In recent times, the Discrete Element Method (DEM) has emerged as the computational modelling tool of choice for many engineers who want to design, optimise and troubleshoot bulk material handling systems. DEM gives engineers a detailed understanding of complex bulk material flows in a 3D environment, a level of insight not possible with most empirical models. It also offers a far more cost-effective alternative to physical scale modelling, which typically represents a substantial financial investment. Using DEM, engineers can troubleshoot and prevent common material handling problems such as unexpected stagnation zones, blockages, segregation, excessive wear, and dust generation.
Despite this potential value, any large-scale DEM analysis should be developed based on a strategic calibration methodology. Calibration is a critical step to help ensure that bulk solids simulated in DEM adequately capture the varying behaviours and flowabilities of the materials being handled. The choice of calibration test needs to be relevant to the flow regime of the intended large-scale application. Without calibration, DEM results only hold illustrative value and may become misleading when used to inform engineering decisions. In this article, we explore some of the typical physical tests used for DEM calibration that have been applied by many engineers in both academia and industry.
The most common type of DEM calibration test is the angle of repose (AoR) test. As the name suggests, these tests use the distinct angle formed by a stable body of bulk material as the metric to compare simulated and physical systems.
Angle of repose tests can be categorised based on how the angle is formed, with the most common variations being the static, drained, poured, and dynamic angle of repose.
Animations 1 – Variation of four angle of repose tests – Simulations from Rocky
Of these variations, the static angle of repose test captures a quasi-static flow regime. On the other hand, the drained and poured angle of repose tests represent a flow regime where the bulk solid transitions from a flowing to a static state – suitable for applications such as transfer chutes and conveyors. The dynamic angle of repose, predominantly measured using a rotating drum test, is instead suited to mixing drums or rotating mills, where the dominant flow regime is mixing or tumbling. All variations of the angle of repose test provide a metric to calibrate particle-particle interactions such as sliding friction, rolling resistance (for spheres), and even adhesion, for cohesive materials, at a bulk scale that is relevant to the intended large-scale application.
The key benefit of the angle of repose test is that it’s based on a simple concept and easy to set up. However, a major limitation is that it’s only representative of bulk material flows under zero or low consolidation. This makes it inadequate to rely on angle of repose testing alone to calibrate DEM models for applications subjected to a wide range of consolidation stresses, such as in discharging tall storage silos or filling large stockpiles. Another major drawback is that these tests, in isolation, cannot distinguish between bulk behaviours dominated by high friction/mechanical interlocking and those dominated by cohesive effects.
For these scenarios, direct shear testers are the cornerstone of conventional flow properties testing for bulk materials handling and can act as a reference for calibrating DEM under high consolidation. Using direct shear tests, the flowability of both the real and simulated bulk solid can be systematically quantified, capturing behaviour across the full spectrum from free-flowing to no-flow materials. Two commonly used shear testers in the bulk handling industry are the Jenike direct shear tester (translational shear) and the Schulze ring shear tester (rotational shear). Typical dimensions and testing procedures for the Jenike and Schulze shear tests are documented in ASTM standards D6128 and D6773, respectively.
While these shear cells are part of standardised flow properties testing procedures, their typical dimensions usually impose limits on the maximum particle size. Although typical sizes are sufficient for testing fine, powdery materials, they are not adequate for containing an indicative DEM sample of bulk solids with upscaled particulates.
Standard shear cell testing, as prescribed by ASTM D6128 and D6773, is inherently a fines-fraction test, with samples limited to particles below roughly 6 mm. Yet DEM simulations of large-scale equipment rarely represent bulk solids at their true particle size. For computational feasibility, particles are effectively always scaled up and can readily reach sizes well beyond what a standard shear cell was ever designed to test. This leaves a disconnect between the flow properties measured on the fines fraction and the flow behaviour DEM engineers actually need to calibrate at a coarser, scaled-up particle size.
Closing this gap will require either shear testing equipment capable of handling larger, more representative particle sizes, or modifications to the representative DEM shear cell calibration model. To this end, LEAP Australia has investigated the prospects of undertaking DEM calibration using a scaled-up computational model of a ring shear cell tester.
If you’d like to hear more about where this is headed, join LEAP Australia’s application engineers at the upcoming BULK2026 expo in Melbourne to discuss these practices in more detail.