X-ray Microtomography of Fatigue Crack Closure as a Function of Applied Load In Al-Li 2090 T8E41 Samples

1999 ◽  
Vol 591 ◽  
Author(s):  
R. Morano ◽  
S.R. Stock ◽  
G.R. Davis ◽  
J.C. Elliott
Keyword(s):  
Fatigue Crack ◽  
Crack Closure ◽  
Applied Load ◽  
Load Ratio ◽  
Compact Tension ◽  
Load Level ◽  
Crack Face ◽  
X Ray ◽  
Prolonged Contact ◽  
Crack Face Contact

ABSTRACTCrack closure is held to be responsible for very low fatigue crack growth rates in many alloys such as Al-Li 2090 T8E41, and early crack face contact during unloading or prolonged contact during loading seems to reduce the driving “force” for crack extension. High resolution x-ray computed tomography (i.e., microtomography) allows one to image the entire volumes of samples and to quantify opening as a function of applied load over the entire crack surface. Crack closure results are reported for a fatigue crack grown under load ratio R=0.1 in a compact tension sample of Al-Li 2090 T8E41; the crack was free to choose its path unconstrained by side-grooves which are normally used to suppress crack deflection. The inter-relationship between crack path, crack face contact and applied load level are discussed.

Numerical Study of the Influence of the Crack Front Curvature in the Evolution of the Plastic Zone along the CT Specimen Thickness

2011 ◽  
Vol 465 ◽  
pp. 119-122 ◽  
Author(s):  
Daniel Camas ◽  
Pablo Lopez-Crespo ◽  
Antonio González-Herrera
Keyword(s):  
Fatigue Crack ◽  
Finite Elements ◽  
Plastic Zone ◽  
Crack Closure ◽  
Crack Front ◽  
Numerical Study ◽  
Load Level ◽  
Specimen Thickness ◽  
Aluminum Specimen ◽  
Front Curvature

This paper presents a numerical study of the influence of the load level and the crack front curvature on the plastic zone in the area close to the crack front. The aim of the work is to determine the influence of these parameters on fatigue crack closure. For this, a CT aluminum specimen has been modelled tri-dimensionally and several finite elements calculations have been made considering a large combination of the variables under consideration.

Experimental and Numerical Investigation of Plasticity-Induced Fatigue Crack Closure in Overmatched Welds

2013 ◽  
Author(s):  
Diego F. B. Sarzosa ◽  
Claudio Ruggieri
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Compact Tension ◽  
Cyclic Stress ◽  
Growth Behavior ◽  
Weld Strength ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior

This work provides a numerical and experimental investigation of fatigue crack growth behavior in steel weldments including crack closure effects and their coupled interaction with weld strength mismatch. A central objective of this study is to extend previously developed frameworks for evaluation of crack closure effects on fatigue crack growth rates (FCGR) to steel weldments while, at the same time, gaining additional understanding of commonly adopted criteria for crack closure loads. Very detailed non-linear finite element analyses using 3-D models of compact tension C(T) fracture specimens with square groove, weld centerline cracked welds provide the evolution of crack growth with cyclic stress intensity factor which is required for the estimation of the closure loads. Fatigue crack growth tests conducted on plane-sided, shallow-cracked C(T) specimens provide the necessary data against which crack closure effects on fatigue crack growth behavior can be assessed. Overall, the present investigation provides additional support for estimation procedures of plasticity-induced crack closure loads in fatigue analyses of structural steels and their weldments.

An Efficient Way to Characterize the Fatigue Crack Growth Based on Numerical Analysis

2009 ◽  
Vol 417-418 ◽  
pp. 653-656
Author(s):  
Ya Zhi Li ◽  
Jing He ◽  
Zi Peng Zhang
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Length ◽  
Crack Growth ◽  
Crack Closure ◽  
Load Ratio ◽  
Specimen Thickness

The behavior of plasticity induced fatigue crack closure (PICC) in middle tension specimen was analyzed by the elastic-plastic finite element method. For the constant-K (CK) loading cases, the opening stress intensity factor are independent of crack length. The level of increases with the maximal applied stress intensity factor for given load ratio and increases with for fixed . The in plane strain state is much smaller than that in plane stress state. The results under CK loadings can be deduced to constant amplitude cyclic loading case during which the load ratio, maximal load level, crack length and specimen thickness are all the factors affecting the crack closure effect. The phenomena revealed in the analysis are beneficial in understanding the driving force mechanism of the fatigue crack growth.

Investigation Into Crack Closure Effects for Fatigue Crack Growth Under Negative R Conditions

2020 ◽  
Author(s):  
Ben Pellereau ◽  
Chris Currie ◽  
Jonathan Mann ◽  
Ben Coult
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Load Ratio ◽  
304L Stainless Steel ◽  
Corner Crack ◽  
Growth Equations ◽  
Growth Laws ◽  
Maximum Stress Intensity

Abstract Fatigue crack growth laws are typically dependent on the ratio between minimum and maximum Stress Intensity Factor (SIF), referred to as the load ratio (R). When part of the SIF range is compressive (and hence R is negative) the amount of growth for a given SIF range is reduced due to crack closure effects. Methods for capturing the effect of crack closure were presented in a previous PVP paper [1]. These methods are based around defining a scaling factor (q0) which is dependent on R and applied to the SIF range before calculated growth. Equations were provided for both best fit and bounding q0 factors. This paper presents a comparison between these methods and results of testing. The specimens used were square cross-section bars and were made from Type 304L stainless steel with an initial corner crack. A range of load ranges and R ratios (including some positive R values) were used and the testing was undertaken at 250°C in both air and a simulated PWR environment. The growth rate observed in the tests was used to derive the effective q0 factor observed in each stage of the testing. These values were then compared with the q0 methods that are used in actual defect tolerance calculations. The results agreed very closely with the derived best estimate q0 curves, with no discernible difference between the air and water results.

Investigation of the Stress Fields Around a Fatigue Crack in Aluminium Alloy 5091

2008 ◽  
Vol 571-572 ◽  
pp. 119-124 ◽  
Author(s):  
M. Rahman ◽  
Michael E. Fitzpatrick ◽  
Lyndon Edwards ◽  
S. Pratihar ◽  
Matthew J. Peel ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Aluminium Alloy ◽  
Crack Tip ◽  
Fatigue Loading ◽  
Compact Tension ◽  
European Synchrotron Radiation Facility ◽  
Stress Fields ◽  
Small Scale ◽  
X Ray Diffraction ◽  
X Ray

There have been many theoretical studies to predict the stress fields around the tip of a growing fatigue crack. However, until recently the highly-localized, small scale nature of the stresses has meant that direct measurement has not been possible. With the current generation of synchrotron X-ray sources, sub-millimetre sampling dimensions are now possible, and it has become possible to evaluate directly the stresses at the tip of a fatigue crack and to see how the stresses evolve as the result of an overload, for example. In this paper we present results of synchrotron X-ray diffraction analysis of the stress fields around a fatigue crack in aluminium alloy 5091 (Al-Mg-Li-C-O); this is a dispersion-strengthened alloy with a fine grain size, which makes it ideal for such experiments. Compact tension (CT) specimens were prepared with constant amplitude fatigue loading. The energy dispersive X-ray diffraction (EDXRD) technique was used for measuring strains around the crack tip along the mid thickness of the specimen under in-situ loading. The measurement was carried out at the ESRF (European Synchrotron Radiation Facility), Grenoble, France on the ID15A beam line. The experimental crack tip stresses have been compared with the analytical fracture mechanics solution.

High resolution X-ray tomography of micromechanisms of fatigue crack closure

2006 ◽  
Vol 55 (1) ◽  
pp. 47-50 ◽  
Author(s):  
K.H. Khor ◽  
J.-Y. Buffiére ◽  
W. Ludwig ◽  
I. Sinclair
Keyword(s):  
Fatigue Crack ◽  
High Resolution ◽  
Crack Closure ◽  
X Ray ◽  
Fatigue Crack Closure
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