A Simple Model for Fatigue Crack Growth Near Stress Concentrations

1991 ◽  
Vol 113 (4) ◽  
pp. 542-548 ◽  
Author(s):  
R. C. McClung
Keyword(s):  
Fatigue Crack ◽  
Simple Model ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Local Stress ◽  
Growth Data ◽  
Stress Concentrations

Fatigue crack growth rates are often difficult to predict for short cracks growing near stress concentrations. This paper presents a simple model to predict those growth rates which incorporates the phenomenon of crack closure. Crack opening stresses are shown to change significantly as cracks grow away from notches, and the simple model is designed to describe those changes. The effective stress range ratio, U, is assumed to be dependent on the local stress at the crack tip location in a corresponding uncracked body. The value of U changes with the normalized maximum stress in unnotched bodies, and this dependence can be quantified with elastic-plastic finite element models or simpler modified-Dugdale crack analyses. The local stress distribution is estimated with a Neuber analysis. A semi-empirical stress intensity factor solution is constructed and calibrated with known exact solutions. The crack growth rate is then calculated with the modified Paris law, taking crack growth constants from long crack data. The model is illustrated with a specific case study, the growth of cracks from center notches in an SAE 1026 steel. Experimental crack growth data for notches of different sizes and shapes compare favorably with the calculations. The scheme is contrasted with previous models for notch fatigue cracks. The implications of the simple model for other fatigue design problems are explored, highlighting the simplicity and generality of the model.

Fatigue Crack Growth Properties of 16MnR and 316L Steels at High Temperature

2005 ◽  
Author(s):  
Zengliang Gao ◽  
Weiming Sun ◽  
Weiya Jin ◽  
Ying Wang ◽  
Fang Zhang
Keyword(s):  
Fatigue Crack ◽  
High Temperature ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Pressure Vessels ◽  
Effect Of Temperature ◽  
Growth Properties ◽  
Crack Growth Rates

Fatigue failures often take place in high temperature pressure vessels and equipment because of fluctuation of pressure and temperature. Fatigue crack growth properties of materials at high temperatures are very important for safety assessment of high temperature equipment. A series of fatigue crack growth tests were carried out, and fatigue crack growth rates were determined at 25∼500°C for typical steels 316L and 16MnR. The laws of fatigue crack growth of two materials at different temperatures and the effect of temperature on fatigue crack growth rates were studied. The results show that the crack growth rates increase with temperature for 316L steel. Both the exponent n and constant C for Paris law change with temperature. The fatigue cracks of 16MnR propagate at 150 °C and 300 °C more slowly than at room temperature and 425 °C. The fatigue crack growth rate at 425 °C is the highest for temperature range of 25–425 °C.

A Practical Criterion on Fatigue Crack Growth Rates at Notches and Its Application to Part-Through-Thickness Fatigue Cracks in Notched Plates Subjected to Cyclic Bending

2006 ◽  
Author(s):  
Hiroshi Matsuno
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Stress Field ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Equivalent Stress ◽  
Cyclic Bending ◽  
Bending Loads ◽  
Crack Growth Rates

In the present paper, an equivalent stress ratio concept, which has hitherto been developed by author [1–3], is applied to problems of part-through-thickness fatigue crack growth in notched plates subjected to cyclic bending loads, and a criterion for estimating fatigue crack growth rates is derived on the basis of the concept. In order to take a great variety of practical notches into consideration, a bending stress field of a notched plate containing a part-through-thickness fatigue crack emanating from a notch root is simplified by the elementary beam theory, and the stress field is characterized in accordance with classification of notch morphology: (a) an unnotch type, (b) a transverse type notch such as a groove, a shoulder, a trapezoidal protuberance, etc., which is disposed along a width of a plate, and (c) a through-thickness type notch such as a circular and elliptical hole, a side-groove, etc. Experimental results on part-through-thickness fatigue cracks emanating from artificial flaws at notch roots in plates subjected to cyclic bending loads are analyzed. Growth rates of fatigue cracks in the notches are estimated based on the proposed criterion and the devised convenient method for calculating stress intensity factors, and they are compared with experimental ones.

Modeling to the Fatigue Crack Growth Rates of the Cast Steel for Chinese Railway Rolling Wagon Bogie Frames

2010 ◽  
Vol 118-120 ◽  
pp. 105-110
Author(s):  
Yong Xiang Zhao ◽  
Bing Yang
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Cast Steel ◽  
Fatigue Cracking ◽  
Present Material ◽  
Fracture Roughness ◽  
Crack Growth Rates

Compact tensional specimens are fatigued for modeling the fatigue crack growth rates of the cast steel for Chinese railway rolling wagon bogie frames. Typical fracture surface observations indicate that the fatigue cracks grew with distinct fatigue striations, river-like flowers, and second cracks in perpendicular to the fatigue crack path. Lots of dimples appeared in the transient fracture district to indicate that present material is ductile. Similar to the previous NASGRO’s exploration, a full modeling is proposed from fatigue cracking threshold to the transient fracture corresponding to the material fracture roughness. Availability has been verified to be applied for the present material. In addition, this modeling is very simple that the modeling can be performed by the conventional tests of fatigue cracking thresholds, growth rates, and fracture roughness values.

Closure and Growth of Fatigue Cracks at Notches

1992 ◽  
Vol 114 (1) ◽  
pp. 1-7 ◽  
Author(s):  
R. C. McClung ◽  
H. Sehitoglu
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Local Stress ◽  
Element Model ◽  
Rate Of Change ◽  
Growth Effect ◽  
Growth Data ◽  
Stress Ratios

The closure behavior of fatigue cracks growing out of notches is studied with an elastic-plastic finite element model. Crack opening stresses are shown to change significantly as the crack extends. Opening stresses are low at first and then gradually rise to stable values as the crack tip moves away from the notch field. These transient changes are not limited to the region of the original inelastic notch field. The rate of change of opening stresses with increasing crack length is a function of both nominal maximum stress and nominal stress ratio. Stable levels are reached more quickly at higher stress ratios and lower maximum stresses. These transient changes in Sopen have been emulated with a simple model which considers only changes in Sopen due to changes in the local stress field. The numerical results are quantitatively consistent with observed trends in experimental crack growth data, which show that accelerated crack growth can occur beyond the original notch plastic boundary. Finite element results and experimental data also both suggest that the accelerated short crack growth effect for cracks near notches is much less pronounced at higher stress ratios.

Improvement of Fatigue Crack Growth Resistance by Serrated Grain Boundary at High Temperature

1991 ◽  
Vol 113 (1) ◽  
pp. 9-14 ◽  
Author(s):  
Hiroshi lizuka ◽  
Manabu Tanaka ◽  
Fumio Ashihara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Crack Growth Resistance ◽  
Fatigue Crack Growth Resistance ◽  
Crack Growth Rates

Effects of serrated grain boundaries on the improvement of fatigue-crack growth resistance were investigated using austenitic 21Cr-4Ni-9Mn heat-resisting steel at 973K in air. Grain boundaries were serrated by grain-boundary reaction precipitates. The crack-growth rates were considerably decreased in the specimens with the serrated grain boundaries. The fatigue cracks were largely deflected by the serrated grain boundaries, and brittle intergranular fracture was retarded. The improvement of the crack-growth resistance was obtained especially under the conditions of low crack-growth rates of less than 30 μm/cycle. The widths and the heights of the deflected portions of the cracks were in the range from about a few μm to 30 μm.

Influence of Plastic Prestrain on the Fatigue Crack Growth Resistance (da/dN vs. ΔK) of ASTM A36 Structural Steel

2015 ◽  
Author(s):  
Gustavo Henrique B. Donato ◽  
Fábio Gonçalves Cavalcante
Keyword(s):  
Mechanical Properties ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Pressure Vessels ◽  
Engineering Structures ◽  
Fatigue Crack Growth Resistance ◽  
Crack Growth Rates

High responsibility components operating under cyclic loading can have their resistance against initiation and growth of fatigue cracks highly influenced by previous thermomechanical processing. Within the interest of the present work, different manufacturing processes and installation techniques incorporate cold plastic straining to engineering structures; two typical examples on the oil and gas fields are: i) the offshore pipelines installation method called reeling; ii) the fabrication of pipes using the UOE method and pressure vessels through calendering. Within this scenario, this work investigates the effects of plastic prestrain on the fatigue crack growth rates (da/dN vs. ΔK) of a hot-rolled ASTM A36 steel. Different from previous results from the literature, in which prestrains were applied directly to machined samples, in this work uniform prestraining was imposed to steel strips (1/2” thick) and specimens were then extracted to avoid (or minimize) residual stress effects. Prestrain levels were around 4, 8 and 14% and C(T) specimens were machined from original and prestrained materials according to ASTM E647 standard. Fatigue crack growth tests were carried out under load control in an MTS 810 (250 kN) equipment using R = 0.1. Results revealed that plastic prestraining considerably reduced crack growth rates for the studied material, which was expected based on the literature and hardening behavior of the studied material. However, results also revealed two interesting trends: i) the larger is the imposed prestrain, the greater is the growth rate reduction in a nonlinear asymptotic relationship; ii) the larger is imposed ΔK, the more pronounced is the effect of prestraining. Crack closure effects were also investigated, but revealed no influence on the obtained mechanical properties. Consequently, results could be critically discussed based on effective crack driving forces and elastic-plastic mechanical properties, in special those related to flow and hardening. The conclusions and success of the employed methods encourage further efforts to incorporate plastic prestrain effects on structural integrity assessments.

Fatigue Crack Growth Comparison between Sleeved and Non-Sleeved Pipeline

2008 ◽  
Vol 41-42 ◽  
pp. 105-112 ◽  
Author(s):  
M. Law ◽  
Valerie Linton ◽  
Erwin Gamboa
Keyword(s):  
Fatigue Crack ◽  
Simple Model ◽  
Fatigue Crack Growth ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Reduction ◽  
Crack Opening ◽  
Composite Repair ◽  
Pipeline Section ◽  
Hoop Stresses

A section of gas pipeline containing dormant stress corrosion cracks was removed from service and pressure cycled, and the crack growth from fatigue was measured. Crack growth was able to be conservatively calculated by BS7910. Parts of the pipeline section had composite repair sleeves placed over it in order to compare fatigue crack growth of sleeved and unsleeved cracks. Sleeved cracks consistently showed less crack growth than unsleeved cracks; this is believed to be due to reduced hoop stresses in the pipe under the composite repair sleeve and reduced crack opening. A simple model of the sleeve repair was developed which was consistent with the measured strains in the pipe. The application pressure of the sleeve repair affects the amount of stress reduction in the pipe and the amount of crack growth experienced. Two possible methods of repair of SCC affected pipelines were validated by this work.

Analysis on Fatigue Crack Growth Rates Under a Wide Range of Stress Ratios

1986 ◽  
Vol 108 (2) ◽  
pp. 209-213 ◽  
Author(s):  
M. Kurihara ◽  
A. Katoh ◽  
M. Kawahara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Crack Opening ◽  
Wide Range ◽  
Stress Ratios ◽  
Crack Opening Stress ◽  
Crack Growth Rates

In the present study, a series of fatigue crack growth tests were carried out in order to examine the effects of stress ratio R upon crack growth rates, together with the crack closure behaviors. Fatigue tests were conducted with center-notched specimens of two kinds of pressure vessel steels (500 MPa class and 800 MPa class) under cyclic axial loading in various stress ratios R ranging from −5 to +0.8. Crack opening stress levels were determined by the unloading elastic compliance method. An expression of fatigue crack growth rates under a wide range of stress ratios was proposed, taking into account the relationship between stress ratio R and crack opening stress ratio U. The crack growth behaviors near the threshold conditions were also discussed.

A Methodology for Predicting Variability in Microstructurally Short Fatigue Crack Growth Rates

1997 ◽  
Vol 119 (2) ◽  
pp. 171-179 ◽  
Author(s):  
Ken Gall ◽  
Huseyin Sehitoglu ◽  
Yavuz Kadioglu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Growth Parameters ◽  
Fatigue Cracks ◽  
Upper And Lower Bounds ◽  
Short Cracks ◽  
Band Size ◽  
Crack Growth Rates

A finite element model, which implements single crystal constitutive relationships, was used to simulate fatigue cracks growing at the microstructural level. Plastic deformation (slip) was allowed along two specified microscopic crystallographic planes. As the orientations of the slip systems were changed several crucial fatigue crack growth parameters, measured over all possible orientations, were found to vary: (1) crack tip forward slip band size, rp, 0.03 ≤ rp/(Kmax/λo)2 ≤ 0.31 where λo is the critical resolved shear stress on a slip system, (2) crack opening displacement, δ, 1.2 ≤ δ/(Kmax2/Emσo) ≤ 7.8 where Em and σo are the elastic modulus and yield stress of a polycrystalline material with many randomly oriented double slip crystals, and(3) crack closure level, Sopen/Smax, 0.02 ≤ Sopen/Smax ≤ 0.35. Corresponding to these differences in crack growth parameters, crack growth laws were used to estimate the expected changes in crack growth rates when microstructurally short cracks grow through grains with different crystallographic orientations. The resulting predictions form approximate upper and lower bounds on crack growth rates for microstructurally short cracks. For several different materials, the crack growth rate variability predictions were in the range 7 ≤ (da/dN)(max)/(da/dN)(min) ≤ 37, which is consistent with experimentally measured variations.

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