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

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

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.

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

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

Top row - 2024, 6061 Bottom Row - 7075, Brass 260

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

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

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

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

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

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

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

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

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

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

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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

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

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

Microstructure FFT Titanium Alloy 21

Microstructure FFT 22

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

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