Corrosion morphology is a key factor that influences the reliability and service life of a structure. As most structures service under stress corrosion, there is a great need to understand the effect of stress on the formation conditions of different morphologies. This paper introduces a numerical method to simulate the evolution of surface morphologies. The results indicate that a corroded surface will become rougher and sharper with an increase in stress, and as a consequence, the corrosion morphology will transfer from a flatter surface to a pit and then a crevice. The critical stress values for different morphologies (crevice, pit, and a flatter surface) were captured. Among the three morphologies, the flatter surface and pit maintain a fixed shape, also known as stable morphology. As stress exceeds a critical value, crevices are generated, and the morphology evolution becomes unstable. On the basis of the simulation results, the influence of morphology on the service life of the structure was evaluated. The corrosion velocity of a rough surface exceeds that of a flat surface, and this reduces the service life of the structure more significantly. With a rise in applied stress, the acceleration of corrosion presents a quadratically increasing relationship with applied stress.

The depth dependence of the indentation hardness, i.e., the indentation size effect (ISE), was manifested as an increase or decrease in hardness when penetration depth decreases, which was observed by previous experiments. Most scholars believe it is generated by strain gradient. However, additional opinions argue that other factors, similar to the strain gradient, can also contribute to the ISE. Importantly, if such an ISE occurs in an experiment, one needs to distinguish its causes. In this study, two external factors were considered, i.e., the specimen surface defect and indenter tip irregularity, which can lead to the hardness–depth-dependent relationships of the ISE. Moreover, a theoretical model was established to interpret the two dependent relationships and validated via finite element simulations. The simulation results showed that both external factors lead to significant hardness–depth dependences, in great agreement with theoretical derivations. Moreover, the simulation results demonstrated that the surface defect and indenter tip irregularity have a unified influence on the ISE, which is attributed to a sole depth deviation δ. Lastly, the ISE based on both external factors was eliminated and the real hardness was obtained. Based on this, when an ISE appears, it can be distinguished whether it is caused by external factors or strain gradient.