introduction to digital image correlation (dic)
TRANSCRIPT
![Page 1: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/1.jpg)
Ian McEnteggart,
Instron® Composites Marketing Manager
An Introduction to
Digital Image Correlation (DIC)
![Page 2: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/2.jpg)
2
What is Digital Image Correlation?
Images Displacement Strain
Analysis of image
surface over time Use of cross correlation to
determine displacement
Strain calculated
from displacement
An optical method to measure deformation on an object’s surface
![Page 3: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/3.jpg)
3
• Non-contact strain measurement
• Full-field data (like thousands of tiny extensometers)
• Extract “conventional” 1D strain plots
• Identify strain hot spots over a large area
• Don’t need to know where to place the strain gauge/extensometer
before the test starts
• Validate correct specimen alignment
What are the Benefits of DIC?
![Page 4: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/4.jpg)
4
Sample Preparation
• Apply speckle pattern using:
• Airbrush
• Standard spray aerosol
• Brush—flicking
• Transferable stickers
• Rubber stamp
• Some materials can be left without speckling:
• Certain composites
• Concrete
• Textiles/fabric
![Page 5: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/5.jpg)
5
How Does It Work?
![Page 6: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/6.jpg)
6
Calculating Full-Field Displacement
• Repeated for each subset over the entire surface
• The result is a regular map of displacements over the
entire specimen surface
Specimen
surface image Split into
small subsets
Pattern
recognized
for each
subset
As the specimen deforms, axial (x)
and transverse (y) displacements
for each subset are calculated
![Page 7: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/7.jpg)
7
Calculating Strain
• Strain at each location is
calculated using central
differencing
• Strain calculated in the x and y
directions separately
• For the x direction:
∆𝐿 = 𝐿𝑡 − 𝐿0
𝜀 = ∆𝐿
𝐿0
![Page 8: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/8.jpg)
8
Analysis of Various Strain and Displacement Data
Axial
Strain Transverse
Strain Shear
Strain
Poisson’s
Ratio
Minimum
Normal Strain
Maximum
Normal Strain
Axial
Displacement Transverse
Displacement
![Page 9: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/9.jpg)
9
Extracting 1D Plots
• Use virtual extensometer for
calculating strain/displacement
between to points.
• Use virtual strain gauge for
calculating average strain over a
defined area.
![Page 10: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/10.jpg)
Advanced Video Extensometer (AVE) 2
& DIC Replay
![Page 11: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/11.jpg)
11
AVE 2: Versatile and Capable • Doesn’t require operator to attach extensometer, reducing
operator influence and increasing consistency
• 1 micron accuracy—measure modulus to ISO 527
• Patented LED lighting and fan system eliminates
environmental influences
• Measures both tensile and compressive strain
• Can be used on chambers for cold and hot tensile tests
• Can be used for full-field strain measurement using
Digital Image Correlation Software
![Page 12: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/12.jpg)
12
DIC Replay
• Streamlined full-field strain package tailored for the materials testing market
• Allows users to analyze advanced strain characteristics after the test
• No PhD degree required!
Simple integration & convenient mounting
•Consumes images saved by Instron® AVE camera
•No spaghetti cabling
•Synchronizes with data collected from the testing system
![Page 13: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/13.jpg)
13
Why Instron DIC?
Integrated and
synchronous
collection of all
data from
testing system,
e.g. force and
camera
Only 1 PC Integrated camera and
lighting unit sits on the
frame out of the way of
testing area. Polarized
light is used so ambient
light doesn’t matter.
Easy to use,
where users
can focus on
analyzing and
understanding
their results
rather than
assembling test
rigs.
![Page 14: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/14.jpg)
14
DIC Application Examples
• Multiple extensometers for the same sample
• Can decide location post test
![Page 15: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/15.jpg)
15
DIC Application Examples
• Component—Identify strain “hot spots”
![Page 16: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/16.jpg)
16
DIC Application Examples
• Foam specimen—Traditional strain measurement was not possible
• Speckled with felt pen • Split seen
in DIC
• Virtual extensometers at
25mm and 50mm GLs
![Page 17: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/17.jpg)
17
DIC Application Examples
• Composite Laminate—Open-Hole Tension
• Complex 2D strain distribution
• Measure all components of 2D strain tensor
(axial, transverse, shear), along with
maximum and minimum principle strains
Shear Strain
Axial Strain
![Page 18: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/18.jpg)
18
What Can We Do Next?
• If you’re interested in further discussions:
• Arrange a demonstration on site by our sales engineer
• Visit our applications laboratories and bring samples
• Send samples for us to test
![Page 19: Introduction to Digital Image Correlation (DIC)](https://reader031.vdocument.in/reader031/viewer/2022012322/55c15932bb61eb43408b4587/html5/thumbnails/19.jpg)
Thanks for your time!