Power of photo-stress analysis in unravelling the mechanics of granular materials and its applications in interdisciplinary research

Granular materials, such as various grains and granulated powders, are essential in numerous industrial applications and natural processes, including the chemical, pharmaceutical, food, and materials processing industries. They also play a significant role in geotechnical phenomena like the shear-driven collapses of embankments and landslides, which can lead to extensive damage and disruptions. Despite a significant surge in research activities and advancements in discrete element modelling (DEM) tools since the late 1970s, understanding the mechanical characteristics of granular materials remains complex. Experimental techniques such as photo stress analysis (PSA), Nuclear Magnetic Resonance (NMR), and X-ray tomography (XRT) offer valuable insights, yet there is still a lack of detailed information on how granular materials respond mechanically at the microscale under various loading conditions. This knowledge gap affects industrial product quality, equipment safety, production efficiency, operational costs, environmental compliance, and overall safety. In this paper, we initially focus on our scientific contributions to the development of photo stress analysis (PSA) in unravelling the load-transmission characteristics of granular materials of varying sizes and structures (two-dimensional and quasi-three-dimensional) under different mechanical loading environments and applications. Where relevant, discrete element modelling (DEM) complements PSA to enhance our understanding of granular mechanics. We then present the application of PSA to selected key interdisciplinary areas from our recent work, demonstrating the power of PSA. Despite current challenges in applying PSA to three-dimensional granular systems, the results reported here significantly advance our fundamental understanding of the particle-scale and micromechanical characteristics in granular mechanics and particulate engineering. This work highlights the potential of PSA in addressing various inter- and multidisciplinary research problems in the future.