RESUMO
Many researchers have proposed vibration-based damage-detection approaches for continuous structural health monitoring. Translation to real applications is not always straightforward because the proposed methods have mostly been developed and validated in controlled environments, and they have not proven to be effective in detecting real damage when considering real scenarios in which environmental and operational variations are not controlled. This work was aimed to develop a fully-automated strategy to detect damage in operating tie-rods that only requires one sensor and that can be carried out without knowledge of physical variables, e.g., the axial load. This strategy was created by defining a damage feature based on tie-rod eigenfrequencies and developing a data-cleansing strategy that could significantly improve performance of outlier detection based on the Mahalanobis squared distance in real applications. Additionally, the majority of damage-detection algorithms presented in the literature related to structural health monitoring were validated in controlled environments considering simulated damage conditions. On the contrary, the approach proposed in this paper was shown to allow for the early detection of real damage associated with a corrosion attack under the effects of an intentionally uncontrolled environment.
Assuntos
Algoritmos , VibraçãoRESUMO
The low-density steels represent a topic of great interest within the scientific world because of the great demand from the steel market of increasingly lighter materials, also featured by an optimal mix of the mechanical properties. In this work, the corrosion and hot oxidation resistance of a Fe-15%Mn-9.5%Al-6.5%Ni-1%Cr-0.43%C were analyzed and related to the microstructural features. The material behavior was analyzed both in the as-cast and in the heat-treated state. For the corrosion test, the experimental plan was fulfilled using four different concentrations of HCl and four temperatures. In the case of hot oxidation resistance, the exposure time and the temperature effects were evaluated. The corrosion resistance in HCl was comparable to the stainless steel, and the iso-corrosion curves showed excellent resistance of the 1300 °C solution-treated material, especially at low temperatures, but it is also good at high temperatures due to the hot oxidation.
RESUMO
Shot peening is a surface process commonly used in the aeronautic and automotive industries to improve fatigue resistance. Shot peening is proven to be beneficial in the fatigue behavior of components, but rarely has its influence on wear and pitting corrosion resistance been evaluated. In this work, shot peening was performed on AISI F55-UNS S32760 super-duplex stainless steel samples previously submitted to various thermal treatments, to obtain different initial microstructures and properties. Samples have been characterized in terms of microstructure morphology, local chemical composition, microhardness of each constituent phase, and energy dissipation modes. The enhanced properties provided by shot peening has been evaluated through residual stress depth profiles and Full Width at Half Maximum (FWHM) using X-ray diffraction (XRD), surface hardness, surface roughness, and corrosion resistance through salt spray fog tests. The 1400 °C solution thermal treatment was identified as the optimum initial condition, which maximizes the advantages of the shot peening treatment, even pitting corrosion resistance. These results are related to the uniformity of austenite and ferrite in terms of microstructure morphology, micromechanical properties, and alloying elements distribution.