Effect of finite contact area on impact stresses in polycrystalline graphite beams

Abstract

Theoretical work is reported on the determination of the stresses produced by a single impact load in rod specimens of polycrystalline graphites, typically 0.1 m long and 0.015 m diameter, simply supported at the ends. The impact force function was calculated from the theory of Timoshenko, the effects of a finite area between rod and impactor being included by varying the radius of curvature of the impactor. Results have been obtained for the maximum tensile stress as a function of time produced by an impactor of mass 0.29 kg striking with a velocity of 1.3 ms −1. Compared with some previous calculations for a point impact force, the effect of a larger contact area was found to reduce the contributions of the higher order vibrational modes. However, even for the largest radius of cuvature of the impactor studied, 1 m, the net effect on the predicted stresses was to reduce their values by only a few per centage from those obtained for a point contact force.