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.

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.

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.

scholarly journals Advantageous Description of Short Fatigue Crack Growth Rates in Austenitic Stainless Steels with Distinct Properties

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 475
Author(s):  
Lukáš Trávníček ◽  
Ivo Kuběna ◽  
Veronika Mazánová ◽  
Tomáš Vojtek ◽  
Jaroslav Polák ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Growth Rates ◽  
Large Scale ◽  
J Integral ◽  
Scale Yielding ◽  
Residual Fatigue ◽  
Crack Growth Rates

In this work two approaches to the description of short fatigue crack growth rate under large-scale yielding condition were comprehensively tested: (i) plastic component of the J-integral and (ii) Polák model of crack propagation. The ability to predict residual fatigue life of bodies with short initial cracks was studied for stainless steels Sanicro 25 and 304L. Despite their coarse microstructure and very different cyclic stress–strain response, the employed continuum mechanics models were found to give satisfactory results. Finite element modeling was used to determine the J-integrals and to simulate the evolution of crack front shapes, which corresponded to the real cracks observed on the fracture surfaces of the specimens. Residual fatigue lives estimated by these models were in good agreement with the number of cycles to failure of individual test specimens strained at various total strain amplitudes. Moreover, the crack growth rates of both investigated materials fell onto the same curve that was previously obtained for other steels with different properties. Such a “master curve” was achieved using the plastic part of J-integral and it has the potential of being an advantageous tool to model the fatigue crack propagation under large-scale yielding regime without a need of any additional experimental data.

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