Multiaxial Fatigue Tests Research Articles

Fatigue strength of SS400 steel under non-proportional loading

This study discusses fatigue properties of low carbon steel, type SS400 steel, under non-proportional loading. Multiaxial fatigue tests under proportional and non-proportional loading conditions with various stress amplitudes were carried out using a hollow cylinder specimen at room temperature. In the test, three types of stress paths were employed. They are a push-pull, a reversed torsion and a circle loading. The circle loading is a cyclic loading combined the push-pull and the reversed torsion loading in which axial and shear stress waveforms have 90 degrees phase differences. From the obtained test results, poor evaluations of failure life under non-proportional loading are indicated when the life is correlated by the equivalent strain range based on von Mises ??eq and the non-proportional strain range ??NP. A modified strain parameter is presented which can evaluate the failure life in high and low strain levels under non-proportional loading.

Development of Bending and Torsion Fatigue Testing Machine for Multiaxial Non-Proportional Loading

This study presents a newly developed multiaxial high cycle fatigue testing machine which can load a cyclic bending loading and a reversed torsion loading onto an hour-glass shaped solid bar specimen. This testing machine can perform the fatigue tests with a high frequency under a proportional and a non-proportional loading conditions. In the non-proportional loading, principal directions of stress and strain are changed in a cycle. In the testing machine, the loading is generated by centrifugal force caused by the revolving weights attached to rotational wheels. The maximum frequency of the testing machine is 50Hz. A material tested was a type 304 stainless steel. In the test, two types of loading paths are employed, a proportional loading and a non-proportional loading. The former is a cyclic bending loading and the latter a combining cyclic bending and reversed torsion loading in the developed testing machine. In this study, an applicability of the testing machine is evaluated by carrying out the tests under these loading conditions.

Multiaxial Fatigue of 6061-T6 Aluminum Alloy under Corrosive Environment

Aluminium alloys are widely used in the fields of automobile, machinery and naval construction. To investigate the effect of non-proportional loadings and corrosive environment on the fatigue resistance of 6061-T6 aluminum alloy, a set of uniaxial and multiaxial low cycle fatigue tests were carried out. Firstly, the results of uniaxial tests showed that the alloy exhibited cyclic hardening then cyclic softening. With the increase of stress amplitude the cyclic softening became pronounced. The increasing of plastic deformation was basically cyclically stable with small plastic strain amplitude accumulation when the stress amplitude was lower than 200MPa ,while it was increasing rapidly when the stress amplitude was higher than 220MPa. Secondly, it was observed that non-proportional cycle additional hardening of 6061-T6 aluminum alloy was little. While the fatigue life was badly affected by the loading paths. Thirdly ,the fatigue corrosion interactions were also talked about in details by performing the tests under the same loading conditions with corrosive environment. The experiment proved that the seawater corrosion has huge impact on fatigue life under pH 3. Finally, a multi-axial fatigue life prediction model was used to predict the fatigue life with or without the corrosive environment which showed a good agreement with experimental data.

Prediction of multiaxial fatigue life for notched specimens of titanium alloy TC4

Both the proportional and nonproportional multiaxial fatigue tests were conducted on two kinds of notched specimens of titanium alloy TC4. The multiaxial fatigue critical area of notched specimen is considered as the location experiencing the maximum damage. It is unsatisfactory to predict the multiaxial fatigue life with the local stress and strain in the fatigue critical area. The critical distance concepts are employed in the multiaxial life prediction method for notched specimens. The proposed method was checked by the test data of TC4 notched specimens. The prediction results are almost within a factor of three scatter band of the test results.

Reprint of “Multiaxial fatigue property of Ti–6Al–4V using hollow cylinder specimen under push-pull and cyclic inner pressure loading”

This paper studies a multiaxial fatigue crack mode and a fatigue life of Ti–6Al–4V. Load controlled fatigue tests at room temperature were carried out using a hollow cylinder specimen under multiaxial loading with principal stress ratio λ equal to 0, 0.4, 0.5 and 1.0 and loading ratio R kept constant and equal to 0. λ is defined as λ=σ2/σ1, where σ1 and σ2 are maximum and intermediate/minimum principal stresses, respectively. Here, the test at λ=0 is a uniaxial loading test and that at λ=1.0 an equi-biaxial loading test. A testing machine employed was a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loading with inner pressure into the hollow cylinder specimen. Based on the obtained results in this study, multiaxial fatigue properties are examined, where the fatigue life evaluation and the crack mode are discussed. The fatigue life is reduced with an increase of λ, due to cyclic ratcheting and crack mode in multiaxial loading. The crack mode is also affected by the surface condition resulting from cut-machining.

The Influence of Multiaxial Superimposed Static Mean Stress on High-Cycle Fatigue Life of Cu-ETP Copper

High–cycle multiaxial fatigue tests under proportional and non-proportional loading conditions with various combinations of superimposed static mean stresses was carried out on Cu-ETP copper. The results show differences in fatigue life between various ratios of mean stresses. These results are similar to others described in the literature.

Multiaxial fatigue strength of type 316 stainless steel under push–pull, reversed torsion, cyclic inner and outer pressure loading

Multiaxial fatigue tests under non-proportional loading in which principal directions of stress and strain are changed in a cycle were carried out using a developed multiaxial fatigue testing machine which can load a push–pull and reversed torsion loading with cyclic inner and outer pressure. This paper presents the developed testing machine and experimental results under several multiaxial loading conditions including non-proportional loading. In strain control tests, the failure life is reduced in accordance with increasing inner pressure at each strain path. The failure life can be correlated by von Mises' equivalent stress amplitude relatively well independent of not only inner pressure but also loading path. In load control tests, the failure life is reduced largely by non-proportional loading but the influence of inner and outer pressure on the failure life is relative small.

Multiaxial fatigue property of Ti–6Al–4V using hollow cylinder specimen under push-pull and cyclic inner pressure loading

This paper studies a multiaxial fatigue crack mode and a fatigue life of Ti–6Al–4V. Load controlled fatigue tests at room temperature were carried out using a hollow cylinder specimen under multiaxial loading with principal stress ratio λ equal to 0, 0.4, 0.5 and 1.0 and loading ratio R kept constant and equal to 0. λ is defined as λ=σ2/σ1, where σ1 and σ2 are maximum and intermediate/minimum principal stresses, respectively. Here, the test at λ=0 is a uniaxial loading test and that at λ=1.0 an equi-biaxial loading test. A testing machine employed was a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loading with inner pressure into the hollow cylinder specimen. Based on the obtained results in this study, multiaxial fatigue properties are examined, where the fatigue life evaluation and the crack mode are discussed. The fatigue life is reduced with an increase of λ, due to cyclic ratcheting and crack mode in multiaxial loading. The crack mode is also affected by the surface condition resulting from cut-machining.

Crack mode and life of Ti-6Al-4V under multiaxial low cycle fatigue

This paper studies multiaxial low cycle fatigue crack mode and failure life of Ti-6Al-4V. Stress controlled fatigue tests were carried out using a hollow cylinder specimen under multiaxial loadings of ?=0, 0.4, 0.5 and 1 of which stress ratio R=0 at room temperature. ? is a principal stress ratio and is defined as ?=sigmaII/sigmaI, where sigmaI and sigmaII are principal stresses of which absolute values take the largest and middle ones, respectively. Here, the test at ?=0 is a uniaxial loading test and that at ?=1 an equi-biaxial loading test. A testing machine employed is a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loadings with inner pressure onto the hollow cylinder specimen. Based on the obtained results, this study discusses evaluation of the biaxial low cycle fatigue life and crack mode. Failure life is reduced with increasing ? induced by cyclic ratcheting. The crack mode is affected by the surface condition of cut-machining and the failure life depends on the crack mode in the multiaxial loading largely.

A multiaxial high-cycle fatigue life evaluation model for notched structural components

A model for multiaxial high-cycle fatigue life evaluation of notched structural components is proposed, which considers the impact of the stress field on fatigue life by utilizing the Theory of Critical Distances (TCD) and Finite Element Method (FEM). The maximum shear stress range plane is defined as the critical plane, and the damage parameters are the maximum effective shear stress amplitude and the maximum effective normal stress, which are obtained by averaging the stress in the hemisphere volume around the maximum stress point. To validate the accuracy of the model, multiaxial fatigue tests are carried out for both smooth and notched specimens of Aluminum–Silicon alloy. The results indicate that the evaluated life and experimental life have a good agreement.

Influence of Phase Shift and Amplitude Ratio on the Principal Stresses and Directions in Multiaxial Fatigue Testing

The maximum values of normal and shear stresses are the basic parameters which influence directly the initiation and propagation of multiaxial fatigue cracks.Based on the above, the first part of the paper presents an analysis of principal stresses (normal and shear) in case of symmetrical tension-compression loadings with superimposed phase-shifted symmetrical torsion cycles. The influence of stress amplitude ratio and phase shift on the maximum (normal and shear) stresses and on the directions of the planes along which these act is analyzed and graphically represented using stress hodographs.The second part of the paper highlights the possibility of using the maximum value of the normal or shear stress as base parameter for durability studies under multiaxial fatigue, based on existing experimental data. The mentioned data is correlated with the results of an original experimental program carried out by the authors on 41Cr4 steel and conclusions are formulated with regard to the role of maximum shear stress in life-time calculation.

Microstructural study of multiaxial low cycle fatigue

This paper discusses the relationship between the stress response and the microstructure under tension-torsion multiaxial proportional and nonproportional loadings. Firstly, this paper discusses the material dependency of additional hardening of FCC materials in relation with the stacking fault energy of the materials. The FCC materials studied were Type 304 stainless steel, pure copper, pure nickel, pure aluminum and 6061 aluminum alloy. The material with lower stacking fault energy showed stronger additional hardening, which was discussed in relation with slip morphology and dislocation structures. This paper, next, discusses dislocation structures of Type 304 stainless steel under proportional and nonproportional loadings at high temperature. The relationship between the microstructure and the hardening behavior whether isotropic or anisotropic was discussed. The re-arrangeability of dislocation structure was discussed in loading mode change tests. Microstructures of the steel was discussed in more extensively programmed multiaxial low cycle fatigue tests at room temperature, where three microstructures, dislocation bundle, stacking fault and cells, which were discussed in relation with the stress response. Finally, temperature dependence of the microstructure was discussed under proportional and nonproportional loadings, by comparing the microstructures observed at room and high temperatures.

Fatigue Life of Type 316 Stainless Steel under Wide Ranged Multiaxial Loading

Each type of testing machine has its own characteristics, but most of multiaxial fatigue studies have been performed by a push-pull and reversed torsion loading testing machine. This type of testing machine can perform multiaxial fatigue tests under non-proportional loading in which principal directions of stress and strain are changed in a cycle. However, a principal strain ratio range performable in this testing method is −1≤ ϕ ≤−ν, where ϕ and ν are the principal strain ratio and the Poisson's ratio. This study discusses about stress and strain states and multiaxial fatigue testing method. In order to perform fatigue test in −1≤ϕ≤+1 under non-proportional loading, a multiaxial fatigue testing machine of combining the push-pull and reversed torsion loading and cyclic inner and outer pressures is also developed. Then, this paper presents experimental results under several multiaxial loadings carried by the testing machine, too.

Microstructural-based Analysis and Modelling of the Fatigue Behaviour of Cast Al-Si Alloys

This paper describes a microstructural-based high cycle fatigue behaviour model applied to cast Al-Si alloys used in an automobile context. These materials are characterized by the presence of different microstructural heterogeneities at different scales: the aluminium matrix (DAS/SDAS and the precipitation hardening level), inclusions (Si particles and intermetallic) and casting defects (porosity). It is shown that the effects of these factors on the HCF damage mechanisms are important and can depend on the loading mode. A multiaxial fatigue test campaign has been carried out using three cast aluminium alloys, fabricated by different casting processes (gravity die casting and lost foam casting), associated with several heat treatment(T7 and Hot Isostatic Pressing-HIP). The HIP treatment is used to eliminate or minimise the porosity. The first part of the article is dedicated to the experimental characterization of the HCF damage mechanisms. With regard to the effect of the casting defects, a study of natural fatigue crack growth and artificial long crack growth is presented and subsequently used to choose an appropriate fatigue strength criterion to take into account the effect of defects, for different loading modes (tension, torsion and combined tension-torsion). Finally, a flexible modelling framework, providing the possibility of combining any two suitable criteria, which leads to the construction of a multiaxial Kitagawa-Takahashi diagram, is used.

Fatigue strength of severely notched specimens made of Ti–6Al–4V under multiaxial loading

AbstractThe present paper deals with multiaxial fatigue behaviour of severely notched components made of titanium grade 5 alloy (Ti–6Al–4V). The experimental tests have been carried out under combined Mode I and Mode III loadings, both in phase and out of phase. Cylindrical specimens weakened by circumferential notches have been employed. Different nominal load ratios have been applied in the tests (R = −1, 0 and 0.5). The specimens had a notch‐tip radius smaller than 0.1 mm, a notch depth equal to 6 mm and an opening angle of 90°. The results obtained by multiaxial fatigue testing are depicted in comparison with data from pure modes of loading on smooth and notched samples, characterized by a load ratio in the range −3 ≤ R ≤ 0.5. A large bulk of new fatigue data (more than 160) is summarized in the manuscript. The data are first plotted in terms of the nominal stress amplitudes, and then they are reanalysed by means of the local energy measured in the control volumes surrounding the notch tip. The dependence of the size of the control radius as a function of the loading mode is analysed. A very different behaviour is found for tension and torsion, corresponding to a different notch sensitivity.

Evaluation of multiaxial fatigue life prediction criteria for PEEK

Multiaxial fatigue test were conducted on PEEK under four loading paths and several criteria were used for life prediction. Predictions based on Fatemi–Socie criterion fall out of the factor-of-two line on the conservative side for proportional loading and non-proportional loading. The normal strain-based Smith–Watson–Topper criterion yield good prediction for proportional loading but non-conservative prediction for non-proportional loading. Taking the contribution from shear component into consideration, the Chen–Xu–Huang criterion achieve satisfactory results for both proportional loading and non-proportional loading, but with non-conservative prediction for pure torsion loading. To consider general cracking behavior, the modified SWT criterion is adopted and good agreement between experimental data and prediction values is achieved.

Multiaxial fatigue behavior of AISI 316L subjected to strain-controlled and ratcheting paths

To investigate the material behavior of a stainless steel grade AISI 316L, subjected to loading conditions typical for the primary cooling circuit of a light water nuclear reactor, a set of uniaxial, torsional and multiaxial low cycle fatigue and strain-controlled ratcheting tests has been carried out. The main goal of these experiments is to analyze how the cyclic deformation response is influenced by strain amplitudes, loading paths and ratcheting, and to estimate how fatigue life is affected by these elements. Finally, the performance of three advanced multiaxial fatigue criteria (i.e. Smith–Watson–Topper, Fatemi–Socie and Jiang) has been critically evaluated for all the considered loading cases.

Fatigue Failure Life of SS400 Steel under Non-Proportional Loading in High Cycle Region

This study discusses fatigue properties of low carbon steel under multiaxial non-proportional loading and an evaluation of failure life. Multiaxial fatigue tests under non-proportional loading with various stress amplitudes were carried out using a hollow cylinder specimen in low and high cycle regions at room temperature. In the test, three types of strain/stress path were employed. They are a push-pull, a reversed torsion and a combined push-pull and reversed torsion loadings in which stress amplitudes used were constant and random. This study evaluates an effect of non-proportional loading on fatigue life in the high cycle fatigue region to discuss the applicability of ΔεNP proposed by Itoh et al. on life evaluations in the high cycle region and under random loading.

Considerations on the Necessity of Determining Principal Stresses and Directions for Analysis of Material Durability under Multiaxial Fatigue

A special situation arises when multiaxial fatigue loadings are present, given not only the time-dependency of extreme principal stress values, but also the fact that principal plane positions change during one load cycle (non-proportional loading). Thus, the analysis of principal stress and principal direction variation becomes a very important step, necessary to be carried out before starting any multiaxial fatigue testing. Based on the above, the authors present a generalized method for computing principal stresses and determining principal plane positions, applicable for cyclic tension-torsion loadings with zero mean stresses but with different phase shifts and amplitude ratios. Based on original experimental data and data collected from the literature, the authors point out in the final part of the paper that the maximum principal shear stress can be considered as the main parameter for plotting Wöhler curves.

A multiaxial fatigue approach to Rolling Contact Fatigue in railways

Railway sector plays an important role in the means of transportation and the safety of wheels and rails is a greater concern for the manufacturers and operators of the railway network. In the wheel–rail contact, damage may occur due to wear or fatigue and in the latter case Rolling Contact Fatigue (RCF) is a growing problem due to the operation increase of high speed railway trains, where increased number of loading cycles due to the passage of the wheels over the rails, will be present in the wheel–rail contact. The present study focuses on the RCF failure analysis, analytical, numerical and experimental approaches are applied to investigate the problem. It is widely known that Hertz contact theory was the first approach to explain the stress state in the contact area through the calculation of the curvature of ellipse of contact and the stresses governing rolling contact between wheel and rail. The contact zone was studied for semi-elliptical shape, governed with multiaxial, out-of-phase state of stress with constant change in directions of principal stresses occurring due to rolling. Following, Finite Element analysis of the wheel–rail contact was implemented with the realistic loads, boundary conditions and material properties. Since a multiaxial stress state is present in the contact zone with normal and shear stresses, multiaxial fatigue tests in tension torsion were carried out on specimens taken from wheels and rails. Results from the multiaxial fatigue tests were analysed through multiaxial fatigue models, either stress invariant or critical plane models, such as modified Sines, Findley, Wang–Brown, Fatemi–Socie and Smith–Watson and Topper. Orientation of fatigue crack paths were also predicted by applying the above models and comparisons with measured crack orientation were carried out. The difficulties of the experimental measurement and analysis of the crack initiation are discussed and analysed within this complex stress state where alternate shear stresses are present in a strong compression stress and in a confined zone environment.