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A Non-Intrusive Fluorescent Pattern for Internal Microscale Strain Measurements Using Digital Image Correlation



Ami Ahure Powell, William Mulhearn, Shawn Chen, Stephan J. Stranick, Jeffrey Gilman, Mark Iadicola, Jeremiah Woodcock


A non-intrusive and non-disruptive internal fluorescent pattern is designed, developed, and tested using digital image correlation (DIC), an effective non-contact optical method, to measure deformation at internal planes of a polymer matrix material. The working principle relies on a small amount (only 0.05 %) of a photoactivatable dye, spirolactam of Rhodamine B, which is covalently bound into an epoxy network and generated through the entire sample volume. A lithographic chrome mask, etched with transparent semi-randomly spaced circular features, is used as a contact mask on top of the polymer substrate while the dye is activated with ultraviolet light. The resulting microscale fluorescent pattern, collimated through more than 400 µm of the sample thickness, can be observed using a 514 nm excitation wavelength with a confocal microscope. This new patterning technique method applies internal patterns without introducing physical particles to the polymer specimen hence preventing significant changes to the mechanical properties of the material. The feasibility of the internal fluorescent pattern for DIC measurement was established and quantified through a sequence of assessments including noise floor, rigid body motion, and several uniaxial tests. Results show that this new non-intrusive and non-disruptive method of DIC patterning can measure strain fields on sub-surface planes in a transparent polymer matrix, without bias from material deformation above that plane.
Experimental Techniques


DIC, speckle techniques, microscale, polymers, materials science, internal deformation


Ahure Powell, A. , Mulhearn, W. , Chen, S. , Stranick, S. , Gilman, J. , Iadicola, M. and Woodcock, J. (2023), A Non-Intrusive Fluorescent Pattern for Internal Microscale Strain Measurements Using Digital Image Correlation, Experimental Techniques, [online],, (Accessed February 25, 2024)
Created February 1, 2023, Updated February 16, 2023