Cyclic Stress-strain Relationship Research Articles

Energy-Based Unified Models for Predicting the Fatigue Life Behaviors of Austenitic Steels and Welded Joints in Ultra-Supercritical Power Plants.

The development of a cost-effective and accurate model for predicting the fatigue life of materials is essential for designing thermal power plants and assessing their structural reliability under operational conditions. This paper reports a novel energy-based approach for developing unified models that predict the fatigue life of boiler tube materials in ultra-supercritical (USC) power plants. The proposed method combines the Masing behavior with a cyclic stress-strain relationship and existing stress-based or strain-based fatigue life prediction models. Notably, the developed models conform to the structure of the modified Morrow model, which incorporates material toughness (a temperature compensation parameter) into the Morrow model to account for the effects of temperature. A significant advantage of this approach is that it eliminates the need for tensile tests, which are otherwise essential for assessing material toughness in the modified Morrow model. Instead, all material constants in our models are derived solely from fatigue test results. We validate our models using fatigue data from three promising USC boiler tube materials-Super304H, TP310HCbN, and TP347H-and their welded joints at operating temperatures of 500, 600, and 700 °C. The results demonstrate that approximately 91% of the fatigue data for all six materials fall within a 2.5× scatter band of the model's predictions, indicating a high level of accuracy and broad applicability across various USC boiler tube materials and their welded joints, which is equivalent to the performance of the modified Morrow model.

Seismic damage behaviors of structural steels under different constitutive and damage models

Previous studies have established a variety of cumulative damage models (CDMs) for either structural materials or members to perform an exquisite evaluation on plastic-induced deterioration of structural engineering under severe seismic actions. Nevertheless, the existing CDMs consider different influencing factors and hence tend to produce significantly different simulation performance. On the other hand, the influencing variables of CDMs are likely affected by the description on the cyclic stress-strain relation. Thus, the quantification of seismic damage is affected by the selection of both CDM and constitutive model. Existing relative studies mainly focus on the development and refinement of theoretical models. However, the understanding on simulation performance difference induced by the selection of models is still limited. This paper is aiming to clarify the influence of different constitutive models and CDMs on the cumulative damage behaviors simulated. Firstly, three types of cyclic constitutive models and nine CDMs are reviewed and their material parameters are summarized. The CDMs selected include the deformation-type models, the energy-type models and the combined-type models. Based upon different CDMs, the low-cycle fatigue (LCF) curves of mild structural steel are generated and compared to the corresponding Coffin-Manson relations. Subsequently, the damage evolutionary curves of different CDMs are simulated based upon several representative cyclic loading protocols. The influence of constitutive models and CDMs on the LCF curves and damage evolutionary curves are thoroughly studied. Besides, the sensitivity of CDMs on strain ratios and the influence of cyclic loading protocols on damage evolutionary curves are simultaneously clarified. The research findings can lay a solid foundation for the selection and combination of the relative analytical models with regards to different circumstances.

Constitutive model for reinforcing bars including bar buckling and low-cycle fatigue

In this paper, a path-dependent cyclic stress–strain model for reinforcing bars that incorporates the effect of bar buckling, low-cycle fatigue damage and loading history is proposed. A comprehensive experimental campaign is conducted to investigate the hysteretic behaviour of buckling-prone bars and the test results are used to develop and calibrate cyclic average stress versus average strain relationship for reinforcing bars. The parameters considered in this study include the slenderness ratio of reinforcing bars, grade of reinforcing bars and the loading history. Through a detailed analysis of test results, the effect of geometrical nonlinearity on the hysteretic response of the bar is evaluated and an analytical model simulating the effect of buckling on hysteretic response of the bar is developed. The cyclic model proposed herein captures the post-buckling stress deterioration, reduction of compressive stresses due to residual tensile strains (i.e. plastic strains), and reduction of unloading and reloading stiffnesses due to buckling and low-cycle fatigue damage in reinforcing bars. Comparison between experimental and analytical results shows that the proposed model can reliably predict the cyclic response of reinforcing bars including the effects of buckling and low-cycle fatigue.

A damage coupled elasto-plastic constitutive model of marine high-strength steels under low cycle fatigue loadings

To investigate the low cycle fatigue (LCF) performance and damage behaviours of marine high strength steels (HSSs), experimental analysis and constitutive modelling are carried out in this study. Basic mechanical properties are obtained by the monotonic tensile tests. Cyclic loading tests with different loading protocols are conducted to examine the cyclic stress-strain response. Based on the experimental data, the evolutions of peak stress, yield surface radius, backstress and LCF damage are discussed. The Ramberg-Osgood model and Manson-Coffin equation are fitted to characterize the cyclic stress-strain relation and LCF damage behaviours, respectively. Based on the continuum damage mechanics, a damage coupled cyclic elasto-plastic constitutive model is proposed to describe the hysteresis behaviours of marine HSSs. The model parameters are calibrated, and the model accuracy for stress-strain response and fatigue damage prediction is then verified by experimental data.

Low-cycle fatigue behaviour of hot-rolled titanium-clad bimetallic steel

Titanium-clad (TC) bimetallic steel is able to integrate the superior corrosion resistance of titanium alloy into traditional corrosion-susceptible structural steels, producing prominent life-cycle safety, serviceability and durability. Nevertheless, the relevant seismic performance and fatigue behaviour reported in existing literature are still limited and insufficient to support the codification for structural design of such advanced steel. In order to develop proper plastic/seismic design methodology for TC bimetallic steel structure, the cyclic behaviours and low-cycle fatigue life prediction of such metal must be thoroughly investigated. This paper aims to study the low-cycle fatigue behaviour of hot-rolled bonded TC bimetallic steel manufactured from TA2 titanium alloy and Q355B structural steel. The strain amplitude of low-cycle fatigue (LCF) test ranges from 0.5% to 2.5%, and the strain ratio applied herein includes 0 and -1. The experimental phenomenon, LCF failure mechanism, cyclic stress-strain relationship of different tests are thoroughly compared and discussed. Besides, the influence of strain rate and bond strength are simultaneously demonstrated. The LCF life are fitted and validated through Basquin-Coffin-Manson model, Kuroda model and energy method, respectively. The research outcomes demonstrate that the LCF cracks of TC bimetallic steel tend to be initiated at the cladding layer and propagated into the substrate layer due to a coupled buckling-fatigue failure mechanism. Several representative fatigue behaviour of conventional mild (CM) steels including the three-stage cyclic softening and mean stress relaxation have not been observed in this experimental study. The strain rate exhibits distinct influence on the LCF life and failure mechanism. Both Basquin-Coffin-Manson model and energy method can provide more favourable prediction accuracy for LCF life of TC bimetallic steel than the Kuroda model. Generally the LCF life of TC bimetallic steel is shorter than that of structural steels, stainless steels, titanium alloys and stainless-clad (SC) bimetallic steels. The test records and fatigue-life model parameters obtained can lay a solid foundation for seismic analysis and damage evaluation of TC bimetallic steel structure.

A simplified prediction method on Chaboche isotropic/kinematic hardening model parameters of structural steels

The Chaboche combined isotropic/kinematic hardening model has gained wide popularity due to its outstanding description on cyclic stress-strain relations of different structural metals. However, the calibration on material parameters of Chaboche model needs to perform at least a cyclic loading test to gain the experimental data, leading to a considerable time and economic cost. To reduce such calibration expense, a simplified calibration approach was proposed in this paper. Firstly, the Chaboche model parameters of various structural steels, including low yield point steels, mild steels, and high strength steels, were calibrated based upon 171 experimental stress-strain curves by using an identical calibration procedure. Secondly, these parameters calibrated were correlated with the monotonic yield strength and fitted through suitable description formulations. Subsequently, a four-steps prediction method of Chaboche model parameters was proposed to replace the traditional complex calibration approach. Based upon the new prediction method, the values of all Chaboche model parameters can be directly obtained when monotonic yield strength is known. Furthermore, the simulation performance of this new prediction method was validated by comparing a series of simulation stress-strain relations with their experimental counterparts. The probabilistic distribution types of these parameters were accordingly identified and the corresponding statistical parameters were fitted. This study provides a simplified prediction method and a probabilistic description on different Chaboche model parameters, producing a foundation for random analysis of stress-strain behaviors on various structural steels.

High Temperature Fatigue Behavior and Failure Mechanism of Ti-45Al-4Nb-1Mo-0.15B Alloy

Strain-controlled low cycle fatigue experiments were carried out on the TiAl alloy Ti-45Al-4Nb-1Mo-0.15B at 400 °C and 750 °C to reveal the cyclic mechanical behavior and failure mechanism. The TiAl alloy presents stable cyclic characteristics under fatigue loading at elevated temperatures. No obvious cyclic softening or cyclic hardening was manifested during experiments. The cyclic stress–strain relationship is well described by the Ramberg–Osgood equation. The fatigue lifetime at different temperatures has a log-linear relationship with the total strain ranges. The fracture morphology indicates the main fracture mode of fatigue specimens at 400 °C is a brittle fracture, while there is a ductile fracture at 750 °C. Meanwhile, the trans-lamellar fracture is dominant for the lamellar microstructure and the percentages of the inter-lamellar fracture decreases with the strain amplitude.

Experimental investigation on the mechanical behavior of hybrid steel-polypropylene fiber reinforced concrete under conventional triaxial cyclic compression

Hybrid fiber reinforcing technology has gained a wide recognition in concrete built infrastructure. The cyclic stress–strain relation of hybrid fiber reinforced concrete (HFRC) plays a crucial role in the elastoplastic analysis of HFRC that further determines the structural damage progression and hysteretic behaviors. This paper investigates the mechanical behavior of HFRC subjected to conventional triaxial cyclic compression. A total of 48 HFRC cylindrical specimens are tested for different fiber volume fraction, fiber aspect ratio and confining pressure. The acoustic emission behavior of HFRC is analyzed with an elaboration of failure pattern transition as well as the mechanism analysis of fiber effects, and the macroscopic mechanical properties evolutions in terms of triaxial compressive strength, plastic behavior and stiffness deterioration were also investigated. It is clearly indicated from the test results that the incorporation of hybrid fibers together with the applying confinement can significantly enhance the mechanical property of concrete with the failure pattern transformed from a tensile failure to a shear failure mode. An increment in the strength of HFRC is observed as the steel fiber dosage increases. The polypropylene fiber contributes largely on improving the plastic behavior of HFRC at an expense of a slight decrease in the compressive strength. It is noted that the effect of confinement outweigh the fiber inclusion in restriction of damage degradation whilst the fiber effect is more pronounced as the confinement is low. Thereafter, the stiffness deterioration in terms of Young’s modulus, shear modulus, bulk modulus and Poisson’s ratio are investigated. The results show that the Young’s modulus and shear modulus of HFRC monotonously reduce during the damage process, whilst the Poisson’s ratio would monotonously increase and the bulk modulus exhibits a hyperbolic evolution form. Applying confinement and adding fibers can restrain the deterioration process of the stiffness, and the influences of fibers on stiffness deterioration are more significant under a low confinement level than that under a high level.

Fatigue crack initiation and energy-based life analysis for Q345qD bridge steel at low temperatures

The lack of in-depth understanding on the low-temperature fatigue cracking performance has limited the extensive application of the Q345qD bridge steel in cold and severely cold regions. This study investigates the resistance to the fatigue crack initiation of the Q345qD steel through a series of strain-controlled fatigue tests of smooth coupons at room and low temperatures. Experimental results present the cyclic stress-strain relationship, non-Masing properties and Coffin-Manson-type fatigue crack initiation resistance. Thereafter, this study analyzes the effect of low temperatures on the stain-controlled fatigue life of the studied Q345qD steel using the different energy approaches. Results indicate that the low temperatures within -60 °C increase the resistance to the fatigue crack initiation and the cyclic strain-hardening coefficients. A comparison with other structural steels demonstrates the excellent fatigue performance of the Q345qD steel at room and low temperatures. Since the corresponding stress amplitudes of the Q345qD steel under each cyclic strain range exhibit some strain-range-dependent cyclic softening/hardening behavior, the plastic strain energy density and the concept of fatigue toughness are more suitable and effective to predict the fatigue life of the Q345qD steel at room and low temperatures. Finally, a simple and accurate method for calculating the plastic strain energy density has been proposed.

Analytical model of concrete-filled FRP-steel composite tube columns under cyclic axial compression

The concrete-filled FRP (Fiber-reinforced Polymer)-steel composite tube (CFCT) column is a new structure that integrates the advantages of various materials. The establishment of the cyclic stress-strain relationship under axial loading is of great importance for the seismic analysis and design method of this new structure. In this study, the stress-strain behaviors of six CFCT columns with various FRP thicknesses and types under cyclic axial loading were investigated. The experimental results reveal that the failure process is homologous to that of the CFCT column under monotonic axial compression. CFCT columns that are confined by carbon FRP (CFRP) can achieve higher strength and deformation capacity. The ratio of the plastic strain to the unloading strain enhances with the number of loading cycles. When the axial strain develops to 0.02, the ratio tends to be close to 1.0, and the plastic strain becomes difficult to recover. CFRP plays a more important role in inhibiting the development of plastic deformation compared with basalt FRP (BFRP). On the basis of experimental results, a complete design-oriented stress-strain model is established to predict the cyclic stress-strain relationship of CFCT columns for the first time, and this model includes equations for predicting the returning strain, the plastic strain and the unloading and reloading loading paths. The proposed model can predict the main features of the cyclic stress-strain behaviors of CFCT columns accurately and conveniently both before and after FRP fracture.

Low-cycle fatigue behavior of 7075-T6 aluminum alloy at different strain amplitudes

Low-cycle fatigue (LCF) life and failure mechanism of 7075-T6 high strength aluminum alloys were investigated under MTS 809. The cycling stress response and the cyclic stress—strain relationships under different strain amplitudes were investigated. Using Manson-Coffin law, the three parameter exponential function equation and the damage function model of tensile hysteresis energy (Ostergren equation), the regression analysis of LCF test data was carried out, it was found that the fatigue life prediction results of the three parameter exponential function equation were better than the other two life prediction methods in terms of statistical analysis methods of standard deviation and dispersion band. Analysis of microstructure and fatigue failure fracture revealed that fatigue crack initiated at the interface of precipitations and α-phase aluminium substrate in surface or near surface of the sample.

A modified model for predicting cyclic stress–strain relationship of fiber reinforced polymer grid reinforced engineered cementitious composites

AbstractTo verify the universality of the cycling model of carbon fiber reinforced polymer (CFRP) grid reinforced engineered cementitious composite (CFRP‐ECC) material, a complementary experiment was carried out to investigate the cycling behavior of basalt fiber reinforced polymer (BFRP) grid reinforced ECC (BFRP‐ECC) composite material using both traditional measurement and digital image correlation system. Elastic modulus, layers, and surface treatment of BFRP grid and the loading schemes were considered as the major variables in the experiment. Compared with the CFRP‐ECC, BFRP‐ECC had better ultimate and residual deformation capabilities. Test results also showed that the effective strain of the internal BFRP grid reached 80–90% of the ultimate material strain, therefore, higher loading capacity of BFRP‐ECC material was obtained. A unified model was proposed to analyze the cyclic stress–strain behavior for both BFRP‐ECC and CFRP‐ECC materials. The validation of the analysis model was verified through comparisons between the predicted values and the test results.

Cyclic behavior and strain energy-based fatigue damage analysis of mooring chains high strength steel

This study investigates the low-cycle fatigue behavior of mooring chains high-strength steel grade R4 under different strain amplitudes and strain ratios at room temperature. A fatigue test program has been carried out on small low cycle fatigue specimens cut from large mooring chains. The experimental results characterize the cyclic stress-strain relationship, the mean stress relaxation behavior, and the cyclic plasticity parameters of the material. Strain energy density is correlated with fatigue life through a simple power-law expression and very well represented by Basquin-Coffin-Mansion relationship. Further, a non-linear elastic-plastic material model is calibrated to the experimental stress-strain curves and used for the estimation of energy dissipation in the specimens under applied cyclic loads. The predicted fatigue life using the calibrated material parameters demonstrates a close agreement with the experimental fatigue life. Numerical simulations are carried out to analyze local plastic straining and assess crack initiation at the pit site of corroded mooring chains considering the multiaxial stress state. An energy-based approach is employed to estimate the number of cycles needed for a crack to initiate from an existing corrosion pit.

A novel test method based on small specimens for obtaining low-cycle-fatigue properties of materials

In this study, a novel method for low-cycle-fatigue (LCF) tests on small funnel and Ring specimens to obtain the Manson–Coffin law of materials is proposed based on the median energy equivalence principle. It includes a method for solving the cyclic stress-strain relationship of the material according to the cycling stability curve of load amplitude–displacement amplitude, and another method for acquiring the conversion relationship between the measuring displacement amplitudes and local strain amplitudes of the specimen. LCF experiments under constant displacement amplitude loading were performed on small funnel and Ring specimens, as well as standard straight-round bar specimens of the two materials, G115 and 16Mn. The results indicated that the uniaxial cyclic stress–strain relationship and Manson–Coffin law results of the G115 and 16Mn materials obtained by the new method were highly consistent with those obtained by the traditional standard method.

Stress-strain behaviour of reinforced dredged sediment and expanded polystyrenes mixture under cyclic loading

Reinforced soil and Expanded Polystyrenes (EPS) mixture (RSEM) is a geomaterial which has many merits, such as light weight, wide strength range, easy for construction, and economic feasibility. It has been widely applied to improve soft ground, solve bridge head jump, fill cavity in pipeline and widen highway. Reutilizing dredged sediment to produce RSEM as earthfill can not only consume a large amount of waste sediment but also significantly reduce the construction cost. Therefore, there is an urgent need understand the basic stress-strain characteristics of reinforced dredged sediment-EPS mixture (RDSEM). A series of cyclic triaxial tests were then carried out on the RDSEM and control clay. The effects of cement content, EPS beads content and confining pressure on the cyclic stress-strain behaviour of RDSEM were analyzed. It is found that the three stages of dynamic stress-strain relationship of ordinary soil, vibration compaction stage, vibration shear stage and vibration failure stage are also applicative for RDSEM. The cyclic stress-strain curves of RDSEM are lower than that of control clay in the vibration compaction stage because of its high moisture content. The slopes of backbone curves of RDSEMs in the vibration shear stage are larger than that of control clay, indicating that the existence of EPS beads provides plastic resistance. With the increase of cement content, the cyclic stress-strain relationship tends to be steeper. Increasing cement content and confining pressure could improve the cyclic strength and cyclic stiffness of RDSEM.

Experimental cyclic behavior and constitutive modeling of high strength structural steels

High strength structural steels have recently achieved increasing application in civil and structural engineering worldwide. For instance, the sony center tower located in Berlin were constructed through steel truss made of S460 and S690 high strength steel whose nominal yield stress is 460 MPa and 690 MPa respectively. The utilization of high strength steel considerably reduced the structure deadweight and produced larger architecture space. Besides, steel connections of one military steel bridge in Mittådalenthe, Sweden were fabricated of 960 MPa ultra-high strength steel. This application remarkably increases the construction convenience since high strength steel presents excellent ability to reduce member size as well as improve structure performance. Nevertheless, limited test data have been available on the monotonic properties and cyclic behavior of these structural steels. In this study, uniaxial coupons were tested for four types of Chinese high strength structural steels, including grades Q460D, Q550D, Q690D as well as ultra-high strength structural steel Q890D, to investigate their stress-strain response and energy-dissipation behavior under monotonic and various cyclic strain demands. The monotonic test results of the tested steels were then compared with the requirements of current seismic design codes GB 50011-2010 and Eurocode8. Besides, cyclic strength, deformability and energy dissipation capacity were evaluated through the tested strain-stress loops. The experimental observations in cyclic tests show that cyclic softening, which significantly affects the shape of cyclic loops and energy dissipation capacity, is an important hysteretic characteristic for all tested high strength structural steels. Moreover, cyclic backbones of these four steels were calibrated using Ramberg-Osgood model. To fundamentally define the cyclic stress-strain relationship, essential parameters of three commonly used constitutive models, including Chaboche model, Dong-Shen model and Giuffre-Menegotto-Pinto model were calibrated based on the experimental data under cyclic loading. Those calibrated models were then employed in simulations of aforementioned cyclic loading tests and their validity were compared. Good agreements between experimental response and simulated performance by Dong-Shen model were achieved, demonstrating that the calibrated Dong-Shen model can elaborately describe the cyclic behavior of these four types of high strength structural steels.

Static and cyclic response of low-strength recycled aggregate concrete strengthened using fiber-reinforced polymer

Concrete production using recycled aggregates (RAs) from construction and demolition waste is known to have a lower strength performance than natural aggregate concrete. Many studies have been carried out to improve the strength properties of recycled aggregate concrete (RAC). One widely accepted strategy is to use fiber-reinforced polymer (FRP) jackets as external confinement material to enhance the compressive strength and ductility performance of RAC, especially in the seismic retrofit of RAC members. Most existing research has focused on normal strength concrete subjected to monotonic loading. However, retrofitting or repair work is more common for concrete structures with low concrete strength. In addition, cyclic behavior research focused on FRP-confined low-strength RAC is also rare due to the lack of sufficient experimental data. In this study, 29 concrete specimens were cast using varying proportions of RAs mixed with natural coarse aggregates. In this case, poor quality natural aggregates were selected to achieve a low concrete strength. Thickness of the carbon FRP (CFRP) jacket, loading types (monotonic or cyclic), and the RAs replacement ratio were the main test parameters of this experimental work. The mechanical properties of CFRP-confined RAC were analyzed and discussed from the failure mode perspective; these included peak strength, ultimate strain, and cyclic stress-strain relationships. Test results show that strength enhancement by FRP confinement was much more pronounced in lower strength RAC than in normal strength concrete, whereas the ductility improvement was almost consistent. Confinement rigidity and recycled aggregate replacement ratio had little effect on cyclic stress-strain behavior, in terms of unloading and reloading paths, as well as in plastic strain. The adhered cement mortar on RAs weakened the impact brought by confinement when repeated unloading and reloading were applied. This was especially true during cyclic loading, which generated a large deformation.

Low cycle fatigue test and enhanced lifetime estimation of high-strength steel S550 under different strain ratios

This study investigates the low-cycle fatigue (LCF) behavior of the high-strength steel S550 (commonly used in ship and floating structures) under different strain amplitudes with different strain ratios at a room temperature. The test results characterize the cyclic stress-strain relationship, the mean stress relaxation behavior and the cyclic plasticity parameters of S550 steels. The scanning electron microscopy (SEM) examinations on the failure surface reveal the fatigue crack initiation and growth mechanism. Based on the experimental results, this study presents two enhanced approaches to estimate the low-cycle fatigue life of S550 steels. The energy-based approach modifies the original Smith-Watson-Topper model using the applied energy calculated in the first cycle to enhance the accuracy and facilitate engineering implementations. The damage mechanics-based approach calibrates the material parameters from the measured total fatigue life by combining the fatigue crack initiation model and the damage growth model. The computed fatigue life using the calibrated material parameters demonstrates a close agreement with the measured fatigue life in the experiment.

Extremely Low Cycle Fatigue Behaviors of Anti-Seismic Steel HRB400 Reinforcing Steel Bars under Strong Earthquakes

The extremely low cycle fatigue (ELCF) behaviors of anti-seismic steel HRB400 reinforcing steel bars were comprehensively studied following the cyclic push-pull loading tests with extremely high strain amplitudes (up to ±12.8%). The cyclic stress response characteristics and cyclic stressstrain relationships were investigated. The cyclic response characteristics were closely related to the strain amplitudes, and the secondary hardening phenomenon appeared under some strain amplitudes. The strain-life data from the axial tests were used to derive suitable Coffin-Manson parameters for the test material. The scanning electron microscope (SEM) morphology revealed ELCF damage mechanisms were distinctive of those typical from LCF. Compared with the common low-cycle fatigue (LCF) fracture region, several unique features in the ELCF regime can be noticed, including the deviations of the fatigue life from the Coffin-Manson law and the transformation of fatigue cracking modes.

Deformation and damage mechanisms of a bimodal 12Cr-ODS steel under high-temperature cyclic loading

The present study reports on the high-temperature low-cycle fatigue (LCF) behavior of a ferritic bimodal 12Cr oxide dispersion strengthened steel. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The measured cyclic stress response showed four distinct stages which include instant initial cyclic softening followed by gradual cyclic hardening thereafter continuous linear cyclic softening and finally crack initiation and growth stage. The rate and amount of these stages depend on both strain amplitude and testing temperature. The cyclic stress-strain and strain-life relationships were obtained through the test results, and related LCF parameters were calculated. Microstructural investigations, using electron microscopy, were carried out to shed light on the deformation mechanisms. At 550°C, no appreciable microstructural evolution occurred, which is consistent with the manifestation of Masing behavior. A propensity towards cross-slip and hence the formation of three-dimensional dislocation structures increased with increase in loading amplitude and testing temperature, which assisted in accumulating higher inelastic strain and led to slightly higher cyclic hardening at these conditions. Furthermore, W-enriched Laves phase particles precipitated at grain boundaries. The evolution of cell structures with strain amplitude at 650°C resulted in a small deviation from Masing behavior. The damage studies revealed multiple surface initiated transgranular cracks under higher strain amplitudes and a single surface initiated transgranular crack under lower strain amplitudes. The different stages of the crack path, whose durations depend on the testing conditions, revealed distinct fatigue fracture features.