A Novel Strength Model for Cement Marine Clay Based on the Mechanical-Chemical Coupling Behavior

Crucial mechanical-chemical (MC) interactions occur during the cement hydration process in cement marine clay; however, the role of such an important element of the resulting strength has been subject to less investigation, particularly from the theoretical perspective. To overcome this scientific gap, an efficient strength-based model accounting for the coupled MC processes is proposed here. Based on the analysis of the cement hydration mechanism, the porosity was chosen as the main factor to characterize the influence of the MC interactions on the overall response. To verify the accuracy of the MC model, the unconfined compressive strength (UCS) experiment was conducted for the cement marine clay samples, and the corresponding simulation model was constructed using COMSOL multiphysics®. In addition, a comparison between the predicted results by the existing three strength models and the proposed MC model was performed. Subsequently, the sensitivity analysis and identification of mechanical parameters were carefully carried out. The obtained results show that the UCS strength for Taizhou clay ranges from 10.21 kPa to 354.2 kPa as the cement content increases from 10% to 20%, and the curing time varies from 3 days to 28 days. The mechanical parameters in the MC model can be obtained according to the porosity level. A reasonably good agreement between the UCS strength results of simulations and the experimentally observed data is reported. Additionally, the predicted UCS strength results by the MC model demonstrate the best correspondence with the measured values, indicating the high efficacy of the established model.

Effect of pH and Al Cations on Chromate Inhibition of Galvanic-Induced Corrosion of AA7050-T7451 Macro-Coupled to 316SS

The performance of chromate in protecting AA7050-T7451 coupled to 316SS in simulated fastener environments, including those representative of the boldly exposed surfaces and downhole conditions, was investigated utilizing a number of electrochemical and surface characterization techniques. The influence of pH and Al3+ on the galvanic coupling behavior and damage evolution on AA7050 as a function of chromate concentration were assessed. The degree of chromate inhibition was observed to decrease as pH decreased, owing to chromate speciation and reduced capacity to suppress the hydrogen evolution reaction (HER) compared to the oxygen reduction reaction (ORR). The addition of 0.1 M Al3+ significantly increased HER kinetics and produced a large buffer effect which overwhelmed the ability of chromate to slow damage propagation on AA7050. Assessment of cathodes indicated that Cu was more important than 316SS in driving damage initiation, but less active than 316SS in supporting high-rate damage propagation in simulated crevice environments. The implications of this study for actual bimetallic systems are discussed.

Wilson loops in $$ \mathcal{N} $$ = 4 SO(N) SYM and D-branes in AdS5 × ℝℙ5

We study the half-BPS circular Wilson loop in $$ \mathcal{N} $$ N = 4 super Yang-Mills with orthogonal gauge group. By supersymmetric localization, its expectation value can be computed exactly from a matrix integral over the Lie algebra of SO(N). We focus on the large N limit and present some simple quantitative tests of the duality with type IIB string theory in AdS5× ℝℙ5. In particular, we show that the strong coupling limit of the expectation value of the Wilson loop in the spinor representation of the gauge group precisely matches the classical action of the dual string theory object, which is expected to be a D5-brane wrapping a ℝℙ4 subspace of ℝℙ5. We also briefly discuss the large N, large λ limits of the SO(N) Wilson loop in the symmetric/antisymmetric representations and their D3/D5-brane duals. Finally, we use the D5-brane description to extract the leading strong coupling behavior of the “bremsstrahlung function” associated to a spinor probe charge, or equivalently the normalization of the two-point function of the displacement operator on the spinor Wilson loop, and obtain agreement with the localization prediction.