scholarly journals Stick-slip Dynamics in Penetration Experiments on Simulated Regolith

2021 ◽  
Vol 2 (6) ◽  
pp. 243
Author(s):  
Jack Featherstone ◽  
Robert Bullard ◽  
Tristan Emm ◽  
Anna Jackson ◽  
Riley Reid ◽  
...  
Keyword(s):  
Mechanical Response ◽  
External Perturbation ◽  
Chain Structure ◽  
Contact Forces ◽  
Optimized Design ◽  
Gravitational Acceleration ◽  
Stick Slip ◽  
Microgravity Conditions ◽  
Flexible Probe ◽  
Probe Insertion

Abstract The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, Martian, lunar, and microgravity. We identify discrete, stick-slip failure events that increase in frequency as a function of the gravitational acceleration. In microgravity environments, stick-slip behaviors are negligible, and we find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the mechanical response of regolith on rubble-pile asteroids is likely quite distinct from that found on larger planetary objects, and scaling terrestrial experiments to microgravity conditions may not capture the full physical dynamics.

scholarly journals Probing regolith-covered surfaces in low gravity

2021 ◽  
Vol 249 ◽  
pp. 02005
Author(s):  
Jonathan E. Kollmer ◽  
Jack Featherstone ◽  
Robert Bullard ◽  
Tristan Emm ◽  
Anna Jackson ◽  
...  
Keyword(s):  
Granular Medium ◽  
Gravitational Acceleration ◽  
Low Gravity ◽  
Stick Slip ◽  
Parabolic Flights ◽  
Cohesive Forces ◽  
2D System ◽  
Flexible Probe ◽  
Effective Design ◽  
Different Levels

The surfaces of many planetary bodies, including asteroids, moons, and planets, are composed of rubble-like grains held together by varying levels of gravitational attraction and cohesive forces. Future instrumentation for operation on, and interacting with, such surfaces will require efficient and effective design principles and methods of testing. Here we present results from the EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) which flew on several reduced gravity parabolic flights. EMPANADA studies the effects of the insertion of a flexible probe into a granular medium as a function of ambient gravity. This is done for an idealized 2D system as well as a more realistic 3D sample. To quantify the dynamics inside the 2D granular material we employ photoelasticity to identify the grain-scale forces throughout the system, while in 3D experiments we use simulated regolith. Experiments were conducted at three different levels of gravity: martian, lunar, and microgravity. In this work, we demonstrate that the photoelastic technique provides results that complement traditional load cell measurements in the 2D sample, and show that the idealized system exhibits similar behaviour to the more realistic 3D sample. We note that the presence of discrete, stick-slip failure events depends on the gravitational acceleration.

Dynamic modeling, optimized design, and fabrication of a 2DOF piezo-actuated stick-slip mobile microrobot

2019 ◽  
Vol 133 ◽  
pp. 514-530 ◽  
Author(s):  
Navid Asmari Saadabad ◽  
Hamed Moradi ◽  
Gholamreza Vossoughi
Keyword(s):  
Dynamic Modeling ◽  
Optimized Design ◽  
Stick Slip

Interface Engineering of CNT/Polymer Nanocomposites With Tunable Damping Properties

2018 ◽  
Author(s):  
Michela Talò ◽  
Giulia Lanzara ◽  
Maryam Karimzadeh ◽  
Walter Lacarbonara
Keyword(s):  
Load Transfer ◽  
Mechanical Response ◽  
Material Design ◽  
Tensile Tests ◽  
Nanocomposite Films ◽  
Damping Capacity ◽  
Interfacial Region ◽  
Material Damping ◽  
Stick Slip ◽  
Multi Walled Carbon Nanotubes

In this work, the arising of stick-slip dissipation as well as the global mechanical response of carbon nanotube (CNT) nanocomposite films are tailored by exploiting a three-phase nanocomposite. The three phases are represented by the CNTs, a polymer coating localized on the CNTs surface and a hosting matrix. In particular, a polystyrene (PS) layer coats multi-walled carbon nanotubes (MWNTs) that are randomly dispersed in a polyimide (PI) matrix. The coating phase is strongly bonded to the CNTs outer sidewalls ensuring the effectiveness of the load transfer mechanism and reducing the material damping capacity. The coating phase can be thermally-activated to modify, and in particular, decrease the CNT-matrix interfacial shear strength (ISS) thus facilitating the stick-slip onset in the nanocomposite. The ISS decrease finds its roots in a partial degradation of the coating phase and, in particular, in the formation of voids. By weakening the CNT/polymer interfacial region, a significant enhancement in the material damping capacity is observed. An extensive experimental campaign consisting of monotonic and cyclic tensile tests proved the effectiveness of this novel multi-phase material design.

scholarly journals Numerical and experimental analysis of the bi-stable state for frictional continuous system

2020 ◽  
Vol 102 (3) ◽  
pp. 1361-1374
Author(s):  
D. Tonazzi ◽  
M. Passafiume ◽  
A. Papangelo ◽  
N. Hoffmann ◽  
F. Massi
Keyword(s):  
Stable State ◽  
Continuous System ◽  
External Perturbation ◽  
Element Model ◽  
Dynamical Response ◽  
Continuous Systems ◽  
Sliding Velocity ◽  
Stable States ◽  
Stick Slip ◽  
Stable Solutions

AbstractUnstable friction-induced vibrations are considered an annoying problem in several fields of engineering. Although several theoretical analyses have suggested that friction-excited dynamical systems may experience sub-critical bifurcations, and show multiple coexisting stable solutions, these phenomena need to be proved experimentally and on continuous systems. The present work aims to partially fill this gap. The dynamical response of a continuous system subjected to frictional excitation is investigated. The frictional system is constituted of a 3D printed oscillator, obtained by additive manufacturing that slides against a disc rotating at a prescribed velocity. Both a finite element model and an experimental setup has been developed. It is shown both numerically and experimentally that in a certain range of the imposed sliding velocity the oscillator has two stable states, i.e. steady sliding and stick–slip oscillations. Furthermore, it is possible to jump from one state to the other by introducing an external perturbation. A parametric analysis is also presented, with respect to the main parameters influencing the nonlinear dynamic response, to determine the interval of sliding velocity where the oscillator presents the two stable solutions, i.e. steady sliding and stick–slip limit cycle.

A Bistable Shape Memory Microswitch

2009 ◽  
Author(s):  
Johannes Barth ◽  
Berthold Krevet ◽  
Manfred Kohl
Keyword(s):  
Shape Memory ◽  
Mechanical Response ◽  
Contact Forces ◽  
Soft Magnetic ◽  
Actuation Mechanism ◽  
Magnetic Components ◽  
Magnetic Retention ◽  
Freely Suspended ◽  
Novel Concept ◽  
Magnetic Disc

A novel concept of a bistable microswitch is presented, which combines an antagonistic shape memory alloy (SMA) actuation mechanism with two end positions and magnetic components to maintain these positions in power-off state. The layout of the antagonistic SMA actuation mechanism consists of two mechanically coupled freely suspended TiNi microbridges of 20 μm thickness, which are prestrained with respect to each other. The electro-thermo-mechanical response of the coupled microbridges is investigated for various degrees of prestrain to determine the maximum actuation stroke, minimum required magnetic retention force and maximum switching force. For magnetic retention, the ferromagnetic attraction of different hard and soft magnetic microstructures is studied. By varying the diameter of a hard magnetic cylinder for a given diameter of a soft-magnetic disc and fixed thicknesses, the ferromagnetic attraction force displays a pronounced optimum. First demonstrator microswitches with outer dimensions of about 7×7×4 mm3 are presented, which show large work outputs, featuring strokes and contact forces up to 84 μm and 60 mN, respectively.

scholarly journals Modelling elastic structures with strong nonlinearities with application to stick–slip friction

2014 ◽  
Vol 470 (2161) ◽  
pp. 20130593 ◽  
Author(s):  
Robert Szalai
Keyword(s):  
Point Contact ◽  
Linear Structure ◽  
Transformation Method ◽  
Friction Model ◽  
Contact Forces ◽  
Stick Slip ◽  
Lipschitz Continuous ◽  
Contact Points ◽  
Dimensional Equation ◽  
Low Dimensional

An exact transformation method is introduced that reduces the governing equations of a continuum structure coupled to strong nonlinearities to a low-dimensional equation with memory. The method is general and well suited to problems with isolated discontinuities such as friction and impact at point contact. It is assumed that the structure is composed of two parts: a continuum but linear structure and finitely many discrete but strong nonlinearities acting at various contact points of the elastic structure. The localized nonlinearities include discontinuities, e.g. the Coulomb friction law. Despite the discontinuities in the model, we demonstrate that contact forces are Lipschitz continuous in time at the onset of sticking for certain classes of structures. The general formalism is illustrated for a continuum elastic body coupled to a Coulomb-like friction model.

scholarly journals A new methodology to simulate subglacial deformation of water saturated granular material

2015 ◽  
Vol 9 (4) ◽  
pp. 3617-3660 ◽  
Author(s):  
A. Damsgaard ◽  
D. L. Egholm ◽  
J. A. Piotrowski ◽  
S. Tulaczyk ◽  
N. K. Larsen ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Fluid Pressure ◽  
Fluid Phase ◽  
Large Degree ◽  
Numerical Approach ◽  
Unconsolidated Sediments ◽  
Close Monitoring ◽  
Stick Slip ◽  
Rate Dependent ◽  
Water Saturated

Abstract. The dynamics of glaciers are to a large degree governed by processes operating at the ice–bed interface, and one of the primary mechanisms of glacier flow over soft unconsolidated sediments is subglacial deformation. However, it has proven difficult to constrain the mechanical response of subglacial sediment to the shear stress of an overriding glacier. In this study, we present a new methodology designed to simulate subglacial deformation using a coupled numerical model for computational experiments on grain-fluid mixtures. The granular phase is simulated on a per-grain basis by the discrete element method. The pore water is modeled as a compressible Newtonian fluid without inertia. The numerical approach allows close monitoring of the internal behavior under a range of conditions. The rheology of a water-saturated granular bed may include both plastic and rate-dependent dilatant hardening or weakening components, depending on the rate of deformation, the material state, clay mineral content, and the hydrological properties of the material. The influence of the fluid phase is negligible when relatively permeable sediment is deformed. However, by reducing the local permeability, fast deformation can cause variations in the pore-fluid pressure. The pressure variations weaken or strengthen the granular phase, and in turn influence the distribution of shear strain with depth. In permeable sediments the strain distribution is governed by the grain-size distribution and effective normal stress and is typically on the order of tens of centimeters. Significant dilatant strengthening in impermeable sediments causes deformation to focus at the hydrologically more stable ice–bed interface, and results in a very shallow cm-to-mm deformational depth. The amount of strengthening felt by the glacier depends on the hydraulic conductivity at the ice–bed interface. Grain-fluid feedbacks can cause complex material properties that vary over time, and which may be of importance for glacier stick-slip behavior.

scholarly journals Stick-Slip Dynamics in Fiber Bundle Models with Variable Stiffness and Slip Number

2021 ◽  
Vol 9 ◽  
Author(s):  
Zoltán Halász ◽  
Imre Kállai ◽  
Ferenc Kun
Keyword(s):  
Fiber Bundle ◽  
Mechanical Response ◽  
Permanent Deformation ◽  
Variable Stiffness ◽  
Plastic Behavior ◽  
Stick Slip ◽  
Maximum Deformation ◽  
Local Material ◽  
Macro Scale ◽  
Analytic Expressions

We present an extension of fiber bundle models to describe the mechanical response of systems which undergo a sequence of stick-slip cycles taking into account the changing stiffness and the fluctuating number of slip events of local material elements. After completing all stick-slip cycles allowed, fibers can either ultimately break or can keep their final stiffness leading to softening or hardening of the bundle, respectively. Under the assumption of global load sharing we derive analytic expressions for the constitutive response of the bundle with both quenched and annealed disorder of the failure thresholds where consecutive slips occur. Our calculations revealed that on the macro-scale the bundle exhibits a plastic behavior, which gets more pronounced when fibers undergo a higher number of stick-slip cycles with a gradually degrading stiffness. Releasing the load a permanent deformation remains, which increases monotonically for hardening bundles with the maximum deformation reached before unloading starts, however, in the softening case a non-monotonous behavior is obtained. We found that the macroscopic response of hardening bundles is more sensitive to fluctuations of the number of stick-slip cycles allowed than of the softening ones. The quenched and annealed disorder of failure thresholds gives rise to the same qualitative macro-scale behavior, however, the plastic response is found to be stronger in the annealed case.

Disc Brake Ring-Element Modeling Involving Friction-Induced Vibration

2002 ◽  
Vol 8 (8) ◽  
pp. 1085-1104 ◽  
Author(s):  
V. N. Pilipchuk ◽  
R. A. Ibrahim ◽  
P. G. Blaschke
Keyword(s):  
Friction Force ◽  
Frequency Component ◽  
Contact Forces ◽  
High Frequency Component ◽  
Transverse Motion ◽  
Disc Brake ◽  
Radial Vibrations ◽  
Stick Slip ◽  
Contact Loads ◽  
The Moment

This paper presents the analytical modeling and dynamic characteristics of disc brake systems under equal contact loads on both sides of the disc. The friction force acting on the pad is assumed to be concentrated along its trailing edge due to the moment arising from the friction force, and thus results in a redistribution of normal forces. In view of equal contact forces, the disc will not experience transverse motion but only tangential and radial vibrations. The only nonlinearity involved in the model arises mainly from contact forces. The dependence of the friction coefficient between the pad and disc is smoothed at zero relative velocity to avoid the problem of differential inclusion. Some preliminary numerical results of the disc and pad are obtained. The results exhibit the occurrence of stick-slip with a relatively small high frequency component during the sliding regime. The later component is mainly due to higher elastic in-plane modes of the disc, whereas the stick-slip component is a global disc-pad motion involving the lowest pad mode.

scholarly journals Mixed Finite Element Method for Static and Dynamic Contact Problems with Friction and Initial Gaps

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Lanhao Zhao ◽  
Zhi Liu ◽  
Tongchun Li
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Mixed Finite Element ◽  
Iteration Process ◽  
Mixed Finite Element Method ◽  
Contact Problems ◽  
Dynamic Contact ◽  
Contact Forces ◽  
Stick Slip ◽  
Element Method

A novel mixed finite element method is proposed for static and dynamic contact problems with friction and initial gaps. Based on the characteristic of local nonlinearity for the problem, the system of forces acting on the contactor is divided into two parts: external forces and contact forces. The displacement of structure is chosen as the basic variable and the nodal contact force in contact region under local coordinate system is selected as the iteration variable to confine the nonlinear iteration process in the potential contact surface which is more numerically efficient. In this way, the sophisticated contact nonlinearity is revealed by the variety of the contact forces which are determined by the external load and the contact state stick, slip, or separation. Moreover, in the case of multibody contact problem, the flexibility matrix is symmetric and sparse; thus, the iterative procedure becomes easily carried out and much more economical. In the paper, both the finite element formulations and the iteration process are given in detail for static and dynamic contact problems. Four examples are included to demonstrate the accuracy and applicability of the presented method.

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