Limitations of small-scale yielding for fatigue crack growth

Published on Jul 1, 2021in Engineering Fracture Mechanics3.426
· DOI :10.1016/J.ENGFRACMECH.2021.107806
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Abstract
Abstract null null The work described here has led to a simple criterion that defines the boundary of the small-scale yielding, SSY, regime to avoid invalid use of the LEFM parameter, ΔK, as the characterising parameter for fatigue crack growth rate. The approach proposed is based on the analysis of crack tip opening displacement, CTOD, and its separation into elastic and plastic components. SSY conditions are shown to dominate when the elastic component of CTOD is larger than 75% of the total CTOD measured at a distance of 8 μm (the finite element mesh size) behind the crack tip, i.e., Δδe/Δδt >75%. Large-scale yielding, LSY, conditions become dominant for relatively large values of plastic CTOD, Δδe/Δδt
References36
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#1bruno marques (UC: University of Coimbra)H-Index: 2
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Abstract Fatigue crack growth (FCG) is simulated here by node release, which is made when the accumulated plastic strain reaches a critical value. The numerical procedure is very robust, showing a very fast stabilization and independence relatively to the load considered for node release. A critical accumulated plastic strain of 110% was obtained for the 2024-T351 aluminium alloy, comparing the experimental value of da/dN for a crack length of 26.5 mm and a stress ratio of 0.1, with plane strain...
7 CitationsSource
#1Mikel Escalero (University of Oviedo)H-Index: 2
#2Miguel Muñiz-Calvente (University of Oviedo)H-Index: 11
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Abstract The effective stress intensity factor range Δ K eff is commonly considered to govern the fatigue crack growth and may be estimated through the crack opening stress S op and the constraint factor α . In the literature closed-form expressions have been developed for estimating both variables in a center-cracked plate with elastic-perfectly plastic behavior subjected to remote uniform stresses. However, such expressions are frequently adopted regardless of geometry, material and loading an...
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Abstract The plastic CTOD range, δ p , which quantifies crack tip plastic deformation, is used to study fatigue crack propagation instead of the classical ΔK elastic parameter. A da/dN-δ p model was defined for the 304L stainless steel. da/dN was obtained experimentally in standard CT specimens while δ p was predicted numerically using the finite element method. The numerical models replicated the experimental tests in terms of geometry, material properties and loading. The da/dN-δ p model was u...
18 CitationsSource
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Abstract Crack tip opening displacement (CTOD) was measured using digital image correlation (DIC) and resolved into elastic and plastic CTOD components via an offset compliance technique. The plastic CTOD range gave a single linear correlation for fatigue crack growth rate at stress ratios of 0.1 and 0.6 in compact-tension (CT) specimens of Grade 2 titanium. A sensitivity analysis was performed to find the optimum position in the crack wake to make the CTOD measurements. The results are the firs...
22 CitationsSource
#1Sebastien Dezecot (INSA Lyon: Institut national des sciences Appliquées de Lyon)H-Index: 3
#1Sebastien Dezecot (INSA Lyon: Institut national des sciences Appliquées de Lyon)H-Index: 2
Last. Jean-Yves Buffiere (INSA Lyon: Institut national des sciences Appliquées de Lyon)H-Index: 39
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Low cycle fatigue crack growth tests have been performed at 250 °C in order to study fatigue crack growth under large scale yielding conditions in a material widely used at high temperature by the automotive industry for cylinder head applications. The studied material was a cast aluminum alloy AlSi7Cu3Mg (close to A319) produced by Lost Foam Casting. Two different microstructures were investigated: one containing large natural pores and another where pores have been removed by Hot Isostatic Pre...
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Abstract The major challenge in the mechanics of elastic-plastic fatigue crack growth is to find a physically based driving force parameter to correlate the crack growth rates under different loading conditions. Specifically, a parameter that can provide single-valued correlation of crack growth rates, in stress-controlled and strain-controlled fatigue, is needed. Approaches of the past used either cyclic strain (strain intensity factor) or nonlinear-fracture-mechanics based (cyclic J-integral, ...
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#1Fernando Antunes (UC: University of Coimbra)H-Index: 24
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Abstract Fatigue crack growth (FCG) is usually studied using ΔK, however several limitations have been found in the use of da/dN-ΔK curves. Therefore, the FCG in the 2050-T8 aluminium alloy is studied here using the plastic CTOD. Experimental work was developed to obtain FCG in M(T) specimens. The experimental procedure was replicated numerically in terms of geometry, loading and material behaviour. The cyclic plastic behaviour of the material was modeled using stress-strain curves obtained in l...
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Cited By1
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#1Edmundo R. Sérgio (UC: University of Coimbra)
#2Fernando Antunes (UC: University of Coimbra)H-Index: 24
Last. Diogo M. Neto (UC: University of Coimbra)H-Index: 13
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Fatigue is one of the most prevalent mechanisms of failure. Thus, the evaluation of the fatigue crack growth process is fundamental in engineering applications subjected to cyclic loads. The fatigue crack growth rate is usually accessed through the da/dN-ΔK curves, which have some well-known limitations. In this study a numerical model that uses the cyclic plastic strain at the crack tip to predict da/dN was coupled with the Gurson–Tvergaard–Needleman (GTN) damage model. The crack propagation pr...
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