Effects of restraint parameters using PIPER 6y in reclined seating during frontal impact

The effects of postural support padding modifications to child restraints for children with disability on crash protection

OBJECTIVE

Many children with physical disabilities need additional postural support when sitting and supplementary padding is used on standards approved child restraints to achieve this when traveling in a motor vehicle. However, the effect of this padding on crash protection for a child is unknown. This study aimed to investigate the effect of additional padding for postural support on crash protection for child occupants in forward facing child restraints.

METHODS

Forty frontal sled tests at 49 km/h were conducted to compare Q1 anthropometric test device (ATD) responses in a forward-facing restraint, with and without additional padding in locations to increase recline of the restraint, and/or support the head, trunk and pelvis. Three padding materials were tested: cloth toweling, soft foam, and expanded polystyrene (EPS). The influence of padding on head excursion, peak 3 ms head acceleration, HIC15, peak 3 ms chest acceleration and chest deflection were analyzed.

RESULTS

The influence of padding varied depending on the location of use. Padding used under the restraint to increase the recline angle increased head injury metrics. Toweling in multiple locations which included behind the head increased head excursion and chest injury metrics. There was minimal effect on injury risk measures with additional padding to support the sides of the head or the pelvis position. Rigid EPS foam, as recommended in Australian standards and guidelines, had minimal effect on injury metrics when used inside the restraint, as did tightly rolled or folded toweling secured to the restraint at single locations around the body of the child.

CONCLUSIONS

This study does not support the use of postural support padding to increase recline of a forward-facing restraint or padding behind the head. Recommendations in published standards and guidelines to not use foam that is spongy, soft or easily compressed, with preference for secured firm foam or short-term use of tightly rolled or folded toweling under the child restraint cover is supported. This study also highlights the importance of considering the whole context of child occupant protection when using additional padding, particularly the change in the child's seated position when adding padding in relation to the standard safety features of the restraint.

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.

Personalization of human body models and beyond via image registration

Finite element human body models (HBMs) are becoming increasingly important numerical tools for traffic safety. Developing a validated and reliable HBM from the start requires integrated efforts and continues to be a challenging task. Mesh morphing is an efficient technique to generate personalized HBMs accounting for individual anatomy once a baseline model has been developed. This study presents a new image registration-based mesh morphing method to generate personalized HBMs. The method is demonstrated by morphing four baseline HBMs (SAFER, THUMS, and VIVA+ in both seated and standing postures) into ten subjects with varying heights, body mass indices (BMIs), and sex. The resulting personalized HBMs show comparable element quality to the baseline models. This method enables the comparison of HBMs by morphing them into the same subject, eliminating geometric differences. The method also shows superior geometry correction capabilities, which facilitates converting a seated HBM to a standing one, combined with additional positioning tools. Furthermore, this method can be extended to personalize other models, and the feasibility of morphing vehicle models has been illustrated. In conclusion, this new image registration-based mesh morphing method allows rapid and robust personalization of HBMs, facilitating personalized simulations.