Probabilistic High Cycle Fatigue Assessment Process for Integrally Bladed Rotors (original) (raw)
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International Journal of Fatigue, 2003
The EFS (Electrochemical Fatigue Sensor) is a device that is based on a study of electrochemical-mechanical interactions, providing information about the status of fatigue damage in a material, and promises to become a useful non-destructive, niche testing tool. The EFS has been shown to function for several commercial alloys, as well as in different environments. The present work is to confirm the feasibility of applying the EFS for assessing fatigue damage in duplex stainless steels. A second goal is to investigate the possibility of using an aggressive environment as an electrolyte within the EFS device. In doing so, corrosion-fatigue testing was conducted in EFS solutions at three different pH values: 8.4, 6 and 2. The results show that the fatigue life is longer at a pH value of 6. Such an unexpected environmental effect is discussed and related to the dissolution of the surface roughness generated by cyclic deformation, together with a higher repassivation rate.
Procedia Structural Integrity, 2017
During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
Chemical Composition Influence on Duplex Stainless Steels "475°C Embrittlement
Duplex stainless steels (DSSs) are prone to age hardening and embrittle over a wide temperature range depending on their chemical composition. This is mainly due to precipitation phenomena that may occur inside ferrite grains and at ferrite-austenite grain boundaries. The aim of this work is the analysis of chemical composition influence on fatigue crack propagation resistance of "475°C embrittled" duplex stainless steels. Fatigue crack propagation resistance of 21 Cr 1 Ni, 22 Cr 5 Ni and 25 Cr 7 Ni duplex stainless steels was investigated considering both as received and 475°C embrittled conditions (1000h). Microstructural analyses were performed using a transmission electron microscope (TEM). Thin foils for TEM observations were prepared by a preliminary mechanical thinning, down to 100 µm thickness, followed by twin-jet polishing in a solution of 2-butoxiethanol (90%) and perchloric acid (10%) at -3÷-1°C, using a voltage of 20-35V depending the composition of the steel....
Fatigue Behaviors in Duplex Stainless Steel Studied Using In-situ SEM/EBSD Method
Procedia Materials Science, 2014
Austenite and ferrite in duplex stainless steels have different physical and mechanical properties. They can behave different during cyclic loading. To understand the fatigue behaviors of these two phases, an in-situ SEM/EBSD fatigue test has been performed. Flat specimens made from the specimens of pre-fatigue tested with three point bending were cyclically loaded in a scanning electron microscope via a compact test rig. By in situ/ex situ SEM/EBSD examination, slip activities and propagation of the fatigue cracks have been studied. Microstructures along the path of the fatigue crack were characterized. The different phase properties seem to lead to certain difference in the slip activity and formation of PSBs. Inhomogeneous slip activities and local strain concentrations were also found, which developed with increasing number of load cycles. Crack propagation behaviors in grain and cross the grain or phase boundaries have been discussed. Crack deflection occurs at the phase boundaries, but crack branching occurs mainly in the grains due to the dislocation slip. In-situ SEM/EBSD fatigue test confirms that crack propagation deflection and formation of crack branches can significantly reduce the crack propagation rate.
Revue de Métallurgie, 2011
Increasing interest in duplex stainless steels is due to their ability to combine elevated mechanical properties (strength, fatigue. . . ) and an optimal resistance to many types of corrosion like Stress Corrosion Cracking or Intergranular Sensitization. Given high chromium content of the standard and super-duplex steels along with molybdenum and nitrogen alloying additions, they also exhibit an excellent resistance to pitting and crevice corrosion in halide-containing media generally equivalent to austenitic and super-austenitic with similar Pitting Resistance Equivalent. Further aspects of the question are reviewed in introduction of the present paper including passive film and metallurgical features such as two-phase microstructure, presence of non metallic inclusions, precipitates or intermetallic phases. Then, this work addresses the problems of corrosion testing of duplex stainless steels. It is intended in particular to shed light on some points of practical importance regarding electrochemical characterization best practices. Thus, a reliable ranking of materials, including new lean grades, requires a relevant choice of corrosion criteria and polarization methods. The determination of both pitting potentials and critical pitting temperatures is achieved by using a combination of several electrochemical tests based on potentiodynamic, potentiostatic as well as galvanostatic experiments together with a statistical analysis when needed.
Materials Science and Engineering: A, 2004
Interrupted cyclic deformation tests up to 20% of fatigue life were performed on electropolished specimens of a thermally aged superduplex stainless steel. Crystallographic orientation results obtained by electron back-scattering diffraction analysis allowed to determine the individual orientation of each individual grain as well as the plastically active slip systems. Electron back-scattering diffraction results demonstrate the requirement for the accomplishment of several conditions for a slip system to become active. These conditions were found to be different for austenite and ferrite.
Effect of aqueous corrosion on the high cycle fatigue strength of a martensitic stainless steel
Ecf19, 2013
This study is devoted to the investigation of the aqueous corrosion effect on the high cycle fatigue (HCF) strength of a martensitic stainless steel used in aeronautic applications. HCF tests (between 10 5 and 10 7 cycles) were carried out in two environments: (i) in air and (ii) in a 0.1 M NaCl aqueous solution (pH = 6) with two load ratios (R=-1 and 0.1). The corrosion fatigue strength at 10 7 cycles was found to be 50% the fatigue strength in air. Surface crack initiation was observed in air, while in solution crack initiated at corrosion pits. Electrochemical behaviour of passive film was investigated during in situ fatigue tests in NaCl solution by monitoring the free potential and galvanostatic impedance EIS tests. Based on fractography analysis and electrochemical test results, fatigue crack initiation mechanisms in air and in NaCl solution were investigated. A scenario of fatigue crack initiation is proposed based on physical evidences. Local passive film ruptures are the principal cause of the corrosion fatigue crack initiation. This scenario implies combined processes of local passive film rupture (induced by the cyclic loading) stress assisted corrosion and enhanced pitting development. This aspects will be discussed by comparing the characteristic time of repassivation of the steel to the mechanical characteristic times (loading frequency, plasticity development). No loading frequency effect was observed between 10 and 120 Hz because the characteristic time of repassivation of the steel is very low compared to the period of the cyclic loading. But the existence of threshold stress amplitude has been shown, below which there is no passive film failure under cyclic loading, and, consequently no corrosion fatigue crack initiation after 10 7 cycles.
Transactions of the Indian Institute of Metals, 2019
The aim of the present work was to study the impact, fatigue crack growth and corrosion behavior of 2205 duplex stainless steel (DSS) when subjected to one of the most influential thermal aging condition that promotes deleterious secondary precipitation. Formation of Cr-and Mo-rich r-phase was confirmed by EDX analysis which deteriorated impact toughness causing the material to fail following quasi-cleavage mode of fracture. Susceptibility of DSS 2205 to pitting corrosion assessed though Potentiodynamic polarization technique was enhanced by thermal aging, but sensitization performance evaluated via double-loop electrochemical potentiokinetic reactivation (DLEPR) technique did not show much degradation. However, fatigue crack growth behavior testing divulged drastic enhancement in impediment to crack propagation by the matrix after thermal aging.
Materials Research, 2019
Duplex stainless steels are materials with high mechanical strength, toughness, and corrosion resistance, properties that make them rather appealing for the application on chemical and petrochemical industries. However, the exposure of such materials to high temperatures promotes the precipitation of deleterious intermetallic phases that cause significant damage to the mechanical and corrosion properties of these materials. In this study, the UNS S31803 duplex stainless steel received a thermal treatment at a temperature of 830 °C for 30, 90, and 180 minutes. After the treatment, the precipitates were characterized by backscattered electrons (BSE) and chemical composition mapping, and the properties of impact toughness were assessed by Charpy V-notch test for the different treatment conditions. The corrosion resistance properties were assessed by cyclic potentiodynamic polarization study. The thermal treatments at 830 °C resulted in a considerable reduction of impact toughness, and the corrosion resistance was also reduced in longer treatment times along with the loss of the passivation ability of the materials treated.