NUMERICAL AND EXPERIMENTAL INVESTIGATION OF FAILURE MECHANISM OF ROCK
USING DIGITAL IMAGE CORRELATION (DIC) TECHNIQUE
Sudipta Bhattacharjee
ATDC, Indian Institute of Technology, Kharagpur, India
*Debasis Deb
Department of Mining Engineering, Indian Institute of Technology, Kharagpur, India
(*Corresponding author: deb.kgp@gmail.com)
ABSTRACT
Rock failure process is generally recorded or measured using conventional sensors like strain gauges, seismic,
micro-seismic, acoustic, electromagnetic and other techniques (Lei et al., 2000; Gale et al., 2001; Frid and Vozoff,
2005; Niccolini et al., 2013). The above sensors are either to be pasted on the surface of the rock sample or placed
very near to it to capture the response of the sample with the increment of load. This requires precise tools to cut or
polish the locations where sensors are to be placed. Moreover, deformation or acoustic or micro-seismic activities
are recorded only at the locations where sensors are pasted.
Recent development in Digital Image Correlation (DIC) technique has shown promise to measure deformation /
strain at every location of the surface of a sample. In DIC, two images taken within a small time interval of the
same object and is compared to estimate the change in reflectance as a function of displacement, velocity or rate of
strain at each pixel while the object is undergoing through a loading process.
In this study, DIC technique has been implemented using 4-noded quadrilateral elements and displacement/strain are
estimated at each node. The results of FEM-DIC method is then compared with existing subset based DIC method
using digitally generated reference and deformed images as shown in Figure 1 and Figure 2. Simulated images have
been used to verify this algorithm, as well as to study the impact of speckle size on the accuracy. For this purpose
four typical deformation configuration: (i) rigid body translation with U(r) = (u,0)T, (ii) rigid body rotation with
U(r) = (εy, -εx)T, (iii) uni-axial tensile with U(r) = (εx, 0)T , and pure shear with U(r) = (εy, εx)T have been used to
calibrate the developed DIC algorithm and the results shows that FEM based DIC performs better as compared to
existing subset based DIC method. Here u is velocity along x-direction, εx is strain along x-direction and εy is strain
along y-direction.
0.00012
FEM based DIC
Subset based DIC
0.0001
Error
0.00008
Reference
0.00006
0.00004
0.00002
Current
0
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
Strain (ε)
Figure 1 – Performance comparison for rigid body rotation deformation configuration
The study is further extended to evaluate the performance of FEM-DIC method on deformation analysis of a granite
rock sample under uni-axial loading condition. An experimental setup is developed to acquire data from load cell,
axial and lateral strain gauges pasted on the sample and camera concurrently with a time interval of 1 s. These data
are being analyzed and compared to validate FEM-DIC method with those obtained using strain gauges and as well
as with subset based DIC method. The preliminary results show that FEM-DIC method is an effective tool for
determination of displacements or strains of the entire surface of a rock sample in a non-contact manner. This
method demonstrates the applicability to investigate rock failure mechanism for the entire sample in a laboratory set
up as well as monitoring of pillar failure mechanism in underground mines.
0.0001
0.00009
FEM based DIC
Subset based DIC
0.00008
0.00007
Error
0.00006
0.00005
0.00004
0.00003
0.00002
0.00001
0
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
Strain (ε)
Figure 2 – Performance comparison for uni-axial tensile deformation configuration
KEYWORDS
Digital Image Correlation (DIC) , Finite Element Method (FEM), Rock Failure
References
Frid V. and Vozoff K. (2005). Electromagnetic radiation induced by mining rock failure. International journal of
coal geology 64(1):57-65
Gale W., Heasley K., Iannacchione A., Swanson P., Hatherly P., and King A. (2001). Rock damage characterization
from microseismic monitoring. In: Proceedings of the 38th US Rock Mechanics Symposium, Washington, DC, 1313
Lei X., Kusunose K., Rao M., Nishizawa O., and Satoh T (2000). Quasi-static fault growth and cracking in
homogeneous brittle rock under triaxial compression using acoustic emission monitoring. Journal of Geophysical
Research: Solid Earth (1978-2012) 105(B3):6127-6139
Niccolini G., Borla O., Lacidogna G., Schiavi A., and Carpinteri A. (2013). Failure precursors in rocks and concrete.
In: ECF19