ANALYTIC SOLUTIONS FOR DIAMETRAL POINT LOAD STRENGTH TESTS

This paper investigates the tensile stress distribution within a solid circular cylinder of diameter D and length 2L subjected to double dia metral indenters or diametral point load strength test (PLST). The con tact problem between the indenters and the cylinder is solved analytic ally, and exact solution for stress distribution is obtained through t he use of displacement functions and double Fourier expansion in theta - and z-coordinates. Numerical results show that the tensile stress at the center of the cylinders, in general, decreases with Poisson's rat io nu and increases with 2L/D for 2L/D < 1, but remains roughly consta nt for 2L/D > 1. This prediction agrees exactly with the shape effect observed experimentally for the PLST for marbles, granite, and tuff fo und in Hong Kong and with previous published results for other rocks. The magnitude of tensile stress at the center is about three times the prediction obtained by using Wijk's formula, but seems more comparabl e with experimental results. The size effect of the point load strengt h index observed experimentally is also predicted by our theory.