Low Cycle Fatigue Damage Research Articles

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.

On the consideration of loading interaction in combined high and low cycle fatigue life prediction

AbstractBased on the analysis of the test data and Miner's rule, a combined high and low cycle fatigue (CCF) life prediction model considering the loading interaction is established by introducing coupled damage. The coupled damage is determined by multiplying the high cycle fatigue damage and the low cycle fatigue damage by a coupled damage coefficient . According to the analysis of the test data, the coupled damage coefficient is positively correlated with the high cycle stress ratio . In addition, an interaction factor, which reflects the loading interaction effect, is introduced to correct the coefficient . The CCF experimental data of four materials are employed for model verification and comparison among the proposed model, Miner's rule, and Trufyakov–Kovalchuk model (T–K model). The proposed model exhibits a relatively higher prediction accuracy and is more suitable for predicting the fatigue life of CCF.

A mesoscopic damage model for the low-cycle fatigue of an extruded magnesium alloy

This paper presents a novel mesoscopic damage model to characterize the low-cycle fatigue damage evolution of an extruded AZ31 magnesium (Mg) alloy, taking into account the effect of twinning. The damage caused by the slip bands (SBs)–twin boundaries (TBs) and SBs–grain boundaries (GBs) interactions is treated based on the Tanaka–Mura model and the Eshelby inclusion theory. Strain energy values at the TBs and GBs are defined as the TB and GB damage variables, respectively. Explicit formulae for the TB and GB damage evolution are derived from the characteristics of the {101¯2} extension twin and the basal texture. A fracture energy-based crack initiation criterion is established, and the proposed damage model is validated against the existing experimental results. The model demonstrates its ability to reproduce the damage evolution processes, and the predictions of the crack initiation life are within the twice error band.

Deformation mechanisms of low cycle fatigue of a fourth generation Ni-based single crystal superalloy

Ni-based single-crystal superalloys are extensively employed in turbine blades for aircraft and industrial gas engines. The blades are subjected to complex thermal and stress impacts during service, which may cause sudden low-cycle fatigue damage and subsequent flight accidents. To investigate the relationship between the microstructure and mechanical properties, fatigue-damaged microstructures are compared under cyclic deformation at 800 and 900 °C using combined electron microscope characterizations. With an increase in temperature, the deformation is more concentrated in the γ matrix channels and the cyclic deformation behaviors stabilizes, whereas cutting the γ′ phase becomes difficult with decreasing slip bands. In addition, the significance of interfacial dislocation networks in enhancing cyclic stability and hindering cyclic tension–compression asymmetry is discussed.

Life prediction model based on toughness exhaustion under combined high and low cycle fatigue loading

It is very important to establish a life prediction model that evaluates the combined high and low cycle fatigue (CCF) damage of materials. Based on the toughness exhaustion, this paper develops a CCF life prediction model considering loading interaction effect. The loading interaction factor is proposed to reflect the interaction effect between high cycle fatigue and low cycle fatigue. The proposed model does not require any additional material parameters and is convenient for application. The experimental data of four materials including GH4033 Ni-basis alloy, TC11 titanium alloy, LY12-CZ aluminum alloy, and 45 steel are applied to verify the proposed model. Comparing the prediction results of the proposed model with the Miner’s rule and the T-K model, the results show that the predicted results of the proposed model are more satisfactory.

Low cycle fatigue properties assessment and damage influence on DP 500/800 steel sheet

A dual phase (DP500/800) steel sheet (1.6 mm thickness) was evaluated by means of low cycle fatigue (LCF). The fatigue properties of the material were assessed by means of the cyclic elastic modulus determination at half-life as well as by the plastic strain amplitude measurements. Both methods show a good correlation and high reliability, however, the plastic strain amplitude approach tends to fit better to the experimental results. From a parametric analysis performed, it was observed that the plastic strain amplitude approximation could be more suitable to assess the fatigue properties for LCF of the material due to an improved correlation of the computed cyclic elastic modulus in comparison to the cyclic elastic modulus measurements at half-life. Both methods showed that, for strain amplitudes higher than εa = 0.004, the cyclic elastic modulus tends to be lower than 210 GPa, meanwhile for lower strain amplitudes, the cyclic elastic modulus tends to increase. An evaluation by X-ray Diffraction technique allowed to determine that the increment of residual equivalent strain contributes to the cyclic elastic modulus diminution.

Low cycle fatigue lifetime and deformation behaviour prediction of nickel-based single crystal superalloy considering thickness debit effect

Through stress-controlled low cycle fatigue (LCF) experiments, LCF performances for thickness debit effect of nickel-based single crystal superalloy DD6 with [001] orientation are investigated. Based on scanning electron microscope (SEM) observation, the formation mechanism of thickness debit effect and the damage mechanism under LCF loads are revealed. Then, considering the thickness debit effect of nickel-based single crystal superalloy DD6, an improved slip-based damage model is developed. Predicted LCF lifetimes are mainly within a scatter band of factor 2, and the predicted laws between LCF lifetimes and wall-thicknesses are in good agreement with the experimental data, which verifies the rationality and accuracy of the thickness-sensitive LCF damage model established in this paper. Furthermore, a damage-coupled crystallographic constitutive model reflecting thickness debit effect is developed. For DD6 specimens with different wall-thicknesses, the predicted results of the stress-controlled LCF deformation behaviours including the whole-lifetime ratcheting behaviours show good agreement with the experimental data.

Influence of ground motion duration on seismic behavior of RC bridge piers: The role of low-cycle fatigue damage of reinforcing bars

This paper assesses the influence of ground motion duration on seismic behavior of reinforced concrete (RC) bridge piers using spectrally equivalent short- and long-duration ground motions. Special attention is paid to the role of low-cycle fatigue damage of reinforcing bars. To this end, an experimentally validated nonlinear fiber-based beam-column element considering buckling and low-cycle fatigue of longitudinal bars is adopted for nonlinear dynamic analyses and fragility modeling. An advanced material level damage index is used to account for both the maximum response (strain damage) and cumulative damage (low-cycle fatigue damage of longitudinal bars). The dynamic analysis results indicate that the strain damage is the major failure mechanism for RC bridge piers under short-duration ground motions. Under long-duration ground motions, by contrast, the strain damage is prominent at the early excitation stage, while the low-cycle fatigue damage may dominate the late excitation stage. In particular, the role of low-cycle fatigue is more prominent for RC bridges against long-duration ground motions with significant durations beyond 50 s and peak ground velocities over 30 cm/s. The fragility analysis demonstrates that, ignoring the low-cycle fatigue damage of longitudinal bars will obviously underestimate the seismic fragility of RC bridge piers under long-duration ground motion, and the influences is more significant at more severe damage states. Therefore, the low-cycle fatigue damage of reinforcing bars is one of the main failure modes of RC bridge piers under long-duration ground motion, and should be considered in the seismic design,

An experimental validation of unified mechanics theory for predicting stainless steel low and high cycle fatigue damage initiation.

An experimental campaign of stainless-steel specimen tests has been completed. Three different types of tests have been performed: UTS (Ultimate Tensile Strength), LCF (Low Cycle Fatigue) and HCF (High Cycle Fatigue). This experimental campaign has been conceived and performed to validate the fatigue damage initiation prediction capabilities of UMT (Unified Mechanics Theory). Two different formulations have been used for LCF and HCF. For the latter, a modification to the existing approach is proposed in this paper. Good agreement has been found between UMT predictions and experimental results.

Assessment of prior fatigue damage and a new approach to predict remanent creep rupture of P92 steel

The quantitative assessment of prior fatigue damage plays a critical role in predicting the remanent creep life of as-service high-temperature components. However, the creep prediction models widely used in engineering show inherent limitations in remanent creep life prediction. In this study, under the framework of continuum damage mechanics, different types of damage variables are proposed and introduced into the four conventional creep life models to evaluate their capabilities to capture prior fatigue-effected creep life. Results show that four creep life models with tensile elongation-based damage variable all give more accurate predictions of creep life than the models coupled with other damage variables irrespective of prior low cycle fatigue and creep-fatigue damage. It is remarkable that the tensile elongation-based damage variable can be easily obtained by low-cost tensile tests. Additionally, comparisons of prediction ability among different creep models illustrate that Wilshire model incorporated with tensile elongation-based damage variable is considered as the best approach to assess the remanent creep life after various cyclic loadings, which will enrich the existing creep life design by considering prior fatigue damage.

Experimental research on seismic behaviors of RC columns considering buckling of HRB600 longitudinal steel bars

The inelastic buckling of longitudinal bars and premature fracture that followed can always be observed in laboratory research and earthquake damage of reinforced concrete (RC) columns. The buckling deformation and accompanied fracture of HRB600 high-strength steel bars are more significant than those of conventional reinforcing bars, but the buckling properties of HRB600 reinforcement and the influence of premature fracture on the seismic performance of RC columns are far from clear. In this paper, low cyclic loading tests were conducted on six full-scale RC columns reinforced with HRB600 reinforcement by changing the slenderness ratios of longitudinal bars and the axial compression ratios of columns, and the lateral buckling displacements of longitudinal bars were measured by an identified method. Based on the lateral buckling displacements, the buckling behaviors of longitudinal bars were analyzed. It shows that cover concrete has a significant constraint effect on preventing buckling of HRB600 reinforcement. The inelastic buckling behaviors and premature fracture of HRB600 bars on the ultimate deformation capacity and ductility of RC columns were investigated according to the lateral buckling displacements and ductility coefficient. It is found that the increase of the slenderness ratio would cause larger buckling displacements making the local plastic deformation concentration and low-cycle fatigue damage of HRB600 reinforcement more serious, resulting in the premature fracture of longitudinal bars and decrease of ductility of RC columns. Furthermore, a series of individual bars accompanied by the RC columns were tested. Based on the average stress–strain curves, the effects of yield strength and slenderness ratio were discussed. Former researches of conventional longitudinal bars were involved to form a comparison group with HRB600 bars. The results indicate that the deformation capacity reserves of HRB600 reinforcement after 85% peak load were significantly lower compared with conventional bars. It is suggested to limit the application of RC columns reinforced with HRB600 longitudinal bars in high seismic intensity areas and improve the limitation on the slenderness ratio of high-strength steel bars.

Effect of twinning and precipitation on low-cycle fatigue damage behaviour of extruded AZ80 magnesium alloy

In this paper, the fatigue behaviour and failure mechanisms of extruded AZ80 magnesium alloy samples were studied with different initial structures. The results show that the twinning-twinning behavior was inhibited to a certain extent by fine grain and precipitates, but the initiation of fatigue cracks was promoted. Studies of the fatigue life and fracture mechanism show that both residual twins and precipitated phases can cause fatigue crack initiation, but less fatigue damage is caused by the twin-induced cracks than by second phase-induced.

Unified viscoplasticity model for type 316 stainless steel subjected to isothermal and anisothermal-mechanical loading

316FR-type low carbon stainless steel is usually used for many advanced gas cooled reactor (AGR) power plants which are subjected to operating temperatures in the range of 500–650 °C under thermo-mechanical loading, which may lead to isothermal low cycle fatigue (LCF) and thermal mechanical fatigue (TMF) damage. The strain controlled thermo-mechanical fatigue test with and without holding time was carried out for 316FR-type stainless steel under the temperature cycling between 500 °C and 650 °C, and the strain ranges are Δε = ± 0.4%, ±0.8%, ±1.0% and ±1.2%, respectively. Within the framework of Abdel Karim and Ohno model, an improved unified viscoplastic constitutive model (UVM) is proposed to simulate the cyclic plastic behavior of 316FR stainless steel. The improved UVM includes strain rate sensitivity, temperature rate dependence, static recovery, average stress evolution and strain range dependence of cyclic hardening. And then based on the radial return mapping and backward Euler integration methods, the implicit stress integration algorithm and the new expressions of the consistent tangent modulus are derived respectively, the improved UVM is implemented by a User Material Subroutine into ABAQUS software again. The good correlation between simulation results and experimental data is obtained.

Low cycle fatigue crack propagation and damage evolution of concrete beams reinforced with GFRP bar

This paper studies the low cycle fatigue (LCF) behavior of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) beams by utilizing experimental and analytical investigation. Static and LCF three-point bending tests were carried out on 12 over-reinforced GFRP RC beams and six under-reinforced steel RC beams. The failure modes, fatigue lives, load-deflection, strain, and crack propagation were analyzed. The fatigue life of the steel RC beam with the same maximum stress level was lower than the GFRP RC beam, while the GFRP RC beam illuminated a larger failure mid-span deflection. For GFRP RC beams, the average fatigue lives with the maximum stress levels Sσmax=0.85Pu, 0.70Pu, and 0.65Pu, were 896, 8491, and 19949, respectively (Pu = the ultimate static flexural loading capacity). The average fatigue life of the highest stress level (0.85Pu) was approximately 22 times the lowest stress level (0.65Pu). Bending shear failure, and concrete crush were the dominant fatigue failure mode for GFRP and steel RC beams. The relationship between fatigue stress range and fatigue life was investigated based on fitting and reliability analysis. The stress intensity factor of the type I crack of the GFRP RC beam was deduced theoretically. The fatigue crack clarified a three-stage development trend (crack initiation, stable crack propagation, unstable crack propagation). When the crack continued to expand until it ran through the whole section, the beam was damaged. The fatigue crack propagation was fitted according to the experimental data. The deflection, dynamic stiffness, and damage evolution law of steel and GFRP RC beams were deducted. The fatigue life prediction models based on crack propagation and damage evolution were derived.

Quantitative description of low-cycle fatigue damage accumulation in contact interaction zone by local strain evolution

The novel non-destructive method for quantitative description of low-cycle fatigue damage accumulation is expanded to a case of contact interaction in the stress concentration area. Investigated objects are plane aluminium specimens with the centred hole filled by cylindrical steel inclusion. The specimen is subjected to cyclic pull-push loading. The key point, that defines scientific novelty and powerfulness of the developed approach, consists of involving local deformation parameters as current damage indicators. Required strain values follow from distributions of all three displacement components along the filled hole edge measured by reflection hologram interferometry. The data, which are derived at different stages of low-cycle fatigue for the single specimen, provide normalized dependencies of local strain values from number of loading cycle, which are a source of damage accumulation functions. These functions are constructed for the specimen with the filled hole and geometrically analogous specimen with the open hole. Obtained data quantitatively describe a difference in damage accumulation rates for two cases.

Evaluation of fatigue and creep-fatigue damage levels on the basis of engineering damage mechanics approach

Progressive degradation of material mechanical properties in the low cycle fatigue (LCF) and creep-fatigue (CF) interaction at high temperature affects the safe operation of in-service materials. By considering material degradation, the present work aims to establish a method for evaluating LCF and CF damage levels with wide applicability. Material-level data accumulations as well as theoretical foundations of LCF and CF are presented, including interrupted LCF and CF tests, subsequent tensile tests and energy-based damage models. A damage variable representing the degradation of material mechanical properties is then defined based on the tensile plastic strain energy density (TPSED), the physical mechanism of which is reflected in the microstructure evolution and fracture appearance. By taking into consideration the material degradation threshold in the traditional damage summation rule, a new three-dimensional (3D) damage interaction diagram is established, where the additional third axis indicates the material degradation level. Finally, taking GH4169 alloy and P92 steel as examples, this work demonstrates the implemented procedures of damage level evaluation, which has been validated via the experimental data.

Low Cycle Fatigue Crack Damage Behavior of TC21 Titanium Alloy with Basketweave Microstructure

Low cycle fatigue (LCF) crack initiation, propagation and damage behaviors of TC21 alloy with basketweave microstructure were investigated. The process of LCF damage was observed by a long-focus optical microscopic imaging system, and fatigue crack propagation was analyzed through in-situ SEM fatigue. The results indicated that LCF crack damage displayed different sensitivity to cyclic stress. LCF microcracks initiated from slip bands and propagated through the microcrack coalescences at high stress, while LCF cracks tended to initiate at the αL/β interface and connect with these interface microcracks. Furthermore, the LCF damage model was established on the basis of Lemaitre damage theory. When the maximum stress exceeded yield stress, LCF damage increased sharply and fatigue life decreased significantly, which agreed with experiment data.

Energy-based design method for special concentrically braced frames considering low-cycle fatigue damage of braces

Energy-based design methods have been widely used to evaluate structural performance in last few decades. However, energy-based design methods of SCBF proposed by previous researches did not fully consider the low-cycle fatigue damage of braces. To study energy-based design method of SCBF considering the effect of low-cycle fatigue damage of braces, inelastic dynamic time history analysis of six SCBF models is performed and experimental data is evaluated in this paper. Energy input spectrum of SCBF is modified and energy demand of braces are proposed by dynamic time history analysis. Energy dissipation capacity of braces based on low-cycle fatigue damage of braces is set up through the results of tests on braces and braced frames. A practical energy-based design method of SCBF is proposed by obeying the principle that energy demands are smaller than energy dissipation capacity of braces. An integral design process of energy-based design method of SCBF is shown in this paper by a designed SCBF example. The configuration detailing of braces meeting the regulations of AISC 341 is relatively stricter compared with the security domain of proposed energy-based design method. The configuration detailing of braces is not only related to ductility of the structure, but also intensity of design ground motion according to the energy-based design method proposed by this paper.

Research on thermomechanical fatigue life prediction of regenerative cooling thrust chamber

The ratcheting effect of the liner wall structure in the thrust chamber of liquid rocket engine under cyclic load is studied, and its service life is predicted. Firstly, the 3-D heat transfer analysis of the wall of the thrust chamber is carried out while explaining the mechanism of its "dog room" failure. Based on the results of the heat transfer analysis, the stress-strain evolution of the structure under cyclic load is analyzed by nonlinear plane strain finite element method. According to the finite element analysis results, the ratcheting effect of the liner wall structure is described and the ratcheting damage is calculated. The low cycle fatigue damage is calculated by using modified Morrow model, and the creep damage is also calculated using Norton model. Finally, the total damage of thrust chamber liner wall is calculated by using Miner linear cumulative damage law and the thermomechanical fatigue life of the structure is estimated. The result shows that the middle point of the lower surface of the liner wall will fail first, and the calculated service life is 33 times, which is good agreement with its actual service life. In the total damage of the weak point, ratcheting damage, creep damage and low cycle fatigue damage account for 52%, 32% and 16% respectively, indicating that the ratcheting effect is the main reason for the failure of the thrust chamber structure. The research results of this paper provide important engineering reference for the structural optimization design and rapid life prediction of regenerative cooling thrust chamber of liquid rocket engine and the future reusable aerospace power.

Employing sequential experiments to gain insights on the interaction between creep and fatigue damage in Ni‐base superalloys

AbstractThe interaction between creep and fatigue damage in Ni‐base superalloy CMSX‐8 was explored using a sequential workflow that decouples creep and fatigue steps to quantify how accumulated creep damage interacts with subsequent isothermal low‐cycle fatigue (LCF) and vice versa. Two workflows were considered: creep followed by LCF and LCF followed by creep. For the first workflow, the subsequent LCF was evaluated at temperatures of 20°C, 750°C, and 1100°C. It was found that the extent of deleterious interaction of prior creep on LCF depended on increasing subsequent fatigue test temperature. For the LCF followed by creep, fatigue tests were first conducted at 20°C and 1100°C to 60% of life, and then creep was conducted at 800°C, where primary creep is promoted, or 900°C, where primary creep is absent. LCF damage accumulated at 1100°C accelerated creep and decreased ductility, while fatigue damage at room temperature had minimal effect on the creep behavior.