Growth behavior of short surface fatigue cracks in 2 1/4 Cr-1 Mo steel (original) (raw)
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Influence of High Strength Steel Microstructure on Fatigue Crack Growth Rate
This study examines the effect of high strength steel microstructure morphology on fatigue crack growth rate (FCGR). To achieve this aim, three different heat treatment methods (normalizing, austempering quenching and tempering) were considered and all the steel specimens were initially heated to 950 0 C austenization temperature for ninety minutes and then processed via the different heat treatment methods before viewing the resultant microstructures under light optical microscope (LOM). Fatigue crack growth rate tests were conducted on the resultant microstructures with compact tension specimens at room temperature as prescribed by American standard testing method E647. Results of FCGR tests showed normalized microstructure has the lowest FCGR (6.2698E-06), followed by quenched and tempered (7.9519E-06), as-received (8.15E-06) and austempered (9.6667E-06) microstructure considering a low stress intensity factor range. The trend of results showed insignificant effect of microstructure over the Paris regime growth indicating fatigue crack growth rate is not a reliable parameter for correlating rate of crack propagation to microstructure.
Influence of stress ratio on fatigue crack growth in mild steel
Engineering Fracture Mechanics, 1995
Crack propagation experiments were performed on a mild steel side edge notched specimen for various load ranges and stress ratios at constant maximum loads. The life of the specimen increased as the load ratio increased. The crack growth data were analysed in terms of AKeff as a function of stress ratio R. Good results were determined for U = 0.7 + 0.15R(2 + R) in both cases. Two crack growth rate equations were also developed.
Materials Science and Engineering: A, 1991
Cylindrical specimens of 12% CrMoV steel were tested under high temperature, low cycle fatigue (HTLCF) conditions to investigate the growth of microcracks which nucleate at the surface. Results are presented which indicate that the microcracks maintain an equilibrium shape under HTLCF conditions, making it possible to estimate crack depth from a measure of the crack length along the surface. The individual growth of these microstructurally small cracks was monitored using a surface replication technique during periodic interruptions of the experiments. Crack growth rate data for different microcracks are compared on the basis of the cyclic J-integral AJ to examine the use of fracture mechanics for predicting HTLCF microcrack growth. A determination of AJ is shown to be successful in characterizing the growth of fatigue microcracks in 12% Cr steel at elevated temperatures despite differences in overall orientation at the surface. Good agreement with fatigue crack growth data for through-cracks in CrMoV steels at high temperatures further demonstrates the usefulness of AJ for predicting HTLCF microcrack growth. The results also suggest that large extrapolations of the observed correlation between AJ and crack growth rate could result in unacceptable errors owing to the relative contribution of oxidation damage at the crack tip. 0921-5093/91/$3.50
Mechanisms of fatigue crack growth in low alloy steel
Acta Metallurgica, 1973
A study has been made of fatigue crack propagation in a low alloy steel which is subject to temper embrittlement. Effects of mean stress on the growth rate have been examined and comparisons between temper embrittled and unembrittled conditions have been made. Whereas ...
Fatigue Crack Growth under Mode I, II and III for Plane-strain and Plane-stress Conditions
Procedia Engineering, 2014
Fatigue crack growth (FCG) could be encountered in many mechanical components, which can be made from either thin or thick steel plates (or shells) and, therefore, be subjected to a plane-stress or a plane-strain condition, respectively. The loads applied in a solid body containing a narrow notch or a sharp crack will induce a yield zone near its tip with a dimension that will depend on the mechanical properties of the material, as well as on the thickness of the body, the crack length and the magnitude of the loads applied. Crack propagation can then occur under mode I, II, III or mixed-mode for general loading. The paper presents J I , J II and J III integral functions, which were correlated with the elastic stress intensity factors K I , K II and K III , for thin and thick CT specimens. The evaluation of J-Integral values was carried out for different crack lengths, along the crack front, and using the Finite Element Method (FEM), with collapsed nodes and midside nodes dislocated to ¼ of the edge's length, in order to simulate the crack tip singularity. Interaction between in-plane, in-plane sliding and out-of-plane modes are also discussed in the paper. In addition, FCG rates under mode I, mode III and a mixed-mode (mode I+III) were experimentally determined, at room temperature, for a high-strength Cr-Mn austenitic stainless steel.
Theoretical analysis on the behaviour of short fatigue cracks
International Journal of Fatigue, 2002
Based on the Navarro-Rios model, the boundaries of short crack growth are predicted. Theoretical analysis reveals that the extent of short crack growth regime is principally governed by the relation between the fatigue limit and the cyclic yield stress of the material. Materials with low values of s FL /s cy show extensive short crack behaviour, while in material with high values of s FL /s cy short crack behaviour is very limited. The results of the analysis are validated with experimental data.
Short fatigue crack behaviour under low cycle fatigue regime
International Journal of Fatigue, 2017
This paper addresses the important issue of the description of short fatigue crack behaviour. It is typical for these cracks that they propagate under large scale yielding conditions at the crack tip, which means that the non-linear fracture mechanics has to be applied. This paper presents results of experiments designed to measure the short crack growth rates in five different materials-316L steel, Eurofer 97 steel, ODS Eurofer steel, Duplex 2205 steel and Al 6082 alloy. The crack growth rates of these materials are described using different fracture mechanics parametersthe stress intensity factor, the J-integral and the plastic part of the J-integral. These approaches are evaluated and compared. The comparison revealed that the plastic part of the J-integral is the parameter governing the short crack growth rate in large scale yielding conditions. Moreover, crack growth rate data from all the tested materials measured at various loading levels lies on a unique curve. This remarkable observation suggests that the crack growth rate is determined by the extent of energy spent to plastic deformation, irrespective of the other materials properties.
Effect of specimen thickness on fatigue crack growth rate
Nuclear Engineering and Design, 2000
Fatigue tests were performed on the compact tension (CT) specimens of Type 304 stainless steel and Inconel 718. To investigate the effects of specimen thickness on crack tip deformation and fatigue crack growth rate (FCGR), specimens of different thickness were used. In the analysis, the elastic plastic fracture mechanics (EPFM) parameter known as the cyclic J-integral, DJ was adopted to observe the local plasticity at the crack tip and compared with the linear elastic fracture mechanics (LEFM) parameter known as the stress intensity factor range, DK. The results show that FCGR is a function of specimen thickness, the effect of which is accelerated as specimen thickness increases. Therefore, it is thought that not only applied stress level but also specimen thickness should be taken into account in the measurement of FCGR, which is not considered in ASTM E 647 (ASTM E 647, 1995. Standard test method for measurement of fatigue crack growth rates.).
Effect of microstructure on appearance of near-threshold fatigue fracture in Cr–Mo–V steel
International Journal of Fracture, 2009
Near-threshold fatigue crack growth behavior in 25Cr2NiMo1V steel with different microstructures was investigated by utilizing the load-shedding technique at ambient temperature. Crack surface morphology was observed by SEM with special emphases on the incidence of intergranular fracture and the influence on crack growth rates. Results show that the maximum intergranularity occurs at the K corresponding to the cyclic plastic zone size being equivalent to the prior austenitic grain size. Two types of crack growth mode were observed in the near-threshold regime, i.e., the crystallographic mode of crack growth and the striation mode of crack advance. The incidence of faceted fracture was mainly rationalized by comparing the cyclic plastic zone size with the grain size. It is concluded that, in the crystallographic mode, lower crack growth rates in samples with higher heat treatment temperatures are caused by a greater degree of roughness-induced crack closure (RICC), faceted fracture induced crack closure (FFICC), and oxide-induced crack closure (OICC). The faceted fracture shows negligible influence on crack growth rates when cracks grow in a striation controlled mode.