X-Ray Diffraction Measurements of Crack Tip Stresses as a Crack Advances through a Single Overload Affected Zone

1979 ◽  
Author(s):  
Donald R. Holloway
Keyword(s):  
Crack Tip ◽  
X Ray Diffraction ◽  
X Ray ◽  
Single Overload

scholarly journals In situ through-thickness analysis of crack tip fields with synchrotron X-ray diffraction

2019 ◽  
Vol 127 ◽  
pp. 500-508 ◽  
Author(s):  
P. Lopez-Crespo ◽  
J.V. Peralta ◽  
J.F. Kelleher ◽  
P.J. Withers
Keyword(s):  
Crack Tip ◽  
X Ray Diffraction ◽  
X Ray ◽  
Crack Tip Fields

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.

scholarly journals Direct Observation of Elastic and Plastic Strain Fields During Ductile Tearing of a Ferritic Steel

2016 ◽  
Author(s):  
Harry E. Coules ◽  
Graeme C. M. Horne ◽  
Matthew J. Peel ◽  
Sam J. Oliver ◽  
Derreck G. A. Van Gelderen ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Plastic Strain ◽  
Crack Tip ◽  
Image Correlation ◽  
Pressure Vessel Steel ◽  
X Ray Diffraction ◽  
Residual Stress Field ◽  
Ductile Tearing ◽  
X Ray

Residual and thermal stresses have a considerable effect on the process of brittle fracture. In addition to this, the effect of these stresses on elastic-plastic fracture is known to be significant. This is accounted for in structural integrity assessment methodologies such as R6 Rev 4 and BS 7910:2013 by introducing factors representing the interaction between primary and secondary stresses (those that do and do not contribute towards plastic collapse, respectively). The initiation of ductile tearing in a ferritic pressure vessel steel was studied experimentally. Energy-dispersive X-ray diffraction was used to determine lattice strains in the vicinity of a crack tip in modified compact tension specimens at incremental loading steps until the initiation of ductile tearing. The X-ray diffraction measurements allowed the stress field to be evaluated with a high spatial resolution. At the same time, the pattern of total strain at the surface of the specimen was observed using digital image correlation. Prior to the experiment, two samples were subjected to localised out-of-plane compression ahead of the crack tip to introduce a residual stress field and hence significant crack loading in the absence of external load. Stress and strain field data for cracked specimens, with and without a pre-existing residual stress field, indicated significant differences in the development of plastic strain up to the point of tearing initiation. It is shown that this can only be explained when both residual stress and prior material hardening are taken into account.

In Situ Stress Measurement Method Based on X-Ray Diffraction under Biaxial Tensile Loading

2011 ◽  
Vol 675-677 ◽  
pp. 615-618
Author(s):  
Dong Ying Ju ◽  
J.G. Wang ◽  
Minoru Abe
Keyword(s):  
Stress Distribution ◽  
Applied Stress ◽  
Stress Measurement ◽  
Biaxial Tension ◽  
Crack Tip ◽  
Tension Test ◽  
X Ray Diffraction ◽  
X Ray ◽  
Biaxial Tensile ◽  
Stress Ratios

The purpose of this investigation is to detect damage from stress distribution in the surface of near pre-crack tip by using X-ray diffraction technique during biaxial tension test. An measurements apparatus to measure stress distribution along pre-crack direction was fabrication by use of a biaxial tensile test device and a stress analyzer based on single exposure technique with one position sensitive proportional counter. Stress distribution with different tensile applied stress ratios were measured during biaxial tension test. As results, the shape of actual stress was keeping increase with increasing tensile applied stress. At maximum applied stress, the residual stress increases with the increasing distance from the crack tip; after reaching a maximum it gradually diminish.

scholarly journals Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy

2015 ◽  
Vol 373 (2036) ◽  
pp. 20130157 ◽  
Author(s):  
P. J. Withers
Keyword(s):  
Fracture Mechanics ◽  
Three Dimensional ◽  
Crack Tip ◽  
Quantitative Measure ◽  
Phase Changes ◽  
X Ray Diffraction ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Crack Face ◽  
X Ray

To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

scholarly journals The interaction of fatigue cracks with a residual stress field using thermoelastic stress analysis and synchrotron X-ray diffraction experiments

2017 ◽  
Vol 4 (11) ◽  
pp. 171100 ◽  
Author(s):  
Khurram Amjad ◽  
David Asquith ◽  
Eann A. Patterson ◽  
Christopher M. Sebastian ◽  
Wei-Chung Wang
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Crack Tip ◽  
Thermoelastic Stress ◽  
Thermoelastic Stress Analysis ◽  
X Ray Diffraction ◽  
Cold Expansion ◽  
X Ray ◽  
Stress Zone ◽  
Plastic Zones

This article presents an experimental study on the fatigue behaviour of cracks emanating from cold-expanded holes utilizing thermoelastic stress analysis (TSA) and synchrotron X-ray diffraction (SXRD) techniques with the aim of resolving the long-standing ambiguity in the literature regarding potential relaxation, or modification, of beneficial compressive residual stresses as a result of fatigue crack propagation. The crack growth rates are found to be substantially lower as the crack tip moved through the residual stress zone induced by cold expansion. The TSA results demonstrated that the crack tip plastic zones were reduced in size by the presence of the residual compressive stresses induced by cold expansion. The crack tip plastic zones were found to be insignificant in size in comparison to the residual stress zone resulting from cold expansion, which implied that they were unlikely to have had a notable impact on the surrounding residual stresses induced by cold expansion. The residual stress distributions measured along the direction of crack growth, using SXRD, showed no signs of any significant stress relaxation or redistribution, which validates the conclusions drawn from the TSA data. Fractographic analysis qualitatively confirmed the influence on crack initiation of the residual stresses induced by the cold expansion. It was found that the application of single compressive overload caused a relaxation, or reduction in the residual stresses, which has wider implications for improving the fatigue life.

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