Rolf H. Eppinger

Chestband Analysis of Human Tolerance to Side Impact

A series of 26 human cadaver tests with chestband instrumentation and accelerometers were completed to assess side impact injury tolerance. A Heidelberg-type sled test system was used with thorax, abdomen, and pelvic load plates. Tests were conducted at two different velocities: 24 kph and 32 kph. Test conditions included rigid wall, padded wall, and pelvic offset. Accelerations were recorded at rib 4, rib 8, and T12. Up to three chestbands were placed on each surrogate. Injury criteria including the Average Spine Acceleration (ASA) 15N, Thoracic Trauma Index (TTI), normalized chest deflection, and Viscous Criterion (VC) were computed. Resulting injuries ranged from Abbreviated Injury Scale (AIS) 0 to AIS 5. Rib fractures were the most common injury. In general, measured parameters were higher for high velocity tests compared to low velocity tests. The padded wall condition produced lower peak forces, accelerations, and chest deflections compared to the rigid wall condition. A new injury criterion combining TTI and the maximum normalized chest deformation parameter (Max%C) was derived. This criterion yielded the best statistical outcomes compared to any of the other injury criteria. The present test protocol including extensive measurements of cadaver specimens provides a means to develop a most efficacious injury criterion for side impact. (A) For the covering abstract of the conference see IRRD E201172.

A THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF THE HUMAN BRAIN UNDER COMBINED ROTATIONAL AND TRANSLATIONAL ACCELERATIONS

Finite element modelling has been used to study the evolution of strain in a model of the human brain under impulsive acceleration loadings. A cumulative damage measure, based on the calculation of the volume fraction of the brain that has experienced a specific level of stretch, is used as a possible predictor for deformation-related brain injury. The measure is based on the maximum principal strain calculated from an objective strain tensor that is obtained by integration of the rate of deformation gradient with appropriate accounting for large rotations. This measure is used here to evaluate the relative effects of rotational and translational accelerations, in both the sagittal and coronal planes, on the development of strain damage in the brain. A new technique for the computational treatment of the brain-dura interface is suggested and used to alleviate the difficulties in the explicit representation of the cerebrospinal fluid layer existing between the two solid materials.

The Axial Injury Tolerance of the Human Foot/Ankle Complex and the Effect of Achilles Tension

Axial loading of the foot/ankle complex is an important injury mechanism in vehicular trauma that is responsible for severe injuries such as calcaneal and tibial pilon fractures. Axial loading may be applied to the leg externally, by the toepan and/or pedals, as well as internally, by active muscle tension applied through the Achilles tendon during pre-impact bracing. The objectives of this study were to investigate the effect of Achilles tension on fracture mode and to empirically model the axial loading tolerance of the foot/ankle complex. Blunt axial impact tests were performed on forty-three (43) isolated lower extremities with and without experimentally simulated Achilles tension. The primary fracture mode was calcaneal fracture in both groups. However, fracture initiated at the distal tibia more frequently with the addition of Achilles tension (p < 0.05). Acoustic sensors mounted to the bone demonstrated that fracture initiated at the time of peak local axial force. A survival analysis was performed on the injury data set using a Weibull regression model with specimen age, gender, body mass, and peak Achilles tension as predictor variables (R2 = 0.90). A closed-form survivor function was developed to predict the risk of fracture to the foot/ankle complex in terms of axial tibial force. The axial tibial force associated with a 50% risk of injury ranged from 3.7 kN for a 65 year-old 5th percentile female to 8.3 kN for a 45 year-old 50th percentile male, assuming no Achilles tension. The survivor function presented here may be used to estimate the risk of foot/ankle fracture that a blunt axial impact would pose to a human based on the peak tibial axial force measured by an anthropomorphic test device.

Dynamic Axial Tolerance of the Human Foot-Ankle Complex

Dynamic axial impact tests to isolated lower legs were conducted at the Medical College of Wisconsin laboratory in the USA. The aim is to develop a more definitive and quantitative relationship between biomechanical parameters such as specimen age, axial force, and injury. Twenty-six intact adult lower legs excised from unembalmed human cadavers were tested under dynamic loading using a mini-sled pendulum device. Results from these tests were combined with the data from the studies by Wayne State University and Calspan Corporation, both in the USA. The total sample size available was 52. Statistical analysis of these data was performed using Weibull techniques. Age and dynamic axial force were the most significant discriminant variables that defined the injury risk function. Consequently, the probability of foot-ankle injury was described in terms of specimen age and force. The findings are a first step towards the quantification of the dynamic tolerance of the human foot-ankle complex under the axial impact modality.For the covering abstract of the conference see IRRD 891635.

Computational Analysis of Head Impact Response Under Car Crash Loadings

A computational procedure for estimating damage on the soft tissue of the brain, by replicating transitional and rotational dynamic loads experienced during actual crash testing has been described. Data from 3-2-2-2 array of accelerometers located within the dummy headpart are used to extract a complete 6 DOF characterization of the headpart translational and rotational velocity and momentum field. These data are used as input to a finite element model of the brain to compute Cumulative Strain Damage Measure values in response to dynamic loads applied using actual crash test data.

DEVELOPMENT OF AN IMPROVED THORACIC INJURY CRITERION

In this study, seventy-one frontal impact sled tests were conducted using post-mortem human subjects in the drivers position in an effort to better understand thoracic trauma in frontal impacts. Various contemporary automotive restraint systems were used. The resulting injury from the impact was determined through radiography and detailed autopsy, and its severity was coded according to the Abbreviated Injury Scale (AIS). The measured mechanical responses were analyzed using statistical procedures. In particular, linear logistic regression was used to develop models which associate the measured mechanical parameters to the observed thoracic injury response. Univariate and multivariate models were developed taking into consideration potential confounders and effect modifiers. The risk factors used in the models were normalized concerning the size and weight of the specimen. The gender and age of specimen at time of death were found not to be confounders in this data set. A linear combination of the 3-msec clip value of maximum resultant spine acceleration and maximum normalized chest deflection from an array of five measurements provided the goodness of fit measure. This linear combination was found to have significantly better injury predictive ability, for thoracic trauma in human subjects under any restraint environment, than other existing injury criteria such as VCmax ( Maximum Viscous Criterion), chest deflection, or chest acceleration alone. For the covering abstract of the conference see IRRD E201429.

QUANTIFICATION OF SIDE IMPACT RESPONSES AND INJURIES

Side impacts have been shown to produce a large portion of both serious and fatal injuries within the total automotive crash problem. These injuries are produced as a result of the rapid changes in velocity an automobile occupants body experiences during a crash. Any improvement to the side impact problem will be brought about by means which will ultimately modify the occupants rapid body motions to such a degree that they will no longer produce injuries of serious consequence. Accurate knowledge of both the bodys motion and resulting injuries under a variety of impact conditions is needed to achieve this goal. Possession of this knowledge will then permit development of accurate anthropomorphic test devices and injury criteria which can be used to create effective injury countermeasures in vehicles.

Thoracic trauma assessment formulations for restrained drivers in simulated frontal impacts

Using cadaveric specimens, sixty-three simulated frontal impacts were performed to examine and quantify the performance of various contemporary automotive restraint systems. To characterize the mechanical responses during the impact, test-specimens were instrumented with accelerometers and chest bands. The resulting thoracic injury severity was determined using detailed autopsy and was classified using the Abbreviated Injury Scale.

Instrumentation of Human Surrogates for Side Impact

The validity of chestband under side impact loading conditions was assessed through a single 40-channel chestband and a NHTSA SID. The chestband was wrapped around the thorax section at the SID at its uppermost portion. Six tests were run at 4.5, 5.7 and 6.7 m/s impact velocities with round and flat surface impactors. These tests established the validity of using the chestband in side impact. After establishing the feasibility of the chestband, its practically in obtaining data from human cadavers with varying input conditions was determined. Five tests were done, each with a different configuration. Overall, the tests showed the robustness of the chestband.

Human Response to and Injury from Lateral Impact

Lateral impacts have been shown to produce a large portion of both serious and fatal injuries within the total automotive crash problem. These injuries are produced as a result of the rapid changes in velocity that an automobile occupants body experiences during a crash. In an effort to understand the mechanisms of these injuries, an experimental program using human surrogates (cadavers) was initiated. Initial impact velocity and compliance of the lateral impacting surface were the primary test features that were controlled, while age of the test specimen was varied to assess its influence on the injury outcome. Instrumentation consisted of 24 accelerometer channels on the subjects along with contact forces measured on the wall both at the thoracic and pelvic level. The individual responses and resulting injuries sustained by 11 new subjects tested at the University of Heidelberg are presented in detail. An examination of the relationship between forces applied and responses observed in the thorax is discussed. The average injuries for different sled test conditions are presented based on a total of 42 cadaver tests (11 of which are the ones discussed above). The comparison of rigid wall and padded wall sled tests is made based on these average injuries. For the covering abstract of the conference see HS-036 716. (Author/TRRL)