Research On The Evaluation Of Fatigue Microcrack Expansion Of Powder Superalloy Based On Ultrasound

Powder superalloy,as key component material of advanced aircraft engine,results in fatigue,microcrack and crack growth due to mechanical alternative load function in long-term service process till the components have crack and lose efficacy.Therefore,the nondestructive evaluation of key component materials would play a key role in damage monitoring and residual life predication.The microcrack damage of powder superalloy is evaluated and researched with nonlinear Rayleigh wave technology,and the initiation and expansion process of fatigue microcracks is tracked.The main contents are as below:First,the ultrasonic nonlinear response mechanism of fatigue damage is researched,and the propagation characteristics and nonlinear growth mechanism of Rayleigh wave are analyzed to theoretically specify the possibility of nonlinear evaluation method of fatigue damage.Second,the preparation method and test scheme of two kinds of surface microcracks are designed to obtain a series of microcrack specimen in different fatigue damage states;The extension characters of fatigue microcracks of powder superalloy are researched to work out the small crack expansion rate and achieve the in-situ monitoring of fatigue microcracks expansion.Finally,the test system of nonlinear Rayleigh wave is established and the optimal test parameters are selected.The test system is used to test the microcrack prepared in two schemes to work out the corresponding relation between ultrasonic parameters and surface microcrack depth;The initiation and expansion process of fatigue microcracks is tracked to get the change rule of Rayleigh wave’s nonlinear coefficient and fatigue damage.The research results indicate that the microcrack in powder superalloy can be detected with nonlinear Rayleigh wave technology,and the nonlinear coefficient is more sensitive to the depth change of microcrack in comparison of fundamental current amplitude;Nonlinear coefficient tends to increase at first and then decrease with the accumulation of fatigue damage,is relatively sensitive to the early fatigue microcracks damage,and can achieve the quantitative characterization of fatigue microcracks with depth less than 0.25 λ.uut the nonlinear effect caused by macroscopic defect is relatively weak.