Abstract
The intensity gradient method (G2 method), namely computing the light intensity gradient-squared, is a widely used non-invasive experimental method to extract stress information from quasi-two-dimensional photoelastic granular materials. Previous works show that calibrated G2 is an accurate measure of global stress. However, whether it can be used at the particle scale aside from the special case of diametric loading remains unclear. We test here the applicability and limitations of G2 as particle scale stress indicator and specify its dependence on relevant experimental parameters of the particles, light conditions, and imaging system. We first propose an explicit formula to calculate the relationship between the G2 value and stress based on the linear elasticity and photoelasticity theories, and then validate our formula by numerical and experimental tests. We find that G2 is proportional to , the sum of magnitudes of the contact forces, for disc particles when forces are not large. We also observe that, for large enough resolution, G2 does not change with the number of contacts as well as the direction of the contact forces under same value. However, we find that this relation between G2 and is not universal for any particle shape. As an example, we show that a square particle can have dramatically different values of G2 under the same contact forces with different contact types (point-edge contact and edge–edge contact).
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.