Abstract
Traditionally, strain gauge, extensometer, and reflection tracking markers have been used to measure the deformation of materials under loading. However, the anisotropy and inhomogeneity of most biological materials restricted the accessibility of the real strain field. Compared to the video extensometer, digital image correlation has the advantage of providing full-field displacement as well as strain information. In this study, a digital image correlation method (DIC) measurement system was employed for chicken breast bio-tissue deformation measurement. To increase the contrast for better correlation, a mixture of ground black pepper and white sesame was sprayed on the surface of samples. The first step was to correct the distorted image caused by the lens using the inverse distorted calibration method and then the influence of subset size and correlation criteria, sum of squared differences (SSD), and zero-normalized sum of squared differences (ZNSSD) were investigated experimentally for accurate measurement. Test results of the sample was translated along the horizontal direction from 0 mm to 3 mm, with an increment of 0.1 mm and the measurement result was compared, and the displacement set on the translation stage. The result shows that the error is less than 3%, and accurate measurement can be achieved with proper surface preparation, subset size, correlation criterion, and image correction. Detailed examination of the strain values show that the strain εx is proportional to the displacement of crosshead, but the strain εy indicates the viscoelastic behavior of tested bio-tissue. In addition, the tested bio-tissue’s linear birefringence extracted by a Mueller matrix polarimetry is for comparison and is in good agreement. As noted above, the integration of the optical parameter measurement system and the digital image correlation method is proposed in this paper to analyze the relationship between the strain changes and optical parameters of biological tissue, and thus the relative optic-stress coefficient can be significantly characterized if Young’s modulus of biological tissue is known.
Highlights
IntroductionThe deformation of materials under loading is often measured by strain gauges and extensometers when their mechanical properties are approached
The present study mainly aims to use a CCD camera and the digital image correlation (DIC) method to measure the surface displacement of the test specimen, applying the self-developed DIC technology to achieve non-contact full-field strain measurement in bio-tissue tensile testing, which is difficult for conventional sensors to measure accurately and quantitatively
In the tensile testing of the chicken breast, it was taken to evaluate the displacement field calculated by the DIC program written based o cut into thin slices that were 0.5 mm thick, which were put into the tensile test machine
Summary
The deformation of materials under loading is often measured by strain gauges and extensometers when their mechanical properties are approached. Conventional methods can be used to measure the strain of a single point or the average strain of a region. Biological tissues, which are often inhomogeneous and anisotropic, are different from conventional materials in terms of size and strength. The actual deformation of biological tissues cannot be observed using conventional methods. The digital image correlation (DIC) is a non-contact
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