Pelvic restraint cushion sled test evaluation of pelvic forward motion

Influence of a Passenger Position Seating on Recline Seat on a Head Injury during a Frontal Crash

Presently, most passive safety tests are performed with a precisely specified seat position and carefully seated ATD (anthropomorphic test device) dummies. Facing the development of autonomous vehicles, as well as the need for safety verification during crashes with various seat positions such research is even more urgently needed. Apart from the numerical environment, the existing testing equipment is not validated to perform such an investigation. For example, ATDs are not validated for nonstandard seatback positions, and the most accurate method of such research is volunteer tests. The study presented here was performed on a sled test rig utilizing a 50cc Hybrid III dummy according to a full factorial experiment. In addition, input factors were selected in order to verify a safe test condition for surrogate testing. The measured value was head acceleration, which was used for calculation of a head injury criterion. What was found was an optimal seat angle −117°—at which the head injury criteria had the lowest represented value. Moreover, preliminary body dynamics showed a danger of whiplash occurrence for occupants in a fully-reclined seat.

Effect of various restraint configurations on submarining occurrence across varied seat configurations in autonomous driving system environment

OBJECTIVE

Self-driving technology will bring novelty in vehicle interior design and allow for a wide variety of occupant seating choices. Previous studies have shown that the increased risk of submarining exhibited by reclined occupants cannot be fully mitigated by changes in the seat configuration alone. This study aims to investigate the effects of three restraint countermeasures on cases with marginal submarining events and estimate their effect on submarining risk and injury prediction metrics.

METHODS

Vehicle environment frontal crash Finite Element (FE) simulations were performed with the two simplified Global Human Body Model Consortium (GHBMC) occupant models: small female and midsize male. The baseline occupant restraints consisted of a frontal airbag, a seatback-integrated 3-point belt with a lap belt anchor pre-tensioner, and a retractor-mounted pre-tensioner and load limiter. Based on submarining thresholds identified in previous studies, three baseline configurations were identified for each occupant size. For each baseline case three restraint system modifications were evaluated. The modifications consisted of the introduction of a pelvis restraint cushion airbag (PRC), the use of a knee airbag (KAB) and the modification of the of the passenger airbag location (PAB). Simulations were performed using the USNCAP 56 km/h frontal crash pulse. Occupant kinematic data was extracted from each simulation to investigate how changes in the restraint system configuration affects submarining.

RESULTS

Overall, in only one of the investigated cases did the proposed restraint modification prevent submarining occurrence, however each of the restraint modifications reduced the pelvis excursion over the baseline scenario. The presence of the PRC airbag showed the highest reduction in pelvis forward excursion for the female model. The presence of the KAB and the modified location of the PAB also contributed to reductions in excursion to a smaller degree. For the male surrogate, the KAB showed the highest reduction in pelvis forward excursion. The presence of the PRC led to a reduction in the lumbar spine shear force.

CONCLUSIONS

Submarining may be a major challenge to overcome for reclined occupants in autonomous driving systems. This suggests that there may not be a single generalizable currently-existing countermeasure able to effectively prevent marginal submarining cases in reclined positions.

A finite element-guided mathematical surrogate modeling approach for assessing occupant injury trends across variations in simplified vehicular impact conditions

A finite element (FE)-guided mathematical surrogate modeling methodology is presented for evaluating relative injury trends across varied vehicular impact conditions. The prevalence of crash-induced injuries necessitates the quantification of the human body's response to impacts. FE modeling is often used for crash analyses but requires time and computational cost. However, surrogate modeling can predict injury trends between the FE data, requiring fewer FE simulations to evaluate the complete testing range. To determine the viability of this methodology for injury assessment, crash-induced occupant head injury criterion (HIC₁₅) trends were predicted from Kriging models across varied impact velocities (10-45 mph; 16.1-72.4 km/h), locations (near side, far side, front, and rear), and angles (-45 to 45°) and compared to previously published data. These response trends were analyzed to locate high-risk target regions. Impact velocity and location were the most influential factors, with HIC₁₅ increasing alongside the velocity and proximity to the driver. The impact angle was dependent on the location and was minimally influential, often producing greater HIC₁₅ under oblique angles. These model-based head injury trends were consistent with previously published data, demonstrating great promise for the proposed methodology, which provides effective and efficient quantification of human response across a wide variety of car crash scenarios, simultaneously. This study presents a finite element-guided mathematical surrogate modeling methodology to evaluate occupant injury response trends for a wide range of impact velocities (10-45 mph), locations, and angles (-45 to 45°). Head injury response trends were predicted and compared to previously published data to assess the efficacy of the methodology for assessing occupant response to variations in impact conditions. Velocity and location were the most influential factors on the head injury response, with the risk increasing alongside greater impact velocity and locational proximity to the driver. Additionally, the angle of impact variable was dependent on the location and, thus, had minimal independent influence on the head injury risk.

Kinematic and Injury Response of Reclined PMHS in Frontal Impacts

Frontal impacts with reclined occupants are rare but severe, and they are anticipated to become more common with the introduction of vehicles with automated driving capabilities. Computational and physical human surrogates are needed to design and evaluate injury countermeasures for reclined occupants, but the validity of such surrogates in a reclined posture is unknown. Experiments with post-mortem human subjects (PMHS) in a recline posture are needed both to define biofidelity targets for other surrogates and to describe the biomechanical response of reclined occupants in restrained frontal impacts. The goal of this study was to evaluate the kinematic and injury response of reclined PMHS in 30 g, 50 km/h frontal sled tests. Five midsize adult male PMHS were tested. A simplified semi-rigid seat with an anti-submarining pan and a non-production threepoint seatbelt (pre-tensioned, force-limited, seat-integrated) were used. Global motions and local accelerations of the head, pelvis, and multiple vertebrae were measured. Seat and seatbelt forces were also measured. Injuries were assessed via post-test dissection. The initial reclined posture aligned body regions (pelvis, lumbar spine, and ribcage) in a way that reduced the likelihood of effective restraint by the seat and seatbelt: the occupant's pelvis was initially rotated posteriorly, priming the occupant for submarining, and the lumbar spine was loaded in combined compression and bending due to the inertia of the upper torso during forward excursion. Coupled with the high restraining forces of the seat and seatbelt, the unfavorable kinematics resulted in injuries of the sacrum/coccyx (four of five PMHS injured), iliac wing (two of five PMHS injured), lumbar spine (three of five PMHS injured), and ribcage (all five PMHS suffered sternal fractures, and three of five PMHS suffered seven or more rib fractures). The kinematic and injury outcomes strongly motivate the development of injury criteria for the lumbar spine and pelvis, the inclusion of intrinsic variability (e.g., abdomen depth and pelvis shape) in computational simulations of frontal impacts with reclined occupants, and the adaptation of comprehensive restraint paradigms to predicted variability of occupant posture.

Submarining sensitivity across varied seat configurations in autonomous driving system environment

OBJECTIVE

Self-driving technology will bring novelty in vehicle interior design and allow for a wide variety of occupant seating choices. Thus, vehicle safety systems may be challenged to protect occupants over a wider range of potential postures. This study aims to investigate the effects of the seat cushion angle on submarining risk, lumbar spine loads and pelvis excursion for reclined occupants in frontal crashes.

METHODS

Frontal crash finite element simulations were performed with two of the simplified Global Human Body Model Consortium (GHBMC) occupant models: the small female and the midsize male. Occupant restraints consisted of a frontal airbag, a seatback-integrated 3-point belt with a lap belt anchor pre-tensioner, and a retractor pre-tensioner with a force limiter. For each simulation, parameters including seat cushion angle (3°, 8°, 13°), seatback recline angle (0°, 10°, 20°, 30°), and knee bolster (KB) position relative to the occupant (baseline and no KB) were varied. A full-factorial simulation matrix was performed using the USNCAP 56 km/h frontal crash pulse. Occupant kinematics data were extracted from each simulation to investigate how changes in seat cushion angle, anthropometry, seatback angle, and KB position would affect submarining across all simulated cases.

RESULTS

Overall, the F05-OS female model was more likely to submarine when compared to the male occupant model. The threshold for submarining was also affected by the seat cushion angle, seatback angle and KB distance. For the F05-OS model, increasing the seat cushion angle to 13° prevented submarining in the 10° seatback angle case, regardless of the KB position. Similarly, the 13° cushion angle prevented submarining for the M50-OS in the 30° seatback angle configuration but only in the presence of a KB. The results further show an increased lumbar flexion load with increased seat recline angle, as well as occupant-to-KB distance, although an opposite trend with the increased seat cushion angle.

CONCLUSIONS

Submarining may be a major challenge to overcome for reclined occupants in autonomous driving systems. This study shows that seat cushion angle plays a role in restraining occupants in recline scenarios, but it is not sufficient to prevent submarining without additional countermeasures.

Submarining sensitivity across varied anthropometry in an autonomous driving system environment

Objective: Self-driving technology will bring novelty in occupant seating choices and vehicle interior design. Thus, vehicle safety systems may be challenged to protect occupants over a wider range of potential postures and seating choices. This study aims to investigate the effects of occupant size, seat recline, and knee bolster position on submarining risk and injury prediction metrics for reclined occupants in frontal crashes.Methods: Frontal crash finite element (FE) simulations were performed with the 3 simplified Global Human Body Model Consortium (GHBMC) occupant models: small female, midsize male, and large male. Additionally, a detailed GHBMC midsize male model was used to compare with selected simplified cases. For each simulation, parameters including seatback recline angle (0.9°, 10.9°, 20.9°, 30.9°) and knee bolster position relative to the occupant (baseline, close, far, and no knee bolster) were varied. Impacts were simulated with the U.S. New Car Assessment Program 56 km/h frontal crash pulse. Occupant kinematics data were extracted from each simulation in a full-factorial sensitivity study to investigate how changes in anthropometry, seating position, and knee bolster position would affect submarining across all simulated cases.Results: Overall, increasing the occupant-to-knee bolster distance resulted in more submarining cases. The threshold for submarining was also affected by the seat recline angle. The lowest threshold observed occurred with 10.9° of recline with the small female model. Submarining was observed at recline angles at and above 20.9° for the midsize male model and 30° for the large male model. The initial lap belt position, pelvis orientation, and their relationship were good predictors of submarining. Increased lumbar flexion moment was observed with increased seat recline angle as well as occupant-to-knee bolster distance. The detailed GHBMC model was more prone to submarining than the simplified model.Conclusions: Submarining may be a major challenge to overcome for reclined occupants, which may become more prevalent with autonomous driving systems. This study shows that the angle of recline, anthropometric variation, and position of the knee bolster affect the risk of submarining. To our knowledge, this is the first study to computationally evaluate the occupant protection implications of seatback recline for multiple body sizes, postures, and positions relative to the vehicle interior.

Development of an injury risk curve for pelvic fracture in vertical loading environments

OBJECTIVE

Pelvis injury mechanisms are dependent upon loading direction (frontal, lateral, and vertical). Studies exist on the frontal and lateral modes; however, similar studies in the vertical mode are relatively sparse. Injury risk curves and response corridors are needed to delineate the biomechanical responses. The objective of the study was to derive risk curves for pelvis injuries using postmortem human subjects (PMHSs).

METHODS

Published data from whole-body PMHSs loaded axially through the pelvis were analyzed. Accelerometers were placed on the pelvis/sacrum and seat. Specimens were loaded along the inferior to superior direction using a horizontal sled or a vertical accelerator device. Specimens were positioned supine in the horizontal sled and seated upright on the vertical accelerator. Pre- and posttest images were obtained and autopsies were completed to document the pathology. Variables used in the development of risk curves included velocity, acceleration, time to peak acceleration, pulse duration of acceleration, and jerk for the seat and sacrum. Survival analysis was used for risk curves. To determine the best predictor of pelvis injury, the Brier Score metric (BSM) was used. The best parametric distribution was determined using the corrected Akaike information criterion (AICc). Injury data points were treated as either uncensored or left/interval censored. Noninjury data points were treated as right censored.

RESULTS

Twenty-four PMHS specimens were identified from 3 published data sets. Fifteen PMHS specimens sustained injuries and 9 remained intact. The BSM ranged from 1.24 to 24.75 and, in general, the BSMs for the seat metric-related scores were greater than the sacrum data. The sacrum acceleration was the optimal metric for predicting pelvis tolerance (lowest BSM). The Weibull distribution had the lowest AICc, with right and left/interval-censored data. This was also true when injury data were treated as exact (uncensored) observations. The 50% probability of injury was associated with 229 G for the uncensored analysis and 139 G for the censored analysis, and the quality indices in both cases were in the "good" range.

CONCLUSIONS

Statistical determination of the best injury metric will help improve the accuracy of injury prediction, prioritize instrumentation choice in dummy development, and improve design criteria for crash mitigation. The present study showed that injury risk curves using response data are better biomechanical descriptors of human responses than exposure data. These data are important in automotive safety because complex loading of the pelvis, including submarining, occurs in frontal car crashes.