Neck Axial Force Research Articles

The effect of chin-to-chest contact on upper neck axial force in UN Regulation No. 129 frontal impact tests of child restraint systems

Objective The objective of this study was to investigate the effect of chin-to-chest contact on upper neck axial force in United Nations (UN) Regulation No. 129 frontal impact tests of child restraint systems. Methods Frontal impact pilot experiments were carried out according to the test procedure in UN Regulation No. 129. Q-Series child dummies were seated in a small convenience sample of forward-facing child restraint systems. The timing and duration of chin-to-chest contact were determined using the procedure for calculating external head impact force in SAE J2052. Results Chin-to-chest contact was observed in all of our experiments and generated a tensile peak in the upper neck axial force of the Q-Series dummies. Prior to chin-to-chest contact, a purely inertial, noncontact peak was observed in the axial tension force. The tensile peak due to chin-to-chest contact was often greater than the inertial, noncontact peak force. Conclusions Chin-to-chest contact can increase axial neck tension force beyond the level it would reach under purely inertial loading. Adopting upper neck axial force in regulation, without considering how the force is generated, might encourage child restraint designs that mitigate only chin-to-chest contact, rather than the true inertial neck loading.

Implications of head and neck restraint test repeatability for specification improvement

Objective: Since 2005, National Association for Stock Car Auto Racing, Incorporated (NASCAR) drivers have been required to use a head and neck restraint system (HNR) that complies with SFI Foundation, Inc. (SFI) 38.1. The primary purpose of the HNR is to control and limit injurious neck loads and head kinematics during frontal and frontal oblique impacts. The SFI 38.1 performance specification was implemented to establish a uniform test procedure and minimum standard for the evaluation of HNRs using dynamic sled testing. The purpose of this study was to evaluate the repeatability of the current SFI 38.1 test setup and explore the effects of a polyester seat belt restraint system.Method: Eight sled tests were conducted using the SFI 38.1 sled test protocol with additional test setup constraints. Four 0° frontal tests and 4 30° right frontal (RF) oblique tests were conducted. The first 3 tests of each principal direction of force (PDOF) used nylon SFI 16.1 seat belt restraint assemblies. The fourth test of each PDOF used polyester SFI 16.6 seat belt restraint assemblies. A secondary data set (Lab B Data) was also supplied by the HNR manufacturer for further comparisons. The International Organization for Standardization (ISO) 18571 objective comparison method was used to quantify the repeatability of the anthropomorphic test device (ATD) resultant head, chest, and pelvis acceleration and upper neck axial force and flexion extension bending moment time histories across multiple tests.Results: Two data sets generated using the SFI 38.1 test protocol exhibited large variations in mean ISO scores of ATD channels. The 8 tests conducted with additional setup constraints had significantly lower mean ISO score coefficients of variation (CVs). The Lab B tests conducted within the current specification but without the additional test setup constraints had larger mean ISO score standard deviation and CV for all comparisons. Specifically, tests with the additional setup constraints had average CVs of 3.3 and 2.9% for the 0° and 30° RF orientations, respectively. Lab B tests had average CVs of 22.9 and 24.5%, respectively. Polyester seat belt comparisons had CVs of 5.3 and 6.2% for the 0° and 30° RF orientations, respectively.Conclusion: With the addition of common test setup constraints, which do not violate the specification, the SFI 38.1 test protocol produced a repeatable test process for determining performance capabilities of HNRs within a single sled lab. A limited study using polyester webbing seat belt assemblies versus the nylon material called for in SFI 38.1 indicates that the material likely has less effects on ATD upper neck axial force and flexion extension bending moment time histories than the test setup freedom currently available within the specification. The additional test setup constraints are discussed and were shown to improve ATD response repeatability for a given HNR.

The Effect of Direct Head Impact in Judo on Internal of Cervical Spine

PURPOSE: Judo is one of the popular combat sports, which is played worldwide and organized even in the Olympic Games. Serious neck injuries, however, have been occasionally noted in judo trainings and/or competitions. Since the pattern and severity of neck injuries largely depend on the kinematic motion of the thrown player, it is essential to investigate the mechanisms of neck injury from biomechanical view point in various different throwing techniques. Thus, the aim of this study was to evaluate a predictive indicator of cervical spine injury, neck injury criterion (Nij) with direct head impact by Judo throwing techniques using an anthropomorphic test device (ATD). METHODS: Two male judo experts (thrower) repeatedly threw the ATD for 5 times by Seoi-nage (Seoi), Osoto-gari (Osoto) and Ouchi-gari (Ouchi) techniques to make ATD's head hit directly to the mat. A 6-axis load cell (force transducer), mounted in the ATD’s cervical spine, assessed neck axial force and bending moment in each trial. To evaluate the the ATD’s neck load quantitatively, we calculated the Nij value from the neck axial force and bending moment. Kinematic data of the ATD’s whole body were also recorded during trials, using high-speed digital video cameras. RESULTS: In all trials, the largest neck loads were observed at the phase of the head contact to the mat. The peak Nij values of ATD ranged from 0.63 to 1.60 (Seoi), 0.54 to 0.58 (Osoto) and 0.19 to 0.29 (Ouchi). The average Nij value in Seoi (1.03±0.19, mean±S.E.) trials was significantly higher than those in Osoto (0.56±0.01) and Ouchi (0.24±0.02) trials (p<0.05, respectively). In three out of five tests, Nij value in Seoi trial exceeded 1.0 implying the real human tolerance limit for neck loading. However, in other two trials (Osoto and Ouchi), Nij values were less than 1.0. CONCLUSIONS: When thrown forward, the judo player might be accompanied with a direct contact of parietal and/or frontal regions of the head to the mat and suffered from neck injuries. Judo throwing technique, Seoi, has higher risk of serious neck injuries than the other techniques thrown backward including Osoto and Ouchi.

Evaluation of Hybrid III and THOR-M neck kinetics and injury risk under various restraint conditions during full-scale frontal sled tests

Objective: The objective of this research was to compare the kinetics and predicted injury risks of the Hybrid III (HIII) and Test device for Human Occupant Restraint (THOR)-M necks during full-scale frontal sled tests under 3 safety restraint conditions: knee bolster (KB), knee bolster and steering wheel airbag (KB/SWAB), and knee bolster airbag and steering wheel airbag (KBAB/SWAB).Methods: Twelve sled tests were performed for the HIII and THOR-M, and 8 matched sled tests were performed using postmortem human surrogates (PMHSs). The tests were designed to match the 2012 Toyota Camry New Car Assessment Program (NCAP) full-scale crash test. Upper and lower neck forces and moments were collected from the HIII and THOR-M load cells. Inverse dynamics was used to calculate PMHS upper neck forces and moments from acceleration data until the time of head contact. The PMHSs experienced head contact with the SWAB before appreciable neck loading occurred. Therefore, PMHS neck forces and moments were only compared to the HIII and THOR-M for the KB condition. Neck injury risks were calculated for the HIII and THOR-M and were compared to the injuries observed for the PMHSs.Results: The HIII had greater upper and lower neck shear forces than the THOR-M, whereas both surrogates had similar upper and lower neck axial forces. The HIII also experienced greater peak upper neck bending moments than the THOR-M, which experienced negligible upper neck bending moments. Before head contact, the PMHSs experienced upper neck flexion, and the HIII experienced extension. The HIII and THOR-M injury risk curves predicted less than a 50% risk of an Abbreviated Injury Scale (AIS) 3+ injury. No AIS 3+ neck injuries were observed for the PMHS tests, but at least one AIS 2 injury was observed per condition.Conclusions: The results of this study showed that the HIII and THOR-M had different neck kinetics for these restraint conditions. In particular, the THOR-M experienced lower upper neck shear forces and bending moments. These differences are likely due to the very different neck designs of the anthropomorphic test dummies (ATDs), particularly the increased compliance of the THOR-M neck. Despite these differences, both ATDs still predicted a similar risk of AIS 3+ neck injury.

Optimization of the Chin Bar of a Composite-Shell Helmet to Mitigate the Upper Neck Force

The chin bar of motorcycle full-face helmets is the most likely region of the helmet to sustain impacts during accidents, with a large percentage of these impacts leading to basilar skull fracture. Currently, helmet chin bars are designed to mitigate the peak acceleration at the centre of gravity of isolated headforms, as required by standards, but they are not designed to mitigate the neck force, which is probably the cause of basilar skull fracture, a type of head injury that can lead to fatalities. Here we test whether it is possible to increase the protection of helmet chin bars while meeting standard requirements. Fibre-reinforced composite shells are commonly used in helmets due to their lightweight and energy absorption characteristics. We optimize the ply orientation of a chin bar made of fibre-reinforced composite layers for reduction of the neck force in a dummy model using a computational approach. We use the finite element model of a human head/neck surrogate and measure the neck axial force, which has been shown to be correlated with the risk of basilar skull fracture. The results show that by varying the orientation of the chin bar plies, thus keeping the helmet mass constant, the neck axial force can be reduced by approximately 30% while ensuring that the helmet complies with the impact attenuation requirements prescribed in helmet standards.

Investigation of the THOR Anthropomorphic Test Device for Predicting Occupant Injuries during Spacecraft Launch Aborts and Landing.

The objective of this study was to investigate new methods for predicting injury from expected spaceflight dynamic loads by leveraging a broader range of available information in injury biomechanics. Although all spacecraft designs were considered, the primary focus was the National Aeronautics and Space Administration Orion capsule, as the authors have the most knowledge and experience related to this design. The team defined a list of critical injuries and selected the THOR anthropomorphic test device as the basis for new standards and requirements. In addition, the team down-selected the list of available injury metrics to the following: head injury criteria 15, kinematic brain rotational injury criteria, neck axial tension and compression force, maximum chest deflection, lateral shoulder force and displacement, acetabular lateral force, thoracic spine axial compression force, ankle moments, and average distal forearm speed limits. The team felt that these metrics capture all of the injuries that might be expected by a seated crewmember during vehicle aborts and landings. Using previously determined injury risk levels for nominal and off-nominal landings, appropriate injury assessment reference values (IARVs) were defined for each metric. Musculoskeletal deconditioning due to exposure to reduced gravity over time can affect injury risk during landing; therefore a deconditioning factor was applied to all IARVs. Although there are appropriate injury data for each anatomical region of interest, additional research is needed for several metrics to improve the confidence score.

Head and neck responses in oblique motorcycle helmet impacts: a novel laboratory test method

The dynamics of a Hybrid III dummy's head and neck in helmeted impacts using a novel oblique impact test were studied. Three impact conditions were investigated that simulated a range of motorcyclist head impacts and provided estimates of head and neck injury using published injury assessment reference values. The resultant linear and angular accelerations in the coronal plane were significantly higher for an impact to the side of the head when compared with frontal impacts. Neck axial forces were recorded, ranging from 2.1 to 3.4 kN. Linear regression analyses were conducted to determine the correlation coefficients that characterised the relationships between dummy responses and impact and sled velocities. Linear regression curves showed that increasing the impact and sled velocities resulted in an increase of the head angular accelerations. The neck axial force was found to positively correlate with the impact and sled velocities in the lateral impacts.

Whiplash injury criteria investigation with a global head-neck torso model

In this study, a minimum complexity head-neck-thorax model validated in the frequency domain was coupled to a car seat-head rest complex on Madymo software to establish more accurate neck injury criteria and associated tolerance limits. A total of 87 accident cases were then simulated using three seats. Several injury criteria, such as Neck Fx, Neck Fz, T1 acceleration, Neck Injury Criterionmax, Nkm and Neck Displacement Criterion, were calculated and correlated to the risk of AIS1 neck injury. A similar work has been done with the BioRID II model to compare the predictive risk curves obtained on both models. This comparison was expressed in terms of Nagelkerke R² values obtained with these analyses. It appears that the minimum complexity head-neck-thorax model gives a higher correlation than the BioRID II model for all parameters and that the lower neck axial force is shown as the best candidate to correlate with the neck injury.

Hybrid III ATD in Inverted Impacts: Influence of Impact Angle on Neck Injury Risk Assessment

The purpose of this paper is to present a protocol of inverted drop-tests using a 50th percentile Hybrid III Anthropomorphic Test Device (ATD) and investigate the influence of angle and velocity at impact on neck injury risk assessment. The tests were based on existing cadaveric experimental protocols for inverted seated positions. In this study selected ATD impact orientations were also assessed in both the sagittal and coronal planes. Twenty-six tests were performed at impact velocities from 1.4 to 3.1 m s(-1). The drop tests confirmed previously described behavior of the ATD in axial loading of its head/neck/thorax complex. They also showed a significant influence of the initial impact angle on neck injury criteria currently used by researchers in rollover crashworthiness tests. At 1.4 m s(-1), the peak upper neck axial force of 4350 N was reduced by an average 1760 +/- 80 N for configurations with 30 degrees initial impact angle in any plane, compared to a reference inverted vertical configuration. The N(ij) was also significantly influenced. For a given impact velocity, an out-of-both-planes initial configuration resulted in the highest combined outputs. Based on these results, similar dynamic conditions (intrusion velocity, impact duration) may result in significantly different loadings of the Hybrid III neck.

Computer Simulations of Contact Forces for Airbags with Different Folding Patterns During Deployment Phase

An explicit finite element method was used to study the neck load and the contact force between an occupant and an airbag during an out-of-position frontal automobile crash. Two different folding patterns and two different mounting angles of the airbag were simulated. For the four cases simulated, the occupant’s neck axial force ranged from 156 to 376% of the data obtained from in-position sled tests using the Hybrid III dummy. The neck shear force ranged from 87 to 229% and the neck flexion moment ranged from 68 to 127% of in-position experimental results. In both 300 mounting angle simulations, the neck axial forces were higher than that of the two simulations with 00 mounting angles, but the trend for the neck shear force was the opposite. Although the kinematics of the model appear reasonable, the numbers generated by the model must be reviewed with great caution because the model has not been fully validated.

Computer Simulations of Contact Forces for Airbags with Different Folding Patterns During Deployment Phase

An explicit finite element method was used to study the neck load and the contact force between an occupant and an airbag during an out-of-position frontal automobile crash. Two different folding patterns and two different mounting angles of the airbag were simulated. For the four cases simulated, the occupant’s neck axial force ranged from 156 to 376% of the data obtained from in-position sled tests using the Hybrid III dummy. The neck shear force ranged from 87 to 229% and the neck flexion moment ranged from 68 to 127% of in-position experimental results. In both 300 mounting angle simulations, the neck axial forces were higher than that of the two simulations with 00 mounting angles, but the trend for the neck shear force was the opposite. Although the kinematics of the model appear reasonable, the numbers generated by the model must be reviewed with great caution because the model has not been fully validated.