Crash Test Evaluation of Whiplash Injury Risk

This paper implements a biomechanical model and actual tipover trajectory data to assess the risk of head and neck injuries in standup forklift accidents. Seven accident scenarios were analyzed for right tipover, left tipover and off-dock accidents both with and without a door on the operator compartment. Each model had specific data including human anthropometry and trajectory input into the modeling and analysis software packages, Visual-Safe MAD and MADYMO. For all three accident scenarios, each of the seven biomechanical models was analyzed for Injury Assessment Reference Values (IARVs) including angular velocity (omega, omega), angular acceleration (alpha, alpha), Head Injury Criterion (HIC), Neck Injury Criterion--shear, tension and bending (NIC) and the biomechanical Neck Injury Predictor (N(ij)). The study concluded that, in general, the addition of a door to the standup forklift operator compartment leads to a reduction in injury during tipover and off-dock accidents. The ability to brace for impact is not included in these MADYMO models. Bracing is far more effective with an enclosed compartment provided by a latching rear door.

Influence of anthropometry on the kinematics of the cervical spine and the risk of injury in sled tests in female volunteers

Common quantitative assessments of neck injury criteria do not predict anatomical neck injuries and lack direct relations to design parameters of whiplash-protection systems. This study aims to provide insights into potential soft tissue-level injury sites based on the interactions developed in-between different anatomical structures in case of a rear-end collision. A detailed finite element human model has exhibited an excellent biofidelity when validated against volunteer impacts. Three head restraint arrangements were simulated, predicting both the kinematic response and the anatomical pain source at each arrangement. Head restraint’s contribution has reduced neck shear and head kinematics by at least 70 percent, minimized pressure gradients acting on ganglia and nerve roots less than half. Posterior column ligaments were the most load-bearing components, followed by the lower intervertebral discs and upper capsular ligaments. Sprain of the interspinous ligamentum flavum at early stages has caused instability in the craniovertebral structure causing its discs and facet joints to be elevated compressive loads. Excessive hyperextension motion, which occurred in the absence of the head restraint, has promoted a stable avulsion teardrop fracture of the fourth vertebral body’s anteroinferior aspect and rupture the anterior longitudinal ligament. The observed neck injuries can be mathematically related to head–torso relative kinematics. These relations will lead to the development of a comprehensive neck injury criterion that can predict the injury level. This, in turn, will impose a significant impact on the design processes of vehicle anti-whiplash safety equipment.

Objectives: The objective of this study is to examine the effectiveness of the active head restraint system in reducing neck injury risk of car occupants in low-speed rear impacts. Methods: A human body FE model “THUMS” was used to simulate head and neck kinematics of the occupant and to evaluate loading to the neck. Joint capsule strain was calculated to predict neck injury risk as well as NIC. The validity of the model was confirmed comparing its mechanical responses to those in human subjects in the literatures. Seat FE models were also prepared representing one with a fixed head restraint and the other one with an active head restraint system. The active head restraint system was designed to move the head restraint forward and upward when the lower unit was lower unit was loaded by the pelvis. Rear impact simulations were performed assuming a triangular acceleration pulse at a delta-V of 25 km/h. Results : The model reproduced similar head and neck motions to those measured in the human volunteer test, except for active muscular responses. The calculated joint capsule strain also showed a good match with those of PMHS tests in the literature. A rear-impact simulation was conducted using the model with the fixed head restraint. The result revealed that NIC was strongly correlated with the relative acceleration between the head and the torso and that its maximum peak appeared when the head contacted the head restraint. It was also found that joint capsule strain grew in later timing synchronizing with the relative displacement. Another simulation with the active head restraint system showed that both NIC and joint capsule strain were lowered owing to the forward and upward motion of the head restraint. A close investigation of the vertebral motion indicated that the active head restraint reduced the magnitude of shear deformation in the facet joint, which contributed to the strain growth in the fixed head restraint case. Conclusions: Rear-impact simulations were conducted using a human body FE model, THUMS, representing an average-size male occupant. The cervical system including the facet joint capsules was incorporated to the model. The validity of the model was examined comparing its mechanical responses to those in the literature such as the whole body motion of the volunteer subject and the vertebral motion in the PMHS tests. Rear-impact simulations were conducted using the validated THUMS model and two prototype seat models; one had a fixed head restraint and the other one was equipped with an active head restraint system. The active head restraint system works moving the head restraint forward and upward when the lower unit is loaded by the pelvis. The head and neck kinematics and responses were analyzed from the simulation results. The force and acceleration rose at the pelvis first, followed by T1 and the head. The early timing of force rise and its magnitude indicated that the pelvis force was a good trigger for the active head restraint system. The results showed that the head was supported earlier in a case with the active head restraint system, and both NIC and joint capsule strain were lowered. The study also analyzed the mechanism of strain growth in the joint capsules. Relatively greater strain was observed in the direction of the facet joint surface, which was around 45 degrees inclined to the spinal column. The forward and upward motion of the active head restraint were aligned with the direction of the joint deformation and contributed to lower strain in the joint capsules. The results indicated that the active head restraint could help reduce the neck injury risk not only by supporting the head at an early timing but also through its trajectory stopping the joint deformation.

Injury assessment reference values (IARV) predicting neck injuries are currently not available for side facing seated aircraft passengers in crash conditions. The aircraft impact scenario results in inertial loading of the head and neck, a condition known to be inherently different from common automotive side impact conditions as crash pulse and seating configurations are different. The objective of this study is to develop these IARV for the European Side Impact Dummy-2 (ES-2) previously selected by the US-FAA as the most suitable ATD for evaluating side facing aircraft seats. The development of the IARV is an extended analysis of previously published PMHS neck loads by identifying the most likely injury scenarios, comparing head-neck kinematics and neck loads of the ES2 versus PMHS, and development of injury risk curves for the ES2. The ES2 showed a similar kinematic response as the PMHS, particularly during the loading phase. The ES2 exhibited a stiffer response than the PMHS in the thoracic region, resulting in a faster rebound and smaller excursions in the vertical direction. Neck loads were consistent with results from previous authors and served as the basis for the ES2 neck injury risk curve developed here. Regression analysis of the previously published PMHS neck loads indicated that the tension force at the occipital condyles was the only neck load component with a significant correlation (Pearson r2 = 0.9158) to AIS3+ classified injuries. Tension force in the ES2 upper neck showed a weaker but still significant correlation with injury severity (r2 = 0.72) and is proposed to be used as an IARV with a tolerance of 2094 N for 50% AIS3+ risk. Although the prime focus of this study is on loading conditions typical in an aircraft crash environment, it is expected that the proposed IARV's can be used as an extension of typical automotive conditions, particularly for military vehicles and public transport applications where side facing upright seating configurations are more common.

Helmet mounted displays provide increased pilot capability, but can also increase the risk of injury during ejection. The National Highway Transportation Safety Administration's (NHTSA's) neck injury criteria (Nij) metric is evaluated for understanding the impact of helmet mass on the risk of injury and modified risk curves are developed which are compatible with the needs of the aviation community. Existent human subject data collected under various accelerative and head loading conditions were applied to understand the sensitivity of the Nij construct to changes in acceleration and helmet mass, as well as its stability with respect to gender, body mass, neck circumference, and sitting height. A portion of this data was combined with data from an earlier postmortem human subject study to create pilot study modified risk curves. These curves were compared and contrasted with the NHTSA risk curves. A statistically significant difference in the peak mean Nij was observed when seat acceleration increased by 2 G, but not when helmet mass was varied from 1.6 kg to 2 kg at a constant seat acceleration of 8 G. Although NHTSA risk curves predict a 13% risk of AIS 2+ injury for the 8-G, 2-kg helmet condition mean Nij of 0.138, no AIS 2+ injuries were observed. Modified risk curves were produced which predict a 0.91% risk of AIS 2+ injury under these conditions. The Nij was shown to be sensitive to changes in acceleration and generally robust to anthropometric differences between individuals. Modified risk curves are proposed which improve risk prediction at lower Nij values.

<div class="htmlview paragraph">Accident cases involving cars without head restraints are compared with cars having this device to evaluate the effectiveness of head restraints, their position when impact occurred and to provide some details concerning the relationship between occupant position, seat back damage and cervical injury. A reduction in non-dangerous cervical injury was associated with the head restraint group. However, due to small numbers this could not be confirmed, statistically.</div> <div class="htmlview paragraph">Approximately 73 percent of the adjustable head rests were in their lowest position. The position of the occupant on the seat strongly influenced injury. Larger amounts of rearward rotation of the seat back were associated with lower injury severity than limited rotation.</div> <div class="htmlview paragraph">Injuries to the cervical region resulting from automobile accidents have been the subject of a number of research reports. Concern over these injuries culminated in Federal Motor Vehicle Safety Standard Number 202 which requires that a head restraint be provided for front seat occupants of cars manufactured since 1 January 1969.</div> <div class="htmlview paragraph">The term most commonly associated with neck injuries observed in rear impact accidents is “whiplash.” Although the term has been derided by many authors as describing an injury mechanism and not a diagnosis, it continues to have widespread usage. The injury it is intended to describe results from hyperextension or hyperflexion of the neck as the head rotates to the rear in a rear end collision. The resulting injury may range from pain or simple muscular sprains to torn ligaments, cervical fractures or dislocations, or combinations of these injuries.</div> <div class="htmlview paragraph">A report by Kihlberg<sup><span class="xref">1</span></sup> indicated that neck injury was more frequent among front seat passengers than among rear seat passengers in the same car, and that the frequency of driver's injuries did not differ substantially from that of their rear passengers. Seat back damage, i. e., rearward bending of the seat, was associated with a lower frequency of neck injury to the occupant although this damage usually occurred in the more severe accidents. Kihlberg also found that the frequency of neck injury did not appear to be related to the height of the occupants, possibly because the top of the seat back is lower than the neck and shoulder area for most adults. Interestingly enough, neck injury was up to twice as frequent among women as among men. No explanation was found for this difference but it was hypothesized that the neck structure of women might not be as strong as that of men.</div> <div class="htmlview paragraph">In the present report, head restraint position and neck injuries among occupants of cars with head restraints are compared with those among occupants of cars without such devices.</div>

Current neck injury criteria used to evaluate whiplash injuries are based on the kinematics or kinetics of the occupant’s head and neck during rear impacts. The occupant’s response is affected by many factors including impact severity, seat design and occupant related factors such as gender and posture. Most of the current finite element models are concerned with modeling the head and neck, ignoring the interaction of the seat with the occupant during rear collision. In this work the Global Human Body Model Consortium (GHBMC) finite element model was used to study these interaction effects with emphases on the effect of seat belt, headrest and seat stiffness on the occupant’s response during rear-end collisions and evaluate the response using three neck injury criteria. The study shows the dramatic importance of the occupant’s seat restraint and head rest upon occupant safety. Specifically, the occupant ramping during rear impacts can be prevented by using the seat belt. Furthermore, the headrest reduces the head displacement and rotation. Our work further reveals that the head displacement reduction can lead to higher moments, axial and shear forces at the neck, especially for cases involving poorly adjusted or stiffer headrest.

Although blast mitigation seats are historically designed to protect the 50th percentile male occupant based on mass, the scope of the occupant centric platform (OCP) Technology Enabled Capability Demonstration (TEC-D) within the U.S. Army Tank Automotive Research Development Engineering Center (TARDEC) Ground System Survivability has been expanded to encompass lighter and heavier occupants which represents the central 90th percentile of the military population. A series of drop tower tests were conducted on twelve models of blast energy-attenuating (EA) seats to determine the effects of vertical accelerative loading on ground vehicle occupants. Two previous technical publications evaluated specific aspects of the results of these drop tower tests on EA seats containing the three sizes of anthropomorphic test devices (ATDs) including the Hybrid III 5th percentile female, the Hybrid III 50th percentile male, and the Hybrid III 95th percentile male. The first publication addressed the overall trends of the forces, moments, and accelerations recorded by the ATDs when compared to Injury Assessment Reference Values (IARVs), as well as validating the methodology used in the drop tower evaluations1. Review of ATD data determined that the lumbar spine compression in the vertical direction could be used as the “go/no-go” indicator of seat performance. The second publication assessed the quantitative effects of Personal Protective Equipment (PPE) on the small occupant, as the addition of a helmet and Improved Outer Tactical Vest (IOTV) with additional gear increased the weight of the 5th percentile female ATD more than 50%2. Comparison of the loading data with and without PPE determined that the additional weight of PPE increased the overall risk of compressive injury to the lumbar and upper neck of the small occupant during an underbody blast event. Using the same data set, this technical paper aimed to evaluate overall accelerative loading trends of the 5th percentile female ATD when compared to those of the 50th percentile male ATD in the same seat and PPE configuration. This data trend comparison was conducted to gain an understanding of how seat loading may differ with a smaller occupant. The focus of the data analysis centered around the lumbar spine compression, as this channel was the most likely to exceed the IARV limit for the 5th percentile female ATD. Based on the previous analysis of this data set, the lightest occupant trends showed difficulty in protecting against lumbar compression injuries with respect to the 5th percentile female’s IARV, whereas the larger occupants experienced fewer issues in complying with their respective IARVs for lumbar compression. A review of pelvis acceleration was also conducted for additional kinetic insight into the motion of the ATDs as the seat strokes. This analysis included a review of how the weight and size of the occupant may affect the transmission of forces through a stroking seat during the vertical accelerative loading impulse.

Average male and female virtual dummy model (BioRID and EvaRID) simulations with two seat concepts in the Euro NCAP low severity rear impact test configuration

<div class="htmlview paragraph">The BioRID-II (Biofidelic Rear Impact Dummy) has been developed as a testing tool to measure automotive seat and head restraint system performance in low-speed rear end crashes and to help with understanding of whiplash neck injuries. The present paper focuses on the current Abaqus BioRID-II model which has been developed by Dassault Systemes Simulia Corp. (SIMULIA) in cooperation with the German Association for Research in Automobile Technology FAT, utilizing an extensive suite of material, component and full dummy experiments in the universal Chalmers seat in order to calibrate and validate the model response. The Abaqus BioRID-II model uses connector elements extensively to model complex connections and instrumentation, and to help improve runtime efficiency by reducing the number of degrees of freedom in the model. The assembly process for the actual BioRID-II dummy introduces nontrivial initial deformations and stresses in the critical components of the neck and spine, which must be accounted for in the model itself; the Abaqus BioRID-II model leverages both the explicit and the implicit solution techniques available in the Abaqus product suite to accomplish this. Finally, a comparison between Abaqus simulation results against available experimental test data is included in the paper, suggesting the usefulness of the model in evaluating dummy response and seat performance. Although the responses of most of the variables monitored in the Abaqus dummy are matching well the experimental responses, the authors would like to underline that this paper presents the current development status of this dummy and that there is an ongoing effort to improve its quality.</div>

This paper examines the characteristics of rear impact crashes. General information about rear impact collisions is derived from recent data from the National Automotive Sampling System, General Estimates System (NASS/GES) and Fatality Analysis Reporting System (FARS) as reported in the annual National Highway Traffic Safety Administration (NHTSA) Traffic Safety Facts. Additional details about the frequency, severity, type, and cause of injuries to front seat outboard occupants is analyzed using the National Automotive Sampling System, Crashworthiness Data System (NASS/CDS) data from 1997 to 2005. Serious head and neck injuries are focused on for further analysis. Specific cases from the CDS database that meet this classification are examined. Federal Motor Vehicle Safety Standard (FMVSS) 301-R test data is used to analyze occupant, seat, and vehicle kinematics in single impact rear collisions and to look at the occupant rebound velocity. The 301-R analysis found the forward velocity of the dummy's head after rebound was as high at 6 m/sec. Analysis of NASS cases of vehicle-to-vehicle rear crashes found numerous contacts with frontal components even in the absence of a frontal crash. However, the most severe and frequent injuries were attributed to the seat back and head restraint. Severe injuries were observed in seats with and without deformation.

Soft tissue neck injuries sustained in low speed rear-end collisions are of continued concern in road traffic. To assess the risk of sustaining such injuries, various neck injury criteria have been proposed. In this study a new candidate for such an injury predictor called N km was developed. It is based on a linear combination of shear forces acting in the sagittal direction and extension/flexion bending moments, both measured at the occipital condyles. Results from a total of 40 sled tests, all performed using the same test procedure, with various car front seat models, and using a Hybrid III/TRID as well as a BioRID dummy, were evaluated in order to validate the new criterion. Additionally, a mathematical model was set up to determine the behavior of the N km at a higher crash pulse than the one used in the sled tests. It was shown that the new criterion offers the additional possibility to assess the kinematic phase of forward motion. Furthermore, the influence of the seat design on its protective potential could be related to the N km values obtained and thus, the new criterion is eligible to be part of a standard seat test procedure.

Cervical spine curvature during simulated rear crashes with energy-absorbing seat

Benchmark testing of existing seat designs reveals poor performance in low-speed rear impacts. The neck injury criterion (NIC) exceeds the limiting value of 15 for almost all seats without a whiplash protection system. As only few new car models offer this, a system for retrofit installation was developed and tested. The Retrofit Anti Whiplash System, AWS, consists of a yielding device which is fitted to the seat rails and allows the whole seat to rotate and move backwards. This reduces thorax acceleration and thus the NIC value. As the force required to actuate the device depends on the position of the seat, the system offers optimum protection for large and small occupants.Tests with the rear impact dummy BioRID show a noticeable reduction in NIC compared to the standard seat. Loadings to the neck at a rear impact speed change of a Delta v of 15 km/h (9.3 mph) with AWS are in the same magnitude as at 9 km/h (5.6 mph) without AWS. MADYMO simulations with real crash pulses have been performed, and...