Papers by Keyword: Fatigue Crack Growth Rate (da/dN)

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Authors: Y.M. Baik, K.S. Kim
Abstract: Crack growth in compact specimens of type 304 stainless steel is studied at 538oC. Loading conditions include pure fatigue loading, static loading and fatigue loading with hold time. Crack growth rates are correlated with the stress intensity factor. A finite element analysis is performed to understand the crack tip field under creep-fatigue loading. It is found that fatigue loading interrupts stress relaxation around the crack tip and cause stress reinstatement, thereby accelerating crack growth compared with pure static loading. An effort is made to model crack growth rates under combined influence of creep and fatigue loading. The correlation with the stress intensity factor is found better when da/dt is used instead of da/dN. Both the linear summation rule and the dominant damage rule overestimate crack growth rates under creep-fatigue loading. A model is proposed to better correlate crack growth rates under creep-fatigue loading: 1 c f da da da dt dt dt Ψ −Ψ     =         , where Ψ is an exponent determined from damage under pure fatigue loading and pure creep loading. This model correlates crack growth rates for relatively small loads and low stress intensity factors. However, correlation becomes poor as the crack growth rate becomes large under a high level of load.
Authors: Bum Joon Kim, Byeong Soo Lim
Abstract: Various hold periods in a cyclic wave of fatigue load were introduced to investigate loading frequency effects on crack growth behavior and microstructural damage. The crack growth path and microstructural damage characteristics at 600°C in tempered martensitic 9Cr-2W (P92) HAZ of welded steel were studied. Generally, low frequency effect with increasing hold periods affects microstructural damage with microvoids/cavities nucleation due to the effect of creep. Results showed that the fatigue crack growth behavior was sensitive to the loading frequency. As frequency decreased, the fatigue crack growth rate increased and the crack path mode changed from transgranular to intergranular in terms of microstructural damage. As the loading frequency decreased, it was found that the microvoids /cavities and microcracks that formed along the prior austenite grain boundaries ahead of the main crack contributed to the intergranular crack growth.
Authors: I.N. Fridlyander, E.A. Tkachenko, V.V. Berstenev, G.V. Cherepok, L.V. Latushkina, I.P. Zhegina, V.A. Grinevich
Authors: Bokkyu Lim, Young Woo Choi
Abstract: Effect of nitriding on fatigue crack initiation and growth rate has been studied on Ni-Cr-Mo steel. Specimens were nitrided for 15hr at 680°C. The fatigue limit of nitrided specimens were superior to those of annealed(680°C, 15 hr) specimens. Based on detailed observations of slip band and micro crack initiation, it is concluded that the excellent fatigue limit of nitrided specimens is attributed to improved slip initiation resistance by nitriding. The characteristic of fatigue crack growth rate of nitrided specimens was investigated by comparing with those of annealed specimens. It was found that by nitriding the crack growth rate was markedly decreased and the threshold stress intensity factor range was improved. It is concluded that the excellent fatigue limit of nitrided specimens is also attributed to improved fatigue crack growth rate and threshold stress intensity factor range by nitriding.
Authors: Bokkyu Lim, Young Woo Choi
Abstract: Single phase bainite structure which is obtained by the conventional austempering treatment reduces the ductility of ductile cast iron. Because of the reduction of ductility it is possible to worsen the fatigue properties. Therefore, semi austempered ductile iron which is treated from  +ϒ is prepared to investigate the static strength and fatigue properties in comparison with fully austempered ductile iron (is treated from ϒ). In spite of semi austempered ductile iron shows the 86% increase of ductility. Also, semi austempered ductile iron shows the higher fatigue limit and lower fatigue crack growth rate as compared with fully austempered ductile iron. By the fractographical analysis, it is revealed that the ferrite obtained by semi austempering process brings about the plastic deformation(ductile striation) of crack tip and gives the prior path of crack propagation. The relatively low crack growth rate in semi austempered specimen is caused by above fractographical reasons
Authors: G. Madhusudhan Reddy, A.A. Gokhale, V.K. Saxena, K. Prasad Rao
Authors: Qing Fen Li, Huocai Ni, Sang Lin Yang, Zhaoxia Cui, Xian Hai Peng, Li Quan Wang
Authors: Matthew J. Crill, David J. Chellman, Ed S. Balmuth, Mike Philbrook, K. Paul Smith, Alex Cho, Michael Niedzinski, Raphael Muzzolini, Jim Feiger
Abstract: Crack turning or delamination behavior of AA 2050-T87 and AA 7050-T7451 ESE(T) and hourglass coupons under cyclic fatigue conditions is presented. Fatigue crack growth rate curves, fracture surface examinations, and the preferred manner of crack growth for each alloy are discussed in an effort to better understand fatigue crack growth behavior of aluminum-lithium alloys in structural components under service conditions.
Authors: Young Pyo Kim, Cheol Man Kim, Woo Sik Kim, Kwang Seon Shin
Abstract: A clear understanding of fatigue properties for the pipeline steel and its weld is important to provide information for pipeline design during pipeline construction and predict pipeline fatigue life during pipeline operation. The materials used in this study are API 5L X65 pipeline steel generally used for natural gas transmission. This pipeline was welded by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) with V-groove configuration. The fatigue crack growth behaviors of pipeline steel and its girth weld according to crack growth directions and stress ratios were investigated over a wide range of stress intensities in laboratory air.
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