Microstructure Characterization Using X-ray Computed Tomography ...

Microstructure Characterization Using X-ray Computed Tomography

Description of X-ray CT

¾ X-ray CT is a nondestructive technique used for materials microstructure characterization ¾ The scan procedure is as follows: » A source transmits X-rays with certain intensity » Part of the radiation gets absorbed, part gets scattered, and the rest penetrate through the specimen » The intensity of the transmitted X-rays are measured by the X-ray detector » The specimen rotates 360 to transmit rays from all possible directions » The linear attenuation coefficients (μ), which are a property of the material, are used to estimate the different phases of the specimen and to construct the images: I = I o exp ∫ − μ (x , y ) ds ray

1

X-ray CT Process

Tomography

Image processing

2-D images

2-D analysis

3-D analysis

X-ray CT Equipment ¾ The X-Tek X-ray Core Scanner offers both microfocusCT and high power mini-CT within the same cabinet system. ¾ By utilising the precision manipulator to move the sample between two adjacent beam lines the system provides an intuitive method of interchanging between microfocus-CT and mini-CT. ¾ The system is capable of taking microfocus data up to 225kV and scatter free data (at resolutions up to 200mm/pixel) up to 350kV on denser samples.

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225 kV X-ray Source

100 mm diameter specimen

350 kV X-ray Source Specimen Carrier

225 kV X-ray Source

50 mm diameter specimen

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X-ray CT Equipment ¾ X-ray source specification » Source 1: X-Tek 350 kV Mini-focus X-ray Source X-ray Tube: Target: Power: Focal spot: Cooling:

Metal/Ceramic 350/0.5 Tungsten 600W 0.5mm to EN 122543 Closed Loop air-oil

» Source 2: X-Tek 225 kV Micro-focus X-Ray Source X-ray tube: Fitted with 225-Watt air cooled target Voltage: 20 to 225kV Beam current: 0 to 2mA max Power: 225W Focal spot size: 3 - 5μm

X-ray CT Equipment ¾ CT Manipulator specification – 350kV cabinet » The system is fitted with a high precision 5-axis manipulator with the following specifications: 9 Precision stepper motor driven ball screws with joy-stick and CNC control Options capable of 10000:1 speed variation 9 X,Y,Z axis travel 600mm (0.0025mm to 25mm/sec) 9 Rotate axis – continuous rotation stage (72 degrees/sec to 8.3x10-4 degrees/sec) 9 Max loading capacity 25kg 9 Precision over whole scan area better than +/- 0.2mm

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X-ray CT Equipment ¾ Imaging Specification » Imaging System 1: Microfocus beam-line Imaging System Detector type: Intensifier: Scintillator: Glass: Digitisation: Camera:

AREA – for Cone beam CT Industrial 6 inch X-ray image intensifier Low burn scintillator (Caesium Iodide) Non-browning glass 10bit digitisation with OCI (on Chip Integration) 768 x 572 pixel CCD camera

» Imaging System 2: High Energy, Scatter Free X-ray detector for mini-CT Detector type: LINEAR – for CT geometry and scatter rejection Detector length: 307mm Pixel size: 200mm x 200mm, binning X2, X4, X8 Dynamic Range: 12 bit, 4096 grey scales 350kV radiation protection / collimation

Applications

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Analysis of Air Void Distribution Thresholded Image to identify the amount and size of air voids

Grayscale image resulting from image processing

N

n=

14%

Statistical analysis of air voids

Percent Air Voids (%)

12% 10% 8%

∑ i =1

( Av )i AT N

Three dimensional air void structure

6% 4% 2% 0% Minimum

1st Quartile

Median

F (t ) = 1 − e

3rd Maximum Average Quartile

( θ )β

− t

,

t>0

Analysis of Connectivity and Air Void Flow Paths

k=

0.80

0.60

u c

0.40

0.20

3

2

2

0.00 0.00

Damage decreases

γ c.T .S μ n

1.00

N /N Nc/N u

¾ A method was developed for the analysis of air void connectivity and flow paths. ¾ This method was used to relate air void structure to permeability and moisture damage.

0.20

2

= 0.91 R2R=0.91

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

average diameter (mm) Average Diameter E(x)

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Simulation of Fluid Flow and Permeability ¾ Input: » X-ray CT image » Microstructure dimensions » Fluid properties

¾ Output: » Flow fields » Permeability directional distribution

Measurements of Moisture Transport ¾ An experimental setup using X-ray CT was used to: » Monitor water transport in asphalt mix » Calculate capillary rise » Estimate the capillary contact angle of the asphalt mix

Saturated specimen during X-ray CT scanning

Three dimensional view of the air voids filled with water due to capillary action after different soaking periods

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Discrete Element Analysis of Asphalt Mix Microstructure

Forensic Evaluation of Compaction Percent Air Voids (%) 0%

2%

4%

6%

8%

10%

12%

14%

0 20

D epth (m m )

40 60

Stone Filled

80 100 120

RBL

140 160

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Analysis of Mastic Damage

60

(1)

7.0E+07

55

6.0E+07

50

5.0E+07

45

FIP

(2)

4.0E+07

40 Nt

3.0E+07

35

2.0E+07

Stiffness 1.0E+07

SIP

(4)

30 25

Phase angle

0.0E+00

Phase angle (degree)

Stiffness (Pa)

8.0E+07

20 0

2000

4000

6000

8000

10000

No. of loading cycles

Analysis of Asphalt Mix Damage

M

Void Content =

∑A i =1

AT

v

Roundness =

P2 4πAv

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Analysis of Aggregate Shape

Traprock

∞

Uncrushed Gravel

Limestone

⎛ (2n + 1)(n − m)! ⎞ m imφ Ynm (θ ,φ ) = ⎜⎜ ⎟⎟ Pn (cos(θ )) e ⎝ 4π (n + m)! ⎠

n

r (θ ,φ ) = ∑ ∑ a nmYnm (θ ,φ ) n =0 m = − n

2π π

a nm = ∫ ∫ dφ dθ sin (θ ) r (θ ,φ ) Ynm* 0 0

Three-Dimensional Distribution of Aggregates Due to Compaction and Loading The aggregate distribution is included in a mechanistic model for predicting asphalt pavement performance L30B

L-Undeformed

18% 16% 14%

Frequency

12% 10% 8% 6% 4% 2% 0% 0

10

20

30

40

50

60

70

80

90

10