Research on Strain Modulation of Spectral Reflectance in Soft Materials

Background Strain on soft materials plays a fundamental role in understanding the mechanical behavior of engineering soft machines and devices. However, it is challenging to noninvasively measure strain distribution on soft materials in situ . Objective In this study, we investigate the mechanism for the strain modulation of spectral reflectance in soft materials like silica gels. This mechanism is about the effect of strain-induced roughness variance on the spectral reflectance. Methods Based on a simplified Torrance-Sparrow model, we established a theoretical relationship related the reflectance variance to the strain undergone by the specimen. By HSI, we measure the reflectance changes caused the strain; by CLSM experiment, we determine the surface roughness under different strains. Results The theoretical model is verified by the reflectance analysis based HSI and the roughness analysis based on CLSM. The calibrated model parameters respectively from HSI and CLSM obtain a good agreement. Conclusions For soft materials similar to silicone rubber, within the strain range covered in this paper, the surface roughness of the material has a linear relationship with strain, while the reflectance has an inverse quadratic relationship with roughness. Our proposed mechanism provides a possibility for non-contact strain measurement based on HSI.