithm implemented in Matlab® code, as a 2D system of rigid bodies interconnected by springs and joints. The research has been oriented to assess the capability of simulating a 16g frontal impact of a sled equipped with the seat of a regional aircraft on which an anthropomorphic dummy is arranged. This sled test, for which experimental data were available, has been used as test case; inertial and structural properties of the system have also been experimentally and numerically evaluated in order to make the numerical model compliant with the real one.

Study regarding the influence of airbag deployment time on the occupant injury level during a frontal vehicle collision

The aim of this paper was to analyse the influence of airbag deployment delay upon the head of the occupant in the case of frontal collision using simulations in PC Crash and MADYMO dummy as the occupant. The study will also take into account the pretension delay of the seat-belt which is activated along with the airbag. Frontal airbags on both the passenger and the driver were analysed including the occupant kinematics during the collision. Also, to validate the simulation, a comparison was done with a real crash test. We predict that by increasing the delay of deployment, the head acceleration will increase due to the fact the head travels close to the instrument panel/steering wheel, and the force of the airbag will generate a significant acceleration upon the head. To better assess the potential injury of the occupant, the head injury criteria (HIC) will be calculated and correlated with the Abbreviated injury scale (AIS) code.

Factors Affecting Diffuse Axonal Injury under Blunt Impact and Proposal for a Head Injury Criteria: A Finite Element Analysis.

Diffuse axonal injury (DAI) is the most common pathological feature of brain injury which accounts for half of the traumatic lesions in the United States. Although direct shear strain measures indicate DAI, it is localized and varies greatly in the brain. It has limitations when correlated with the possibility and severity of DAI in different brain regions along different planes for variable factors. Rather, a statistical strain measure such as peak shear strain possibility (PSSP) is proposed as a head injury criteria. In this study, computer tomography (CT) was used to derive a finite element model of the skull-brain complex including viscoelastic behavior for brain material. It was simulated under blunt impact for variable factors such as five impact directions, four impact velocities, and four head sizes. Nodal shear strain measures were obtained for seven brain regions along three planes. Proposed PSSPs for different shear strain level (10%90%) were calculated. Considering 30% shear strain as the critical level, PSSPs were 0.49 for corpus callosum and 0.71 for the brain stem along the sagittal plane, and 0.63 for frontal impact. Among eighty simulation cases (240 strain measures), the corpus callosum and brain stem have the highest possibility (30%) of DAI. Frontal impact is the most dangerous direction, followed by side-back and back impact. For all impact directions, the highest PSSP along the sagittal plane indicates the predominance of rotational motion of the brain for causing DAI. Head size variation has the least effect on DAI possibility. At higher impact velocities, DAI possibility increases nonlinearly. Hence, these proposed criteria are expected to predict DAI under variable factors.

A Study of the Effect of the Front-End Styling of Sport Utility Vehicles on Pedestrian Head Injuries.

Background The number of sport utility vehicles (SUVs) on China market is continuously increasing. It is necessary to investigate the relationships between the front-end styling features of SUVs and head injuries at the styling design stage for improving the pedestrian protection performance and product development efficiency. Methods Styling feature parameters were extracted from the SUV side contour line. And simplified finite element models were established based on the 78 SUV side contour lines. Pedestrian headform impact simulations were performed and validated. The head injury criterion of 15 ms (HIC15) at four wrap-around distances was obtained. A multiple linear regression analysis method was employed to describe the relationships between the styling feature parameters and the HIC15 at each impact point. Results The relationship between the selected styling features and the HIC15 showed reasonable correlations, and the regression models and the selected independent variables showed statistical significance. Conclusions The regression equations obtained by multiple linear regression can be used to assess the performance of SUV styling in protecting pedestrians' heads and provide styling designers with technical guidance regarding their artistic creations.

Analysis of pedestrian-to-ground impact injury risk in vehicle-to-pedestrian collisions based on rotation angles

IntroductionDue to the diversity of pedestrian-to-ground impact (secondary impact) mechanisms, secondary impacts always result in more unpredictable injuries as compared to the vehicle-to-pedestrian collisions (primary impact). The purpose of this study is to investigate the effects of vehicle frontal structure, vehicle impact velocity, and pedestrian size and gait on pedestrian-to-ground impact injury risk. MethodA total of 600 simulations were performed using the MADYMO multi-body system and four different sizes of pedestrians and six types initial gait were considered and impacted by five vehicle types at five impact velocities, respectively. The pedestrian rotation angle ranges (PRARs) (a, b, c, d) were defined to identify and classify the pedestrian rotation angles during the ground impact. ResultsThe PRARs a, b, and c were the ranges primarily observed during the pedestrian landing. The PRAR has a significant influence on pedestrian-to-ground impact injuries. However, there was no correlation between the vehicle velocity and head injury criterion (HIC) caused by the secondary impact. In low velocity collisions (20, 30km/h), the severity of pedestrian head injury risk caused by the secondary impact was higher than that resulting from the primary impact. ConclusionsThe PRARs defined in this study are highly correlated with the pedestrian-to-ground impact mechanism, and can be used to further analyze the pedestrian secondary impact and to predict the head injury risk. Practical applicationsTo reduce the pedestrian secondary impact injury risk, passive and active safety countermeasures should be considered together to prevent the pedestrian's head-to-ground impacts, particularly in the low-velocity collisions.