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The fracture toughness (KIC) of Mode I cracked sandstone exposed to sodium sulfate was investigated in this study. The uniaxial behavior of sandstone specimens soaked in different sodium sulfate solutions was determined for different strain rates. The results revealed that the strain rate has a significant and positive influence on the deformation and strength characteristics of sandstone. Compression strength gradually increased with strain rate at an increased slope, but peak strain decreased gradually with an increase in strain rate. The physical–mechanical characteristics and brittleness of sandstone gradually declined with increasing immersion time under sodium sulfate attack, but its plasticity increased significantly. There were holes and pitting corrosions in specimen surfaces exposed to sodium sulfate attack, and the edges and corners were somewhat weakened. Chemical damage variables were proposed to analyze the damage degree of sandstone, based on the change in porosity. Based on the testing results, regression analysis was conducted to determine the relations between ion concentrations (Ca2+ and Mg2+) in corresponding sodium sulfate solutions and for corresponding degrees of damage, and indirectly realize correlations between physical–mechanical characteristics, damage degree, and ion concentration. [ABSTRACT FROM AUTHOR]

With the actual environments of the joint rock in the bank slope of the Three Gorge Reservoir region (in China) as the background and considering the research concept that the effect of sodium sulfates and the dry–wet (D–W) cycle on rocks as interactive and inseparable, a test plan for D–W cycles was designed to study the D–W cycle damage of the mechanical characteristics and their correlations with the strength properties of sandstone with a Mode-I crack exposed to a sodium sulfate attack. Based on the crack's propagation radius and a damage variable reflecting a change in porosity, the degree of D–W cycle mechanical degradation was quantitatively analyzed. The mechanical characteristic of sandstone exhibited obvious damage under sodium sulfate attack and D–W cycles, among which the degree of D–W cycle degradation of the KIC was the greatest, whereas the internal friction angle was relatively the lowest. Meanwhile, apparent consistency was observed between the KIC and compression, and between the KIC and tensile strength of specimen exposed to the sodium sulfates attack under D–W cycles. Moreover, an evident corresponding relationship existed among the deterioration damage of the mechanical properties, corresponding ion concentrations dissolved in sodium sulfate solution, and deterioration degree of the physical characteristics of sandstone. Meanwhile, the correlation relationships among physical and mechanical properties, D–W cycle damage degree, and ion concentration were obtained. [ABSTRACT FROM AUTHOR]

The effect of porosity on the effective thermal conductivities calculation for continuous SiC fiber reinforced SiC matrix composites (SiC f /SiC) was studied in this work by finite element modeling. A three-dimensional representative volume element (RVE) containing detailed geometric features (fibers, matrix, fiber coatings and pores) was generated to rebuild the microstructure of SiC f /SiC and used to numerically calculate the effective transversal and longitudinal thermal conductivities of SiC f /SiC. Markworth model and parallel model were chosen as theoretical models to calculate the transversal and longitudinal thermal conductivities respectively. The numerical results obtained by RVE models were validated by comparison with the theoretical and experimental results. The results highlight the existing theoretical models cannot well predict the transversal thermal conductivity of SiC f /SiC with the existence of pores. In the analysis of the effect of porosity, real pore structure in SiC f /SiC was investigated to revel the relationship between porosity and the effective thermal conductivities. In the case of longitudinal thermal conductivity, the parallel model plus the linear term of porosity can still be used to predict the longitudinal thermal conductivity. As for the transversal thermal conductivity, a more proper Markworth model for SiC f /SiC transversal thermal conductivity calculation calibrated by incorporating porosity is proposed to efficiently calculate the transversal thermal conductivity at the end of this paper. [ABSTRACT FROM AUTHOR]