Adaptive characterization of recrystallization kinetics in IF steel by electron backscatter diffraction

In this study, a rigorous methodology for quantifying recrystallization kinetics by electron backscatter diffraction is proposed in order to reduce errors associated with the operator's skill. An adaptive criterion to determine adjustable grain orientation spread depending on the recrystallization stage is proposed to better identify the recrystallized grains in the partially recrystallized microstructure. The proposed method was applied in characterizing the microstructure evolution during annealing of interstitial‐free steel cold rolled to low and high true strain levels of 0.7 and 1.6, respectively. The recrystallization kinetics determined by the proposed method was found to be consistent with the standard method of Vickers microhardness. The application of the proposed method to the overall recrystallization stages showed that it can be used for the rigorous characterization of progressive microstructure evolution, especially for the severely deformed material.     

Variability of intact rock mechanical properties for some metamorphic rock types and its implications on the number of test specimens

Intact rock strength and stiffness properties are commonly used in rock mass mechanical characterization, and their evaluation is usually based on laboratory tests. Due to the variability that affects strength and stiffness parameters, the determination of the number of laboratory-tested specimens required to obtain a reliable reference value is very useful. However, many studies reported in apposite literature focused only on the variability of strength parameters. This study investigates the variability of some of the most important strength and stiffness properties (unconfined compressive strength, indirect tensile strength, tangent and secant Young’s moduli, Poisson’s ratio) by applying statistical methods (statistical decision theory and statistical inference theory). A data set of 451 laboratory tests was used, performed on three rock types. The statistical analyses were applied with the aim of assessing how closely intact rock laboratory data follow a normal distribution and determining the minimum number of specimens required to obtain a reliable average value of the parameters in relation to a targeted precision index for a confidence level of 95 %. The results indicate that the minimum number of samples needed varies depending on rock and test types. Among the stiffness properties, tangent Young’s modulus has a lower variability than both the secant modulus and the Poisson’s ratio, whereas in terms of strength parameters, unconfined compressive strength is subject to greater variability than indirect tensile strength.     

Fatigue crack in large-scale tubular joints for offshore structures

Tubular members have been used for constructing offshore structures. Large-scale fatigue tests of welded tubular K-joints under the balanced in-plane bending brace were carried out to investigate the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The experimental results were verified by numerical approaches and compared with the IIW, DnV RP-C203 and API RP 2A-WSD design curves. The test results based on the hot spot stress were in agreement with the design curves. The SCF factor for tubular K-jo...