**4. Conclusion**

Bending fatigue test and tensile test were performed on aluminum alloy 2025 specimens and acoustic emission characteristics were recorded and examined in each of the tests. One of the purposes of this project was to investigate the feasibility of the acoustic emission method in detecting the initiation and growth of fatigue crack growth in Bonanza f33 propellers. The analysis of this method was performed by examining specimens of propeller with aluminum alloy 2025.

The first part of the tests, bending fatigue test with the aim of crack initiation and recording the acoustic emission signals emitted from the aluminum alloy 2025 specimen. After reviewing and analyzing the amplitude vs. standard cycle diagram and cumulative count vs. standard cycle diagram, it was determined that the sharp increase of the signal amplitude to the maximum signal and the sharp increase of the slope of the cumulative count occurs in the same standard cycle. This time can be attributed to crack initiation. The slope of the count vs. standard cycle at the start of crack initiation increases more than four times this slope from the start of the test.

The second part of the tests, the tensile test was performed to grow the cracks created in the previous stage and record the acoustic emission signals caused by the growth of fatigue cracks in aluminum alloy 2025. To determine the condition of the specimens and plot a stress–strain curve, first the tensile test was performed on a specimen of aluminum alloy 2025 without a notch. After plotting the stress–strain curve, the yield stress was equal to 275 MPa and the ultimate stress was equal to 381.67 MPa.

Analysis of the parameters and diagrams of count and stress vs. time in the tensile test shows an increase in the count with increasing force. The highest rate of crack growth occurs at the end of each test, because the highest number of counts, which indicates the internal events of a specimen, is observed at the end

*Determining the Characteristics of Acoustic Emission in the Fatigue Crack Growth of Aluminum… DOI: http://dx.doi.org/10.5772/intechopen.99360*

of the test. An increase in the number of counts in the loading phase indicates the growth of cracks.

As a final conclusion, despite the brittle material of aluminum alloy 2025, the acoustic emission method is a reliable, accurate, and high-efficiency method to identify the initiation and growth of fatigue crack in this aluminum alloy.
