Anisotropic Friction Model Research Articles

EELS-DARTS: A Planetary Snake Robot Simulator for Closed-Loop Autonomy Development

EELS-DARTS is a simulator designed for autonomy development and analysis of large degree of freedom snake-like robots for space exploration. A detailed description of the EELS-DARTS simulator design is presented. This includes the versatile underlying multibody dynamics representation used to model a variety of distinct snake robot configurations as well as an anisotropic friction model for describing screw–ice interaction. Additional simulation components such as graphics, importable terrain, joint controllers, and perception are discussed. Methods for setting up and running simulations are discussed, including how a snake robot’s autonomy stack closes the commands and information loop with the simulation via ROS. Multiple use cases are described to illustrate how the simulation is used to aid and inform robot design, autonomy development, and field test use throughout the project’s life cycle. A validation analysis of the screw–ice contact model is performed for the surface mobility case. Lastly, an overview of simulation use for planning operations during a recent field test to the Athabasca Glacier in Canada is discussed.

Modeling anisotropic friction in triaxial overbraiding simulations

Triaxial overbraiding is a highly intricate textile manufacturing process that involves interlacing yarns in three directions, enhancing reinforcement of the final composite compared to biaxial braids. Predictive process simulation is a cost-effective approach to optimizing the manufacturing process. Previous research on biaxial overbraiding simulations indicates that yarn-yarn friction has a significant effect on the braid angle and convergence zone length. This study presents an extended yarn interaction model; it utilizes a fast frontal approach and a Eulerian on Lagrangian method to simulate the complex interlacing of multiple yarns in triaxial overbraiding, including yarn-yarn and yarn-ring friction. Experiments were conducted to evaluate the effect of UD yarn tension on the convergence zone length and braid angle, and to validate the simulations. The model validation shows that a recently proposed anisotropic yarn-yarn friction model predicts braid angle more accurately than an isotropic friction model.

Design and validation of a finite element model of the aponeurotic and free Achilles tendon.

The Achilles tendon (AT) is a common injury site. Ruptures are usually located in the free tendon but may cross the myotendinous junction into the aponeurotic region. Considering the possibility of aponeurotic region involvement in AT ruptures, a novel three dimensional (3D) finite element (FE) model that includes both the aponeurotic and free AT regions and features subtendon twisting and sliding was developed. It was hypothesized that the model would be able to predict in vivo data collected from the literature, thus being considered valid, and that model outputs would be most sensitive to subtendon twist configurations. The 3D model was constructed using magnetic resonance images. The model was divided into soleus and gastrocnemius subtendons. In addition to a frictionless contact condition, the interaction between subtendons was modeled using two contact formulations: sliding with anisotropic friction and no sliding. Loads were applied on the tendon's most proximal cross-section and anterior surface, with magnitudes estimated from in vivo studies. Model outputs were compared with experimental data regarding 3D deformation, transverse plane rotation, and nodal displacements in the free tendon. The FE model adequately simulated the free tendon behavior regarding longitudinal strain, cross-section area variation, transverse plane rotation, and sagittal nodal displacements, provided that subtendon sliding was allowed. The frictionless model exhibited noticeable medial transverse sliding of the soleus subtendon, which was present to a much lesser degree in the anisotropic friction model. Model outputs were most sensitive to variations in subtendon twist and dispersion of the collagen fiber orientations. Clinical Significance: This Achilles tendon finite element model, validated using in vivo experimental data, may be used to study its mechanical behavior, injury mechanisms, and rupture risk factors.

The Matchstick Model for Anisotropic Friction Cones

AbstractInspired by frictional behaviour that is observed when sliding matchsticks against one another at different angles, we propose a phenomenological anisotropic friction model for structured surfaces. Our model interpolates isotropic and anisotropic elliptical Coulomb friction parameters for a pair of surfaces with perpendicular and parallel structure directions (e.g. the wood grain direction). We view our model as a special case of an abstract friction model that produces a cone based on state information, specifically the relationship between structure directions. We show how our model can be integrated into LCP and NCP‐based simulators using different solvers with both explicit and fully implicit time‐integration. The focus of our work is on symmetric friction cones, and we therefore demonstrate a variety of simulation scenarios where the friction structure directions play an important part in the resulting motions. Consequently, authoring of friction using our model is intuitive and we demonstrate that our model is compatible with standard authoring practices, such as texture mapping.

Friction Variability in Planar Pushing Data: Anisotropic Friction and Data-Collection Bias

Friction plays a key role in manipulating objects. Most of what we do with our hands, and most of what robots do with their grippers, is based on the ability to control frictional forces. This paper aims to better understand the variability and predictability of planar friction. In particular, we focus on the analysis of a recent dataset on planar pushing by Yu et al. [1] devised to create a data-driven footprint of planar friction. We show in this paper how we can explain a significant fraction of the observed unconventional phenomena, e.g., stochasticity and multi-modality, by combining the effects of material non-homogeneity, anisotropy of friction and biases due to data collection dynamics, hinting that the variability is explainable but inevitable in practice. We introduce an anisotropic friction model and conduct simulation experiments comparing with more standard isotropic friction models. The anisotropic friction between object and supporting surface results in convergence of initial condition during the automated data collection. Numerical results confirm that the anisotropic friction model explains the bias in the dataset and the apparent stochasticity in the outcome of a push. The fact that the data collection process itself can originate biases in the collected datasets, resulting in deterioration of trained models, calls attention to the data collection dynamics.

Variational modeling of thermomechanical fracture and anisotropic frictional mortar contact problems with adhesion

Phase-field formulations to fracture and sophisticated mortar contact formulations are well established techniques nowadays. For a wide range of applications, these two variationally consistent approaches could already demonstrate their superiority compared with more traditional methods in terms of generality, performance and accuracy. In the present contribution we combine both methodologies in a unified computational framework to deal with large deformation thermo-fracture mechanical contact problems. In particular, a temperature dependent model for the critical fracture energy density as well as a phase-field dependent model for the heat conduction are taken into account along with a temperature dependent contact model. To be specific, an adhesive anisotropic friction model is considered for the contact in tangential direction, whereas an exponential adhesion model is applied for the normal contact definition. These models are incorporated within the thermal phase-field approach in a thermodynamically consistent formulation. Eventually, a variety of representative numerical examples demonstrates the capabilities of this novel framework.

An anisotropic friction model in non-bonded flexible risers

The present paper addresses small scale friction tests and an anisotropic friction model to predict friction for the interface between the anti-wear tape and tensile armors in non-bonded flexible risers. Small scale friction tests were carried out to study the static and dynamic friction behavior, measuring the transition distance between static and dynamic friction and the associated friction coefficients under variable contact pressure. In addition, the anti-wear tape shear modulus was measured to validate the analytical solution of shear interaction stick stiffness, K0, applied in previously proposed friction models. As grooves in the anti-wear tape surface were observed in the full scale test pipe, an anisotropic friction model was formulated and implemented into a computer code. Since the slip behavior will be influenced by the friction scaling factors, the K0 and the sliding direction, numerical studies were carried out to investigated their effects on the friction forces and the axial stress ranges at the outermost fiber position. This was followed by a sensitivity study with respect to the effect of applying 1D (loxodromic) and 2D (geodesic) friction models on the axial stress range at the same position. At last, the effect of applying measured transition behavior in the static friction model was investigated.

Finite Element Modeling of Frictional and Material Anisotropy During Forming of Steel Cylindrical Cups

The article presents a method of determining the anisotropic friction model in metal forming using multilayer artificial neural networks based on experimental data obtained from the pin-on-disk tribometer. The experimental results show that the friction coefficient depends on the measured angle from the rolling direction and corresponds to the surface topography. Both the friction and material anisotropic models were implemented into a finite element (FE) model built using the commercial FE-package ABAQUS/Standard. When both the material and friction anisotropy are taken into account in the finite element analysis, this approach gives the most approximate numerical results to real processes.

Elastoplastic formulation for friction with orthotropic anisotropy and rotational hardening

In various fields of engineering, it is important to clarify the frictional sliding behavior over a wide scale. In this study, we formulate an anisotropic friction model with the orthotropy and rotation of a sliding surface based on the elastoplastic theory. This model can also describe preliminary microscopic sliding and rate-dependent frictional response. Further, basic experimental results of anisotropic frictional sliding can be pertinently represented by the present model. We also employ this model with the finite element method and analyze typical frictional contact problems. We then demonstrate the effect of anisotropy parameters on the numerical results.

Consistent finite-element approach to Brownian polymer dynamics with anisotropic friction

In the last decades simulation tools for Brownian dynamics of polymers have attracted more and more interest. Here we present a mathematically consistent finite element approach to the simulation of Brownian polymer dynamics. The viscous damping forces are accounted for by an anisotropic friction model. By comparison with theoretical predictions and experimental data we demonstrate the reliability and efficiency of this method.

Brush up your painting skills

Most present-day interactive paint applications lack the means of adequately capturing a user’s gestures and translating them into realistic and predictable strokes, despite the importance of such a mechanism. We present a novel brush design that adopts constrained energy optimization to deform the brush tuft according to the user’s input movement. It incorporates bidirectional paint transfer and an anisotropic friction model. The main advantage of our method is its ability to handle a wide range of brush tuft shapes that are animated using a freeform deformation lattice, which is associated with the tuft’s geometry. This way, almost no conditions or limitations are placed upon the appearance of the brush. Examples range from round brushes modeled as polygon meshes, to flat brushes with individual bristles. Less common deformable tools that are used to apply or remove paint on the canvas, like sponges, can be created as well. The model is integrated in our interactive painting system for creating images with watery paint.

Macroscopic friction laws and shear yielding of glassy solids

Molecular simulations of yield in models of glassy polymers and amorphous metals are used to test classic yield criteria. Bulk systems follow the pressure-modified von Mises criterion, which is based on an isotropic, energy-driven model of yield. Thin films follow the Mohr–Coulomb criterion, which is based on an anisotropic friction model. The difference in behavior is correlated with a change in shear mechanism, and the connection between thin film results and macroscopic friction laws is discussed.

Three‐dimensional finite element computations for frictional contact problems with non‐associated sliding rule

AbstractThis paper presents an algorithm for solving anisotropic frictional contact problems where the sliding rule is non‐associated.The algorithm is based on a variational formulation of the complex interface model that combine the classical unilateral contact law and an anisotropic friction model with a non‐associated slip rule. Both the friction condition and the sliding potential are elliptical and have the same principal axes but with different semi‐axes ratio. The frictional contact law and its inverse are derived from a single non‐differentiable scalar‐valued function, called a bi‐potential. The convexity properties of the bi‐potential permit to associate stationary principles with initial/boundary value problems. With the present formulation, the time‐integration of the frictional contact law takes the form of a projection onto a convex set and only one predictor–corrector step addresses all cases (sticking, sliding, no‐contact). A solution algorithm is presented and tested on a simple example that shows the strong influence of the slip rule on the frictional behaviour. Copyright 2004 John Wiley & Sons, Ltd.

Anisotropic friction model of DNA electrophoresis in polymer solutions: Comparison with direct observations

AbstractThe electrophoresis of DNA chains in uncrosslinked polymer solutions with a Brownian dynamics simulation with an anisotropic friction tensor was analyzed. According to the degree of anisotropy, three types of migration behavior are obtained: fluctuation without or with periodicity between U‐shaped and compact conformations, or migration with linear conformation. We found good agreement between our simulation results and the direct observations of DNA by fluorescence microscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1316–1322, 2003

Dynamics of DNA in entangled polymer solutions: An anisotropic friction model

We studied the electrophoretic behavior of DNA chains in linear-polymer solutions using Brownian dynamics with an anisotropic friction model in a three-dimensional space and projected on the x axis. For the three-dimensional model with a chain segment equal to 1/8 of the Kuhn length, a chain migrates with U-shaped conformation with low anisotropy of friction. With high anisotropy of friction, a chain always migrates with linear-shaped conformation with high segment-density regions, which remain at the same positions in space. This migration mode agrees with the observation of DNA in highly entangled solutions [Ueda et al., Biophys. Chem. 71, 113 (1998)]. The projection model also reproduces the linear-shaped motion. We clarified that the essential conditions for linear shaped motion are the sufficient chain length of DNA, the small mesh size, and strong confinement by entanglement with solvent polymers.

An anisotropic friction and wear model

The classical Coulomb friction condition and the sliding rule are generalized in order to account for friction anisotropy. A model of two surfaces with anisotropic layout of asperities interacting elastically is first considered in order to generate limit friction condition and a sliding rule. Next, a class of phenomenological models is considered in order to simulate anisotropic friction, sliding and wear rate of contacting surfaces.