Fatigue Crack Closure Research Articles

Kinetics of fatigue crack growth and crack closure effect in long term operating steel manufactured at the turn of the 19th and 20th centuries

In this paper the fatigue crack growth behaviour in structural components from the old 19th century structures (e.g. bridges) has been investigated. The delivered material for investigation was extracted from a beam made of puddled iron, commonly used in the 19th century. The obtained results from several ancient railway metallic bridges (located in Lower Silesia, Poland) have shown the presence of microstructural degradation processes in puddled iron. The kinetic fatigue fracture diagrams (KFFD) have been obtained for post-operated steel. The problem of crack closure has been involved in fatigue crack growth process during the experiments and its understanding is fundamental for the analysis of stress ratio effects on KFFD. An experimental and numerical approach has been considered for the evaluation of the crack closure/opening forces based on the hysteresis loop deformation. The implemented algorithm in the numerical environment gives promising results in the description of the kinetics of fatigue crack growth of the old metallic materials with consideration of crack closure effects. The problem of fatigue crack growth rate description from the energy point of view has been presented and discussed. The Universal Graph method (based on Dimensional Analysis approach) was used for phenomenological formulation of the kinetic equation.

Crack closure in near-threshold fatigue crack propagation in railway axle steel EA4T

The paper is focused on fatigue crack propagation in the threshold area of the EA4T railway axle steel. Railway axles represent one of the most critical components for safety of trains. The main aim of this paper is to describe fatigue crack closure mechanisms in EA4T, which significantly influence the threshold value – a crucial parameter for determination of residual fatigue lifetime of railway axles. Investigated fatigue crack closure mechanisms are: plasticity induced crack closure, roughness-induced crack closure and oxide-induced crack closure. One part of this paper is focused on comparison of crack closure determined by NASGRO relationship (including plasticity induced crack closure mechanism only) with the experimentally obtained one. Difference between these two approaches is explained by presence of roughness and oxide induced crack closure. Based on theoretical models different sources of fatigue crack closure mechanisms was separated and evaluated. The significance of oxide-induced crack closure was confirmed based on experimental measurement of fatigue crack propagation in low humidity air. Finally, the effect of a reduced threshold value in low-humidity air on residual fatigue lifetime of railway axles is demonstrated.

Fatigue crack closure: a review of the physical phenomena.

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.

Measuring fatigue crack growth and closure in Polyether Ether Ketone (PEEK)

Throughout industry, polymers are being used to replace parts that were previously fabricated from metals. Thus, the fatigue resistance of polymers needs to be well understood. Polyether Ether Ketone (PEEK) is often chosen for its good mechanical properties and high glass transition temperature. In this paper, the experiments and methods to study fatigue crack growth and subsequent crack closure are presented. Compact specimens made of PEEK were used to experimentally monitor fatigue crack growth at R=0.1 and R=0.7. Some unique aspects of the experiments include the use of compression pre-cracking and a back-face strain gauge to measure crack length. While measuring crack closure was the primary focus of the experiments, crack growth rate versus stress intensity factor range results were also generated. Using remote methods of measuring crack closure show that PEEK experiences a small level of crack closure, though the effects are minimal. However, indirect methods of measuring crack closure show that the phenomenon is more prevalent in the material than what was measured. Further research for continuing the study of fatigue crack closure in PEEK are discussed.

Fatigue crack propagation analysis for multiple weld toe cracks in cut-out fatigue test specimens from a girth welded pipe

Multiple fatigue cracks are prevalent in welded structures. Current fatigue assessment code procedures employ various simplifications in the treatment of multiple cracks that result in over-conservative life predictions. In this work, crack coalescence and fatigue crack closure are incorporated into established models of crack propagation analysis. The model is verified by fatigue tests of cut-out welded steel pipes (butt weld) subject to four-point bending fatigue. A large number of starting weld toe cracks are determined from the experiments, with 12–22 cracks used in the fatigue life prediction of the fatigue tested pipes. The fatigue crack growth approach proposed is taken into account to predict remaining life more accurately compared to the threshold stress intensity factor approach used in the BS 7910 standard.

Modified CCS fatigue crack growth model for the AA2019-T851 based on plasticity-induced crack-closure

Several fatigue cracks growth laws have been suggested over the past 50years. Recently, a fatigue crack propagation law was proposed by Castillo-Canteli-Siegele (CCS model) based on the assumption that fatigue crack growth takes the form of a Gumbel cumulative distribution function. Besides many physical aspects, the fatigue crack propagation laws need to account for fatigue crack opening and closure effects. Thus, in this paper a modification of the CCS fatigue crack growth law is proposed to account for the crack opening and closure effects, as well as the stress R-ratio effect, Rσ. The fatigue crack opening and closure effects are taken into account using a plasticity-induced crack-closure model. Other fatigue crack closure models can also be used in the proposed modification of the CCS crack growth model through the quantitative parameter U=ΔKeff/ΔK. This modified CCS crack propagation model using the effective stress intensity factor range, ΔKeff, is a new version of an explicit fatigue crack propagation model, supported by mathematical and physical assumptions. In this paper, the proposed model is applied using the fatigue crack growth data and mechanical properties that were collected for the 2219-T851 aluminium alloy. Based on the plasticity-induced crack-closure model, which was first formulated by Newman, and in this paper modified with a boundary correction factor, Fw, the crack opening stress intensity factor, Kop, and quantitative parameter U are determined. The results showed a good agreement between the proposed modification of the CCS fatigue crack propagation model taking into account the plasticity-induced crack-closure model with the boundary correction factor and experimental results of the fatigue crack propagation data for the 2219-T851 aluminium alloy.

磁歪効果を利用した微小疲労き裂情報の測定

Small fatigue crack closure is observed as a thing with a possibility that the influence of change of the stress level and a stress ratio, etc. to the crack growth behavior can be explained, and until now various researches have been done. Although there is a method using the strain gage as the dynamic measurement method required for the elucidation of a minute fatigue crack, in respect of generating of minute fatigue cracks being directly contacted to a measuring object thing, and there is a problem in durability or measurement of the crack growth behavior, it may not necessarily be effective. Then, its attention was paid to the magnetostriction effect which is one of the magnetic actions of a ferromagnetic substance. Measurement of the opening stress of the minute fatigue crack under dynamic load and crack length performed by measuring the magnetic field change by the magnetostriction effect, without needing the contact to an object with simple equipment.

Fatigue Crack Growth Behavior of High Manganese Austenitic TWIP Steels

Fatigue crack growth (FCG) behavior of three high manganese austenitic twin-induced plasticity (TWIP) steels with different stacking fault energy (SFE) was investigated, aiming at studying the correlation between the FCG resistance and the SFE of the steels. FCG tests were performed using three-point bending specimens at room temperature at stress ratio of 0.1 under the control of stress intensity factor range. Test results showed that the fatigue threshold values of these steels decrease with increasing the SFE. However, in the Paris regime, the crack growth rates of the steels do not appear to correlate directly with SFE. These results are discussed according to the degree of fatigue crack closure and the deformation mode of crack tip zone.

Corrosion fatigue performance of TC4 plates with holes in aviation kerosene

In this paper, a series of tests have been conducted to investigate the corrosion fatigue performance of TC4 titanium alloy plates with holes in aviation kerosene. For comparison, fatigue tests were also conducted in air. The fracture surfaces of all specimens were examined using scanning electron microscopy (SEM) in order to disclose the mechanism of fatigue failure. The results reveal that the crack initiation life of a plate with hole in kerosene is about 76%–91% of its total fatigue life. The total fatigue life and the crack initiation life of plates with holes are decreased by kerosene. The dispersibility of measured fatigue life data of plates with holes in kerosene is higher than that in air. And due to fatigue crack closure, corrosive crack propagation life of plates with holes in kerosene is longer than that in air.

Combined action of crack closure and residual stress under periodic overloads: A fractographic analysis

The close relationship between sequence-sensitive near-tip residual stress and threshold stress intensity raises questions about load interaction models currently in use to estimate fatigue crack growth under variable amplitude loading. In an attempt to address them, experiments were performed on an Al–Cu alloy under specially designed load sequences with periodic overloads. Fractographic evidence from these tests confirms that fatigue crack closure, together with sequence sensitive variation in threshold stress intensity appear to explain all observed results. The fractographic data provide quantitative inputs for improved modeling of variable-amplitude fatigue, particularly at near-threshold crack growth rates. This study appears to suggest that conventional approaches based on the Wheeler and Willenborg residual stress models can provide reasonable estimates only by coincidence. They model the wrong parameter at lower fatigue crack growth rates and may simply not be valid at other growth rates.

Fatigue crack closure in submicron-thick freestanding copper films

The fatigue crack closure in approximately 500-nm-thick freestanding copper films were investigated by in situ field emission scanning electron microscope (FESEM) observations of the fatigue crack opening/closing behavior at three stress ratios of R=0.1, 0.5, and 0.8 in the low–Kmax (maximum stress intensity factor) region of Kmax<4.5MPam1/2. The direct observation of fatigue cracks clarified that crack closure occurred at R=0.1 and 0.5, while the fatigue crack was always open at R=0.8. Changes in the gage distance across the fatigue crack during a fatigue cycle were measured from the FESEM images, and the crack opening stress intensity factor Kop was evaluated on the basis of the stress intensity factor K vs. the gage distance relationship. The effective stress intensity factor range ΔKeff=Kmax−Kop was then evaluated. The R-dependence of the da/dN vs. ΔKeff relationship was smaller than that of the da/dN vs. ΔK relationship. This suggests that ΔKeff is a dominating parameter rather than ΔK in the fatigue crack propagation in the films. This paper is the first report on the presence of the fatigue crack closure in submicron-thick freestanding metallic films.

Determination of crack surface displacements for a radial crack emanating from a semi-circular notch using weight function method

A radial crack emanating from a semi-circular notch is of significant engineering importance. Accurate determination of key fracture mechanics parameters is essential for damage tolerance design and fatigue crack growth life predictions. The purpose of this paper is to provide an efficient and accurate closed-form weight function approach to the calculation of crack surface displacements for a radial crack emanating from a semi-circular notch in a semi-infinite plate. Results are presented for two load conditions: remote applied stress and uniform stress segment applied to crack surfaces. Based on a correction of stress intensity factor ratio, highly accurate analytical equations of crack surface displacements under the two load conditions are developed by fitting the data obtained with the weight function method. It is demonstrated that the Wu-Carlsson closed-form weight functions are very efficient, accurate and easy-to-use for calculating crack surface displacements for arbitrary load conditions. The method will facilitate fatigue crack closure and other fracture mechanics analyses where accurate crack surface displacements are required.

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

The appropriateness of some common similitude principles with respect to describing and predicting fatigue damage propagation is discussed. Linear elastic fracture mechanics have provided a basis to describe damage growth using stress intensity factors or strain energy release rates, both related to the work of Griffith and Irwin. The fatigue crack growth equations presented in the literature are discussed, and it is demonstrated that the principles of similarity in current methodologies have not yet been well established. As a consequence, corrections for the stress ratio effect are misunderstood. An alternative principle of similitude using cyclic work and strain energy release is proposed.

Assessment of fatigue crack closure under in-phase and out-of-phase thermomechanical fatigue loading using a temperature dependent strip yield model

In this paper fatigue crack closure under in-phase and out-of-phase thermomechanical fatigue (TMF) loading is studied using a temperature dependent strip yield model. It is shown that fatigue crack closure is strongly influenced by the phase relation between mechanical loading and temperature, if the temperature difference goes along with a temperature dependence of the yield stress. In order to demonstrate the effect of the temperature dependent yield stress, the influence of in-phase and out-of-phase TMF loading is studied for a polycrystalline nickel-base superalloy. By using a mechanism based lifetime model, implications for fatigue lives are demonstrated.

Closure measurement and analysis for small cracks from natural discontinuities in an aluminium alloy

Some materials such as 7050-T7451 and β-annealed Ti–6Al–4V exhibit very rough fatigue crack surfaces which suggests that roughness induced crack closure might be a significant issue. The present work examined a range of data for 7050-T7451 material which included experimental results under constant amplitude and variable amplitude/spectrum loading. Crack closure was either measured directly, or the effects were inferred through results from previous fractographic investigations. Analyses using an updated and improved version of the FASTRAN crack growth code combined with the experimental data were used to identify a new approach to correlate closure levels and crack growth behaviour. The new approach includes direct compliance based crack opening measurements to correlate the baseline constant amplitude properties and then using a cycle-by-cycle strip yield model with realistic constraint factors to model crack growth under spectrum loading. The new approach is consistent with fundamental differences in fatigue crack closure levels under constant and variable amplitude/spectrum loading which have been identified at the individual cycle by cycle level down to very small crack sizes. The new approach is shown to work very well for a range of cases considered here, and it provides a very useful insight into this complex behaviour.

Fatigue Crack Growth Fundamentals in Shape Memory Alloys

In this study, based on a regression of the crack tip displacements, the stress intensity range in fatigue is quantitatively determined for the shape memory alloy Ni2FeGa. The results are compared to the calculated stress intensity ranges with a micro-mechanical analysis accounting for the transformation-induced tractions. The effective stress intensity ranges obtained with both methods are in close agreement. Also, the fatigue crack closure levels were measured as 30 % of the maximum load using virtual extensometers along the crack flanks. This result is also in close agreement with the regression and micro-mechanical modeling findings. The current work pointed to the importance of elastic moduli changes and the residual transformation strains playing a role in the fatigue crack growth behavior. Additional simulations are conducted for two other important shape memory alloys, NiTi and CuZnAl, where the reductions in stress intensity range were found to be lower than Ni2FeGa.

Investigation on Microstructure and Fatigue Characteristics of Spray-Formed SiCp/Al–20Si Composite

The microstructures, high-cycle fatigue properties, fatigue crack growth and fatigue facture surfaces of spray-formed composite and its matrix alloy were investigated, respectively. The results show that the high-cycle fatigue properties of SiCp/Al–20Si composites are superior, as SiC particles improve the mechanical properties of composite. The fracture of Si and the interfacial debonding including both Al/Si and Al/SiC were the principle mechanisms in the fatigue fracture of composite materials. Detailed quantitative analyses indicates that the extensive SiC particle cracking induces a high level of fatigue crack closure, which effectively reduces the crack growth rate, resulting in superior fatigue crack propagation properties for a given ΔK, i.e. lower crack growth rate and higher intrinsic threshold stress intensity factor as compared to the matrix alloy. Crack deflections around SiC particles and particle cracking are the principle mechanisms of interaction between SiC particles and crack tip.

G0300207 磁気的特性を利用した微小疲労き裂情報の測定

Small fatigue crack closure is observed as a thing with a possibility that the influence of change of the stress level and a stress ratio, etc. to the crack growth behavior can be explained, and until now various researches have been done. Although there is a method using the strain gage as the dynamic measurement method required for the elucidation of a minute fatigue crack, in respect of generating of minute fatigue cracks being directly contacted to a measuring object thing, and there is a problem in durability or measurement of the crack growth behavior, it may not necessarily be effective. Then, its attention was paid to the magnetostriction effect which is one of the magnetic actions of a ferromagnetic substance. Measurement of the opening stress of the minute fatigue crack under dynamic load and crack length performed by measuring the magnetic field change by the magnetostriction effect, without needing the contact to an object with simple equipment. Moreover, it measured by having changed cross-sectional shape of the specimen. Resulting in, opening stress of the minute fatigue crack opening stress was able to measure about specimen regardless of the cross-sectional shape of the specimen. However, at this stage, it is possible to perform a crack length measurement can only specimen having a circular cross-section.

Observation and modeling of physically short fatigue crack closure in terms of in-situ SEM fatigue test

Abstract Crack closure and opening behavior of physically short fatigue crack tip was investigated in microstructures with different grain sizes by using the in-situ SEM fatigue test. A gradually decreased crack closure zone near the crack tip was observed which depended on the microstructures, crack size and stress levels. A new parameter involving the load level, grain size, specimen dimensions and crack length was proposed to interpret the physically short crack closure development. The contribution of the gradient crack closure zone on the physically short fatigue crack growth behavior was evaluated by using the modified partial crack closure model. A generalized fatigue crack growth driving force was finally determined and correlated well with the physically short crack growth rate.

Microstructure dependent fatigue crack growth in Al–Mg–Sc alloy

The fatigue crack growth behavior of Al–Mg–Sc alloy was investigated by tensile testing and fatigue testing. Different annealing treatments were applied to the alloy. Microstructure characterization of the alloy was carried out by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and optical microscopy (OM). The size of Al3(Sc1−xZrx) particle was calculated by software. The fatigue crack growth (FCG) rate (da/dN) was discussed with stress intensity factor range (ΔK) in Paris׳s region. The Paris exponent m and constants C were used to calculate the fatigue life. The fatigue process and crack closure effects were discussed with the yield strength and tensile strength of Al–Mg–Sc alloy. Results show that the microstructure, tensile strength and fatigue crack growth rate were greatly dependent on the annealing temperature, and the high resistance of Al–Mg–Sc alloy was mainly due to the combination microstructures of sub-grains, dislocations and these Al3(Sc1−xZrx) precipitates.