1. Analysis of Metallic Structure with Ultrasonic Nondestructive Evaluation
By: Carter Sawin and Will Marks
Mentored by: Dr. Peter Collins and Matt Kenney

2. Goals
To analyze various treatments for samples of aluminum and brass with ultrasonic non-destructive evaluation (NDE)
As ordered / cold worked / heat treated
To develop an understanding of how the fast Fourier transform (FFT) operates in MATLAB
Linking the FFT from NDE to micro structural features that are present but not visible

3. Alloys Used Brass 260 Aluminum 2024 Aluminum 6061 Aluminum 7075
Cartridge brass, most ductile yellow brass
Aluminum 2024
Cu, average machinability
Aluminum 6061
Mg and Si, good machinability
Aluminum 7075
Zi, average machinability
Cartridge Brass is most famously used for bullet casings, plumbing, and fasteners. Good cold-working properties
Al 2024 has a high strength-to-weight ratio and excellent fatigue resistance. Often used in aircraft structures
Al 6065 is used as a construction material and for aircraft and automotive parts.
Al 7075 is very strong and also expensive. Used in sports equipment like bikes and lacrosse sticks and in firearms.

4. Cutting and Treatment Al samples were all ordered at 6in*6in*2in
Final samples are 1in*2in*1in
Brass sample was ordered at 6in*6in*1in
Cold working
One sample for each metal
Heat treating
Two samples for each Al alloy, one for brass

5. Cold Working Aluminum first machined down to 2in*2in*3in
Rolled in industrial roller
Samples cut out afterwards
Goal was 50% reduction
Material issues prevented this
15% reduction instead due to equipment
issues

6. Top row , 6061
Bottom Row , Brass 260

7. Heat Treatment Two samples of each metal underwent heat treatment
Precipitation heat treatment (aging) was used
Recrystallized grain structure and strengthened samples
Samples first heated to annealing temperature.
Breaks down metallic structure for recrystallization
Samples then quenched to prepare for aging
Ageing process strengthens metal by incorporating the precipitates created into the grain structure

8. Ultrasonic NDE Uses high frequency sound pulses
Picks up an “echo” from reflected sound waves
Detects imperfections in metals
Can also examine grain structure of metal samples
Will perform at the Center for Nondestructive Evaluation

9. The Fourier Transform Takes an input of a spatial domain (image)
Outputs the frequency domain
Calculates for each pixel of an image
We used fft in MATLAB to perform our calculations

10. Parts of the FFT Process
Will go through the various parts of the FFT process
Describe what information can be obtained with FFT This is the original image that is used in the following slides

11. Magnitude of the Image Image mean is spot in center
Not much information for complex images
Use a logarithmic transform to get more information 11
Found by taking the absolute value of the absolute value of the FT
Center spot only part visible because the range of the intensity values of the FT are too large to be shown
More information can be gained from the mag in simpler striped images.
Can show the frequency and direction of stripes or other patterns

12. Logarithmic Transform
Extracts more information from magnitude
Lines show dominating directions in image 12

13. Phase of the Image Acts as a map for recreating the image
Creates a matrix of phase angles
Values between -π and π
Recreating the image with just the mag does not work 13

14. Combining the Phase and Mag
Multiply magnitude with the phase
Needs to be in complex double form (a+bi) for ifft
Operation combines and puts in correct form
Taking ifftn of this recreates the original image 14

15. Recreating a Full Image
Need to split image in two,
FFT both sides, and use those
to recreate the full original
image. 15

16. Seeing the Whole Picture
Two successful methods that achieved the final goal
First method: Instead of cutting the original image in half, taking those FFTs, the two image halves were taken, but the entire original resolution was preserved by filling the half without information with middle-grey. 16

17. 17

18. Results
The image is nearly identical to the original image, but the original image’s contrast is clearer. Image is therefore, less crisp.
Cannot preserve lightest lights and darkest darks 18

19. Split Recreation with Phase
Take average mag of the ffts
Combine average mag with phases
Use cat to put sides together 19

20. Results Result is not as sharp and a little darker
Darkness comes from averaging of magnitudes 20

21. Microstructure FFT
Titanium Alloy 21

22. Microstructure FFT 22

23. NDE and FFT
Knowledge of FFT allows us to effectively analyze the results of the NDE of our Aluminum and brass samples
FFTs allow for pattern analysis of the samples
Lets us analyze the effects of heat treatment and cold working on metal samples
Can easily compare and contrast the two 23

24. Future plans Not finished as of now In the following weeks:
Test samples
Compare and contrast the results of the ultrasound between the as ordered, heat treated, and cold worked samples 24