An Interplay Between the Weakening and Strengthening Effects of Interstitial Water on the Strength of Porous Brittle Solids

The paper is devoted to a study of factors that provide the nonlinear mechanical influence of pore fluid on the stress state, strength, and fracture of permeable brittle materials. Two key factors are considered: pore pressure and viscous stresses in the interstitial fluid. Using a coupled dynamic model implemented in the numerical method of homogeneously deformable discrete elements, we verified for the first time that Stefan’s viscous stress is responsible for the nontrivial and widely discussed effect of a significant increase in the dynamic strength of brittle solids in a fluid-saturated state compared to the dry state. Considering watered high-strength concrete, a quantitative estimate of the dimensionless factor of Stefan’s stress was derived. The contributions of shearing and tearing-off fracture mechanisms to the total damage of a concrete sample under uniaxial compression with different strain rates are analyzed.