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.

Comparison of Axial Force Attenuation Characteristics in Two Different Lower Extremity Anthropomorphic Test Devices.

INTRODUCTION: Any type of boot or footwear is designed to attenuate and distribute loading to the bottom of the foot. Anthropomorphic test device (ATDs) are used to assess potential countermeasures against these loads. The specific aims of this study were to compare and quantify force attenuation characteristics as a function of input energy for Hybrid-III and Mil-Lx ATD human surrogates. MATERIALS AND METHODS: Two lower leg ATD surrogates (Mil-Lx and Hybrid-III) were tested to investigate the influence of a commercially available military boot on lower extremity force response and assess such differences against previously published postmortem human surrogate studies. The testing apparatus impacted the bottom of the foot using a rigid plate at velocities from 2 to 10 m/s. Tests were conducted on each ATD to obtain axial force response with and without boots as a function of input energy. RESULTS: Peak forces ranged from 1 to 16.4 kN for the Hybrid-III, and 1 to 8.4 kN for the Mil-Lx for similar input conditions. The average force attenuation for the Hybrid-III at upper and lower load cells was 71% (59%-80%) and 70% (58%-78%). The average attenuation for the Mil-Lx at upper and lower load cells was 20% (13%-28%) and 37% (36%-37%), respectively. At the knee load cell, the attenuated peak loads ranged from 62% to 81% for the Hybrid-III and 16% to 30% for the Mil-Lx. CONCLUSIONS: Force attenuation characteristics in the booted vs unbooted configuration of the Mil-Lx were significantly different than force attenuation characteristics of the H3 and may better represent in vivo forces during vertical impact injuries, such as IED blasts. Hence for military relevant applications where boots are used, the Mil-Lx may provide a more conservative evaluation of lower extremity protection systems.

Effect of muscle activation scheme in human head-neck model on estimating cervical spine ligament strain from military volunteer frontal impact data.

Cervical spine (c-spine) injuries are a common injury during automobile crashes. The objective of this study is to verify an existing head-neck (HN) finite element model with military volunteer frontal impact kinematics by varying the muscle activation scheme from previous literature. Proper muscle activation will allow for accurate percent elongation (strain) of the c-spine ligaments and will serve to establish ligamentous response during non-injury frontal impacts. Previous human research volunteer (HRV) frontal impact sled tests reported kinematic data that served as the input for HN model simulation. Peak sled acceleration (PSA) was varied between 10G and 30G for HRVs. Muscle activation was shifted to begin at 0 ms at start of impact to allow for proper muscle contraction in the HN model. Then, extensor muscle activation magnitude was varied between 20 and 100% to determine the proper activation necessary to match kinematic outputs from the model with experimental results. The model was validated against 10G test recorded response. Ligament strain was measured from multiple ligaments along the c-spine once the model was verified. The 40% activated extensor muscle scheme was deemed the most biofidelic, with CORA scores of 0.743 and 0.686 for head X linear acceleration and angular Y acceleration for 10G pulse. All PSA groups scored well with this muscle activation. Most ligaments were buffered well by the active simulation, with only the interspinous ligament nearing physiologic injury. With the HN model verified against additional kinematic data, simulations with higher accelerations to predict areas of injury in real life crash scenarios are possible.

Surface wave analysis of the skin for penetrating and non-penetrating projectile impact in porcine legs.

Secondary blast injuries may result from high-velocity projectile fragments which ultimately increase medical costs, reduce active work time, and decrease quality of life. The role of skin penetration requires more investigation in energy absorption and surface mechanics for implementation in computational ballistic models. High-speed ballistic penetration studies have not considered penetrating and non-penetrating biomechanical properties of the skin, including radial wave displacement, resultant surface wave speed, or projectile material influence. A helium-pressurized launcher was used to accelerate 3/8″ (9.525 mm) diameter spherical projectiles toward seventeen whole porcine legs from seven pigs (39.53 ± 7.28 kg) at projectile velocities below and above V50. Projectiles included a mix of materials: stainless steel (n = 26), Si3N4 (n = 24), and acetal plastic (n = 24). Tracker video analysis software was used to determine projectile velocity at impact from the perpendicular view and motion of the tissue displacement wave from the in-line view. Average radial wave displacement and surface wave speed were calculated for each projectile material and categorized by penetrating or non-penetrating impacts. Two-sample t-tests determined that non-penetrating projectiles resulted in significantly faster surface wave speeds in porcine skin for stainless steel (p = 0.002), plastic (p = 0.004), and Si3N4 ball bearings (p = 0.014), while ANOVA determined significant differences in radial wave displacement and surface wave speed between projectile materials. Surface wave speed was used to quantify mechanical properties of the skin including elastic modulus, shear modulus, and bulk modulus during ballistic impact, which may be implemented to simulate accurate deformation behavior in computational impact models.

Occupant Injury and Response on Oblique-Facing Aircraft Seats: A Computational Study.

Increased interest in the airline industry to enhance occupant comfort and maximize seating density has prompted the design and installation of obliquely mounted seats in aircraft. Previous oblique whole-body sled tests demonstrated multiple failures, chiefly distraction-associated spinal injuries under oblique impacts. The present computational study was performed with the rationale to examine how oblique loading induces component level responses and associated injury occurrence. The age-specific human body model (HBM) was simulated for two oblique seating conditions (with and without an armrest). The boundary conditions consisted of a 16 g standard aviation crash pulse, 45 deg seat orientation, and with restrained pelvis and lower extremities. The overall biofidelity rating for both conditions ranged from 0.5 to 0.7. The validated models were then used to investigate the influence of pulse intensity and seat orientation by varying the pulse from 16 g to 8 g and seat orientation from 0 deg to 90 deg. A total of 12 parametric simulations were performed. The pulse intensity simulations suggest that the HBM could tolerate 11.2 g without lumbar spine failure, while the possibility of cervical spine failure reduced with the pulse magnitude <9.6 g pulse. The seat orientation study demonstrated that for all seat angles the HBM predicted failure in the cervical and lumbar regions at 16 g; however, the contribution of the tensile load and lateral and flexion moments varied with respect to the change in seat angle. These preliminary outcomes are anticipated to assist in formulating safety standards and in designing countermeasures for oblique seating configurations.

Calcaneus fracture pattern and severity: Role of local trabecular bone density.

Calcaneus fracture is the most common tarsal bone fracture and is associated with external loads resulting from vehicle crashes, under body blasts, or sports. Almost 50% of weight bearing by the foot occurs through the calcaneus and its surgical fixation remains a challenging procedure. Postmortem human subjects were used to measure the regional trabecular BMD of the calcaneus. Mean age, height and weight of the included 14 specimens was 69 years, 177 cm and 80 kg respectively. Using a custom mode within Quantitative Computed Tomography clinical software; calcaneal trabecular BMD in the anterior and posterior regions was quantified. Tolerance data and calcaneus fracture patterns were also available for these specimens from previous tests. The posterior region of the calcaneus had a higher mean BMD (114 mg/cc) than the anterior region (81 mg/cc). These BMD differences also paralleled injury outcome of specimens from axial loading with 50% of specimens resulting in high severity anterior region calcaneal fractures and 36% of specimens resulting in low severity posterior calcaneal fractures. These findings may be reflective of the lower BMD in the anterior region, although the load was uniformly distributed across the plantar surface of the foot. Severity of fracture was greater (intraarticular/crush) in the anterior region as compared to fractures of the posterior region. The BMD ratio between anterior and posterior was significant (p = 0.02) between anterior region fractures and posterior region fractures. The ratio parameter may indicate that the disparity in trabecular BMD between anterior and posterior calcaneus regions is more important in predicting injury outcome than the absolute BMD value of each region.

Repeated measures analysis of projectile penetration in porcine legs as a function of storage condition.

Buried blast explosions create small projectiles which can become lodged in the tissue of personnel as far away as hundreds of meters. Without appropriate treatment, these lodged projectiles can become a source of infection and prolonged injury to soldiers in modern combat. Human cadavers can be used as surrogates for living humans for ballistic penetration testing, but human cadavers are frozen during transport and storage. The process of freezing and thawing the tissue before testing may change the biomechanical properties of the tissue. The goal of the current study was to understand penetration threshold differences between fresh, refrigerated, and frozen tissue and investigate factors that may contribute to these differences. A custom-built pneumatic launcher was used to accelerate 3/16″ stainless steel ball bearings toward porcine legs that were either tested fresh, following refrigerated storage, or following frozen storage. A generalized linear mixed model, accounting for within-animal dependence, owing to repeated observations, was found to be the most appropriate for these data and was used for analysis. The "generalized" model accommodated non-continuous observations, provided a straight-forward way to implement the repeated measures, and provided a risk estimate for projectile penetration. Both storage condition (p = 0.48) and leg (p = 0.07) were shown to be not significant and the confidence intervals for those variables were overlapping. As all covariates were found to be non-significant, a single model containing all impacts was used to develop a V50, or velocity at which 50% of impacts are expected to penetrate. From this model, 50% probability of penetration occurs at 137.3 m/s with 95% confidence intervals at 132.0 and 144.0 m/s. In this study, the fresh legs and previously frozen legs allowed penetration at similar velocities indicating that previously frozen legs were acceptable surrogates for fresh legs. This study only compared the penetration threshold in tissues that had been stored in differing conditions. To truly study penetration, more conditions will need to be studied including the effects of projectile mass and material, the effects of projectile shape, and the effects of clothing or protective layers on penetration threshold.

Cervical spine degeneration specific segmental angular rotational and displacements: A quantitative study.

BACKGROUND: The objective of the present isolated spine study was to evaluate the kinematic differences between groups of normal and degenerated cervical spine specimens. Previous studies on cervical spine degeneration support the existence of the unstable phase during the degeneration process; however, there is a lack of quantitative data available to fully characterize this early stage of degeneration. METHOD: For this effort five degenerated and eight normal cervical spines (C2-T1) were isolated and were subject to pure bending moments of flexion, extension, axial rotation and lateral bending. The specimen quality was assessed based on the grading scale. In the present study, the degeneration was at the C5-C6 level. A four-camera motion analysis system was used to measure the overall primary and segmental motions. FINDING: In the extension mode, the degenerated group demonstrated a significant larger angular rotation as well as antero-posterior displacement at the degenerated level (C5-C6). In contrast, in flexion mode, the degenerated group measured a drastic decrease in angular rotation, at the adjacent level (C6-C7). In other modes of loading as well as in other segmental levels, the degenerated group had similar segmental motion as the normal group. INTERPRETATION: These preliminary results provide single level degeneration specific cervical spine kinematics. The finding demonstrates the influence of degeneration on the kinematics of the normal sub adjacent segment. The degenerated group observed larger translation displacement in the extension mode, which would potentially be a critical parameter in assisting early detection of cervical spine spondylosis with just a functional X-ray scan.

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.

Time and temperature sensitivity of the hybrid III lumbar spine.

OBJECTIVE: Researchers have found a variety of uses for the Hybrid III (HIII) dummy that fall beyond the scope of its original purpose as an automotive crash test dummy. Some of these expanded roles for the HIII introduce situations that were not envisioned in the dummy's original design parameters, such as a relatively rapid succession of tests or outdoor testing scenarios where temperature is not easily controlled. This study investigates how the axial compressive stiffness of the HIII lumbar spine component is affected by the duration of the time interval between tests. Further, it measures the effect of temperature on the compressive stiffness of the lumbar spine through a range of temperatures relevant to indoor and outdoor testing. METHODS: High-rate axial compression tests were run on a 50th percentile male HIII lumbar component in a materials testing machine. To characterize the effects of tests recovery intervals, between-test recovery was varied from 2 hours to 1 minute. To quantify temperature effects, environmental temperature conditions of 12.5°, 25°, and 37.5 °C were tested. RESULTS: During repeated compressive loading, the force levels decreased consistently across long and short rest intervals. Even after 2 hours of rest between tests, full viscoelastic recovery was not observed. Temperature effects were pronounced, resulting in compressive force differences of 261% over the range of 12.5° to 37.5 °C. Compared to the stiffness of the lumbar at 25 °C, the stiffness at 37.5 °C fell by 40%; at 12.5 °C, the stiffness more than doubled, increasing by 115%. CONCLUSIONS: A modest decrease in temperature can be sufficient to dramatically change the response and repeatability of the lumbar HIII component in compressive loading. The large magnitude of the temperature effect has severe implications in its ability to overwhelm the contributions of targeted test variables. These findings highlight the importance of controlling, monitoring and reporting temperature conditions during HIII testing, even in indoor laboratory environments.

Pelvic Injury Risk Curves for the Military Populations From Lateral Impact.

INTRODUCTION: Current methods for transporting military troops include nonstandard seating orientations, which may result in novel injuries because of different types/directions of loading impact. The objective of this study is to develop pelvic injury risk curves (IRCs) under lateral impacts from human cadaver tests using survival analysis for application to military populations. METHODS: Published data from lateral impacts applied to whole-body cadaver specimens were analyzed. Forces were treated as response variables. Demographics and body mass index (BMI) were covariates. Injury risk curves were developed for forces without covariates, for males, females, 83 kg body mass, and 25 kg/m2 BMI. Mean and ± 95% confidence interval IRCs, normalized confidence interval sizes at discrete risk levels, and quality indices were obtained for each metric-covariate combination curve. RESULTS: Mean age, stature, total body mass, and BMI were 70.1 ± 8.6 years, 1.67 ± 0.1 m, 67.0 ± 14.4 kg, and 23.9 ± 3.97 kg/m2, respectively. For a total body mass of 83 kg, peak forces at 10%, 25%, and 50% probability levels were 5.7 kN, 7.4 kN, and 9.6 kN, respectively. For males, peak forces at the 10%, 25%, and 50% probability levels were 4.8 kN, 6.4 kN, and 8.4 kN, respectively. For females, peak forces at the 10%, 25%, and 50% probability levels were 3.0 kN, 4.0 kN, and 5.2 kN, respectively. Other data and risk curves are given. CONCLUSIONS: The IRCs developed in this study can be used as injury criteria for the crashworthiness of future generation military vehicles. The introduction of BMI, sex, and total body mass as covariates quantified their contributions. These IRCs can be used with finite element models to assess and predict injury in impact environments to advance Soldier safety. Manikins specific to relevant military anthropometry may be designed and/or evaluated with the present IRCs to assess and mitigate musculoskeletal injuries associated with this posture and impact direction.

An Improved Method for Developing Injury Risk Curves Using the Brier Metric Score.

Many injury metrics are routinely proposed from measured or derived quantities from biomechanical experiments using post mortem human subjects (PMHS). The existing literature did not provide guidance on deciding between parameters collected in an experiment that would be best to use for the development of human injury probability curves (HIPC). The objective of this study was to use the Brier Metric Score (BMS) to identify the most appropriate metric from an experiment that predicts injury outcomes. The Brier Metric Score assesses how well a metric predicts the outcome for a censored data point (a lower BMS is better). Survival analysis was then conducted with the selected metric and the best distribution was selected using Akaike information criterion (AIC). Confidence intervals (CIs) and the normalized confidence interval width (NCIS) were calculated for the injury probability curve. The testing and validation of the methods described were performed using biomechanics data in the open literature. The methods for the HIPC development procedure detailed herein have been rigorously tested and used in the generation of WIAMan HIPCs and Injury Assessment Reference Curves (IARCs) for the WIAMan ATD, but can also be used in other ATD or PMHS injury risk curve development.

Trabecular bone mineral density correlations using QCT: Central and peripheral human skeleton.

Musculoskeletal injuries to the lower leg and foot-ankle joint are associated with external mechanical loads resulting from motor vehicle crashes, under body blasts, falls from height, or sports. As an intrinsic material property, the bone mineral density (BMD) is related to bone strength. The clinically recognized biological sites for BMD evaluation are the hip and spine. The focus of this study was to define the correlation between BMD from standard clinical sites (hip and lumbar spine) compared to BMD from non-standard sites (foot-ankle-distal tibia bones). Twenty-one post-mortem human subjects (PMHS) with mean age, height, and mass of 63 ± 11 years, 179 ± 7 cm, and 86 ± 13 kg, respectively were used for analysis. Clinical BMD software (Mindways Software, Inc.) was used for trabecular BMD quantification using quantitative computed tomography (QCT). In quantification of BMD of the foot-ankle-distal tibia (hind foot), the trabecular BMD of the talus (316 ± 86mg/cc) was highest followed by the distal tibia (238 ± 72 mg/cc) and then calcaneus (147 ± 51 mg/cc). To correlate BMD values from foot bone regions with the central skeleton BMD values within the same PMHS, there were 18 lumbar spine and 12 hip BMDs available. The BMD of the distal tibia correlated best with the hip intertrochanter BMD (R2 of 0.72). Calcaneus BMD best correlated with the hip femoral neck BMD (R2 = 0.64). In summary, the hind foot bone BMD values correlated better with the hip as compared to the lumbar spine BMD from the same PMHS. These findings indicate that, in the absence of a direct measure of foot-bone BMD, hip BMD might be a better predictor of injury risk to hind foot rather than lumbar spine BMD, or alternatively, calcaneal trabecular BMD can be used to predict the risk of injury to hip. Further, these relationships between central and peripheral regions can also be implemented in finite element models for improved failure predictions.

Pelvis injury risk curves in side impacts from human cadaver experiments using survival analysis and Brier score metrics.

Objectives: Post Mortem Human Surrogate (PMHS) experiments are used for describing tolerance and improve safety. For nearside impacts, the United States Standard Federal Motor Vehicle Safety Standards (FMVSS-214) used PMHS tests and binary regression methods to achieve these goals. Since this promulgation, Parametric Statistical Survival Modeling (PSSM) has become a de facto standard for developing injury risk curves (IRCs). This study is focused on pelvic injuries from side impacts. The objectives are as follows. Analyze impactor-based intact PMHS tests and develop IRCs at different AIS levels using the force metric and examine the effectiveness of other force-related variables on IRCs.Methods: Impactor-driven pelvic tests conducted using whole body PMHS were selected from published studies. The dataset had 63 tests. Peak force, 3-ms clip force, and impulse were used to develop IRCs for Abbreviated Injury Scores (AIS) AIS2+ and AIS3+, i.e., groups A and B. Brier Score Metric (BSM) was used for ranking metrics. 95% confidence intervals were computed, Normalized Confidence Interval Sizes (NCIS) were determined, and quality of the IRCs were obtained.Results: Impulse best described the underlying response of the pelvis. BSMs were the lowest for the impulse for both groups. At 10% and 50% probabilities, impulses were 71 Ns and 125 Ns for group A and 79 Ns and 160 Ns for group B; peak forces were 3.8 kN and 7.1 kN and 4 kN and 10 kN for groups A and B; and clip forces were 2.7 kN and 6.5 kN and 3.6 kN and 8.6 kN, for groups A and B. NCIS at discrete probability levels, qualities of risk curves, and individual IRCs are given.Conclusion: This study underscores the importance of using impulse to describe pelvis injury criteria in lateral impacts. These findings are applicable to anthropomorphic test devices, as matched pair tests are done to determine dummy-based injury criteria/injury assessment risk curves (IARCs). Although IRCs have been developed for WorldSID, it may be appropriate to use impulse-based IARCs. Because THOR is a potential device for automated vehicle environments, it may be appropriate to develop THOR-based IARCS. The present IRCs act as fundamental human-based injury criteria. These responses can also be used in human body and subsystem computational models.

THOR dummy chest deflection response in oblique and lateral far-side sled tests.

Objective: The focus of this study is side impact. Though occupant injury assessment and protection in nearside impacts has received considerable attention and safety standards have been promulgated, field studies show that a majority of far-side occupant injuries are focused on the head and thorax. The 50th percentile male Test Device for Human Occupant Restraint (THOR) has been used in oblique and lateral far-side impact sled tests, and regional body accelerations and forces and moments recorded by load cells have been previously reported. The aim of this study is to evaluate the chestband-based deflection responses from these tests. Methods: The 3-point belt-restrained 50th percentile male THOR dummy was seated upright in a buck consisting of a rigid flat seat, simulated center console, dashboard, far-side side door structure, and armrest. It was designed to conduct pure lateral and oblique impacts. The center console, dashboard, simulated door structure, and armrest were covered with energy-absorbing materials. A center-mounted airbag was mounted to the right side of the seat. Two 59-gage chestbands were routed on the circumference of the thorax, with the upper and lower chestbands at the level of the third and sixth ribs, respectively, following the rib geometry. Oblique and pure lateral far-side impact tests with and without airbags were conducted at 8.3 m/s. Maximum chest deflections were computed by processing temporal contours using custom software and 3 methods: Procedures paralleling human cadaver studies, using the actual anchor point location and actual alignment of the InfraRed Telescoping Rods for the Assessment of Chest Compression (IR-TRACC) in the dummy on each aspect-that is, right or left,-and using the same anchor location of the internal sensor but determining the location of the peak chest deflection on the contour confined to the aspect of the sensor; these were termed the SD, ID, and TD metrics, respectively. Results: All deformation contours at the upper and lower thorax levels and associated peak deflections are given for all tests. Briefly, the ID metrics were the lowest in magnitude for both pure lateral and oblique modes, regardless of the presence or absence of an airbag. This was followed by the TD metric, and the SD metric produced the greatest deflections. Conclusion: The chestbands provide a unique opportunity to compute peak deflections that parallel current IR-TRACC-type deflections and allow computation of peak deflections independent of the initial point of attachment to the rib. The differing locations of the peak deflection vectors along the rib contours for different test conditions suggest that a priori attachment is less effective. Further, varying magnitudes of the differences between ID and TD metrics underscore the difficulty in extrapolating ID outputs under different conditions: Pure lateral versus oblique, airbag presence, and thoracic levels. Deflection measurements should, therefore, not be limited to an instrument that can only track from a fixed point. For improved predictions, these results suggest the need to investigate alternative techniques, such as optical methods to improve chest deflection measurements for far-side occupant injury assessment and mitigation.

Development of a Methodology for Simulating Complex Head Impacts With the Advanced Combat Helmet.

Blunt impact assessment of the Advanced Combat Helmet (ACH) is currently based on the linear head response. The current study presents a methodology for testing the ACH under complex loading that generates linear and rotational head motion. Experiments were performed on a guided, free-fall drop tower using an instrumented National Operating Committee for Standards on Athletic Equipment (NOCSAE) head attached to a Hybrid III (HIII) or EuroSID-2 (ES-2) dummy neck and carriage. Rear and lateral impacts occurred at 3.0 m/s with peak linear accelerations (PLA) and peak rotational accelerations (PRA) measured at the NOCSAE head center-of-gravity. Experimental data served as inputs for the Simulated Injury Monitor (SIMon) computational model to estimate brain strain. Rear ACH impacts had 22% and 7% higher PLA and PRA when using the HIII neck versus the ES-2 neck. Lateral ACH impacts had 33% and 35% lower PLA and PRA when using HIII neck versus the ES-2 neck. Computational results showed that total estimated brain strain increased by 25% and 76% under rear and lateral ACH impacts when using the ES-2 neck. This methodology was developed to simulate complex ACH impacts involving the rotational head motion associated with diffuse brain injuries, including concussion, in military environments.

Forces and moments in cervical spinal column segments in frontal impacts using finite element modeling and human cadaver tests.

Experiments have been conducted using isolated tissues of the spine such as ligaments, functional units, and subaxial cervical spine columns. Forces and or moments under external loading can be obtained at the ends of these isolated/segmented preparations; however, these models require fixations at the end(s). To understand the response of the entire cervical spine without the artificial boundary/end conditions, it is necessary to use the whole body human cadaver in the experimental model. This model can be used to obtain the overall kinematics of the head and neck. The forces and moments at each vertebral level of the cervical column segments cannot be directly obtained using the kinematic and mass property data. The objective of this study was to determine such local loads under simulated frontal impact loading using a validated head-neck finite element model and experiments from whole body human cadaver tests, at velocities ranging from 3.9 to 16 m/s. The specimens were prepared with a nine linear accelerometer package on the head, and a triaxial accelerometer with a triaxial angular rate sensor on T1, and a set of three non-collinear retroreflective targets were secured to the T1 using the accelerometer mount. A similar array of targets was attached to the skull. Head accelerations were computed at the center of gravity of the head using specimen-specific physical properties. Upper and lower neck forces were computed using center of gravity acceleration data. This dataset was used to verify a previously validated finite element model of the head-neck model by inputting the mean T1 accelerations at different velocities. The model was parametrically exercised from 4 to 16 m/s in increments of 3 m/s to determine the forces and moments in the local anatomical system at all spinal levels. Results indicated that, with increasing velocities, the axial loading was found to be level-invariant, while the shear force and moment responses depended on the level. The nonuniform developments of the segmental forces and moments across different spinal levels suggest a shift in instantaneous axis of rotations between the across different spinal levels. Such differential changes between contiguous levels may lead to local spinal instability, resulting in long-term effects such as accelerated degeneration and spondylosis. The study underscored the need to conduct additional research to include effects of posture and geometrical variations that exist between males and females for a more comprehensive understanding of the local load-sharing in frontal impacts.

Analysis of Force Mitigation by Boots in Axial Impacts using a Lower Leg Finite Element Model.

Lower extremity injuries caused by floor plate impacts through the axis of the lower leg are a major source of injury and disability for civilian and military vehicle occupants. A collection of PMHS pendulum impacts was revisited to obtain data for paired booted/unbooted test on the same leg. Five sets of paired pendulum impacts (10 experiments in total) were found using four lower legs from two PMHS. The PMHS size and age was representative of an average young adult male. In these tests, a PMHS leg was impacted by a 3.4 or 5.8 kg pendulum with an initial velocity of 5, 7, or 10 m/s (42-288 J). A matching LS-DYNA finite element model was developed to replicate the experiments and provide additional energy, strain, and stress data. Simulation results matched the PMHS data using peak values and CORA curve correlations. Experimental forces ranged between 1.9 and 12.1 kN experimentally and 2.0 and 11.7 kN in simulation. Combat boot usage reduced the peak force by 36% experimentally (32% in simulation) by compressing the sole and insole with similar mitigations for calcaneus strain. The simulated Von Mises stress contours showed the boot both mitigating and shifting stress concentrations from the calcaneus in unbooted impacts to the talus-tibia joint in the booted impacts, which may explain why some previous studies have observed shifts to tibia injuries with boot or padding usage.

Three-dimensional kinematic corridors of the head, spine, and pelvis for small female driver seat occupants in near- and far-side oblique frontal impacts.

OBJECTIVES: Analyses of recent automotive accident data indicate an increased risk of injury for small female occupants compared to males in similar accidents. Females have been shown to be more susceptible to spinal injuries than males. To protect this more vulnerable population, advanced anthropomorphic test devices (ATDs) and computer human body models are being developed and require biofidelity curves for validation. The aim of this study is to generate female-specific 3D kinematic corridors in near- and far-side oblique frontal impacts for the head, spine, and pelvis. METHODS: Eight specimens were procured and prescreened for mass, stature, and quantitative computed tomography bone mineral density and preexisting injuries to minimize biologic variability. Sets of 4 noncolinear retroreflective targets were placed on the back of the head; dorsal spine at T1, T8, and L2; and posterior sacrum. Instrumented computed tomography scans were obtained to measure the orientation and position of the markers relative to anatomic fiducials. The specimens were placed on a buck representative of a generic automotive driver's seat environment designed to minimize lower-extremity and pelvic motion. The buck was oriented such that the buck centerline was seated 30° from the impact vector in either a near- or far-side oblique frontal configuration. Preposition of the occupant was specified to the 50th percentile male H-point location, thigh and tibial angles, and torso angle. Impact was delivered via a servo-acceleration sled to the base of the buck with a 30 km/h 9 g trapezoidal pulse. Occupants were restrained by a standard 3-point belt that had a custom load-limiter device set to 2 kN at the D-ring side of the shoulder belt. Target motion was recorded at 1 kHz using a 3D optical motion capture system. Anatomic motion of the head, spine, and pelvis was calculated relative to the seat, and the average response was determined from 4 near-side and 4 far-side tests. The borders of the corridor were determined by calculating a standard deviational ellipse in the x, y, and z planes at each time step. RESULTS: Plots of the biofidelity corridors for near- and far-side tests are shown in planes parallel to the seat from the lateral, rear, and overhead directions. Averaged peak excursions in the fore/aft and lateral directions are compared for the near- and far-side corridors. Near-side female and male tests are similarly compared. CONCLUSIONS: In general, average peak excursions were greater in the far-side configuration than in the near-side configuration. Peak excursion results compared well with similar tests conducted on male postmortem human subjects (PMHS). The kinematic corridors developed in the current study serve as a set of biofidelity corridors for the development of current and future physical and computational surrogates.