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  Prepress links for publications from the 67th Stapp Car Crash Conference are now available on the SAE International website.

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  The Stapp Journal is now accepting paper submissions on an ongoing basis.

Stapp Car Crash Journal Vol. 67

Machine-Learning-Accelerated Simulations for the Design of Airbag Constrained by Obstacles at Rest

Authors

José E. Valenzuela del Río, Elena Arvanitis, and Lucia Mirabella—Siemens Technology, United States; Richard Lancashire, Karan Chatrath, and Peter Ritmeijer—Siemens Industry Software, Netherlands

Abstract

Predicting airbag deployment geometries is an important task for airbag and vehicle designers to meet safety standards based on biomechanical injury risk functions. This prediction is also an extraordinarily complex problem given the number of disciplines and their interactions. State-of-the-art airbag deployment geometry simulations (including time history) entail large, computationally expensive numerical methods such as finite element analysis (FEA) and computational fluid dynamics (CFD), among others. This complexity results in exceptionally large simulation times, making thorough exploration of the design space prohibitive. This paper proposes new parametric simulation models which drastically accelerate airbag deployment geometry predictions while maintaining the accuracy of the airbag deployment geometry at reasonable levels; these models, called herein machine learning (ML)-accelerated models, blend physical system modes with data-driven techniques to accomplish fast predictions within a design space defined by airbag and impactor parameters. These ML-accelerated models are evaluated with virtual test cases of increasing complexity: from airbag deployments against a locked deformable obstacle to airbag deployments against free rigid obstacles; the dimension of the tested design spaces is up to six variables. ML training times are documented for completeness; thus, airbag design explorers or optimization engineers can assess the full budget for ML-accelerated approaches including training. In these test cases, the ML-accelerated simulation models run three orders of magnitude faster than the high-fidelity multi-physics methods, while accuracies are kept within reasonable levels within the design space.

Examination of Crash Injury Risk as a Function of Occupant Demographics

Authors

Dainius Dalmotas, Aline Chouinard, Jean-Louis Comeau, Alan German, Glenn Robbins—D.J. Dalmotas Consulting, Inc.; Priya Prasad—Prasad Engineering, Inc.

Abstract

The objectives of the present study were to provide insights on the issue of how injury risk is influenced by occupant demographics such as gender, age, and size; and to quantify the differences in the context of representative, commonly-occurring real-world crashes. To achieve these objectives, the analyses were confined to either single-event collisions or collisions which were judged to be well-defined based on the absence of any significant secondary impact(s). These analyses were conducted using the Crash Investigation Sampling System (CISS) for calendar years 2017 to 2021. Both logistic regression and conventional descriptive analyses were carried out.

In the case of gender, the findings of the current study show close agreement with those of many other recent investigations which have attempted to quantify under what circumstances females show more elevated rates of injury relative to their male counterparts given the same level bodily insult. Available evidence suggests that the introduction of widespread use of small female dummies in the late 1990's and the early 2000's in North America, in both frontal and side testing, brought about significant safety benefits to females. Indeed, females may have benefited more than males in terms of overall risk reduction.

Even so, the current study, like others, provides evidence of the existence of certain female- specific injuries. The most problematic of these are AIS 2+ and AIS 3+ upper-extremity and lower-extremity injuries. They are among the most frequently observed injuries for females, and the incidence of these injuries is consistently greater than that for males.

Owing to sample size considerations in CISS, comparisons of body region injuries between males and females have largely been confined to drivers in the two-vehicle collision subsets. Here, male drivers consistently showed higher rates of injury to the chest at the AIS 2+ and the AIS 3+ levels relative to their female counterparts. However, in the case of the AIS 2+ chest injury rates, the male rates were only 2 to 6 percent higher.

Male drivers showed higher rates of head injury at the AIS 2+ injury level than their female counterparts. However, likely due to the high penetration of airbags in the samples analyzed, AIS 3+ head injuries were infrequent among both genders, at well below one percent. In frontal collisions, the AIS 3+ head injury rate remained low at under one percent, even at relatively high collision severities (40–69 kph).

The descriptive findings noted above were also reflected in the logistic regression results. Overall, it was found that the odds of females sustaining MAIS 3+ (or fatality) are 4.5% higher than the odds for males, while the odds of females sustaining MAIS 2+ (or fatality) are 33.9% higher than the odds for males.

The logistic regression analyses, the driver survival rate analyses, and the curb weight difference by gender analyses, all highlight the need to carefully control for both the vehicle occupied, and the other involved vehicle, when calculating risk ratios by gender. Female driver vehicle preferences in term of vehicle class/size differ significantly from those of their male counterparts, with females favouring smaller, lighter vehicles.

These preferences are evident even within a defined vehicle class. Conversely, some of the heaviest vehicles, like pickup trucks, are driven almost exclusively (~ 85%) by males. Consequently, in a small car-to-large pickup collision, the female car driver may be currently at a weight disadvantage upwards of 1,800 kg. As the North American fleet moves exclusively to electric vehicles, the weight disadvantage can be expected to climb to upwards of 3,000 kg during the transition period between electric and non-electric vehicles. In the absence of improvements to promote greater vehicle acceleration compatibility in such collisions, female risk in two-vehicle collisions can be expected to increase.

Over the past four decades, we have seen a steady increase in the average weight of the US adult population, both among males and females. The average adult female now weighs nominally 77 kg, a weight that corresponds to, or is marginally lower than, the weight of adult 50th percentile male crash test dummies used in vehicle crash testing. While we see an increasing risk in overall severity levels with increasing weight and BMI, the increases lag well behind those observed with increasing age.

This is particularly the case with MAIS 3+ injuries. Older drivers, i.e. those above 50 years of age, show MAIS 3+ injury rates 4.5 times higher than those of their younger counterparts. As the percentage of the elderly in the adult population will continue to increase over the coming decade, there is a continuing need to improve protection for this group, particularly with respect to the chest. Efforts to improve chest protection for the elderly can be expected to provide additional protection to younger adults. However, what represents the optimum level of load- limiting and load-distribution of the chest needs to be further studied.

Comparison of Adult Female and Male PMHS Pelvis and Lumbar Response to Underbody Blast

Authors

Hollie Pietsch—US Army DEVCOM Ground Vehicle Systems Center, Wayne State University; Danielle Cristino, Matthew Mason, Andrew Kemper, and Warren Hardy—Virginia Tech, Center for Injury Biomechanics; Kerry Danelson— Wake Forest School of Medicine, Department of Orthopedic Surgery; John Bolte IV—The Ohio State University; John Cavanaugh—Wayne State University, Department of Biomedical Engineering (Retired)

Abstract

The goal of this study was to gather and compare kinematic response and injury data on both female and male whole-body Post-Mortem Human Surrogates (PMHS) responses to Underbody Blast (UBB) loading. Midsized males (50th percentile, MM) have historically been most used in biomechanical testing and were the focus of the Warrior Injury Assessment Manikin (WIAMan) program, thus this population subgroup was selected to be the baseline for female comparison. Both small female (5th percentile, SF) and large female (75th percentile, LF) PMHS were included in the test series to attempt to discern whether differences between male and female responses were predominantly driven by sex or size. Eleven tests, using 20 whole-body PMHS, were conducted by the research team. Preparation of the rig and execution of the tests took place at the Aberdeen Proving Grounds (APG) in Aberdeen, MD. Two PMHS were used in each test. The Accelerative Loading Fixture (ALF) version 2, located at APG's Bear Point range was used for all male and female whole-body tests in this series. The ALF was an outdoor test rig that was driven by a buried explosive charge, to accelerate a platform holding two symmetrically mounted seats. The platform was designed as a large, rigid frame with a deformable center section that could be tuned to simulate the floor deformation of a vehicle during a UBB event. PMHS were restrained with a 5-point harness, common in military vehicle seats. Six-degree-of-freedom motion blocks were fixed to L3, the sacrum, and the left and right iliac wings. A three-degree-of freedom block was fixed to T12. Strain gages were placed on L4 and multiple locations on the pelvis. Accelerometers on the floor and seat of the ALF provided input data for each PMHS' feet and pelvis. Time histories and mean peak responses in z-axis acceleration were similar among the three PMHS groups in this body region. Injury outcomes were different and seemed to be influenced by both sex and size contributions. Small females incurred pelvis injuries in absence of lumbar injures. Midsized males had lumbar vertebral body fractures without pelvis injuries. And large females with injuries had both pelvis and lumbar VB fractures. This study provides evidence supporting the need for female biomechanical testing to generate female response and injury thresholds. Without the inclusion of female PMHS, the differences in the injury patterns between the small female and midsized male groups would not have been recognized. Standard scaling methods assume equivalent injury patterns between the experimental and scaled data. In this study, small female damage occurred in a different anatomical structure than for the midsized males. This is an important discovery for the development of anthropomorphic test devices, injury criteria, and injury mitigating technologies. The clear separation of small female damage results, in combination with seat speeds, suggest that the small female pelvis injury threshold in UBB events lies between 4–5 m/s seat speed. No inference can be made about the small female lumbar threshold, other than it is likely at higher speeds and/or over longer duration. Male lumbar spine damage occurred in both the higher- and lower lower-rate tests, indicating the injury threshold would be below the seat pulses tested in these experiments. Large females exhibited injury patterns that reflected both the small female and midsized male groups—with damaged PMHS having fractures in both pelvis and lumbar, and in both higher- and lower- rate tests. The difference in damage patterns between the sex and size groups should be considered in the development of injury mitigation strategies to protect across the full population.

Investigation of THOR-AV 5F Biofidelity in Sled Test Conditions with a Semi-Rigid Seat

Authors

Z. Jerry Wang—Humanetics Innovative Solutions, Inc.; John Humm and Hans W. Hauschild—Medical College of Wisconsin

Abstract

THOR-AV 5F, a modified THOR-5F dummy, was designed to represent both upright and reclined occupants in vehicle crashworthiness studies. The dummy was evaluated in four test conditions: a) 25° seatback, 15 km/h, b) 25° seatback, 32 km/h, c) 45° seatback, 15 km/h, d) 45° seatback, 32 km/h. The dummy's biomechanical responses were compared against those of postmortem human subjects (PMHS) tested in the same test conditions. The latest National Highway Traffic Safety Administration (NHTSA) BioRank method was used to provide a biofidelity ranking score (BRS) for each data channel in the tests to assess the dummy's biofidelity objectively. The evaluation was categorized into two groups: restraint system and dummy. In the four test conditions, the restraint system showed good biofidelity with BRS scores of 1.49, 1.47, 1.15, and 1.79, respectively. The THOR-AV 5F demonstrated excellent biofidelity in three test conditions: 25° seatback, 15 km/h (BRS = 0.76); 25° seatback, 32 km/h (BRS = 0.89); and 45° seatback, 32 km/h (BRS = 0.93). In the fourth test condition, 45° seatback, 15 km/h, the dummy demonstrated good biofidelity with a BRS score of 1.06. The dummy demonstrated good durability. No damage was identified with a full inspection conducted after the tests.

In the chosen test conditions, no lap-belt submarining was observed for the three PMHS. One PMHS sustained an AIS2 pelvic ring fracture and another one sustained an AIS4 injury with complete separation of the left and right sacroiliac joints. Lumbar disc ruptures and vertebral fractures were observed for the three PMHS (AIS 2 and AIS3 coding). The number of separated rib fractures were very different from one PMHS to another (0, 6 and 33). Response corridors for the external forces and kinematics were built and are presented in the paper. The results are discussed by comparing with existing data for which the backseat was in standard posture.

Frontal-Crash Occupant Protection in the Rear Seat: Submarining and Abdomen/Pelvis Response in Midsized Male Surrogates

Authors

Allison J. Guettler, Samuel T. Bianco, Devon L. Albert, David M. Boyle, Andrew R. Kemper, and Warren N. Hardy—Virginia Tech, Center for Injury Biomechanics

Abstract

Frontal-crash sled tests were conducted to assess submarining protection and abdominal injury risk for midsized male occupants in the rear seat of modern vehicles. Twelve sled tests were conducted in four rear-seat vehicle-bucks with twelve post-mortem human surrogates (PMHS). Select kinematics responses and submarining incidence were compared to previously observed performance of the Hybrid III 50th-percentile male and THOR-50M ATDs (Anthropomorphic Test Devices) in matched sled tests conducted as part of a previous study. Abdominal pressure was measured in the PMHS near each ASIS (Anterior Superior Iliac Spine), in the inferior vena cava, and in the abdominal aorta. Damage to the abdomen, pelvis, and lumbar spine of the PMHS was also identified. In total, five PMHS underwent submarining. Four PMHS, none of which submarined, sustained pelvis fractures and represented the heaviest of the PMHS tested. Submarining of the PMHS was produced in two out of four vehicles. In the matched tests, the Hybrid III never underwent submarining while the THOR-50M submarined in three out of four vehicles. Submarining occurred in vehicles having both conventional and advanced (pretensioner and load limiter) restraints. The dominant factors associated with submarining were related to seat pan geometry. While the THOR-50M was not always an accurate tool for predicting submarining in the PMHS, the Hybrid III could not predict submarining at all. The results of this study identify substantive gaps in frontal-crash occupant protection in the rear seat for midsized males and elucidates the need for additional research for rear-seat occupant protection for all occupants.

Evaluation of DAMAGE Algorithm in Frontal Crashes

Authors

Priya Prasad—Prasad Engineering, Inc.; Saeed D. Barbat and Anil Kalra— Ford Motor Company; Dainius Dalmotas—D.J. Dalmotas Consulting, Inc.

Abstract

With the current trend of including the evaluation of the risk of brain injuries in vehicle crashes due to rotational kinematics of the head, two injury criteria have been introduced since 2013—BrIC and DAMAGE. BrIC was developed by NHTSA in 2013 and was suggested for inclusion in the US NCAP for frontal and side crashes. DAMAGE has been developed by UVa under the sponsorship of JAMA and JARI and has been accepted tentatively by the EuroNCAP. Although BrIC in US crash testing is known and reported, DAMAGE in tests of the US fleet is relatively unknown. The current paper will report on DAMAGE in NCAP-like tests and potential future frontal crash tests involving substantial rotation about the three axes of occupant heads. Distribution of DAMAGE of three-point belted occupants without airbags will also be discussed. Prediction of brain injury risks from the tests have been compared to the risks in the real world. Although DAMAGE correlates well with MPS in the human brain model across several test scenarios, the predicted risk of AIS2+ brain injuries are too high compared to real-world experience. The prediction of AIS4+ brain injury risk in lower velocity crashes is good, but too high in NCAP-like and high speed angular frontal crashes.

Driving Behavior during Left-Turn Maneuvers at Intersections on Left-Hand Traffic Roads

Authors

Yasuhiro Matsui and Masashi Narita—National Traffic Safety and Environment Laboratory, Japan; Shoko Oikawa—Tokyo Metropolitan University, Japan

Abstract

Understanding left-turn vehicle-pedestrian accident mechanisms is critical for developing accident-prevention systems. This study aims to clarify the features of driver behavior focusing on drivers' gaze, vehicle speed, and time to collision (TTC) during left turns at intersections on left-hand traffic roads. Herein, experiments with a sedan and light-duty truck (< 7.5 tons GVW) are conducted under four conditions: no pedestrian dummy (No-P), near-side pedestrian dummy (Near-P), far-side pedestrian dummy (Far-P) and near-and-far side pedestrian dummies (NF-P). For NF-P, sedans have a significantly shorter gaze time for left-side mirrors compared with light-duty trucks. The light-duty truck's average speed at the initial line to the intersection (L1) and pedestrian crossing line (L0) is significantly lower than the sedan's under No-P, Near-P, and NF-P conditions, without any significant difference between any two conditions. The TTC for sedans is significantly shorter than that for trucks with near-side pedestrians (Near-P and NF-P) and far-side pedestrians in Far-P. These insights can contribute to the ongoing development of accident-prevention safety systems for left-turning maneuvers at intersections.

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