This paper presents a feasibility study of visualizing the strain distribution of structural elements using opal film. Opal film with an initial peak wavelength of 510 nm was employed in tensile and four-point bending tests to evaluate the feasibility of visualizing the strain distribution using this type of film. The experimental results of the tensile and four-point bending tests show that the peak wavelength has a linear relationship with the first invariant of the strain. The slope of the experimentally obtained relationship between these variables showed good agreement with the theoretically predicted slope. In the four-point bending test, visualization of the first invariant of the strain using opal film was successfully demonstrated, thereby confirming the feasibility of strain visualization using opal film.
