Research Facility
Digital Image Correlation Technique
H. Tan, C. Liu, Y. Huang and P.H. Geubelle, 2005. The cohesive law for the particle/matrix interfaces in high explosives. Journal of the Mechanics and Physics of Solids, 53, 1892-1917.
Funding support
- U.S. Department of Energy and the U.S. Department of Defense/Office of Land Warfare & Munitions under the Joint DoD/DOE Munitions Technology Development Program
- ASCI Center for Simulation of Advanced Rockets at the University of Illinois supported by the U.S. Department of Energy through the University of California under Subcontract No. B523819
- ONR (U.S. Office of Naval Research) Composites for Marine Structures Program (Grant No. N00014-01-1-0205, Program Manager Y. D. S. Rajapakse)
Modified Compact Tension Specimen
A specially modified compact tension specimen has been developed for the digital image correlation investigation of the crack tip whole field deformation. The length, width, and thickness of the sample are 152.4 mm, 69.85 mm, and 6.35 mm, respectively. A notch with 0.508mm in width and 50.8mm in length is cut along the center of the specimen. Meanwhile, in order for the crack to propagate along the center of the specimen, a shallow groove is machined on the back of the specimen and along the center through the entire specimen. The radius of the groove is about 1.58 mm. Two loading pins are inserted through the two holes located at two opposite ends of the specimen and are symmetric with respect to the notch. A wedge pushes the two loading pins apart and opens the notch. A special loading fixture is made to ensure that only the force component perpendicular to the notch is transferred to the specimen. An INSTRON load frame is used to load the specimen in displacement-controlled loading, and the loading speed is set at 0.2 mm/min. A dotmatrix pattern is painted on the surface of the specimen prior to test in order to provide a gray-scale variation, which will be used in the correlation calculations.
Using the digital image
correlation technique, sequences of images are converted to the whole field of
deformation gradients and then to strain components. The full field of view has
the size of 
and
we used an 8-bit CCD digital camera with the resolution of 640 pixel by 480
pixel. This gives the resolution of 0.052 mm/pixel. According to Bruck et al.
(1989) and Vendroux and Knauss (1998), digital image correlation technique can
achieve resolution of measuring displacement on the order of 0.005 pixel, which
translates to about 0.26 mm in our experimental setup. The computation was
carried out with a subset region of 31 pixel by 31 pixel centered at every
computational point. The choice of the subset size is based on our experimental
study of the heterogeneous explosive which shows that the minimum size of
representative volume element for this material is around 1.5 mm.
Applied load versus pin separation
Full field images of deformation and strain at the crack tip area
Cohesive law of PBX 9501 under quasi-static loading
