Naturally Accepted Boundary Conditions for the Brazilian Disc Test and the Corresponding Stress Field

The stress field developed in the Brazilian disc is determined assuming that the disc is under the influence of a combination of two load distributions, namely normal (radial)- and shear (frictional)-stresses, both of them acting along two finite symmetric arcs of the disc periphery. The nature of the two distributions as well as the extent of the loaded arcs are obtained from the solution of the respective contact problem according to which the disc and the jaw are considered as a system of two elastic plane bodies in contact pressed against each other. Emphasis is given to the stresses due to friction since the stress field due to the specific distribution of radial pressure is already known. It is concluded that the role of friction cannot be ignored, especially in the immediate vicinity of the contact rim. Moreover, for high surface roughness the overall transverse normal stress component in this region becomes of tensile nature indicating increased possibility of premature local cracking (taking into account the low tensile strength of the materials tested using the Brazilian disc test). On the other hand, the stress field at the disc’s center is totally insensitive to both the exact distribution of radial pressure and also to the presence or absence of friction. It is thus indicated that in case fracture in the immediate vicinity of the contact rim is by some means suppressed (reducing for example drastically the coefficient of friction) the results of the Brazilian disc test correspond, in a satisfactory manner, to those predicted by Hondros’ classic approach.