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.

Experimental evaluation of underride analysis techniques and empirical validation of a new analytical technique.

Accident reconstructionists are often faced with damage patterns and locations on vehicles that are not well defined by available barrier impact data. One such example is a frontal underride collision. Underride impacts occur when there is a height mismatch between the primary structural components of the impacting vehicles, and the vehicle with the lower height is forced beneath the structure of the other vehicle. The lack of structural engagement typically allows for significantly different damage patterns due to the inherently lower stiffness of the underriding vehicle's contacting surfaces coupled with complex interactions between varying surfaces. In this study, a series of two-vehicle impact tests between a small pickup (bullet vehicle) and a large dump truck (target vehicle) were performed and studied. These tests involved a severe underride configuration in which the dump truck bed's vertical alignment was above the base of the windshield of the pickup. Coupled with these impacting surfaces was a single vertical support, a remnant of a commonly referred to ICC (Interstate Commerce Commission) bumper, which caused a narrow object-type impact, but did not extend down to the pickup's bumper. Multiple prior authors' analytical and empirical relationships to predict impact speed based on crush damage were evaluated using the results of these tests as well as other published underride tests. No single model was sufficient at predicting the mixed mode of impact present in these impact scenarios. However, a system of equations was developed to predict the impact parameters utilizing a combination of previously reported methods and a new empirical relationship presented in this study. This new method shows high correlation and supports the authors' hypothesis that separate crush models can be applied to multiple discrete areas of a vehicle and then combined to form a more complete predictive systematic model.

Fracture tolerance of the small female elbow joint in compression: the effect of load angle relative to the long axis of the forearm.

The purpose of this study was to develop a fracture tolerance for the elbow joint, or proximal ends of the ulna and radius, relative to the fracture risk under side-impact airbag loading. Forty experiments were performed on the elbow joints of small female cadavers. The energy source, a pneumatic impactor, was configured to apply compressive loads that match the onset rate, peak force, and momentum transfer of previously conducted side-impact airbag tests with small female subjects. Three initial orientations of the impact load angle relative to the longitudinal axis of the forearm were selected based on analysis of side-impact airbag tests with the instrumented dummy upper extremity. These included loading directions that are 0 degrees , 20 degrees , and 30 degrees superior of the longitudinal axis of the forearm. Post-test necropsy revealed that 11 of the 40 tests resulted in chondral, osteochondral, or comminuted fractures of the proximal radial head or the distal trochlear notch. Using the fracture outcome as the binary variable, a generalized estimating equations statistical analysis showed a significant correlation between elbow load angle (p < 0.01) and risk of fracture, as well as peak elbow force (p = 0.04) and risk of fracture. Using data that were mass scaled to the 5(th) percentile female, the analysis produced a multivariate fracture risk function that predicts a 50% risk of elbow fracture at a compressive elbow load of 1780 N and load angle of 30 degrees superior to the longitudinal axis of the forearm (p < 0.01). It is anticipated that this tolerance will be used to reduce the risk of elbow fractures from side airbag deployment.