Bioinspired Granular Media Friction Pad: A Universal System for Friction Enhancement on Variety of Substrates

The granular media friction pad (GMFP) inspired by the biological smooth attachment pads of cockroaches and grasshoppers employs passive jamming, to create high friction forces on a large variety of substrates. The granular medium inside the pad is encased by a flexible membrane which at contact formation greatly adapts to the substrate profile. Upon applying load, the granular medium undergoes the jamming transition and changes from fluid-like to solid-like properties. The jammed granular medium, in combination with the deformation of the encasing elastic membrane, results in high friction forces on a multitude of substrate topographies. Here we explore the effect of elasticity variation on the generation of friction by varying granular media filling quantity as well as membrane modulus and thickness. We systematically investigate contact area and robustness against substrate contamination, and we also determine friction coefficients for various loading forces and substrates. Depending on the substrate topography and loading forces, a low filling quantity and a thin, elastic membrane can be favorable, in order to generate the highest friction forces.

Towards a macroscopically consistent discrete method for granular materials: Delaunay strain-based formulation

We demonstrate that the Delaunay-based strain definition proposed by Bagi (Mech Mater 22:165–177, 1996) for granular media can be straightforwardly translated into a particle-based numerical method for continua. This method has a number of attractive features, including linear completeness and satisfaction of the patch test, exact conservation of linear and angular momenta in the absence of external forces and torques, and anti-symmetry of the gradient vectors for any two points not both on the boundary of the computational domain. The formulation in effect relies on nodal (particle) interpolation of the deformation gradient and is therefore inherently unstable. Drawing on the analogy with granular media, a pairwise interaction between particles is included to alleviate this issue. The underlying idea is to define a local, non-affine deformation of each bond or contact, and to introduce pairwise forces via a stored-energy functional expressed in terms of the corresponding local displacements. In this manner, a generalisation of the Ganzenmüller (Comput Methods Appl Mech Eng 286:87–106, 2015) hourglass stabilisation procedure to non-central forces is obtained. The performance of the method is demonstrated in a range of problems. This work can be considered a first step towards the development of a macroscopically consistent discrete method for granular materials.

Virtual Energy Management for Physical Energy Savings in a Legged Robot Hopping on Granular Media

We discuss an active damping controller to reduce the energetic cost of a single step or jump of dynamic locomotion without changing the morphology of the robot. The active damping controller adds virtual damping to a virtual leg spring created by direct-drive motors through the robot’s leg linkage. The virtual damping added is proportional to the intrusion velocity of the robot’s foot, slowing the foot’s intrusion, and thus the rate at which energy is transferred to and dissipated by the ground. In this work, we use a combination of simulations and physical experiments in a controlled granular media bed with a single-leg robot to show that the active damping controller reduces the cost of transport compared with a naive compression-extension controller under various conditions.

High-performance process fluids used for vibration finishing of parts with granular media made of natural material “Baykalit”

The results of studies of the technological capabilities of granular media made of natural material “Baykalit” in the conditions of vibration technological systems are presented. Baikalit is a siliceous rock-fine-grained quartzite (microquartzite) - with an aggregate structure of quartz grains measuring 1.5-3 microns with sharp boundaries between these very grains. The granules obtained as a result of crushing the mineral rock Baikalit have a sufficiently high hardness (at least 6.0 - 7.0 on the Mohs scale). The presence of many wedge-shaped vertices along the perimeter of the granules and the arbitrariness of the shape allows us to consider them as a universal cutting tool that has access to various surfaces of complexity. It is shown that vibration treatment with granular media made of natural material “Baykalit” reduces the height of the initial surface micrprofile by 0.2-0.3 microns and is an effective way to remove burrs when processing parts with a surface microprofile height of more than 0.63 microns. The use of process fluids, which include increasing the wetting capacity of both Baikalit and processed workpieces, reduces the technological time of vibration processing by 1.5 times. The presence of components in the process fluid, such as protective colloids (Na CMC), prevents the sludge from sticking to the galtovochnye bodies, that is, prevents the “salting” of their profile, reduces the rigidity of the layer on the surface of the galtovochnyh bodies and workpieces, which contributes to productivity growth.

Granular Media Friction Pad for Robot Shoes—Hexagon Patterning Enhances Friction on Wet Surfaces

For maximizing friction forces of the robotic legs on an unknown/unpredictable substrate, we introduced the granular media friction pad, consisting of a thin elastic membrane encasing loosely filled granular material. On coming into contact with a substrate, the fluid-like granular material flows around the substrate asperities and achieves large contact areas with the substrate. Upon applying load, the granular material undergoes the jamming transition, rigidifies and becomes solid-like. High friction forces are generated by mechanical interlocking on rough substrates, internal friction of the granular media and by the enhanced contact area caused by the deformation of the membrane. This system can adapt to a large variety of dry substrate topologies. To further increase its performance on moist or wet substrates, we adapted the granular media friction pad by structuring the outside of the membrane with a 3D hexagonal pattern. This results in a significant increase in friction under lubricated conditions, thus greatly increasing the universal applicability of the granular media friction pad for a multitude of environments.