The Experts below are selected from a list of 6009 Experts worldwide ranked by ideXlab platform
Colin Thornton - One of the best experts on this subject based on the ideXlab platform.
-
on elastic plastic normal contact force models with and without adhesion
Powder Technology, 2017Co-Authors: Colin Thornton, Sharen J Cummins, Paul W ClearyAbstract:The simple problem of the normal impact of a sphere with a target wall is used to evaluate various elastic-plastic normal contact force models reported in the literature. Both non-adhesive and adhesive contact force models are considered, including both models based on contact mechanics theory and other simpler models frequently used in Discrete Element Modelling (DEM). In the context of non-adhesive, elastic perfectly plastic interactions involving idealised spheres, it is demonstrated that, for piecewise linear models, a variable unloading stiffness needs to be scaled to the square root of the maximum relative approach, in order to obtain a realistic velocity dependency of the Coefficient of Restitution. In the case of elastic perfectly plastic adhesive interactions of spherical particles, it is demonstrated that some existing models are unphysical and lead to qualitatively wrong dependencies of the Coefficient of Restitution on the magnitude of the impact velocity.
-
an investigation of the comparative behaviour of alternative contact force models during elastic collisions
Powder Technology, 2011Co-Authors: Colin Thornton, Sharen J Cummins, Paul W ClearyAbstract:Abstract Rebound kinematics are compared for both viscous dissipation and plastic dissipation models for an inelastic sphere obliquely impacting a target wall for a range of normal Coefficients of Restitution. The models are quite consistent for high normal Coefficients of Restitution but significant differences are noted between the models as the normal Coefficient of Restitution reduces. The reasons for the differences, in terms of the rebound tangential surface velocities, are explained for both plastic and viscous dissipation models. A new ‘partially latching spring’ model is proposed that provides realistic predictions of the contact force magnitude and contact duration. Finally, a general condition for sliding to occur throughout inelastic impacts is identified for any value of the normal Coefficient of Restitution.
-
a theoretical model for the stick bounce behaviour of adhesive elastic plastic spheres
Powder Technology, 1998Co-Authors: Colin Thornton, Zemin NingAbstract:Abstract The paper considers the normal impact of elastic-perfectly plastic spheres, with and without interface adhesion, and presents an analytical solution for the Coefficient of Restitution which is expressed in terms of the impact velocity, the critical sticking velocity and the velocity below which the interaction is assumed to be elastic.
Dan B. Marghitu - One of the best experts on this subject based on the ideXlab platform.
-
experimental and theoretical analysis of the elasto plastic oblique impact of a rod with a flat
International Journal of Impact Engineering, 2015Co-Authors: Hamid Gheadnia, Ozdes Cermik, Dan B. MarghituAbstract:Abstract In this study, the elasto-plastic oblique impact of a rod with a flat has been analyzed experimentally and theoretically. Nine different flattening and indentation contact models have been used to simulate the impact. The models have been compared theoretically in terms of the linear and the angular motion, the contact force during the impact, and the permanent deformation. A 3D infrared camera has been used in order to capture the motion of the rod before and after the impact. Experimental results for the Coefficient of Restitution and the rebound angular velocity have been compared with the presented models. Selecting the appropriate contact model is important on predicting the motion of the system for the simulations. For the impact angle θ = 45 ° our previous model matches the experimental results. For the impact angle θ = 17.2 ° it has been shown that all of the presented contact models show smaller values for Coefficient of Restitution and rebound angular velocity compare to the experiments.
-
differential formulation for the Coefficient of Restitution of a rigid link
Applied Mechanics and Materials, 2015Co-Authors: Dorian Cojocaru, Dan B. MarghituAbstract:The differential impact equations of motion are developed using an nonlinear contact force. The nonlinear equations of motion are written using symbolical MATLAB and are solved using numerical techniques. The impact equations are based on the Kogut-Etsion model. The numerical results are obtained for different geometries of the link, different Coefficients of friction, and different initial conditions. The Coefficient of Restitution (COR) is discussed for specific cases. The results can be used for the impact of mobile robots with different type of surfaces.
-
Predicting the Coefficient of Restitution of impacting elastic-perfectly plastic spheres
Nonlinear Dynamics, 2010Co-Authors: Robert L. Jackson, Itzhak Green, Dan B. MarghituAbstract:The current work presents a different methodology for modeling the impact between elasto-plastic spheres. Recent finite element results modeling the static deformation of an elasto-plastic sphere are used in conjunction with equations for the variation of kinetic energy to obtain predictions for the Coefficient of Restitution. A model is also needed to predict the residual deformation of the sphere during rebound, or unloading, of which several are available and compared in this work. The model predicts that a significant amount of energy will be dissipated in the form of plastic deformation such that as the speed at initial impact increases, the Coefficient of Restitution decreases. This work also derives a new equation for the initial critical speed which causes initial plastic deformation in the sphere that is different than that shown in previously derived equations and is strongly dependant on Poisson’s Ratio. For impacts occurring above this speed, the Coefficient of Restitution will be less than a value of one. This work also compares the predictions between several models that make significantly different predictions. The results of the current model also compare well with some existing experimental data. Empirical fits to the results are provided for use as a tool to predict the Coefficient of Restitution.
-
predicting the Coefficient of Restitution of impacting elastic perfectly plastic spheres
Part B: Magnetic Storage Tribology; Manufacturing Metalworking Tribology; Nanotribology; Engineered Surfaces; Biotribology; Emerging Technologies; Spe, 2006Co-Authors: Robert L. Jackson, Itzhak Green, Dan B. MarghituAbstract:The current work presents a different meth- odology for modeling the impact between elasto- plastic spheres. Recent finite element results modeling the static deformation of an elasto-plastic sphere are used in conjunction with equations for the variation of kinetic energy to obtain predictions for the coeffi- cient of Restitution. A model is also needed to predict the residual deformation of the sphere during rebound, or unloading, of which several are available and com- pared in this work. The model predicts that a signifi- cant amount of energy will be dissipated in the form of plastic deformation such that as the speed at initial im- pact increases, the Coefficient of Restitution decreases. This work also derives a new equation for the initial critical speed which causes initial plastic deformation in the sphere that is different than that shown in pre- viously derived equations and is strongly dependant on Poisson's Ratio. For impacts occurring above this speed, the Coefficient of Restitution will be less than a value of one. This work also compares the predictions between several models that make significantly differ-
Paul W Cleary - One of the best experts on this subject based on the ideXlab platform.
-
on elastic plastic normal contact force models with and without adhesion
Powder Technology, 2017Co-Authors: Colin Thornton, Sharen J Cummins, Paul W ClearyAbstract:The simple problem of the normal impact of a sphere with a target wall is used to evaluate various elastic-plastic normal contact force models reported in the literature. Both non-adhesive and adhesive contact force models are considered, including both models based on contact mechanics theory and other simpler models frequently used in Discrete Element Modelling (DEM). In the context of non-adhesive, elastic perfectly plastic interactions involving idealised spheres, it is demonstrated that, for piecewise linear models, a variable unloading stiffness needs to be scaled to the square root of the maximum relative approach, in order to obtain a realistic velocity dependency of the Coefficient of Restitution. In the case of elastic perfectly plastic adhesive interactions of spherical particles, it is demonstrated that some existing models are unphysical and lead to qualitatively wrong dependencies of the Coefficient of Restitution on the magnitude of the impact velocity.
-
an investigation of the comparative behaviour of alternative contact force models during elastic collisions
Powder Technology, 2011Co-Authors: Colin Thornton, Sharen J Cummins, Paul W ClearyAbstract:Abstract Rebound kinematics are compared for both viscous dissipation and plastic dissipation models for an inelastic sphere obliquely impacting a target wall for a range of normal Coefficients of Restitution. The models are quite consistent for high normal Coefficients of Restitution but significant differences are noted between the models as the normal Coefficient of Restitution reduces. The reasons for the differences, in terms of the rebound tangential surface velocities, are explained for both plastic and viscous dissipation models. A new ‘partially latching spring’ model is proposed that provides realistic predictions of the contact force magnitude and contact duration. Finally, a general condition for sliding to occur throughout inelastic impacts is identified for any value of the normal Coefficient of Restitution.
Thorsten Poschel - One of the best experts on this subject based on the ideXlab platform.
-
hydrodynamics of binary mixtures of granular gases with stochastic Coefficient of Restitution
Journal of Fluid Mechanics, 2015Co-Authors: Dan Serero, Nina Gunkelmann, Thorsten PoschelAbstract:A hydrodynamic description of dilute binary gas mixtures comprising smooth inelastic spheres interacting by binary collisions with a random Coefficient of Restitution is presented. Constitutive relations are derived using the Chapman–Enskog perturbative method, associated with a computer-aided method to allow high-order Sonine polynomial expansions. The transport Coefficients obtained are checked against DSMC simulations. The resulting equations are applied to the analysis of a vertically vibrated system. It is shown that differences in the shape of the distributions of the Coefficient of Restitution are sufficient to produce partial segregation.
-
complex velocity dependence of the Coefficient of Restitution of a bouncing ball
Physical Review Letters, 2013Co-Authors: P Muller, Michael Heckel, Achim Sack, Thorsten PoschelAbstract:We investigate the Coefficient of normal Restitution as a function of the impact velocity, e(v), for inelastic spheres. We observe oscillating behavior of e(v) which is superimposed to the known decay of the Coefficient of Restitution as a function of impact velocity. This remarkable effect was so far unnoticed because under normal circumstances it is screened by statistical scatter. We detected its clear signature by recording large amounts of data using an automated experiment. The new effect may be understood as an interplay between translational and vibrational degrees of freedom of the colliders. Both characteristics of the oscillation, the wavelength and the amplitude, agree quantitatively with a theoretical description of the experiment.
-
Coefficient of Restitution and linear dashpot model revisited
Granular Matter, 2007Co-Authors: Thomas Schwager, Thorsten PoschelAbstract:With the assumption of a linear–dashpot interaction force, the Coefficient of Restitution, $$\varepsilon_d^0(k, \gamma)$$ , can be computed as a function of the elastic and dissipative material constants, k and γ by integrating Newton’s equation of motion for an isolated pair of colliding particles. If we require further that the particles interact exclusively repulsive, which is a common assumption in granular systems, we obtain an expression $$\varepsilon_d(k, \gamma)$$ which differs even qualitatively from the known result $$\varepsilon_d^0(k, \gamma)$$ . The expression $$\varepsilon_d(k, \gamma)$$ allows to relate Molecular Dynamics simulations to event-driven Molecular Dynamics for a widely used collision model.
Sharen J Cummins - One of the best experts on this subject based on the ideXlab platform.
-
on elastic plastic normal contact force models with and without adhesion
Powder Technology, 2017Co-Authors: Colin Thornton, Sharen J Cummins, Paul W ClearyAbstract:The simple problem of the normal impact of a sphere with a target wall is used to evaluate various elastic-plastic normal contact force models reported in the literature. Both non-adhesive and adhesive contact force models are considered, including both models based on contact mechanics theory and other simpler models frequently used in Discrete Element Modelling (DEM). In the context of non-adhesive, elastic perfectly plastic interactions involving idealised spheres, it is demonstrated that, for piecewise linear models, a variable unloading stiffness needs to be scaled to the square root of the maximum relative approach, in order to obtain a realistic velocity dependency of the Coefficient of Restitution. In the case of elastic perfectly plastic adhesive interactions of spherical particles, it is demonstrated that some existing models are unphysical and lead to qualitatively wrong dependencies of the Coefficient of Restitution on the magnitude of the impact velocity.
-
an investigation of the comparative behaviour of alternative contact force models during elastic collisions
Powder Technology, 2011Co-Authors: Colin Thornton, Sharen J Cummins, Paul W ClearyAbstract:Abstract Rebound kinematics are compared for both viscous dissipation and plastic dissipation models for an inelastic sphere obliquely impacting a target wall for a range of normal Coefficients of Restitution. The models are quite consistent for high normal Coefficients of Restitution but significant differences are noted between the models as the normal Coefficient of Restitution reduces. The reasons for the differences, in terms of the rebound tangential surface velocities, are explained for both plastic and viscous dissipation models. A new ‘partially latching spring’ model is proposed that provides realistic predictions of the contact force magnitude and contact duration. Finally, a general condition for sliding to occur throughout inelastic impacts is identified for any value of the normal Coefficient of Restitution.