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This paper introduces a fractional-order model integrated with a damage variable to effectively characterize the stress or strain responses under strain- or stress-controlled cyclic loading. We derive a relationship among mean stress, ratcheting strain, and cyclic number from the established fractional constitutive relationship. Experimental validation with polymeric data demonstrates the validity of our model, indicating how fractional order captures the effects of various loading conditions—including mean stress, temperature, and loading rate—on ratcheting strain responses. Additionally, our model offers a simpler mathematical framework than the existing models, without compromising accuracy. [ABSTRACT FROM AUTHOR]

A systematic acquisition of fatigue test data was conducted under different stress ratio conditions to investigate the effect of mean stress on the fatigue properties of carbon/glass hybrid thermoplastic composite rods. Our findings revealed that as the stress ratio increased with a higher mean stress, the stress dependency of the fatigue life also increased, and the slope of the S‐N curve became gentler. Under identical stress ratio conditions, hybrid rods with a greater volume fraction of carbon fiber exhibited the highest strength and a more gradual slope of the S‐N curve. To account for mean stress effects, an equivalent stress amplitude was introduced, resulting in data collapse at around 107 cycles, rendering this approach an industrially useful method to predict fatigue behavior when working with limited experimental datasets. This study presents a practical technique for estimating fatigue strength under mean stress through a weighted average efficiency and equivalent stress amplitude. Highlights: This study empirically explores how mean stress influences carbon/glass hybrid rods.Our findings unveil the correlation between material structure and fatigue performance.A practical method for estimating fatigue strength, which considers mean stress, is proposed. [ABSTRACT FROM AUTHOR]

The hydraulic testing of pre-existing fractures (HTPF) is one of the most promising in situ stress measurement methods, particularly for three-dimensional stress tensor determination. However, the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14–15 tests (under different conditions) for reliable results. In this study, we modified the HTPF method by considering the shear stress on each pre-existing fracture, which increased the number of equations for the stress tensor determination and decreased the number of tests required. Different shear stresses were attributed to different fractures by random sampling; therefore, the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method. Thereafter, we constrained the stress tensor based on the tensile strength criterion, compressive strength criterion, and vertical stress constraints. The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor. Two stress-measurement campaigns in Weifang (Shandong Province, China) and Mercantour road tunnel (France) were implemented to highlight the validity and efficiency of the modified HTPF (M-HTPF) method. The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures, neglecting the stress gradient. The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed. The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.

To assess the contribution of residual stress to the improvement of high‐cycle fatigue (HCF) properties, HCF tests are performed on Ti‐6Al‐4V specimens with different residual stress levels but no other evident surface state modification induced by machining. Results indicate that compressive residual stress induced by machining significantly improves the HCF performance of Ti‐6Al‐4V specimens. Of all the specimens, the fatigue strength of specimens with a surface residual stress level of −400 MPa is increased by approximately 16.4%. Furthermore, to accurately predict the fatigue life based on three mean stress correction equations (e.g., Walker, Goodman, and Smith–Watson–Topper), the method of reducing surface residual stress by a reduction factor and then adding to the mean stress is proposed. A reduction factor of 0.55 is found to be appropriate for the alloy under the test condition, with majority of the predicted data falling within a factor of three scatter band. [ABSTRACT FROM AUTHOR]

The need for new railway bridges is driven by the growing volume of transportation demands for both passenger and freight traffic on railway networks. In the design of these bridges, the fatigue limit state is a criterion that usually limits the allowable applied load level and thus also the utilization of the high strength of the steel material. Therefore, improving the fatigue performance of welded details by high‐frequency mechanical impact (HFMI) treatment leads to a more efficient design. However, the fatigue performance of HFMI‐treated welds is known to be affected by the mean stress and this needs to be considered in the design of treated welded details in steel bridges. This is rather straightforward if the bridge is subjected to cycles from one type of train but becomes cumbersome when several different sets of trains (e. g. axle loads, axle distances) cross the bridge. In this article, a factor to take the mean stress effect (including self‐weight and traffic load variations) into account is derived from traffic data measured in Sweden. Moreover, the mean stress effect is also predicted using the different fatigue load models in the Eurocode. These models either consist of one‐load patterns such as LM71, SW/0, and SW/2 or are composed of different trains with different combinations. It was found that the mean stress effect is underestimated by the first group of models. On the other hand, the mean stress predicted by the light traffic mix is found to be close to that calculated using real traffic data, while other mixes (standard and heavy) underestimate the mean stress effect. Therefore, a correction factor to account for the mean stress effects in real traffic is derived (called here λHFMI). This factor can be used to correct the design stress range for fatigue verification of HFMI‐treated welded details in railway bridges. [ABSTRACT FROM AUTHOR]

In this study, experimental investigations were conducted to create fatigue limit diagrams for NSSC180 ferritic stainless steel, which is used for automobile exhaust system parts, subjected to excess deformation, in order to clarify the relationship between the mean stress and fatigue limit. The fatigue tests were conducted under a fixed maximum stress, which allowed a fatigue design diagram to be obtained. The results indicated that the fatigue limit curve has a region where the effect of increasing the mean stress on the decrease in the fatigue limit is more moderate than that predicted by a modified Goodman line. Furthermore, it was found that a fatigue design based on static crack initiation is more appropriate than the modified Goodman line for higher values of mean stress. [ABSTRACT FROM AUTHOR]

Fatigue failure is the main problem affecting the safety of structural members. It is of great engineering significance to predict the fatigue life accurately. Based on the damage evolution model with mean stress correction, a numerical method for fatigue life prediction considering both crack initiation and propagation was established combined with finite element method. To verify this method, fatigue tests and numerical simulations of aluminum alloy plates with holes under different stress levels were carried out. The results show that the crack propagation process and the fatigue lives can be effectively predicted by the proposed fatigue numerical method, and the error band of the predicted lives is less than two times. [ABSTRACT FROM AUTHOR]

The modified 9Cr–1Mo steel and Inconel (IN) 617 superalloy are high‐temperature alloys of prime importance in several industrial applications. Both of these are used at elevated temperature for various piping and tubing components and undergo asymmetric cyclic loading; therefore, it is highly essential to assess their resistance to accumulation of inelastic strain (ratcheting) under asymmetric stress cycling. In this study, ratcheting behavior of these alloys is compared at the homologous temperature of 0.42, under uniaxial asymmetric stress loading with positive mean stress. Deformation behavior of the tested samples is analyzed by transmission electron microscope. While there is homogeneous deformation in the modified 9Cr–1Mo steel, there is intersection of slip bands and presence of dislocation tangles in the IN 617 alloy. Fracture surface of the modified 9Cr–1Mo steel, tested under asymmetric cyclic loading, reveals typical ductile fracture resulting from tensile loading, whereas there is characteristic fatigue fracture of the IN 617 alloy. [ABSTRACT FROM AUTHOR]

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Uniaxial strain‐controlled fatigue tests were carried out on a 304L austenitic stainless‐steel specimens in air at 300°C and in pressurized water reactor (PWR), without or with the application of a mean stress, at different total strain amplitudes. For strain amplitude no less than 0.2%, a deleterious effect of PWR water on fatigue life is observed, associated with the enhancement of both crack initiation and propagation. Besides, the fatigue life is reduced by the application of a mean stress for a fixed strain amplitude in a given environment. In particular, due to the acceleration of crack initiation stage by an enhancement of the plastic strain accumulation, the PWR water effect on fatigue life is re‐activated for strain amplitude below 0.2% in the presence of a mean stress. The fatigue life reduction under mean stress application is mostly related to the maximum stress level and strain amplitude, rather than the generated ratcheting strain. Highlights: The results of strain‐controlled fatigue tests in air and in PWR water are presented.The application of a mean stress affects the fatigue strength in both environments.The effect of environment and mean stress on initiation and propagation is analyzed.A modified SWT equation is proposed. [ABSTRACT FROM AUTHOR]

The influence of pre‐strain on the tensile and fatigue properties of a dual phase DP600 steel was studied. The material was pre‐strained by uni‐axial tension in rolling and transverse direction. Thereafter, specimens were cut from the deformed plates in parallel or orthogonal to pre‐strain direction. It was found that pre‐strain increases yield and tensile strength. Results suggested that strain path change primarily affects the elastic‐plastic transition during early stage of reloading. Pre‐strained specimens showed an increase in high cycle regimes as a consequence of yield strength increment, irrespective of imposed pre‐straining direction. A modified stress life equation that accounts for pre‐strain was proposed and showed good agreement with experimental data. Bake hardening enhanced both tensile and high cycle fatigue resistance. Walker equation was successfully fitted to account for tensile mean stress. In low cycle fatigue, negligible influence of pre‐strain was observed due to cyclic softening and residual stress relaxation. Highlights: A DP600 steel sheet is characterized under different pre‐strain conditions and after baking.Experiments indicate that pre‐strain and bake hardening are beneficial in HCF.Modified Basquin equations to account for the effect of pre‐strain and bake hardening are proposed.Walker mean stress correction shows good agreement with experimental data. [ABSTRACT FROM AUTHOR]

In this work, a fatigue stress equation associated with equivalent life is proposed based on the intrinsic damage dissipation energy. This method can be treated as an optimization towards Walker's equation owing to the similarity between them. Compared to Walker's equation, a modification of SWT function, the proposed equation is attached to a material parameter directly correlating with the fatigue strength exponent, which eliminates the need to conduct additional HCF experiments. The analysis of experimental results from the existing literature allowed for the comparative validation of the suggested equation with two existing equations that have wide acceptance and simplicity, namely the Goodman relationship and SWT function, which revealed a better performance of the suggested model. The proposal provides great potential for its simplicity in the evaluation of HCF lifetime under tensional fatigue loading with mean stress, further optimizing towards Walker's equation. [ABSTRACT FROM AUTHOR]

In the present research, the effects of normal mean stress acting on fatigue evolution are considered well in critical plane multiaxial models, whereas shear mean stress effects have rarely attracted attention. These models may result in nonconservative predictions under asymmetric loadings with substantial shear mean stress. Therefore, an improved critical energy model is introduced to solve multiaxial fatigue issues on the basis of the Fatemi-Socie model and the Walker model, which consider normal mean effect, shear mean stress effect, and additional hardening effect. Moreover, experimental data from GH4169, wrought Ti-6Al-4V, and TC4 are employed to validate the proposed model. Results show that the proposed model can reasonably predict fatigue life under various loadings, particularly for asymmetric loadings. [ABSTRACT FROM AUTHOR]

The uniaxial ratchetting-fatigue interaction of extruded AZ31 magnesium (Mg) alloy is investigated by uniaxial stress-controlled cyclic tests at room temperature and with addressing the roles of different plastic deformation mechanisms. Different stress levels are prescribed to reflect the cyclic plasticity of the alloy controlled by diverse deformation mechanisms (i.e., dislocation slipping, deformation twinning and detwinning ones), and then the influences of stress level and stress rate on the ratchetting and fatigue life are discussed. The experimental results demonstrate that different evolution characteristics of whole-life ratchetting and fatigue life presented during cyclic tests with various mean stresses, stress amplitudes and stress rates are determined by the dominated plastic deformation mechanisms. It's worth noting that the ratchetting can occur in the compressive direction even in the cyclic tests with a positive (tensile) mean stress, and the fatigue life increases first and then decreases with the increase of mean stress on account of the interaction between dislocation slipping and twinning/detwinning mechanisms. Comparing the fatigue lives obtained in the asymmetric stress-controlled and symmetrical strain-controlled cycle tests, it is seen that the ratchetting deformation causes an additional damage, and then leads to a shortening of fatigue life.

A constant life diagram (CLD) is the most common method for illustrating the relationship between stress ratios, mean stress and alternating stress. In this study, three CLD models are used to illustrate how mean stress and material anisotropy interact for several stress ratios, R = 0.5, 2, 0.1, − 0.5, − 2, and 10 to affect the fatigue life of non-hybrid [NH]4 and hybrid [H]4 composites. When modeling fatigue life data using each of these models, the linear piecewise model is found to be the most accurate for predicting the fatigue behavior of [NH]4 and [H]4 composites for all stress ratios. Using a linear piecewise model, constant life curves were able to connect all data points for each stress ratio. The S–N curves drawn for each stress ratio reveals that the linear model underestimates the fatigue life of non-hybrid and hybrid composites, resulting in a conservative design. Kawai's model, on the other hand, exaggerates the fatigue life of [NH]4 and [H]4 composites, implying an overestimation of fatigue life. As a result, designers can use a linear piecewise model to accurately predict the fatigue strength of fiber-reinforced composites for various stress ratios. [ABSTRACT FROM AUTHOR]

A numerical turbine-blade fatigue-life analysis method is suggested. This method comprises a stationary thermal 3D finite element (FE) analysis of the hot run for the combined high-cycle fatigue (HCF) and creep analysis, and a follow-on (one-way coupled) quasi-stationary structural 3D FE analysis (including six load steps) of a single and two half turbine blades and the related disk and rotor section and a (modified Goodman equation based) post-processing fatigue life analysis for the highest HCF-loaded point of the turbine blade. For the low-cycle fatigue (LCF) analysis, this includes a transient thermal 3D FE analysis of two full loading cycles, a follow-on (one-way coupled) quasi-stationary structural 3D finite element analysis of a single and two half turbine blades and the related disk and rotor section and a (modified-Langer-equation-based) post-processing fatigue life analysis approach for the highest LCF-loaded point of the turbine blade. Finally, this approach is demonstrated by the numerical HCF, LCF and creep analysis of a generic turbine blade of the first rotor row of a full admission hydrogen turbo pump of a 1 MN thrust class gas generator LOX-LH2 liquid rocket engine (LRE). For this numerical example, the LCF loading turned out to be dominant. Creep turned out to be negligible. [ABSTRACT FROM AUTHOR]

The uniaxial ratchetting-fatigue interaction of extruded AZ31 magnesium (Mg) alloy is investigated by uniaxial stress-controlled cyclic tests at room temperature and with addressing the roles of different plastic deformation mechanisms. Different stress levels are prescribed to reflect the cyclic plasticity of the alloy controlled by diverse deformation mechanisms (i.e., dislocation slipping, deformation twinning and detwinning ones), and then the influences of stress level and stress rate on the ratchetting and fatigue life are discussed. The experimental results demonstrate that different evolution characteristics of whole-life ratchetting and fatigue life presented during cyclic tests with various mean stresses, stress amplitudes and stress rates are determined by the dominated plastic deformation mechanisms. It's worth noting that the ratchetting can occur in the compressive direction even in the cyclic tests with a positive (tensile) mean stress, and the fatigue life increases first and then decreases with the increase of mean stress on account of the interaction between dislocation slipping and twinning/detwinning mechanisms. Comparing the fatigue lives obtained in the asymmetric stress-controlled and symmetrical strain-controlled cycle tests, it is seen that the ratchetting deformation causes an additional damage, and then leads to a shortening of fatigue life. [ABSTRACT FROM AUTHOR]

To improve the accuracy of predicting multiaxial fatigue life, an enhanced multiaxial low-cycle fatigue life model is proposed based on the FS model. This model introduces a correction parameter for the stress-related term to consider the influence of normal stress and shear stress on the critical plane. The feasibility of the model is investigated, and it is validated using fatigue test data from eight different materials. The results indicate that the proposed model is applicable for both symmetric and asymmetric loading conditions under constant amplitude loading, with highly accurate fatigue life prediction results. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • An additively manufactured (AM) AlSi10Mg alloy is studied in HCF and VHCF. • Tests up to VHCF under conventional and ultrasonic frequencies of 110 and 20 k Hz. • No observed loading frequency effect on fatigue strength and fractography. • VHCF limits degrading with increasing tensile mean stress by Gerber relation. • Crack initiated at AM pores from surface to subsurface with increasing VHCF lives. Along the building direction, the fatigue behavior of an additively manufactured (AM) aluminium (AlSi10Mg) alloy was investigated in high-cycle and very-high-cycle regimes by using conventionally electromagnetic resonance and ultrasonic vibration with axial loading frequencies of ∼110 Hz and ∼20 k ± 500 Hz, respectively. No frequency effect was observed on the resulted fatigue strength and the fractography up to 108 cycles at stress ratio R = –1. All cracks initiated at AM pores and the dominating one prefers shifting from specimen surface to subsurface with growing very-high-cycle fatigue (VHCF) lives. As the tensile mean stress increases, fatigue strength sharply drops in high value regime of R ≥ 0.5 with annihilating VHCF occurrence, and the fatigue limits degrade on a Gerber relation beyond 109 cycles. At last, a fatigue failure map was proposed to directly describe the panorama of specimen lives under different external loads. [ABSTRACT FROM AUTHOR]

Interaction of fatigue and creep behavior is the dominant failure mode for high cycle or very high cycle fatigue under high mean stress at high temperature. As for large rotating component working as high-speed at high temperature, such interaction drives the need to update strength assessment and design method. In this work, a constant life diagram incorporating dual-criterion for evaluating the interaction behavior between high cycle/very high cycle fatigue and creep at high temperature was proposed, and then verified using six types of materials data. This dual-criterion method was proved to be more precise for assessing the serious fatigue-creep interaction behavior in long-life regime, that was promising for design and safety assessment of high-temperature rotating components. • Interaction of creep with high cycle or very high cycle fatigue is a dominant failure mode for high-temperature rotating components. • The dual-criterion assessment method considering HCF/VHCF and creep interaction was established and widely verified. • The dual-criterion assessment result is more precise with accuracy improvement for up to as high as 70 %. [ABSTRACT FROM AUTHOR]

An accurate and stable data‐driven model is proposed in this work for fatigue life prediction in presence of mean stresses. Multiple independent extreme learning machines are integrated into the model with distinct neural network configurations to simulate the complex correlations among mean stress levels, material properties, and fatigue lives. Meanwhile, the theoretical prediction, as a representation of domain knowledge, is used to optimize the data‐driven processes of model training and prediction. Extensive experimental data of 13 metallic materials with different mean stress levels are collected from the open literatures for model training and evaluation. The results demonstrate that the proposed model can achieve high accuracy and good stability in fatigue life prediction under mean stress loading conditions, even with a small training dataset, showing great applicability for fatigue life prediction. Highlights: A data‐driven model is proposed for fatigue life prediction under mean stress conditions.The model is hybridized with domain knowledge.The model is more accurate and stable compared with several existing mean stress models.The model has less dependence on the size of training data. [ABSTRACT FROM AUTHOR]

Pore pressure prediction using velocity-mean effective stress relationship is introduced in Madura Subbasin which is located in a compressional tectonic setting. The new workflow accommodates the three principal stresses, those are vertical stress, maximum horizontal stress, and minimum horizontal stress in a form of mean stress as the compaction main inducing agent. The application of this new workflow has resulted in a more accurate pore pressure prediction where the normally used pore pressure prediction method tends to underestimate the actual data. In Dukuh-1 well, as an example, the pore pressure prediction from the new work flow is able to explain the continuous hole problems such as well flows and well kicks that were recorded during drilling. In MDA-2 well, the new pore pressure prediction closely matches the well data in comparison to the normally used prediction. As a result, a more accurate regional pore pressure prediction map using mean stress is generated to aid both hydrocarbon exploration and development activities in the study area. [ABSTRACT FROM AUTHOR]

Ratcheting deformation in association with bulk texture evolution in HSLA steel is studied in this investigation. The cyclic deformation behaviors and damage modes of the specimens are obtained at room temperature, employing asymmetric stress-controlled tests under various combinations of mean stress and stress amplitudes. Bulk texture measurements of the specimens are done adopting an X-ray diffraction analysis. The results exhibit an increase in strain accumulation from 0.23 to 30.61% associated with a sharp reduction in ratcheting life from 3320 to 880 cycles by the increment in mean stress/stress amplitude. A continuous cyclic softening until the final failure is observed for all the ratcheting tests. It is noticed that variation of mean stress is more detrimental than stress amplitude in controlling strain accumulation while the effect of stress amplitude is more pronounced than mean stress for the reduction of ratcheting life. The fracture surface morphology indicates typical striation formation in the crack propagation region along with overload failure. The bulk texture studies indicate that there is a transition between 'ϒ' fiber and 'ζ' fiber during all loading conditions. The texture intensity is increased from 5.71 to 11.68 with progressive ratcheting strain accumulation. Here also, influence of stress amplitude is more significant than the mean stress. [ABSTRACT FROM AUTHOR]

Fatigue enhancement by way of high‐frequency mechanical impact (HFMI) treatment can enable effective design and construction of steel bridges. However, bridges may experience high and varying mean stresses, the effects of which are not covered today by any design recommendation or in the literature on HFMI‐treated joints. In this study, fatigue experiments were conducted with realistic in‐service bridge loading, which revealed the same high fatigue performance as for constant amplitude loading. The effect of mean stress in spectrum loading was quantified and a method to account for it in an equivalent manner is proposed. A design framework has been developed for design and engineering purposes. [ABSTRACT FROM AUTHOR]

We use complex variable methods to derive an analytical solution to the problem in plane elasticity associated with a circular elastic inhomogeneity with an eccentric interphase layer when the matrix is subjected to uniform remote in-plane stresses and the interphase layer undergoes uniform in-plane eigenstrains. The complex coefficients appearing in all three pairs of analytic functions characterizing the elastic fields in the composite are uniquely determined by solving two decoupled sets of linear algebraic equations obtained by enforcing the continuity conditions of tractions and displacements across the two perfect circular interfaces with the aid of analytic continuation. A simple analytical solution is also derived when the circular inhomogeneity becomes a traction-free hole and the interphase layer and the matrix have equal shear modulus but distinct Poisson's ratios. The non-uniform mean stress inside the circular inhomogeneity and the hoop stress along the edge of the circular hole are calculated and illustrated graphically. [ABSTRACT FROM AUTHOR]

Creep–fatigue interaction plays an important role in the failure of high‐temperature components. However, most of the existing life prediction limits materials and testing conditions. The present study was conducted to modify the strain energy density exhaustion model systematically to predict the creep–fatigue life under a wide range of materials, hold times, and total strain ranges. Mean stress effect was considered by the creep–fatigue net tensile hysteretic energy to eliminate the overestimation of fatigue damage in the traditional method, while creep threshold stress was introduced to estimate the creep damage. In addition, a novel failure strain energy model was proposed to describe the correlation among failure strain energy, creep failure mechanisms, and temperatures. Based on the tension‐hold creep–fatigue data of Grade 91 steel, 304 SS, Alloy 617, and 1Cr1Mo0.25V steel, the modified model predicted reasonable lives within a ±1.5 scatter band. [ABSTRACT FROM AUTHOR]

High-frequency mechanical impact (HFMI) is a post-weld treatment method which substantially enhances the fatigue strength of steel weldments. As such, the method enables a more efficient design of bridges, where fatigue is often the governing limit state. Road bridges are typically trafficked by a large variety of lorries which generate load cycles with varying mean stresses and stress ranges. Unlike conventional welded details, the fatigue strength of HFMI-treated welds is known to be dependent on mean stress in addition to the stress range. The possibility of considering the mean stress effect via Eurocode's fatigue load models (FLM3 and FLM4) was investigated in this paper. Moreover, a design method to take the mean stress effect into account was proposed by the authors in a previous work. However, the proposed design method was calibrated using limited traffic measurements in Sweden, and as such, may not be representative of the Swedish or European traffic. In this paper, larger data pools consisting of more than 873,000 and 446,000 lorries from Sweden and the Netherlands, respectively, were used to examine the validity of previous calibration in both countries. The comparison revealed no significant difference between the data pools with regards to the mean stress effect. Additionally, previous calibration provided the most conservative mean stress effect and was considered adequately representative for both countries. The proposed design method was further validated using four composite case study bridges. It was also found that the mean stress effect was mainly influenced by the self-weight, while variation in the mean stress due to traffic had a minor influence on the total mean stress effect. Furthermore, it was found that the mean stress effect could not be accurately or conservatively predicted using FLM3 or FLM4. [ABSTRACT FROM AUTHOR]

• Long life 500,000 cycle residual stress relaxation affects. • Cyclic mean stress relaxation, various plasticity levels. • Predictive methods for inclusion of residual stress relaxation. • High cycle residual stress measurements, XRD. • Neuber stress–strain notch correction, residual stress. • Smith Watson Topper mean stress life model. The presence of residual stress in welded components can have a significant impact on fatigue response. Residual stresses were assessed in thick welded A36 cantilever specimens (T-specimens) at the fatigue critical area. Testing involved subjecting the T-specimens to varying bending stresses and load cycles, leading to different levels of local plasticity at the weldtoe. Extensive X-ray diffraction (XRD) measurements were conducted to analyze the residual stress distribution near the weldtoe. Residual stress states were evaluated in both as-welded specimens and those subjected to fatigue loading with strain amplitudes up to 0.001 at the weldtoe stress concentration zone. The findings suggest that fatigue loading can induce changes in the welding-induced residual stress field, ranging from moderate to significant alterations. Therefore, fatigue life predictions should consider the potential evolution of residual stresses due to cyclic loading, including the effects of cyclic stress relaxation in fatigue life calculations. [ABSTRACT FROM AUTHOR]

• Mean stress would have a significant impact on the fatigue life of titanium alloy. • The conversion mean stress used for the pure fatigue damage calculation. • A thermo-mechanical fatigue life prediction method for titanium alloy was proposed. This paper presents a thermo-mechanical fatigue (TMF) life prediction method for titanium alloy TA15 under multiaxial random amplitude loading. Through strain-controlled TMF tests, it was found that under full-reversed cyclic loading, there was a significant presence of mean stress in the stress response. The induced mean stress led to the anomalous phenomenon where the fatigue life of thermal phase angle out-of-phase (TOP) was shorter than that of thermal phase angle in-phase (TIP). Therefore, a new damage calculation model was proposed, which can take into account the pure fatigue damage considering mean stress conversion and the cumulative environmental damage. Uniaxial TMF tests, constant amplitude multiaxial TMF tests, and random amplitude multiaxial TMF tests are conducted to verify the proposed method. The predicted results for all types of tests are in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The application of corrugation to the internal surface of a cylindrical shell with different notch depth is simulated, for tools with different working profiles. The stress–strain state and damage in the shell on corrugation by different tools are investigated. [ABSTRACT FROM AUTHOR]

The fatigue strength of structures subjected to cyclic loading depends strongly on the stress ratio. Particularly, in case of welded steel structures this fact is not considered in the corresponding standards nor in the guidelines. Experimentally, two approaches are used to study the effect of stress ratio on the fatigue life. On the one hand, based on the S-N curves obtained from tests performed at different stress ratios, the fatigue life under a particular stress range is estimated. On the other hand, the stress amplitude corresponding to a constant fatigue life is estimated by applying the failure criteria for fluctuating stress like the Goodman–Haigh relationship. This paper presents a general probabilistic model, which estimates the S-N and Goodman–Haigh curves for any stress ratio. Afterwards, this model is applied on data obtained from full and partial cyclic compression loading tests performed on welded specimens made of steel St 52-3. The tested details correspond to the permissible notch condition limit occurred in highly stressed structures used to build ships.

The stress ratio effect on the fatigue life of materials is a topic which have been studied by two different approaches. On the one hand, several experiments, performed under different stress ratios are necessary to estimate the corresponding Wöhler curves. Afterwards, these curves are considered to estimate the fatigue life under a particular stress range. On the other hand, fatigue failure criteria for fluctuating stress like the Goodman–Haigh relationship, are applied to estimate the stress amplitude for a constant fatigue life. Based on the Stüssi function, this paper presents a low cost model to estimate Wöhler curves and constant fatigue Goodman–Haigh diagrams. This procedure requires a set of tests performed under a particular stress ratio from LCF to HCF, and data from minimum two additional stress ranges for each subsequent stress ratio. An application on data from Ti‐6Al‐4V samples manufactured by selective laser melting (SLM) is presented. [ABSTRACT FROM AUTHOR]

Fusion reactor components undergo asymmetric cyclic loading,that leads to a progressive increase in plastic strain and causes deterioration in life of engineering components. This investigation deals with fatigue behavior of modified 9Cr–1Mo steel at room temperature and presents the effect of mean stress (σm), stress amplitude (σa) and stress rate ( σ ˙ ) on fatigue life, deformation and fracture behavior under asymmetric cyclic loading. A series of fatigue tests were conducted under asymmetric stress-controlled loading with different combinations of σm (190–210 MPa), σa (400–420 MPa) and σ ˙ (50–450 MPa/s). The plastic strain increased with increase in σm and σa and the fatigue life was reduced, whereas increase in σ ˙ reduced the accumulated plastic strain and the cyclic life was increased. The deformation behavior and microstructural changes under the influence of the three parameters (σm, σa and σ ˙ ) were examined by tranmission electron microscope (TEM). With increase in the three parameters (σm, σa, σ ˙ ), the lath martensitic structure changed to subgrain structure along with dislocation cells and forest dislocations. Scanning electron microscopy revealed unique features of fractured specimens, with progressive reduction in diameter towards the fracture-end, fatigue striations on the tapered circumferential surface and dimples on the fracture surface. [ABSTRACT FROM AUTHOR]

Triaxial and direct shear tests have been performed on rough (tension-induced) and smooth (saw-cut) fractures in Phra Wihan sandstone specimens. Two stress paths are used for the triaxial shear testing: constant confining stress and constant mean stress. It is found that under low confinement both stress paths show similar shearing resistance for the rough fractures. Under high confinement, however, the strengths under constant mean stress are notably lower than those of constant confining stress. The shear strengths of smooth fractures are independent of the stress path. This is supported by the shear strength results obtained from the direct shear testing, which suggests that under low normal stress and unconfined condition the stress path effect is insignificant. It is postulated that fracture roughness and non-linear behavior of fracture wall rock under high confinements are the main factors that cause stress path dependency of rock fractures.

Axial alternating fatigue tests with superimposed static torsional mean stress and shear alternating fatigue tests with superimposed static tensile mean stress are represented. A decrease in the fatigue life of the material was observed with an increase in the shear and static tensile stresses. Marin and modified Crossland methods are analyzed by means of the available experimental data. The two modifications of Sines method are proposed to take into account the static torsional stress effect (Sines+) and different slopes of the S-N curves in tension-compression and torsion tests (Sines++). It is shown that Sines++ model is the most accurate among others.

In laboratory, materials designed for engineering applications, specifically for fatigue, are generally tested under symmetrical cyclic loading (stress ratio, R = −1), but many structural components exhibit less fatigue life than predicted from symmetric loading due to asymmetric cyclic loading during service. This study deals with fatigue behaviour of Zircaloy-2 and presents the effect of mean stress (σm), stress amplitude (σa), stress rate ( σ ˙ ) on fatigue life, deformation and fracture behaviour at 300 °C under asymmetric cyclic loading. A series of fatigue tests are performed at 300 °C under asymmetric stress-controlled loading with different combinations of σm (60–80 MPa), σa (115–135 MPa) and σ ˙ (30–750 MPa/s). Deformation behaviour and microstructural changes under the influence of above parameters (σm, σa and σ ˙ ) are examined by transmission electron microscope. It is observed that plastic strain increases with rise in σm as well as σa and cyclic life is reduced; on the other hand, with increase in σ ˙ accumulation of plastic strain decreases and fatigue life is enhanced. The results are correlated with microstructural changes and fracture behaviour of the material under different test conditions. [ABSTRACT FROM AUTHOR]