Variable mode-mixity during fatigue cycles – crack tip parameters determined from displacement fields measured by digital image correlation

Published on Jun 28, 2017in Fracture and Structural Integrity
· DOI :10.3221/IGF-ESIS.41.42
Michael Vormwald25
Estimated H-index: 25
,
Yigiter Hos4
Estimated H-index: 4
+ 2 AuthorsJorge G. Díaz4
Estimated H-index: 4
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Abstract
This paper focusses on discussing equivalent stress intensity factors and kink angles after a change of mode-mixity from one cycle to the next and when the mode-mixity changes continuously during the fatigue cycles. Thin-walled tubes with through-wall cracks have been loaded by proportional and non-proportional tension and torsion. In the experimental investigation, the region of fatigue crack growth was observed by applying the digital image correlation technique. Data on the variations of the displacement and strain fields during the cycles were acquired and used to determine mixed-mode variations of stress intensity factors associated with opening modes I, II and III. For each specific specimen the crack path was observed in order to relate its curvature – both kinks and continuously developing warped cracks – with the variations of the displacement field and associated stress intensity factors.
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#1Jan Kraft (Technische Universität Darmstadt)H-Index: 1
#2Carl Fällgren (Technische Universität Darmstadt)H-Index: 1
Last. Michael Vormwald (Technische Universität Darmstadt)H-Index: 25
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Abstract The strain energy release rate is calculated numerically for cracks in shells from shell elements by using the modified crack closure integral. This enables the separation of individual strain energy release rates for the different crack opening modes and the calculation of the corresponding stress intensity factors for mixed mode loading situations. The presented formulas are validated by comparing numerical results for a 3d finite element model with results computed from a plane shell...
2 CitationsSource
#1Jorge G. Díaz (Industrial University of Santander)H-Index: 4
Last. Deisy Carolina Páez (Universidad Santo Tomás)
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The present paper shows a way to identify crack tip location (CTL) using edge detection algorithms. Arbitrary crack tip coordinates were fed to Linear Elastic Facture mechanics (LEFM) analytical models to simulate displacement fields. Then, first degree edge detection algorithms were applied to the obtained displacement fields to identify crack edges. Results show excellent correlation between random and identified crack tip coordinates. The paper proves the method and that CTL can be identified...
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Abstract This work is concerned with improvement of experimental methods for studying the influence of the stress-strain state on the spatial time inhomogeneity die to the jerky flow of Al-Mg alloys and carbon steels. The implementation of a complex stress state is based on the use of specimens with special complicated geometry. Mechanical tests were carried out on uniaxial tension of plates with a rigid rim, in the working part of which biaxial tension and combined tension-compression loading i...
2 CitationsSource