Neck Forces Research Articles

Finite element analysis of hip fracture risk in elderly female: The effects of soft tissue shape, fall direction, and interventions

This study investigates the effects of fall configurations on hip fracture risk with a focus on pelvic soft tissue shape. This was done by employing a whole-body finite element (FE) model. Soft tissue thickness around the pelvis was measured using a standing CT system, revealing a trend of increased trochanteric soft tissue thickness with higher BMI and younger age. In the lateroposterior region from the greater trochanter, the soft tissues of elderly females were thin with a concave shape. Based on the THUMS 5F model, an elderly female FE model with a low BMI was developed by morphing the soft tissue shape around the pelvis based on the CT data. FE simulation results indicated that the lateroposterior fall led to a higher femoral neck force for the elderly female model compared to the lateral fall. One reason may be related to the thin soft tissue of the pelvis in the lateroposterior region. Additionally, the effectiveness of interventions that can help mitigating hip fractures in lateroposterior falls on the thigh-hip and hip region was assessed using the elderly female model. The attenuation rate of the femoral neck force by the hip protector was close to zero in the thigh-hip fall and high in the hip fall, whereas the attenuation rate of the compliant floor was high in both falls. This study highlights age-related changes in the soft tissue shape of the pelvis in females, particularly in the lateroposterior regions, which may influence force mitigation for the hip joint during lateroposterior falls.

Trend analysis of rear child occupants’ injury influenced by protection system parameters

As road traffic accidents are the leading cause of child injuries and deaths, the most common frontal impact is offset impact. Taking into consideration the lack of research on rear seat child occupants’ safety in road accidents, this study focuses on 10-year-old child occupants seated in the rear and establishes an analytical model of child injury during frontal offset impact, which is validated using test data from a real car impact of the same model. The study then examines the effects of restraint system parameters, including seat belt force-limited level, seat belt anchorage position, and seat cushion stiffness, on head, neck, and chest-abdomen injury response in the rear seat child occupants. The study found that reducing the seat belt force-limited level appropriately resulted in a significant decrease in the child occupant’s head resultant acceleration by 39.9% and the upper neck force by 53.2%. Meanwhile, increasing the seat cushion stiffness was found to reduce the child occupant’s head resultant acceleration by 18.8%, the upper neck force by 31%, and the abdominal pressure by 34.4%. This study provides a reference for the protection of rear seat child occupants.

Muscle activity on head-first compression responses of a finite element neck model

Effects of muscle activation on human neck kinematic responses under compressive loads have not been understood empirically due to the limitation of testing on in vivo test specimens. Advanced computational models can potentially provide information to improve our understanding of such responses. This study used a previously developed ligamentous finite element (FE) neck model, further integrated with muscles, fleshy tissue, and skin of the neck to predict the influence of passive and active muscles on responses to neck compression. For validation, post-mortem human subject (PMHS) and volunteer responses in frontal sled impacts were used to compare the dynamic response of the model with passive and active muscles, respectively. An objective evaluation of the validation responses suggested the ‘fair’ to ‘good’ biofidelity rating of the muscular system model. The compressive impacts, used to validate the ligamentous FE neck, were methodologically applied in the current study including the muscles with various activation states, flesh, and skin. The contribution of muscles (passive or active) resulted in an increase in the peak lower neck compression and shear forces and in a reduction in the upper neck forces on average; the role of active state dynamics of the muscles was crucial on the magnitude of the forces. Therefore, modeling of the muscles in a computational neck model may not be neglected to study a head-first compressive impact.

Analysis of loading to the hip joint in fall using whole-body FE model

Hip fractures caused by falls are important health problems for the elderly. Many studies used finite element (FE) models of the femur and its surroundings to evaluate the hip fracture risk during the impact phase in a fall. In this study, the whole-body human FE model (THUMS) of a small female was applied from the descent to the impact phase in a fall to understand the effect of the whole body. Brosh’s material model was used for the soft tissue of the hip. A low-BMI and high-BMI model were developed based on THUMS (middle-BMI). For the middle-BMI model, the torso angle and the pelvis impact velocity were 45.2° and 2.62 m/s at the time of pelvis impact. The effective mass changed with time, and was 18.3 kg when the femoral neck force was maximum. The femoral neck force was 2.11 kN for the low-BMI model. The femoral neck forces when wearing a soft and a hard hip protector, and when falling on an energy-absorbing floor were compared for the FE models of human and a hip protector testing system. Though the force attenuation of the protective devices was 32.0–44.3 % in the testing system, the force attenuation in the middle-BMI was 0.1–22.2 %. In the low-BMI model, the attenuation of the soft protector was limited (4.2 %) because the hip protector protruded from the outer surface, so the contact force was concentrated at the hip region. This research suggests the importance of including the whole body to evaluate the hip fracture risk.

Comparative performance of rearward and forward-facing child restraint systems with common use errors: Effect on crash injury risk for a 1-year-old occupant

Objective To compare how errors in child restraint use influence crash injury risk in rearward and forward-facing restraints for a 1-year old occupant. Methods Three convertible child restraint systems (CRS) were subjected to frontal dynamic sled tests at 56 km/h in rearward-facing and forward-facing modes in a correct use (baseline) condition and in five incorrect use conditions: loose securing belt, loose harness, partial harness use, top tether slack, and three minor errors. Excursion, head, and chest 3 ms resultant acceleration, HIC15, and neck forces and moments of a Q1 anthropomorphic test device (ATD) seated in the restraints were measured. The effect of incorrect use on each outcome and restraint type was analyzed. Results The influence of errors varied across different outcome variables, the three restraints tested and orientation modes. Excursion increased in four of five incorrect use conditions in both rearward and forward-facing orientations. A very loose harness increased four of five outcome variables in at least one forward-facing restraint, whereas only excursion was increased when rearward-facing. Overall, there tended to be a more negative effect of incorrect use (demonstrated through increases in outcome variables compared to the baseline) in the forward-facing orientation. Conclusions Overall, errors in use tended to have a larger negative impact on forward-facing restraints than rearward-facing restraints. Given the widespread nature of errors in use, this adds further weight to arguments to keep children rearward-facing to 12 months of age and older. The results also highlight a variation in response to errors across differently designed restraints, suggesting the influence of errors may be minimized by restraint design that is more resistant to errors.

Investigation on the Effect of Malaysian Anthropometric Size in Vehicle Crash Safety by using Finite Element Method


 
 
 In general, most vehicle safety is developed and optimized using a standard crash dummy, in which the sizes and mass of the anthropometric data are primarily referred to the US population. In other words, it can be deduced that the safety configuration of such vehicles is not optimized for Malaysian or even Asian populations, which might cause severe injury. Therefore, in this paper, the injury is investigated using the actual Malaysian anthropometric data. To be specific, the Hybrid III 50th percentile dummy H350 is scaled to Malaysian 50th percentile dummy H350M, integrated into the vehicle, and analyzed using the finite element method. Using the newly H350M, the results showed the neck forces and moments are slightly reduced while the other injury parameters remained similar. There is also a noticeable increase in chest acceleration from 54.1g to 58.0g. The most critical assessment on the head injury by using the HIC15 method has shown a significant increase from 596 to 913, which could lead to severe head injury.
 
 

Optimization of the Impact Attenuation Capability of Three-Dimensional Printed Hip Protector Produced by Fused Deposition Modeling Using Response Surface Methodology.

Fused deposition modeling has provided a cheap and effective method for the rapid production of prototypes and functional products in many spheres of life. In this study, three-dimensional (3D) printing techniques to produce and optimize a hip protector that will assure clinical efficacy are presented. The I-Optimal design was used to optimize the hip protector's significant parameters (infill density, shell thickness, and material shore hardness) to obtain maximum femoral neck force attenuation of the 3D-printed hip protector. A drop impact tower device simulates the impact force at the hip's parasagittal plane during a fall. The results show that the infill density has the most significant influence on attenuation properties, followed by the infill density combined with the material shore hardness. By maximizing all the parameters, it is demonstrated that using an additive manufacturing technique to print hip protectors could be an effective strategy in curbing hip fractures.

Turning turtle: scaling relationships and self-righting ability in Chelydra serpentina.

Testudines are susceptible to inversion and self-righting using their necks, limbs or both, to generate enough mechanical force to flip over. We investigated how shell morphology, neck length and self-righting biomechanics scale with body mass during ontogeny in Chelydra serpentina, which uses neck-powered self-righting. We found that younger turtles flipped over twice as fast as older individuals. A simple geometric model predicted the relationships of shell shape and self-righting time with body mass. Conversely, neck force, power output and kinetic energy increase with body mass at rates greater than predicted. These findings were correlated with relatively longer necks in younger turtles than would be predicted by geometric similarity. Therefore, younger turtles self-right with lower biomechanical costs than predicted by simple scaling theory. Considering younger turtles are more prone to inverting and their shells offer less protection, faster and less costly self-righting would be advantageous in overcoming the detriments of inversion.

Development of a detailed human neck finite element model and injury risk curves under lateral impact

Advanced neck finite element modeling and development of neck injury criteria are important for the design of optimal neck protection systems in automotive and other environments. They are also important in virtual tests. The objectives of the present study were to develop a detailed finite element model (FEM) of the human neck and couple it to the existing head model, validate the model with kinematic data from legacy human volunteer and human cadaver impact datasets, and derive lateral impact neck injury risk curves using survival analysis from the upper and lower neck forces and moments. The detailed model represented the anatomy of a young adult mid-size male. It included all the cervical and first thoracic vertebrae, intervening discs, upper and lower spinal ligaments, bilateral facet joints, and passive musculature. Material properties were obtained from literature. Frontal, oblique, and lateral impacts to the distal end of the model was applied based on human volunteer and human cadaver experimental data. Corridor and cross-correlation methods were used for validation. The CORrelation and Analysis (CORA) score was used for objective assessments. Forces and moments were obtained at the occipital condyles (OC) and T1, and parametric survival analysis was used to derive injury risk curves to define human neck injury tolerance to lateral impact. The Brier Score Metric (BSM) was used to determine the hierarchical sequence among the injury metrics. The CORA scores for the lateral, frontal, and oblique impact loading conditions were 0.80, 0.91, and 0.87, respectively, for human volunteer data, and the mean score was 0.7 for human cadaver lateral impacts. Injury risk curves along with ±95% confidence intervals are given for all the four biomechanical metrics. The OC shear force was the optimal metric based on the BSM. A force of 1.5 kN was associated with the 50% probability level of AIS3+ neck injury. As a first step, the presented risk curves serve as human tolerance criteria under lateral impact, hitherto not available in published literatures, and they can be used in virtual testing and advancing restraint systems for improving human safety.

Assessment of the force attenuation capability of 3D printed hip protector in simulated sideways fall

An innovative 3D printed hip protector has been designed and tested to decrease the possibility of hip fracture in a sideways fall to a hard surface. The main design purpose was to create custom fit hip protector, reduce the manufacturing period and make the protector comfortable to wear. This work compares the new energy shunting 3D printed hip protector design with an existing energy absorbing hip protector. A drop tower mechanical test rig was designed and developed to simulate a sideways fall with sufficient impact energy to fracture an unprotected greater trochanter (GT). The test rig incorporates the actual geometry of a femur made from steel and uses a foam to simulate trochanteric soft tissue over the greater trochanter. Similar impact energy was used for the testing of each hip protector. The weight of the striker mass was maintained, and the height was adjusted to obtain an impact energy of 21–43J to produce femoral neck force of 3–9 kN. Results illustrate that the 3D hip protector compares favorably in attenuating impact force capable of causing hip fracture to a value below the fracture threshold of 3.472 kN. The influence of the 3D hip protector on peak transmitted forces to the vulnerable site of the greater trochanter is shown to be positive. It is anticipated that future protectors can be 3D printed after optimizations to end the bundling of same hip protector for different body geometry.

Safety analysis of battery-powered ride-on toy car with seat and restraint system modifications

ABSTRACT Modified battery-powered ride-on toy cars represent novel rehabilitation tools for children with disabilities. However, safety concerns exist with the use of these battery-power toys and pose a barrier for the growth of adaptive ride-on toy programs due to the lack of evidence demonstrating that modifications made to these cars are safe. Within this context, the purpose of this study was to investigate whether modifications to ride-on toys are sufficient to prevent common injuries and determine how these modifications influence injury metrics. Specifically, we evaluated the effects of common modifications such as various seatbelt configurations and determined how increased seat back height effects neck forces. Results indicated that occupant displacement can be reduced using a lap belt, and further reductions in displacement are achieved with a 5-point harness. Although some injury metrics increased with restraints, none of the collected injury metrics even came close to approaching known tolerance thresholds, and most were well within the range that is experienced by a child in daily life. As the greatest concerns for these ride-on toys are related to displacement, findings from this study support the use of a 5-point harness system to minimize displacement-related injuries with little-to-no added risk.

Finite Element Model of a Deformable American Football Helmet Under Impact.

Despite the use of helmets in American football, brain injuries are still prevalent. To reduce the burden of these injuries, novel impact mitigation systems are needed. The Vicis Zero1 (VZ1) American football helmet is unique in its use of multi-directional buckling structures sandwiched between a deformable outer shell and a stiff inner shell. The objective of this study was to develop a model of the VZ1 and to assess this unique characteristic for its role in mitigating head kinematics. The VZ1 model was developed using a bottom-up framework that emphasized material testing, constitutive model calibration, and component-level validation. Over 50 experimental tests were simulated to validate the VZ1 model. CORrelation and Analysis (CORA) was used to quantify the similarity between experimental and model head kinematics, neck forces, and impactor accelerations and forces. The VZ1 model demonstrated good correlation with an overall mean CORA score of 0.86. A parametric analysis on helmet compliance revealed that the outer shell and column stiffness influenced translational head kinematics more than rotational. For the material parameters investigated, head linear acceleration ranged from 80 to 220g, whereas angular velocity ranged from 37 to 40rad/s. This helmet model is open-source and serves as an in silico design platform for helmet innovation.

Frontal crash seat belt restraint effectiveness and comfort accessories used by older occupants

Objective: Around a quarter of older occupants use some type of comfort or orthopedic aftermarket accessory on the vehicle seat while traveling in a vehicle. The aim of this study was to investigate the effect of comfort accessories on the performance of the seat belt restraint system in a frontal crash in terms of potential injury implications for older occupants.Methods: Eight frontal sled tests (43 km/h, 32 g) were carried out on a deceleration sled fitted with a three-point lap-sash seat belt and a front passenger seat from a common Australian passenger car for each test. A 5th percentile Hybrid III anthropometric test device (ATD) was positioned in the seat and measurements were recorded for head center of gravity acceleration, chest acceleration, neck forces and moments and sternal deflection. Tests were carried out in a baseline condition and with seven comfort accessories. Each comfort accessory was inserted between the ATD and vehicle seat as it is intended to be used, with the ATD otherwise positioned as close as possible to the baseline test position.Results: Initial distance between the seat belt anchor and ATD hip was associated with a statistically significant decrease in Head Injury Criterion and increase in sternal deflection. Submarining was related to the ATD torso recline angle and angle of the lap belt from the seat belt anchor.Conclusions: Accessories placed between the seat back and the lumbar region of an occupant have the potential to increase the risk of submarining due to a change in posture and should be avoided if such a change in posture when seated with an accessory is excessive. Sitting on seat cushions resulted in the greatest increase in seat belt anchor to hip distances and hence largest increase in sternal deflection. Given the fragility, frailty and particular importance of chest injuries among older vehicle occupants, further investigation is needed to determine whether these changes in ATD sternal deflection observed with seat cushion use results in injury threshold limits being exceeded and whether pretensioners and load limiters would ameliorate these effects without causing other negative changes in occupant response or kinematics.

Responses of the scaled pediatric human body model in the rear- and forward-facing child seats in simulated frontal motor vehicle crashes

Objective: The study presents the first-ever endeavor at developing 18-, 24-, 30-, 36-, 42-, and 48-month-old pediatric finite element models from the 6-year-old PIPER human body model as a baseline and comparing their responses systematically in rear-facing and forward-facing simulations across similar boundary conditions.Methods: A 6-year-old PIPER model was scaled down to create anthropometric models of the 18-, 24-, 30-, 36-, 42-, and 48-month-old child using the PIPER scaling tool. The models were installed on a convertible car seat (rear-facing and forward-facing configurations) installed with a 3-point lap–shoulder belt in the rear outboard seat of a 2012 Toyota Camry vehicle model finite element model and setup for full-frontal crash simulation (24 G, 120 ms pulse).Results: The forward-facing models showed higher head resultant accelerations for 24-, 36-, 42-, and 48-month-old models (reduction for rear-facing seats ranging from 10% to 32%). For the 18- and 30-month-old models, the maximum head acceleration showed similar values (difference of less than 10%). Upper neck forces and moments were consistently lower for rear-facing models compared to forward-facing. The neck forces were reduced by 83%–90% and the neck moments were reduced by 63%–85% in the rear-facing models compared to their respective forward-facing configurations. The reduction in head injury criterion (HIC36) for rear-facing models ranged from 14% to 51%. The neck injury criterion (Nij) for all forward-facing models was 6 to 9 times the values of their rear-facing counterpart.Conclusions: The study shows the potential benefit of rear-facing orientation compared to forward-facing for children up to 4 years of age in a controlled environment.

Effectiveness of center-mounted airbag in far-side impacts based on THOR sled tests

Objective: The study aimed to evaluate the protection offered by a center-mounted airbag in far-side impacts using the Test device for Human Occupant Restraint (THOR) anthropometric test device (ATD).Methods: A rigid buck was designed based on a production vehicle. The buck consisted of a rigid seat, center console, dash, and far-side door structure. The center console and dash were covered with paper honeycomb (152 kPa), and the far-side door structure was covered with Ethafoam 220 padding material. The airbag was mounted on the seat, to the right of the occupant. The THOR-M50 ATD was positioned according to the standard seating procedure and restrained using a standard 3-point seat belt with a pretensioner and retractor. The buck was mounted on an acceleration sled in 2 orientations. Four tests at 45° (oblique) and 2 tests at 90° (lateral) orientations were conducted. Tests were performed with and without an airbag at 30 km/h delta-V and 14 g acceleration. The head accelerations, neck forces and moments, thoracic accelerations and forces, pelvis accelerations, anterior superior iliac spine (ASIS) forces and moments, and belt webbing loads were obtained from sensors, and the external kinematics was obtained using an optical motion capture system and high-speed digital cameras.Results: With the center-mounted airbag, in 90° and 45° tests, reductions were observed for the following parameters: head lateral excursions by 6% and 11%, head vertical excursions by 19% and 26%, and peak head resultant accelerations by 36% and 11%. Other regional accelerations, forces, and moments were also reduced for both impact angles. A reduction in seat belt forces with the airbag was observed in 90° tests.Conclusion: The center-mounted airbag reduced the ATD excursions and accelerations in the 45° and 90° tests, thus reducing the risk of injury due to contact with the intruding structure. The results of this study may assist in designing countermeasures for vehicles in far-side impact.

Cross-chest clips in child restraints: A crash testing study

Objective: Cross-chest clips are widely used in North American child restraints but are less common in other countries, partially due to concerns over anterior neck contacts in frontal crashes. They have recently been reported to be associated with lower odds of injury in real-world crashes, but there is a paucity of crash test performance information. This study aimed to compare the dynamic performance of a small child occupant in frontal crash tests with and without cross-chest clips in place.Methods: Frontal sled tests at 49 km/h were conducted to compare 2 cross-chest clip designs to nonuse of a chest clip. Tests using a P3/4 anthropomorphic test device (ATD) to represent the smallest occupant in a forward-facing child restraint were conducted with the chest clips in the recommended position and also in an incorrect lower position and with and without additional harness slack present.Results: Though contacts were observed between the chest clips and the base of the ATD’s neck, there was little difference observed in head excursion or ATD sensor loads in the presence of the chest clips. No detectable change in the neck forces or moments was detected at the time of the neck contacts. The position of the clips did not affect the results. Harness slack increased head excursion, as expected, but this effect did not differ between the tests with and without the clips.Conclusions: Cross-chest clips do not appear to greatly influence the dynamic performance of a forward-facing child restraint in a simulated frontal crash. Taken together with recent research suggesting a potential benefit in injury reduction from the clips in the real world, possibly due to maintaining the harness straps in place on a child’s shoulders, it may be appropriate to re-evaluate safety standards that prevent their use.

Comparison of head impact attenuation capabilities between a standard American football helmet and novel protective equipment that couples a helmet and shoulder pads

Concussive and subconcussive sports-related head impacts are common in the United States, particularly in American football. Football helmets are constantly improving upon their predecessors and are proven to reduce head impact kinematics and the risk of sports-related head injury. All football helmets are required to pass certification testing overseen by the National Operating Committee on Standards for Athletic Equipment (NOCSAE) before they are permitted for use. A new advance in protective equipment involves coupling a helmet and shoulder pads as one connected piece of protective equipment. These protective gears cannot be tested using the standard NOCSAE method as they are worn over a user’s head, neck, and upper torso. We aimed to test the effectiveness of a prototype of a coupled, one-piece design, relative to a standard football helmet, using a custom drop tower method of testing. Relative to the standard football helmet, the coupled design reduced measures of peak linear acceleration at front, side, and rear impacts (p < .001) and peak rotational acceleration at all tested head locations (p < .004). The coupled design was also more effective than the standard helmet in attenuating the resultant upper neck force (p < .004) at all tested head impact locations and resultant upper neck moment at rear and side impact locations (p < .048). Future iterations of coupled, one-piece designs should use the results of this study to make improvements to the device, and further investigations on the effectiveness and safety implications of the protective gear are necessary.

Evaluating the response of the PIPER scalable human body model across child restraining seats in simulated frontal crashes

Objective: Booster seats ensure appropriate belt fit for children that a traditional vehicle seat belt cannot offer to small occupants. In this study, the responses of the PIPER 6-year-old human body model are compared to the traditional Q6 anthropomorphic test dummy (ATD).Methods: Eight frontal impact finite element simulations were run using 4 different child restraining systems on the FMVSS 213 test bench. Kinematics and kinetics were extracted and compared between the 2 child models.Results: The PIPER 6-year-old showed variation by 11.2 ± 14.1% (head resultant acceleration, G), 20.4 ± 50.3% (chest resultant acceleration, G), 272.9 ± 188.4% (chest displacement, mm), 24.8 ± 17.5% (maximum head excursion, mm), −31.5 ± 5.1% (neck force, Fz, N), −73.8 ± 2.8% (neck moment, My, N.m), and −60.4 ± 7.2% (Nij) compared to the Q6. However, the kinematics of both models were nearly similar.Conclusions: The PIPER model has a flexible neck and shows higher chest displacement compared to the Q6. We hypothesize that this is due to the inherent anatomical and mechanical differences between the human body model and the ATD model. More research is needed to explore these differences systematically.

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.

Design for Headrest Including Guides Slot to Reduce the Neck Force in Rear End Impact

Whiplash injuries are one of the most common injuries reported in automotive rear end collisions. Automobile seat back and head restraints play a role in reducing neck injuries during low speed rear end collisions. Currently, many studies are being conducted on ways to reduce neck injuries. These deal with the design parameters that cause neck injuries and do not address the design of the head restraint connection structure. In this paper, we analyze the various trajectories of the headrest and propose a new design for a connection structure that can move along the corresponding trajectory. We model the headrest connection mechanism as a virtual link using kinematic modeling and perform trajectory analysis. Using the trajectory of motion, we select an oblong shape for the guide slot by fitting it with the equation of an ellipse and propose a new headrest connection mechanism. To evaluate the design of the proposed mechanism, we model the shape of the mechanism and test it using dynamic simulation under collision conditions. In addition, we design a prototype for the proposed guide, conduct a sled test, and confirm that the neck force is reduced by the proposed connection structure. In the proposed structure, the values of maximum upper neck shear and tension decreased by more than 20 % compared to existing headrest.