Evaluation of pediatric ATD biofidelity as compared to child volunteers in low-speed far-side oblique and lateral impacts

Standardized Assessment of Gravity Settling Human Body Models for Virtual Testing

The increased use of computational human models in evaluation of safety systems demands greater attention to selected methods in coupling the model to its seated environment. This study assessed the THUMS v4.0.1 in an upright driver posture and a reclined occupant posture. Each posture was gravity settled into an NCAC vehicle model to assess model quality and HBM to seat coupling. HBM to seat contact friction and seat stiffness were varied across a range of potential inputs to evaluate over a range of potential inputs. Gravity settling was also performed with and without constraints on the pelvis to move towards the target H-Point. These combinations resulted in 18 simulations per posture, run for 800 ms. In addition, 5 crash pulse simulations (51.5 km/h delta V) were run to assess the effect of settling time on driver kinematics. HBM mesh quality and HBM to seat coupling metrics were compared at kinetically identical time points during the simulation to an end state where kinetic energy was near zero. A gravity settling time of 350 ms was found to be optimal for the upright driver posture and 290 ms for the reclined occupant posture. This suggests that reclined passengers can be settled for less time than upright passengers, potentially due to the increased contact area. The pelvis constrained approach was recommended for the upright driver posture and was not recommended for the reclined occupant posture. The recommended times were sufficient to gravity settle both postures to match the quality metrics of the 800 ms gravity settled time. Driver kinematics were found to be vary with gravity settling time. Future work will include verifying that these recommendations hold for different HBMs and test modes.

The Influence of a Booster Seat on the Motion of the Reclined Small Female Anthropomorphic Test Device in Low-Acceleration Far-Side Lateral Oblique Impacts

Belt-positioning booster (BPB) seats may prevent submarining in reclined child occupants in frontal impacts. BPB-seated child volunteers showed reduced lateral displacement in reclined seating in low-acceleration lateral-oblique impacts. As submarining was particularly evident in reclined small adult female occupants, we examined if a booster seat could provide similar effects on the kinematics of the small female occupant to the ones found on the reclined child volunteers in low-acceleration far-side lateral oblique impacts. The THOR-AV-5F was seated on a vehicle seat on a sled simulating a far-side lateral-oblique impact (80 deg from frontal, maximum acceleration ∼2 g, duration ∼170 ms). Lateral and forward head and trunk displacements, trunk rotation, knee-head distance, seatbelt loads, and head acceleration were recorded. Three seatback angles (25 deg, 45 deg, 60 deg) and two booster conditions were examined. Lateral peak head and trunk displacements decreased in more severe reclined seatback angles (25-36 mm decrease compared to nominal). Forward peak head, trunk displacements, and knee-head distance were greater with the seatback reclined and no BPB. Knee-head distance increased in the severe reclined angle also with the booster seat (>40 mm compared to nominal). Seat belt peak loads increased with increased recline angle with the booster, but not without the booster seat. Booster-like solutions may be beneficial for reclined small female adult occupants to reduce head and trunk displacements in far-side lateral-oblique impacts, and knee-head distance and motion variability in severe reclined seatback angles.

The effect of reclined seatback angles on the motion of booster-seated children during lateral-oblique low-acceleration impacts

Belt-positioning boosters (BPB) may prevent submarining in novel seating configurations such as seats with reclined seatbacks. However, several knowledge gaps in the motion of reclined child occupants remain as previous reclined child studies only examined responses of a child anthropomorphic test device (ATD) and the PIPER finite element (FE) model in frontal impacts. The aim of this study is to investigate the effect of reclined seatback angles and two types of BPBs on the motion of child volunteer occupants in low-acceleration far-side lateral-oblique impacts. Six healthy children (3 males, 3 females, 6-8 years, seated height: 66±3.2 cm, weight: 25.2±3.2 kg) were seated on two types of low-back BPB (standard and lightweight) on a vehicle seat and restrained by a 3-point simulated-integrated seatbelt on a low-acceleration sled. The sled exposed the participants to a low-speed lateral-oblique (80° from frontal) pulse (2 g). Three seatback recline angles (25°, 45°, 60° from vertical) with two BPB (standard and lightweight) were tested. A 10-camera 3D-motion-capture system (Natural Point Inc.) was used to capture peak lateral head and trunk displacements and forward knee-head distance. Three seat-belt load cells (Denton ATD Inc) captured peak seatbelt loads. Electromyography (EMG, Delsys Inc) recorded muscle activation. Repeated Measure 2-way ANOVAs were performed to evaluate the effect of seatback recline angle and BPB on kinematics. Tukey's post-hoc test for pairwise comparisons was used. P-level was set to 0.05. Peak lateral head and trunk displacement decreased with the increasing seatback recline angle (p < 0.005, p < 0.001, respectively). Lateral peak head displacement was greater in the 25° compared to the 60° condition (p < 0.002) and in the 45° condition compared to the 60° condition (p < 0.04). Lateral peak trunk displacement was greater in the 25° condition than the 45° condition (p < 0.009) and the 60° condition (p < 0.001), and in the 45° condition than the 60° condition (p < 0.03). Overall peak lateral head and trunk displacements and knee-head forward distance were slightly greater in the standard than the lightweight BPB (p < 0.04), however these differences between BPBs were small (∼10 mm). Shoulder belt peak load decreased as the reclined seatback angle increased (p < 0.03): the shoulder belt peak load was statistically greater in the 25° condition than the 60° condition (p < 0.02). Muscle activation from the neck, upper trunk, and lower legs showed great activation. Neck muscles activation increased with the increase in seatback recline angle. Thighs, upper arms, and abdominal muscles showed small activation and no effect of conditions. Child volunteers showed decreased displacement suggesting that reclined seatbacks placed the booster-seated children in a more favorable position within the shoulder belt in a low-acceleration lateral-oblique impact, compared to nominal seatback angles. BPB type seemed to minimally influence the children's motion: the small differences found may have been due to the slight difference in heights between the two BPBs. Future research with more severe pulses is needed to better understand reclined children's motion in far-side lateral-oblique impacts.

Evaluation of static belt fit and belt torso contact for children on belt-positioning booster seats

Objective: Previous studies have indicated that gap between the seatbelt and torso (reduced belt torso contact) for children on belt-positioning booster seats (BPBs) may lead to less torso engagement and increased likelihood of shoulder belt slip-off during evasive vehicle maneuvers, potentially increasing injury risk during crashes. However, current BPB belt fit measures do not quantify belt gap and may not be able to fully discriminate between designs which provide good vs. poor dynamic outcomes. The goal of this study was to evaluate both novel (belt gap characteristics) and conventional measures of seatbelt fit for BPB-seated children.Methods: Ten BPBs and three seatbelt anchor locations were investigated. Fifty volunteers (4-14 years) were recruited and each evaluated on six unique combinations of BPB and seatbelt anchor location on a vehicle rear seat in a laboratory setting. A 3 D coordinate measurement system quantified positions of anatomic, seatbelt, BPB, and vehicle reference points. Novel belt gap (gap size, length, location, and percent torso contact) and conventional belt fit (position of belt on shoulder and pelvis) metrics were calculated using anatomic and seatbelt landmarks. Variation in belt fit and belt gap outcomes due to BPB, seatbelt anchor location, and anthropometry were investigated.Results: BPBs produced significantly different outcomes, while seatbelt anchor location did not. BPBs with features that directly routed the lower portion of the shoulder belt more forward on the buckle side produced the largest (29.3 ± 12.6 mm) and longest (106.9 ± 68.2 mm) belt gap on average, while BPBs that pulled the belt less forward or did not directly route the belt produced the smallest (13.9 ± 6.7 mm) and shortest (16.9 ± 33.9 mm) gap on average. Belt gap outcomes were not strongly correlated with conventional belt fit metrics, indicating that evaluation of belt gap may provide additional insight when attempting to discriminate between BPBs which provide good vs. poor seatbelt engagement during vehicle maneuvers and crashes.Conclusions: This is the first study to evaluate belt gap characteristics for BPB-seated children. Results suggest that belt fit and belt gap are influenced by BPB design, particularly lower shoulder belt routings, and may have implications for belt engagement during dynamic events.

The Lack of Sex, Age, and Anthropometric Diversity in Neck Biomechanical Data

Female, elderly, and obese individuals are at greater risk than male, young, and non-obese individuals for neck injury in otherwise equivalent automotive collisions. The development of effective safety technologies to protect all occupants requires high quality data from a range of biomechanical test subjects representative of the population at risk. Here we sought to quantify the demographic characteristics of the volunteers and post-mortem human subjects (PMHSs) used to create the available biomechanical data for the human neck during automotive impacts. A systematic literature and database search was conducted to identify kinematic data that could be used to characterize the neck response to inertial loading or direct head/body impacts. We compiled the sex, age, height, weight, and body mass index (BMI) for 999 volunteers and 110 PMHSs exposed to 5,431 impacts extracted from 63 published studies and three databases, and then compared the distributions of these parameters to reference data drawn from the neck-injured, fatally-injured, and general populations. We found that the neck biomechanical data were biased toward males, the volunteer data were younger, and the PMHS data were older than the reference populations. Other smaller biases were also noted, particularly within female distributions, in the height, weight, and BMI distributions relative to the neck-injured populations. It is vital to increase the diversity of volunteer and cadaveric test subjects in future studies in order to fill the gaps in the current neck biomechanical data. This increased diversity will provide critical data to address existing inequities in automotive and other safety technologies.

The effect of vehicle countermeasures and age on human volunteer kinematics during evasive swerving events

Objective: Emergency maneuvers such as evasive swerving often precede a crash. These events are typically low-acceleration, time-extended events where the inertial forces have the potential to cause changes to the occupant's initial state (initial posture, position, muscle tension). The objective of this study was to systematically quantify the kinematics of pediatric and adult human volunteers during simulated pre-crash evasive swerving maneuvers and evaluate the effect of age and two vehicle-based countermeasures.Methods: A novel laboratory device was designed to expose subjects to non-injurious loading conditions that mimic real-world evasive swerving events. A four-cycle oscillatory lateral pulse with a maximum acceleration of 0.72 g (0.53 g for the first lateral movement in the first cycle) was applied. Forty seat belt restrained subjects across four age groups - 9-11 years (n = 10), 12-14 years (n = 10), 15-17 years (n = 10) and 18-40 years (n = 10) - were exposed to a series of test conditions (baseline, pre-pretensioned seat belt, sculpted vehicle seat with and without inflated torso bolsters) while their kinematics were captured using 3 D motion capture and muscle activity was recorded. Reaction loads were collected from the shoulder belt and footrest. Data are presented for the first cycle only.Results: Pre-pretensioning the shoulder belt before the onset of acceleration had the greatest restraining effect on the head and trunk for all age groups. In the pre-pretensioning trials, compared to baseline, subjects exhibited 34% and 33% less head excursion, into and out of the shoulder belt respectively. Similar reductions were observed with pre-pretensioning for trunk excursion (45% and 53% reductions, in and out of the belt respectively). Inflating seat torso bolsters reduced lateral kinematics relative to baseline but to a lesser extent than the pre-pretensioner (Head Out of belt: 11%; Head Into Belt: 32% and Trunk Out of Belt: 15%; Trunk Into Belt: 27%). Although there was no overall effect of age on the magnitude of lateral displacement, different age groups employed various neuromuscular strategies to control their kinematics.Conclusion: A pre-pretensioner was an effective vehicle countermeasure during evasive swerving maneuvers as it substantially reduced lateral head and trunk displacement for all age groups. Providing lateral restraint via a sculpted vehicle seat was less effective as the geometry of the torso bolsters when inflated did not provide substantial lateral support.

Biofidelic Evaluation of the Large Omni-Directional Child Anthropomorphic Test Device in Low Speed Loading Conditions

Motor vehicle crashes remain the leading cause of death for children. Traditionally, restraint design has focused on the crash phase of the impact with an optimally seated occupant. In order to optimize restrain design for real-world scenarios, research has recently expanded its focus to non-traditional loading conditions including pre-crash positioning and lower speed impacts. The goal of this study was to evaluate the biofidelity of the large omni-directional child (LODC) ATD in non-traditional loading conditions by comparing its response to pediatric volunteer data in low-speed sled tests. Low-speed (2-4 g, 1.9-3.0 m/s) frontal (0°), far-side oblique (60°), and far-side lateral (90º) sled tests, as well as lateral swerving (0.72 g, 0.5 Hz) tests, were conducted using the LODC. The LODC was restrained using a 3-point-belt with an electromechanical motorized seat belt retractor, or pre-pretensioner. Motion capture markers were placed on the head, torso, and belt. The LODC was compared to previously collected pediatric volunteer data as well as the HIII 10 and Q10. Significant difference between the pediatric volunteers and ATDs were identified by comparing the mean ATD response to the pediatric volunteer 95% CI. The LODC exhibited lower forward head excursion (262 mm) compared to pediatric volunteers (263 - 333 mm) in low-speed frontal sled tests (p<0.05), but was closer to the pediatric volunteers than the HIII 10 (179 mm) and Q10 (171 mm). In lateral swerving, the LODC (429 mm) exhibited greater lateral head excursion (p<0.05) compared to pediatric volunteers (115 - 171 mm). The LODC exhibited a greater reduction in kinematics compared to the pediatric volunteers in all loading conditions with a pre-pretensioner. These data provide valuable insight into the biofidelity of the LODC in non-traditional loading conditions, such as evaluating pre-crash maneuvers on occupant response.

Biofidelity assessment of the 6-year-old ATDs in lateral impact

OBJECTIVES

The objective of this study was to assess and compare the current lateral impact biofidelity of the shoulder, thorax, abdomen, and pelvis of the Q6, Q6s, and Hybrid III (HIII) 6-year-old anthropomorphic test devices (ATDs) through lateral impact testing.

METHODS

A series of lateral impact pendulum tests, vertical drop tests, and Wayne State University (WSU) sled tests was performed, based on the procedures detailed in ISO/TR 9790 (1999) and scaling to the 6-year-old using Irwin et al. ( 2002 ). The HIII used in this study was tested with the Ford-designed abdomen described in Rouhana ( 2006 ) and Elhagediab et al. ( 2006 ). The data collected from the 3 different ATDs were filtered using SAE J211 (SAE International 2003 ), aligned using the methodology described by Donnelly and Moorhouse ( 2012 ), and compared for each body region tested (shoulder, thorax, abdomen, and pelvis). The biofidelity performance in lateral impact for the 3 ATDs was assessed against the scaled biofidelity targets published in Irwin et al. ( 2002 ), the abdominal biofidelity target suggested in van Ratingen et al. ( 1997 ), and the biofidelity targets published in Rhule et al. ( 2013 ). Regional and overall biofidelity rankings for each of the 3 ATDs were performed using both the ISO 9790 biofidelity rating system (ISO/TR 9790 1999) and the NHTSA's external biofidelity ranking system (BRS; Rhule et al. 2013 ).

RESULTS

All 3 6-year-old ATD's pelvises were rated as least biofidelic of the 4 body regions tested, based on both the ISO and BRS biofidelity rating systems, followed by the shoulder and abdomen, respectively. The thorax of all 3 ATDs was rated as the most biofidelic body region using the aforementioned biofidelity rating systems. The HIII 6-year-old ATD was rated last in overall biofidelity of the 3 tested ATDs, based on both rating systems. The Q6s ATD was rated as having the best overall biofidelity using both rating systems.

CONCLUSIONS

All 3 ATDs are more biofidelic in the thorax and abdomen than the shoulder and pelvis, with the pelvis being the least biofidelic of all 4 tested body regions. None of the 3 tested 6-year-old ATDs had an overall ranking of 2.0 or less, based on the BRS ranking. Therefore, it is expected that none of the 3 ATDs would mechanically respond like a postmortem human subject (PMHS) in a lateral impact crash test based on this ranking system. With respect to the ISO biofidelity rating, the HIII dummy would be considered unsuitable and the Q-series dummies would be considered marginal for assessing side impact occupant protection.

Responses of the Q6/Q6s ATD Positioned in Booster Seats in the Far-Side Seat Location of Side Impact Passenger Car and Sled Tests

Passenger car side impact crash tests and sled tests were conducted to investigate the influence of booster seats, near-side occupant characteristics and vehicle interiors on the responses of the Q6/Q6s child ATD positioned in the rear, far-side seating location. Data from nine side impact sled tests simulating a EuroNCAP AEMD barrier test were analyzed with data obtained from 44 side impact crash tests. The crash tests included: FMVSS 214 and IIHS MDB, moving car-to-stationary car and moving car-to-moving car. A Q6 or prototype Q6s ATD was seated on the far-side, using a variety of low and high back booster seats. Head and chest responses were recorded and ATD motions were tracked with high-speed videos. The vehicle lateral accelerations resulting from MDB tests were characterized by a much earlier and more rapid rise to peak than in tests where the bullet was another car. The near-side seating position was occupied by a Hybrid III 10-year-old ATD in the sled tests, and a rear or front facing child restraint or a 5th percentile side impact ATD in the crash tests. Head impacts occurred more frequently in vehicles where a forward facing child restraint was present behind the driver seat for both the low and high back booster seats. Pretensioners were found to reduce lateral head displacements in all sled test configurations but the greatest reduction in lateral excursion was obtained with a high back booster seat secured with LATCH and tested in combination with pretensioners.

Modeling spatial trajectories in dynamics testing using basis splines: application to tracking human volunteers in low-speed frontal impacts

Designing motor vehicle safety systems requires knowledge of whole body kinematics during dynamic loading for occupants of varying size and age, often obtained from sled tests with postmortem human subjects and human volunteers. Recently, we reported pediatric and adult responses in low-speed (<4 g) automotive-like impacts, noting reductions in maximum excursion with increasing age. Since the time-based trajectory shape is also relevant for restraint design, this study quantified the time-series trajectories using basis splines and developed a statistical model for predicting trajectories as a function of body dimension or age. Previously collected trajectories of the head, spine, and pelvis were modeled using cubic basis splines with eight control points. A principal component analysis was conducted on the control points and related to erect seated height using a linear regression model. The resulting statistical model quantified how trajectories became shorter and flatter with increasing body size, corresponding to the validation data-set. Trajectories were then predicted for erect seated heights corresponding to pediatric and adult anthropomorphic test devices (ATDs), thus generating performance criteria for the ATDs based on human response. This statistical model can be used to predict trajectories for a subject of specified anthropometry and utilized in subject-specific computational models of occupant response.