Colorimetric Detection of Mechanical Deformation in Metals using Thin-Film Mechanochromic Sensor

As metals form the backbone of many engineering structures including bridges and buildings, the detection of their mechanical deformation is of technological importance. Several optical techniques such as holographic interferometry, speckle interferometry, and digital image correlation have been developed to map the surface strains and displacements of various materials. However, these techniques have stringent requirements for stability and repeatability, which limit their application outside the laboratory. Herein, a colorimetric method for detecting mechanical deformation in metals based on the color change in an attached mechanochromic sensor is proposed. This study shows that a mechanically adaptable thin-film sensor bonded to a block of metal can not only visualize the surface strain of the metal but also quantitatively measure it. The spatial distribution of the strain field can be mapped with high resolution by capturing the sensor image using a smartphone and analyzing its red, green, and blue components. This colorimetric method is applicable in both indoor and outdoor environments and can also be effective for detecting cracking or cleavage in rigid bodies.