Microstructure Analyses and Multiscale Stochastic Modeling of Steel Structures Operated in Extreme Environment

The article primarily is concerned with the problem of damage accumulation and fracture modeling for steel structures operated at low temperature conditions. The inhomogeneity of the weld joints is other issue associated with the need to examining the microstructure and defects in steel at different scale levels. The next problem is that, extreme environment contains not only the extreme temperature conditions but phase transitions also, fluctuations in temperature, inappropriate in service and repair. Last factors have stochastic behavior and are even uncertain in nature. So these problems are observed and discussed in this paper as theoretical and experimental for building the multiscale model of structural damage accumulation, taking into account the following: the inhomogeneity of the weld, the low-temperature brittle-ductile transition for bcc steels, and the uncertainty factors estimation concept. The applications describe the locomotive tire lifetime estimation at low temperature conditions. The modeling approach is based on Kachanov-Rabotnov structural damage accumulation theory and stochastic crack growth modeling. Bayesian probability approach has been used for uncertainty factor estimation. The experimental part includes the internal friction study of low temperature transition mechanism for bcc steel, the mechanical tension and impact toughness tests for locomotive tire steel, and the low-cycling testing and microhardness estimation of mechanical properties for welded steel probes. The experimental testing shows the impact toughness drop at low temperature. The microstructural study for weld joints reveals the small cracks in heat affected zone, so the size and distance between such defects are used for stochastic modeling visualization of crack propagation and crack velocity estimation. The revealing mechanisms and proposed relationships could be used for theoretical and numerical modelling of damage accumulation and fracture in welded steel structures.