PhD Defense by Joseph Nathaniel Robinson

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Joseph Nathaniel Robinson
(Advisor: Prof. Mavris)

will defend a doctoral thesis entitled,

Rotor Fatigue Life Prediction and Design for Revolutionary Vertical Lift Concepts


Friday, July 22 at 11:00 a.m.

Conference Room #304

Weber Space Science and Technology Building (SST II)


Zoom: gatech.zoom.us


Despite recent technological advancements, rotorcraft still lag behind their fixed-wing counterparts in the areas of flight safety and operating cost. Both must be addressed to ensure the continued competitiveness of vertical lift aircraft. Lifecycle costs and accident rates are strongly driven by scheduled replacement or failure of flight-critical components. Fatigue failure of rotor blades accounts for a significant proportion of these incidents. Traditional fatigue design methods are hindered by a lack of physics-based capabilities in the early design stages. These methods are strongly dependent on extrapolations built on historical fatigue data, and make use of deterministic safety factors based on organizational experience to ensure fatigue reliability.

A new preliminary fatigue design methodology is designed to address these concerns. A multi-disciplinary analysis (MDA) environment combining the rotorcraft performance code NDARC, the comprehensive code RCAS, and the beam analysis program VABS, is developed to provide accurate physics-based stress predictions on flight-critical components. A conceptual transport helicopter design is implemented within the MDA. To account for the computational expense of the MDA, surrogate modeling techniques are used to approximate the stress response across the flight envelope of the transport helicopter. Various surrogate modeling techniques are compared to determine which is the most suitable for predicting fatigue stress.

Next, structural reliability solution methods are investigated as a means to produce high-reliability fatigue life estimates without requiring any deterministic safety factors. The Miner's sum fatigue life prediction model is reformulated as a structural reliability problem, and analytical solutions, sampling solutions, and hybrid solutions are compared using a notional fatigue life problem. These results are validated using a realistic helicopter fatigue life problem.

Finally, the capabilities of the preliminary fatigue design methodology are demonstrated using a series of hypothetical fatigue design exercises. The methodology is used to predict the impact of rotor blade design variables, vehicle layout and configuration, and the design mission requirements. The methodology is proven to be capable of quantifying the influence of most of the tested design variables, paving the way for implementation in a rotorcraft design framework.



  • Prof. Dimitri Mavris – School of Aerospace Engineering (advisor)
  • Dr. Alexia Payan – School of Aerospace Engineering
  • Prof. Marilyn Smith – School of Aerospace Engineering
  • Prof. Daniel Schrage – School of Aerospace Engineering
  • Prof. Kyle Collins – Research Assistant Professor, Embry-Riddle Aeronautical University


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