Objective Evaluation of Whole Body Kinematics in a Simulated, Restrained Frontal Impact

Numerical investigation of driver injury risks in car-to-end terminal crashes using a human finite element model

Although the safety performance of guardrail end terminals is tested using crash tests in the U.S., occupant injury risks are evaluated based on the flail-space model. This approach developed in the early 1980s neglects the influence of safety features (e.g. seatbelt, airbags, etc.) installed in late model vehicles. In this study, a vehicle (sedan, 1100 kg), a guardrail end terminal (ET-Plus) and a human body model (Global Human Body Model Consortium, GHBMC) were integrated to simulate car-to-end terminal crashes. Five velocities, two offsets, and two angles were used as pre-impact conditions. In all the 20 simulations, kinematics and kinetic data were recorded in GHBMC and vehicle models to calculate the GHBMC injury probabilities and vehicle-based injury metrics, correspondingly. Pre-impact velocity was observed to have the largest effect on the occupant injury measures. All the body-region and full-body injury risks increased with the increasing velocity. Meanwhile, the angles had a larger effect than offset to the change of full-body injury risk (9.1% vs. 0.3%). All the vehicle-based metrics had good correlations to full-body injury probabilities. Occupant Impact Velocity (OIVx), Acceleration Severity Index (ASI), and Theoretical Head Impact Velocity (THIV) had a good correlation to chest, thigh, upper tibia, and lower tibia injuries. All the other correlations (e.g. brain/head injuries) were not statistically significant. The results pointed out that more vehicle-based metrics (ASI and THIV) could help improve the predictability in terms of occupant injury risks in the tests. Numerical methodology could be used to assess head and brain injury probabilities, which were not predictable by any vehicle-based metrics.

Subject-Specific Geometry of FE Lumbar Spine Models for the Replication of Fracture Locations Using Dynamic Drop Tests

For traumatic lumbar spine injuries, the mechanisms and influence of anthropometrical variation are not yet fully understood under dynamic loading. Our objective was to evaluate whether geometrically subject-specific explicit finite element (FE) lumbar spine models based on state-of-the-art clinical CT data combined with general material properties from the literature could replicate the experimental responses and the fracture locations via a dynamic drop tower-test setup. The experimental CT datasets from a dynamic drop tower-test setup were used to create anatomical details of four lumbar spine models (T12 to L5). The soft tissues from THUMS v4.1 were integrated by morphing. Each model was simulated with the corresponding loading and boundary conditions from the dynamic lumbar spine tests that produced differing injuries and injury locations. The simulations resulted in force, moment, and kinematic responses that effectively matched the experimental data. The pressure distribution within the models was used to compare the fracture occurrence and location. The spinal levels that sustained vertebral body fracture in the experiment showed higher simulation pressure values in the anterior elements than those in the levels that did not fracture in the reference experiments. Similarly, the spinal levels that sustained posterior element fracture in the experiments showed higher simulation pressure values in the vertebral posterior structures compared to those in the levels that did not sustain fracture. Our study showed that the incorporation of the spinal geometry and orientation could be used to replicate the fracture type and location under dynamic loading. Our results provided an understanding of the lumbar injury mechanisms and knowledge on the load thresholds that could be used for injury prediction with explicit FE lumbar spine models.

Modular incorporation of deformable spine and 3D neck musculature into a simplified human body finite element model

Spinal injuries are a concern for automotive applications, requiring large parametric studies to understand spinal injury mechanisms under complex loading conditions. Finite element computational human body models (e.g. Global Human Body Models Consortium (GHBMC) models) can be used to identify spinal injury mechanisms. However, the existing GHBMC detailed models (with high computational time) or GHBMC simplified models (lacking vertebral fracture prediction capabilities) are not ideal for studying spinal injury mechanisms in large parametric studies. To overcome these limitations, a modular 50th percentile male simplified occupant model combining advantages of both the simplified and detailed models, M50-OS + DeformSpine, was developed by incorporating the deformable spine and 3D neck musculature from the detailed GHBMC model M50-O (v6.0) into the simplified GHBMC model M50-OS (v2.3). This new modular model was validated against post-mortem human subject test data in four rigid hub impactor tests and two frontal impact sled tests. The M50-OS + DeformSpine model showed good agreement with experimental test data with an average CORrelation and Analysis (CORA) score of 0.82 for the hub impact tests and 0.75 for the sled impact tests. CORA scores were statistically similar overall between the M50-OS + DeformSpine (0.79 ± 0.11), M50-OS (0.79 ± 0.11), and M50-O (0.82 ± 0.11) models (p > 0.05). This new model is computationally 6 times faster than the detailed M50-O model, with added spinal injury prediction capabilities over the simplified M50-OS model.

Development and preliminary validation of computationally efficient and detailed 50th percentile female human body models

OBJECTIVE

No vehicle testing standard (physical or computational) employs a mid-sized female human surrogate, despite discrepancies related to injury outcomes for female occupants amongst all vehicle users. We detail the design and preliminary validation of 50th percentile female (F50) computational human body models (HBMs) based on Global Human Body Models Consortium (GHBMC) models.

METHOD

Data for the target geometry was collected as part of the initial generation of GHBMC models. Imaging, surface data, and 15 anthropomorphic measures from a living female subject (60.8 kg and 1.61 m) served as the baseline for model development. Due to the role rib cage geometry plays in biomechanical loading, rib cage morphology from secondary retrospective data was leveraged to identify an average female rib cage based on gross anatomical features. A female rib cage was selected from an existing dataset closest to the mean depth, height, and width of the set, considering only those aged 20 - 50 years. The selected subject among this secondary set also exhibited a 7th rib angle and sternum angle within 5% of the mean measurements, and within the range of previously reported studies. The GHBMC 5th percentile, small female detailed (high biofidelity) and simplified (computationally efficient) models were morphed to match the F50 subject body surface, selected bones, and mean rib cage using established thin plate spline techniques. The models were validated vs. previously published literature studies with an emphasis on rib cage response. Model data was compared to 47 channels of experimental data across four biomechanical hub simulations, two sled test simulations (one of which included all female PMHS), and two robustness simulations to test stability. Model results were mass scaled to the average of the reported corridors. Objective evaluation was conducted using CORA. IRB approval was obtained for all prospective and retrospective data collected or used. The target rib cage was selected from retrospective image data used in prior studies (n = 339 chest CT scans).

RESULTS

The morphed HBMs closely matched the target geometry. The detailed and simplified models had masses and element counts of 61.2 kg and 61.8 kg, and 2.8 million and 0.3 million, respectively. The mass difference is due to a coarser mesh in the simplified model. The simplified model ran 23 times faster than the detailed model on the same hardware. Each model exhibited stability in robustness tests, and the average CORA scores were 0.80 and 0.72 in the detailed and simplified models, respectively. The models performed well in frontal impacts against PMHS corridors after mass scaling.

CONCLUSIONS

Numerous recent studies underscore poorer injury outcomes for female vehicle occupants compared to males. While such outcomes are multifactorial, the average female models introduced in this work offer a novel tool within a widely used family of HBMs to reduce the outcome gap in terms of injury for all drivers. HBMs can be deployed in safety studies or in future regulatory requirements faster and more economically than a resized or newly designed ATDs aimed at the same target population.

Hello, world! VIVA+: A human body model lineup to evaluate sex-differences in crash protection

Finite element Human Body Models are increasingly becoming vital tools for injury assessment and are expected to play an important role in virtual vehicle safety testing. With the aim of realizing models to study sex-differences seen in the injury- and fatality-risks from epidemiology, we developed models that represent an average female and an average male. The models were developed with an objective to allow tissue-based skeletal injury assessment, and thus non-skeletal organs and joints were defined with simplified characterizations to enhance computational efficiency and robustness. The model lineup comprises female and male representations of (seated) vehicle occupants and (standing) vulnerable road users, enabling the safety assessment of broader segments of the road user population. In addition, a new workflow utilized in the model development is presented. In this workflow, one model (the seated female) served as the base model while all the other models were generated as closely-linked derivative models, differing only in terms of node coordinates and mass distribution. This approach opens new possibilities to develop and maintain further models as part of the model lineup, representing different types of road users to reflect the ongoing transitions in mobility patterns (like bicyclists and e-scooter users). In this paper, we evaluate the kinetic and kinematic responses of the occupant and standing models to blunt impacts, mainly on the torso, in different directions (front, lateral, and back). The front and lateral impacts to the thorax showed responses comparable to the experiments, while the back impact varied with the location of impact (T1 and T8). Abdomen bar impact showed a stiffer load-deflection response at higher intrusions beyond 40 mm, because of simplified representation of internal organs. The lateral shoulder impact responses were also slightly stiffer, presumably from the simplified shoulder joint definition. This paper is the first in a series describing the development and validation of the new Human Body Model lineup, VIVA+. With the inclusion of an average-sized female model as a standard model in the lineup, we seek to foster an equitable injury evaluation in future virtual safety assessments.

Occupant safety effectiveness of proactive safety seat in autonomous emergency braking

The proactive safety seat (PSS) is a recently developed active safety system for securing occupant safety in out-of-seat position (OOSP), which was applied in the Hyundai Genesis G80 in 2020. However, there has not been sufficient quantifiable verification supporting the effectiveness of the PSS. The present study was performed to determine the effectiveness of the PSS for occupant safety in OOSP and to identify areas for additional improvement. Six test conditions were considered to determine the effectiveness of the PSS for augmentation of occupant safety in OOSP. Ten healthy men participated in the tests. Compared with the no PSS condition, maximum head excursion and neck rotation were significantly decreased in the PSS condition by 0.6-0.8-fold and 0.6-0.7-fold, respectively (P < 0.05). The PSS condition in which the seat pan was moved forward to the mid position showed a greater effect in reducing the characteristic motions related to submarining, compared with the condition in which the seat pan was moved rearward to the mid position (P < 0.05). These results suggested that PSS augments occupant safety in OOSP. This study provides valuable insights in ameliorating risks to the occupant in unintended seat positions before braking and/or collision.

Development and implementation of a time- and computationally-efficient methodology for reconstructing real-world crashes using finite element modeling to improve crash injury research investigations

Eleven Crash Injury Research and Engineering Network (CIREN) frontal crashes were reconstructed using a novel, time-efficient methodology involving a simplified vehicle model. Kinematic accuracy was assessed using novel kinematic scores between 0-1 and chest injury was assessed using literature-defined injury metric time histories. The average kinematic score across all simulations was 0.87, indicating good kinematic accuracy. Time histories for chest compression, rib strain, shoulder belt force, and steering column force discerned the most causative components of chest injury in all cases. Abbreviated Injury Scale (AIS) 2+ and AIS 3+ chest injury risk functions using belt force identified chest injury with 81.8% success.

Motion Responses by Occupants in Out-of-Seat Positions During Autonomous Emergency Braking

The occupant's posture can be changeable to an inadvertent or unintentional out-of-seat position (OOSP) depend on their convenience. Understanding for OOSP has been demanded, but it is not sufficient; especially when AEB is activated. The aim of the current study was to characterize the motion responses of an occupant in various OOSPs when AEB is activated and to identify if there were any additional risks of injury or discomfort to the occupant. The normal seat position (NSP) and three OOSPs were defined to compare the difference of human responses, and six healthy males were participated. Particularly, the maximum rotation angles of the neck in OOSP2 and OOSP3 differed significantly around 1.3 ± 0.3 and 1.4 ± 0.2 times higher respectively than from in the NSP (p < 0.05). Occupants assuming OOSP3 exhibited motion characteristics were not restrained effectively and characterized a hovering and falling upper body and a slipping pelvis. This study has identified, for the first time, a potential risk of injury or discomfort when AEB is activated while an occupant is in an OOSP. This study may serve as fundamental data for the development of safety system that can improve restraint and counteract any deterioration in occupant safety.

Variations in User Implementation of the CORA Rating Metric

The CORA rating metric is frequently used in the field of injury biomechanics to compare the similarity of response time histories. However, subjectivity exists within the CORA metric in the form of user-customizable parameters that give the metric the flexibility to be used for a variety of applications. How these parameters are customized is not always reported in the literature, and it is unknown how these customizations affect the CORA scores. Therefore, the purpose of this study was to evaluate how variations in the CORA parameters affect the resulting similarity scores. A literature review was conducted to determine how the CORA parameters are commonly customized within the literature. Then, CORA scores for two datasets were calculated using the most common parameter customizations and the default parameters. Differences between the CORA scores using customized and default parameters were statistically significant for all customizations. Furthermore, most customizations produced score increases relative to the default settings. The use of standard deviation corridors and exclusion of the corridor component were found to produce the largest score differences. The observed differences demonstrated the need for researchers to exercise transparency when using customized parameters in CORA analyses.

Comparison of Neck Injury Criteria Values Across Human Body Models of Varying Complexity

Due to the severity and frequency of cervical spine injuries, the neck injury criterion (Nij) was developed to provide a quantitative relationship between forces and moments of the upper neck with accompanied injury risk. The present study was undertaken to evaluate differences in calculated Nij for the Global Human Body Model Consortium's detailed and simplified average 50th percentile male models. The simplified model is a computationally light version of the more detailed model and therefore it is of interest to achieve similar Nij values between the two models. These models were compared in 15 match paired conditions of rigid head impact and a mixture of seven full body rigid hub and sled pulses, for 44 total simulations. Collectively, Nij values of the simplified model were found to exhibit a second-degree polynomial fit, allowing for a conversion to the prediction of the detailed model. Correlates were also derived for impact and inertial loading cases individually, for which the latter may be the subject of future work. The differences in Nij may be attributed to a variety of modeling approach differences related to neck muscles (attachment location and morphometric implementation), localization of head mass within the M50-OS, head geometry, and intervertebral joint space properties. With a primary focus on configurations in the anterior-posterior direction, there is a potential limitation in extensibility to lateral loading cases. In response to the relatively low Nij values exhibited, future work should evaluate the appropriateness of the established critical intercepts of Nij for computational human body models.

Validated thoracic vertebrae and costovertebral joints increase biofidelity of a human body model in hub impacts

Objective: A recent emphasis on nontraditional seating and omnidirectional impact directions has motivated the need for deformable representation of the thoracic spine (T-spine) in human body models. The goal of this study was to develop and validate a deformable T-spine for the Global Human Body Models Consortium (GHBMC) M50-O (average male occupant) human model and to demonstrate improved biofidelity.Methods: Eleven functional spinal units (FSUs) were developed with deformable vertebrae (cortical and trabecular), spinal and costovertebral ligaments, and intervertebral discs. Material properties for all parts were obtained from the literature.FSUs were subjected to quasistatic loads per Panjabi et al. (1976) in 6 degrees of freedom. Stiffness values were calculated for each moment (Nm/°) and translational force (N/µm). Updated costovertebral (CV) joints of ribs 2, 6, and 10 were subjected to moments along 3 axes per Duprey et al. (2010). The response was optimized by maximum force and laxity in the ligaments. In both cases, updated models were compared to the baseline approach, which employed rigid bodies and joint-like behavior. The deformable T-spine and CV joints were integrated into the full M50-O model Ver. 5.0β and 2 full-body cases were run: (1) a rear pendulum impact per Forman et al. (2015) at speeds up to 5.5 m/s. and (2) a lateral shoulder impact per Koh (2005) at 4.5 m/s. Quantitative evaluation protocols were used to evaluate the time history response vs. experimental data, with an average correlation and analysis (CORA) score of 0.76.Results: All FSU responses showed reduced stiffness vs. baseline. Tension, extension, torsion, and lateral bending became more compliant than experimental data. Like the experimental results, no trend was observed for joint response by level. CV joints showed good biofidelity. The response at ribs 2, 6, and 10 generally followed the experimental data.Conclusions: Deformable T-spine and CV joint validation has not been previously published and yielded high biofidelity in rear impact and notable improvement in lateral impact at the full body level. Future work will focus on localized T-spine injury criteria made possible by the introduction of this fully deformable representation of the anatomy.