12 Surface Deformation with Simultaneous Contact Area Measurement for Soft Transparent Media due to Spherical Contact 83 x (mm) surface deflection (mm) Fig. 12.3 A plot of the cross section of the surface deflection. The FTIR data was stacked with layers corresponding to the displacement data given by the universal testing machine which allows a 3D surface to be reconstructed from the contact measurement The FTIR data was used to create a 3D surface by relating the contact area to the corresponding displacement data from the universal testing machine. The result of this analysis is shown in Fig. 12.3 as a cross section of the contact along with the surface deflection measurement of the DIC data. The FTIR data matches up with the surface of the DIC measurement at the edges of previous contact. The contact boundary is found by identifying the edge of the FTIR data. 12.4 Discussion The resulting data found from this method has proven to yield high quality results which can easily be applied to any soft transparent media. Because the shape is so simple, the results can be used to calibrate the displacement data so that other more complex shapes can be tested. The calibration in the radial direction can be found by comparing extensometer displacement, in the radial direction, to the measured deformation. These calibration methods allow us to find the u, v, and w surface displacements which enable stain data to be found. 12.5 Conclusion By indenting a steel ball on a flat PDMS surface with the DIC, FTIR setup, and a universal testing machine to control load rate we are able to obtain a rich set of data which defines the deformation. The analysis of a simple object with known theoretical models for displacement allows for a correction factor to be applied for the u, v, and w-displacements of the surface. This calibration can be used for all other surfaces that are tested on the same surface. Alex McGhee is a graduate student in the mechanical engineering department at the University of Florida specializing in experimental soft matter mechanics.
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