Joseph Pellettiere

Civil Aviation Crash Injury Protection

The Federal Aviation Administration (FAA) has adopted safety requirements intended to protect aircraft occupants during survivable crash scenarios. These requirements include design specifications, static strength tests and dynamic impact tests of seats and restraint systems using instrumented Anthropomorphic Test Devices (ATD). Two orientations of impact test are cited: a combined longitudinal/vertical test with the impact vector 60° from horizontal, and a longitudinal test with the impact vector yawed 10° from the centerline of the aircraft. Injury potential is assessed during the dynamic tests by comparing test results to a set of injury criteria. The static and dynamic test requirements vary by aircraft type due to the differences in energy transmitted to the seats. However, the injury criteria evaluated during these tests are very similar for all aircraft types. The criteria cited in the regulations are: the Head Injury Criteria (HIC), lumbar spine compressive load, shoulder strap load, femur compressive load (for passengers of transport aircraft only), a requirement that the seat belt not bear on the abdomen, and that the shoulder belts (if used) bear on the shoulder.

Assessment of Ear- and Tooth-Mounted Accelerometers as Representative of Human Head Response

Monitoring head accelerations as an indicator of possible brain injury may lead to faster identification of injury and treatments. This study investigates the coupling of a tri-axial accelerometer mounted to a back molar and compares it with that of a tri-axial accelerometer inserted in the boney ear canal. Both of these tri-axial accelerometers were mounted to three post mortem human surrogate (PMHS) skulls, and compared with a rigidly mounted laboratory sensor reference cube. Each specimen was subjected to a high loading from a vertical drop tower and a low frequency cyclic loading from a shaker device. The specimens were subjected to an approximate 150g input acceleration on the drop tower, and up to 35g at a frequency of 9Hz on the shaker device. Each specimen was tested on all three of the anatomical axes on both the drop tower and the cyclic shaker. Both the tooth-mounted accelerometer and the ear-mounted accelerometer were is close agreement with each other, and compared favorably with the rigid reference accelerometers. The coupling of the tooth with the skull did produce an amplification of the resultant acceleration, but maintains the basic biofidelity required to develop a simple transfer function for the sensor data. Planned future work includes testing three PMHS skulls in a similar fashion with the focus of the study being on how the skull deforms under high-g loading. There is evidence that the skull deforms under the loading conditions previously tested, but the magnitude and locations of these deformations remain unknown. A 3D optical system called ARAMIS will be utilized to track real-time skull deformation and analyzed to determine the rate at which the skull deforms and rotates so that these measurements can be compared to established metrics for rotation rates that contribute to concussion and mild traumatic brain injury (mTBI). By having a better understanding of the possible local mechanisms that may contribute to mTBI, better safety systems can be designed to ensure the best possible protection for people ranging from athletes to soldiers.

Impact of Numerical Model Verification and Validation Within FAA Certification

The mission of the Federal Aviation Administration (FAA) is to provide the safest, most efficient aerospace system in the world. The FAA Aircraft Certification Service is responsible for the design and production approval and airworthiness certification of all U.S. civil aviation products. Historically, design approval has required physical tests, however the FAA allows for the use of modeling and simulation (M&S) to demonstrate compliance with federal regulations. This allows an applicant to reduce the number of tests required to certify a design by relying on the results of M&S. As with all M&S use, verification and validation are fundamental in establishing the credibility of the computational models of aircraft components. Through several government-industry workshops, there is an apparent need for better guidance and training for both parties to understand how to communicate M&S and Verification and Validation (V&V) activities to support certification decisions. Current efforts focus on the level of detail required to document the M&S and V&V activities by an applicant such that the FAA can make an informed certification decision resulting in safe aircraft.

Preliminary Calibration and Validation of a Finite Element Model of THOR Mod Kit Dummy

New vehicles are currently being developed to transport crews to space by NASA and several commercial companies. During the takeoff and landing phase, vehicle occupants are typically exposed to spinal and frontal loading. To reduce the risk of injuries during these common impact scenarios, NASA has begun research to develop new safety standards for spaceflight. The THOR, an advanced multi-directional crash test dummy, was chosen by NASA to evaluate occupant spacecraft safety due to its improved biofidelity.Recently, a series of modifications were completed by the National Highway Traffic Safety Administration (NHTSA) to improve the bio-fidelity of the THOR dummy. The updated THOR Modification Kit (THOR-K) dummy was tested at Wright-Patterson (WP) Air Base in various impact configurations, including frontal and spinal loading. A computational finite element (FE) model of the THOR was developed in LS-DYNA software and was recently updated to match the latest dummy modifications. The main goal of this study was to calibrate and validate the FE model of the THOR-K dummy for use in future spacecraft safety studies.An optimization-based method was developed to calibrate the material properties of the pelvic flesh model under quasi-static and dynamic loading conditions. Data in a simple compression test of pelvic flesh were used for the quasi-static calibration. The whole dummy kinematic and kinetic response under spinal loading conditions was used for the dynamic calibration. The performance of the calibrated dummy model was evaluated by simulating a separate dummy test with a different crash pulse along the spinal direction. In addition, a frontal dummy test was also simulated with the calibrated model. The model response was compared with test data by calculating its correlation score using the CORA rating system.Overall, the calibrated THOR-K dummy model responded with high similarity to the physical dummy in all validation tests. Therefore, confidence is provided in the dummy model for use in predicting response in other test conditions such as those observed in the spacecraft landing.Copyright

Certification by analysis and simulation validation

Modelling and simulation is increasingly being used to represent occupant behaviour of human subjects and anthropomorphic test devices. Future trends are towards the application of certification by analysis whereby a product, such as an aircraft seat, can be partially certified through analytical means. A robust and objective method to discriminate different features of the model comparison is needed to determine model validity so that the certification authority can objectively determine the model acceptability. Expert opinion could introduce bias and lead to inconsistent results. In any testing, there is some inherent uncertainty and variation in the measured responses that affects the baseline comparison data. Each individual response should be treated as a separate case. A method derived from Sprague and Geers was developed and applied to occupant models of seat simulations. Using test data, acceptable error levels were calculated that represent the uncertainty and provide consistent and objective results.