b'Ultrasonic Fatigue LifetimeA new fatigue laser ultrasonic measurement system has the potential to become Measurements: A Firsta standard tool to characterize fatigue in metals, including in situ applications Step to Developing awith complex and extreme processing conditions.MechanisticUnderstanding F atigue is the initiation and growth of microscale cracks in a material related to cyclic loading. Fatigue failure always occurs in a sudden manner. Although it is a primary failure mechanism of structure materials, the understanding of fatigue is limited. Due to fatigues stochastic nature, most fatigue models are empirically concluded from many experiments and specimens. It is extremely difficult to predict the fatigue lifetime of a single component, and preventing fatigue relies on costly safety margins.TOTAL APPROVED AMOUNT: $125,000 over 2 years This research explored the possibility of using a laser ultrasonic-based tool to predict fatigue life of individual components and study fatigue mechanisms. PROJECT NUMBER:Ultrasonic waves are sensitive to microscale crack generation and growth during the 20A1052-030 fatigue process. When the ultrasonic waves encounter microcracks, wave velocity, PRINCIPAL INVESTIGATOR:amplitude, and frequency change correspondingly. A system capable of performing Zilong Hua cyclic fatigue test and laser ultrasonic measurements on solid centimeter-size specimens was built, and a zero-group-velocity mode Lamb wave was investigated CO-INVESTIGATORS: to study fatigue. The zero-group-velocity plate wave has a high signal to noise ratio Cody Dennett, INL and is insensitive to the boundary conditions. Experiments using aluminum foil David Hurley, INL revealed a relationship between the zero-group-velocity wave propagation and Michael McMurtrey, INL the microstructure change, such as microstructure defect density increase and new Ryann Rupp, INL defects type generation.COLLABORATOR:Le Mans Universit, FranceFrequency spectrum showng zero-group-velocity plate wave changes before the test (black line) and before the final fracture (red line). Note the frequency peak shift, peak width change, and the appearance of multiple peaks near the main one.104'