A Method for the Analysis of the Growth of Short Fatigue Cracks

1995 ◽  
Vol 117 (4) ◽  
pp. 408-411 ◽  
Author(s):  
A. J. McEvily ◽  
Y.-S. Shin
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Material Constant ◽  
Plastic Zone Size ◽  
Surface Cracks ◽  
Zone Size ◽  
Short Cracks

A method for the analysis of the fatigue crack growth rate for short cracks has been developed and is applied to the case of fatigue crack growth of short surface cracks in a 1045 carbon steel. The method entails three modifications to standard LEFM procedures. These modifications include the use of a material constant to bridge between smooth and cracked specimen behavior, consideration of the plastic zone size to crack length ratio, and incorporation of the development of crack closure. Comparisons are made between calculations based upon this approach and experimental data.

Fatigue Crack Growth Response Following a High-Load Excursion in 2219-T851 Aluminum Alloy

1980 ◽  
Vol 102 (3) ◽  
pp. 280-292 ◽  
Author(s):  
R. P. Wei ◽  
N. E. Fenelli ◽  
K. D. Unangst ◽  
T. T. Shih
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Response ◽  
Plate Thickness ◽  
Fatigue Loading ◽  
Plastic Zone Size ◽  
High Load ◽  
Chemical Environment ◽  
Zone Size

To develop further phenomenological understanding of load interaction effects in fatigue, examinations of the influences of stress intensity (K) level, plate thickness and chemical environment on fatigue crack growth response following a single high-load excursion (overload) were carried out on a 2219-T851 aluminum alloy. An overload ratio (that is, the ratio between the magnitude of the overload and the maximum in the subsequent constant-amplitude fatigue loading) of 2.0 was used. Experiments were carried out in dehumidified argon, air (30 to 70 percent relative humidity), and3.5percent NaCl solution at room temperature. The results showed that delay (as measured by the duration of overload affected crack growth) increased with increasing K level and with decreasing plate thickness, and decreased with increasing aggressiveness of the chemical environment. The high-load excursion (overload) affected crack growth through a region of material ahead of the crack tip. Within this overload affected zone, crack growth rate first increased (sometimes), followed by fairly rapid decrease to a minimum value (delayed retardation), and then increased gradually to its steady-state value. The overload affected zone size was found to depend on K-level, and on crack-tip constraint, and to be independent of chemical environment, and was found to be equal to the appropriate (plane-strain or plane-stress) plastic zone size for the overload. Identification of a delayed retardation zone was made, and identification of this zone with the cyclic plastic zone size for the preceding fatigue loading was suggested. The effects of K level, plate thickness and chemical environment on delay were considered in relation to their respective influences on the overload-affected-zone and delayed-retardation-zone sizes, and on the rate of fatigue crack growth. A residual stress intensity concept for describing fatigue crack growth response within the overload affected zone was considered. With suitable modifications, reasonable estimates of crack growth response could be obtained. Further need for verification and understanding of these modifications are 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.

PREDICTION FOR FATIGUE CRACK GROWTH IN NOTCHED PLATES

2012 ◽  
Vol 06 ◽  
pp. 269-274
Author(s):  
K. SHOJIMA ◽  
K. YANASE ◽  
M. ENDO
Keyword(s):  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Crack Growth Behavior ◽  
Plastic Behavior ◽  
Short Cracks ◽  
Major Factors

The notch is usually unavoidable in designing various mechanical components. As well known, those notches significantly influence the fatigue life and fatigue strength of materials. In addition, most fatigue cracks spend the vast majority of their lives as short cracks, and the behavior of such flaw is of significant importance in determining the fatigue lifetime of notched components. Correspondingly, in this research, we investigate the fatigue crack growth behavior and fatigue strength of notched plates. For the proposed method, the elastic-plastic behavior, the Kitagawa effect and the crack closure are taken into account as the major factors responsible for the peculiar behavior of small fatigue cracks emanating from notches. Regarding the experiment, the fatigue tests were conducted using the plates with a circular notch under uniaxial loading condition. The proposed approach is validated by comparing the predicted results to the experimental data.

Guided Wave Acoustic Emission from Fatigue Crack Growth in Aluminium Plate

2006 ◽  
Vol 13-14 ◽  
pp. 23-28 ◽  
Author(s):  
C.K. Lee ◽  
Jonathan J. Scholey ◽  
Paul D. Wilcox ◽  
M.R. Wisnom ◽  
Michael I. Friswell ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Elastic Waves ◽  
Fatigue Cracks ◽  
Guided Wave ◽  
Experimental Results ◽  
Multiple Reflections ◽  
Alloy Plate

Acoustic emission (AE) testing is an increasingly popular technique used for nondestructive evaluation (NDE). It has been used to detect and locate defects such as fatigue cracks in real structures. The monitoring of fatigue cracks in plate-like structures is critical for aerospace industries. Much research has been conducted to characterize and provide quantitative understanding of the source of emission on small specimens. It is difficult to extend these results to real structures as most of the experiments are restricted by the geometric effects from the specimens. The aim of this work is to provide a characterization of elastic waves emanating from fatigue cracks in plate-like structures. Fatigue crack growth is initiated in large 6082 T6 aluminium alloy plate specimens subjected to fatigue loading in the laboratory. A large specimen is utilized to eliminate multiple reflections from edges. The signals were recorded using both resonant and nonresonant transducers attached to the surface of the alloy specimens. The distances between the damage feature and sensors are located far enough apart in order to obtain good separation of guided-wave modes. Large numbers of AE signals are detected with active fatigue crack propagation during the experiment. Analysis of experimental results from multiple crack growth events are used to characterize the elastic waves. Experimental results are compared with finite element predictions to examine the mechanism of AE generation at the crack tip.

Estimation of the Shape Evolution and the Growth History of an Embedded Crack by Fatigue Loading

2011 ◽  
Author(s):  
Koji Gotoh ◽  
Keisuke Harada ◽  
Yosuke Anai
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Estimation Method ◽  
Estimation Procedure ◽  
Fatigue Loading ◽  
Shape Evolution ◽  
Crack Growth Behaviour ◽  
Embedded Crack

Fatigue life estimation for planar cracks, e.g. part-through surface cracks or embedded cracks is very important because most of fatigue cracks found in welded built-up structures show planar crack morphologies. Fatigue crack growth behaviour of an embedded crack in welded joints is investigated in this study. The estimation procedure of crack shape evolution for an embedded crack is introduced and validation of the estimation procedure of fatigue crack growth based on the numerical simulation of fatigue crack growth with EDS concept for an embedded crack is performed. The validity of the proposed shape evolution estimation method and the fatigue crack growth simulation based on the fracture mechanics approach with EDS concept are confirmed.

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