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• To date, geotechnical instrumentation has been absent from Mars missions. • The Perseverance rover's abrading bit has a similar form factor to a Bevameter. • We study the use of the abrading bit tool to perform soil strength measurements. An instrument for measuring the geotechnical properties of the Martian soil provides high-value science opportunities and high-priority mission-support capabilities that serve reconnaissance, science, and engineering. Such instrument can be used to characterize the terrain for drilling, landing, trafficability, and other surface operations. However, to date, instruments for measuring geotechnical properties have been absent from Mars exploration missions. This paper examines the use of the Mars 2020 Perseverance rover's abrading bit tool to perform regolith strength measurements. The Perseverance rover's abrading bit has a similar form factor to a Bevameter, a tool commonly used to collect engineering geotechnical data to assess terrain traversability. To demonstrate a methodology by which the abrading bit can be employed to characterize soil strength, a portable testbed that mimics the flight system is designed and built using commercial off-the-shelf components. A data-processing pipeline is developed to convert raw measurements to soil strength. Tests were performed on three characterized simulants with different mechanical properties. The results show that the abrading bit is capable of making shear and bearing strength measurements with quantified uncertainties and demonstrate, for the first time, the ability to perform controlled geotechnical analysis using a standard science instrument. [ABSTRACT FROM AUTHOR]

Force chains have been regarded as an important hallmark of granular materials. Numerous studies have examined their evolution, properties, and statistics in highly idealized, often circular-shaped, granular assemblies. However, particles found in nature and handled in industries come in a wide variety of shapes. In this article, we experimentally investigate the robustness of force chains with respect to particle shape. We present a detailed analysis on the particle- to continuum-scale response of granular materials affected by particle shape, which includes the force transmission and mobilized shear strength. The effect of shape is studied by comparing experimental results collected from shear tests performed on 2D analog circular- and arbitrarily shaped granular assemblies. Particle shapes are directly discretized from X-ray CT images of a real sand sample. By inferring individual contact forces using the granular element method (GEM), we provide a direct visualization of the force network, a statistical characterization of the force transmission and a quantitative description of the shear strength in terms of rolling, sliding, and interlocking contact mechanisms. We report that force chains are less prevalent in assemblies of arbitrarily-shaped particles than in circular-shaped samples. Furthermore, interlocking is identified as the essential contact mechanism that (1) furnishes a stable structure for force chains to emerge and (2) explains the enhanced shear strength observed in the arbitrarily-shaped samples. These findings highlight the importance of accounting for particle shape to capture and predict the complex mechanical behavior of granular materials across scales. [ABSTRACT FROM AUTHOR]

Granular materials can behave as harmless sand dunes or as devastating landslides. A granular avalanche marks the transition between these distinct solid-like and fluid-like states. The solid-like state is typically described using plasticity models from critical state theory. In the fluid regime, granular flow is commonly captured using a visco-plastic model. However, due to our limited understanding of the mechanism governing the solid-fluid-like transition, characterizing the material behavior throughout the life cycle of an avalanche remains an open challenge. Here, we employ laboratory experiments of transient avalanches spontaneously generated by a rotating drum. We report measurements of dilatancy and grain kinematics before, during, and after each avalanche. Those measurements are directly incorporated into a rate-dependent plasticity model that quantitatively predicts the granular flow measured in experiments. Furthermore, we find that dilatancy in the solid-like state controls the triggering of granular avalanches and therefore plays a key role in the solid-fluid-like transition. With the proposed approach, we demonstrate that the life cycle of a laboratory avalanche, from triggering to run out, can be fully explained. Our results represent an important step toward a unified understanding of the physical phenomena associated with transitional behavior in granular media. [ABSTRACT FROM AUTHOR]

Particle shape, as one of the most important physical ingredients of granular materials, can greatly alter the characteristic of inter-particle force distribution which is of vital importance in understanding the mechanical behavior of granular materials. However, currently both experimental and numerical studies remain limited in this regard. In this paper, we for the first time validate the ability of the level set discrete element method (LS-DEM) on capturing the inter-particle force distribution among particles of arbitrary shape. We first present the technical detail of LS-DEM; we then apply LS-DEM to simulate experiments of shearing granular materials composed of arbitrarily shaped particles. The proposed approach directly links experimentally measured material properties to model parameters such as contact stiffness without any calibration. Our results show that LS-DEM is able to not only capture the macro scale response such as stress and deformation, but also to reproduce the particle scale contact information such as the distribution of contact force magnitude, contact orientation and contact friction mobilization. Our work demonstrates the promising potential of LS-DEM on studying the mechanics and physics of natural granular material and on aiding design granular particle shape for novel macro-scale mechanical property. [ABSTRACT FROM AUTHOR]