Magnetic Barkhausen emission technique for detecting the overstressing during bending fatigue in case-carburised En36 steel (original) (raw)
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International Journal of Fatigue, 1999
A non-destructive, magnetic Barkhausen emission (MBE) technique has been used to assess various stages of low cycle fatigue (LCF) damage in 9Cr-1Mo ferritic steel. The initial decrease in the MBE peak height in the early stage of LCF cycling indicates the cyclic hardening stage, in which the formation of dislocation tangles reduces the mean free path of the domain wall movement. The increase in the MBE level again on further cycling indicates the progressive cyclic softening stage where the rearrangement of dislocation tangles into cells enhances the domain wall movement. The unaltered behaviour of MBE on continued cycling shows the saturation stage where the stabilization of dislocation substructure maintains the MBE level. Finally, a sharp increase in the MBE peak value identifies surface crack initiation and propagation, which is ascribed to the movement of additional reverse domains produced at the crack surfaces. This study establishes that the MBE technique can be used to assess the progressive degradation in the fatigue life of the ferritic steel components.
Fatigue & Fracture of Engineering Materials & Structures, 2013
grades of structural steel were subjected to fully reversible, constant stress amplitude cyclic loading. The local strain response of the material was measured and recorded during the test, with the applied testing technique enabling the monitoring of hysteresis loop variation for the narrowest cross-section of the hourglass specimen. Changes in hysteresis loop width, representing the local inelastic response of the material, were recorded in order to monitor the density of structural imperfections. Material ratcheting behaviour was observed as changes in the mean strain for selected load cycles. Ratcheting was attributed to local deformation of the material in the vicinity of imperfections such as voids or inclusions, as well as deformation induced by the propagation of microcracks. Definitions of a damage indicator parameter and damage parameter were proposed. The fatigue behaviour of the two investigated grades of steel was finally illustrated in the form of damage curves for different stress amplitudes and for undamaged and fatigue pre-damaged material.
Assessment of fatigue damage development in power engineering steel by local strain analysis
Metallic Materials, 2016
The results of analysis of fatigue damage development in the X10CrMoVNb9-1 (P91) steel specimens subjected to various cyclic loading combinations are presented. The study concerning a quantitative assessment of damage is based on analysis of the fatigue hysteresis evolution in subsequent loading cycles. According to the elaborated algorithms, damage parameters were determined on the basis of two indicators, i.e., average strain and strain amplitude variations. Each of them was responsible for a single damage development mechanism. The average strain characterized ratcheting effect, which is usually related to local generation of plastic strain surrounding microstructural elements. The second damage mechanism called cyclic plasticity is connected with micro slips preceding slip bands formation. The paper also discusses the results of metallographic and fractographic microscopic (SEM) observations of the tested specimens in order to indicate microstructural aspects of fatigue damage development mechanisms.
Materials Science and Engineering: A, 2014
Experi e tal i vestigatio s of i ter al a d effective stresses duri g fatigue loadi g of high-stre gth steel Etude expéri e tale des co trai tes i ter es et effectives da s u acier à haute résista ce sollicité e fatigue Résumé Des essais de fatigue oligocyclique ont été effectués à différentes amplitudes de déformation plastique et à température ambiante, sur un acier à haute résistance, martensitique trempé et revenu. Les composantes internes et effectives de la contrainte d'écoulement ont été analysées par la méthode de Handfield et Dickson. La contrainte interne est affectée par l'amplitude de déformation plastique. Au contraire, l'évolution de la composante athermique de la contrainte effective est indépendante de cette amplitude. La composante thermiquement activée augmente avec l'amplitude de déformation plastique mais reste constante en fonction de la déformation plastique cumulée. Les évolutions microstructurales dans le matériau déformé en fatigue ont été étudiées par microscopie électronique à transmission et par diffraction de rayons X. Les évolutions des contraintes internes et effectives sont alors discutées en fonction de ces observations. Abstract Low cycle fatigue tests are performed on a high strength tempered martensitic steel at different plastic strain amplitudes at room temperature. Internal and effective components of the flow stress are analyzed using Handfield and Dickson's method. The internal stress is affected by the plastic strain amplitude. Conversely, the evolution of the athermal component of the effective stress with the number of cycles is independent of the plastic strain amplitude. The thermal part of the effective stress increases with the plastic strain amplitude, but remains constant with plastic strain accumulation. Microstructural changes in the cyclically deformed material are investigated by means of transmission electronic mycroscopy and X-Ray characterizations. Internal and effective stress evolutions are discussed based on these observations.
Analysis of fatigue fracture surface in the duplex steel with quantitative fractography methods
8th European Congress for Stereology and Image Analysis,, 2001
The austenitic-ferritic Z2CND2205 steel is widely used in the chemical, petrochemical and power industry. The chemical composition of the Z2CND2205 steel and its mechanical properties are given in table 1. Table 1. Chemical composition (in wt %) and mechanical properties of Z2CND2205 steel. C Si Mn P S Cr Ni Mo N 0,019 0,39 1,51 0,022 0,002 22,45 5,50 3,12 0,169 Direction R s [MPa] R m [MPa] A 5 [%] J IC [kJ/m 2 ] T 565 827 35 140 (TL) L 513 790 39 200 (LT)
NDT & E International, 2004
Low alloy steel such as 1.25Cr-0.50 Mo steel is widely used in thermal power plants, petrochemical industries and fertiliser plants. In recent years considerable attention has been paid to estimate the remaining life of a service-exposed component for effective utilising such components beyond the design life. Although these steels are heat treated to obtain a stable microstructure, microstructural changes such as carbide coarsening, increasing inter lamella spacing, formation of more stable carbides, dissolution of carbides, etc. take place due to prolong service exposure at elevated temperatures. This paper describes the systematic investigation on microstructural changes, changes of composition on carbides and their effect on the magnetic Barkhausen emission parameters. The materials were heat-treated at different temperatures (500-700 8C) for various duration of time (0-1000 h) to get wide variation in microstructure. RMS voltage and pulse height distributions of Barkhausen emissions signal were calculated. A good correlation between MBE parameters and microstructural changes has been found. The study will be useful for the non-destructive evaluation of microstructural degradation of in-service 1.25Cr-0.5Mo steel structure.