Human Body Finite Element Model Research Articles

Far-side occupant responses based on current US side-impact protocol using finite element human body models

Most of the applied vehicle side-impact occupant protection research to date has concentrated on near-side occupants. Currently, no regulation exists in North America for the far-side occupant protection. Real-world crash data has shown that occupants seated on the non-struck side, defined as 'far-side' occupants, are still subjected to a risk of injuries. The objective of this study is to investigate body responses for the far-side occupant using current US side impact protocols. Current side impact protocol in the USA is designed to meet side Moving Deformable Barrier (MDB) and fixed oblique pole impact. Two seating cases are addressed; the first case consisted of a far-side occupant in the first row (single occupant) to evaluate the interaction of the occupant to the structure. The second case, a near-side occupant, was added to the far-side occupant (two occupants in a row) to study the interaction of the occupant-to-occupant. A finite element human body model (50th male) was used as a far-side and near-side occupant. Simulation results indicated that the LINCAP barrier could potentially produce the significant head rotational acceleration and thoracic rib deflection if the far-side occupant was included in the existing near-side crash protocols.

Far-side occupant responses based on current US side-impact protocol using finite element human body models

Most of the applied vehicle side-impact occupant protection research to date has concentrated on near-side occupants. Currently, no regulation exists in North America for the far-side occupant protection. Real-world crash data has shown that occupants seated on the non-struck side, defined as 'far-side' occupants, are still subjected to a risk of injuries. The objective of this study is to investigate body responses for the far-side occupant using current US side impact protocols. Current side impact protocol in the USA is designed to meet side Moving Deformable Barrier (MDB) and fixed oblique pole impact. Two seating cases are addressed; the first case consisted of a far-side occupant in the first row (single occupant) to evaluate the interaction of the occupant to the structure. The second case, a near-side occupant, was added to the far-side occupant (two occupants in a row) to study the interaction of the occupant-to-occupant. A finite element human body model (50th male) was used as a far-side and near-side occupant. Simulation results indicated that the LINCAP barrier could potentially produce the significant head rotational acceleration and thoracic rib deflection if the far-side occupant was included in the existing near-side crash protocols.

Helmet to head coupling by multi-body system

The number of fatalities proves that traffic accidents and their consequences are still a serious problem to be solved. Almost half of the people dying on the world’s roads are pedestrians, cyclists, and two-wheeler riders, which are together called vulnerable road users. Future challenges such as multi-modal transport including autonomous cars and other modes of transport bring additional safety issues to be investigated. New impact scenarios, covering multi-directional impacts, can be hardly assessed using hardware dummies. Hence, the numerical simulation using human body models is the technology to be addressed for future safety assessment. Especially for vulnerable road users, the complex dynamical loading must be taken into account. Long impact scenarios with complex loading usually cost a lot of calculation time. The presented work contributes to the numerical assessment of two-wheeler riders’ safety with a further view of the optimization of personal protective equipment. For running plenty of impact scenarios for optimization of the personal protective equipment, the short calculation time is necessary. The paper presents a multibody model of a helmeted two-wheeler rider, which results in a short calculation time for assessing complex impact scenarios. The previously developed and validated human body model is addressed and it is coupled to a helmet model using the multibody system approach. The helmeted human body model is validated in oblique impact scenarios by comparing the results to an existing finite element human body model.

Development of an internal physiological muscle controller within an open‐source Hill‐type material model in LS‐DYNA

AbstractNowadays automotive industry is paying more attention to vehicle safety systems with the aim to reduce the number of injuries and fatalities among road users. Simulations are used throughout the whole research and development process for such systems involving Finite Element Human Body Models (FE HBMs) and the multiphysics simulation software package LS‐DYNA. Because the safety of living (active) humans in traffic situations has to be assured, special material models are applied to generate reflexive or voluntary muscle reactions of the FE HBMs. These elements are governed by an application‐dependent controller, which produce individual activation signals for each of them. The current contribution presents the development of a physiologically inspired controller for muscle elements, enabling the simulation of voluntary or reflexive movements with the FE HBM. As a result, it is possible to control muscle elements internally without any additional superior controller level or complementary coding with LS‐DYNA keywords. A validation example with the calculation of appropriate muscle activation levels through optimization of the controller parameters is given.

A Cortical Thickness Mapping Method for the Coxal Bone Using Morphing.

As human body finite element models become more integrated with the design of safety countermeasures and regulations, novel models need to be developed that reflect the variation in the population's anthropometry. However, these new models may be missing information which will need to be translated from existing models. During the development of a 5th percentile female occupant model (F05), cortical thickness information of the coxal bone was unavailable due to resolution limits in the computed tomography (CT) scans. In this study, a method for transferring cortical thickness information from a source to a target model with entirely different geometry and architecture is presented. The source and target models were the Global Human Body Models Consortium (GHBMC) 50th percentile male (M50) and F05 coxal bones, respectively. To project the coxal bone cortical thickness from the M50 to the F05, the M50 model was first morphed using a Kriging method with 132 optimized control points to the F05 anthropometry. This technique was found to be accurate with a mean nodal discrepancy of 1.27 mm between the F05 and morphed M50 (mM50) coxal bones. Cortical thickness at each F05 node was determined by taking the average cortical thickness of every mM50 node, non-linearly weighted by its distance to the F05 nodes. The non-linear weighting coefficient, β, had a large effect on the accuracy and smoothness of the projected cortical bone thickness. The optimal projection had β = 4 and was defined when the tradeoff between projection accuracy and smoothness was equal. Finally, a quasi-static pelvis compression was simulated to examine to effect of β. As β, increased from 0 to 4, the failure force decreased by ~100 N, whereas the failure displacement increased by 0.9 mm. Results from quasi-static compression tests of the F05 pelvis were comparable to experimental results. This method could be applied to other anatomical regions where cortical thickness variation is important, such as the femur and ribs and is not limited to GHBMC-family models. Furthermore, this process will aid the development of subject-specific finite element models where accurate cortical bone thickness measurements cannot be obtained.

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

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

Importance of asymmetry and anisotropy in predicting cortical bone response and fracture using human body model femur in three-point bending and axial rotation.

Modeling of cortical bone response and failure is critical for the prediction of Crash Induced Injuries (CII) using advanced finite element (FE) Human Body Models (HBM). Although cortical bone is anisotropic and asymmetric in tension and compression, current HBM often utilize simple isotropic, symmetric, elastic-plastic constitutive models. In this study, a 50th percentile male femur FE model was used to quantify the effect of asymmetry and anisotropy in three-point bending and axial torsion. A complete set of cortical bone mechanical properties was identified from a literature review, and the femur model was used to investigate the importance of material asymmetry and anisotropy on the failure load/moment, failure displacement/rotation and fracture pattern. All models were able to predict failure load in bending, since this was dominated by the cortical bone material tensile response. However, only the orthotropic model was able to predict the torsional response and failure moment. Only the orthotropic model predicted the fracture initiation location and fracture pattern in bending, and the fracture initiation location in torsion; however, the anticipated spiral fracture pattern was not predicted by the models for torsional loading. The results demonstrated that asymmetry did not significantly improve the prediction capability, and that orthotropic material model with the identified material properties was able to predict the kinetics and kinematics for both three-point bending and axial torsion. This will help to provide an improved method for modeling hard tissue response and failure in full HBM.

Finite element models of the thigh-buttock complex for assessing static sitting discomfort and pressure sore risk: a literature review

Being seated for long periods, while part of many leisure or occupational activities, can lead to discomfort, pain and sometimes health issues. The impact of prolonged sitting on the body has been widely studied in the literature, with a large number of human-body finite element models developed to simulate sitting and assess seat-induced discomfort or to investigate the biomechanical factors involved. Here, we review the finite element models developed to investigate sitting discomfort or risk of pressure sores. Our study examines finite element models from twenty-seven papers, seventeen dedicated to assessing seating discomfort and ten dedicated to investigating pressure ulcers caused by prolonged sitting. The models’ mesh composition and material properties are found to differ widely. These models share a lack of validation and generally make little allowance for anthropometric diversity.

Failed rib region prediction in a human body model during crash events with precrash braking

ABSTRACTObjective: The objective of this study is 2-fold. We used a validated human body finite element model to study the predicted chest injury (focusing on rib fracture as a function of element strain) based on varying levels of simulated precrash braking. Furthermore, we compare deterministic and probabilistic methods of rib injury prediction in the computational model.Methods: The Global Human Body Models Consortium (GHBMC) M50-O model was gravity settled in the driver position of a generic interior equipped with an advanced 3-point belt and airbag. Twelve cases were investigated with permutations for failure, precrash braking system, and crash severity. The severities used were median (17 kph), severe (34 kph), and New Car Assessment Program (NCAP; 56.4 kph). Cases with failure enabled removed rib cortical bone elements once 1.8% effective plastic strain was exceeded. Alternatively, a probabilistic framework found in the literature was used to predict rib failure. Both the probabilistic and deterministic methods take into consideration location (anterior, lateral, and posterior). The deterministic method is based on a rubric that defines failed rib regions dependent on a threshold for contiguous failed elements. The probabilistic method depends on age-based strain and failure functions.Results: Kinematics between both methods were similar (peak max deviation: ΔXhead = 17 mm; ΔZhead = 4 mm; ΔXthorax = 5 mm; ΔZthorax = 1 mm). Seat belt forces at the time of probabilistic failed region initiation were lower than those at deterministic failed region initiation. The probabilistic method for rib fracture predicted more failed regions in the rib (an analog for fracture) than the deterministic method in all but 1 case where they were equal. The failed region patterns between models are similar; however, there are differences that arise due to stress reduced from element elimination that cause probabilistic failed regions to continue to rise after no deterministic failed region would be predicted.Conclusions: Both the probabilistic and deterministic methods indicate similar trends with regards to the effect of precrash braking; however, there are tradeoffs. The deterministic failed region method is more spatially sensitive to failure and is more sensitive to belt loads. The probabilistic failed region method allows for increased capability in postprocessing with respect to age. The probabilistic failed region method predicted more failed regions than the deterministic failed region method due to force distribution differences.

A Nonlinear Viscoelastic Model for Adipose Tissue Representing Tissue Response at a Wide Range of Strain Rates and High Strain Levels.

Finite element human body models (FEHBMs) are nowadays commonly used to simulate pre- and in-crash occupant response in order to develop advanced safety systems. In this study, a biofidelic model for adipose tissue is developed for this application. It is a nonlinear viscoelastic model based on the Reese et al.'s formulation. The model is formulated in a large strain framework and applied for finite element (FE) simulation of two types of experiments: rheological experiments and ramped-displacement experiments. The adipose tissue behavior in both experiments is represented well by this model. It indicates the capability of the model to be used in large deformation and wide range of strain rates for application in human body models.

High strain rate compressive behaviour of human heart

Thoracic injuries incurred during crashes constitute a significant portion of all fatal and non-fatal injuries. Finite element human body models are used to understand the injury mechanisms to critical organs like the heart for improving crash safety. Major insight can be gained into its injury mechanisms by studying its compressive behaviour at strain rates seen in impact (up to 300/s). This study reports a total of 20 compression tests performed on heart tissues at strain rates ranging from 0.001/s to 200/s. Green strain was calculated from displacements which were obtained from analysis of high speed video recordings. Stresses were calculated from the measured force and initial cross-sectional area. The study showed that the response of heart tissue was non-linear and strain rate dependent. The elastic modulus also varied with strain with values ranging from 1.79e-3 MPa to 3.34 MPa at compressive strain of 15% to 46%.

High strain rate compressive behaviour of human heart

Thoracic injuries incurred during crashes constitute a significant portion of all fatal and non-fatal injuries. Finite element human body models are used to understand the injury mechanisms to critical organs like the heart for improving crash safety. Major insight can be gained into its injury mechanisms by studying its compressive behaviour at strain rates seen in impact (up to 300/s). This study reports a total of 20 compression tests performed on heart tissues at strain rates ranging from 0.001/s to 200/s. Green strain was calculated from displacements which were obtained from analysis of high speed video recordings. Stresses were calculated from the measured force and initial cross-sectional area. The study showed that the response of heart tissue was non-linear and strain rate dependent. The elastic modulus also varied with strain with values ranging from 1.79e-3 MPa to 3.34 MPa at compressive strain of 15% to 46%.

Normalized frontal impact biofidelity kinematic corridors using post mortem human surrogates.

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

Occupant Kinematics in Simulated Autonomous Driving Vehicle Collisions: Influence of Seating Position, Direction and Angle.

This two-part study analyzed occupant kinematics in simulated collisions of future automated driving vehicles in terms of seating configuration. In part one, a frontal collision was simulated with four occupants with the front seats reversed. The left front seat occupant was unbelted while the others were belted. In part two of the study, occupant restraint was examined in various seating configurations using a single seat model with a three-point seatbelt. The seat direction with respect to impact was considered as forward, rearward, and lateral facing in 45 degree increments. The effect of seat recline was also studied in the forward-facing and rear-facing cases by assuming three positions: driving position, resting position and relaxed position. Occupants were represented by human body finite element models. The results of part one showed that the front seat (rear-facing) occupants were restrained by the seatback, resulting in T1 forward displacement less than 100 mm; the rear seat occupants were restrained by the seatbelt resulting larger T1 forward displacement more than 500 mm. The results of the part two showed the directional dependence of occupant restraint. Greater T1 displacements were observed when the occupant faced lateral or front oblique. However, the seatbelt provided some restraint in all directions considered. The seatback generated contact force to the occupant when it was in the impact direction, including the lateral directions. The relaxed position allowed increased excursion compared to the driving position when the occupant faced rearward, but the magnitude of this increase was lower with lower impact speed.

Biomechanics of Lumbar Motion-Segments in Dynamic Compression.

Recent epidemiology studies have reported increase in lumbar spine injuries in frontal crashes. Whole human body finite element models (FEHBM) are frequently used to delineate mechanisms of such injuries. However, the accuracy of these models in mimicking the response of human spine relies on the characterization data of the spine model. The current study set out to generate characterization data that can be input to FEHBM lumbar spine, to obtain biofidelic responses from the models. Twenty-five lumbar functional spinal units were tested under compressive loading. A hydraulic testing machine was used to load the superior ends of the specimens. A 75N load was placed on the superior PMMA to remove the laxity in the joint and mimic the physiological load. There were three loading sequences, namely, preconditioning, 0.5 m/s (non-injurious) and 1.0 m/s (failure). Forces and displacements were collected using six-axis load cell and VICON targets. In addition, acoustic signals were collected to identify the times of failures. Finally, response corridors were generated for the two speeds. To demonstrate the corridors, GHBMC FE model was simulated in frontal impact condition with the default and updated lumbar stiffness. Bi-linear trend was observed in the force versus displacement plots. In the 0.5 m/s tests, mean toe- and linear-region stiffnesses were 0.96±0.37 and 2.44±0.92 kN/mm. In 1.0 m/s tests, the toe and linear-region stiffnesses were 1.13±0.56 and 4.6±2.5 kN/mm. Lumbar joints demonstrated 2.5 times higher stiffness in the linear-region when the loading rate was increased by 0.5 m/s.

DEVELOPMENT AND BIOFIDELITY EVALUATION OF AN OCCUPANT BIOMECHANICAL MODEL OF A CHINESE 50TH PERCENTILE MALE FOR SIDE IMPACT

Finite element modeling has played a significant role in the study of human body biomechanical responses and injury mechanisms during vehicle impacts. However, there are very few reports on similar studies conducted in China for the Chinese population. In this study, a high-precision human body finite element model of the Chinese 50th percentile male was developed. The anatomical structures and mechanical characteristics of real human body were replicated as precise as possible. In order to analyze the model’s biofidelity in side-impact injury prediction, a global technical standard, ISO/TR 9790, was used that specifically assesses the lateral impact biofidelity of anthropomorphic test devices (ATDs) and computational models. A series of model simulations, focusing on different body parts, were carried out against the tests outlined in ISO/TR 9790. Then, the biofidelity ratings of the full human body model and different body parts were evaluated using the ISO/TR 9790 rating method. In a 0–10 rating scale, the resulting rating for the full human body model developed is 8.57, which means a good biofidelity. As to different body parts, the biofidelity ratings of the head and shoulder are excellent, while those of the neck, thorax, abdomen and pelvis are good. The resulting ratings indicate that the human body model developed in this study is capable of investigating the side-impact responses of and injuries to occupants’ different body parts. In addition, the rating of the model was compared with those of the other human body finite element models and several side-impact dummy models. This allows us to assess the robustness of our model and to identify necessary improvements.

Implementation and validation of the extended Hill-type muscle model with robust routing capabilities in LS-DYNA for active human body models

BackgroundIn the state of the art finite element AHBMs for car crash analysis in the LS-DYNA software material named *MAT_MUSCLE (*MAT_156) is used for active muscles modeling. It has three elements in parallel configuration, which has several major drawbacks: restraint approximation of the physical reality, complicated parameterization and absence of the integrated activation dynamics. This study presents implementation of the extended four element Hill-type muscle model with serial damping and eccentric force–velocity relation including Ca^{2+} dependent activation dynamics and internal method for physiological muscle routing.ResultsProposed model was implemented into the general-purpose finite element (FE) simulation software LSDYNA as a user material for truss elements. This material model is verified and validated with three different sets of mammalian experimental data, taken from the literature. It is compared to the *MAT_MUSCLE (*MAT_156) Hill-type muscle model already existing in LS-DYNA, which is currently used in finite element human body models (HBMs). An application example with an arm model extracted from the FE ViVA OpenHBM is given, taking into account physiological muscle paths.ConclusionThe simulation results show better material model accuracy, calculation robustness and improved muscle routing capability compared to *MAT_156. The FORTRAN source code for the user material subroutine dyn21.f and the muscle parameters for all simulations, conducted in the study, are given at https://zenodo.org/record/826209 under an open source license. This enables a quick application of the proposed material model in LS-DYNA, especially in active human body models (AHBMs) for applications in automotive safety.

Computational modeling of blast wave interaction with a human body and assessment of traumatic brain injury

The modeling of human body biomechanics resulting from blast exposure poses great challenges because of the complex geometry and the substantial material heterogeneity. We developed a detailed human body finite element model representing both the geometry and the materials realistically. The model includes the detailed head (face, skull, brain and spinal cord), the neck, the skeleton, air cavities (lungs) and the tissues. Hence, it can be used to properly model the stress wave propagation in the human body subjected to blast loading. The blast loading on the human was generated from a simulated C4 explosion. We used the highly scalable solvers in the multi-physics code CoBi for both the blast simulation and the human body biomechanics. The meshes generated for these simulations are of good quality so that relatively large time-step sizes can be used without resorting to artificial time scaling treatments. The coupled gas dynamics and biomechanics solutions were validated against the shock tube test data. The human body models were used to conduct parametric simulations to find the biomechanical response and the brain injury mechanism due to blasts impacting the human body. Under the same blast loading condition, we showed the importance of inclusion of the whole body.

The effect of precrash velocity reduction on occupant response using a human body finite element model

ABSTRACTObjective: The objective of this study is to use a validated finite element model of the human body and a certified model of an anthropomorphic test dummy (ATD) to evaluate the effect of simulated precrash braking on driver kinematics, restraint loads, body loads, and computed injury criteria in 4 commonly injured body regions.Methods: The Global Human Body Models Consortium (GHBMC) 50th percentile male occupant (M50-O) and the Humanetics Hybrid III 50th percentile models were gravity settled in the driver position of a generic interior equipped with an advanced 3-point belt and driver airbag. Fifteen simulations per model (30 total) were conducted, including 4 scenarios at 3 severity levels: median, severe, and the U.S. New Car Assessment Program (U.S.-NCAP) and 3 extra per model with high-intensity braking. The 4 scenarios were no precollision system (no PCS), forward collision warning (FCW), FCW with prebraking assist (FCW+PBA), and FCW and PBA with autonomous precrash braking (FCW + PBA + PB). The baseline ΔV was 17, 34, and 56.4 kph for median, severe, and U.S.-NCAP scenarios, respectively, and were based on crash reconstructions from NASS/CDS. Pulses were then developed based on the assumed precrash systems equipped. Restraint properties and the generic pulse used were based on literature.Results: In median crash severity cases, little to no risk (<10% risk for Abbreviated injury Scale [AIS] 3+) was found for all injury measures for both models. In the severe set of cases, little to no risk for AIS 3+ injury was also found for all injury measures. In NCAP cases, highest risk was typically found with No PCS and lowest with FCW + PBA + PB. In the higher intensity braking cases (1.0–1.4 g), head injury criterion (HIC), brain injury criterion (BrIC), and chest deflection injury measures increased with increased braking intensity. All other measures for these cases tended to decrease. The ATD also predicted and trended similar to the human body models predictions for both the median, severe, and NCAP cases. Forward excursion for both models decreased across median, severe, and NCAP cases and diverged from each other in cases above 1.0 g of braking intensity.Conclusions: The addition of precrash systems simulated through reduced precrash speeds caused reductions in some injury criteria, whereas others (chest deflection, HIC, and BrIC) increased due to a modified occupant position. The human model and ATD models trended similarly in nearly all cases with greater risk indicated in the human model. These results suggest the need for integrated safety systems that have restraints that optimize the occupant's position during precrash braking and prior to impact.

Thoracoabdominal injury analysis of a 6-year-old pedestrian finite element model in vehicle-pedestrian collisions

A holistic human body finite element model of a 6-year-old pedestrian was completed by integrating the skin, soft tissues and joint ligaments, based on the component models of a 6-year-old child. The complete model was verified by comparing to available cadaveric test data. Then it was used to simulate collisions of midsize car/SUV-paediatric pedestrian at different collision speeds, in order to study the effects of collision speed, and vehicle type on kinematic/biomechanical responses of paediatric chest and abdomen, and to predict the injuries of bones and internal organs according to compression/viscous criterion and strain. Simulation results showed that the number of rib fractures increased with the increase of collision speed in collision simulations of midsize car-paediatric pedestrian, but no rib fracture appeared in simulations of SUV-paediatric pedestrian impact. Maximum values of chest/abdomen/thigh impact forces, maximum deformation/VCmax of paediatric chest and abdomen, and maximum first principal strain of internal organs were proportional to collision speed. Predicted paediatric chest and abdominal injuries, obtained from the midsize car-pedestrian simulations, were found to be consistent when compression/viscous criterion and first principal strain were used as a yardstick for injury assessment. Additionally, compression/viscous criteria had some limitations on the prediction of rib fracture in SUV-pedestrian collision simulations.