Prediction of Constant Amplitude Fatigue Crack Propagation in Surface Flaws

Johnson, W. A.

doi:10.1520/stp35037s

Cited by 7 publications

(4 citation statements)

References 1 publication

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“…where the prime (') symbol denotes the expressions for the 2D/1D transition from part-through 2D to through 1D cracks (20) and the SIF during the transitioning period is then modeled replacing c/t by r' in Eqs. (12)(13)(14)(15)(16)(17)(18). When the imaginary crack depth a' reaches 2.3t, Eq.…”

Section: Transition From 2d Semi-elliptical Surface Cracks To 1d Thromentioning

confidence: 99%

“…Some approximations have been suggested based on the boundary element method [8], however they do not account for the component width effect, a major limitation on practical applications. A simplified model for the 2D-1D crack front transition was proposed by Johnson a long time ago [16]. According to him, after the crack depth reaches the specimen thickness t, the crack can be assumed to keep its elliptical shape in the transition zone.…”

Section: Introductionmentioning

confidence: 99%

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Stress Intensity Factor Equations for the Evolution of Surface and Corner Cracks to Through Cracks

Miranda

Marques²,

Meggiolaro³

et al. 2019

Frattura Ed Integrità Strutturale

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Part-through surface or corner 2D cracks are commonly found in structural components, even because practically all fatigue cracks tend to start this way. It is a reasonable hypothesis to model them assuming the shape of their 2D fronts can be approximated by an elliptical arc, as supported by many fractographic observations. However, their transition to a 1D throughcrack, an important issue in many practical applications, is normally not properly addressed in fatigue life predictions. Although experimental results reveal that the frontiers of surface cracks essentially retain their elliptical shape as they gradually grow into an 1D through-crack, it is usual to assume they are immediately transformed into an 1D through-crack when their depth reaches the cracked component thickness. This crude approximation may create a large jump in stress intensity values, leading to excessively conservative fatigue crack growth predictions; or else, the crude shape jump hypothesis might induce false overload events that can much affect fatigue crack growth retardation models, leading to inadmissible non-conservative life predictions. To minimize such problems, an improved model to describe the transition of 2D surface cracks to 1D through-cracks is proposed and verified by crack propagation tests in two different materials, 4340 steel and polycarbonate (PC). Moreover, fatigue life predictions based on this improved model are compared with experimental results obtained with these two materials.

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Section: Transition From 2d Semi-elliptical Surface Cracks To 1d Thromentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Stress Intensity Factor Equations for the Evolution of Surface and Corner Cracks to Through Cracks

Miranda

Marques²,

Meggiolaro³

et al. 2019

Frattura Ed Integrità Strutturale

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“…Surface "Thumbnail" flaw [25] AKth= l.l where AKth is the threshold stress intensity range, below which no crack growth will occur, and A_ is the corresponding threshold s stress ;…”

Section: Simple Fatigue Damage Modelmentioning

confidence: 99%

Mechanisms of Fatigue Damage in Boron/Aluminum Composites

Johnson

1982

Damage in Composite Materials: Basic Mechanisms, Accumulation, Tolerance, and Characterization

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Fatigue damage mechanisms have been investigated using a series of tension fatigue tests on several laminates of boron/aluminum (6061-0). This study focuses on four aspects of the fatigue response. First, in laminates with 0-deg fibers on the outside, an analysis that identifies “shakedown” conditions is shown to predict the stress amplitude below which no fatigue damage accumulates. Second, a simple fatigue damage accumulation model which relates matrix fatigue cracking and the overall laminate properties is described. A model for the saturation damage stage development is presented. Third, data illustrate that identical laminates, tested in directions 90-deg apart (such that one layup has 90-deg outer plies and the other 0-deg), have different fatigue behaviors due to the stacking sequence. The 90-deg plies on the surface develop cracks earlier than predicted by shakedown. An attempt is made to explain this stacking sequence effect. Finally, variable load history effects on the fatigue damage response are investigated by simple tests. These tests reveal that for a given stress ratio the specimen seeks the saturation damage state for the largest stress range to which it is subjected. It also was found that little damage is generated by shifting a given stress range down, whereas significant damage may be created by shifting it upward.

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“…Grandt et al used the finite‐element alternating method to analyse the transition for a specific scenario . Johnson put forward a method that continues to use the stress intensity solutions for surface flaws through the transition by extending the elliptical crack contours into a fictitious space beyond the back face of the material (Figure F). Once the depth direction of the contour ( a ) becomes greater than the plate thickness ( t ), a becomes a ′ (see Figure ), and the back face crack length ( c ′) can be computed using the following ellipse equation:

\frac{c'^{2}}{c^{2}} + \frac{t^{2}}{a'^{2}} = 1 .

…”

Section: Introductionmentioning

confidence: 99%

Transition modelling of surface flaws to through cracks

Satin

Johnson

Neu

et al. 2020

Fatigue Fract Eng Mat Struct

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Cracks starting at surfaces will grow under fatigue loading conditions both along the surface and in the thickness directions of the component geometry.In those cases where the crack grows through the thickness, the fatigue crack may transition to a corresponding through crack geometry. While the fatigue crack growth behaviour of both the surface flaws and complete through cracks are well understood, the method for modelling the process by which they transition from one to the other is not. This paper seeks to bring greater clarity and understanding to the transition process by implementing a transition method and developing the associated codes and equations to do so based on careful consideration of boundary conditions, experimental data, and finite element simulations. K E Y W O R D S fatigue crack growth, flaw transition, marker banding, part-through cracks, surface flaws

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Prediction of Constant Amplitude Fatigue Crack Propagation in Surface Flaws

Cited by 7 publications

References 1 publication

Stress Intensity Factor Equations for the Evolution of Surface and Corner Cracks to Through Cracks

Stress Intensity Factor Equations for the Evolution of Surface and Corner Cracks to Through Cracks

Mechanisms of Fatigue Damage in Boron/Aluminum Composites

Transition modelling of surface flaws to through cracks

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