Characterized the crack nucleation and early crack growth of PH 13-8 Mo stainless and 4340 steel subjected to fretting fatigue. Linked acoustic emission signals with specific damage accumulation mechanisms. Evaluated a number of critical plane theories in light of fretting fatigue test results, and determined which are applicable to the rotorcraft steels under investigation. Determined that the influence that contact geometry has on crack growth may not be as significant as the influence that other fretting fatigue parameters have. Developed a database for evaluating the growth of small cracks in PH 13-8 Mo stainless steel.
Results show a direct correlation between fatigue surface damage and microstructure, viz.
The objective of this study is to develop a methodology for fatigue reliability and lifetime prediction of metallic structural components, and apply it to components and systems with a potential for experiencing critical failure. Developed a robust, quantitative, waveform-based testing procedure to quantify acoustic emission signals from test samples experiencing torsion fatigue and fretting fatigue. Related waveform characteristics from measured acoustic emission signals to specific deformation and damage phenomena in steel samples under investigation. The objective of this study is to investigate and develop acoustic emission methods for mechanical fault diagnosis. Identified that the phase of loading amplitude is a key parameter in analyzing acoustic emission data as a function of the state of damage or age of a material subjected to fatigue.