Joseph A. Pellettiere

Quantitative Method for Determining Cushion Comfort

Ejection seat cushions in current U.S. Air Force aircraft are not suitable for comfort during extended missions. Specific physiological problems such as buttock, leg and back pain, numbness and tingling in the extremities, and overall fatigue have been documented in past laboratory research and operational use [1,2,3,4,5]. Designing a single cushion to address the physiological problems of the entire aircrew population is a significant challenge. Cushion material selection, cockpit space restrictions, and limited ability to reposition during flight contribute to discomfort during extended missions. Ejection seat dimensions and contours are fixed in most cases, causing accommodation problems for large and small occupants and often times the cushion itself is the only item that can be replaced to improve comfort. A study was performed at the Air Force Research Laboratory at Wright-Patterson Air Force Base to investigate objective test methods for determining cushion comfort. Twenty volunteer subjects (12F, 8M) with a range of anthropometry were tested on a variety of operational and prototype cushions (four cushions total). Tests were conducted over eight-hour durations, during which subjective survey data were gathered along with performance data collected by completion of a cognitive task battery. Peak and average seated pressures and contact areas were measured for each cushion as comparative objective data. In all, 100 eight-hour tests were completed without an incident of deep vein thrombosis (DVT). Peak seated pressures ranged from 0.97 - 3.37 psi. The majority of the subjects showed no decrease in cognitive performance at the end of each test period; however, many showed a decrease in performance mid-study. The subjective measurements were found to correlate with objective parameters collected at the beginning of the test. This leads to the conclusion that seat cushion comfort can be objectively measured, but its impact on the performance of the subject is not very high. The four cushion combinations tested were used to develop a design guideline for peak pressure and contact area both to prevent DVT and to promote comfort for long duration use.

New Sensors to Track Head Acceleration during Possible Injurious Events

Abstract : Instrumented earplugs were first introduced in 2000 by the Air Force Research Lab (AFRL) as a means of measuring head accelerations in race car drivers after it was shown that instrumented helmets slipped on the head during impact events. A version of these earplugs was adopted by the Indy Racing League and Championship Auto Race Teams (CART) in 2003. In 2006, Begeman, Melvin, Troxel and Mellor reported that signals from earplugs mounted in cadavers showed a phase shift at 50 and 100 Hz vibration indicating less than perfect coupling with the head. This led to the development of a new miniature tri-axial accelerometer that is small enough to be placed in the ear canal portion of communication earplugs (earpieces) thereby improving the coupling and thus the reliability of the recordings from drivers undergoing multi-axial crash events.

Quantitative Methods for Determining U.S. Air Force Crew Cushion Comfort

Abstract : Designing a single cushion to address the physiological problems of the entire aircrew population is a significant challenge. Often the cushion itself is the only item that can be replaced to improve comfort. In this study 22 subjects were tested on Operational and prototype cushions, including one dynamic cushion. Tests were conducted over eight-hour durations, during which subjective survey data, cognitive performance data, seated pressures and contact areas, muscular fatigue levels, and lower extremity oxygen saturation were recorded. Peak seated pressures range from 1.22 - 3.22 psi. Oxygen saturation in the lower extremities decreased over the eight hours. Cognitive performance increased over time. Muscle fatigue increased throughout the eight hours regardless of cushion, with the exception of the dynamic cushion which promoted muscular recovery. Subjective comfort levels declined over the eight hours. Subjective measurements correlated with objective parameters for the static cushions. Trade-offs in performance and fatigue mitigation were apparent in the dynamic cushion which also highlighted differences between genders.

Dynamic tensile failure mechanics of the musculoskeletal neck using a cadaver model.

Although the catapult phase of pilot ejections has been well characterized in terms of human response to compressive forces, the effect of the forces on the human body during the ensuing ejection phases (including windblast and parachute opening shock) has not been thoroughly investigated. Both windblast and parachute opening shock have been shown to induce dynamic tensile forces in the human cervical spine. However, the human tolerance to such loading is not well known. Therefore, the main objective of this research project was to measure human tensile neck failure mechanics to provide data for computational modeling, anthropometric test device development, and improved tensile injury criteria. Twelve human cadaver specimens, including four females and eight males with a mean age of 50.1+/-9 years, were subjected to dynamic tensile loading through the musculoskeletal neck until failure occurred. Failure load, failure strain, and tensile stiffness were measured and correlated with injury type and location. The mean failure load for the 12 specimens was 3100+/-645 N, mean failure strain was 16.7+/-5.4%, and mean tensile stiffness was 172+/-54.5 N/mm. The majority of injuries (8) occurred in the upper cervical spine (Oc-C3), and none took place in the midcervical region (C3-C5). The results of this study assist in filling the existing void in dynamic tensile injury data and will aid in developing improved neck injury prevention strategies.

Optimization of Biomechanical Systems for Crashworthiness and Safety

The optimal performance of a safety device for crashworthiness and safety is studied in this paper. The problem is treated as the optimal control and optimization of a biomechanical system consisting of the safety device and occupant. The performance of this system is usually measured by certain injury criteria. The limiting performance analysis is implemented to find the best possible performance for the system. The parametric optimization is introduced for the optimal design of a safety device. Computational modeling and simulation of biomechanical systems is discussed with a brief description of various modeling techniques. The use of an Articulated Total Body model in the limiting performance analysis and parametric optimization is addressed in detail. The optimization of the safety performance of a type of ejection seat cushion is studied.

Modeling and Simulation of OOP Occupant-Airbag Interaction

This paper presents efforts made on the computational modeling and simulation of our-of-position occupant-airbag interaction. The airbag has been modeled using the finite element method with LSDYNA. The investigation in this paper shows that the integration of an FE airbag model with an ATB occupant model is a feasible and effective way of modeling and simulating the biodynamics of an occupant-airbag system. It takes the advantages of the detailed modeling of the airbag provided by FE and the efficient modeling of the occupant provided by ATB. The use of the integrated model in the simulations of unbelted occupant sled impact and static OOP deployment impact has produced fairly realistic demonstrations of the kinematical responses of the occupant.

Development of an updated tensile neck injury criterion

BACKGROUND Ejection neck safety remains a concern in military aviation with the growing use of helmet mounted displays (HMDs) worn for entire mission durations. The original USAF tensile neck injury criterion proposed by Carter et al. (4) is updated and an injury protection limit for tensile loading is presented to evaluate escape system and HMD safety. METHODS An existent tensile neck injury criterion was updated through the addition of newer post mortem human subject (PMHS) tensile loading and injury data and the application of Survival Analysis to account for censoring in this data. The updated risk function was constructed with a combined human subject (N = 208) and PMHS (N = 22) data set. RESULTS An updated AIS 3+ tensile neck injury criterion is proposed based upon human and PMHS data. This limit is significantly more conservative than the criterion proposed by Carter in 2000, yielding a 5% risk of AIS 3+ injury at a force of 1136 N as compared to a corresponding force of 1559 N. DISCUSSION The inclusion of recent PMHS data into the original tensile neck injury criterion results in an injury protection limit that is significantly more conservative, as recent PMHS data is substantially less censored than the PMHS data included in the earlier criterion. The updated tensile risk function developed in this work is consistent with the tensile risk function published by the Federal Aviation Administration used as the basis for their neck injury criterion for side facing aircraft seats.

Validation methods for finite element automobile crash modeling based on wavelet/wavelet packet decompositions

Validation methods for the finite element automobile crash modeling were developed using wavelet analysis. Based on the decompositions on wavelet packet bases, two types of signal energy distributions were established with respect to: (a) frequency index, and (b) time position and frequency index, which provide a common basis for the comparison between the simulation results and the test data in terms of the variation of amplitue with respect to frequency and time. Based on the decompositions on wavelet bases, correlation analysis was used to evaluate the differences in pulse shape and peak timing between the simulation results and the test data for the gross motions and major impact pulses. The use of the methods was illustrated in the validation of a 1997 Honda Accord finite element model for full frontal impact.

Validation Methods and Metrics for Biodynamics Modeling

Problems with the validation of biodynamics modeling and simulation are addressed in this paper. The wavelet analysis is introduced to the point-point comparison, a way of validating biodynamic responses. Biodynamic responses from the actual tests and the model simulations are decomposed on the wavelet or wavelet packet basis. The agreement between the simulation results and test data is evaluated in terms of the signal energy distributions and the correlation functions, which are determined from the wavelet or wavelet packet decompositions. Metrics are developed for the quantitative evaluation. The multi-resolution analysis provided by the wavelet decomposition can be used to effectively handle the model validation at different levels of accuracy and detail. The use of the methods and metrics is illustrated through the validation of a finite element automobile crash model.

Computational Analysis of Performance of Inflatable Toepan Padding for Mitigating Lower Limb Injuries

This paper reports on a computational investigation of the problem of lower limb injuries in automobile frontal crashes with the toepan intrusion, based on the rigid multibody dynamic modeling and simulation. The interaction between the lower limbs and the inflatable toepan padding was described by the contact between the feet and the load distribution plate of the padding. The investigation provided a view of the kinematics and dynamics of the system.