Hamid Ghaednia

A Solution of Rigid–Perfectly Plastic Deep Spherical Indentation Based on Slip-Line Theory

Abstract During indentation, it is often important to determine the relationship between the average pressure and the yield strength. This work uses slip-line theory to determine this relationship for the case of a rigid sphere indenting a frictionless perfectly plastic half-space (i.e., no hardening). The results show that the ratio between the average contact pressure and the yield strength decreases as the depth of indentation is increased. Note that the slip-line analysis does not include the effects of pileup or sink-in deformations. However, the slip-line theory has also been compared to data generated using the finite element method (FEM). The theory and the FEM results appear to agree well.

Experimental and theoretical study of the oblique impact of a tennis ball with a racket

The normal and the oblique impact of a tennis ball with a racket has been studied. An accurate setup has been built in order to provide consistent initial conditions for the impacts. Experiments have been done for a wide range of impact angles and initial velocities. The motion of the ball before, during and after the impact has been recorded using a high-speed camera with 10,000 frames per second. The impact has been divided into two phases, compression and restitution. An expression for the contact force has been provided. The coefficient of restitution and effective coefficient of friction have been analyzed experimentally. For low impact velocities, the coefficient of restitution is constant at different impact angles. The effective coefficient of friction changes as a function of the impact angle. The contact force expression has been determined for the compression and the restitution phases using the experimental data from normal impact experiments. The simulation and experimental results are compared and verified for the normal and the oblique impacts.

Analytical Study of the Oblique Impact of an Elastic Sphere with a Rigid Flat

In this study, an analytical model of the elastic impact of a solid rubber sphere with a rigid flat is analyzed. The linear and angular motion of the sphere have been simulated for the oblique (60°) and normal (0°) impact cases. The impact of the sphere with the rigid flat has been represented with a nonlinear contact force. The damping term of a previous normal contact force has been modified with a new expression. The normal contact force as a function of deflection has been studied for different cases.

Force Analysis for the Impact Between a Rod and Granular Material

The simulation of the normal and oblique impact of a rigid rod with a granular material has been studied. This model solved the inconsistency of the dynamic force at the beginning of the impact. Two different impact angles have been analyzed: the normal impact and the impact with an angle \(\theta =45^\circ \). The penetration depth, the normal velocity of the tip during impact and the normal contact force during the impact have been analyzed. For the normal impact the dynamic force reaches a maximum during the impact, while the static and the normal forces show continuous increase. For the oblique impact the dynamic and the total forces show a maximum during the impact, while the static force is increasing throughout the impact.

Analytical Study of the Oblique Impact of a Rod with a Flat Using an Elasto-Plastic Contact Model

In the current study a flattening contact model, combined with a permanent deformation expression, has been analyzed for the oblique impact case. The model has been simulated for different initial conditions using MATLAB. The initial impact velocity used for the simulations ranges from 0.5 to 3 m/s. The results are compared theoretically for four different impact angles including 20, 45, 70, and 90 degrees. The contact force, the linear and the angular motion, the permanent deformation, and the coefficient of restitution have been analyzed. It is assumed that sliding occurs throughout the impact.