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Technical Paper

The Field Relevance of NHTSA's Oblique Research Moving Deformable Barrier Tests

A small overlap frontal crash test has been recently introduced by the Insurance Institute for Highway Safety in its frontal rating scheme. Another small overlap frontal crash test is under development by the National Highway Traffic Safety Administration (NHTSA). Whereas the IIHS test is conducted against a fixed rigid barrier, the NHTSA test is conducted with a moving deformable barrier that overlaps 35% of the vehicle being tested and the angle between the longitudinal axis of the barrier and the longitudinal axis of the test vehicle is 15 degrees. The field relevance of the IIHS test has been the subject of a paper by Prasad et al. (2014). The current study is aimed at examining the field relevance of the NHTSA test.
Technical Paper

Opportunities for Injury Reduction in US Frontal Crashes: An Overview by Structural Engagement, Vehicle Class, and Occupant Age

An overview NASS study of US frontal crashes was performed to investigate crash involvement, driver injury distributions and rates in airbag equipped vehicles by vehicle class and structural engagement. Frontal crash bins were based on taxonomy of structural engagement, i.e., Full Engagement, Offset, Between Rails and Corner impact crashes. A new classification of Corner impacts included frontal small overlap impacts with side damage as coded by NASS CDS. Belted drivers of two age groups, between 16 and 50 and over 50 years old, were considered. Vehicles were grouped into light and heavy passenger cars and lights trucks, and vans. A method to identify and address overly influential NASS weights was developed based on considerations of weighting factor statistics. The new taxonomy, with an expanded definition of corner impacts, allowed a more comprehensive classification of frontal crash modes.
Technical Paper

Biomechanical Assessment of a Rear-Seat Inflatable Seatbelt in Frontal Impacts

This study evaluated the biomechanical performance of a rear-seat inflatable seatbelt system and compared it to that of a 3-point seatbelt system, which has a long history of good real-world performance. Frontal-impact sled tests were conducted with Hybrid III anthropomorphic test devices (ATDs) and with post mortem human subjects (PMHS) using both restraint systems and a generic rear-seat configuration. Results from these tests demonstrated: a) reduction in forward head excursion with the inflatable seatbelt system when compared to that of a 3-point seatbelt and; b) a reduction in ATD and PMHS peak chest deflections and the number of PMHS rib fractures with the inflatable seatbelt system and c) a reduction in PMHS cervical-spine injuries, due to the interaction of the chin with the inflated shoulder belt. These results suggest that an inflatable seatbelt system will offer additional benefits to some occupants in the rear seats.
Technical Paper

Evaluation of the Field Relevance of Several Injury Risk Functions

An evaluation of the four injury risk curves proposed in the NHTSA NCAP for estimating the risk of AIS≻=3 injuries to the head, neck, chest and AIS≻=2 injury to the Knee-Thigh-Hip (KTH) complex has been conducted. The predicted injury risk to the four body regions based on driver dummy responses in over 300 frontal NCAP tests were compared against those to drivers involved in real-world crashes of similar severity as represented in the NASS. The results of the study show that the predicted injury risks to the head and chest were slightly below those in NASS, and the predicted risk for the knee-thigh-hip complex was substantially below that observed in the NASS. The predicted risk for the neck by the Nij curve was greater than the observed risk in NASS by an order of magnitude due to the Nij risk curve predicting a non-zero risk when Nij = 0. An alternative and published Nte risk curve produced a risk estimate consistent with the NASS estimate of neck injury.
Technical Paper

Impact Response and Biomechanical Analysis of the Knee-Thigh-Hip Complex in Frontal Impacts with a Full Human Body Finite Element Model

Changes in vehicle safety design technology and the increasing use of seat-belts and airbag restraint systems have gradually changed the relative proportion of lower extremity injuries. These changes in real world injuries have renewed interest and the need of further investigation into occupant injury mechanisms and biomechanical impact responses of the knee-thigh-hip complex during frontal impacts. This study uses a detailed finite element model of the human body to simulate occupant knee impacts experienced in frontal crashes. The human body model includes detailed anatomical features of the head, neck, shoulder, chest, thoracic and lumbar spine, abdomen, pelvis, and lower and upper extremities. The material properties used in the model for each anatomic part of the human body were obtained from test data reported in the literature. The human body model used in the current study has been previously validated in frontal and side impacts.
Technical Paper

Interactions of Out-of-Position Small-Female Surrogates with a Depowered Driver Airbag

The objectives of this study were to examine the response, repeatability, and injury predictive ability of the Hybrid III small-female dummy to static out-of-position (OOP) deployments using a depowered driver-side airbag. Five dummy tests were conducted in two OOP configurations by two different laboratories. The OOP configurations were nose-on-rim (NOR) and chest-on-bag (COB). Four cadaver tests were conducted using unembalmed small-female cadavers and the same airbags used in the dummy tests under similar OOP conditions. One cadaver test was designed to increase airbag loading of the face and neck (a forehead-on-rim, or FOR test). Comparison between the dummy tests of Lab 1 and of Lab 2 indicated the test conditions and results were repeatable. In the cadaver tests no skull fractures or neck injuries occurred. However, all four cadavers had multiple rib fractures.
Technical Paper

Biomechanical Analysis of Knee Impact in Frontal Collisions through Finite Element Simulations with a Full Human Body Model

This study applies a detailed finite element model of the human body to simulate occupant knee impacts experienced in vehicular frontal crashes. The human body model includes detailed anatomical features of the head, neck, chest, thoracic and lumbar spine, abdomen, and lower and upper extremities. The material properties used in the model for each anatomic part of the human body were obtained from test data reported in the literature. The total human body model used in the current study has been previously validated in frontal and side impacts. Several cadaver knee impact tests representing occupants in a frontal impact condition were simulated using the previously validated human body model. Model impact responses in terms of force-time and acceleration-time histories were compared with test results. In addition, stress distributions of the patella, femur, and pelvis were reported for the simulated test conditions.
Technical Paper

Analysis and Evaluation of the Biofidelity of the Human Body Finite Element Model in Lateral Impact Simulations According to ISO-TR9790 Procedures

The biofidelity of the Ford Motor Company human body finite element (FE) model in side impact simulations was analyzed and evaluated following the procedures outlined in ISO technical report TR9790. This FE model, representing a 50th percentile adult male, was used to simulate the biomechanical impact tests described in ISO-TR9790. These laboratory tests were considered as suitable for assessing the lateral impact biofidelity of the head, neck, shoulder, thorax, abdomen, and pelvis of crash test dummies, subcomponent test devices, and math models that are used to represent a 50th percentile adult male. The simulated impact responses of the head, neck, shoulder, thorax, abdomen, and pelvis of the FE model were compared with the PMHS (Post Mortem Human Subject) data upon which the response requirements for side impact surrogates was based. An overall biofidelity rating of the human body FE model was determined using the ISO-TR9790 rating method.
Technical Paper

Derivation and Theoretical Assessment of a Set of Biomechanics-based, AIS2+ Risk Equations for the Knee-Thigh-Hip Complex

A set of risk equations was derived to estimate the probability of sustaining a moderate-to-serious injury to the knee-thigh-hip complex (KTH) in a frontal crash. The study consisted of four parts. First, data pertaining to knee-loaded, whole-body, post-mortem human subjects (PMHS) were collected from the literature, and the attendant response data (e.g., axial compressive load applied to the knee) were normalized to those of a mid-sized male. Second, numerous statistical analyses and mathematical constructs were used to derive the set of risk equations for adults of various ages and genders. Third, field data from the National Automotive Sampling System (NASS) were analyzed for subsequent comparison purposes.
Technical Paper

Effect of Head-Neck Position on Cervical Facet Stretch of Post Mortem Human Subjects during Low Speed Rear End Impacts

The purpose of this study was to determine the effect of head-neck position on cervical facet stretch during low speed rear end impact. Twelve tests were conducted on four Post Mortem Human Subjects (PMHS) in a generic bucket seat environment. Three head positions, namely Normal (neutral), Zero Clearance between the head and head restraint, and Body Forward positions were tested. A high-speed x-ray system was used to record the motion of cervical vertebrae during these tests. Results demonstrate that: a) The maximum mean facet stretch at head restraint contact occurs at MS4 and MS5 for the Body Forward condition, b) The lower neck flexion moment, prior to head contact, shows a non-linear relationship with facet stretch, and c) “Differential rebound” during rear end impact increases facet stretch.
Technical Paper

Biomechanics of 4-Point Seat Belt Systems in Frontal Impacts

The biomechanical behavior of 4-point seat belt systems was investigated through MADYMO modeling, dummy tests and post mortem human subject tests. This study was conducted to assess the effect of 4-point seat belts on the risk of thoracic injury in frontal impacts, to evaluate the ability to prevent submarining under the lap belt using 4-point seat belts, and to examine whether 4-point belts may induce injuries not typically observed with 3-point seat belts. The performance of two types of 4-point seat belts was compared with that of a pretensioned, load-limited, 3-point seat belt. A 3-point belt with an extra shoulder belt that “crisscrossed” the chest (X4) appeared to add constraint to the torso and increased chest deflection and injury risk. Harness style shoulder belts (V4) loaded the body in a different biomechanical manner than 3-point and X4 belts.
Technical Paper

Prediction and Analysis of Human Thoracic Impact Responses and Injuries in Cadaver Impacts Using a Full Human Body Finite Element Model

Human thoracic dynamic responses and injuries associated with frontal impact, side impact, and belt loading were investigated and predicted using a complete human body finite element model for an average adult male. The human body model was developed to study the impact biomechanics of a vehicular occupant. Its geometry was based on the Visible Human Project (National Library of Medicine) and the topographies from human body anatomical texts. The data was then scaled to an average adult male according to available biomechanical data from the literature. The model includes details of the head, neck, ribcage, abdomen, thoracic and lumbar spine, internal organs of the chest and abdomen, pelvis, and the upper and lower extremities. The present study is focused on the dynamic response and injuries of the thorax.
Technical Paper

Structural Response of Lower Leg Muscles in Compression: A Low Impact Energy Study Employing Volunteers, Cadavers and the Hybrid III

Little has been reported in the literature on the compressive properties of muscle. These data are needed for the development of finite element models that address impact of the muscles, especially in the study of pedestrian impact. Tests were conducted to characterize the compressive response of muscle. Volunteers, cadaveric specimens and a Hybrid III dummy were impacted in the posterior and lateral aspect of the lower leg using a free flying pendulum. Volunteer muscles were tested while tensed and relaxed. The effects of muscle tension were found to influence results, especially in posterior leg impacts. Cadaveric response was found to be similar to that of the relaxed volunteer. The resulting data can be used to identify a material law using an inverse method.
Technical Paper

The Effects of Skull Thickness Variations on Human Head Dynamic Impact Responses

Variations in human skull thickness affecting human head dynamic impact responses were studied by finite element modeling techniques, experimental measurements, and histology examinations. The aims of the study were to better understand the influences of skull thickness variations on human head dynamic impact responses and the injury mechanisms of human head during direct impact. The thicknesses of the frontal bone of seven human cadaver skulls were measured using ultrasonic technology. These measurements were compared with previous experimental data. Histology of the skull was recorded and examined. The measured data were analyzed and then served as a reference to vary the skull thickness of a previously published three-dimensional finite element human head model to create four models with different skull thickness. The skull thicknesses modeled are 4.6 mm, 5.98 mm, 7.68 mm, and 9.61 mm.
Technical Paper

Lower Limb: Advanced FE Model and New Experimental Data

The Lower Limb Model for Safety (LLMS) is a finite element model of the lower limb developed mainly for safety applications. It is based on a detailed description of the lower limb anatomy derived from CT and MRI scans collected on a subject close to a 50th percentile male. The main anatomical structures from ankle to hip (excluding the hip) were all modeled with deformable elements. The modeling of the foot and ankle region was based on a previous model Beillas et al. (1999) that has been modified. The global validation of the LLMS focused on the response of the isolated lower leg to axial loading, the response of the isolated knee to frontal and lateral impact, and the interaction of the whole model with a Hybrid III model in a sled environment, for a total of nine different set-ups. In order to better characterize the axial behavior of the lower leg, experiments conducted on cadaveric tibia and foot were reanalyzed and experimental corridors were proposed.
Technical Paper

Finite Element Model Development of Sid-Iis

This paper describes the development and validation of a finite element model of the SID-IIs beta+-prototype dummy using a nonlinear explicit finite element code. The geometry of the SID-IIs dummy is modeled with shell and solid elements from digital scans. The material properties are derived from dynamic tests and the model validation is conducted on component, subassembly and full assembly levels. Component level validation of the head/neck, arm, ribs, and lumbar spine is presented. The model validation of the thorax and pelvis subassemblies as well as pendulum calibration tests (shoulder, thorax, abdomen, and pelvis) and rigid-wall sled tests of the fully assembled dummy mode is also presented. The model response compares favorably with experimental data and provides a reasonable level of confidence in the model biofidelity.
Technical Paper

Dynamic Axial Tolerance of the Human Foot-Ankle Complex

Axial loading of the calcaneus-talus-tibia complex is an important injury mechanism for moderate and severe vehicular foot-ankle trauma. To develop a more definitive and quantitative relationship between biomechanical parameters such as specimen age, axial force, and injury, dynamic axial impact tests to isolated lower legs were conducted at the Medical College of Wisconsin (MCW). Twenty-six intact adult lower legs excised from unembalmed human cadavers were tested under dynamic loading using a mini-sled pendulum device. The specimens were prepared, pretest radiographs were taken, and input impact and output forces together with the pathology were obtained using load cell data. Input impact forces always exceeded the forces recorded at the distal end of the preparation. The fracture forces ranged from 4.3 to 11.4 kN.
Technical Paper

Head Injury Potential Assessment in Frontal Impacts by Mathematical Modeling

The potential of head injury in frontal barrier impact tests was investigated by a mathematical model which consisted of a finite element human head model, a four segments rigid dynamic neck model, a rigid body occupant model, and a lumped-mass vehicle structure model. The finite element human head model represents anatomically an average adult head. The rigid body occupant model simulates an average adult male. The structure model simulates the interior space and the dynamic characteristics of a vehicle. The neck model integrates the finite element human head to the occupant body to give a more realistic kinematic head motion in a barrier crash test. Model responses were compared with experimental cadaveric data and vehicle crash data for the purpose of model validation to ensure model accuracy. Model results show a good agreement with those of the tests.
Technical Paper

Human Ankle Impact Response in Dorsiflexion

Although various automobile accident surveys showed between 20 to 30% of lower extremity injuries involved the foot or ankle, there is little information in the existing literature on the the injury mechanisms of ankle injuries for automobile occupants involved in frontal impacts. This study addresses the injury to ankles involving dorsiflexion caused by impact loading to the bottom of the foot. Types of injuries include malleolus fractures and ligament avulsions and ruptures. Nine pair of cadaver and two Hybrid 3 lower limbs were impacted on the bottom of the foot with a 16 kg pneumatically propelled linear impactor. A horizontally oriented bar struck the foot 62 mm distally of the ankle joint with velocities between 3 and 8 m/s. The proximal end of the tibia/fibula was fixed to a rigid support through a triaxial load cell. Load cells on the foot and impactor along with high-speed photography provided the response data of the foot and ankle.
Technical Paper

Dynamic Response and Mathematical Model of the Side Impact Dummy

A series of rigid wall tests have been conducted at three impact velocities to quantify the dynamic response of the Side Impact Dummy (SID) developed by US DOT. This paper reports the chest, pelvis and head responses of the dummy at various filter frequencies and describes the development and verification of the three-dimensional mathematical model of the Side Impact Dummy utilizing the rigid wall test results. The mathematical model uses the mass distribution and the linkage system of the current Part 572, Hybrid II dummy which forms the basic platform of the SID. The unique chest of the dummy is modeled by two systems of linkages simulating the rib cage and the jacket. Also included in the model is the internal hardware of the chest, e.g. a damper, rib stopper and a clavicle simulator at the upper spine. The material and linkage models are based on static and dynamic tests of the dummy components.