Crack Tip Geometry for Fatigue Cracks Grown in Air and Vacuum

2009 ◽  
pp. 400-400-26 ◽  
Author(s):  
CQ Bowles ◽  
J Schijve
Keyword(s):  
Fatigue Cracks ◽  
Crack Tip ◽  
Crack Tip Geometry

Plastic Strain Distribution at the Tips of Propagating Fatigue Cracks

1976 ◽  
Vol 98 (1) ◽  
pp. 24-29 ◽  
Author(s):  
D. L. Davidson ◽  
J. Lankford
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Plastic Strain ◽  
Plastic Zone ◽  
Strain Distribution ◽  
Dimensionless Parameter ◽  
Fatigue Cracks ◽  
Crack Tip ◽  
Cyclic Plastic Zone ◽  
Plastic Zones

The techniques of selected area electron channeling and positive replica examination have been used to study the plastic zones attending fatigue crack propagation in 304 SS, 6061-T6 aluminum alloy, and Fe-3Si steel. These observations allowed the strain distribution at the crack tip to be determined. The results indicate that the concepts of a monotonic and a cyclic plastic zone are essentially correct, with the strains at demarcation between these two zones being 3 to 6 percent. Strain distribution varies as r−1/2 in the cyclic zone and as ln r in the monotonic plastic zone. The strain distributions for all materials studied may be made approximately coincident by using a dimensionless parameter related to distance from the crack tip.

Assessment of Constraint Effects on the Local Behaviour of a Propagating Crack Under Cyclic Loading

2012 ◽  
Author(s):  
M. R. Goldthorpe ◽  
A. H. Sherry
Keyword(s):  
Cyclic Loading ◽  
Best Practice ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Element Model ◽  
Compact Tension ◽  
Stress Constraint ◽  
T Stress ◽  
Constraint Effects

During operation, reactor components experience a range of static and cyclic loading that have the potential to result in environmental-fatigue crack initiation and growth. Recent experimental work has indicated that the ASME XI fatigue ‘in air’ design curves are non-conservative for fatigue cracks propagating in primary water environments at fixed temperatures of relevance to the plant. The approach adopted to assess these tests has, to date, followed current best practice: in which global Linear Elastic Fracture Mechanics (LEFM) loading parameters are used to quantify crack growth rates. To help establish an improved understanding of these data, and to assist in their application to assess plant components, a local crack-tip finite element model has been developed. The model incorporates material constitutive behavior that simulates cyclic deformation of austenitic steel, can take account of plasticity-induced crack closure and can take into consideration cracks in structurally-representative geometries via the T-stress constraint parameter. The results of studies using the model suggest that highly compressive values of the T-stress constraint parameter tend to promote less severe reverse loading of the crack tip compared with high constraint geometries such as pre-cracked compact tension and bend test specimens. These findings indicate that rates of corrosion-fatigue in actual structural geometries might be different from those observed in pre-cracked test specimens.

Modelling the Behavior of Short Fatigue Cracks under Variable Amplitude Loading Using FEM

2007 ◽  
Vol 353-358 ◽  
pp. 985-988
Author(s):  
Yan Hai Xu ◽  
Yong Xiang Zhao
Keyword(s):  
Fatigue Cracks ◽  
Crack Tip ◽  
Strain Range ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Variable Amplitude Loading ◽  
Plastic Strain Range ◽  
Variable Amplitude ◽  
Short Cracks ◽  
Crack Tip Opening

The behavior of short fatigue cracks under variable amplitude loading (VA) was investigated by FEM. The crack closure induced by the crack surface roughness was taken into consideration by using the contact between these crack surfaces. The effects of variable amplitude loading on the performance of short cracks are demonstrated with factors such as grain orientation and misorientation, crack length and the friction efficient between the contacted crack surfaces. Through the two indicators, crack tip opening displacement represented by "CTOD and "CTSD and the plastic strain range of crack tip, the characteristics of short cracks affected by loading blocks are discussed in detail. It is shown from the numerical results that the significance of the design of loading blocks in the fatigue experiments is evident and the performance of short cracks from the variable amplitude loading is more effective due to the closer to practice.

scholarly journals Approximation of the crack-tip field in fatigue cracks in bridge steel specimens: DIC analysis of different constraint levels

2019 ◽  
Vol 13 (49) ◽  
pp. 97-106
Author(s):  
Stanislav Seitl ◽  
Petr Miarka ◽  
Vladimir Ruzicka ◽  
Lucie Malikova ◽  
Alejandro Cruces ◽  
...  
Keyword(s):  
Fatigue Cracks ◽  
Crack Tip ◽  
Crack Tip Field ◽  
Bridge Steel

scholarly journals Strengthening of steel structures with fatigue cracks using adhesively bonded non-prestressed and prestressed CFRP lamellas

2019 ◽  
Author(s):  
Yvonne Ciupack ◽  
Lukas Ledecky ◽  
Yann Kasper ◽  
Achim Geßler ◽  
Matthias Albiez ◽  
...  
Keyword(s):  
Fatigue Cracks ◽  
Crack Tip ◽  
Steel Structures ◽  
Positive Influence ◽  
Fatigue Tests ◽  
Small Scale ◽  
Adhesively Bonded ◽  
Repair Welding ◽  
Reinforcement Measures ◽  
Adhesive Materials

In comparison to classic strengthening methods of fatigue-damaged steel structures, adhesively bonded CFRP lamellas show several advantages. Compared to bolted reinforcement measures and the drilling of the crack tip, crosssectional weakening is avoided. Heat-induced, negatively acting residual stresses and distortions, usually occurring during repair welding, can also be excluded. Therefore, the effectiveness of adhesively bonded CFRP lamellas to enhance the remaining lifetime of fatigue damaged steel structures is examined in a German research project. Selected results are presented in this paper. To characterize the steel, CFRP and adhesive materials, different tests on small scale specimens are carried out. With the help of fatigue tests on CT-samples the remaining fatigue lifetimes of specimens strengthened with adhesively bonded CFRP lamellas is compared to the remaining lifetimes of specimens strengthened by established methods such as drilling the crack tip and repair welding. Based on the evaluation of the crack propagation after the rehabilitation measures, the great potential of adhesively bonded CFRP reinforcements can be deduced. By prestressing the lamellas, the remaining lifetime can generally be increased further. The combination of adhesively bonded CFRP lamellas together with established rehabilitation methods shows a particularly high positive influence on the remaining lifetime of the CT-specimens.

scholarly journals Growth behavior of fatigue cracks in ultrafine grained Cu smooth specimens with a small hole

2015 ◽  
Author(s):  
Masahiro Goto ◽  
Kakeru Morita ◽  
Junichi Kitamura ◽  
Takaei Yamamoto ◽  
Masataka Baba ◽  
...  
Keyword(s):  
Fatigue Cracks ◽  
Maximum Shear Stress ◽  
High Stress ◽  
Crack Tip ◽  
Shear Plane ◽  
Growth Behavior ◽  
Shear Mode ◽  
Aspect Ratios ◽  
Ultrafine Grained ◽  
Loading Axis

In order to study the growth mechanism of fatigue cracks in ultrafine grained copper, stresscontrolled fatigue tests of round-bar specimens with a small blind hole as a crack starter were conducted. The hole was drilled on the surface where an intersection between the shear plane of the final ECAP processing and the specimen surface makes an angle of 45° or 90° with respect to the loading axis. At a low stress ( ? a = 90 MPa), the direction of crack paths was nearly perpendicular to the loading direction regardless of the location of the hole. Profile of crack face was examined, showing the aspect ratio (b/a) of b/a = 0.82. At a high stress ( ? a = 240 MPa), although the growth directions inclined 45° and 90° to the loading-axis were observed depending on the location of the drilling hole, crack faces in these cracks were extended along one set of maximum shear stress planes, corresponding to the final ECAP shear plane. The value of aspect ratios was b/a = 0.38 and 1.10 for the cracks with 45° and 90° inclined path directions, respectively. The role of deformation mode at the crack tip areas on crack growth behavior were discussed in terms of the mixed-mode stress intensity factor. The crack path formation at high stress amplitudes was affected by the in-plane shear-mode deformation at the crack tip.

Controlled Initiation of Short Fatigue Cracks in 316L Steel

2005 ◽  
Author(s):  
D. Stefanescu ◽  
J. Marrow ◽  
M. Preuss ◽  
A. Sherry
Keyword(s):  
Experimental Study ◽  
Stainless Steel ◽  
Crack Opening Displacement ◽  
Crack Nucleation ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Crack Tip ◽  
Image Correlation ◽  
Opening Displacement ◽  
R Ratio

Validation of models for short crack behavior requires accurate measurement of crack opening displacement and crack tip strain fields. Development of reliable measurement procedures, using new techniques such as Image Correlation (IC), requires specimens containing cracks with a well defined geometry. In this paper, results of an experimental study concerning controlled initiation of short fatigue cracks at positive R-ratio in laboratory specimens made from 316L stainless steel are presented. Experimental techniques, including hardness testing and X-ray diffraction were employed in order to investigate the effect of surface preparation on the surface mechanical properties and residual stresses. Crack nucleation is difficult in smooth specimens of 316L austenitic stainless steel at positive R-ratio due to the high fatigue limit and low tensile strength. Specimens with a thin ligament were therefore developed to enable nucleation of a single short fatigue crack. An experimental study of the crack growth aspect ratio evolution was then carried out using a beach marking technique. The technique described in this paper enables single short fatigue cracks of well defined geometry to be nucleated under tensile cyclic loading. Stress corrosion cracks can be developed using the same specimen geometry. Miniature tensile specimens can then be extracted to perform in-situ measurements of the crack opening displacement and crack tip strain field by Image Correlation from Scanning Electron Microscopy observations.

Three Dimensional Replication of Fatigue Cracks by Vacuum Infiltration for Study of Crack Tip Morphology by Scanning Electron Microscopy

1970 ◽  
Vol 28 ◽  
pp. 402-403
Author(s):  
G. G. Shaw
Keyword(s):  
Fatigue Cracks ◽  
Three Dimensional ◽  
Crack Tip ◽  
Vacuum Infiltration ◽  
Three Dimensions ◽  
New Information ◽  
Crack Tips ◽  
Sheet Sample ◽  
Scanning Electron

I. Introduction: Fatigue investigators have been looking at crack tips by examining the surface and by sectioning the crack. Much useful information has been obtained by these methods, but a look at the complete crack in three dimensions with the tip intact yields much new information. This is especially true when one is able to examine the crack tip in full tension or compression or stages in between, by using the following techniques.II. Vacuum Infiltration in Situ: The crack is generated on a fatigue machine using a sheet sample with a notched central hole. If one desires to replicate in full tension, the machine is stopped in tension and the apparatus shown in Figure 1 is clamped to the sides of the sample.

Sign in / Sign up

Export Citation Format

Share Document