A point-wise normalization method for development of biofidelity response corridors

Small Female Occupant Response in Reclined and Upright Seated Postures in Frontal Impacts

The objective of this study was to compare the kinematics of the head-neck, torso, pelvis, and lower extremities and document injuries and their patterns to small female occupants in frontal impacts with upright and reclined postures using an experimental model. Six postmortem human surrogates (PMHS) with a mean stature of 154 ± 9.0 cm and mass of 49 ± 12 kg were equally divided between upright and reclined groups (seatback: 25 deg and 45 deg), restrained by a three-point integrated belt, positioned on a semirigid seat, and exposed to low and moderate crash velocities (15 km/h and 32 km/h respectively). The response between the upright and reclined postures was similar in magnitude and curve morphology. While none of the differences were statistically significant, the thoracic spine demonstrated increased downward (+Z) displacement, and the head demonstrated an increased horizontal (+X) displacement for the reclined occupants. In contrast, the upright occupants showed a slightly increased downward (+Z) displacement at the head, but the torso displaced primarily along the +X direction. The posture angles between the two groups were similar at the pelvis and different at the thorax and head. At 32 km/h, both cohorts exhibited multiple rib failure, with upright specimens having a greater number of severe fractures. Although MAIS was the same in both groups, the upright specimens had more bi-cortical rib fractures, suggesting the potential for pneumothorax. This preliminary study may be useful in validating physical (ATDs) and computational (HBMs) surrogates.

Lower Extremity Injury Risk Curve Development for a Human Body Model in the Underbody Blast Environment

Computational human body models (HBMs) provide the ability to explore numerous candidate injury metrics ranging from local strain based criteria to global combined criteria such as the Tibia Index. Despite these efforts, there have been relatively few studies that focus on determining predicted injury risk from HBMs based on observed postmortem human subjects (PMHS) injury data. Additionally, HBMs provide an opportunity to construct risk curves using measures that are difficult or impossible to obtain experimentally. The Global Human Body Models Consortium (GHBMC) M50-O v 6.0 lower extremity was simulated in 181 different loading conditions based on previous PMHS tests in the underbody blast (UBB) environment and 43 different biomechanical metrics were output. The Brier Metric Score were used to determine the most appropriate metric for injury risk curve development. Using survival analysis, three different injury risk curves (IRC) were developed: "any injury," "calcaneus injury," and "tibia injury." For each injury risk curve, the top three metrics selected using the Brier Metric Score were tested for significant covariates including boot use and posture. The best performing metric for the "any injury," "calcaneus injury" and "tibia injury" cases were calcaneus strain, calcaneus force, and lower tibia force, respectively. For the six different injury risk curves where covariates were considered, the presence of the boot was found to be a significant covariate reducing injury risk in five out of six cases. Posture was significant for only one curve. The injury risk curves developed from this study can serve as a baseline for model injury prediction, personal protective equipment (PPE) evaluation, and can aid in larger scale testing and experimental protocols.

Temporal corridors of forces and moments, and injuries to pelvis-lumbar spine in vertical impact simulating underbody blast

Pelvis and lumbar spine fractures occur in falls, motor vehicle crashes, and military combat events. They are attributed to vertical impact from the pelvis to the spine. Although whole-body cadavers were exposed to this vector and injuries were reported, spinal loads were not determined. While previous studies determined injury metrics such as peak forces using isolated pelvis or spine models, they were not conducted using the combined pelvis-spine columns, thereby not accounting for the interaction between the two body regions. Earlier studies did not develop response corridors. The study objectives were to develop temporal corridors of loads at the pelvis and spine and assess clinical fracture patterns using a human cadaver model. Vertical impact loads were delivered at the pelvic end to twelve unembalmed intact pelvis-spine complexes, and pelvis forces and spinal loads (axial, shear and resultant and bending moments) were obtained. Injuries were classified using clinical assessments from post-test computed tomography scans. Spinal injuries were stable in eight and unstable in four specimens. Pelvis injuries included ring fractures in six and unilateral pelvis in three, sacrum fractures in ten, and two specimens did not sustain any injuries to the pelvis or sacrum complex. Data were grouped based on time to peak velocity, and ± one standard deviation corridors about the mean of the biomechanical metrics were developed. Time-history corridors of loads at the pelvis and spine, hitherto not reported in any study, are valuable to assess the biofidelity of anthropomorphic test devices and assist validating finite element models.

Lower Extremity Validation of a Human Body Model for High Rate Axial Loading in the Underbody Blast Environment

While the use of Human Body Models (HBMs) in the underbody blast (UBB) environment has increased and shown positive results, the potential of these models has not been fully explored. Obtaining accurate kinematic and kinetic response are necessary to better understand the injury mechanisms for military safety applications. The objective of this study was to validate the Global Human Body Models Consortium (GHBMC) M50 lower extremity using a combined objective rating scheme in vertical and horizontal high-rate axial loading. The model's lower extremity biomechanical response was compared to Post Mortem Human Subjects (PMHS) subjects for vertically and horizontally-applied high rate axial loading. Two distinct experimental setups were used for model validation, comprising a total of 33 distinct end points for validation. A combined Correlation and Analysis (CORA) score that incorporates CORA, time-to-peak (TTP) and peak magnitude of the experimental signals and ISO TS 18571 was used to evaluate the model response. For the horizontal impacts, the combined CORA scores were 0.80, 0.84, and 0.81 for compression, force, and strain respectively. For the vertical impacts combined CORA scores for the knee Z force, compression and heel Z displacement ranged from 0.70-0.81, 0.87-0.91, and 0.82-0.99 respectively. The GHBMC lower extremity model showed good agreement with PMHS experimental data in the horizontal and vertical loading environment in 33 unique tests. The accuracy is demonstrated by using the ISO TS 18571 standard and a combined CORA score that takes into consideration the peak and time to peak of the signal. The results of this study show that GHBMC v 6.0 HBM lower extremity can be used for kinetic and kinematic predictions in the UBB environment.

Obese Occupant Response in Reclined and Upright Seated Postures in Frontal Impacts

The American population is getting heavier and automated vehicles will accommodate unconventional postures. While studies replicating mid-size and upright fore-aft seated occupants are numerous, experiments with post-mortem human subjects (PMHS) with obese and reclined occupants are sparse. The objective of this study was to compare the kinematics of the head-neck, torso and pelvis, and document injuries and injury patterns in frontal impacts. Six PMHS with a mean body mass index of 38.2 ± 5.3 kg/m2 were equally divided between upright and reclined groups (seatback: 23°, 45°), restrained by a three-point integrated belt, positioned on a semi-rigid seat, and exposed to low and moderate velocities (15, 32 km/h). Data included belt loads, spinal accelerations, kinematics, and injuries from x-rays, computed tomography, and necropsy. At 15 km/h speed, no significant difference in the occupant kinematics and evidence of orthopedic failure was observed. At 32 km/h speed, the primary difference between the cohorts was significantly larger Z displacements in the reclined occupant at the head (190 ± 32 mm, vs. 105 ± 33 mm p < 0.05) and femur (52 ± 18 mm vs. 30 ± 10 mm, p < 0.05). All the moderate-speed tests produced at least one thorax injury. Rib fractures were scattered around the circumference of the rib-cage in the upright, while they were primarily concentrated on the anterior aspect of the rib-cage in two reclined specimens. Although MAIS was the same in both groups, the reclined specimens had more bi-cortical rib fractures, suggesting the potential for pneumothorax. While not statistical, these results suggest enhanced injuries with reclined obese occupants. These results could serve as a data set for validating the response of restrained obese anthropometric test device (ATDs) and computational human body models.

Header biomechanics in youth and collegiate female soccer

Concerns about the effects of intentional heading in soccer have led to regulatory restrictions on headers for youth players. However, there is limited data describing how header exposure varies across age levels, and few studies have attempted to compare head impact exposure across different levels of play with the same sensor. Additionally, little is known about the biomechanical response of the brain to header impacts. The objective of this study was to evaluate head kinematics and the resulting tissue-level brain strain associated with intentional headers among youth and collegiate female soccer players. Six youth and 13 collegiate participants were instrumented with custom mouthpiece-based sensors measuring six-degree-of-freedom head kinematics of headers during practices and games. Kinematics of film-verified headers were used to drive impact simulations with a detailed brain finite element model to estimate tissue-level strain. Linear and rotational head kinematics and strain metrics, specifically 95th percentile maximum principal strain (ε_1,95) and the area under the cumulative strain damage measure curve (VSM₁), were compared across levels of play (i.e., youth vs. collegiate) while adjusting for session type and ball delivery method. A total of 483 headers (n = 227 youth, n = 256 collegiate) were analyzed. Level of play was significantly associated with linear acceleration, rotational acceleration, rotational velocity, ε_1,95, and VSM₁. Headers performed by collegiate players had significantly greater mean head kinematics and strain metrics compared to those performed by youth players (all p < .001). Targeted interventions aiming to reduce head impact magnitude in soccer should consider factors associated with the level of play.

Whole Body PMHS Response in Injurious Experimental Accelerative Loading Events

Previous studies involving whole-body post-mortem human surrogates (PHMS) have generated biomechanical response specifications for physically simulated accelerative loading intended to reproduce seat and floor velocity histories occurring in under-body blast (UBB) events (e.g.,. References 10, 11, 21 These previous studies employed loading conditions that only rarely produced injuries to the foot/ankle and pelvis, which are body regions of interest for injury assessment in staged UBB testing using anthropomorphic test devices. To investigate more injurious whole-body conditions, three series of tests were conducted with PMHS that were equipped with military personal protective equipment and seated in an upright posture. These tests used higher velocity and shorter duration floor and seat inputs than were previously used with the goal of producing pelvis and foot/ankle fractures. A total of nine PMHS that were approximately midsize in stature and mass were equally allocated across three loading conditions, including a 15.5 m/s, 2.5 ms time-to-peak (TTP) floor velocity pulse with a 10 m/s, 7.5 ms TTP seat pulse; a 13 m/s, 2.5 ms TTP floor pulse with a 9.0 m/s, 5 ms TTP seat pulse; and a 10 m/s, 2.5 ms TTP floor pulse with a 6.5 m/s, 7.5 ms TTP seat pulse. In the first two conditions, the seat was padded with a ~ 120-mm-thick foam cushion to elongate the pulse experienced by the PMHS. Of the nine PMHS tests, five resulted in pelvic ring fractures, five resulted in a total of eight foot/ankle fractures (i.e., two unilateral and three bilateral fractures), and one produced a femur fracture. Test results were used to develop corridors describing the variability in kinematics and in forces applied to the feet, forces applied to the pelvis and buttocks in rigid seat tests, and in forces applied to the seat foam in padded seat tests. These corridors and the body-region specific injury/no-injury response data can be used to assess the performance and predictive capability of anthropomorphic test devices and computational models used as human surrogates in simulated UBB testing.

Characterization of head impact exposure in boys' youth ice hockey

Ice hockey has one of the highest concussion rates among youth sports. Sensor technology has been implemented in contact and collision sports to inform the frequency and severity of head impacts experienced on-ice. However, existing studies have utilized helmet-mounted sensors with limited accuracy. The objective of this study was to characterize head kinematics of contact events in a sample of youth boys' hockey players using a validated instrumented mouthpiece with improved accuracy. Head kinematics from 892 video-verified events were recorded from 18 athletes across 127 sessions. Median peak resultant linear acceleration, rotational velocity, and rotational acceleration of video-verified events were 7.4 g, 7.7 rad/s, and 576 rad/s², respectively. Contact events occurred at a higher rate in games (2.48 per game) than practices (1.30 per practice). Scenarios involving head contact had higher peak kinematics than those without head contact. This study improves our understanding of head kinematics in boys' youth hockey.

Mechanisms and timing of injury to the thoracic, lumbar and sacral spine in simulated underbody blast PMHS impact tests

During an underbody blast (UBB) event, mounted occupants are exposed to high rate loading of the spine via the pelvis. The objective of this study was to simulate UBB loading conditions and examine mechanisms of injury in the thoracic, lumbar and sacral spine. Fourteen instrumented, whole-body, postmortem human subject (PMHS) experiments were performed using the WSU-decelerative horizontal sled system. The specimens were positioned supine on a decelerative sled, which then impacted an energy absorbing system mounted to a concrete barrier. Variables included the peak velocity and time-to-peak velocity for seat and floor, and the presence or absence of personal protective equipment (PPE) and seat padding. Post-test CT scans and autopsies were performed to identify the presence and severity of injuries. Acceleration and angular rate data collected at vertebra T1, T5, T8, T12, and S1 were used to assess injury timing and mechanisms. Additionally, joint time-frequency analysis (JTFA) of the spinal Z acceleration of the sacrum and vertebrae was developed with the aim of verifying spinal fracture timing. Injuries observed in the spine were attributed to axial compression applied through the pelvis, together with flexion moment due to the offset in the center of gravity of the torso, and are consistent with UBB-induced combat injuries reported in the literature. The injury timing estimation techniques discussed in this study provide a time interval when the fractures are predicted to have occurred. Furthermore, this approach serves as an alternative to the estimation methods using acoustic sensors, force and acceleration traces, and strain gauges.

Comparison of Human Surrogate Responses in Underbody Blast Loading Conditions

Impact biomechanics research in occupant safety predominantly focuses on the effects of loads applied to human subjects during automotive collisions. Characterization of the biomechanical response under such loading conditions is an active and important area of investigation. However, critical knowledge gaps remain in our understanding of human biomechanical response and injury tolerance under vertically accelerated loading conditions experienced due to underbody blast (UBB) events. This knowledge gap is reflected in anthropomorphic test devices (ATDs) used to assess occupant safety. Experiments are needed to characterize biomechanical response under UBB relevant loading conditions. Matched pair experiments in which an existing ATD is evaluated in the same conditions as a post mortem human subject (PMHS) may be utilized to evaluate biofidelity and injury prediction capabilities, as well as ATD durability, under vertical loading. To characterize whole body response in the vertical direction, six whole body PMHS tests were completed under two vertical loading conditions. A series of 50th percentile hybrid III ATD tests were completed under the same conditions. Ability of the hybrid III to represent the PMHS response was evaluated using a standard evaluation metric. Tibial accelerations were comparable in both response shape and magnitude, while other sensor locations had large variations in response. Posttest inspection of the hybrid III revealed damage to the pelvis foam and skin, which resulted in large variations in pelvis response. This work provides an initial characterization of the response of the seated hybrid III ATD and PMHS under high rate vertical accelerative loading.

Kinematic and Biomechanical Response of Post-Mortem Human Subjects Under Various Pre-Impact Postures to High-Rate Vertical Loading Conditions

Limited data exist on the injury tolerance and biomechanical response of humans to high-rate, under-body blast (UBB) loading conditions that are commonly seen in current military operations, and there are no data examining the influence of occupant posture on response. Additionally, no anthropomorphic test device (ATD) currently exists that can properly assess the response of humans to high-rate UBB loading. Therefore, the purpose of this research was to examine the response of post-mortem human surrogates (PMHS) in various seated postures to high-rate, vertical loading representative of those conditions seen in theater. In total, six PMHS tests were conducted using loading pulses applied directly to the pelvis and feet of the PMHS: three in an acute posture (foot, knee, and pelvis angles of 75°, 75°, and 36°, respectively), and three in an obtuse posture (15° reclined torso, and foot, knee, and pelvis angles of 105°, 105°, and 49.5°, respectively). Tests were conducted with a seat velocity pulse that peaked at ~4 m/s with a 30-40 ms time to peak velocity (TTP) and a floor velocity that peaked at 6.9-8.0 m/s (2-2.75 ms TTP). Posture condition had no influence on skeletal injuries sustained, but did result in altered leg kinematics, with leg entrapment under the seat occurring in the acute posture, and significant forward leg rotations occurring in the obtuse posture. These data will be used to validate a prototype ATD meant for use in high-rate UBB loading scenarios.

Implications of head and neck restraint test repeatability for specification improvement

Objective: Since 2005, National Association for Stock Car Auto Racing, Incorporated (NASCAR) drivers have been required to use a head and neck restraint system (HNR) that complies with SFI Foundation, Inc. (SFI) 38.1. The primary purpose of the HNR is to control and limit injurious neck loads and head kinematics during frontal and frontal oblique impacts. The SFI 38.1 performance specification was implemented to establish a uniform test procedure and minimum standard for the evaluation of HNRs using dynamic sled testing. The purpose of this study was to evaluate the repeatability of the current SFI 38.1 test setup and explore the effects of a polyester seat belt restraint system. Method: Eight sled tests were conducted using the SFI 38.1 sled test protocol with additional test setup constraints. Four 0° frontal tests and 4 30° right frontal (RF) oblique tests were conducted. The first 3 tests of each principal direction of force (PDOF) used nylon SFI 16.1 seat belt restraint assemblies. The fourth test of each PDOF used polyester SFI 16.6 seat belt restraint assemblies. A secondary data set (Lab B Data) was also supplied by the HNR manufacturer for further comparisons. The International Organization for Standardization (ISO) 18571 objective comparison method was used to quantify the repeatability of the anthropomorphic test device (ATD) resultant head, chest, and pelvis acceleration and upper neck axial force and flexion extension bending moment time histories across multiple tests. Results: Two data sets generated using the SFI 38.1 test protocol exhibited large variations in mean ISO scores of ATD channels. The 8 tests conducted with additional setup constraints had significantly lower mean ISO score coefficients of variation (CVs). The Lab B tests conducted within the current specification but without the additional test setup constraints had larger mean ISO score standard deviation and CV for all comparisons. Specifically, tests with the additional setup constraints had average CVs of 3.3 and 2.9% for the 0° and 30° RF orientations, respectively. Lab B tests had average CVs of 22.9 and 24.5%, respectively. Polyester seat belt comparisons had CVs of 5.3 and 6.2% for the 0° and 30° RF orientations, respectively. Conclusion: With the addition of common test setup constraints, which do not violate the specification, the SFI 38.1 test protocol produced a repeatable test process for determining performance capabilities of HNRs within a single sled lab. A limited study using polyester webbing seat belt assemblies versus the nylon material called for in SFI 38.1 indicates that the material likely has less effects on ATD upper neck axial force and flexion extension bending moment time histories than the test setup freedom currently available within the specification. The additional test setup constraints are discussed and were shown to improve ATD response repeatability for a given HNR.

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

The use of human body models as an additional data point in the evaluation of human-machine interaction requires quantitative validation. In this study a validation of the Global Human Body Models Consortium (GHBMC) average male occupant model (M50-O v. 4.5) in a restrained frontal sled test environment is presented. For vehicle passengers, frontal crash remains the most common mode, and the most common source of fatalities. A total of 55-time history traces of reaction loads and kinematics from the model were evaluated against corresponding PMHS data (n = 5). Further, the model's sensitivity to the belt path was studied by replicating two documented PMHS cases with prominent lateral and medial belt paths respectively. Results were quantitatively evaluated using open source CORA software. A tradeoff was observed; better correlation scores were achieved on gross measures (e.g. reaction loads), whereas better corridor scores were achieved on localized measures (rib deflections), indicating that subject specificity may dominate the comparison at localized anatomical regions. On an overall basis, the CORA scores were 0.68, 0.66 and 0.60 for force, body kinematics and chest wall kinematics. Belt force responses received the highest grouped CORA score of 0.85. Head and sternum kinematics earning a 0.8 and 0.7 score respectively. The model demonstrated high sensitivity to belt path, resulting in a 20-point increase in CORA score when the belt was routed closer to analogous location of data collection. The human model demonstrated overall reasonable biofidelity and sensitivity to countermeasures in frontal crash kinematics.

Modeling Human Volunteers in Multidirectional, Uni-axial Sled Tests Using a Finite Element Human Body Model

A goal of the Human Research Program at National Aeronautics and Space Administration (NASA) is to analyze and mitigate the risk of occupant injury due to dynamic loads. Experimental tests of human subjects and biofidelic anthropomorphic test devices provide valuable kinematic and kinetic data related to injury risk exposure. However, these experiments are expensive and time consuming compared to computational simulations of similar impact events. This study aimed to simulate human volunteer biodynamic response to unidirectional accelerative loading. Data from seven experimental studies involving 212 volunteer tests performed at the Air Force Research Laboratory were used to reconstruct 13 unique loading conditions across four different loading directions using finite element human body model (HBM) simulations. Acceleration pulses and boundary conditions from the experimental tests were applied to the Global Human Body Models Consortium (GHBMC) simplified 50th percentile male occupant (M50-OS) using the LS-Dyna finite element solver. Head acceleration, chest acceleration, and seat belt force traces were compared between the experimental and matched simulation signals using correlation and analysis (CORA) software and averaged into a comprehensive response score ranging from 0 to 1 with 1 representing a perfect match. The mean comprehensive response scores were 0.689 ± 0.018 (mean ± 1 standard deviation) in two frontal simulations, 0.683 ± 0.060 in four rear simulations, 0.676 ± 0.043 in five lateral simulations, and 0.774 ± 0.013 in two vertical simulations. The CORA scores for head and chest accelerations in these simulations exceeded mean scores reported in the original development and validation of the GHBMC M50-OS model. Collectively, the CORA scores indicated that the HBM in these boundary conditions closely replicated the kinematics of the human volunteers across all loading directions.

Similitude assessment method for comparing PMHS response data from impact loading across multiple test devices

Biological tissue testing is inherently susceptible to the wide range of variability specimen to specimen. A primary resource for encapsulating this range of variability is the biofidelity response corridor or BRC. In the field of injury biomechanics, BRCs are often used for development and validation of both physical, such as anthropomorphic test devices, and computational models. For the purpose of generating corridors, post-mortem human surrogates were tested across a range of loading conditions relevant to under-body blast events. To sufficiently cover the wide range of input conditions, a relatively small number of tests were performed across a large spread of conditions. The high volume of required testing called for leveraging the capabilities of multiple impact test facilities, all with slight variations in test devices. A method for assessing similitude of responses between test devices was created as a metric for inclusion of a response in the resulting BRC. The goal of this method was to supply a statistically sound, objective method to assess the similitude of an individual response against a set of responses to ensure that the BRC created from the set was affected primarily by biological variability, not anomalies or differences stemming from test devices.

Normalized frontal impact biofidelity kinematic corridors using post mortem human surrogates

Due to reducing cost and powerful computing resources and the ability of finite element human body models (FEHBM) to predict human body response more realistically, they are gaining acceptance to be a substitute for mechanical surrogates. Unlike mechanical surrogates, FEHBM can realistically simulate human kinematics and kinetics. Moreover, an array of quantities can be directly measured from FEHBMs. However, similar to Anthropomorphic Test Devices (ATDs), in order to evaluate the biofidelity, these models must be validated using PMHS response corridors. Therefore, availability of such PMHS corridors that can be used to validate both ATD and FEHBM kinematics is of primary importance. The current study presents normalized biofidelity corridors of head CG, T1, T12, and sacrum accelerations using PMHS frontal sled tests that were previously conducted. In addition, rotational accelerations and displacements of the head are also presented. The experimental data were collected using four specimens. Each specimens were tested with non-injurious pulses using two different velocities (low: 3.6m/s and medium: 6.9m/s). These data were normalized using mass-based technique to represent mid-sized United States population. Using the normalized data, average and plus/minus one standard deviation response corridors were generated that can be used to evaluate the biofidelity of ATDs and FEHBMs.

Modular use of human body models of varying levels of complexity: Validation of head kinematics

OBJECTIVE

The significant computational resources required to execute detailed human body finite-element models has motivated the development of faster running, simplified models (e.g., GHBMC M50-OS). Previous studies have demonstrated the ability to modularly incorporate the validated GHBMC M50-O brain model into the simplified model (GHBMC M50-OS+B), which allows for localized analysis of the brain in a fraction of the computation time required for the detailed model. The objective of this study is to validate the head and neck kinematics of the GHBMC M50-O and M50-OS (detailed and simplified versions of the same model) against human volunteer test data in frontal and lateral loading. Furthermore, the effect of modular insertion of the detailed brain model into the M50-OS is quantified.

METHODS

Data from the Navy Biodynamics Laboratory (NBDL) human volunteer studies, including a 15g frontal, 8g frontal, and 7g lateral impact, were reconstructed and simulated using LS-DYNA. A five-point restraint system was used for all simulations, and initial positions of the models were matched with volunteer data using settling and positioning techniques. Both the frontal and lateral simulations were run with the M50-O, M50-OS, and M50-OS+B with active musculature for a total of nine runs.

RESULTS

Normalized run times for the various models used in this study were 8.4 min/ms for the M50-O, 0.26 min/ms for the M50-OS, and 0.97 min/ms for the M50-OS+B, a 32- and 9-fold reduction in run time, respectively. Corridors were reanalyzed for head and T1 kinematics from the NBDL studies. Qualitative evaluation of head rotational accelerations and linear resultant acceleration, as well as linear resultant T1 acceleration, showed reasonable results between all models and the experimental data. Objective evaluation of the results for head center of gravity (CG) accelerations was completed via ISO TS 18571, and indicated scores of 0.673 (M50-O), 0.638 (M50-OS), and 0.656 (M50-OS+B) for the 15g frontal impact. Scores at lower g levels yielded similar results, 0.667 (M50-O), 0.675 (M50-OS), and 0.710 (M50-OS+B) for the 8g frontal impact. The 7g lateral simulations also compared fairly with an average ISO score of 0.565 for the M50-O, 0.634 for the M50-OS, and 0.606 for the M50-OS+B. The three HBMs experienced similar head and neck motion in the frontal simulations, but the M50-O predicted significantly greater head rotation in the lateral simulation.

CONCLUSION

The greatest departure from the detailed occupant models were noted in lateral flexion, potentially indicating the need for further study. Precise modeling of the belt system however was limited by available data. A sensitivity study of these parameters in the frontal condition showed that belt slack and muscle activation have a modest effect on the ISO score. The reduction in computation time of the M50-OS+B reduces the burden of high computational requirements when handling detailed HBMs. Future work will focus on harmonizing the lateral head response of the models and studying localized injury criteria within the brain from the M50-O and M50-OS+B.

Biomechanical Response of Military Booted and Unbooted Foot-Ankle-Tibia from Vertical Loading

A new anthropomorphic test device (ATD) is being developed by the US Army to be responsive to vertical loading during a vehicle underbody blast event. To obtain design parameters for the new ATD, a series of non-injurious tests were conducted to derive biofidelity response corridors for the foot-ankle complex under vertical loading. Isolated post mortem human surrogate (PMHS) lower leg specimens were tested with and without military boot and in different initial foot-ankle positions. Instrumentation included a six-axis load cell at the proximal end, three-axis accelerometers at proximal and distal tibia, and calcaneus, and strain gages. Average proximal tibia axial forces for a neutral-positioned foot were about 2 kN for a 4 m/s test, 4 kN for 6 m/s test and 6 kN for an 8 m/s test. The force time-to-peak values were from 3 to 5 msec and calcaneus acceleration rise times were 2 to 8 msec. Compared to the neutral posture, the "off-axis" measures (e.g. shear and bending moment) were much greater in magnitude in plantar- or dorsi-flexed posture. The results as a function of velocity demonstrated uniform increases with increasing test velocities. The response corridors supplied from the present investigation will serve as initial design parameters for the ATD lower leg, and can also be used for validation for a human computational model.

Evaluation of WIAMan Technology Demonstrator Biofidelity Relative to Sub-Injurious PMHS Response in Simulated Under-body Blast Events

Three laboratory simulated sub-injurious under-body blast (UBB) test conditions were conducted with whole-body Post Mortem Human Surrogates (PMHS) and the Warrior Assessment Injury Manikin (WIAMan) Technology Demonstrator (TD) to establish and assess UBB biofidelity of the WIAMan TD. Test conditions included a rigid floor and rigid seat with independently varied pulses. On the floor, peak velocities of 4 m/s and 6 m/s were applied with a 5 ms time to peak (TTP). The seat peak velocity was 4 m/s with varied TTP of 5 and 10 ms. Tests were conducted with and without personal protective equipment (PPE). PMHS response data was compiled into preliminary biofidelity response corridors (BRCs), which served as evaluation metrics for the WIAMan TD. Each WIAMan TD response was evaluated against the PMHS preliminary BRC for the loading and unloading phase of the signal time history using Correlation Analysis (CORA) software to assign a numerical score between 0 and 1. A weighted average of all responses was calculated to determine body region and whole body biofidelity scores for each test condition. The WIAMan TD received UBB biofidelity scores of 0.62 in Condition A, 0.59 in Condition B, and 0.63 in Condition C, putting it in the fair category (0.44-0.65). Body region responses with scores below a rating of good (0.65-0.84) indicate potential focus areas for the next generation of the WIAMan design.

A method for developing biomechanical response corridors based on principal component analysis

The standard method for specifying target responses for human surrogates, such as crash test dummies and human computational models, involves developing a corridor based on the distribution of a set of empirical mechanical responses. These responses are commonly normalized to account for the effects of subject body shape, size, and mass on impact response. Limitations of this method arise from the normalization techniques, which are based on the assumptions that human geometry linearly scales with size and in some cases, on simple mechanical models. To address these limitations, a new method was developed for corridor generation that applies principal component (PC) analysis to align response histories. Rather than use normalization techniques to account for the effects of subject size on impact response, linear regression models are used to model the relationship between PC features and subject characteristics. Corridors are generated using Monte Carlo simulation based on estimated distributions of PC features for each PC. This method is applied to pelvis impact force data from a recent series of lateral impact tests to develop corridor bounds for a group of signals associated with a particular subject size. Comparing to the two most common methods for response normalization, the corridors generated by the new method are narrower and better retain the features in signals that are related to subject size and body shape.