Brian M. Boggess

UPPER EXTREMITY INTERACTION WITH A DEPLOYING SIDE AIRBAG: A CHARACTERIZATION OF ELBOW JOINT LOADING

Computer simulations, dummy experiments with a new enhanced upper extremity and small female cadaver experiments were used to analyze the small female upper extremity response under side airbag loading. After establishing a worst case initial position, three tests were performed with the fifth percentile female hybrid III anthropometric test dummy and six experiments with small female cadaver subjects. A new fifth percentile female enhanced upper extremity was developed for the dummy experiments that included a two-axis wrist load cell in addition to the existing six-axis load cells in both the forearm and humerus. Forearm pronation was also included in the new dummy upper extremity to increase the biofidelity of the interaction with the handgrip. Instrumentation for both the cadaver and dummy tests included accelerometers and MHD angular rate sensors on the forearm, humerus, upper and lower spine. In order to quantify the applied loads to the cadaver hand and wrist from the door mounted handgrip, the handgrip was mounted to the door through a five-axis load cell and instrumented with accelerometers for inertial compensation. All six of the cadaver tests resulted in upper extremity injuries including comminuted mid-shaft humerus fractures, osteochondral fractures of the elbow joint surfaces, a transverse fracture of the distal radius and an osteochondral fracture of the lunate carpal bone. The results from the 6 cadaver tests presented in this study were combined with the results from 12 previous cadaver tests. A multivariate logistic regression analysis was performed to investigate the correlation between observed injuries and measured occupant response. Using inertially compensated force measurements from the dummy mid-shaft forearm load cell, the linear combination of elbow axial force and shear force was significantly (P=0.05) correlated to the observed elbow injuries.

INJURY RISK FUNCTION FOR THE SMALL FEMALE WRIST IN AXIAL LOADING

Previous experiments with human cadavers and side airbags revealed the potential for wrist injuries as a result of the hand becoming entrapped in the handgrip. The purpose of this paper was to develop an injury tolerance for the small female wrist that may be used in the design phase of side airbags in order to reduce the risk of wrist injuries resulting from side air bag deployment. Small female cadaver upper extremities were used to develop the wrist tolerance as a conservative estimate of the most vulnerable section of the driving population. The energy source was a pneumatic impactor that was configured to match the force onset rate, impulse, and peak force in order to simulate the load profile of a deploying side airbag. A total of 17 (n=17) axial impact experiments were performed on the wrists of small female cadavers. Post-test necropsy revealed that 9 of the 17 tests resulted in wrist injuries. The injury patterns were identical to those observed from cadaver tests with side airbags and included fractures of the scaphoid (AIS 2), lunate (AIS 1), distal radius (AIS 3), and distal ulna (AIS 2). Using the injury outcome as the binary variable, a logistic regression analysis was performed. When mass scaled to the fifth female, the analysis produced an injury risk function that predicts a 50% risk of injury at a wrist load of 1700 N (P=0.0037). Risk of injury was found not to be dependent of subject bone mineral density (P=0.49), age (P=0.99), mass (P=0.31), and stature (P=0.69). Based on the similarities in impact load profile and observed injury patterns between the impactor tests and the side airbag tests, it is suggested that the injury risk function will accurately predict the risk of wrist injuries in the automobile crash environment.

Injuries of the head from backface deformation of ballistic protective helmets under ballistic impact.

Modern ballistic helmets defeat penetrating bullets by energy transfer from the projectile to the helmet, producing helmet deformation. This deformation may cause severe injuries without completely perforating the helmet, termed “behind armor blunt trauma” (BABT). As helmets become lighter, the likelihood of larger helmet backface deformation under ballistic impact increases. To characterize the potential for BABT, seven postmortem human head/neck specimens wearing a ballistic protective helmet were exposed to nonperforating impact, using a 9 mm, full metal jacket, 124 grain bullet with velocities of 400–460 m/s. An increasing trend of injury severity was observed, ranging from simple linear fractures to combinations of linear and depressed fractures. Overall, the ability to identify skull fractures resulting from BABT can be used in forensic investigations. Our results demonstrate a high risk of skull fracture due to BABT and necessitate the prevention of BABT as a design factor in future generations of protective gear.

Injury Risk Functions for the 5th Percentile Female Upper Extremity

The widespread implementation of air bags has increased the incidence of upper extremity injuries in the automotive crash environment. The first step in reducing these injuries is to determine applicable upper extremity injury criteria. The purpose of this paper is to develop injury risk functions for the fifth percentile female forearm, humerus, wrist, and elbow. Injury tolerance data for each anatomical region were gathered from experiments with controlled impact loading of disarticulated small female cadaver upper extremities. This technique allowed for the applied load to be directly quantified. All data were mass scaled to the fifth percentile female. In order to develop the risk functions, the logit distribution was integrated for the uncensored data, while logistic regression and generalized estimating equations statistical analysis techniques were used for censored data. The risk functions predict a 50% risk of injury at 128 Nm bending of the humerus, 58 Nm bending of the forearm, 1700 N axial loading of the wrist, and 1780 N axial loading of the elbow. A modified dummy upper extremity has been designed for the evaluation of frontal and side air bag interactions, and it is recommended that the injury criteria be implemented directly in the dummy upper extremity.

Application of the Scientific Method to the Analyses in Forensic Science With Case Example

Analysis of the failure of a mechanical device requires investigation of the circumstances surrounding the failure, inspection of the mechanical device, interpretation of the information gathered during that inspection, and reverse engineering of the incident, with the end goal of reaching a conclusion as to the cause and mechanism of the failure. Often during the process of post-failure forensic analysis, hypotheses are posited to explain the failure. As an investigative engineer, the formulation of hypotheses to explain the failure often occurs after the initial investigation is conducted and the engineer has a general understanding of the conditions present at the time of the failure. If hypotheses are developed before the investigation begins, there may be too many hypotheses to consider. The hypotheses are then tested to determine their strength and false hypotheses are discarded. True hypotheses are assembled into an explanation of the failure. There is often insufficient physical evidence available to establish the exact configuration of a device after a failure. Regardless of the reason why the failed part is not present, the parties involved may dictate a need to determine the cause of the failure. When the device or failed part is not available, other techniques in addition to a physical test of the failed part must be used to test hypotheses and evaluate the cause of the failure. Examples of such techniques are (1) using information on the performance of the machine to determine possible failure mechanisms and progressions and (2) reported accounts of the machine and its environment by operators or surrounding witnesses. The current study investigates the relationship of witness observations to the analysis of example mechanical failures. Various aspects of how witnesses observe and process their observations are discussed as well as the caution needed in considering witness observations due to incomplete observations or potential benefit to the witness. The use of Failure Mode Effects Analysis in determining the cause of a failure is discussed, most notably in an extension of this technique to analyzing operator error. One particular real world example where the allegedly failed part was not available throughout the investigation is discussed in detail. The results of this study show that witness accounts of a failure should be considered by the engineer when determining the cause of a failure and that ignoring witness accounts can lead to unsubstantiated and possibly incorrect conclusions.Copyright