Determination of the stress and strain fields in porous structures by photoelasticity and digital image correlation techniques

Quantitative visualization of the full-field stress and strain in porous structures is of significance to reveal the mechanism of the damage and failure of engineering materials. To quantitatively characterize the full-field stresses and strains, optical measurement methods, such as photoelasticity for determining the stress fields, moiré and digital image correlation (DIC) methods for measuring the strain fields, have been developed in previous works. However, it is challenging to combine these methods to measure stress and strain fields simultaneously because the speckles and gratings for strain measurement will disturb the interference fringes in the photoelasticity. In this study, a method incorporating photoelasticity and DIC techniques was developed to determine the stress and strain fields simultaneously in different porous structures which were fabricated by three-dimensional (3D) printed technique. The tested models were printed with a highly transparent, colourless material and the speckles on the front surface of the tested models were printed with a translucent, magenta material. Under compressive loads, the stress fields in these models were obtained based on the photoelastic patterns and the strain fields were determined by DIC method. The results indicate the proposed method can simultaneously determine the full-field stresses and strains and the comparison of the distribution of the principal stress and strain difference and the distribution of the shear stress and strain verified its good accuracy. In addition, the stress and strain distribution in different pore structures were compared and found that the optimal design of the pore distribution can greatly change the concentration of the stress and strain fields.