Stress distribution within circular cylinders in compression

Abstract

The standard laboratory test involving the use of circular cylindrical specimens of concrete or rock is unsatisfactory. Friction existing between the end surfaces of the specimen and the platens of the loading machine causes development of nonuniform stresses throughout the specimen. These stresses have a major effect on the failure of the tested specimen and will result in incorrect measurement of mechanical property values (Poisson's ratio, modulus of elasticity, ultimate strength, etc.). In the standard test, with the cylinder under axial load, the specimen is in a state of triaxial stress. The greater the friction on the end surfaces, the greater the divergence from uniform axial stress in the cylinder. Only if the end friction is completely eliminated does the division of the load by the cross-sectional area describe the true state of stress. A theoretical solution has been derived for the stress and strain distribution within elastic cylindrical specimens, as a function of the friction at the interface of the specimen and the machine platens. The solution was checked experimentally using an epoxy cylindrical specimen with strain gages embedded within and bonded to its surface. The cylinder was tested under low, medium, and high friction end conditions. Reasonable agreement between the experimental and theoretical solutions was observed in all cases of end conditions.