A significant advance is made, however, when the
contribution of tangential elasticity is included. Mindlin (3)
has developed a theory of tangential compliance for two identical elastic spheres which are pressed together under a constant normal load. He showed that, for small relative tangential loads, an annulus of micro-slip is generated at the boundary of contact. As tangential load increases, the inner radius of this annulus progressively reduces until,
when the critical value of friction force is reached, the surfaces break away in gross-slip. In a later paper, Mindlin and Deresiewicz (4) extended the original theory to cover cases
involving more complex loading.
The authors (5,6) have used a similar approach in making a detailed study of elastic impact which discloses interesting deviations from the predictions of the simple theory. To ensure that the contact area is circular and that normal
motion is not influenced by tangential effects, attention was restricted to the case of the impact, on an elastic half-space, of a body whose centre of mass is also the centre of curvature of a spherical contact surface. Simple examples of such a body are a sphere or a symmetrical slice from a sphere.
The predictions of this theory agree with those of the simple rigid body theory when gross-slip persists throughout the impact, but the occurrence of micro-slip blurs the boundary between the states of sliding and rolling and changes in friction force become continous. The interface behaves somewhat as a pair of mutually perpendicular non-linear springs
which react independently against the body, except that the stiffness of the tangential 'spring' is influenced by the normal compliance. Tangential vibration, distinct from the half-cycle of normal vibration, is excited by the initial conditions and its frequency, characteristically, depends upon the mass distribution of the body.
A significant advance is made, however, when thecontribution of tangential elasticity is included. Mindlin (3)has developed a theory of tangential compliance for two identical elastic spheres which are pressed together under a constant normal load. He showed that, for small relative tangential loads, an annulus of micro-slip is generated at the boundary of contact. As tangential load increases, the inner radius of this annulus progressively reduces until,when the critical value of friction force is reached, the surfaces break away in gross-slip. In a later paper, Mindlin and Deresiewicz (4) extended the original theory to cover casesinvolving more complex loading.The authors (5,6) have used a similar approach in making a detailed study of elastic impact which discloses interesting deviations from the predictions of the simple theory. To ensure that the contact area is circular and that normalmotion is not influenced by tangential effects, attention was restricted to the case of the impact, on an elastic half-space, of a body whose centre of mass is also the centre of curvature of a spherical contact surface. Simple examples of such a body are a sphere or a symmetrical slice from a sphere.The predictions of this theory agree with those of the simple rigid body theory when gross-slip persists throughout the impact, but the occurrence of micro-slip blurs the boundary between the states of sliding and rolling and changes in friction force become continous. The interface behaves somewhat as a pair of mutually perpendicular non-linear springswhich react independently against the body, except that the stiffness of the tangential 'spring' is influenced by the normal compliance. Tangential vibration, distinct from the half-cycle of normal vibration, is excited by the initial conditions and its frequency, characteristically, depends upon the mass distribution of the body.
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