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Background Formyl peptide receptor 1 (FPR1), a key member of Formyl peptide receptors (FPRs) from a G-protein coupled receptor family, was previously well-characterized in immune cells. But the function of FPR1 in osteogenesis and fracture healing was rarely reported. In this study, using the FPR1 knockout (KO) mouse, for the first time, we demonstrated a close correlation of FPR1 function to osteogenic differentiation of bone marrow-derived stem cells (BMSCs) in vitro and bone fracture healing in vivo. Methods Primary BMSCs were isolated from both FPR1 KO and wild type (WT) mice. Osteogenic markers were detected during osteogenic differentiation of BMSCs. Biomechanical and structural properties of femur were compared between healthy WT and KO mice by mechanical test and microcomputed tomographic. A closed, transverse fracture at the femoral midshaft was created to compare bone healing between KO and WT mice. Results The FPR1 mRNA level increased significantly during osteogenesis of BMSCs. More importantly, compared to BMSCs from FPR1 KO mice, WT BMSCs expressed significantly higher levels of common osteogenic markers as well as mineralization at day 14 and 21. In addition, the femur from WT mice had better biomechanical and structural properties than the femur from FPR1 KO mice. Furthermore, at day 35 following femur fracture, bone healing in WT mice was remarkably improved compared to FPR1 KO mice, demonstrated by X-ray appearance, H&E stain, bone density, and bone volume/total volume. Conclusion FPR1 plays an important role in osteogenic differentiation, bone mechanical strength, and regenerative capacity of fractured bone. Knockout of FPR1 reduces osteogenesis and bone healing in vivo and vitro.

The objective of this study was to leverage and compare multiple machine learning techniques for predicting the human body model response in restraint design simulations. Parametric simulations with 16 independent variables were performed. Ordinary least-squares (OLS), least absolute shrinkage and selection operator (LASSO), neural network (NN), support vector regression (SVR), regression forest (RF), and an ensemble method were used to develop response surface models of the simulations. The hyperparameters of the machine learning techniques were optimized through grid search and cross-validation to avoid under-fitting and over-fitting. The ensemble method outperformed other techniques, followed by LASSO, SVR, NN, RF, and OLS. Findings indicated that optimizing the metamodel hyper-parameters are essential to predict the optimum set of restraint design parameters.

Self-driving technology will bring novelty in vehicle interior design and allow for a wide variety of occupant seating choices. Thus, vehicle safety systems may be challenged to protect occupants over a wider range of potential postures. This study aims to investigate the effects of the seat cushion angle on submarining risk, lumbar spine loads and pelvis excursion for reclined occupants in frontal crashes. Frontal crash finite element simulations were performed with two of the simplified Global Human Body Model Consortium (GHBMC) occupant models: the small female and the midsize male. Occupant restraints consisted of a frontal airbag, a seatback-integrated 3-point belt with a lap belt anchor pre-tensioner, and a retractor pre-tensioner with a force limiter. For each simulation, parameters including seat cushion angle (3°, 8°, 13°), seatback recline angle (0°, 10°, 20°, 30°), and knee bolster (KB) position relative to the occupant (baseline and no KB) were varied. A full-factorial simulation matrix was performed using the USNCAP 56 km/h frontal crash pulse. Occupant kinematics data were extracted from each simulation to investigate how changes in seat cushion angle, anthropometry, seatback angle, and KB position would affect submarining across all simulated cases. Overall, the F05-OS female model was more likely to submarine when compared to the male occupant model. The threshold for submarining was also affected by the seat cushion angle, seatback angle and KB distance. For the F05-OS model, increasing the seat cushion angle to 13° prevented submarining in the 10° seatback angle case, regardless of the KB position. Similarly, the 13° cushion angle prevented submarining for the M50-OS in the 30° seatback angle configuration but only in the presence of a KB. The results further show an increased lumbar flexion load with increased seat recline angle, as well as occupant-to-KB distance, although an opposite trend with the increased seat cushion angle. Submarining may be a major challenge to overcome for reclined occupants in autonomous driving systems. This study shows that seat cushion angle plays a role in restraining occupants in recline scenarios, but it is not sufficient to prevent submarining without additional countermeasures.

Previous studies have shown that occupants with obesity are at a greater risk of fatality and serious injury than other occupants in motor vehicle crashes. To provide a more complete description of the most frequent injuries and the most frequently injured body regions for occupants with obesity. Sampled cases (n = 13,470) representing ~4.7 million adult occupants involved in frontal crashes (between 2000 and 2015) were selected from the U.S. National Automotive Sampling System—Crashworthiness Data System database. A retrospective cohort study was performed to study the effect of BMI on the risk of injury to different body regions and to identify the most frequent injuries to occupants with different BMIs. Lastly, in-depth crash analysis cases from the U.S. Crash Injury Research and Engineering Network (CIREN) database were studied to elucidate the source of the most common injuries to occupants with obesity. Occupants with obesity experienced a higher risk of upper extremity (4.79 vs 2.92%), lower extremity (8.37 vs 3.23%), and spine (1.53 vs 1.09%) injuries than other occupants. After adjusting for other variables, the risks of spinal, thoracic, and extremities injuries were found to be affected by the BMI class. Seven out of the ten most common injuries sustained by occupants with obesity were lower extremity injuries, and talus fractures were the most common overall. Direct loading through the plantar surface of the foot by the vehicle toe pan was found to be a likely cause of many of those injuries based on CIREN cases. The injuries of occupants with obesity are different than other occupants which can be attributed to their different interaction with the seat belt and vehicle interior. The findings of this study should be considered for designing restraint systems to protect occupants with obesity in car crashes.

The characterization of human subcutaneous adipose tissue (SAT) under high-rate loading is valuable for development of biofidelic finite element human body models (FE-HBMs) to predict seat belt-pelvis interaction and injury risk in vehicle crash simulations. While material characterization of SAT has been performed at 25°C or 37°C, the effect of temperature on mechanical properties of SAT under high-rate and large-deformation loading has not been investigated. Similarly, while freezing is the most common preservation technique for cadaveric specimens, the effect of freeze-thaw on the mechanical properties of SAT is also absent from the literature. Therefore, the aim of this study was to determine the effect of freezing and temperature on mechanical properties of human SAT. Fresh and previously frozen human SAT specimens were obtained and tested at 25°C and 37°C. High-rate indentation and puncture tests were performed, and indentation-puncture force-depth responses were obtained. While the chance of material failure was found to be different between temperatures and between fresh and previously frozen tissue, statistical analyses revealed that temperature and freezing did not change the shear modulus and failure characteristics of SAT. Therefore, the results of the current study indicated that SAT material properties characterized from either fresh or frozen tissue at either 25°C or 37°C could be used for enhancing the biofidelity of FE-HBMs.

Objective: Emergency braking can potentially generate precrash occupant motion that may influence the effectiveness of restraints in the subsequent crash, particularly for rear-seated occup...

Rollover crashes are the most severe crash mode among all types of traffic crashes. They consist of sequential complex dynamic events with contributions of the vehicle, human, environmental element...

Frontal impacts with reclined occupants are rare but severe, and they are anticipated to become more common with the introduction of vehicles with automated driving capabilities. Computational and physical human surrogates are needed to design and evaluate injury countermeasures for reclined occupants, but the validity of such surrogates in a reclined posture is unknown. Experiments with post-mortem human subjects (PMHS) in a recline posture are needed both to define biofidelity targets for other surrogates and to describe the biomechanical response of reclined occupants in restrained frontal impacts. The goal of this study was to evaluate the kinematic and injury response of reclined PMHS in 30 g, 50 km/h frontal sled tests. Five midsize adult male PMHS were tested. A simplified semi-rigid seat with an anti-submarining pan and a non-production threepoint seatbelt (pre-tensioned, force-limited, seat-integrated) were used. Global motions and local accelerations of the head, pelvis, and multiple vertebrae were measured. Seat and seatbelt forces were also measured. Injuries were assessed via post-test dissection. The initial reclined posture aligned body regions (pelvis, lumbar spine, and ribcage) in a way that reduced the likelihood of effective restraint by the seat and seatbelt: the occupant's pelvis was initially rotated posteriorly, priming the occupant for submarining, and the lumbar spine was loaded in combined compression and bending due to the inertia of the upper torso during forward excursion. Coupled with the high restraining forces of the seat and seatbelt, the unfavorable kinematics resulted in injuries of the sacrum/coccyx (four of five PMHS injured), iliac wing (two of five PMHS injured), lumbar spine (three of five PMHS injured), and ribcage (all five PMHS suffered sternal fractures, and three of five PMHS suffered seven or more rib fractures). The kinematic and injury outcomes strongly motivate the development of injury criteria for the lumbar spine and pelvis, the inclusion of intrinsic variability (e.g., abdomen depth and pelvis shape) in computational simulations of frontal impacts with reclined occupants, and the adaptation of comprehensive restraint paradigms to predicted variability of occupant posture.

To optimize the components of restraint systems for protecting obese (BMI = 35 kg/m2) and normal BMI (BMI = 25) human body models (HBMs) in frontal crash simulations, and to compare the two optimized designs. The Life Years Lost metric, which incorporates the risk of injury and long-term disability to different body regions, was used as the optimization objective function. Parametric simulations, sampled from a 15-parameter design space using the Latin Hypercube technique, were performed and metamodels of the HBM responses were developed. A genetic algorithm was applied to the metamodels to identify the optimized designs. While most of the restraint parameters between the optimized design for obese and normal BMI HBMs were similar, the main difference was that the restraint for the obese HBM included an under-the-seat airbag, which mitigated its lower extremity excursion, improved its torso kinematics, and decreased its lower extremity and lumbar spine injury risks. The optimized designs for both HBMs included an inflatable seat belt, which reduced the risk of thoracic injury. The design recommendations from this study should be considered to improve safety of occupants with obesity.

Objective: Compare injuries for occupants in multiple event (ME) crashes where a less severe event preceded a more severe event to occupants in similar single event (SE) crashes. Methods: Occupants in ME crashes from NASS-CDS years 2000–2015 where the most severe event occurred subsequent to a less severe event were matched to occupants in SE crashes where the SE was similar to the most severe event in the ME crash. Occupants were matched based on occupant, vehicle, and crash characteristics and were compared across 21 detailed body regions using conditional logistic regression. Finite element (FE) simulations were performed with human surrogate models (detailed GHBMC and Hybrid III) and in both low- and high-speed conditions (n = 8 total simulations). At each speed, the crash simulations with both human body models reproduced a common multidirectional ME crash scenario, where the second impulse was more severe and similar to the SE impulse. Relative injury risk was assessed, and ME versus SE were computed and compared to those from the field data. Results: 1,663 ME occupants were matched to 3,217 SE occupants. ME occupants had higher MAIS2+ and MAIS3+ injury risk, and showed directionally higher injury risk in all but one body region. Eleven out of the 27 injury groups had higher injury risk in ME (false discovery rate (FDR)1.54). In FE simulations, ME displayed larger anterior and lateral displacement compared to SE. Head and thorax injury risk was increased in ME simulations by up to 5-fold. The detailed GHBMC and Hybrid III exhibited different kinematics and injury risk across all simulations, as did low- and high-speed conditions. Conclusions: The field data and FE simulations suggest that a first, less severe crash event results in occupants having greater injury risk when they are involved in a second, more severe crash event than if they were involved only in the second event. Several factors could cause this increase in injury risk, such as improper interaction with safety systems and airbags after the first event renders the occupant out-of-position.

Vehicle safety systems have substantially decreased motor vehicle crash-related injuries and fatalities, but injuries to the lumbar spine still have been reported. Experimental and computational analyses of upright and, particularly, reclined occupants in frontal crashes have shown that the lumbar spine can be subjected to axial compression followed by combined compression-flexion loading. Lumbar spine failure tolerance in combined compression-flexion has not been widely explored in the literature. Therefore, the goal of this study was to measure the failure tolerance of the lumbar spine in combined compression and flexion. Forty 3-vertebra lumbar spine segments were pre-loaded with axial compression and then subjected to dynamic flexion bending until failure. Clinically relevant middle vertebra fractures were observed in twenty-one of the specimens, including compression and burst fractures. The remaining nineteen specimens experienced failure at the potting grip interface. Since specimen characteristics and pre-test axial load varied widely within the sample, failure forces (mean 3.4 kN, range 1.6-5.1 kN) and moments (mean 73 Nm, range 0-181 Nm) also varied widely. Tobit univariate regressions were performed to determine the relationship between censored failure tolerance and specimen sex, segment type (upper/lower), age, and cross-sectional area. Age, sex, and cross-sectional area significantly affected failure force and moment individually (p, 24 pages, 10 tables/figures

The mechanical behavior of subcutaneous adipose tissue (SAT) affects the interaction between vehicle occupants and restraint systems in motor vehicle crashes (MVCs). To enhance future restraints, injury countermeasures, and other vehicle safety systems, computational simulations are often used to augment experiments because of their relative efficiency for parametric analysis. How well finite element human body models (FE-HBMs), which are often used in such simulations, predict human response has been limited by the absence of material models for human SAT that are applicable to the MVC environment. In this study, for the first time, dynamic multidirectional unconfined compression and simple shear loading tests were performed on human abdominal SAT specimens under conditions similar to MVCs. We also performed multiple ramp-hold tests to evaluate the quasilinear viscoelasticity (QLV) assumption and capture the stress relaxation behavior under both compression and shear. Our mechanical characterization was supplemented with scanning electron microscopy (SEM) performed in different orientations to investigate whether the macrostructural response can be related to the underlying microstructure. While the overall structure was shown to be visually different in different anatomical planes, a preferred orientation of any fibrous structures could not be identified. We showed that the nonlinear, viscoelastic, and direction-dependent responses under compression and shear tests could be captured by incorporating QLV in an Ogden-type hyperelastic model. Our comprehensive approach will lead to more accurate computational simulations and support the collective effort on the research of future occupant protection systems. Statement of significance There is an urgent need to characterize the mechanical behavior of human adipose tissue under multiple dynamic loading conditions, and to identify constitutive models that are able to capture the tissue response under these conditions. We performed the first series of experiments on human adipose tissue specimens to characterize the multi-directional compression and shear behavior at impact loading rates and obtained scanning electron microscope images to investigate whether the macrostructural response can be related to the underlying microstructure. The results showed that human adipose tissue is nonlinear, viscoelastic and direction dependent, and its mechanical response under compression and shear tests at different loading rates can be captured by incorporating quasi-linear viscoelasticity in an Ogden-type hyperelastic model.

Highly automated vehicles may permit alternative seating postures, which could alter occupant kinematics and challenge current restraint designs. One predicted posture is a reclined seated position. While the spine of upright occupants is subjected to flexion during frontal crashes, the orientation of reclined occupants tends to subject the spine to high compressive loads followed by high flexion loads. This study aims to investigate kinematics and mechanisms of loading in the thoracolumbar spine for a reclined seated posture through the use of postmortem human subjects (PMHS). Frontal impact sled tests (50 kph delta-v) were conducted on five adult midsize male PMHS seated with the torso reclined to 50 degrees with respect to the vertical. The PMHS were seated on a semi-rigid seat and restrained by a seat-integrated three-point belt with dual lap-belt pretensioners and a shoulder-belt pretensioner with a 3 kN load-limiter. 3-D kinematic trajectories of five chosen vertebrae, and the pelvis were measured relative to the vehicle buck. Intervertebral pressure transducers were installed at three locations in the lumbar column to detect load timing. Three PMHS suffered fractures at L1. Combined compression and flexion of the thoracolumbar spine occurred in all tests, but the magnitude of peak flexion varied across the PMHS. During the PMHS' forward excursion, the pelvis rotated anteriorly in two tests and posteriorly in two tests (lap-belt submarining occurred in one). In one test, the pelvis mount interacted with the seat, but did not affect kinematics. Anterior rotation of the pelvis caused increased extension of the lumbar spine, which exacerbated lumbar compression in two of the PMHS; the one subject whose pelvis kinematic tracking was lost exhibited similar compression kinematics. Posterior rotation of the pelvis enabled lumbar flexion, which decreased lumbar compression, but lead to lap-belt submarining in one case. Lumbar kinematics for these reclined frontal impacts were sensitive to changes in initial posture of the spine (magnitude of lordosis or kyphosis) and pelvis (pitch angle). To our knowledge, this study is the first to analyze thoracolumbar kinematics and resulting injuries of a reclined seating posture using PMHS.

Mechanical models of adipose tissue are important for various medical applications including cosmetics, injuries, implantable drug delivery systems, plastic surgeries, biomechanical applications such as computational human body models for surgery simulation, and blunt impact trauma prediction. This article presents a comprehensive review of in vivo experimental approaches that aimed to characterize the mechanical properties of adipose tissue, and the resulting constitutive models and model parameters identified. In particular, this study examines the material behavior of adipose tissue, including its nonlinear stress–strain relationship, viscoelasticity, strain hardening and softening, rate-sensitivity, anisotropy, preconditioning, failure behavior, and temperature dependency.

Objective: Up to one-half of drivers swerve before a crash, which may cause vehicle motions that displace an occupant from a normal seated position. How these altered postures affect occupant restr...

Background: With active safety and automated vehicle features becoming more available, unanticipated pre-crash vehicle maneuvers, such as evasive swerving, may become more common, and they may influence the resulting effectiveness of occupant restraints, and consequently may affect injury risks associated with crashes. Therefore, the objective of this study was to quantify the influence of age on key occupant kinematic, kinetic, and muscular responses during evasive swerving in on-road testing. Methods: Seat belt-restrained children (10&ndash, 12 years old), teens (13&ndash, 17 years old), and adults (21&ndash, 33 years old) experienced two evasive swerving maneuvers in a recent model sedan on a test track. Kinematics, muscle activity, and seat belt load distribution were determined and analyzed. Results: Compared to teens and adults, children showed greater head and trunk motion (p &lt, 0.03), but similar muscle activation in the into-the-belt direction of swerving. In the out&ndash, of-the-belt direction, children showed head and trunk motion more similar to teens and adults (p &lt, 0.02), but with greater muscle activation. Conclusions: Children showed different neuromuscular control of head and trunk motion compared to older occupants. This study highlights differences in the relationship between kinematics and muscle activation across age groups, and provides new validation data for active human body models across the age range.

This study aims to evaluate the assumption of geometric similitude inherent to equal-stress equal-velocity scaling by determining if scale factors created with different anthropometry metrics result in different scaled injury tolerance predictions. This assumption will be evaluated when equal-stress equal-velocity scaling is employed across dissimilar (e.g., 50th male to small female) and similar (e.g., small female to a reference small female anthropometry) anthropometries. Three average male and three small female lower extremity specimens that were tested in ankle inversion/eversion were selected for scaling analysis. Three additional female specimens were selected as a reference dataset, such that the accuracy of the scaled data could be compared to an independent measured dataset. The failure moments, total height and total weight for these donors were determined from literature. Additional anthropometry metrics (leg length, calcaneus height, and bimalleolar width) were taken from each of their respective CT scans. Scale factors were calculated from these previously determined anthropometric metrics for the six donors selected for scaling analysis by targeting the averaged anthropometry metrics of the reference small female dataset. Equal-stress equal-velocity scaling was applied to the failure moments from literature using different scale factors. The mean predicted failure tolerance and standard deviation for scaled data using different scale factors were compared to one another and to the mean failure tolerance from the reference (unscaled) small female dataset. When using average male data to predict ankle failure moment for a small female anthropometry, scaled moments were statistically significantly different from measured small female failure moment. Furthermore, scaled failure moments predicted using scale factors based on different anthropometry metrics were found to be significantly different from one another. Conversely, predicted mean failure moment using scaled female data of a similar size to the reference data was not significantly different from measured female failure moment, and the predicted failure moments were not significantly affected by choice of scale factor. This study shows that an injury metric predicted with equal-stress equal-velocity scaling is sensitive to choice of scale factor when employing scaling across occupants of dissimilar size and sex. This conclusion suggests error can be introduced into scaled response due to choice of anthropometry metric used to create a scale factor, and therefore, anthropometry metrics used to create scale factors should be justified mechanistically and shown to apply across size and sex before being employed.

Objective: Precrash occupant motion may affect head and trunk position and restraint performance in a subsequent crash, particularly for young children. Others have studied seat belt–restra...

Objective: To meet increasing customer demand, many vehicle manufacturers are now offering a panoramic sunroof option in their vehicle lineup. Currently, there is no regulatory or consumer test aimed at assessing the potential for ejection mitigation of roof glazing, which leaves manufacturers to develop internal performance standards to guide designs. The goal of this study was to characterize the variety of occupant-to-roof impacts involving unbelted occupants in rollover crashes to determine the ranges of possible effective masses and impact velocities. This information can be used to define occupant retention requirements and performance criteria for roof glazing in occupant ejection protection. Methods: This study combined computational (MADYMO and LS-Dyna) simulations of occupant kinematics in rollover crashes with laboratory rollover crash tests using the dynamic rollover test system (DRoTS) and linked them through controlled anthropomorphic test device (ATD)-to-roof (“drop”) impact tests. The DRoTS and the ATD drop tests were performed to explore impact scenarios and estimate dummy-to-roof impact impulses. Next, 13 sets of vehicle kinematics and deformation data were extracted from a combination of vehicle dynamics and finite element model simulations that reconstructed variations of rollover crash cases from the field data. Then occupant kinematics data were extracted from a full-factorial sensitivity study that used MADYMO simulations to investigate how changes in anthropometry and seating position would affect occupant–roof impacts across all 13 cases. Finite element (FE) simulations of ATD and Global Human Body Models Consortium (GHBMC) human body model (HBM) roof impacts were performed to investigate the most severe cases from the MADYMO simulations to generate a distribution of head-to-roof impact energies. Results: From the multiparameter design of experiment and experimental study, kinematics and energy output were extracted and analyzed. Based on dummy-to-roof impact force and dummy-to-roof impact velocity, the most severe rollover scenarios were identified. In the DRoTS experiments followed by the drop tests, the range of identified impact velocities was between 2 and 5.8 m/s. However, computational simulations of the rollover crashes showed higher impact velocities and similar effective masses. The largest dummy-to-roof impact velocity was 11 m/s. Conclusions: This study combined computational and experimental analyses to determine a range of possible unbelted occupant-to-roof impact energies. These results can be used to determine design parameters for an impactor for the assessment of the risk of roof glazing ejection for unbelted occupants in rollover crashes.

Objective: Self-driving technology will bring novelty in occupant seating choices and vehicle interior design. Thus, vehicle safety systems may be challenged to protect occupants over a wider range of potential postures and seating choices. This study aims to investigate the effects of occupant size, seat recline, and knee bolster position on submarining risk and injury prediction metrics for reclined occupants in frontal crashes. Methods: Frontal crash finite element (FE) simulations were performed with the 3 simplified Global Human Body Model Consortium (GHBMC) occupant models: small female, midsize male, and large male. Additionally, a detailed GHBMC midsize male model was used to compare with selected simplified cases. For each simulation, parameters including seatback recline angle (0.9°, 10.9°, 20.9°, 30.9°) and knee bolster position relative to the occupant (baseline, close, far, and no knee bolster) were varied. Impacts were simulated with the U.S. New Car Assessment Program 56 km/h frontal crash pulse. Occupant kinematics data were extracted from each simulation in a full-factorial sensitivity study to investigate how changes in anthropometry, seating position, and knee bolster position would affect submarining across all simulated cases. Results: Overall, increasing the occupant-to–knee bolster distance resulted in more submarining cases. The threshold for submarining was also affected by the seat recline angle. The lowest threshold observed occurred with 10.9° of recline with the small female model. Submarining was observed at recline angles at and above 20.9° for the midsize male model and 30° for the large male model. The initial lap belt position, pelvis orientation, and their relationship were good predictors of submarining. Increased lumbar flexion moment was observed with increased seat recline angle as well as occupant-to–knee bolster distance. The detailed GHBMC model was more prone to submarining than the simplified model. Conclusions: Submarining may be a major challenge to overcome for reclined occupants, which may become more prevalent with autonomous driving systems. This study shows that the angle of recline, anthropometric variation, and position of the knee bolster affect the risk of submarining. To our knowledge, this is the first study to computationally evaluate the occupant protection implications of seatback recline for multiple body sizes, postures, and positions relative to the vehicle interior.

A mechanics education testbed comprised of instructional modules written in Mathematica was developed in order to increase the effectiveness of course delivery through an integrated computation, visualization, and animation approach with the aim of accelerating the learning process. Overall, 25 modules were developed for Statics and another 20 modules for Mechanics of Materials during the AY2017-18. The testbed complements class instruction and motivates self-learning by illustrating basic mechanics concepts relative to homework problems and textbook examples. Its features include visualization, parametrization, and trial-and-error simulation capabilities that enable students to view simulated phenomena from different perspectives, thereby leaving a lasting impression which facilitates quicker absorption of the mechanics concepts than the traditional approach. The parametrization feature enables variation of boundary and initial conditions, as well as other parameters that affect the simulated phenomenon to demonstrate each parameter’s influence on the system response. These capabilities enable students to employ the trial-and-error approach in acquiring an intuitive understanding of the visualized phenomenon, validated through direct calculation. Student comments are summarized and survey results are analyzed and related to individual student performance. Student assessment confirms the testbed’s effectiveness and provides helpful suggestions for further enhancement/development. Representative modules are presented to demonstrate their functions and capabilities.

The goal of this study was to assess the behaviour of an obese Human Body Model (HBM) in frontal sled tests. The results of rear-seat sled tests with an obese (BMI = 35) Post Mortem Human Surrogate (PMHS) were used to evaluate the performance of the obese HBM in matching conditions. Also, the responses of a non-obese HBM (BMI = 25) and the obese HBM were compared in a front-seat frontal impact test. In the rear-seat tests, both the obese HBM and the obese PMHS experienced a large forward excursion, delayed lap belt engagement with the pelvis, and a reclined-to-upright torso angle throughout the tests, which were the effects of large body mass and thick flesh. In the front-seat simulations, the obese HBM experienced a larger excursion than the non-obese HBM. The obese HBM can be a useful tool to design and optimise restraint system for front-seat occupants with obesity.

Understanding the mechanical properties of human adipose tissue, and its influence on seat belt-pelvis interaction is beneficial for computational human body models that are developed for injury prediction in the vehicle crashworthiness simulations. While various studies have characterized adipose tissue, most of the studies used porcine adipose tissue as a surrogate, and none of the studies were performed at loading rates relevant for motor vehicle collisions. In this work, the mechanical response of human and porcine adipose tissue was studied. Two dynamic loading modes (compression and simple shear) were tested in adipose tissue extracted from the human abdomen and porcine back. An Ogden hyperelastic model was used to fit the loading response, and specific material parameters were obtained for each specimen. Two-sample t-tests were performed to compare the effective shear moduli and peak stresses from porcine and human samples. The material response of the human adipose tissue was consistent with previous studies. Porcine adipose tissue was found to be significantly stiffer than human adipose tissue under compression and shear loading. Also, when material model parameters were fit to only one loading mode, the predicted response in the other mode showed a poor fit.

Objective: The objective of the current study was to evaluate the whole-body kinematic response of the Total Human Model for Safety (THUMS) occupant model in controlled laboratory rollover tests by comparing the model response to postmortem human surrogate (PMHS) kinematic response targets published in 2014. Methods: A computational model of the parametric vehicle buck environment was developed and the AM50 THUMS occupant model (Ver 4.01) was subjected to a pure dynamic roll at 360°/s in trailing-side front-row seating position. A baseline configuration was defined by a baseline posture representing the average of all PMHS postures, with a friction coefficient of 0.4 for the belt and 0.6 for the seat. To encompass challenges in controlling boundary conditions from the PMHS tests and ensure the robustness of the model evaluation, a total of 12 simulations were performed to investigate the following: 1. The effect of initial posture by adding 3 additional postures representing PMHS extremes.2. The effect of belt tension by varying tension from the nominal vehicle retractor belt tension of 5 N to the 35 N belt tension used in the PMHS tests.3. The effect of friction between the environment (belt, seat) and THUMS. The effect of initial posture by adding 3 additional postures representing PMHS extremes. The effect of belt tension by varying tension from the nominal vehicle retractor belt tension of 5 N to the 35 N belt tension used in the PMHS tests. The effect of friction between the environment (belt, seat) and THUMS. Trajectories (head, T1, T4, T10, L1, and sacrum), spinal segment rotations (head-to-T1, T1-to-T4, T4-to-T10, T10-to-L1, and L1-to-sacrum) relative to the rollover buck and spinal segment elongation/compression calculated from the simulations were compared to PMHS corridors using a correlation method (CORA). Results: THUMS baseline response showed lower correlation (overall CORA score = 0.63) with the PMHS response in rollover compared to other crash modes. THUMS and PMHS demonstrated similar kinematic responses in the longitudinal axis and vertical axis but significantly different lateral excursion relative to the seat. In addition, no spinal elongation was observed for THUMS compared to the PMHS. The posture, pretension, and belt frictions were found to alter model kinematics, especially on THUMS lateral axis motion. The posture was judged to be the most sensitive parameter evaluated because a change of 30 mm in the lateral axis results in up to an 80 mm of change in observed displacement. Conclusions: Though the model response in the lateral axis is significantly different than that of the PMHS, it is unclear whether this difference is the result of extrinsic factors (posture, pretension, and friction), where exact values in experiment are unknown or by model intrinsic factors (e.g., spine stiffness). These differences in occupant kinematics could potentially subject the PMHS and THUMS to very different loading conditions under roof impact in rollover crashes: different occupant posture and different roof impact location. Therefore, different injury mechanisms and severity might be predicted by the current model relative to the PMHS. Consequently, though the information provided in the current study could be useful for improving model biofidelity for rollover crashes, additional studies are required to properly solve this issue.

Objective: Recreational off-highway vehicle (ROHV) crashes are of concern because sales of these vehicles have been growing rapidly and because newer vehicles tend to have significantly greater performance than older models. We evaluated the available data to understand trends in ROHV crashes and the factors that contributed to serious injury. Methods: We combined information from (1) the Fatality Analysis Reporting System (FARS), (2) a database compiled by the Consumer Product Safety Commission, and (3) a vehicle sales database. These aggregated data were used to describe trends, demographics, and frequent causes of serious injuries and fatalities. Results: On-road fatal crashes grew from 0 in the year 2000 to 37 in 2015; at the same time, sales grew from approximately 100,000 to 400,000 vehicles annually. Much of the increase in ROHV sales was in 2 new, higher performance classes of vehicles. Further, seat belt and helmet use in this cohort was rare (at least 46% unbelted, only 2% confirmed to be helmeted) and drinking and driving was common (57% of crashes in FARS). These vehicles appear to have increased potential for rollover, which often led unbelted occupants to be ejected, putting them at risk of being injured as the vehicle rolled on top of them. Conclusions: Serious ROHV crashes have grown with sales. Resulting injuries appear to be strongly influenced by inconsistent seat belt use, frequent drunk driving, and increased propensity for the vehicles to roll over.

The goal of this study was to evaluate how well an in-laboratory rollover crash test methodology that constrains vehicle motion can reproduce the dynamics of unconstrained full-scale steering-induced rollover crash tests in sand.Data from previously-published unconstrained steering-induced rollover crash tests using a full-size pickup and mid-sized sedan were analyzed to determine vehicle-to-ground impact conditions and kinematic response of the vehicles throughout the tests. Then, a pair of replicate vehicles were prepared to match the inertial properties of the steering-induced test vehicles and configured to record dynamic roof structure deformations and kinematic response.Both vehicles experienced greater increases in roll-axis angular velocities in the unconstrained tests than in the constrained tests; however, the increases that occurred during the trailing side roof interaction were nearly identical between tests for both vehicles. Both vehicles experienced linear accelerations in the constrained tests that were similar to those in the unconstrained tests, but the pickup, in particular, had accelerations that were matched in magnitude, timing, and duration very closely between the two test types. Deformations in the truck test were higher in the constrained than the unconstrained, and deformations in the sedan were greater in the unconstrained than the constrained as a result of constraints of the test fixture, and differences in impact velocity for the trailing side.The results of the current study suggest that in-laboratory rollover tests can be used to simulate the injury-causing portions of unconstrained rollover crashes. To date, such a demonstration has not yet been published in the open literature. This study did, however, show that road surface can affect vehicle response in a way that may not be able to be mimicked in the laboratory. Lastly, this study showed that configuring the in-laboratory tests to match the leading-side touchdown conditions could result in differences in the trailing side impact conditions.

While rollover crashes are rare, approximately one third of vehicle occupant fatalities occur in rollover crashes. Most severe-to-fatal injuries resulting from rollover crashes occur in the head or neck region, due to head and neck interaction with the roof during the crash. While many studies have used anthropomorphic test devices (ATDs) to predict head and neck injury, the biofidelity of ATDs in rollover has not been established. This study aims to build on previous research to compare the dynamic response and injuries sustained by four post mortem human surrogates (PMHS) to those predicted by six different ATDs in full-scale rollover crash tests. Additionally, this study evaluates injuries sustained by PMHS relative to possible contributing factors including occupant kinematics, occupant anthropometry, and vehicle roof deformation. While the vehicle kinematics and roof deformation were comparable for all tests, three out of the four PMHS sustained cervical spine injury, but only the tallest specimen sustained cervical spine fracture. Neck flexion at the time of head-to-roof contact appears to have affected cervical spine injury risk in these cases. Despite the injuries sustained in the PMHS, none of the six ATDs measured forces or accelerations that exceeded injury assessment reference values (IARVs), which adds to recent literature illustrating substantial differences between ATDs and PMHS in a rollover-like scenario.

OBJECTIVE: To provide an objective basis on which to evaluate the repeatability of vehicle crash test methods, a recently developed signal analysis method was used to evaluate correlation of sensor time history data between replicate vehicle crash tests. The goal of this study was to evaluate the repeatability of rollover crash tests performed with the Dynamic Rollover Test System (DRoTS) relative to other vehicle crash test methods. METHODS: Test data from DRoTS tests, Deceleration Rollover Sled (DRS) tests, frontal crash tests, frontal offset crash tests, small overlap crash tests, Small Overlap Impact (SOI) crash tests, and oblique crash tests were obtained from the literature and publicly available databases (the National Highway Traffic Safety Administration vehicle database and the Insurance Institute for Highway Safety TechData) to examine crash test repeatability. RESULTS: Signal analysis of the DRoTS tests showed that force and deformation time histories had good to excellent repeatability, while vehicle kinematics showed only fair repeatability due to the vehicle mounting method for one pair of tests and slightly dissimilar mass properties (2.2%) in a second pair of tests. Relative to the DRS, the DRoTS tests showed very similar or higher levels of repeatability in nearly all vehicle kinematic data signals with the exception of global X' (road direction of travel) velocity and displacement due to the functionality of the DRoTS fixture. Based on the average overall scoring metric of the dominant acceleration, DRoTS was found to be as repeatable as all other crash tests analyzed. Vertical force measures showed good repeatability and were on par with frontal crash barrier forces. Dynamic deformation measures showed good to excellent repeatability as opposed to poor repeatability seen in SOI and oblique deformation measures. CONCLUSIONS: Using the signal analysis method as outlined in this paper, the DRoTS was shown to have the same or better repeatability of crash test methods used in government regulatory and consumer evaluation test protocols. Language: en

This study aimed to develop and validate a finite element (FE) model of a human clavicle which can predict the structural response and bone fractures under both axial compression and anterior-posterior three-point bending loads. Quasi-static non-injurious axial compression and three-point bending tests were first conducted on a male clavicle followed by a dynamic three-point bending test to fracture. Then, two types of FE models of the clavicle were developed using bone material properties which were set to vary with the computed tomography image density of the bone. A volumetric solid FE model comprised solely of hexahedral elements was first developed. A solid-shell FE model was then created which modelled the trabecular bone as hexahedral elements and the cortical bone as quadrilateral shell elements. Finally, simulations were carried out using these models to evaluate the influence of variations in cortical thickness, mesh density, bone material properties and modelling approach on the biomechanical responses of the clavicle, compared with experimental data. The FE results indicate that the inclusion of density-based bone material properties can provide a more accurate reproduction of the force-displacement response and bone fracture timing than a model with uniform bone material properties. Inclusion of a variable cortical thickness distribution also slightly improves the ability of the model to predict the experimental response. The methods developed in this study will be useful for creating subject-specific FE models to better understand the biomechanics and injury mechanism of the clavicle.

a b s t r a c t Fractal dimension (FD) can be used to characterize microstructure of porous media, particularly bone tissue. The porous microstructure of cortical bone is observable in micro-CT (CT) images. Estimations of fractal dimensions of CT images of coupons of human cortical bone are obtained. The same sam- ples were tested on a tensile test machine and Young's modulus (YM) and Failure stress were obtained. When both types of measures were compared, a clear correlation was found (R = −81%, P < 0.01). Young's modulus of each sample and the FD of its CT images are correlated. From the assumption that cortical bone is approximately a fractal set, a non-linear constitutive relation involving FD is obtained for YM. Experimental results show good agreement with this constitutive relation. Additional parameters in the non-linear relation between YM and FD have been estimated from experimental results and related to physical parameters.

The goal of this study was to characterize the rollover crash and to evaluate the repeatability of the Dynamic Rollover Test System (DRoTS) in terms of initial roof-to-ground contact conditions, vehicle kinematics, road reaction forces, and vehicle deformation.Four rollover crash tests were performed on 2 pairs of replicate vehicles (2 sedan tests and 2 compact multipurpose van [MPV] tests), instrumented with a custom inertial measurement unit to measure vehicle and global kinematics and string potentiometers to measure pillar deformation time histories. The road was instrumented with load cells to measure reaction loads and an optical encoder to measure road velocity. Laser scans of pre- and posttest vehicles were taken to provide detailed deformation maps.Initial conditions were found to be repeatable, with the largest difference seen in drop height of 20 mm; roll rate, roll angle, pitch angle, road velocity, drop velocity, mass, and moment of inertia were all 7% different or less. Vehicle kinematics (roll rate, road speed, roll and pitch angle, global Z' acceleration, and global Z' velocity) were similar throughout the impact; however, differences were seen in the sedan tests because of a vehicle fixation problem and differences were seen in the MPV tests due to an increase in reaction forces during leading side impact likely caused by disparities in roll angle (3° difference) and mass properties (2.2% in moment of inertia [MOI], 53.5 mm difference in center of gravity [CG] location).Despite those issues, kinetic and deformation measures showed a high degree of repeatability, which is necessary for assessing injury risk in rollover because roof strength positively correlates with injury risk (Brumbelow 2009). Improvements of the test equipment and matching mass properties will ensure highly repeatable initial conditions, vehicle kinematics, kinetics, and deformations.

Road traffic injuries could become the fifth leading cause of death globally by 2030 unless appropriate countermeasures are taken. Reliable reconstruction of collisions is essential for understanding and hence reducing the injuries sustained by pedestrians. The significant influence of vehicle speed, pedestrian speed and pedestrian gait on pedestrian transverse motion and rotation about the longitudinal axis has been qualitatively noted in the literature, but there has been no quantitative approach to this problem. The MADYMO multibody pedestrian model is widely used for collision reconstruction, but its validation to date mostly remains limited to body segment trajectories in the vertical plane along the direction of vehicle travel. In this article, the MADYMO pedestrian model is compared to staged tests and a real collision in terms of head trajectory, longitudinal and transverse head translations relative to the primary contact location of the pedestrian on the vehicle, impact location on the head (and hence longitudinal rotation of the body), head impact time and head impact velocity. It is shown that the model can reproduce staged cadaver and dummy tests in terms of head trajectory (mostly within 10%), longitudinal head translation (within 17%), transverse translation (two cases: errors of 0% and 19%), impact location on the head (within 45° in the majority of cases), head impact time (mean difference of 8.7 ms) and head impact velocity (mean difference of 1.8 m/s). A sensitivity analysis showed that the model is largely unaffected by changes in vehicle stiffness and vehicle–pedestrian friction, while variations in the pedestrian stance and the height of the vehicle front have a considerable effect on the kinematics of a collision. This is the first time that the MADYMO pedestrian model has been evaluated with regard to transverse motion and longitudinal rotation of the pedestrian. The results presented here mean that the MADYMO model is appropriate for further analysis of the influence of gait on pedestrian post-impact kinematics.

To serve as tools for assessing injury risk, the biofidelity of whole-body pedestrian impact dummies should be validated against reference data from full-scale pedestrian impact tests. To facilitate such evaluations, a simplified generic vehicle-buck has been recently developed that is designed to have characteristics representative of a generic small sedan. Three 40 km/h pedestrian-impact tests have been performed, wherein Post Mortem Human Surrogates (PMHS) were struck laterally in a mid-gait stance by the buck. Corridors for select trajectory measures derived from these tests have been published previously. The goal of this study is to act as a companion dataset to that study, describing the head velocities, body region accelerations (head, spine, pelvis, lower extremities), angular velocities, and buck interaction forces, and injuries observed during those tests. Scaled, transformed head accelerations exceeded 80 g prior to head contact with the windshield for two of the three tests. Head xaxis angular velocity exceeded 40 rad/s prior to head contact for all three tests. In all cases the peak resultant head velocity relative to the vehicle was greater than the initial impact speed of the vehicle. Corridors of resultant head velocity relative to the vehicle were also developed, bounded by the velocities observed in these tests combined with those predicted to occur if the PMHS necks were perfectly rigid. These results, along with the other kinematic and kinetic data presented, provide a resource for future pedestrian dummy development and evaluation.

In 2008, fatalities resulting from vehicle rollover events accounted for over one third of all fatalities resulting from motor vehicle crashes. This study describes the initial phase of a detailed computational study aimed at developing causal relationships between crash, occupant, and vehicle parameters and injury outcome using state-of-the-art computational methods. This initial phase examines the sensitivity of vehicle kinematics and structural deformation by isolating the roof-to-ground interaction phase of the rollover event using an LS-DYNA finite element full-vehicle model. Structural deformation is quantified by a measure of the maximum roof intrusion into the occupant space (average = 44 cm, range = 9–66 cm). Roll angle, pitch angle and drop height have a significant effect on structural deformation, while roll rate and yaw angle do not show significant effects. Drop height alone accounts for 70% of the variability in peak roof crush and vertical acceleration, metrics that are related to causal m...

The goal of this study was to evaluate the repeatability afforded by a rollover test system in terms of the test conditions, vehicle and occupant response, and vehicle deformations. Eight full-scale rollover tests were performed using three 2002 Ford Explorer vehicles, instrumented with anthropomorphic test devices and arrays of accelerometers and angular velocity sensors, to examine both intra- and inter-vehicle repeatability in five non-destructive low-speed (LS) and three full-thrown high-speed (HS) rollover crash tests using the deceleration rollover sled method. The cart was accelerated to the target velocity (LS: 19.3 km/h, n = 5; HS: 48.3 km/h, n = 3) and then decelerated (soil trip simulation) to initiate vehicle roll. All five LS and the first two HS tests showed a high degree of repeatability (peak lateral acceleration: 5.3 ± 0.2 g LS and 5.5–6.5 g HS; peak roll rate: 134 ± 12 deg/s LS and 237.3–237.4 deg/s HS; peak curb force: 92.4 ± 2.0 kN LS and 92.6–92.9 kN HS; peak dummy head resultant acce...

Resumen La biomecanica del impacto o de las lesiones necesita de un equipo multidisciplinario en sus investigaciones, ya que se ven involucrados profesionales de diversas areas, como fisica, ingenieria, medicina, biologia o matematicas, entre otras. Esta disciplina se centra principalmente en el estudio de las lesiones de los accidentes de trafico y en situaciones militares, por lo que se aplica tanto en lesiones intencionales como no intencionales. Las lesiones traumaticas intencionales o accidentales suponen una parte considerable de la carga de trabajo en los Institutos de Medicina Legal (IML). Dado que la biomecanica se ocupa del estudio de este tipo de lesiones, es evidente que los profesionales de la medicina forense deben tener conocimientos profundos de esta disciplina. A nuestro entender, las principales utilidades en el ambito de la medicina forense son el conocimiento de mecanismos lesivos y su aplicabilidad en los criterios de causalidad.

Compression of the leg induces bending in the tibia, which can lead to tensile failure of the bone in the midshaft. The purpose of this study was to determine the orientation of the compressive load vector in the human tibia. Five cadaveric lower extremities were instrumented with in situ 6-axis tibial and fibular load cells and subjected to quasistatic axial leg compression tests in two knee positions and nine ankle positions. For each test, the location and angle of the line of action were calculated at the tibial midshaft. The line of action was extended to the bone ends in order to determine the locations of the effective centers of pressure on the tibial plafond and tibial plateau. The effective center of pressure on the tibial plafond consistently migrated anteriorly in dorsiflexion, laterally in eversion, posteriorly in plantarflexion, and medially in inversion. An opposite pattern was observed on the tibial plateau. When the knee was flexed, the effective center of pressure was generally isolated to a small area in the posterior portion of the medial tibial condyle. The percentage of the axial load borne by the fibula varied from -8% to 19%, and was related to the inversion/eversion angle of the ankle (p

Rollover crashes are a serious public health problem in United States, with one third of traffic fatalities occurring in crashes where rollover occurred. While it has been shown that occupant kinematics affect the injury risk in rollover crashes, no anthropomorphic test device (ATD) has yet demonstrated kinematic biofidelity in rollover crashes. Therefore, the primary goal of this study was to assess the kinematic response biofidelity of six ATDs (Hybrid III, Hybrid III Pedestrian, Hybrid III with Pedestrian Pelvis, WorldSID, Polar II and THOR) by comparing them to post mortem human surrogate (PMHS) kinematic response targets published concurrently; and the secondary goal was to evaluate and compare the kinematic response differences among these ATDs. Trajectories (head, T1, T4, T10, L1 and sacrum), spinal segment (head-to-T1, T1-to-T4, T4-T10, T10-L1, and L1-to-sacrum) rotations relative to the rollover buck, and spinal segment extension/compression were calculated from the collected kinematics data from an optical motion tracking system. Response differences among the ATDs were observed mainly due to the different lateral bending stiffness of the spine from their varied architecture, while the additional thoracic joint in Polar II and THOR did not seem to provide more flexion/extension compliance than the other ATDs. In addition, the ATD response data were compared to PMHS response corridors developed from similar tests for assessing ATD biofidelity. All of the ATDs, generally, drifted outboard and upward during the tests similar to the PMHS. However, accompanied with this upward and outward motion, the ATD head and upper torso pitched forward (~10 degrees) while the PMHS' head and upper torso pitching rearward (~10 to ~15 degrees), due to the absence of flexion/extension compliance in the ATD spine. The differences in these pitch motions resulted in a difference of 130 mm to 160 mm in the longitudinal position of the head at 195 degrees of roll angle. Finally, substantially less lateral spinal bending was also observed in the ATDs compared to the PMHS. The results of the current study suggests there is greater upper spine flexion/extension, and lateral bending stiffness in all of the ATDs in comparison to the PMHS, and provided information for improvement of ATD biofidelity in future for rollover crashes.

Planar impacts with objects and other vehicles may increase the risk and severity of injury in rollover crashes. The current study compares the frequency of injury measures (MAIS 2+, 3+, and 4+; fatal; AIS 2+ head and cervical spine; and AIS 3+ head and thorax) as well as vehicle type distribution (passenger car, SUV, van, and light truck), crash kinematics, and occupant demographics between single vehicle single event rollovers (SV Pure) and multiple event rollovers to determine which types of multiple event rollovers can be pooled with SV Pure to study rollover induced occupant injury. Four different types of multiple event rollovers were defined: single and multi-vehicle crashes for which the rollover is the most severe event (SV Prim and MV Prim) and single and multi-vehicle crashes for which the rollover is not the most severe event (SV Non-Prim and MV Non-Prim). Information from real world crashes was obtained from the National Automotive Sampling System – Crashworthiness Data System (NASS-CDS) for the period from 1995 through 2011. Belted, contained or partially ejected, adult occupants in vehicles that completed 1–16 lateral quarter turns were assigned to one of the five rollover categories. The results showed that the frequency of injury in non-primary rollovers (SV Non-Prim and MV Non-Prim) involving no more than one roof inversion is substantially greater than in SV Pure, but that this disparity diminishes for crashes involving multiple inversions. It can further be concluded that for a given number of roof inversions, the distribution of injuries and crash characteristics in SV Pure and SV Prim crashes are sufficiently similar for these categories to be considered collectively for purposes of understanding etiologies and developing strategies for prevention.

Background Previous epidemiological studies have highlighted the high risk of injury to the head, thorax, and cervical spine in rollover crashes. However, such results provide limited information on whole-body injury distribution and multiple region injury patterns necessary for the improvement and prioritization of rollover-focused injury countermeasures. Methods Sampled cases representing approximately 133,000 U.S. adult occupants involved in rollover crashes (between 1995 and 2013) sustaining moderate-to-severe injuries were selected from the National Automotive Sampling System Crashworthiness Data System database. A retrospective cohort study, based on a survey of population-based data, was used to identify relevant whole body injury patterns. Results Among belted occupants injured in rollover crashes, 79.2% sustained injuries to only one body region. The three most frequently injured (AIS2+) body regions were head (42.1%), upper extremity (28.0%), and thorax (27.1%). The most frequent multi-region injury pattern involved the head and upper extremity, but this pattern only accounted for 2.3% of all of occupants with moderate or worse injuries. Conclusions The results indicated that for rollover-dominated crashes, the frequently observed injury patterns involved isolated body regions. In contrast, multi-region injury patterns are more frequently observed in rollovers with significant planar impacts. Identification of region-specific injury patterns in pure rollover crashes is essential for clarifying injury mitigation targets and developing whole-body injury metrics specifically applicable to rollovers.

Postmortem human surrogates were positioned in a mid-gait pedestrian stance and struck laterally by a vehicle buck traveling at a speed of 40 km/h. Three tests were performed with a midsize passenger car buck, and two tests were performed with a sport utility vehicle buck. Each subject was equipped with two chest bands positioned at the level of the 4th and 8th ribs to measure changes in cross-sectional shape of the upper and lower chest. Absolute and normalized deflection, deflection velocity, and the viscous criterion were calculated for frontal and lateral dimensions. Deformation-time histories were generated for the midsagittal and midcoronal chords passing through the chest centroid as well as for off-centroidal chords. Despite being positioned initially perpendicular to the impacting vehicle, the subjects exhibited maximal loading of the anterolateral thorax. Therefore, a polar coordinate system was centered at the initial chest centroid position and radial changes of chest deformation were recorded. Though similar in application to the standard frontal and lateral impact analyses, this radial technique appears better suited to the pedestrian environment in that it identifies a single position of maximum deformation rather than tracking only preselected locations. Maximum deformation levels and rates of deformation indicated that peak values were in the range of those resulting from traditional frontal and lateral sled tests as well as frontal and side dummy certification tests. Provided that consideration is given to the oblique nature of the loading, the results indicate that conventional injury criteria and biofidelity requirements used for occupant dummies could be reasonably applied to the pedestrian environment.

The nonlinear viscoelastic structural response of the major human knee ligaments when subjected to complex loading histories is investigated, with emphasis on the collateral ligaments. Bone-ligament-bone specimens are tested in knee distraction loading, where the ligaments are in the anatomical position corresponding to a fully extended knee. Temporal nonlinearities for time scales in the range of $$1 \le t \le 500\,$$ s are characterized with a dedicated series of loading histories. In particular, the response to several complex sequences of step-and-hold tests and loading-unloading cycles is investigated. The separability of the time and deformation dependent behavior, as assumed for the often used quasi linear viscoelastic (QLV) theory, is found to be insufficient for describing the response in the time range considered. Non-recoverable inelastic flow is observed in this time range. A phenomenological 1-dimensional nonlinear viscoelastic model that qualitatively describes the experimentally observed inelastic phenomena is presented.