Extremely Low Cycle Fatigue Research Articles

Effect of Strain Rate on the Extremely Low-Cycle Fatigue of Fe-15Mn-10Cr-8Ni-4Si Bidirectional-TRIP Steel

Effect of Strain Rate on the Extremely Low-Cycle Fatigue of Fe-15Mn-10Cr-8Ni-4Si Bidirectional-TRIP Steel

A MICROMECHANICAL STUDY ON DP600 STEEL UNDER EXTREMELY LOW-CYCLE FATIGUE

A MICROMECHANICAL STUDY ON DP600 STEEL UNDER EXTREMELY LOW-CYCLE FATIGUE

Fracture prediction for square hollow section braces under extremely low cycle fatigue

This paper examines the extremely low cycle fatigue (ELCF) fracture of concentrically loaded square hollow section (SHS) braces subjected to cyclic loading. Numerical analyses are presented for both individual bracing members and bracing members integrated into concentrically braced frames (CBFs). The behaviour of the individual members was predicted using solid finite element (FE) simulations that employed a ductile fracture model and a nonlinear damage evolution rule. The solid FE model, which was validated using data from experiments, could adequately predict both the hysteretic response and the ELCF fracture cracking process. The coupled effects of instabilities (i.e. local and global buckling) and fracture on the ELCF performance of the braces were assessed, and the rotation capacity prior to fracture was quantified. This quantified rotation capacity was then incorporated into fibre-based FE models of CBFs as a member-level fracture criterion. The structure-level simulations were able to accurately capture the complex interactions between the frame components, i.e. the columns, beams, brace–gusset–plate​ connections and beam-to-column connections, and hence replicate the overall behaviour of CBFs, specifically, two-storey chevron braced frames. The influence of cross-section and member slenderness was evaluated and the importance of considering both in the development of cross-section slenderness limits was highlighted. The combined member- and structure-level simulation approach is proposed as an accurate and efficient means of assessing the seismic performance of CBFs.

Effect of Pre-corrosion by Salt Spray on Extremely Low Cycle Fatigue Performance of HRB400E Seismic Steel Bar

Effect of Pre-corrosion by Salt Spray on Extremely Low Cycle Fatigue Performance of HRB400E Seismic Steel Bar

Extremely Low Cycle Fatigue Failure Behavior of Box-column to I-beam Welded Joints

In this paper, cyclic loading tests are carried out to study the extremely-low-cycle fatigue (ELCF) failure behavior of the beam-to-column welded joints of steel structures subjected to severe seismic excitation. Firstly, the fatigue crack evolution and local strain of the weld zone obtained from experiments are adopted to investigate ELCF failure behavior for steel structures. In these experiments, three large scale specimens of box-column to I-beam connection are controlled by different cycle displacement ranges greater than the yield displacement. Secondly, the crack initiation and propagation law as well as the damage and deterioration mechanism are examined; then, the preliminary criterion for crack initiation for the box-column joint is proposed. Finally, failure characteristics and strain distribution of the box-column joint are analyzed. This study shows that the ELCF failure of the box-column to the I-beam joint is multiaxial and nonproportional. Based on the crack initiation and propagation along the thickness direction of the beam flange, the crack macro-penetration mode can be divided into two categories, i.e., standard failure mode and mixed failure mode. Moreover, load drop, change rate of load drop, and loading amplitude are key factors of the damage mechanism.

Influence of Microstructure on Low-Cycle and Extremely-Low-Cycle Fatigue Resistance of Low-Carbon Steels

The goals of this study were to quantify and explain the effects of microstructure on the resistance of low-carbon steels to low-cycle fatigue and to extremely low-cycle fatigue (ELCF). Three different microstructures (ferrite–pearlite, ferrite–martensite, and ferrite–bainite–martensite) were tested, and their fatigue properties were analyzed using the strain-based Coffin–Manson model and an energy-based model. According to the Coffin–Manson model, ferrite–pearlite showed the best ELCF resistance, whereas in the energy-based model that considers the effect of tensile strength ferrite–bainite–martensite revealed the highest ELCF resistance. At similar tensile strength, ferrite–bainite–martensite had longer ELCF life than ferrite–martensite; the difference may be a result of the smaller strain incompatibility between bainite and ferrite than between ferrite and martensite. In all three microstructures, cracks initiated at the surface and propagated into the interior; this result indicates that fracture mode was not altered during cyclic loading at high strain amplitudes. Ferrite–martensite microstructure developed many sub-cracks surrounding a main crack; they could facilitate propagation of a main crack, and thereby degrade fatigue life at high strain amplitudes.

Prediction of ductile fracture for circular hollow section bracing members under extremely low cycle fatigue

The fracture behaviour of concentrically loaded circular hollow section (CHS) bracing members under extremely low cycle fatigue (ELCF) is examined in this paper. Finite element (FE) models capable of predicting fracture initiation and propagation on cyclically loaded braces were developed. A structural steel ductile fracture criterion, together with a damage accumulation rule that can account for the effects of both stress triaxiality and Lode angle, was adopted in the FE models. The FE models were validated against the available test results from different experimental programmes and shown to provide an accurate prediction of both the hysteretic response and the ELCF fracture cracking process. The coupling effects of buckling and fracture on the ELCF performance of braces were assessed through a parametric study. This parametric study examined the influences of the geometry, material and manufacturing process on the local and global deformation, and the ductility of the braces. Predictive equations for the localized strains and member ductility were proposed based on a plastic hinge model. The seismic performance of a chevron braced frame was also evaluated in terms of storey drift angle according to the requirements of the current design code.

Extremely-Low-Cycle Fatigue Damage for Beam-to-Column Welded Joints Using Structural Details.

The multiaxial fatigue critical plane method can be used to evaluate the extremely-low-cycle fatigue (ELCF) damage of beam-to-column welded joints in steel frameworks subjected to strong seismic activity. In this paper, fatigue damage models using structural detail parameters are studied. Firstly, the fatigue properties obtained from experiments are adopted to assess ELCF life for steel frameworks. In these experiments, two types of welded specimens, namely, plate butt weld (PB) and cruciform load-carrying groove weld (CLG), are designed according to the structural details of steel beam and box column joints, in which both structural details and welded factors are taken into account. Secondly, experiments are performed on three full-scale steel welded beam-to-column joints to determine the contribution of stress and/or strain to damage parameters. Finally, we introduce a modification of the most popular fatigue damage model of Fatemi and Socie (FS), modified by us in a previous study, for damage evaluation, and compare this with Shang and Wang (SW) in order to examine the applicability of the fatigue properties of PB and CLG. This study shows that the modified FS model using the fatigue properties of CLG can predict the crack initiation life and evaluate the damage of beam-to-column welded joints, and can be subsequently used for further investigation of the damage evolution law.

Extremely - low cycle fatigue fracture of Q235 steel at different stress triaxialities

This study presents an experimental and numerical investigation on the Extremely-Low Cycle Fatigue (ELCF) behavior of Q235 structural steel under different stress states and large strain amplitudes. A set of Q235 structural steel cylindrical specimens of different radii of curvature were selected to examine the effect of the triaxial state of stress on the fracture behavior. Cyclic axial tension-compression loading tests characterized by large strain amplitudes were conducted to obtain the hysteresis loops and the failure process by measuring both macroscopic and microscopic fracture morphologies. The results shows that, the failure behavior of Q235 steel in ELCF loading is a mixture of fatigue fracture and ductile fracture. Specimens with different stress triaxialities are characterized by different failure modes. A fracture criterion, namely the Combinatory Work Density Model (CWDM), was calibrated based on the test results. Furthermore, a cyclic plasticity constitutive model, i.e., the Chaboche model, was calibrated to describe the yield and cyclic hardening behaviors of the Q235 structural steel. Finite element (FE) simulations in the commercial software ABAQUS accounting the calibrated CWDM and Chaboche model were carried out to evaluate the fracture characteristics with different stress triaxialities and their stress-strain hysteretic curves under ELCF loading. The simulation results demonstrate that the developed FE model can reproduce the hysteretic characteristics and capture the failure process of Q235 structural steel. The proposed practical numerical tool can be used for the ELCF failure prediction in steel structures under complex stress state.

Damage Evolution Due to Extremely Low-Cycle Fatigue for Inconel 718 Alloy

This paper evaluates the damage evolution process under extremely low-cycle fatigue (ELCF). The study explores the damage behavior under different stress states. The influence of the multiaxial state of stress on the metal’s life is determined. Two different stress states were examined: (a) axisymmetric and (b) plane-strain. The study is based on the modified Mohr–Coulomb (MMC) ductile fracture criterion that was extended to cover the ELCF regime in a previous research study. Four distinctive geometries are designed to study the effect of different stress states on ELCF life and damage evolution. The damage model is calibrated for life prediction to agree with the ELCF experimental results. The investigation of the damage evolution behavior is dependent on equivalent plastic strain, stress triaxiality, Lode angle, and cyclic loading effect. The damage evolution is extracted from Abaqus finite element simulations and plotted versus the equivalent plastic strain. The damage accumulation shows nonlinear evolution behavior under cyclic loading conditions. SEM images were taken to further study the microscopic failure mechanisms of ELCF.

A comparison of seismic low cycle fatigue and extremely low cycle fatigue on steel moment frames with reduced beam section connection (RBS)

Damage to the connections of buildings with steel moment frames during past earthquakes indicates that the damage to some buildings cannot be justified by the mechanisms of common failure. This is due to the effects of low cycle fatigue (LCF) and extremely low cycle fatigue (ELCF) on the moment frame connections. On the other hand, studies on moment connections have mostly focused on the permitted connection capacity, and the issue of fatigue (LCF and ELCF) has not been considered in these types of connections. The present study focused on the effects of LCF and ELCF on a prequalified reduced beam section connection (RBS) in the steel moment frames of a 6-floor commercial complex and compared these two effects. The results showed that although the RBS connections of the studied structure were not damaged by LCF and ELCF, low cycle fatigue was effective when the behavior of the structure’s material was linear. The extremely low cycle fatigue index was significant when the connection’s material stresses, caused by an earthquake, exceeded the yield stress. In addition, the comparison of the damage ratios induced in the LCF method and the failure indices in the ELCF method on different floors indicated that the ratios of these two indices were consistent across all the floors.

Cyclic behaviour of double-tube buckling-restrained braces for boiler steel plant structures

An inner-stiffened double-tube buckling-restrained brace (BRB) is proposed for boiler steel plants in the low-to-medium seismicity regions. The test specimen is of 15.0 m length, consisting of a 15.0 m inner tube with inner stiffeners at both ends and a 12.2 m outer tube for lateral deformation restraint. The full-scale test was conducted to reproduce the cyclic behaviour of the proposed double-tube steel BRB in the plant structures at a practical manufacturing level. The structural performance of the proposed BRB under extremely low cycle fatigue (ELCF), including the strength, deformation capacity, hysteretic response and the failure mode, was investigated. The finite element (FE) model incorporating a material fracture model was established and verified, which could predict the fracture initiation and propagation accurately. The parametric study was carried out to further assess the influence of the stiffener arrangement, material property, gap size and controlling metric of the imperfection on the cyclic behaviour of the proposed BRB. The experimental and numerical investigations demonstrated that the proposed braces could achieve a stable and saturated hysteretic curve. The failure mode of the test specimen was the stress concentration induced fracture which initiated at the stiffener tips of the inner tube. On the basis of the parametric study, the optimized BRB could achieve a high equivalent ratio of critical viscous damping at the loading amplitude of 1/75 L.

Ultimate strength and failure characteristics research on steel box girders under cyclic-bending moments

The ultimate strength of hull girder is the most important safety guarantee. For a long time, ultimate strength research of ship hull girder is usually under monotonically increasing bending moment. In fact, under extreme ocean wave conditions, the hull girder is more likely to withstand extreme cyclic-bending moments. Under which, the ultimate bearing capacity of the hull girder may be dominated by cyclic buckling failure, extreme low-cycle fatigue failure or the coupling of the two failure modes. In this paper, the ultimate strength and failure characteristics of five steel box girder models are studied under two different kinds of cyclic-bending moments (repeated sagging and alternate sagging/hogging). The two box girder models subjected to alternate sagging/hogging bending moments seem to be fractured due to the extremely low-cycle fatigue. The rest of the three models exposed to cyclic sagging bending moments are collapsed by cyclic buckling accompanying accumulated plastic deformation. The experiment shows that the extreme cyclic-bending moments will significantly reduce the ultimate bearing capacity and fatigue limit of ship girder, and lead to disaster.

Elliptical hollow section steel cantilever beams under extremely low cycle fatigue flexural load – A finite element study

A comprehensive non-linear finite element (FE) study carried out on elliptical hollow section (EHS) steel cantilever beams of 1740mm2 cross-sectional area and 1500mm long under extremely low cycle fatigue (ELCF) uni-directional flexural load along major and minor axes separately is presented using the general FE package, Abaqus. The aspect ratio (major to minor axis diameter ratio), a/b and shell thickness, t of EHS beam models are varied between 1–2.33 and 4–6mm respectively. The effect of a/b ratio and section slenderness on cyclic rotation capacity and flexural over-strength of the EHS FE beam models is investigated in this study. It is observed that the effect of a/b on rotation capacity under major axis bending is significant. Also, the cyclic flexural over-strength is not significantly affected by a/b ratio. New slenderness limits for circular hollow sections under bending are proposed. Modified slenderness parameters for EHSs under bending based on equivalent circular hollow section approach are derived. Empirical expressions for predicting cyclic rotation capacity and flexural over-strength of EHS beams are derived based on the FE study.

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.

A unified material model for multiaxial ductile fracture and extremely low cycle fatigue of Inconel 718

This paper summarizes an extensive work of experimental and numerical studies of extremely low cycle fatigue (ELCF) on IN718 under room temperature. The ELCF is focused on low numbers of cyclic loading (fewer than 100cycles) of fatigue failure. The IN718 cyclic plasticity behavior and the Bauschinger effect are studied and simulated using the well-known nonlinear kinematic hardening law by J.L. Chaboche and his co-workers under different strain amplitudes and different stress states. Moreover, the Vocé isotropic hardening law was used in combination with the Bai-Wierzbicki plasticity model. The Bai-Wierzbicki plasticity model was used to capture the effect of different stress states on ELCF based on the stress triaxiality and Lode angle parameters. On the other hand, the modified Mohr–Coulomb (MMC) ductile fracture model for monotonic loading was extended by a new damage evolution rule to cover the ELCF regime. A new parameter was introduced to represent the effect of the cyclic loading at ELCF. The new parameter is responsible to capture the change of non-proportional loading direction between the current stress and the backstress tensors. A comparison between the experimental data and the finite element simulation results (by Abaqus/Explicit) shows excellent correlations. Lastly, a fractographic examinations and fracture modes simulations are presented.

Structural performance of elliptical hollow section (EHS) steel tubular braces under extremely low cycle fatigue loading - a finite element study

A comprehensive non-linear analysis of EHSs under extremely-low-cycle fatigue (ELCF) loading is necessary to accurately assess their cyclic energy dissipation, which is one of the primary factors in the selection of brace parameters, for enhanced seismic performance. This study emphasizes the cyclic response of twenty EHS finite element modeled steel braces of constant cross-sectional steel area, A and wall thickness, t, by employing a non-linear combined isotropic/kinematic hardening material model in Abaqus. Cross-sectional aspect ratio (major to minor axis diameter ratio, a/b) and non-dimensional global slenderness (λ¯) ranging between 1–2 and 0.3–2 respectively, are considered. Parametric studies are conducted to investigate the hysteresis behaviour of EHS models at various displacement ductility levels under cyclic axial displacement loading history based on the recommendations of ECCS. It is observed that cross-sectional aspect ratio has less significance on compressive resistance and energy dissipation values at cyclic displacements of higher displacement ductility levels for sections with non-dimensional global slenderness ratio greater than ~0.8. Design curves for post-buckling compressive resistance of HSS braces at various displacement ductility levels as per AISC LRFD methodology are also proposed.

Extremely-low-cycle fatigue behaviors of Cu and Cu–Al alloys: Damage mechanisms and life prediction

The extremely-low-cycle fatigue (ELCF) behaviors of pure Cu and Cu–Al alloys are comprehensively studied following the cyclic push–pull loading tests with extremely high strain amplitudes (up to ±9.5%). Compared with the common low-cycle fatigue (LCF) region, several unique features in the ELCF regime can be noticed, including the deviations of fatigue life from the Coffin–Manson law, the non-negligible proportion occupied by the cyclic hardening stage of the whole fatigue life, special microstructures formed by cyclic loading containing deformation twins, shear bands and ultra-fine grains and the transformation of fatigue cracking modes. All these characteristics indicate the existence of special interior fatigue damage mechanisms of ELCF. To help discover the new damage mechanisms under ELCF, a model of fatigue life prediction with a hysteresis energy-based criterion is proposed. Based on the analysis of the experimental and modeling results, two intrinsic factors determining the ELCF properties were concluded: the capacity of ELCF damage, and the defusing and dispersion ability of the external mechanical work. The former can be evaluated by a parameter of the model called the intrinsic fatigue toughness W0, which is related to the microstructure evolution condition, the cyclic hardening ability, the deformation homogeneity and possibly the static toughness. The latter can be represented by the damage transition exponent β, which can be enhanced by improving the planarity, reversibility and uniformity of plastic deformation, reflecting the decline in the degree of surface damage and the dispersion of fatigue cracks. For Cu–Al alloys with increasing Al content, cooperation between an increasing damage capacity and a decreasing damage accumulation rate leads to a comprehensive improvement in the ELCF properties.

Ductile crack initiation and propagation in steel bridge piers subjected to random cyclic loading

Results from five cyclic tests of steel bridge piers are presented to examine the extremely low-cycle fatigue (ELCF) behavior of steel bridge piers under random cyclic loading. It is observed that using test results of constant cyclic loading to predict the ELCF behavior under random loading may be not effective. In this study, the random cyclic loading patterns are determined using dynamic analytical results. The effect of various parameters, including axial force ratio, earthquake ground motion type and repeated earthquakes, is investigated. The dynamic analysis suggests that all of these parameters are shown to have a large influence on ELCF behavior of structures. The test data reveal that the sudden increase or decrease displacement amplitude has a significant effect on the ELCF behavior, including the ductile crack initiation, propagation and final failure. Meanwhile, a four staged failure criterion is presented and effectively employed to investigate the ductile fracture of steel bridge piers with thick-walled box section.

Extremely low cycle fatigue prediction of steel beam-to-column connection by using a micro-mechanics based fracture model

Beam-to-column connections in steel moment resisting frames may suffer extremely low cycle fatigue (ELCF) during earthquakes. The cyclic void growth model (CVGM), a micro-mechanics based fracture model, was adopted to predict ELCF fracture of the beam-to-column connections. The validity of the model was verified by the experimental results of nine full-scale connection tests. In addition, refined finite element model was employed to simulate the cyclic behaviors of the connection tests, and the CVGM fracture index was calculated based on the stress and strain time histories. The number of cycles and the cumulative deformations to ELCF fracture predicted by CVGM agreed well with the experimental results. The presented methodology showed reasonable good accuracy to predict ELCF fracture of beam-to-column connection under inelastic cyclic loadings.