Mechanical properties of 4 rocks at different temperatures and fracture assessment using the strain energy density criterion

Abstract

This work aims to analyse the fracture behaviour of rocks with U-shaped notches subjected to mode I loading and to different temperature conditions. To this end, an energy-based approach is used called the Strain Energy Density (SED) criterion. This study attempts to extend a previous work of the authors where the SED criterion was successfully applied to U-notched components subjected to mode I loading conditions at room temperature. In this case, the effect of temperature is considered as a new variable.The research analyses four different types of isotropic rocks with different lithologies, namely a Floresta sandstone, a Moleano limestone, a Macael marble and a Carrara marble. An exhaustive laboratory campaign was performed to define the main mechanical properties of the selected rocks at different temperatures. In total, 144 tensile splitting (Brazilian) tests, 120 uniaxial compression tests, 410 thermal expansion measurements and more than 790 four-point bending tests have been executed under different thermal conditions. On the other hand, the range of temperatures analysed varies from room temperature up to 250 ºC, which is a common band in geothermal applications.Temperature has proven to be a significant parameter when analysing the fracture behaviour of the four selected rocks. Its influence on the main mechanical properties of the rocks (tensile strength, fracture toughness, compressive strength, Young’s modulus, Poisson’s ratio) has been studied and similar trends have been observed for the marbles, but different or even opposite ones for the sandstone and limestone. Overall, the application of the SED criterion has led to relatively accurate fracture predictions under different temperature conditions. This methodology assumes a linear-elastic behaviour of the rocks at the studied range of temperatures. For this reason, the failure load predictions become less accurate when non-linearities are not negligible, as in the case of the Carrara marble.