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Masing/non-Masing behavior of material plays an important role in the strain energy-based methods of fatigue life prediction. Materials under fatigue are found to show three distinct categories of behavior viz. Masing, non-Masing (Type-I: when master curve can be constructed) and non-Masing (Type-II: when master curve cannot be constructed). The master curve method available in the literature for the estimation of cyclic plastic strain energy density (CPSED) can be used only for Type-I non-Masing and Masing behaviors of materials. Moreover, it could be used for estimation only, not for prediction of CPSED. Very recently (in 2021), a new method, as summarized in this article, was proposed for the prediction of CPSED and fatigue life of material irrespective of Masing or non-Masing (Type-I and Type-II) behavior. Although the method was developed, the validation of the proposed method with different Type-II non-Masing behavior materials remained a matter of further investigation. As Type-II non-Masing behavior was not highlighted earlier in the literature, such data is not readily available. In this article, we conducted low cycle fatigue tests on SS 304L material, and after an extensive literature review and analysis, three materials’ data for each of Type-I and Type-II non-Masing behaviors could be collected. The method of prediction of CPSED and fatigue life is summarized and implemented on the six different materials. The CPSED and fatigue life could be predicted within a scatter band of 1.2 and 2, respectively. This article confirms the universal nature of the new method of CPSED and fatigue life prediction.

Understanding the grain boundary deformation dynamics is very crucial to designing materials with stable microstructures. With this quest, the deformation behavior of coherent twin boundary under cyclic shear loading has been studied in {\alpha}-Fe using molecular dynamics simulations to understand the influence of strain amplitude and temperature. Twin boundary exhibited shear coupled migration along with cyclic irreversibility character at lower temperatures and gained almost perfect reversibility at higher temperatures of around 1500 K. TB exhibited more sliding than migration with an increase in temperature. The stress associated with the migration of twins was observed to fluctuate around its average value. This was caused by layer by layer propagation of twin boundary through the activity of 1/6 = 1/12 + 1/12 type edge partial dislocations on "\{"112"\}" twin plane. Complete twin reversibility and complex TB migration were noticed in the presence of multiple parallel twin nanowires. Twin migration was observed at the larger size nanowires with a proper combination of boundary conditions and strain rates; otherwise, it was absent. The influence of shear strain amplitude in offsetting the twin boundary was found to be minimal., Comment: 29 pages, 16 figures, 3tables, Journal paper

Fretting fatigue experiments were conducted on a modified 9Cr-1Mo (P91) steel under flat-on-flat contact with maximum applied cyclic stress (σ ) levels of 450 MPa, 500 MPa and 550 MPa at a stress ratio of 0.3 and a contact pressure of 100 MPa. A decrease in the cyclic life was observed with increase in σ . Chaboche model with isotropic and kinematic hardening was employed in finite element analysis to evaluate the stress distribution near the contact pad and along contact surface under fretting fatigue conditions. In addition, the contact-related parameters such as contact pressure, contact shear stress and relative tangential motion were also assessed. The relative tangential motion was found to increase with increasing σ . Besides, the peak values of normal stress (parallel to applied loading direction) and maximum principal stress were observed around the leading and trailing edges of the contact pad at the σ . The amplitude of relative tangential motion as well as slip zone increases with σ . The orientations of the principal plane and shear plane to the applied cyclic loading direction are -89.5~̵̊ and -134.5~̵̊, irrespective of the σ . The fracture surface of the failed specimen revealed that the direction of the crack was nearly perpendicular to the applied stress. Smith-Watson-Topper parameter was used for estimating the crack initiation life with σ . It has been noticed that the fraction and dominance of crack initiation or propagation phase depend on the imposed cyclic condition for the steel.

Quantitative assessment of non-Masing behavior is studied, and a new method is proposed for the estimation of cyclic plastic strain energy density and fatigue life. Low cycle fatigue tests were performed on 304L stainless steel employing strain amplitudes ranging from ±0.25% to ±1.0% at a strain rate of 3 × 10-3 s-1. The material exhibited Masing behavior at lower strain amplitudes and non-Masing behavior at higher strain amplitudes. Secondary hardening was observed at relatively higher strain amplitudes. Both the secondary hardening and non-Masing response were found to be associated with the deformation induced martensitic transformation. The master curve approach, which is generally used for the analysis of non-Masing response, could not be used as experimental data could not be represented in the form of a master curve. The proposed method of quantification of non-Masing response could estimate the cyclic plastic strain energy density of 304L stainless steel well within a scatter band of 1.2. The fatigue life of 304L stainless steel could also be predicted within a scatter band of 2. The proposed approach could also estimate the cyclic plastic strain energy density and fatigue life of materials of different grades within scatter factors of 1.2 and 2, respectively.

Notches introduced in the plain specimen result in the multiaxial state of stress that exists in the actual components due to the presence of flaws and defects. In the present work, low cycle fatigue life estimation of plain and notched specimens of 316 LN stainless steel is carried out at room temperature and 823 K. The plain and notched specimens with different notch radii were subjected to varying strain amplitudes ranging from ± 0.25 to ± 1.0% at a strain rate of 3 × 10−3 s−1. The fatigue life decreased in the presence of notch for all strain amplitudes at both the temperatures. The decrease in fatigue life was found to be more at room temperature than at 823 K. The fatigue life of the notched specimen decreased by approximately 94.2% compared to plain specimen at room temperature. However, at 823 K the decrease in fatigue life for notched specimen was approximately 84.6%. Low cycle fatigue life of the plain and notched specimens was estimated by Neuber’s rule and finite element analysis approach. Neuber’s rule overestimated the fatigue life by maximum factor of 2.6 for specimens at room temperature and by maximum factor of 5 for specimens at 823 K. However, it gives closer approximation at higher strain amplitudes at 823 K. Life estimation by finite element analysis at room temperature was within a factor of 1.5 as compared to experimental life, whereas it underestimated the fatigue life within a factor of 6 at high temperature.

In the present study, low cycle fatigue (LCF) behaviour of tungsten (W) alloyed 9Cr steel (Grade 92 steel) base metal and its weld joints has been investigated. LCF tests on both base metal and weld joint were conducted under fully reversed, total axial strain control mode employing a triangular waveform at 823 K, under a constant strain rate of 3 × 10−3 s−1 with strain amplitudes varying from ±0.25% to ±1%. Both base metal and weld joint exhibited continuous softening with the weld joint exhibiting a lower stress response than base metal. At lower strain amplitudes, weld joint exhibited lower fatigue life than that of base metal whereas at higher strain amplitude, both the materials exhibited comparable fatigue life. Weld joints failed in the base metal for all the strain amplitudes at 823 K except at the strain amplitude ±0.25% where weld joint failed in inter-critical region. Effect of temperature on LCF behaviour of weld joints and base metal at various temperatures ranging from 300 K to 873 K under constant strain amplitude of ±0.6% and strain rate 3 × 10−3 has been investigated. At all the temperatures, weld joints failed in the base metal region. The material exhibited dynamic strain ageing phenomenon in the temperature range 473–673 K. Oxidation was found to show more adverse effects on fatigue life beyond 673 K.

Creep-fatigue interaction (CFI) behavior of 9Cr-1.8W-0.5Mo-VNb steel (Grade 92 steel) base metal and its weld joint has been investigated at 823 K using a constant strain rate of 3 × 10–3 s−1. Both the base metal and the weld joint exhibited continuous softening with an almost equal cyclic stress response. The fatigue life decreased with increasing hold time. The hold applied in the compressive peak strain proved more deleterious compared to the tensile hold, indicating a compressive dwell sensitivity. Besides, the weld joints showed a greater reduction in fatigue life compared to the base metal. Fracture surfaces of the tested specimens revealed the prevalence of secondary cracks and extensive oxidation in the material. Weld joint specimens failed in the base metal region in all the tests. Evidence of dynamic strain aging in the form of serrations in the stress-strain hysteresis loops was also noted.

The selection of structural materials for elevated temperature applications relies on the availability of proper design codes based on adequate data pertaining to the properties at service-relevant loading conditions. Two of the most widely used high temperature design codes, viz, the ASME Boiler and Pressure Vessel Code and the RCC-MRx code are at variance with each other on the bilinear interaction point in the creep-fatigue interaction diagram for modified 9Cr–1Mo ferritic steel. In view of this, a detailed investigation was carried out on the creep-fatigue interaction behavior of this alloy with special emphasis on the evaluation of the creep-fatigue damage and construction of the interaction diagram. Tests were performed on two chemical variants of the steel at two temperatures (773 K and 823 K) using the strain amplitudes of ±0.25%, ±0.4%, ±0.6% and ±0.8%. Hold times of different durations in the range, 1–60 min, were imposed in the tensile and compressive peak strains to introduce the creep damage. The ASME creep-fatigue interaction diagram was observed to be a more conservative design approach for the alloy.

Accuracy in the estimation of low cycle fatigue life of modified 9Cr-1Mo steel notched specimen by different analytical methods such as linear rule, Neuber’s rule, strain energy density method and numerical method such as finite element analysis have been studied in this investigation. The fatigue tests on notched specimens having notch radius of 1.25 mm, 2.5 mm and 5.0 mm were carried out at 823 K with net stress amplitudes of 250 MPa, 300 MPa and 350 MPa. The fatigue tests on smooth specimens were carried out with strain amplitudes ranging from ±0.3% to ±0.8% with a strain rate of 3 × 10−3 s−1 at 823 K to evaluate the fatigue life of notched specimen through strain-life approach. In order to predict the cyclic stress response of the material, Chaboche non-linear hardening model was employed considering two back stress components. Predicted hysteresis loops for smooth specimen were well in agreement with experimental results. Estimated fatigue lives of notched specimens by analytical methods and ...

Understanding the mechanical behavior of the key elements in alloys, at the nano scale leads to the design of optimum microstructure against fatigue failure. In the present study, low cycle fatigue simulations have been carried out on defect free single crystal Cu (face centered cubic) nano wire of size about 7.23 × 7.23 × 14.46 nm (aspect ratio of 2:1) at temperature 10 K by using molecular dynamics simulations. Yielding was found to be initiated from corners of the nano wire by forming stacking faults. It was observed that cyclic stress response of the model system depended on microstructure which was at the starting of reverse loading. Potential energy was used as a tool to investigate the fatigue deformation characteristics of the Cu nano wire. It was observed that the competition between hexagonal close packed atoms and disordered atoms [especially point defects, surface atoms and non-crystalline atoms (other than surface atoms)] governed the cyclic characteristics of the model system.

In the present investigation, effect of thermal ageing on low cycle fatigue (LCF) behaviour of Reduced Activation Ferritic Martensitic steel has been assessed by finite element analysis. The steel was thermally aged at 873 K for 3000 hour. Low cycle fatigue tests were carried out on both the as-received and thermally aged material at strain rate of 3×10−3 s−1 at 823 K, over strain amplitudes in the range of ± 0.25 to ± 0.8%. Continuous cyclic softening till final failure, except for initial few cycles especially at relatively lower strain amplitudes, was observed in both the material conditions. Thermal ageing resulted in marginally higher cyclic stress response accompanied by lower fatigue life. The differences in fatigue responses have been attributed to the coarsening of precipitates on thermal ageing. Finite element analysis has been carried out considering combined isotropic and kinematic hardening as material model to estimate the effect of thermal ageing on the response of material under LC...

In the present investigation, the low cycle fatigue behaviour of 316 LN stainless steel has been studied. The multiaxial state of stress has been introduced by incorporating a notch in the smooth specimens. In order to vary the state of stress in the specimens, notch radii of 5, 2.5 and 1.25 mm were incorporated. Low cycle fatigue tests have carried out on smooth and notched specimens of the steel at strain amplitudes ranging from ±0.25 to ±0.8 % at room temperature. Presence of a notch decreased the fatigue life appreciably. The fatigue life was found to decrease with increase in the strain amplitude for smooth and notched specimens and percentage decrease was higher for relatively sharper notches. The local strain at the notch root has been estimated by carrying out finite element analysis considering a material nonlinearity and using the combined kinematic and isotropic hardening model. The fatigue life of the notched specimens has been subsequently estimated using Coffin–Manson relationship relating the strain and fatigue life. The fatigue life for notched specimen has also been estimated by Neuber’s rule. It is observed that Neuber’s rule overestimated the fatigue life whereas finite element method estimated close to the experimental values.

Low cycle fatigue (LCF) behaviour of modified 9Cr-1Mo steel (P91 steel) has been investigated. The LCF tests were carried out at room temperature (300 K) and 823 K employing strain amplitudes ranging from ±0.3 to ±0.8 % and a strain rate of 3 × 10−3 s−1. The fatigue life was found to decrease with increase in strain amplitude and temperature. Material exhibited higher extent of cyclic softening at 823 K than that at room temperature. In order to estimate the response of the steel to the cyclic loading, Chaboche hardening model was employed considering elasto-plastic response of the material. The predicted hysteresis loops and cyclic stress response of the steel obtained from the FE analysis showed good agreement with experimentally obtained results.

In the present investigation, effect of notch on low cycle fatigue behaviour of 316 LN stainless steel have been assessed by carrying out low cycle fatigue (LCF) tests on smooth and notched specimens of steel. The LCF experiments were carried out at strain amplitudes ranging from ±0.3 to ±1.0 % and at a strain rate of 3 × 10−3 s−1 at room temperature. The material exhibited prolonged softening after a few initial cycles of hardening followed by saturation and final failure. The gradual softening following initial hardening was not observed for the highest strain amplitude of 1 %. Fatigue life was found to decrease in presence of notch. The extent of decrease in fatigue life was higher for relatively sharper notch. Fatigue life of the notched specimens has been estimated based on the local plastic strain using finite element analysis and Neuber’s rule. The FE analysis approach was found to underestimate the fatigue life in presence of notch, whereas Neuber’s rule overestimated the fatigue life.

To understand the effect of multiaxial state of stress at laboratory scale, specimens with different kinds of notches are widely used. In this investigation, the effect of notch root radii on low cycle fatigue life of P91 steel has been studied. Fatigue tests were carried out on notched specimens having notch radius of 1.25, 2.5 and 5.0 mm at net stress amplitudes of 250, 300 and 350 MPa at 823 K. To estimate the fatigue life in the presence of a notch based on local strain at the notch root, different analytical approximation methods such as linear rule, Neuber’s rule and strain energy density approach have been employed. The fatigue life could be predicted within a factor of ±16 on experimental fatigue life. The difference among the predicted fatigue lives by the different analytical methods decreased with increasing notch radii. The strain energy density method and linear rule predicted nearly equal fatigue lives in all the cases.