On the transition of short cracks into long fatigue cracks in reactor pressure vessel steels

Abstract

Abstract. Short fatigue cracks, having dimension less than 1 mm, propagate at much faster rates (da/dN) even at lower stress intensity factor range (da/dN) as compared to the threshold stress intensity factor range obtained from long fatigue crack growth studies. These short cracks originate at the sub-grain level and some of them ultimately transit into critical long cracks over time. Therefore, designing the components subjected to fatigue loading merely on the long crack growth data and neglecting the short crack growth behavior can overestimate the component's life. This aspect of short fatigue cracks become even more critical for materials used for safety critical applications such as reactor pressure vessel (RPV) steel in nuclear plants. In this work, the transition behaviour of short fatigue crack gowth into long fatigue crack is studied in SA508 Grade 3 Class I low alloy steel used in RPVs. In-situ characterization of initiation, propagation and transition of short fatigue cracks is performed using fatigue stage for Scanning Electron Microscope (SEM) in addition to digital microscopes fitted over a servo-hydraulic fatigue machine and correlated with the microtructural information obtained using electron backscatter diffraction (EBSD). SA508 steel having an upper bainitic microstructure have several microstructural interfaces such as phase and grain boundaries that play a significant role in controlling the short fatigue crack propagation. Specially designed and prepared short fatigue specimens (eletro-polished) with varying initial crack lengths of the order of tens of microns are used in this study. The transition of such short initial cracks into long cracks is then tracked to give detailed insight into the role of each phase and phase/grain boundary with an objective of establishing Kitagawa-Takahashi diagram for the given RPV steel. The behavior of the transited long cracks is then compared with the crack propagation behavior obtained using conventional CT specimens. The outcome of this research will enhance information on the integrity of the components made from RPV steel used in Indian nuclear power plants.

Synthesis, Biological Evaluation, in silico ADMET and Molecular Docking of new 1,4‐Dihydropyridine Derivatives Bearing Ether Substitution as Calcium Channel Blockers

“…In the next step, the monobromo derivatives ( 3 a – b ) were synthesized using pyridinium bromide‐perbromide in the presence of pyridine in chloroform. Finally, the reaction of the synthesized monobromo dihydropyridines ( 3 a – b ) with aliphatic and aromatic alkoxides led to desired dihydropyridine compounds ( 5 a – h ) [23] . The general procedure of synthesis is depicted in Figure 2.…”

“…Finally, the reaction of the synthesized monobromo dihydropyridines (3 a-b) with aliphatic and aromatic alkoxides led to desired dihydropyridine compounds (5 a-h). [23] The general procedure of synthesis is depicted in Figure 2. The compounds were purified by preparative thin-layer chromatography and identified by mass spectroscopy, IR and 1 H-NMR.…”

On the role of vacancy-hydrogen complexes on dislocation nucleation and propagation in metals

“…Also in the oil and gas industry, the structural materials which are mainly nickel based superalloys are subjected to high-pressure and high temperature environment under corrosive gases such as CO 2 and H 2 S [1]. Thus, the introduction of hydrogen at high temperature and pressure conditions causes undesirable consequences in these industrially important nickel based alloys and other metals, such as loss of ductility, strength, fracture toughness, and causes earlier crack nucleation while causing fast crack propagation thus affecting their fatigue life [1][2][3][4][5]. This deterioration in the properties of metals is commonly referred to as hydrogen embrittlement (HE).…”

Cobalt supported on alumina as green catalyst for Biginelli reaction in mild conditions: effect of catalyst preparation method

“…These are currently the subject of intense focus due to their wide spectra of biological activities [9][10][11][12] such as anticancer, antifungal and anti HIV [13]. The Biginelli reaction is a new approach to "green chemistry" because it is a multicomponent reaction in which three or more starting chemicals are used as inputs for product formation, thus minimizing the number of intermediate steps [14,15].…”