Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part I: Stress Level and Stress Ratio Effects at Constant Amplitude

1976 ◽  
Vol 98 (2) ◽  
pp. 179-184 ◽  
Author(s):  
A. M. Sullivan ◽  
T. W. Crooker
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Level ◽  
Stress Ratio ◽  
High Strength ◽  
Nominal Stress ◽  
Constant Amplitude ◽  
Stress Intensity Range

High-strength pressure vessel steel surface flaw or part-through crack (PTC) specimens were selected for studies of fatigue crack growth rate (da/dN) under constant amplitude cycling to assess the effects of varied stress ratio R (minimum nominal stress/maximum nominal stress, σmin/σmax) and stress level (maximum nominal stress/yield stress, σmax/σys). Analyzed within the framework of linear elastic fracture mechanics, these studies warrant the following conclusions regarding fatigue-crack growth in this material: • Crack growth does not appear to be influenced by stress level, per se, even for stress levels approaching net section yield. • It is moderately influenced by both positive (tension-tension) and negative (tension-compression) stress ratios. • It is principally related to the tensile range of cyclic stress as expressed by the fracture mechanics stress-intensity range parameter, ΔK. Utilizing the results of this investigation, a normalizing relationship expressing da/dN as a function of both ΔK and R, which is applicable to both positive and negative values, is discussed. It is concluded that the stress-intensity range ΔK provides a viable analytical approach to fatigue crack-growth analyses relevant to high-strength pressure vessels.

Experimental Technique for Elevated Temperature Mode I Fatigue Crack Growth Testing of Ni-Base Metal Foils

2006 ◽  
Vol 129 (4) ◽  
pp. 594-602 ◽  
Author(s):  
L. Liu ◽  
J. W. Holmes
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Constant Amplitude ◽  
Stress Intensity Range ◽  
Metallic Foils

Details are provided for an experimental approach to study the tensile fatigue crack growth behavior of very thin metallic foils. The technique utilizes a center-notched specimen and a hemispherical bearing alignment system to minimize bending strains. To illustrate the technique, the constant amplitude fatigue crack growth behavior of a Ni-base superalloy foil was studied at temperatures from 20°C to 760°C. The constant amplitude fatigue tests were performed at a frequency of 2Hz and stress ratio of 0.2. The crack growth rate versus stress intensity range data followed a Paris relation with a stress intensity range exponent m between 5 and 6; this exponent is significantly higher than what is commonly observed for thicker materials and indicates very rapid fatigue crack propagation rates can occur in thin metallic foils.

Mechanisms of Fatigue Crack Growth in WC-Co Cemented Carbides

2005 ◽  
Vol 297-300 ◽  
pp. 1120-1125 ◽  
Author(s):  
Myung Hwan Boo ◽  
Chi Yong Park
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Stress Ratio ◽  
Cemented Carbides ◽  
Stress Intensity Factor Range

In order to study the influence of stress ratio and WC grain size, the characteristics of fatigue crack growth were investigated in WC-Co cemented carbides with two different grain sizes of 3 and 6 µm. Fatigue crack growth tests were carried out over a wide range of fatigue crack growth rates covering the threshold stress intensity factor range DKth. It was found that crack growth rate da/dN against stress intensity factor range DK depended on stress ratio R. The crack growth rate plotted in terms of effective stress intensity factor range DKeff still exhibited the effect of microstructure. Fractographic examination revealed brittle fracture at R=0.1 and ductile fracture at R=0.5 in Co binder phase. The amount of Co phase transformation for stress ratio was closely related to fatigue crack growth characteristics.

Fatigue Crack Growth Rate Curve for Nickel Based Alloys in PWR Environment

2007 ◽  
Author(s):  
Yuichiro Nomura ◽  
Katsumi Sakaguchi ◽  
Hiroshi Kanasaki
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Stress Ratio ◽  
Austenitic Stainless Steels ◽  
Rising Time

Japanese reference fatigue crack growth rate (FCGR) curves for ferrite and austenitic stainless steels in light water reactor environments are prescribed in JSME S NA1-2004. However, similar reference FCGR curve for nickel-based alloys for pressurized water reactors (PWR) are not prescribed. In order to propose reference FCGR curve for nickel-based alloys, under high stress ratio and low rising time, the effect of the welding method, the effect of specimen orientation and low stress intensity range fatigue crack propagation tests of nickel-based alloys 600, 132 and 82 weld metals were conducted as part of the Environmental Fatigue Test (EFT) projects of Japan Nuclear Energy Safety Organization (JNES). The results show that the effect of heat, welding methods, specimen orientations and environmental water conditions on the FCGR was not significant for Alloys 600, 132 and 82. The FCGR increased with increase of stress ratio, and cyclic loading frequency. According to the procedure for determining the reference FCGR curve of austenitic stainless steels in PWR environment of nickel-based alloys is proposed based on the reference data and the results of this study. The reference FCGR curve for nickel-based alloys in PWR environment are determined as a function of stress intensity factor range, temperature, load rising time and stress ratio.

Some Applications of Fractal Fracture Mechanics to Describe the Fatigue Behaviour of Materials

2008 ◽  
Vol 378-379 ◽  
pp. 355-370 ◽  
Author(s):  
Andrea Carpinteri ◽  
Andrea Spagnoli ◽  
Sabrina Vantadori
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Limit ◽  
Threshold Stress ◽  
Threshold Stress Intensity ◽  
Stress Intensity Range

As is well-known, fatigue limit, threshold stress intensity range and fatigue crack growth rate are influenced by the specimen or structure size. Limited information on size effect is available in the literature. In the present paper, by employing some concepts of fractal geometry, new definitions of fatigue limit, fracture energy and stress intensity factor, based on physical dimensions different from the classical ones, are discussed. Then, size-dependent laws for fatigue limit, threshold stress intensity range and fatigue crack growth rate are proposed. Some experimental results are examined in order to show how to apply such theoretical scaling laws.

Effect of Load Ratio on Fatigue Failure Micromechanisms of Railway Axle Steel

2015 ◽  
Vol 770 ◽  
pp. 209-215
Author(s):  
Pavlo Maruschak ◽  
Andriy Sorochak ◽  
Sergey V. Panin
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Fatigue Failure ◽  
Stress Ratio ◽  
Load Ratio ◽  
Railway Axle

The paper presents the basic regularities of fatigue failure of the railway wheelset axle material – OsL steel (C - 0,40—0,48 %; Mn - 0,55—0,85 %; Si - 0,15—0,35 %; P < 0,04%; S < 0,045 %; Cr < 0,3 %; Ni < 0,3 %; Cu < 0,25 %). It was revealed that under loading stress ratio R = 0, fatigue crack growth is 2 ... 4 times lower than that at the asymmetry R = -1. In doing so, amplitude of stress intensity factor vary in the range of 20 – 35 MPa√m. The micromechanisms of fatigue crack growth are described and systematized, while physical-mechanical interpretations of the relief morphology at different stages of its growth are offered.

Long Fatigue Cracks — Microstructural Effects and Crack Closure

MRS Bulletin ◽  
1989 ◽  
Vol 14 (8) ◽  
pp. 25-36 ◽  
Author(s):  
P.K. Liaw
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Load Ratio ◽  
Stress Intensity Range ◽  
Intensity Range

Fracture mechanics technology is an effective tool for characterizing the rates of fatigue crack propagation. Generally, fatigue crack growth rate (da/dN) in each loading cycle can be presented as a function of stress intensity range (ΔK), where ΔK = Kmax — Kmin, Kmax and Kmin are the maximum and the minimum stress intensities, respectively. A typical fatigue crack growth rate curve of da/dN versus ΔK can be divided into three regimes, i.e., Stage I (near-threshold), Stage II (Paris), and Stage III (fast) crack growth regions, as shown in Figure 1.Depending on the region of crack growth, fatigue crack growth behavior can be sensitive to microstructure, environment, and loading conditions [e.g., R (load) ratio = Kmin / Kmax]. In the nearthreshold region, fatigue crack growth rates are very slow, ranging from approximately 10−10 to 10−8 m/cycle. In this region, the fatigue crack growth rate curve eventually reaches a threshold stress intensity range, ΔKth, below which the crack would not grow or grow at an extremely slow rate. Typically, the value of ΔKth is operationally defined as the stress intensity range which gives a corresponding crack growth rate of 10−10 m/cycle. In the nearthreshold region, the influence of microstructure, environment, and load ratio on the rates of crack propagation is very significant.

An Experimental Study of Fatigue Crack Propagation of 16MnR Pressure Vessel Steel in Mode-I Constant Amplitude Loading

2012 ◽  
Vol 455-456 ◽  
pp. 1073-1078
Author(s):  
Wen Feng Tu ◽  
Zeng Liang Gao ◽  
Zhao Ji Hu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Stress Ratio ◽  
Mode I ◽  
Specimen Thickness ◽  
Pressure Vessel Steel ◽  
Constant Amplitude ◽  
Vessel Steel

An experimental investigation was performed on fatigue crack growth behavior of a 16MnR pressure vessel steel. Standard compact tension (CT) specimens with three specimen thicknesses and notch sizes were subjected to Mode I constant amplitude loading with several stress ratios and loading amplitudes. The results revealed that the stress ratio had an insignificant influence on the fatigue crack growth of the material. The stable fatigue crack growth rate (FCGR) was accelerated as specimen thickness increased. The fatigue crack was extended in terms of the curve crack shape. The crack front at the surface was retarded compared to that at the interior along thickness direction, and the crack front at the mid-thickness plane reached the maximum value of the crack length. The similar curve crack shape was obtained in the stable crack growth stage. The maximum difference of the crack front along thickness direction was increased with the increasing of the specimen thickness. The early crack growth from the notch was effected by the size of the notch, the stress ratio and loading amplitude.

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