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

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
4. SFC 10mm plain Bar
5. SFC 12mm Ribbed Bar
6. NC 10mm Plain Bar
7. NC 10mm Ribbed Bar
9. NC 16mm Plain 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
Time(min)
Load(KN)
Elongation (mm)
200mm Overlap 150mm Overlap 100mm Overlap

• 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
Time(min)
Load(KN)
Elongation (mm)
SFC O10 NC O10 NC T10
SFC= Steel Fibre Concrete
NC= Normal Concrete
O= Normal Bar T= Ribbed Bar

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
Time(min)
Load(KN)
Elongation (mm)
NC T12 SFC T12
SFC= Steel Faber Concrete
NC= Normal Concrete
O= Normal Bar

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
Time(min)
Load(KN)
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
Displacemnet(mm)
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
Displacement(mm)
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
Displacemnet(mm)
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
Displacemnet(mm)
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
Displacemnet(mm)
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
Displacemnet(mm)
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
Displacements(mm)
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
Displacemnet(mm)
Time (min)

2D) and LVDT for The eleventh Specimen
25
0
1
2
3
4
5
6
0 5 10 15 20 25
Displacemnet(mm)
Time (min)

• 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_tresc
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
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
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
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
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
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

• X and Y coordinates, horizontal and vertical axes.
27

• U: Displacement Contour (mm) in x-D. for 8th specimen when load is 67 KN.
28

• V: Displacement Contour (mm) in y-D. for 8th specimen when load is 67 KN.
29

• exx: Normal strain contour in x-D. for 8th specimen when load is 67 KN.
30

• eyy: Normal strain contour in y-D. for 8th specimen when load is 67 KN.
31

• exy: Normal Shear strain contour for 8th specimen when load is 67 KN.
32

• e1: Principal strain contour in x-D. for 8th specimen when load is 67 KN.
33

• e2: Principal strain contour in y-D. for 8th specimen when load is 67 KN.
34

• gamma: Principal Shear strain contour for 8th specimen when load is 67 KN.
35

• Normal Strain in x-direction in failure mode of 8th specimen
36

• Normal Strain in x-direction during test for 8th specimen
37

• 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.
38

• 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;
39
3.26)31(73.473.4 5.5.
cc fE (Gpa)































12
22
11
12
22
11
8.00
012.
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(NormalStress)(N/mm2)
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
42
-60 -50 -40 -30 -20 -10 0 10 20
Sy(NormalStress)(N/mm2)
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
43
-60 -50 -40 -30 -20 -10 0 10 20
Sxy(NormalShearStress)
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
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
87 KN
75 KN
62.5 KN
50 KN
37.5 KN
25 KN
12.5 KN
0

Vertical Line (y=100mm)
46
-200 -150 -100 -50 0 50 100 150 200
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
3
22
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
3
22
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 3
22
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
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
67 KN
62 KN
52 KN
42 KN
32 KN
22 KN
12 KN
0

52
-40 -30 -20 -10 0 10 20 30 40 50 60
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
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
67 KN
62 KN
52KN
42 KN
32 KN
22 KN
12 KN
0

Vertical Line (x=5mm)
55
-200 -150 -100 -50 0 50 100 150 200
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.
57

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.
58

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.
60

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

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