Human and Porcine Lumbar Endplate Injury Risk in Repeated Flexion-Compression.

Low back pain (LBP) affects 50-80% of adults at some point in their lifetime, yet the etiology of injury is not well understood. Those exposed to repeated flexion-compression are at a higher risk for LBP, such as helicopter pilots and motor vehicle operators. Animal injury models offer insight into in vivo injury mechanisms, but interspecies scaling is needed to relate animal results to human. Human (n = 16) and porcine (n = 20) lumbar functional spinal units (FSUs) were loaded in repeated flexion-compression (1 Hz) to determine endplate fracture risk over long loading exposures. Flexion oscillated from 0 to 6° and peak applied compressive stress ranged from 0.65 to 2.38 MPa for human and 0.64 to 4.68 MPa for porcine specimens. Five human and twelve porcine injuries were observed. The confidence intervals for human and porcine 50% injury risk curves in terms of stress and cycles overlapped, indicating similar failure behavior for this loading configuration. However, porcine specimens were more tolerant to the applied loading compared to human, demonstrated by a longer time-to-failure for the same applied stress. Optimization revealed that time-to-failure in human specimens was approximately 25% that of porcine specimens at a given applied stress within 0.65-2.38 MPa. This study determined human and porcine lumbar endplate fracture risks in long-duration repeated flexion-compression that can be directly used for future equipment and vehicle design, injury prediction models, and safety standards. The interspecies scale factor produced in this study can be used for previous and future porcine lumbar injury studies to scale results to relevant human injury.

Shear shock wave injury in vivo: High frame-rate ultrasound observation and histological assessment.

Using high frame-rate ultrasound and ¡1µm sensitive motion tracking we previously showed that shear waves at the surface of ex vivo and in situ brains develop into shear shock waves deep inside the brain, with destructive local accelerations. However post-mortem tissue cannot develop injuries and has different viscoelastodynamic behavior from in vivo tissue. Here we present the ultrasonic measurement of the high-rate shear shock biomechanics in the in vivo porcine brain, and histological assessment of the resulting axonal pathology. A new biomechanical model of brain injury was developed consisting of a perforated mylar surface attached to the brain and vibrated using an electromechanical shaker. Using a custom sequence with 8 interleaved wide beam emissions, brain imaging and motion tracking were performed at 2900 images/s. Shear shock waves were observed for the first time in vivo wherein the shock acceleration was measured to be 2.6 times larger than the surface acceleration ( 95g vs. 36g). Histopathology showed axonal damage in the impacted side of the brain from the brain surface, accompanied by a local shock-front acceleration of >70g. This shows that axonal injury occurs deep in the brain even though the shear excitation was at the brain surface, and the acceleration measurements support the hypothesis that shear shock waves are responsible for deep traumatic brain injuries.

Female vs. male relative fatality risk in fatal motor vehicle crashes in the US, 1975-2020.

Motor vehicle accidents are the leading cause of death for young adults 18-29 years old worldwide, resulting in nearly 1 million years of life lost annually in the United States. Despite improvements in vehicle safety technologies, young women are at higher risk of dying in car crashes compared with men in matched scenarios. Vehicle crash testing primarily revolves around test dummies representative of the 50th percentile adult male, potentially resulting in these differences in fatality risk for female occupants compared to males. Vehicle occupants involved in fatal car crashes were matched using seating location, vehicle type, airbag deployment, seatbelt usage, and age. The relative risk for fatality (R) between males and females was calculated using a Double Pair Comparison. Young women (20s-40s) are at approximately 20% higher risk of dying in car crashes compared with men of the same age in matched scenarios. In passenger cars, 25-year-old female occupants in passenger car crashes from 1975-2020 exhibit R = 1.201 (95% CI 1.160-1.250) compared to 25-year-old males, and R-1.117 (95% CI 1.040-1.207) for passenger car crashes from 2010-2020. This trend persists across vehicle type, airbag deployment, seatbelt use, and number of vehicles involved in a crash. Known sex-based differences do not explain this large risk differential, suggesting a need for expanded test methodologies and research strategies to address as-yet unexplored sex differences in crash fatalities. These differences should be further investigated to ensure equitable crash protection.

Translating Cadaveric Injury Risk to Dummy Injury Risk at Iso-energy.

Injury risk assessment based on cadaver data is essential for informing safety standards. The common 'matched-pair' method matches energy-based inputs to translate human response to anthropometric test devices (ATDs). However, this method can result in less conservative human injury risk curves due to intrinsic differences between human and ATDs. Generally, dummies are stiffer than cadavers, so force and displacement cannot be matched simultaneously. Differences in fracture tolerance further influence the dummy risk curve to be less conservative under matched-pair. For example, translating a human lumbar injury risk curve to a dummy of equivalent stiffness using matched-pair resulted in a dummy injury risk over 80% greater than the cadaver at 50% fracture risk. This inevitable increase arises because the dummy continues loading without fracture to attenuate energy beyond the 'matched' cadaver input selected. Human injury response should be translated using an iso-energy approach, as strain energy is well associated with failure in biological tissues. Until cadaver failure, dummy force is related to cadaver force at iso-energy. Beyond cadaver failure, dummy force is related to cadaver force through failure energy. This method does not require perfect cadaver/dummy biofidelity and ensures that energy beyond cadaver failure does not influence the injury risk function.

A Novel Paradigm to Develop Regional Thoracoabdominal Criteria for Behind Armor Blunt Trauma Based on Original Data.

INTRODUCTION: For behind armor blunt trauma (BABT), recent prominent BABT standards for chest plate define a maximum deformation distance of 44 mm in clay. It was developed for soft body armor applications with limited animal, gelatin, and clay tests. The legacy criterion does not account for differing regional thoracoabdominal tolerances to behind armor-induced injury. This study examines the rationale and approaches used in the legacy BABT clay criterion and presents a novel paradigm to develop thoracoabdominal regional injury risk curves. MATERIALS AND METHODS: A review of the original military and law enforcement studies using animals, surrogates, and body armor materials was conducted, and a reanalysis of data was performed. A multiparameter model analysis describes survival-lethality responses using impactor/projectile (mass, diameter, and impact velocity) and specimen (weight and tissue thickness) variables. Binary regression risk curves with ±95% confidence intervals (CIs) and peak deformations from simulant tests are presented. RESULTS: Injury risk curves from 74 goat thorax tests showed that peak deflections of 44.7 mm (±95% CI: 17.6 to 55.4 mm) and 49.9 mm (±95% CI: 24.7 to 60.4 mm) were associated with the 10% and 15% probability of lethal outcomes. 20% gelatin and Roma Plastilina #1 clay were stiffer than goat. The clay was stiffer than 20% gelatin. Penetration diameters showed greater variations (on a test-by-test basis, difference 36-53%) than penetration depths (0-12%) across a range of projectiles and velocities. CONCLUSIONS: While the original authors stressed limitations and the importance of additional tests for refining the 44 mm recommendation, they were not pursued. As live swine tests are effective in developing injury criteria and the responses of different areas of the thoracoabdominal regions are different because of anatomy, structure, and function, a new set of swine and human cadaver tests are necessary to develop scaling relationships. Live swine tests are needed to develop incapacitation/lethal injury risk functions; using scaling relationships, human injury criteria can be developed.

Facial Fracture Injury Criteria from Night Vision Goggle Impact.

INTRODUCTION: Military personnel extensively use night vision goggles (NVGs) in contemporary scenarios. Since NVGs may induce or increase injuries from falls or vehicular accidents, biomechanical risk assessments would aid design goal or mitigation strategy development.METHODS: This study assesses injury risks from NVG impact on cadaver heads using impactors modeled on the PVS-14 NVG. Impacts to the zygoma and maxilla were performed at 20° or 40° angles. Risks of facial fracture, neurotrauma, and neck injury were assessed. Acoustic sensors and accelerometers assessed time of fracture and provided input variables for injury risk functions. Injuries were assessed using the Abbreviated Injury Scale (AIS); injury severity was assessed using the Rhee and Donat scales. Risk functions were developed for the input variables using censored survival analyses.RESULTS: The effects of impact angle and bone geometry on injury characteristics were determined with loading area, axial force, energy attenuation, and stress at fracture. Probabilities of facial fracture were quantified through survival analysis and injury risk functions. These risk functions determined a 50% risk of facial bone fracture at 1148 N (axial force) at a 20° maxillary impact, 588 N at a 40° maxillary impact, and 677 N at a 20° zygomatic impact. A cumulative distribution function indicates 769 N corresponds to 50% risk of fracture overall.DISCUSSION: Results found smaller impact areas on the maxilla are correlated with higher angles of impact increasing risk of facial fracture, neck injuries are unlikely to occur before fracture or neurotrauma, and a potential trade-off mechanism between fracture and brain injury.Davis MB, Pang DY, Herring IP, Bass CR. Facial fracture injury criteria from night vision goggle impact. Aerosp Med Hum Perform. 2023; 94(11):827-834.

The Human Lumbar Spine During High-Rate Under Seat Loading: A Combined Metric Injury Criteria.

Modern changes in warfare have shown an increased incidence of lumbar spine injuries caused by underbody blast events. The susceptibility of the lumbar spine during these scenarios could be exacerbated by coupled moments that act with the rapid compressive force depending on the occupant's seated posture. In this study, a combined loading lumbar spine vertebral body fracture injury criteria (Lic) across a range of postures was established from 75 tests performed on instrumented cadaveric lumbar spine specimens. The spines were predominantly exposed to axial compressive forces from an upward vertical thrust with 64 of the tests resulting in at least one vertebral body fracture and 11 in no vertebral body injury. The proposed Lic utilizes a recommended metric (κ), based on prismatic beam failure theory, resulting from the combination of the T12-L1 resultant sagittal force and the decorrelated bending moment with optimized critical values of Fr,crit = 5824 N and My,crit = 1155 Nm. The 50% risk of lumbar spine injury corresponded to a combined metric of 1, with the risk decreasing with the combined metric value. At 50% injury risk the Normalized Confidence Interval Size improved from 0.24 of a force-based injury reference curve to 0.17 for the combined loading metric.

Using Wavelet Analysis to Distinguish Cavitation Acoustic Emissions From Blunt Impact Noise.

Cavitation has been shown to have implications for head injury, but currently there is no solution for detecting the formation of cavitation through the skull during blunt impact. The goal of this communication is to confirm the wideband acoustic wavelet signature of cavitation collapse, and determine that this signature can be differentiated from the noise of a blunt impact. A controlled, laser induced cavitation study was conducted in an isolated water tank to confirm the wide band acoustic signature of cavitation collapse in the absence of a blunt impact. A clear acrylic surrogate head was impacted to induce blunt impact cavitation. The bubble formation was imaged using a high speed camera, and the collapse was synched up with the wavelet transform of the acoustic emission. Wideband acoustic response is seen in wavelet transform of positive laser induced cavitation tests, but absent in laser induced negative controls. Clear acrylic surrogate tests showed the wideband acoustic wavelet signature of collapse can be differentiated from acoustic noise generated by a blunt impact. Broadband acoustic signal can be used as a biomarker to detect the incidence of cavitation through the skull as it consists of frequencies that are low enough to potentially pass through the skull but high enough to differentiate from blunt impact noise. This lays the foundation for a vital tool to conduct CSF cavitation research in-vivo.

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.

Acoustic emissions in vertebral cortical shell failure.

Understanding the initiation of bony failure is critical in assessing the progression of bone fracture and in developing injury criteria. Detection of acoustic emissions in bone can be used to identify fractures more sensitively and at an earlier inception time compared to traditional methods. However, high rate loading conditions, complex specimen-device interaction or geometry may cause other acoustic signals. Therefore, characterization of the isolated local acoustic emission response from cortical bone fracture is essential to distinguish its characteristics from other potential acoustic sources. This work develops a technique to use acoustic emission signals to determine when cortical bone failure occurs by characterization using both a Welch power spectral density estimate and a continuous wavelet transform. Isolated cortical shell specimens from thoracic vertebral bodies with attached acoustic sensors were subjected to quasistatic loading until failure. The resulting acoustic emissions had a wideband frequency response with peaks from 20 to 900 kHz, with the spectral peaks clustered in three bands of frequencies (166 ± 52.6 kHz, 379 ± 37.2 kHz, and 668 ± 63.4 kHz). Using these frequency bands, acoustic emissions can be used as a monitoring tool in biomechanical spine testing, distinguishing bone failure from structural response. This work presents a necessary set of techniques for effectively utilizing acoustic emissions to determine the onset of cortical bone fracture in biological material testing. Acoustic signatures can be developed for other cortical bone regions of interest using the presented methods.

Primary blast wave protection in combat helmet design: A historical comparison between present day and World War I.

Since World War I, helmets have been used to protect the head in warfare, designed primarily for protection against artillery shrapnel. More recently, helmet requirements have included ballistic and blunt trauma protection, but neurotrauma from primary blast has never been a key concern in helmet design. Only in recent years has the threat of direct blast wave impingement on the head-separate from penetrating trauma-been appreciated. This study compares the blast protective effect of historical (World War I) and current combat helmets, against each other and 'no helmet' or bare head, for realistic shock wave impingement on the helmet crown. Helmets included World War I variants from the United Kingdom/United States (Brodie), France (Adrian), Germany (Stahlhelm), and a current United States combat variant (Advanced Combat Helmet). Helmets were mounted on a dummy head and neck and aligned along the crown of the head with a cylindrical shock tube to simulate an overhead blast. Primary blast waves of different magnitudes were generated based on estimated blast conditions from historical shells. Peak reflected overpressure at the open end of the blast tube was compared to peak overpressure measured at several head locations. All helmets provided significant pressure attenuation compared to the no helmet case. The modern variant did not provide more pressure attenuation than the historical helmets, and some historical helmets performed better at certain measurement locations. The study demonstrates that both historical and current helmets have some primary blast protective capabilities, and that simple design features may improve these capabilities for future helmet systems.

Assessing Surgical Task Load and Performance: A Comparison of Simulation and Maritime Operation.

INTRODUCTION: This study examined the effects of simulated and actual vessel motion at high seas on task load and surgical performance. METHODS: This project was performed in phases. Phase I was a feasibility study. Phase II utilized a motion base simulator to replicate vessel motion. Phase III was conducted aboard the U.S. Naval Ship Brunswick. After performing surgical tasks on a surgical simulation mannequin, participants completed the Surgical Task Load Index (TLX) designed to collect workload data. Simulated surgeries were evaluated by subject matter experts. RESULTS: TLX scores were higher in Phase III than Phase II, particularly at higher sea states. Surgical performance was not significantly different between Phase II (84%) and Phase III (89%). Simulated motions were comparable in both phases. CONCLUSIONS: Simulated motion was not associated with a significant difference in surgical performance or deck motion, suggesting that this simulator replicates the conditions experienced during surgery at sea on the U.S. Naval Ship Brunswick. However, Surgical TLX scores were dramatically different between the two phases, suggesting increased workload at sea, which may be the result of time at sea, the stress of travel, or other factors. Surgical performance was not affected by sea state in either phase.

Efficacy of Medical Operations and Layout Planning Onboard Nontraditional US Navy Vessels at High Seas.

INTRODUCTION: Attempting to expedite delivery of care to wounded war fighters, this study aimed to quantify the ability of medical and surgical teams to perform lifesaving damage control and resuscitation procedures aboard nontraditional US Navy Vessels on high seas. Specifically, it looked at the ability of the teams to perform procedures in shipboard operating and emergency rooms by analyzing motion of personnel during the procedures. METHODS: One hundred and twelve damage control and resuscitation procedures were performed during a voyage of the US Naval Ship Brunswick in transit from Norfolk, Virginia, to San Diego, California. The ability of personnel to perform these procedures was quantified by the use of motion link analysis designed to track the movement of each participant as they completed their assigned tasks. RESULTS: The link analysis showed no significant change in the number of movements of participants from the beginning to the end of the study. However, there was a learning effect observed during the study, with teams completing tasks faster at the end of the study than at the beginning. CONCLUSION: This shows that the working conditions aboard the US Naval Ship Brunswick were satisfactory for the assigned tasks, indicating that these medical operations may be feasible aboard nontraditional US Navy vessels.

Direct Observation of Low Strain, High Rate Deformation of Cultured Brain Tissue During Primary Blast.

The Veterans Health Administration determined that over 250,000 U.S. service members were diagnosed with a traumatic brain injury (TBI) between 2008 and 2018, of which a great proportion were due to blast exposure. Although the penetrating (secondary) and inertia-driven (tertiary) phases of blast-induced TBI (bTBI) have been studied thoroughly and are known to be injurious, primary blast brain injury has been less studied. We investigated the biomechanics of primary bTBI in our previously developed in vitro shock tube model with a fluid-filled sample receiver. Using stereoscopic, high-speed cameras and digital image correlation (DIC), we mapped the deformation of organotypic hippocampal slice cultures (OHSCs) following a range of blast exposures to characterize the induced strains. As blast exposure increased, tissue strain increased, although the levels remained relatively low (maximum < 9%), with strains rates between 25 and 85 s-1. Both strain magnitude and rate were highly correlated with the in-air blast impulse and in-fluid peak pressure parameters. Comparing biomechanical parameters to previously reported blast-induced electrophysiological dysfunction, a threshold for deficits in long-term potentiation (LTP) was observed for strains between 3.7 and 6.7% and strain rates between 25 and 33 s-1. This is the first study to experimentally determine primary blast-induced strain and strain rates in hippocampal tissue.

The response of the pediatric head to impacts onto a rigid surface.

The study of pediatric head injury relies heavily on the use of finite element models and child anthropomorphic test devices (ATDs). However, these tools, in the context of pediatric head injury, have yet to be validated due to a paucity of pediatric head response data. The goal of this study is to investigate the response and injury tolerance of the pediatric head to impact. Twelve pediatric heads were impacted in a series of drop tests. The heads were dropped onto five impact locations (forehead, occiput, vertex and right and left parietal) from drop heights of 15 and 30 cm. The head could freely fall without rotation onto a flat 19 mm thick platen. The impact force was measured using a 3-axis piezoelectric load cell attached to the platen. Age and drop height were found to be significant factors in the impact response of the pediatric head. The head acceleration (14%-15 cm; 103-30 cm), Head Injury Criterion (HIC) (253%-15 cm; 154%-30 cm) and impact stiffness (5800%-15 cm; 3755%-30 cm) when averaged across all impact locations increased with age from 33 weeks gestation to 16 years, while the pulse duration (66%-15 cm; 53%-30 cm) decreased with age. Increases in head acceleration, HIC and impact stiffness were also observed with increased drop height, while pulse duration decreased with increased drop height. One important observation was that three of the four cadaveric heads between the ages of 5-months and 22-months sustained fractures from the 15 cm and 30 cm drop heights. The 5-month-old sustained a right parietal linear fracture while the 11- and 22-month-old sustained diastatic linear fractures.

The role of cervical muscles in mitigating concussion.

OBJECTIVES: Increased neck strength has been hypothesized to lower sports related concussion risk, but lacks experimental evidence. The goal is to investigate the role cervical muscle strength plays in blunt impact head kinematics and the biofidelity of common experimental neck conditions. We hypothesize head kinematics do not vary with neck activation due to low short term human head-to-neck coupling; because of the lack of coupling, free-head experimental conditions have higher biofidelity than Hybrid III necks. METHODS: Impacts were modeled using the Duke University Head and Neck Model. Four impact types were simulated with six neck conditions at eight impact positions. Peak resultant linear acceleration, peak resultant angular acceleration, Head Injury Criterion, and Head Impact Power compared concussion risk. To determine significance, maximum metric difference between activation states were compared to critical effect sizes (literature derived differences between mild and severe impact metrics). RESULTS: Maximum differences between activation conditions did not exceed critical effect sizes. Kinematic differences from impact location and strength can be ten times cervical muscle activation differences. Hybrid III and free-head linear acceleration metrics were 6±1.0% lower and 12±1.5% higher than relaxed condition respectively. Hybrid III and free-head angular acceleration metrics were 12±4.0% higher and 2±2.7% lower than relaxed condition respectively. CONCLUSIONS: Results from a validated neck model suggest increased cervical muscle force does not influence short term (<50ms) head kinematics in four athletically relevant scenarios. Impact location and magnitude influence head kinematics more than cervical muscle state. Biofidelic limitations of both Hybrid III and free-head experimental conditions must be considered.

On the relative importance of bending and compression in cervical spine bilateral facet dislocation.

BACKGROUND: Cervical bilateral facet dislocations are among the most devastating spine injuries in terms of likelihood of severe neurological sequelae. More than half of patients with tetraparesis had sustained some form of bilateral facet fracture dislocation. They can occur at any level of the sub-axial cervical spine, but predominate between C5 and C7. The mechanism of these injuries has long been thought to be forceful flexion of the chin towards the chest. This "hyperflexion" hypothesis comports well with intuition and it has become dogma in the clinical literature. However, biomechanical studies of the human cervical spine have had little success in producing this clinically common and devastating injury in a flexion mode of loading. METHODS: The purpose of this manuscript is to review the clinical and engineering literature on the biomechanics of bilateral facet dislocations and to describe the mechanical reasons for the causal role of compression, and the limited role of head flexion, in producing bilateral facet dislocations. FINDINGS: Bilateral facet dislocations have only been produced in experiments where compression is the primary loading mode. To date, no biomechanical study has produced bilateral facet dislocations in a whole spine by bending. Yet the notion that it is primarily a hyper-flexion injury persists in the clinical literature. INTERPRETATION: Compression and compressive buckling are the primary causes of bilateral facet dislocations. It is important to stop using the hyper-flexion nomenclature to describe this class of cervical spines injuries because it may have a detrimental effect on designs for injury prevention.

Long-term complications of glycogen storage disease type Ia in the canine model treated with gene replacement therapy.

BACKGROUND: Glycogen storage disease type Ia (GSD Ia) in dogs closely resembles human GSD Ia. Untreated patients with GSD Ia develop complications associated with glucose-6-phosphatase (G6Pase) deficiency. Survival of human patients on intensive nutritional management has improved; however, long-term complications persist including renal failure, nephrolithiasis, hepatocellular adenomas (HCA), and a high risk for hepatocellular carcinoma (HCC). Affected dogs fail to thrive with dietary therapy alone. Treatment with gene replacement therapy using adeno-associated viral vectors (AAV) expressing G6Pase has greatly prolonged life and prevented hypoglycemia in affected dogs. However, long-term complications have not been described to date. METHODS: Five GSD Ia-affected dogs treated with AAV-G6Pase were evaluated. Dogs were euthanized due to reaching humane endpoints related to liver and/or kidney involvement, at 4 to 8 years of life. Necropsies were performed and tissues were analyzed. RESULTS: Four dogs had liver tumors consistent with HCA and HCC. Three dogs developed renal failure, but all dogs exhibited progressive kidney disease histologically. Urolithiasis was detected in two dogs; uroliths were composed of calcium oxalate and calcium phosphate. One affected and one carrier dog had polycystic ovarian disease. Bone mineral density was not significantly affected. CONCLUSIONS: Here, we show that the canine GSD Ia model demonstrates similar long-term complications as GSD Ia patients in spite of gene replacement therapy. Further development of gene therapy is needed to develop a more effective treatment to prevent long-term complications of GSD Ia.

Time and temperature sensitivity of the Hybrid III neck.

The Hybrid III (HIII) dummy is one of the most widely used anthropomorphic test devices (ATDs) in the world, and researchers have found a variety of uses for it outside of its original purpose as an automotive crash test dummy. These expanded roles have introduced situations outside the dummy's original design parameters, where a number of tests must be run in relatively rapid succession or where it may not be possible to control the temperature of the test environment. OBJECTIVE: This study has 2 aims. The first is to determine how the duration of the time interval between tests affects the axial compression performance of the HIII neck. The second is to quantify the effect of temperature on the neck's compressive stiffness through a range of temperatures relevant to indoor or outdoor testing. METHODS: To characterize the effects of different test conditions, a series of high-rate axial compressive tests was run on a 50th percentile male HIII neck component in a materials testing machine. Between-test recovery intervals were varied from 2 h to 1 min, and temperature conditions of 0, 12.5, 25, and 37.5 °C were tested. RESULTS: Though the duration of the recovery interval had little impact on the recorded force (less than 1%), the component did exhibit considerable strain creep over the course of the test. Temperature had a strong influence on the compressive stiffness of the component. Compared to the stiffness at 25 °C (near room temperature), the stiffness of the neck at 37.5 °C fell by 15%; at 0 °C, the stiffness more than doubled. CONCLUSIONS: This study demonstrates that though the duration of the recovery interval between tests has a small influence on neck stiffness, temperature effects should not be overlooked because they influence neck compressive stiffness considerably. The relationship between recorded force and temperature is well represented by exponential decay models. These findings highlight the importance of monitoring and controlling for temperature effects during all HIII testing.