Costin Untaroiu

Abstract: Due to the lack of sufficient data for children, validation of the impact response of a child dummy or a child finite element (FE) model is a big challenge. This study used multi-body simulations along with optimization techniques for estimating impact conditions of a particular child pedestrian accident case selected from an in-depth pedestrian accident database. FE child model simulations with failure criteria were run using the estimated impact conditions, and the predicted and observed injuries were compared. The results of ...

Abstract A better coupling of the occupant to the car seat in the early phase of a frontal crash using pretensioner systems may potentially avoid head-vehicle contact and reduces the likelihood of the submarining effect. However, the high belt forces developed during pre-tensioning may also increase the risk of abdominal injuries to the vehicle occupant. The main objective of this study was to investigate the biomechanical response and injury outcome to the thorax and the abdominal regions in static deployment tests using two pre- ...

Since the limited space between the car structure and an occupant makes it difficult to manage side impact energy, much biomechanical investigation has been done by subjecting the pelvis to lateral loading. In this study, the dummy finite element model was partially modified to ...

The THOR dummy has been developed and continuously improved by NHTSA to provide manufactures an advanced tool that can be used to assess injury risk in crash tests. The main goal of this study is to evaluate a commercial rigid-body Thor Dummy Model in frontal crash environment using test data and objective rating methods. The kinematics of the Thor-NT dummy,

Tibia fractures and dislocations among vehicle occupants injured in traffic collisions are costly and debilitating. The current criterion for predicting the occurrence of tibial shaft fracture in crash tests, the Tibia Index, relies on the combined bending and compressive strength at the mid-shaft location of the tibia. Recent studies have shown that tibial curvature and fibular load-sharing may influence the

Rotor balancing is a requirement for the smooth operation of high-speed rotating machinery. In field balancing, minimization of the residual vibrations at important locations/speeds under practical constraints is usually a challenging task. In this paper, the generalized minmax coefficient influence method is formulated as an optimization problem with flexible objective functions and constraints. The optimization problem is cast in a Linear Matrix Inequality (LMI) form and a balancing code is developed to solve it. Two balancing ...

The liver is the most frequently injured abdominal organ in frontal vehicle collisions. To better predict the liver biomechanical response and injury risk during numerical simulations of traffic accidents, accurate material models of the liver should be incorporated in human finite element (FE) models. This study presents a total of 18 tension tests performed on fr esh human samples of

Three-dimensional kinematics of body targets are frequently tracked during vehicle impact tests using instrumented cubes. While the components of linear acceleration and angular velocity are recorded in a cube local coordinate system, transformation to a global coordinate system is required to reconstruct the whole body motions. This paper presents a methodology for local-to-global kinematic transformations using a finite element cube

The THOR dummy has been developed and continuously improved by NHTSA to provide manufactures an advanced tool that can be used to assess injury risk in crash tests. The main goal of this study is to evaluate a commercial rigid-body Thor Dummy Model in frontal crash environment using test data and objective rating methods. The kinematics of the Thor-NT dummy, restrained by a standard belt system and positioned in a rigid seat, was recorded by means of a 3D VICON motion capture system in a 40 km/h frontal sled test. In the numerical study, the test setup was modeled in Madymo environment, and the TNO Thor Dummy model was positioned using the same procedure employed in testing. Small spheres were attached to the dummy model at the locations of Vicon markers and their 3D displacements were calculated from the crash simulation with the sled test deceleration pulse. The time histories of the 3D photo-target displacements and the interaction forces of dummy with the sled and the belt obtai...

Clavicle fractures are common injuries in three-point belt restrained occupants involved in frontal and lateral car collisions. Therefore, better understanding of clavicle loading which occurs during an impact and clavicle structural/material properties could help in the optimization of seatbelt restraint systems. Six clavicles from three post mortem human subjects were tested in a three point -bending test setup with pinned-pinned boundary conditions. The clavicle extremities were fixed into potting cups which were able to rotate freely about a single rotational axis (inferior-superior axis) and then, were loaded in the anterior-posterior direction by an impactor at the middle shaft level. Two tests were performed on each clavicle: a) A noninjurious quasi-static test (1mm/s impactor rate) up to approximately 400 N b) A dynamic test (1m/s impactor rate) to failure. Reaction forces and moments were measured at both clavicle supports. The results showed an averaged clavicle stiffness ...

Tibia fractures and dislocations among vehicle occupants injured in traffic collisions are costly and debilitating. The current criterion for predicting the occurrence of tibial shaft fracture in crash tests, the Tibia Index, relies on the combined bending and compressive strength at the mid-shaft location of the tibia. Recent studies have shown that tibial curvature and fibular load-sharing may influence the injury prediction of the leg and that the distal third section of the tibial shaft is the most commonly fractured shaft section in frontal crashes. In order to provide biomechanical injury data of the leg for a possible re-evaluation of the Tibia Index, the dynamic combined strength of twenty human legs at the distal third region was determined using varying axial compressive pre-load in the range of 2 to 8 kN followed by anterior-posterior impact loading close to the distal third region. The injury boundary of the leg in terms of the axial load and applied bending moment obtai...

The pubic rami fracture is a common pelvic injury for vehicle occupants as well as for pedestrians struck during side impacts. While many studies have investigated the structural properties of the pelvis in lateral loading, relatively few investigations have compared the applied loads with local response of the pubic rami. The aims of this study are to investigate the force transmission paths and strain distribution for the anterior (ie, rami) and posterior (ie, sacrum) regions of the pelvis under acetabular impact loading. Eight male postmortem ...

Abstract: Material and structural properties of human tissues under impact loading are needed for the development of physical and computational models used in pedestrian and vehicle occupant protection. Obtaining these global properties directly from the data of biomechanical tests is a challenging task due to nonlinearities of tissue-test setup systems. The objective of this study was to develop subject-specific finite element (FE) techniques for material identification of human tissues using Successive Response Surface Methodology ...

Abstract: Two post-mortem human subjects were subjected to dynamic, non-injurious (up to 20 % chest deflection) anterior shoulder belt loading at 0.5 m/s and 0.9 m/s loading rates. The human surrogates were mounted to a stationary apparatus that supported the spine and shoulder ...

Abstract: Previous full-scale pedestrian impact experiments using post-mortem human surrogates (PMHS) and sled-mounted vehicle bucks have shown that vehicle shape relative to pedestrian anthropometry may influence pedestrian kinematics and injury mechanisms. While a ...

The goal of this study was to develop a mathematical model of the 50th percentile male lower extremity capable of predicting injury risk and simulating the kinetic and kinematic response of the pedestrian lower extremity under vehicle impact loading. The hip-to-foot multibody model was developed for the MADYMO software platform using exterior and interior geometry and inertial properties from a detailed finite element model (FEM) of the human lower extremity and stiffness and failure tolerance data from the literature. The leg and thigh models' structural and contact parameters were simultaneously optimized to validate model response in simulations replicating previous dynamic bending experiments. The aggregate model's full-scale kinematic response was verified by comparing 3-D local (knee bending angles) and global (linear accelerations and velocities) frame leg and thigh kinematics from vehicle impact simulations with data generated from seven vehicle-pedestrian (PMHS) impact experiments. By optimizing contact and structural response variables, the applied moment vs. deflection response of the leg and thigh showed excellent correlation with the experimental corridor averages in component-level bending simulations. The full-scale kinematic response of the 50th percentile male model showed good correlation with the PMHS response data in both the rate of valgus knee bending (approximately 3 degress/ms) and in the timing and magnitude of the peak thigh and leg accelerations (250 g and 400 g). Additionally, as a result of vehicle interaction, both the model and the experiments showed that the thigh and leg are initially accelerated upward (100 g) and downward (100 g), respectively, and then downward (60 g) and upward (100 g), respectively. The model also predicted a valgus knee injury and a tibia fracture similar to those seen in the PMHS. The use of a facet surface model of the lower extremity skin and simultaneous optimization of the model's structural response and contact parameters resulted in a model capable of accurately predicting the detailed kinematic response of the lower extremity under vehicle impact loading at 40 km/h. The model can be scaled to represent varying pedestrian anthropometries and can assess the risks associated with sustaining the most common pedestrian injuries. As a vehicle design tool, the model can be used to optimize front-end designs, or it can be used in combination with a detailed FEM to reduce the vast design space prior to FE simulations. Additionally, the model can be used as a tool to study pedestrian impact kinematics, real-world case reconstructions, or particular vehicle countermeasures.

A crack adds to the shaft a local flexibility, which establishes the decrease of natural frequencies of the system. There are studied two types of open crack in a crankshaft: a transverse crack and a circumferential crack. Considering some locations and depths for the crack, the natural frequencies and the vibration modes were established by the transfer matrix method.

Bone fractures occur frequently at mid-shaft femoral site during frontal and offset automotive crashes. Because these injuries are expensive, it is crucial to understand the injury mechanisms if this injury is to be prevented. The experimental investigation of ...

The dynamic stability of a Jefcott rotor with a transverse crack is studied. For the surface crack it used open crack model and breathing crack model. The latter case conducted to a system of differential equations with periodic coefficients. The instability regions are determined in a plane, function of crack depth and the rotational speed of rotor, using Floquet theory.

Abstract: Due to the lack of sufficient data for children, validation of the impact response of a child dummy or a child finite element (FE) model is a big challenge. This study used multi-body simulations along with optimization techniques for estimating impact conditions of a particular child pedestrian accident case selected from an in-depth pedestrian accident database. FE child model simulations with failure criteria were run using the estimated impact conditions, and the predicted and observed injuries were compared. The results of ...

The liver is one of the most frequently injured abdominal organs during motor vehicle crashes. Realistic numerical assessments of liver injury risk for the entire occupant population require incorporating inter-subject variations into numerical models. The main objective of this study was to quantify the shape variations of human liver in a seated posture and the statistical distributions of its material properties. Statistical shape analysis was applied to construct shape models of the livers of 15 adult human subjects, recorded in a typical seated (occupant) posture. The principal component analysis was then utilized to obtain the modes of variation, the mean model, and 95% statistical boundary shape models. In addition, a total of 52 tensile tests were performed on the parenchyma of three fresh human livers at four loading rates (0.01, 0.1, 1, and 10 s^-1) to characterize the rate-dependent and failure properties of the human liver. A FE-based optimization approach was employed to identify the material parameters of an Ogden material model for each specimen. The mean material parameters were then determined for each loading rate from the characteristic averages of the stress-strain curves, and a stochastic optimization approach was utilized to determine the standard deviations of the material parameters. Results showed that the first five modes of the human liver shape models account for more than 60% of the overall anatomical variations. The distributions of the material parameters combined with the mean and statistical boundary shape models could be used to develop probabilistic finite element (FE) models, which may help to better understand the variability in biomechanical responses and injuries to the abdominal organs under impact loading.

Introduction/Objective: In an effort to continually improve upon the design of the test device for human occupant restraint (THOR) dummy, a series of modifications have recently been applied. The first objective of this study was to update the THOR head-neck finite element (FE) model to the specifications of the latest dummy modifications. The second objective was to develop and apply a new optimization-based methodology to calibrate the FE head-neck model based on experimental test data. The calibrated head-neck model was validated against both frontal and lateral impact test data. Finally, the sensitivities of the model, in terms of head and neck injury criteria, to pre-test positioning conditions were evaluated in a frontal crash test simulation.
Methods: The updated parts of the head-neck THOR FE model were re-meshed from CAD geometries of the modified parts. In addition, further model modifications were made to improve the effectiveness of the model (e.g., model stability). A novel calibration methodology, which incorporates the CORA (CORelation and Analysis) rating system with an optimization algorithm implemented in Isight software, was developed to improve both kinematic and kinetic responses of the model in various THOR dummy certification and biomechanical response tests. A parametric study was performed to evaluate head and neck injury criteria values in the calibrated head-neck model, during a 40 km/h frontal crash test, with respect to variation in the THOR model upper body and belt pre-test position.
Results: Material parameter optimization was shown to greatly improve the updated model response by increasing the average rating score from 0.794 ± 0.073 to 0.964 ± 0.019. The calibrated neck showed the biggest improvement in the pendulum flexion simulation from 0.681 in the original model up to 0.96 in the calibrated model. The fully calibrated model proved to be effective at predicting dummy response in frontal and lateral loading conditions during the validation phase (0.942 average score). Upper body position was shown to have a greater effect on head-neck response than belt position. The pre-test positioning variation resulted in a 10% maximum change in HIC36 values and 14% maximum change in NIJ values.
Conclusion: The optimization-based calibration methodology was effective as it markedly improved model performance. The calibrated head-neck model demonstrated application in a crash safety analysis, showing slight head-neck injury sensitivity to pre-test positioning in a frontal crash impact scenario.

Cadaveric tissue models play an important role in the assessment and optimization of novel restraint systems for reducing abdominal injuries. However, the effect of tissue preservation by means of freezing on the material properties of abdominal tissues remains unknown. The goal of this study was to investigate the influence of frozen storage time on the material responses of the liver parenchyma in tensile loading.

Specimens from ten bovine livers were equally divided into three groups: fresh, 30-day frozen storage, and 60-day frozen storage. All preserved specimens were stored at −12 °C. Dog-bone specimens from each preservation group were randomly assigned to one of the three strain rates (0.01 s−1, 0.1 s−1, and 1.0 s−1) and tested to failure in tensile loading. The local and global material response of the liver parenchyma specimens were investigated based on the experimental data and optimized analytical material models.

The local and global failure strains decreased significantly between fresh specimens and specimens preserved for 30 days (p<0.05), and between fresh specimens and specimens preserved for 60 days (p<0.05) for all three loading rates. Changes on the material model parameters were also observed between fresh and preserved specimens. Preservation by means of frozen storage was found to affect both the material and failure response of bovine liver parenchyma in tensile loading. The stiffness of the tissue increased considerably with increased preservation time and increased strain rate. The stiffness changes between fresh and preserved tissues could be caused by the dehydration of the hepatic cells as a result of the freezing and thawing processes.

Significant changes (p<0.05) between the failure strain of previously frozen liver parenchyma samples and fresh samples were demonstrated at both global and local levels in this study. In addition, nonlinear and viscoelastic characteristics of the liver parenchyma were observed in tension for both fresh and preserved samples.

The liver is one of the most frequently injured abdominal organs during motor vehicle crashes. Realistic car crash simulations require incorporating strain-rate dependent mechanical properties of soft tissue in finite element (FE) material models. This study presents a total of 30 tension tests performed on fresh bovine liver parenchyma at various loading rates in order to characterize the biomechanical and failure properties of liver parenchyma. Each specimen, cut in a standard dog-bone shape, was tested until failure at one of three loading rates (0.01 s−1, 0.1 s−1, 1 s−1) using a tensile testing setup. Load and acceleration recorded from each specimen grip were employed to calculate the time history of force at specimen ends. The shapes of all specimens were reconstructed from laser scans recorded prior to each test and then used to develop specimen-specific FE models. A first-order Ogden material model and the time histories of specimen end displacement were assigned to each specimen FE model. The failure Green-Lagrangian strain showed averages around 50% and no significant dependence on loading rates, but the failure 2nd Piola—Kirchhoff stress showed rate-dependence with average values ranging from 33 kPa to 94 kPa. The FE models with material model parameters identified using a simulation-based optimization replicated well the time history of load recorded during the test. The FE simulations with model parameters identified using an analytical approach or based on the displacement of optical markers showed a significantly stiffer response and lower failure stress/strain than the FE specimen-specific models. This study provides novel biomechanical and failure data which can be easily implemented in FE models and used to assess injury risk in automobile collisions.

Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short seals, they lack accuracy in cases of seals with complex geometry or with large aspect ratios (above 1.0). In this paper, the linearized rotordynamic coefficients for a seal with a large aspect ratio are calculated by means of a three-dimensional CFD analysis performed to predict the fluid-induced forces acting on the rotor.

During car collisions, the shoulder belt exposes the occupant's clavicle to large loading conditions which often leads to a bone fracture. To better understand the geometric variability of clavicular cortical bone which may influence its injury tolerance, twenty human clavicles were evaluated using statistical shape analysis. The interior and exterior clavicular cortical bone surfaces were reconstructed from CT-scan images. Registration between one selected template and the remaining 19 clavicle models was conducted to remove translation and rotation differences. The correspondences of landmarks between the models were then established using coordinates and surface normals. Three registration methods were compared: the LM-ICP method; the global method; and the SHREC method. The LM-ICP registration method showed better performance than the global and SHREC registration methods, in terms of compactness, generalization, and specificity. The first four principal components obtained by using the LM-ICP registration method account for 61% and 67% of the overall anatomical variation for the exterior and interior cortical bone shapes, respectively. The length was found to be the most significant variation mode of the human clavicle. The mean and two boundary shape models were created using the four most significant principal components to investigate the size and shape variation of clavicular cortical bone. In the future, boundary shape models could be used to develop probabilistic finite element models which may help to better understand the variability in biomechanical responses and injuries to the clavicle.

Objective: More than half of occupant Lower Extremity (LEX) injuries during automotive frontal crashes are in the Knee-Thigh-Hip (KTH) complex. The objective of this study is to develop a detailed and biofidelic Finite Element (FE) occupant LEX model that may improve current understanding of mechanisms and thresholds of KTH injuries.

Methods: Firstly, the pelvis, thigh-knee-hip, and foot models, developed in our previous studies, were connected into an occupant lower limb model. Further validations, including posterior cruciate ligament (PCL) stretching, thigh lateral loading KT, and KTH impact loading, were then performed to verify the injury predictability of the model under complex frontal and lateral loading corresponding to automotive impacts. Finally, a sensitivity study was performed with the whole lower limb model to investigate the effect of the hip joint angle to acetabulum injury tolerance in frontal impacts.

Results: The whole lower limb model showed to be stable under severe impacts along the knee, foot and lateral components. In addition, the biomechanical and injury responses predicted by the model correlate well with the corresponding test data. An increase of hip joint extension angle from -300 to +200 relative to neutral posture showed an increase of 19% to 58% hip injury tolerance.

Conclusions : The stability and biofidelity response of the PLEX model indicates its potential application in future frontal and lateral impact FE simulations.

With fast development in high performance computer area and modeling techniques, design of injury countermeasures based on numerical simulations could make the process more cost-efficient. To reduce the risks and uncertainties associated with the use of predictive models for design decision making, an increased attention should be paid to the validation process of human dummy models. The main goal of this study was to assess a numerical THOR dummy model in frontal crash environment using kinetic and kinematic test data and various validation metrics. A THOR-NT dummy positioned on a rigid planar seat and restrained by a standard 3-point shoulder and lap belt system was subjected to two frontal crash sled tests with “initial velocity 40 km/h”. In the numerical analysis, the dummy model was positioned in a test setup model using the same procedure employed in testing. The dynamic and kinematic data of dummy model were compared with corresponding test data using validation metrics implemented in two rating systems. The overall dummy kinematics, the 3D displacement time histories of certain dummy body regions, and the interaction forces of dummy with the sled and the belt obtained in simulation were in reasonable agreement with the corresponding test data. Generally, the rating scores showed to be sensitive to the validation metrics and to the weighting factors used in the assessment process. The current average score of THOR model positioned it in the “fair-to-acceptable” range, which would recommend it for use in impact simulations. The results of this study and the validation methodology may be used for further refinement of the current THOR model, in setting up future dummy tests, the assessment of other human dummy models, and the improvement of model rating methods.

Ankle and subtalar joint injuries of vehicle front seat occupants are frequently recorded during frontal and offset vehicle crashes. A few injury criteria for foot and ankle were proposed in the past; however, they addressed only certain injury mechanisms or impact loadings. The main goal of this study was to investigate numerically the tolerance of foot and ankle under complex loading which may appear during automotive crashes. A previously developed and preliminarily validated foot and leg finite element (FE) model of a 50th percentile male was employed in this study. The model was further validated against postmortem human subjects (PMHS) data in various loading conditions that generates the bony fractures and ligament failures in ankle and subtalar regions observed in traffic accidents. Then, the foot and leg model were subjected to complex loading simulated as combinations of axial, dorsiflexion, and inversion loadings. An injury surface was fitted through the points corresponding to the parameters recorded at the time of failure in the FE simulations. The compelling injury predictions of the injury surface in two crash simulations may recommend its application for interpreting the test data recorded by anthropometric test devices (ATD) during crash tests. It is believed that the methodology presented in this study may be appropriate for the development of injury criteria under complex loadings corresponding to other body regions as well.

The mechanical properties of brain under various loadings have been reported in the literature over the past 50 years. Step-and-hold tests have often been employed to characterize viscoelastic and nonlinear behavior of brain under high-rate shear deformation; however, the identification of brain material parameters is typically performed by neglecting the initial strain ramp and/or by assuming a uniform strain distribution in the brain samples. Using finite element (FE) simulations of shear tests, this study shows that these simplifications have a significant effect on the identified material properties in the case of cylindrical human brain specimens. Material models optimized using only the stress relaxation curve under predict the shear force during the strain ramp, mainly due to lower values of their instantaneous shear moduli. Similarly, material models optimized using an analytical approach, which assumes a uniform strain distribution, under predict peak shear forces in FE simulations. Reducing the specimen height showed to improve the model prediction, but no improvements were observed for cubic samples with heights similar to cylindrical samples. Models optimized using FE simulations show the closest response to the test data, so a FE based optimization approach is recommended in future parameter identification studies of brain.

To investigate the possible changes in material properties of cadaveric abdominal organs due to the preservation methods, the indentation data obtained from porcine abdominal organs (kidney, liver, and spleen) preserved by cooling and freezing are analyzed statistically in this study. Indentation tests were first conducted on fresh specimens. One half of the specimens of each organ were then frozen (preserved at −12 °C), and the other half of the specimens were cooled (preserved at 4 °C). All preserved specimens were retested after 20 days. Force and displacement data recorded during indentation were analyzed using a quasi-linear viscoelastic model. The results show that both cooling and freezing storage increased the kidney stiffness. In contrast, both storage methods decreased the stiffness of the spleen specimens. While cooling increased the liver stiffness, no significant changes of the instantaneous elastic response were observed in the liver specimens preserved by freezing. The liver and spleen’s reduced relaxation responses and the liver’s instantaneous elastic response were significantly different when comparing between cooling and freezing effects after 20 days of preservation. This study showed that both cooling and freezing storage methods significantly changed the material properties of abdominal organs, especially the instantaneous elastic response. More research is needed in investigating the effect of preservation on failure properties and mechanical properties under large deformation.

Rotordynamic instability due to fluid flow in seals is a well known phenomenon that can occur in pumps as well as in steam turbines and air compressors. While analysis methods using bulk-flow equations are computationally efficient and can predict dynamic properties fairly well for short seals, they often lack accuracy in cases of seals with complex geometry or with large aspect ratios (L/D above 1.0). This paper presents the linearized rotordynamic coefficients for a liquid seal with large aspect ratio subjected to incompressible turbulent flow. The fluid-induced forces acting on the rotor are calculated by means of a three-dimensional computational fluid dynamics (3D-CFD) analysis, and are then expressed in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients. For comparison, the seal dynamic coefficients were calculated using two other codes: one developed with the bulk flow method and one based on the finite difference method. The three sets of dynamic coefficients calculated in this study were used then to predict the rotor dynamic behavior of an industrial pump. These estimations were then compared to the vibration characteristic measured during the pump shop test, results indicating that the closest agreement was achieved utilizing the CFD generated coefficients. The results of rotor dynamic analysis using the coefficients derived from CFD approach, improved the prediction of both damped natural frequency and damping factor for the first mode, showing substantially smaller damping factor which is consistent with the experimentally observed instability of the rotor-bearing system. As result of continuously increasing computational power, it is believed that the CFD approach for calculating fluid excitation forces will become the standard in industry.