Enlightening force chains: a review of photoelasticimetry in granular matter

Abstract

A photoelastic material will reveal its internal stresses when observed through polarizing filters. This eye-catching property has enlightened our understanding of granular materials for over half a century, whether in the service of art, education, or scientific research. In this review article in honor of Robert Behringer, we highlight both his pioneering use of the method in physics research, and its reach into the public sphere through museum exhibits and outreach programs. We aim to provide clear protocols for artists, exhibit-designers, educators, and scientists to use in their own endeavors. It is our hope that this will build awareness about the ubiquitous presence of granular matter in our lives, enlighten its puzzling behavior, and promote conversations about its importance in environmental and industrial contexts. To aid in this endeavor, this paper also serves as a front door to a detailed wiki containing open, community-curated guidance on putting these methods into practice (Abed-Zadeh et al. in Photoelastic methods wiki https ://git-xen.lmgc.univ-montp 2.fr/Photo Elast icity /Main/wikis /home, 2019).

Contact force network evolution in active earth pressure state of granular materials: photo-elastic tests and DEM

“…It is possible to determine more precisely the limit between low-and high-stress response by inspecting the evolution of average grain image brightness I with a load. The typical example can be found in Zadeh et al [44] for the diametrically loaded disk: in a range of small stress the mean image intensity monotonically increases with the applied force, but there is a threshold above which the mean light intensity plateaus and starts to vary cyclically. The relationship for the glass granule tested in the immersion liquid and shown in Fig.…”

“…Q-2D testing of granular samples involves relatively big artificial flat grains (disks, ellipsoids, pentagons and other shapes) cut from polymer sheets or made using other techniques, discussed by Zadeh et al [44]. The grains are placed in loading frame, usually horizontally oriented, to form a 2D granular samples.…”

“…'Granular physics' Q-2D tests concentrate on measuring grain contact forces, their statistical distributions and impact on macro-scale phenomena. The current state of micro-mechanical photo-elastic research on granular materials is discussed by Daniels et al [49], Amon et al [50] and Zadeh et al [44]. The number of grains used in P-3D tests is large (in the order of 10 6 ), especially in comparison with typical Q-2D tests (in the order of 10 3 ).…”

Jamming Grains Come Full Circle

“…The ratio of the numbers of big and small particles is 1=3. Particles have reflective paint on their bases to enable reflective photoelasticimetry [34][35][36][37]. The total number of particles is varied from 1447 to 2101, which corresponds to 0.56 < ϕ < 0.82.…”

“…1(d)] give stress and contact information. We measure the pressure P, defined as the trace of the force moment tensor [1,10], using the averaged squared intensity gradient [9,10,36,37,39,40] of the polarized image [31]. A sheared system must develop a nonzero P to resist finite shear stress τ.…”