Warning: include_once(../article_type.php): failed to open stream: No such file or directory in /home/suxhorbncfos/public_html/cerj/CERJ.MS.ID.555783.php on line 199
Warning: include_once(): Failed opening '../article_type.php' for inclusion (include_path='.:/opt/alt/php56/usr/share/pear:/opt/alt/php56/usr/share/php') in /home/suxhorbncfos/public_html/cerj/CERJ.MS.ID.555783.php on line 199
Throughout the years of development in laboratory testing of concrete some need has been urged to measure the deformations on the specimens. As there are some methods for this purpose such as putting sensors on the specimens, the need for a new method was still existed. Old fashion methodologies utilize long cables for measuring deformations. On the other hand, digital image correlation (DIC) is a remote technique which can be applied without any physical interaction with the specimen. Being relatively a low-cost option and measuring the displacements in micro level of precision made it very desirable for the researchers over the years. Materials such as concrete can be assumed to heterogeneous as it consists of steel reinforcements, pozzolans, cement, water, and aggregates. Therefore, failures along the concrete specimens can vary from very simple to very complex. Considering these reasons, determining any failure before happening or observing an existing deformation before the failure can be very critical. This paper represents the application of DIC on concrete specimens from relatively small laboratory samples to full-scale in-place specimens. A special attention has been made to the visualizing the failure modes of concrete with DIC. Some notable usages have been observed and noted.
Surface displacement measurement of materials is an important part of various laboratory experiments. The DIC technique is an innovative particle tracking method by which the in-plane surface deformations are measured by comparing the digital images of a specimen surface taken during the experiment . The increasing diffusion of DIC can be explained by its flexibility, scalability to a wide range of dimensions, the robustness of its operating principle, and its (apparent) ease of use” . DIC was defined as “a non-contact whole-field imaging technique that employs tracking and image registration for accurate two-dimensional (2D) and three-dimensional (3D) deformation and strain measurements. It is a technique based on surface analysis methods which involve monitoring and identifying changes in a pattern applied to the surface of objects under observation, that have been subjected to some form of mechanical pressure or strain as shown in (Figure 1). DIC method was developed in the early 1980’s for measuring surface displacements and deformation with the first system developed at the University of South Carolina” [3 & 4] .This method “requires a digital imaging system to optically record images of the surfaces before and after deformation. The pair of gray level functions of the images were then compared using advanced image correlation and processing
algorithms to determine the displacement and deformation gradients. Unlike laser speckle techniques, which required an optically rough, reflective surface and minimal vibration, the only requirement for surface condition was a visually speckled surface” . A faster approach for image correlation was later developed by Sutton, et al. . Instead of using the iterative approach, such as a coarse-fine method, a second order Newton-Raphson method was employed. A special technique “was then added to achieve a higher probability of convergence. This correlation method was later evolved into measuring in-plane and out-of-plane displacements using two video cameras separated by a predetermined distance. The lines of sight from two cameras may either be parallel to each other”  or form a pan angle between them . “As soon as two image points are matched by correlation methods, the three-dimensional coordinates of the physical point may be determined. A surface contour may be generated from one pair of stereo images, while a deformation measurement requires the correlation of four images: a stereo pair before deformation and another after deformation. DIC of speckle patterns for engineering applications has been used extensively in many applications to measure displacement components and deformation gradients of an object’s surface due to deformation for over four decades” .
DIC is based on “sets of images of the surface of the specimen
in the undeformed (reference) and deformed states (Figure 2).
DIC can be implemented both in a bi-dimensional (2D-DIC, with
a single camera) and a tri-dimensional (3D-DIC, using two or
more cameras) version. A calibration is necessary to initialize
the spatial correlation processes of DIC. The images are divided
in smaller sub-images (facets), and a matching algorithm is used
to match the facets between the reference and deformed states.
The displacement field is then computed. Subsequently, the strain
field is obtained by derivation” .
Friction Stir welding “is solid state welding process for joining
metals by plasticizing and consolidating materials around the
bond line using thermal energy produced from localized friction
forces .This welding method is applied in many aerospace
applications and is often required to inspect the welded region
for the integrity of the welds. The material properties of the weld
samples such as the Young’s modulus, yield stresses were also
determined from the stress-strain graphs obtained by using the
SPDIC tool. In addition, the pseudo colored strain contour maps
as shown in (Figure 3) indicated the area of maximum strain and
thereby predicting crack initiation in the sample” [11-12].
Particulate composites used for rocket fuels were analyzed
by using DIC techniques. The main objective of this work “was to
determine the high strain regions under low loading conditions
that would possibly indicate regions of eventual failure under high
loading conditions. This is important since the underlying causes
of failure such as microcracks or other surface/bulk defects are not always detected by traditional NDE techniques. (Figure 4)
shows the strain fields generated by using DIC for the particulate
composite test sample. From the results obtained, it was
demonstrated that there is a statistical distribution of high strain
regions within the particulate composites. Based on the result
obtained, it was demonstrated that DIC method may be used to
identify very early on regions of eventual failure, and may also
be used to change the distribution of particles in the particulate
composite so as to obtain improved material properties” .
Rotor blades “are usually subjected to high stresses due
to their weight and the force created by irregular winds. DIC
technique has been successfully employed to analyze these rotor
blades under normal to shear stress conditions as well as in the
bending fatigue test. GOM recently demonstrated the application
of DIC technique to monitor the strain fields on composite rotor
blade for helicopter drones in the laboratory environment
subjected to bending test” .
DIC technique “has also been successfully implemented to
inspect the shear panel subjected to shear load for mapping
whole-field out-of-plane displacement (buckling). GOM recently
demonstrated that the out-of-plane displacement map generated
from ARAMIS DIC software was in good agreement with the FEA
The concrete specimens, depending on its shape, can fail
under various types of failures. The failure mode depends highly
on the shape of the specimen as well as the action of forces i.e.
compression, tension etc. In cubically shaped concrete specimen’s
failure can be explosive or non-explosive, and its failure shape can
vary due to compression and shearing. In cylindrical specimens,
i.e. cores, failure mode are generally non-explosive and its shape
is depended on the type of forces acting on the specimen such as splitting, shear or splitting and shear. Also, during the testing of
the concrete specimen’s failure mode can be affected by lateral
restraint. It is the inequality of lateral expansion between the
steel plate of the compression apparatus and the actual specimens
surface that is subjected to compression. The effect of lateral
restraint eventually increases the shear stress which affects
the failure mode of the specimen. This shear stress causes the
specimen to fail through the center of it and with any explosive
effect. In addition, the failure generally starts from the surface
where the specimen is in contact with the platen of the apparatus. Generally, engineering materials for construction including
concrete, steel, rock etc. have some similar characteristics under
certain amount of loading. Typical examples of failures are
flexural compression failure, shear failure, compression failure
and buckling failure. Flexural failures occur when the shear
strength of the specimen is higher than the flexural strength.
Shear failures happen when the internal strength of the material
which is controlled by various parameters exceeded by the
applied load (Figure 5). Compression failures occur when the
specimen is axially loaded until the yield stress of the concrete is
expected to be exceeded. In this type of failure lateral expansion is
generally not expected. When the specimen has a certain amount
of height/width ratio buckling failure can be expected. Compared
to compression failure, buckling can be easily achieved since the
strength of the specimen will be much lower as well as the load
carrying capacity. Eventually, buckling will be observed outwards.
Choi & Shah  have utilized digital image correlation
technique to measure the deformations on concrete specimens.
The material itself assumed to be heterogenous thus making this
technique intriguing for such conditions. The authors have aimed
to use the technique to visualize the micro-cracks propagation.
They have found out that the deformations along the specimens
are not uniform even in the elastic range by using contour maps.Authors have noted that the technique can be very well used for
measuring the deformations as well as the crack propagation
throughout the laboratory testing. Shah & Choi  have chosen
digital image correlation technique to observe and visualize the
complex failure pattern in concrete blocks under compression.
They have also pointed out that DIC is very useful in determining
the microscopic fractures and strain localizations under loading
McGinnis et al.  have considered digital image correlation
technique for determining the in-situ stresses in concrete
structures. They have performed three-dimensional technique
and used core-drilling method for determining the displacements.
The core-drilling method can be used to determine stresses using
displacements. They have found out that the normal stresses were
calculated by an accuracy of 7 % with 3D digital image correlation
technique which was accepted as an accurate approximation.
Küntz et al.  have investigated the in-situ behavior of a shear
along a bridge on a reinforced concrete beam. They have analyzed
the behavior under static loading conditions by using a truck
passing and stopping from different locations. The authors have
concluded that this method can be used also for studying fatigue
behavior of concrete structures under this kind of conditions.
Corr et al.  have analyzed the surface contact area between
carbon fiber reinforced polymer and concrete blocks by using
digital image correlation technique. They have investigated
the displacement and fracturing around that region in terms of
the principles of fracture mechanics. According to their study,
they have indicated that DIC technique can be used for accurate
measurement of the displacements along the deforming materials.
Also, they have noted that based on this kind of experiments it
was even possible to build a constitutive law by using fracture
mechanics for experiments.
Helm  has utilized digital image correlation technique for
a challenging problem in concrete specimens. The author wanted
to measure the surface displacements of the specimens with
multiple crack propagation which he mentioned that it was a very
challenging task. Author have noted that DIC technique is very
effective for measuring multiple growing crack patterns. Shah &
Kishen  have investigated the contact behavior between the
different concrete specimens by using digital image correlation
technique. The specimens have different compressive strengths
and characteristics. Authors have pointed out that they were able
to calculate the surface and sliding displacements as well as the
properties of the cracks including the location, size and width.
Forquin  have utilized digital image correlation technique
to determine the crack propagation speed in concrete specimens
under tension. The author has used rocking spalling test on
dry and wet samples for this purpose. He concluded that DIC
technique is much more accurate than conventional methods
such as crack gauges for this kind of experiments. Boulekbache
et al.  have aimed to determine the fracture mechanism
of concrete specimens under splitting tensile test with digital
image correlation technique. The authors have utilized steel
fiber reinforced specimens for this purpose. They have also
investigated the effect of fiber addition and compressive strength
on the behavior of the specimen during the test. They have found
out that there are two different fracture mechanism where there
were a main crack and secondary cracks after the main have been
Hamrat et al.  have done experiment on fiber reinforced
concrete beams to determine the flexural cracking behavior of
the specimens with different strength characteristics. They have
investigated the physical properties of cracks including size and
initiation as well as the displacements. They have noted that DIC
technique can be very precise for displacement measurements.
Also, according to their findings one of the most important aspect
of digital image correlation technique is that it can be used to
determine the cracks before happening. Some of the notable
researches have been mentioned in this study related with the
application of digital image correlation techniques in concrete
specimens. It has been spotted that this technique has been
used for generally the same application over the years. However,
some intriguing usages can also be seen. A short summary of the
literature review according to this study is given in Table 1.
Sutton MA, Orteu JJ, Schreier H (2009) Image correlation for shape, motion, and deformation measurements: basic concepts, theory and applications. Springer Science & Business Media.
Chu TP, Poudel A (2014) Digital Image Correlation Techniques for Aerospace Applications. In ASNT Annual Conference pp. 37-44.
Chu TP, Mahajan AM (2002) Measurement of High Strain Regions in Particulate Composites Using Digital Image Correlation. In Proceedings of the Tenth US-Japan Conference on Composite Materials: Stanford University, Stanford, California. DEStech Publications pp: 183.
https://civildigital.com/failure-modes-beams/ (as of 05.06.2019)
https://www.dailycivil.com/types-column-failure/ (as of 05.06.2019)