Plasticity-induced, roughness-induced and oxide-induced crack closures are reviewed. Special attention is devoted to the physical origin, the consequences for the experimental determination and the prediction of the effective crack driving force for fatigue crack propagation. Plasticity-induced crack closure under plane stress and plane strain conditions require, in principle, a different explanation; however, both types are predictable. This is even the case in the transition region from the plane strain to the plane stress state and all types of loading conditions including constant and variable amplitude loading, the short crack case or the transition from small-scale to large-scale yielding. In contrast, the prediction of roughness-induced and oxide-induced closures is not as straightforward.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/ffe.12578

Fatigue crack closure: a review of the physical phenomena.

The problems arising as a result of aging aircraft, rail and civil infrastructure have focused attention on tools for predicting the growth of cracks from small naturally occurring material discontinuities. To this end, the present paper discusses on the difference between the analysis tools needed for ab initio design and sustainment, modelling of cracks that grow from small naturally occurring material discontinuities and ways to determine the short crack da/dN versus ΔK data from long crack American Society for Testing and Materials (ASTM) tests. It also discusses how existing equations can be used to predict short crack growth and how to account for the variations seen in crack growth histories. Attention is also focused on the recent Federal Aviation Administration limit of validity ruling and the effect of the environment on widespread fatigue damage in civil transport aircraft.

Fatigue crack growth and damage tolerance

In this paper a review of the literature on crack closure/opening load and crack tip shielding effects determination methods is presented. Commonly used ‘subjective’ (visual) and ‘non-subjective’ approaches have been included. Procedures associated with the determination of an effective crack driving force for both Elber type and that of partial (or incremental) crack closure models have been covered. Comparison among different methods of analyses based on compliance and fatigue crack growth rate measurements is discussed together with their implications and difficulties in fatigue crack growth correlations.

Methods for crack opening load and crack tip shielding determination: a review

This article is concerned with the fatigue life prediction in specimens of 7475-T7351 high strength aluminum alloy subjected to random fatigue loading. Fatigue life predictions are made using the root mean square model. This model is chosen because it has been defined as the most simple and effective one for fatigue life prediction in the components subjected to random loading by the authors of this article. The analysis procedure used in this study is relatively simple. The loading history for each specimen is analyzed to determine the root mean square maximum and minimum stresses and predictions are then made by assuming that the tests have been conducted under constant amplitude loading at the root mean square maximum and minimum stresses. The ratios of the predicted lives range from 3.22 to 1.52. These ratios are fairly good considering that the normal scatter in fatigue crack growth rates may range from a factor of two to four under identical load conditions. Moreover, an attempt has been made to imp...

/pdf/fatigue-life-prediction-under-random-loading-conditions-in-s69exrqqzf.pdf

Fatigue Life Prediction under Random Loading Conditions in 7475-T7351 Aluminum Alloy using the RMS Model

http://pure.tudelft.nl/ws/files/8929993/IJF_2016.pdf

How proper similitude can improve our understanding of crack closure and plasticity in fatigue

A fatigue crack growth model for metals is presented in this two part paper. The model is based on experimental evidence obtained on the aluminium alloy Al 7475-T7351. In Part I of this paper, the physical basis of the model is discussed. The model accounts for residual compressive stresses ahead of the crack front and crack closure, which constitute an intrinsic and extrinsic effect, respectively. The centre of this model is the crack propagation stress intensity factor, K PR . There are two basic sequences involving a load step following constant amplitude loading which cause two different types of transitional processes that are fundamental to fatigue crack growth. An increase in the maximum load causes instant and 'dynamic' changes in K PR . This transition in K PR is cycle dependent. An example is a multiple overload sequence. A decrease in the maximum load causes a crack growth dependent transition. Crack growth retardation after a tensile overload is an example of this type of a transition. The general description of these two transitional processes constitutes the complete solution for the fatigue crack growth problem in metals for Mode 1 loading. Part I of this paper provides the general description of the two transitional processes in terms of K PR . In Part II, the results of Part I are generalised, which leads to a new fatigue crack growth prediction model for variable amplitude loading.

A model for fatigue crack growth, part I: phenomenology*

A fatigue crack growth prediction model for metals is presented. It is based on experimental evidence obtained on the aluminium alloy Al 7475-T7351, which is presented in Part I of this paper. This part of the paper generalises the results from Part I and develops a new fatigue crack growth prediction model for variable amplitude loading. The central parameter of this model is the crack propagation stress intensity factor, K PR . The general description of the relatively simple loading sequences in Part I of this paper in terms of K PR leads to a scheme that is denoted as the 'Fatigue Crack Growth Map.' This map defines all possible crack growth conditions and is the heart of the crack growth prediction method. It is shown that any arbitrary loading spectrum consists only of three different types of load cycles, Type I, II and III. This paper elaborates on the specific conditions that lead to a specific type of cycle and explains the determination of the corresponding K PR value. The model determines K PR cycle by cycle throughout a loading spectrum. K PR determines the driving force, ΔK eff , for the following cycle. The model requires the knowledge of the yield strength and the intrinsic threshold value, ΔK T , for the material, as well as five different functions that also depend on the material. Phenomenologically, the model accounts for residual compressive stresses ahead of the crack front, the intrinsic response of the material and crack closure, which is an extrinsic effect. A few variable amplitude loading sequences are presented to compare predictions of K PR with experiments. The results are in encouraging agreement.

A model for fatigue crack growth, part II: modelling*

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A model for fatigue crack growth, part I: phenomenology*

A model for fatigue crack growth, part II: modelling*