digital image correlation

Master Project

1

Title: Application of 2-dimensional Digital Image

Correlation for mapping bond strain and stress distribution in concrete

Student:

Reza Aghlara (MA081038)

Supervisor:

Dr. Redzuan Abdullah

June 2010

Aim and Objectives 1. Application of 2-Dimensional Digital Image Correlation (2D-DIC) for

finding motion and deformation on concrete.

2. Mapping bond strain and stress component distribution on front plane of concrete pull-out specimen.

2

Rational of the study (Problem Statement)

1. 2D-DIC is a new method in the practical area, It is important to

researchers to know;

How someone can trust to the 2D-DIC? What's the accuracy rate of this measurement? What's the feature of this method? What are the requirements for doing this measurement?

• So, to answer these questions, more study and experiment should

have be done in this field.

3


2. Having full-field strain and stress measurements of concrete pull-out specimen can be helpful to whom are interested in realizing bond behavior precisely and it may change some conception or may find new ideas in the bond field. It is worth to note that finding of strain contour based on theoretical method as Finite Element Method depends on many factors, and bond simulation can not be done easily. But 2D-DIC strain analysis is based on experimental work and more reliable.

4

The Strain Contour of FEM Vs. 2D-DIC


3. 2D-DIC is more economical in comparison with the other common measurement method in lab works. For example, the below figure shows the configuration of a specimen have been done in previous for bond study purpose.

Study of The Bond with applying Strain Gauges

5

Study of The Bond with applying Strain Gauges

Scope and Limitation of the Project • Real bond stress distribution of a concrete pull-out specimen is 3-dimensional,

around the bar in concrete. 2D-DIC is capable to measure deformation on a plane. So the stress distribution due to the bond on the surface of the specimen will be calculated in this project.

• The bond strength depends on a lot of parameters as concrete property, bar

diameter and so on. The purpose of this project is mapping of stress distribution of bond and the effect of parameters to the bond is not the scope of the work.

• The ultimate bond strength may can be find with 2D-DIC but it needs different

configuration of specimen and it is not intention of this project.

6

Methodology of the Study (1/6)• Dimension of Specimens: • Eleven Specimen had been built with same dimension as above, with different

bar diameter as 10, 12, 16mm. the design of concrete mix has done based on the lab manual (C1) and the average gained 28 days cylindrical compressive strength was 31 Mpa. Three specimens concrete had steel fibre in mixture. Three of specimens had bars in both sides with overlapping in different length in concrete.

7

100 mm

400 mm

55 mm

400 mm

100

Methodology of the Study (2/6)

8

Material preparing

Molding and Bar installing

Casting

Curing


• List of specimen are as below and tests have been done respectively. SFC is the short of Steel Fiber Concrete and NC for Normal Concrete as well.

1. 20cm Overlap with 10mm Bar 2. 10cm Overlap with 10mm Bar 3. 15cm Overlap with 10mm Bar 4. SFC 10mm plain Bar 5. SFC 12mm Ribbed Bar 6. NC 10mm Plain Bar 7. NC 10mm Ribbed Bar 8. NC 12mm Ribbed Bar 9. NC 16mm Plain Bar 10. NC 16mm Ribbed Bar 11. SFC 16mm Ribbed Bar

9


• After doing Speckle pattern to specimen, the pull-out test have been done according figure.

• Some points on the test setup: Adjusting loading Speed .05 (KN/S). Installing LVDT as displacement recorder. Automatically taking picture per 2 second. Synchronizing between taking pictures and LVDT record.

10


• These are the last taken images of every test.

11

1 2 3 4 5 6 7 8 9 10 11


• After finishing pull-out test the below steps have been done respectively:

1. 2D-DIC analysis with Rapid Correlator and VIC-2D in order to find

displacement of the point which recorded by LVDT in all specimens.

2. Selecting two test results that their correlation results are close to LVDT result.

3. Doing Strain analysis for 2 selected test.

4. Mapping Strain Distribution.

5. Mapping Stress Distribution.

12

Data Collection and Analysis • Load-Elongation Chart for Specimens with various overlap length

Diameter

13

0

1

2

3

4

5

6

7

8

9

10

11

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Tim

e (m

in)

Loa

d (K

N)

Elongation (mm)

200mm Overlap 150mm Overlap 100mm Overlap

Data Collection and Analysis • Load-Elongation Chart for Specimens with 10mm Diameter

14

0

2

4

6

8

10

12

14

16

18

0

5

10

15

20

25

30

35

40

45

50

55

0 1 2 3 4 5 6

Tim

e (m

in)

Loa

d (K

N)

Elongation (mm)

SFC O10 NC O10 NC T10

SFC= Steel Fibre Concrete NC= Normal Concrete O= Normal Bar T= Ribbed Bar

Data Collection and Analysis

• Load-Elongation Chart for Specimens with 12mm Diameter

15

0

5

10

15

20

25

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

0 1 2 3 4 5 6

Tim

e (m

in)

Loa

d (K

N)

Elongation (mm)

NC T12 SFC T12

SFC= Steel Faber Concrete NC= Normal Concrete O= Normal Bar

Data Collection and Analysis • Load-Elongation Chart for Specimens with 12mm Diameter

16

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6

Tim

e (m

in)

Loa

d (K

N)

Elongation (mm)

NC T16 SFC T16 NC O16

SFC= Steel Fibre Concrete NC= Normal Concrete O= Normal Bar T= Ribbed Bar

Discussion of Results • Displacement of one point by correlation analysis (Rapid correlator and Vic-

2D) and LVDT for the Second Specimen

17

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5

Dis

plac

emne

t (m

m)

Time (min)

LVDT DIC ( Rapid Correlator) DIC (Vic-2D)


2D) and LVDT for The third Specimen

18

0

1

2

3

4

5

6

7

8

9

10

11

0 1 2 3 4 5 6

Dis

plac

emen

t (m

m)

Time (min)

DIC ( Rapid Correlator) LVDT DIC (Vic-2D)


2D) and LVDT for The fifth Specimen

19

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15

Dis

plac

emne

t (m

m)

Time (min)



2D) and LVDT for The Sixth Specimen

20

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 1 2 3 4 5 6 7 8 9 10

Dis

plac

emne

t (m

m)

Time (min)



2D) and LVDT for The Seventh Specimen

21

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 1 2 3 4 5 6 7 8 9 10

Dis

plac

emne

t (m

m)

Time (min)



2D) and LVDT for The eighth Specimen

22

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20

Dis

plac

emne

t (m

m)

Time (min)



2D) and LVDT for The ninth Specimen

23

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 5 10 15 20

Dis

plac

emen

ts (m

m)

Time (min)

LVDT DIC (Rapid Correlator) DIC (Vic-2D)


2D) and LVDT for The tenth Specimen

24

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25

Dis

plac

emne

t (m

m)

Time (min)



2D) and LVDT for The eleventh Specimen

25

0

1

2

3

4

5

6

0 5 10 15 20 25

Dis

plac

emne

t (m

m)

Time (min)


Discussion of Results • According to Previous charts, 2 specimens which have closer correlation

displacement to LVDT result, were selected to the strain analysis. Similarly, Vic-2D have been selected to correlation analysis because of reliable results in displacement.

• After inputting the taken images as data to software, making an image as reference, defining area of interest (AOI) and calibration, the program was run to analysis of the strain for 8th and 11th specimens.

• Totally the results of the software can be shown as table and contour as following:

26

"x" "y" "u" "v" "sigma" "x_c" "y_c" "u_c" "v_c" "exx" "eyy" "exy" "e1" "e2" "gamma" "e_tresca" "e_vonmises"786 73 -0.2 -9.0 0.02081 -62.5 197.4 -0.05 3.1 -0.00014 -0.00666 -0.00180 0.00033 -0.00713 -0.25255 0.00373 0.00365

791 73 -0.1 -9.2 0.02340 -60.8 197.4 -0.05 3.1 -0.00018 -0.00623 -0.00179 0.00031 -0.00672 -0.26699 0.00351 0.00344

796 73 -0.1 -9.2 0.02249 -59.0 197.4 -0.04 3.2 -0.00018 -0.00581 -0.00178 0.00034 -0.00633 -0.28196 0.00333 0.00325

801 73 -0.1 -9.3 0.02111 -57.3 197.4 -0.03 3.2 -0.00014 -0.00541 -0.00178 0.00040 -0.00595 -0.29653 0.00318 0.00308

806 73 0.0 -9.3 0.02083 -55.6 197.4 -0.02 3.2 -0.00009 -0.00503 -0.00176 0.00048 -0.00559 -0.30996 0.00303 0.00292

811 73 0.0 -9.3 0.02144 -53.9 197.4 -0.01 3.2 -0.00003 -0.00466 -0.00174 0.00055 -0.00524 -0.32155 0.00289 0.00277

Discussion of Results • X and Y coordinates, horizontal and vertical axes.

27

Discussion of Results • U: Displacement Contour (mm) in x-D. for 8th specimen when load is 67 KN.

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Discussion of Results • V: Displacement Contour (mm) in y-D. for 8th specimen when load is 67 KN.

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Discussion of Results • exx: Normal strain contour in x-D. for 8th specimen when load is 67 KN.

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Discussion of Results • eyy: Normal strain contour in y-D. for 8th specimen when load is 67 KN.

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Discussion of Results • exy: Normal Shear strain contour for 8th specimen when load is 67 KN.

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Discussion of Results • e1: Principal strain contour in x-D. for 8th specimen when load is 67 KN.

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Discussion of Results • e2: Principal strain contour in y-D. for 8th specimen when load is 67 KN.

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Discussion of Results • gamma: Principal Shear strain contour for 8th specimen when load is 67 KN.

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Discussion of Results • Normal Strain in x-direction in failure mode of 8th specimen

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Discussion of Results • Normal Strain in x-direction during test for 8th specimen

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Discussion of Results • So far, the strains have been found in every point of specimen by correlation

analysis. For having stress distribution on face of specimen, the specimen is assumed plain stress.

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Discussion of Results • According to Mechanic of material, constitutive equation for plane stress is;

• Average compressive concrete strength of specimens are 31 Mpa, so based on ACI318, Young module is calculated as below:

• With having E and assuming v=.2 the equation is simplified as;

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3.26)31(73.473.4 5.5. cc fE (Gpa)

12

22

11

12

22

11

8.00012.02.1

83.27395

Main Finding of the Project

• The normal and shear stress distribution have been calculated for specimen of 11th in 87 KN.

40

-184

-149

-115

-81

-46

-12

22

57

91

125

160

194

-62 -45 -28 -11 6

Sx(N/mm2)

-100--50 -50-0 0-50 50-100

-184

-149

-115

-81

-46

-12

22

57

91

125

160

194

Sy (N/mm2)

-200--100 -100-0 0-100 100-200

-184

-149

-115

-81

-46

-12

22

57

91

125

160

194

-62 -45 -28 -11 6

Sxy

-40--20 -20-0 0-20 20-40


• Normal Stress (Sx) changes by load increasing for specimen 11th on a horizontal Line (y=100mm)

41

-60 -50 -40 -30 -20 -10 0 10 20

Sx (N

orm

al S

tres

s) (N

/mm

2)

X-Coordinates on the width of Specimen (mm)

87 KN

75 KN

62.5 KN

50 KN

37.5 KN

25 KN

12.5 KN

0


• Normal Stress (Sy) changes by load increasing for specimen 11th on a horizontal Line (y=100mm)

42

-60 -50 -40 -30 -20 -10 0 10 20

Sy (N

orm

al S

tres

s) (N

/mm

2)


87 KN

75 KN

62.5 KN

50 KN

37.5 KN

25 KN

12.5 KN

0


• Normal Shear Stress (Sxy) changes by load increasing for specimen 11th on a horizontal Line (y=100mm)

43

-60 -50 -40 -30 -20 -10 0 10 20

Sxy

(Nor

mal

She

ar S

tres

s)


87 KN

75 KN

62.5 KN

50 KN

37.5 KN

25 KN

12.5 KN

0


• Normal Stress (Sx) changes by load increasing for specimen 11th on a Vertical Line (y=100mm)

44

-200 -150 -100 -50 0 50 100 150 200

Sx (N

orm

al S

tres

s) (N

/mm

2)

Y-Coordinates on the length of Specimen (mm)

87 KN

75 KN

62.5

50 KN

37.5

25 KN

12.5 KN

0


• Normal Stress (Sy) changes by load increasing for specimen 11th on a Vertical Line (y=100mm)

45

-200 -150 -100 -50 0 50 100 150 200

Sy (N

orm

al S

tres

s) (N

/mm

2)


87 KN

75 KN

62.5 KN

50 KN

37.5 KN

25 KN

12.5 KN

0


• Normal Shear Stress (Sxy) changes by load increasing for specimen 11th on a Vertical Line (y=100mm)

46

-200 -150 -100 -50 0 50 100 150 200

Sxy

(Nor

mal

She

ar S

tres

s)


87 KN

75 KN

62.5 KN

50 KN

37.5 KN

25 KN

12.5 KN

0


• The normal stress 3D distribution in x-direction (Sx) (N/mm²) have been calculated for specimen of 8th in 62 KN.

47

-178

-151

-124

-96

-69

-42

-14

13

41

68

95

123

150

177

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

200

-33-15

322

40

150-200

100-150

50-100

0-50

-50-0

-100--50

-150--100

-200--150

-250--200

-300--250

-350--300


• The normal stress 3D distribution in y-direction (Sy) (N/mm²) have been calculated for specimen of 8th in 62 KN.

48

-178

-151

-124

-96

-69

-42

-14

13

41

68

95

123

150

177

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

-33-15

322

40

50-100

0-50

-50-0

-100--50

-150--100

-200--150

-250--200

-300--250

-350--300

-400--350


• The Normal Shear stress 3D distribution (Sxy) (N/mm²) have been calculated for specimen of 8th in 62 KN.

49

-178

-151

-124

-96

-69

-42

-14

13

41

68

95

123

150

177

-80

-60

-40

-20

0

20

40

60

-33 -15 322 40

40-60

20-40

0-20

-20-0

-40--20

-60--40

-80--60


• Normal Stress (Sx) changes by load increasing for specimen 8th on a horizontal Line (y=100mm)

50

-40 -30 -20 -10 0 10 20 30 40 50

Sx (N

orm

al S

tres

s) (N

/mm

2)


67 KN

62 KN

52 KN

42 KN

32 KN

22 KN

12 KN

0


• Normal Stress (Sy) changes by load increasing for specimen 8th on a horizontal Line (y=100mm)

51

-40 -30 -20 -10 0 10 20 30 40 50 60

Sy (N

orm

al S

tres

s) (N

/mm

2)


67 KN

62 KN

52 KN

42 KN

32 KN

22 KN

12 KN

0


• Normal Shear Stress (Sxy) changes by load increasing for specimen 8th on a horizontal Line (y=100mm)

52

-40 -30 -20 -10 0 10 20 30 40 50 60Sxy

(Nor

mal

She

ar S

tres

s)


67 KN

62 KN

52 KN

42 KN

32 KN

22 KN

12 KN

0


• Normal Stress (Sx) changes by load increasing for specimen 8th on a Vertical Line (x=5mm)

53

-200 -150 -100 -50 0 50 100 150 200

Sx (N

orm

al S

tres

s) (N

/mm

2)


67 KN

62 KN

52KN

42 KN

32 KN

22 KN

12 KN

0 KN


• Normal Stress (Sy) changes by load increasing for specimen 8th on a Vertical Line (x=5mm)

54

-200 -150 -100 -50 0 50 100 150 200

Sy (N

orm

al S

tres

s) (N

/mm

2)


67 KN

62 KN

52KN

42 KN

32 KN

22 KN

12 KN

0


• Normal Shear Stress (Sxy) changes by load increasing for specimen 8th on a Vertical Line (x=5mm)

55

-200 -150 -100 -50 0 50 100 150 200

Sxy

(Nor

mal

She

ar S

tres

s)


67 KN

62 KN

52KN

42 KN

32 KN

22 KN

12 KN

0 KN

Conclusion

• From this research, we can realize that by taking some measurements into

accounts, the result of 2D Digital Image Correlation, with Nikon D80 which used for taking images, can be acceptable to some great extent. Some of these measurements are Camera setting during test, Specimens form, speckle pattern, using proper controller instrument during test as LVDT or extensometer and having efficient software to analysis the strain.

• Totally, the differences of correlation displacement with LVDT result for test 2,8 and 11 are respectively .08mm, .04mm and .39mm.

• The finding of this project and given points in recommendation may be helpful to students want to do some measurement with 2D-DIC to have less errors in their project.

56

Conclusion

• Mapping full-field 3D Strain and Stress distribution due to the bond can help and improving our understanding about its behavior in concrete.

• Ultimately The computed deformation fields with 2D-DIC can be used to validate the FEM or theoretical analysis and to bridge the gap between experiment, simulation and theory.

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Recommendation

• For camera setting, following suggestions are useful and will give acceptable

result, Shoot Mode: Auto or Sport Mode F-number (aperture) : 3.5 – 4 Shutter Speed (Exposure time) : 60-100 µs Camera Distance from Specimen: 1.5 m Illumination : Yes Flash: No

• Camera should be adjusted in a level strong tripod and be fixed during the test

and optical view of camera should be perpendicular to front face of Specimen.

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Recommendation

• Synchronization should be prepared between speed rate of loading, speed rate of imaging and recording of LVDT or other controller instruments.

• For having more accurate measurement the q-imaging and cooled camera should be used.

• For study of bond, the configuration of specimen should design somehow, any

unwanted strain or stress will not disturb and combine with bond stress.

• The specimen configuration should be designed somehow during loading any unwilling motion has not been occurred. Its better 2 sides be involved to avoid free motion.

• On the face of specimen should some points defined with accurate distance for calibration purpose in correlation software.

59

Recommendation

• The speckle pattern is very important to match process in software. It can be

done with white and black spray.

• For having best result, it is suggested after every experimental test, correlation analysis to examine, in order to find unexpected errors.

• For having more confidence on result of correlation analysis, using more

controller instruments is necessary like LVDT and Extensometer.

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Recommendation

• More investigation field in bond by 2D-DIC can be suggested as:

Anchorage length of different diameter of reinforcement. Finding Theoretical formula for bond strength. Obtaining exact requirement of concrete area around different diameter of bar. Behavior of bond stress in vicinity of discontinuity area.

61

Thanks

62

digital image correlation

Engineering