The deformation modulus of rocks is usually estimated only by compression tests. However, most rocks show bi-modular behavior, consisting of deformation modulus having different values in compression and tension; usually in compression the deformation modulus is greater than tension. Due to the direct tensile test being a more complex test to carry out, the tensile strength is usually estimated by the indirect tensile test (Brazilian test). Consequently, there are researchers who propose methods estimating the tensile deformation modulus with the Brazilian test. In the present paper, the deformation modulus of Porto granite samples with different densities (weathering degree) was obtained in three different ways: in the uniaxial compression test, in the direct tensile test, and in the Brazilian test (diametric load) and then compared. From the results, it is concluded that in general the deformation modulus obtain only by the Brazilian test cannot be considered representative of direct traction.
Alencar et al. (Mon,) studied this question.