Low Cycle Fatigue Performance Research Articles

Experimental study of mechanical properties of beam-column joint of a replaceable energy-dissipation connector-precast concrete frame

A type of replaceable energy-dissipation connector - precast concrete frame is proposed, in which the replaceable energy dissipation connectors are assembled on the upper and lower sides of the beam end with a direct load-transfer path. The connectors can induce plastic deformation of the frame concentrated in the connectors themselves, while the main structural members, such as beams and columns, can remain elastic under strong earthquakes. Additionally, the seismic rehabilitation of the frame could be easily achieved by replacing the damaged connectors. Pseudo-static tests on an exterior beam-column joint of the frame were conducted, including the initial working condition and the seismic rehabilitation working condition. The test results revealed that a stable hysteretic property could be obtained in the joint, while a high energy-dissipation capacity was also confirmed. Plastic deformation was concentrated in the connectors, while a few cracks could be seen in the concrete components. The seismic rehabilitation working condition revealed that the initial stiffness and the hysteretic property could remain the same as those of the initial working condition. The formula for the initial rotational stiffness of the joints is derived at the end of the paper, indicating that the calculated results of the test specimens are consistent with the test results. • A new type of beam-column joint named replaceable energy dissipation connectors-fabricated concrete frame (REDC-PCF). • Construction and rehabilitation method of the REDC-PCF. • Construction of the REDC with buckling-restrained devices. • Stable hysteretic property and high low-cycle fatigue performance on the REDC-PCF.

Influence of uniaxial and biaxial pre-straining on the low cycle fatigue performance of DP590 steel

The present work aims to examine the low cycle fatigue (LCF) behavior of dual-phase (DP590) steel subjected to different pre-straining (uniaxial and equi-biaxial) paths. The LCF tests reveal all specimens showed continuous cyclic softening throughout the fatigue life. However, the rate of cyclic softening is higher for the equi-biaxial pre-strain specimen. The rotation of one maximum shear stress plane during fatigue cycling after equi-biaxial pre-straining introduces non-proportional loading condition, thereby significantly reducing the fatigue life. The larger lattice rotation and in-grain misorientation due to the non-proportional loading is notable for the equi-biaxial pre-strain specimen.

Experimental study on the cumulative damage constitutive model of high-performance steel Q345GJ under cyclic loading

GJ series steel is a new type of high-performance structural steel, which has emerged in China steel construction, and it has been widely utilized in steel-framed building structures. To investigate the low cycle fatigue performance and cumulative damage behaviors and find a suitable constitutive relationship of GJ series steel under cyclic loading, a total of eighteen Q345GJ steel low cycle fatigue experiments have been carried out. The mechanical behavior of Q345GJ steel were discussed, including monotonic loading behavior, hysteresis loading behaviors and energy dissipation capacity. Based on the cyclic behavior of GJ series steel, a modified cumulative damage model was recommended. Then, with comparison of the Q345GJ tests data (including the data in public papers) under various loading systems, the model proposed in this paper is proved correct and can be used to simulate the cyclic behavior of Q345GJ members.

Low-cycle fatigue performance of high-strength steel reinforcing bars considering the effect of inelastic buckling

A comprehensive experimental study was carried out to examine the low-cycle fatigue performance of ASTM A1035 Grade 690 rebars under cyclic-strain reversals with total strain amplitudes ranging from 1% to 4%. 12.7- and 15.8-mm diameter unmachined rebars were tested. To evaluate the effect of inelastic buckling on the low-cycle fatigue performance, bar unsupported length was varied between 6db and 15db in 3dbincrements, where db is the bar diameter. Rebar buckling was not completely prevented even in specimens with bar unsupported length of 6db, hence cyclic stress-strain responses were unsymmetrical for all the specimens. However, decreasing the strain amplitude and bar unsupported length generally increased the fatigue life and total energy dissipation of ASTM A1035 Grade 690 reinforcing bars. Existing strain and energy-based fatigue-life models’ constants were calibrated using the generated experimental fatigue data. The proposed models are applicable to ASTM A1035 Grade 690 rebars subjected to cyclic-strain reversals with total strain amplitude ranging from 1% to 4%. The results revealed that utilizing the previous fatigue-life models with constants calibrated using data obtained from tests on other types and grades of steel with nearly identical monotonic tensile stress-strain responses compared to that of ASTM A1035 Grade 690 steel would lead to inaccurate fatigue life predictions. The effect of inelastic buckling was incorporated into the proposed models by correlating their constants with a buckling parameter. Based on the proposed models’ predictions, ASTM A1035 Grade 690 reinforcing bars were found to have the potential to be used in reinforced concrete columns designed for a maximum target ductility demand of 2 provided that the center-to-center spacing between the transverse reinforcements is limited to 6db.

An efficient approach for optimum shape design of steel shear panel dampers under cyclic loading

The low-cycle fatigue performance of shear panel damper (SPD) highly depends on the geometry of its shape and the criterion considered for its design. The main contribution of the current study is to find the optimum shape of the SPD subjected to cyclic loading by considering two different objective functions. The maximum equivalent plastic strain and the ratio of energy dissipation through plastic deformation to the maximum equivalent plastic strain are selected as the first and second objective functions, respectively. Since the optimization procedure requires high computational efforts, a hybrid computational approach is used to perform two paramount phases of estimating the inelastic responses of the SPD and solving the optimization problem. In the first phase, as an alternative for the time-consuming finite element analysis of the SPD, a weighted-support vector machine model is developed to predict the inelastic responses of the SPDs during the optimization process. In the second phase, the optimum shape of the SPD is found by using the whale optimization algorithm (WOA). The results indicate that both design criteria lead to the optimum-shaped SPDs with a significant improvement in their low cycle fatigue performance in comparing with the initial rectangular shape while a slight reduction in their energy dissipation capacity. Moreover, the second design criterion is slightly better in the performance improvement of the optimum-shaped SPDs compared with the first one. In addition, the weighted-based SVM approach can accurately predict the inelastic responses of the SPDs under cyclic loading, and its combination with WOA results in finding the optimum solutions quickly.

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

Low Cycle Fatigue of an Ultrafine Grained AA5083 Aluminum Alloy Composite Produced by Cryomilling

Low cycle fatigue (LCF) properties were investigated for a novel cryomilled AA5083 aluminum composite with duplex coarse and ultrafine grain sizes and reinforced with boron carbide particulates, referred to as trimodal material. Fully reversed cyclic tests were conducted under plastic strain control at plastic strain amplitudes from 0.15 to 0.6 pct using a constant plastic strain rate in a servo-hydraulic testing system. A nonlinear elastic modulus was used to calculate the elastic contribution to the measured total strain. The LCF performance of this trimodal material is compared to previous results for unreinforced AA5083 aluminum alloy with bimodal grain size (85/15 pct CM/UM) and its coarse-grained wrought counterpart, AA5083-H131. Stress response curves for the trimodal material revealed slow hardening until failure associated with the presence of particulate reinforcements. The very small asymmetry between tension and compression stresses reflects a lack of strain localization beyond the initial cycles. The trimodal and 85/15 pct CM/UM alloys have similar and superior low cycle fatigue strength compared to AA5083-H131. From the Coffin-Manson plot, the trimodal material has a shorter fatigue life than 85/15 pct CM/UM alloy and AA5083-H131 for high plastic strain amplitudes, but nearly identical life at low amplitudes. Microcracks were observed near the dominant crack on trimodal specimen surfaces at failure. Back-scattered images revealed that particulates altered the crack propagation direction; cracks nearly always propagated around particulates.

Experimental and numerical investigations on seismic performance of RC bridge piers considering buckling and low-cycle fatigue of high-strength steel bars

In order to promote the application of high-strength steel bars (HSSB) in reinforced concrete (RC) bridge structures, the mechanical properties of HSSB as well as seismic performance of high-strength RC piers were investigated by experimental study and numerical analysis. First, monotonic and low cycle fatigue tests of HRB400E and HTRB600 steel with different slenderness ratios (L/D) were conducted to comparatively study their mechanical properties. Then, quasi-static cyclic tests of seven rectangular RC piers were conducted to study the effects of concrete cover, longitudinal reinforcement yield strength, concrete strength and axial load ratio on seismic behavior of RC piers. Finally, a fiber-based beam-column element was used to simulate the mechanical behavior of steel material and nonlinear response of RC piers. Material tests indicate that HTRB600 steel has lower uniform and fracture elongations, as well as inferior low-cycle fatigue performance than HRB400E steel. Increase of the slenderness ratio (L/D) severely weakens low-cycle fatigue life of steel bars, and the low-cycle fatigue parameters of steel can be fitted for each slenderness ratio, respectively. Even though HTRB600 steel has relatively lower ductility and inferior low-cycle fatigue performance, the RC piers with HTRB600 steel still have higher or at least comparable deformation capacity than that with HRB400E steel. This results from the reduction of strain demands of longitudinal bars by the utilization of HSSB in RC piers. Removing the concrete cover neighboring the longitudinal bars in the plastic hinge region has trivial impact on bar buckling and ultimate displacement of RC piers, which confirms that the concrete cover has already spalled off prior to the initiation of longitudinal reinforcement buckling. With identical steel strength and tie configuration, the ultimate displacement of RC pier with C80 concrete is significantly lower than that with C40 and C60 concrete, while the latter two have similar deformation capacity. Increase of axial load ratio (from 0.06 to 0.18) obviously reduces ultimate displacement of RC piers, since the concrete in the compression zone endures greater compressive stress under higher axial load and thus compressive failure occurs earlier. The ReinforcingSteel material model in OpenSees is calibrated by experimental data to accurately simulate the buckling and low-cycle fatigue properties of HRB400E and HTRB600 steel. The fiber-based finite element model (FEM) can predict the strain development of longitudinal bars of RC piers under cyclic loading, and the resulting low-cycle fatigue damage of steel material as well as strength degradation of RC piers. Combined with experimental study and FEM, this paper reveals the influence mechanisms of different factors on the seismic performance of RC piers in detail.

Orientation-dependent low cycle fatigue performance of nickel-base single crystal superalloy at intermediate temperature range

Slip deformation is the predominant fatigue damage form of nickel-based single crystals at intermediate temperature range (near 760℃). Under different crystal orientations, the dominant slip system may be an octahedral or cubic slip system. This paper explores the dominant slip systems under different crystal orientations through crystal plastic finite element analysis, and determines the fatigue damage parameter that can characterize both the octahedral deformation and the cubic deformation. The results show that within a certain orientation range close to the <111> orientation, the dominant slip system of the nickel-based single crystal is the cubic slip system. For an orientation far deviating from the <111> orientation, the dominant slip system is the octahedral slip system. Through finite element calculation, this paper gives the distribution diagram of the dominant slip system in the standard pole figure. The fatigue data of nickel-based single crystals with different orientations in the existing literature are used for verification, and the results show that the dominant slip system can be effectively determined by using the distribution diagram, and the proposed fatigue damage parameter can effectively characterize the fatigue damage of different slip systems. Compared with the condition where the distribution of the dominant slip system is not considered, the method proposed in this paper has effectively improved the fatigue life prediction ability.

Influence and Sensitivity of Temperature and Microstructure on the Fluctuation of Creep Properties in Ni-Base Superalloy.

In this work, the sensitivity zone of microstructure and temperature for precipitation-strengthened nickel-based superalloys, used for turbine applications in aero-engines, has been firstly established. Heat treatment experiments with different solution temperatures were carried out. The microstructure evolution and creep residual strain sensitivity, low cycle fatigue properties, and tensile properties are analyzed, and the essential reason for the fluctuation of the mechanical properties of nickel-based superalloys was revealed. The main results obtained are as follows: following subsolvus solution heat treatment with a temperature of 1020 °C, samples have a high primary γ′I phase content, which is beneficial to low creep residual strain. Above the supersolvus solution temperature of 1040 °C, the creep residual strain value and low cycle fatigue performance fluctuate significantly. The essential reason for the dramatic fluctuation of performance is the presence of γ′ phases in different sizes and quantities, especially following the solution heat treatment in the temperature-sensitive zone of the γ′I phase, which is likely to cause huge fluctuations in the microstructure of tertiary γ′III phases. A zone of particular sensitivity in terms of temperature and microstructure for the γ′I phase is proposed. The range of suitable solution temperatures are discussed. In order to maintain stable mechanical properties without large fluctuations, the influence of the sensitivity within this temperature and microstructure zone on the γ′ phase should be considered.

Characterization of Closed‐Cell Aluminum Foam‐Polyurethane Composites under Cyclic Compression

Herein, the mechanical properties of closed‐cell aluminum foam‐polyurethane composites (AF‐PU composites) under cyclic compression are studied experimentally. The results show that AF‐PU composites with PU coating at the bottom exhibit great deformation recovery ability and excellent reversible energy dissipation capacity, which is mainly associated with the presence of PU coating at the bottom. The high stiffness of AF‐PU composites is also possessed. The reversible energy dissipation of AF‐PU composites with PU coating at the bottom is primarily caused by the recoverable extrusion of PU coating at the bottom. Also, AF‐PU composites with PU coating at the bottom indicate an excellent low cycle fatigue performance, which verifies the reliability of AF‐PU composites with PU coating at the bottom utilized for repetitive energy dissipation applications. The results presented herein are conducive to broadening the scope of the application of closed‐cell AF.

Effect of substrate pre‐treatment on the low cycle fatigue performance of tungsten carbide‐cobalt coated additive manufactured 316 L substrates

AbstractNumerous studies already identified that the fatigue strength of 316 L parts processed by laser beam melting (LBM) is distinctly affected by the surface integrity. Among others, surface defects as well as residual stresses are of crucial importance. Despite new findings in the field of surface engineering of laser beam melting (LBM) parts, the low cycle fatigue strength of thermally sprayed additively manufactured substrates has not been in the focus of research to date. This study aims at evaluating the effect of different pre‐treatments onto 316 L substrates processed by laser beam melting (LBM) prior to the deposition of a high velocity oxy‐fuel (HVOF) sprayed tungsten carbide‐cobalt coating and their effect on the low cycle fatigue strength. Therefore, 316 L substrates were examined in their as‐built state as well as after grit blasting with regards to the surface roughness, strain hardening effects, and residual stresses. To differentiate between topographical effects and residual stress related phenomena, stress‐relieved 316 L substrates served as reference throughout the investigations. The tungsten carbide‐cobalt coated and differently pre‐treated 316 L substrates were mechanically tested under quasi‐static and dynamic load conditions. Besides the low cycle fatigue strength, the fracture toughness as well as the fracture mechanism were identified based on fracture surface analysis.

Experimental study of earthquake-resilient prefabricated opening-web steel channel beam-column joint with double FCPs

In order to facilitate floor assembly and pipeline paving, this paper puts forward a new kind of prefabricated opening-web steel channel beam-column joint with double flange cover plates (POWSCBCJ) which is based on the design concept of plastic damage concentration and replaceable damage components. Six quasi-static reciprocating loading tests were carried out on four joints, and the hysteretic curves, skeleton curves, slip curves and strain curves of each specimen were obtained. The effects of thickness of flange cover plate (FCP), the quantity of connecting bolts and the bolts spacing of FCP and other parameters on the seismic performance and post-earthquake repairable performance of the joint are mainly investigated, and the post-earthquake repairable function, and fatigue performance of the joint under low-cycle reciprocating load are evaluated. Experimental study shows that this kind of joint has good bearing capacity, seismic performance and low-cycle fatigue performance. The joint can transfer the plastic hinge to the replaced FCP by strengthening the flange of the cantilever beam and weakening the FCP, so as to protect the major components such as beams and columns, and the joint function can be quickly repaired by replacing the energy dissipation components after earthquake; the repaired joint also has good bearing capacity and seismic capacity. Each design parameter has great influence on the bearing capacity and energy dissipation capacity of the joint.

Low-cycle fatigue performance of remelted laser powder bed fusion (L-PBF) biomedical Ti25Ta

In this study, the fatigue performance of additively manufactured Ti25Ta, produced by laser powder bed fusion (L-PBF) using pre-mixed powder is investigated. Ti25Ta shows promise as a biomedical implant alloy, due to its high strength to elastic modulus ratio. However, the fatigue response of L-PBF Ti25Ta is yet unknown and understanding fatigue behaviour is crucial for cyclically loaded implants.The Ti25Ta alloy was produced employing single melt and remelt scanning strategies. It was shown that the remelt strategy had a positive effect on reducing the amount of remaining partially melted Ta particles from 2.07 ± 0.01 vol % to 0.22 ± 0.01 vol % while only slightly increasing the porosity from 0.15 ± 0.01 vol % to 0.37 ± 0.01 vol %. Furthermore, it was found that the remelt strategy resulted in alloy strengthening and a randomised orientation of the α′ lath microstructure.Machined fatigue samples were tested in the low-cycle fatigue regime under strain-controlled conditions. The alloy demonstrated a superior yield stress normalised fatigue performance compared with commercially pure (CP) Ti, and Ti–6Al–4V ELI, and was second only to pure Ta. However, the Ti25Ta L-PBF material retains less than half the elastic modulus of all the compared materials. The remelt samples showed an increased stress response due to their higher strength and an increased elastic modulus, however a reduced number of cycles to failure. This was attributed to reduced ductility and increased crack propagation rate. It is believed that remelt scan parameter optimisation can further enhance the performance of this alloy.

Local Strain-Based Low-Cycle Fatigue Assessment of Joint Structure in Steel Truss Bridges During Earthquakes

During the 2011 Tohoku Earthquake, a truss bridge joint structure was cracked due to large cyclic deformation, making us recognize the importance of assessing the seismic performance of joint structures in truss bridges from the viewpoint of low-cycle fatigue. In this study, seismic response analysis of an actual deck truss bridge was performed under different seismic waves, and local strain behavior generated at welded joints around a joint structure was clarified using a zooming analysis technique. The results revealed the possibility that welded joints for a lateral gusset-plate in a joint structure can be cracking sites during earthquakes. In addition, it was indicated that seismic isolation bearings can significantly reduce the local strain at the joint structure and improve its low-cycle fatigue performance. Moreover, as a simple countermeasure, weld toe treatment by grinding is also effective to decrease the possibility of low-cycle fatigue cracking at the joint structure.

The fatigue performance of titanium alloys joined via the powder interlayer bonding method

This study investigated the fatigue performance of two forged variations of α + β titanium alloys, namely Ti-6Al-4V (Ti-6-4) and Ti-6Al-2Sn-4Zr-6Mo (Ti-6-2-4-6) joined via the powder interlayer bonding (PIB) process. Both alloys were bonded at relevant temperatures in the specific alloy’s α + β region. Modifications to the microstructure during the bonding process where it recrystalised into a bi-modal structure, resulted in improved low cycle fatigue (LCF) response for the Ti-6-4 alloy. This improvement is seen throughout the fatigue curve when compared to the LCF performance of the as received Ti-6-4 material. The improvement in LCF performance resulting from the microstructure transformation overcomes any reduction in performance that can be attributed to retained porosity after the bonding cycle. While the HCF performance of the Ti-6-2-4-6 alloy joined via the PIB process fell below that of the as received β-forged billet material, the fatigue performance compares well with previous HCF results for welded material. Unlike the Ti-6-4 alloy, the β-forged Ti-6-2-4-6 alloy does not benefit from the transformation of its microstructure throughout the bond region.

Cyclic behavior and constitutive model of high strength low alloy steel plate

Cyclic loading tests with different protocols were conducted for a high strength low alloy steel. Based on the test results, the low cycle fatigue and extremely low cycle fatigue performance of the high strength steel was discussed and an appropriate constitutive model was established. The experimental results implied that the low and extremely cycle fatigue failure showed different fracture features. For low cycle fatigue, there was a strong negative linear correlation between the fatigue life and the strain amplitude in the log–log scale. However, they did not conform the linear relation when transiting to the low cycle fatigue. The steel represented obvious cyclic softening and good energy dissipation capacity. With the increase of strain amplitude, the softening degree decreased and equivalent damping ratio increased. The cyclic stress–strain curve could be descried by the Ramberg-Osgood model, and the strength coefficient and strain hardening exponent of this steel were larger than those of steel with lower strength. A combined hardening model was calibrated to describe the cyclic plasticity of the steel, and it was verified by the simulation results.

Exploring factors controlling pre-corrosion fatigue of 316L austenitic stainless steel in hydrofluoric acid

While the low-cycle fatigue performance of metals is significantly influenced by corrosion, the corrosion damages and therefore the fatigue mechanisms induced by different solutions are different. In this paper, the pre-corrosion fatigue behavior of 316L austenitic stainless steel in hydrofluoric acid (HF) are studied. To characterize the corrosion type as well the extent of corrosion, the corrosion behavior of 316L austenitic stainless steel at different HF concentrations are investigated. Combined uniform corrosion and pitting corrosion are observed, with grooves formed by the superposition of several etched pits. Two methods are proposed to characterize corrosion damages, and the fatigue life is found to negatively correlate with the corrosion damage. To characterize fatigue crack initiation mechanisms, fracture surfaces of corroded fatigue specimens are examined with an emphasis on crack initiation sites. It is found that the crack initiates from multiple sources caused by multiple pits, and the surface average annular width of the pitting is found to be a more important factor controlling the fatigue life than the depth of pits. The results in this study are expected to provide insights into the understanding of failure mechanisms of equipment in fluorine chemical industry.

Cyclic Plasticity of the As-Built EOS Maraging Steel: Preliminary Experimental and Computational Results

This short communication offers a preliminary view on ongoing research conducted on the as-built EOS maraging steel 300. The material’s cyclic elastoplastic characteristics under strain-controlled loading have been investigated experimentally. Specimens fabricated under two primary orientations, horizontally and vertically to the build plate, have been tested. The obtained stress–strain hysteresis loops exhibited symmetry, with the vertical specimen showing a higher plastic strain energy dissipation capability than the horizontal specimen. Modelling of the material’s elastoplastic behaviour was performed with a commonly used kinematic hardening rule, combined with both isotropic and anisotropic yield functions and elasticity moduli. The obtained simulations of the hysteresis loops, from the implementation of these two plasticity models, indicate the advantage of the anisotropic modelling approach over the isotropic approach. The anisotropic plasticity model describes in a more representative way the inherent elastic and plastic anisotropy of the as-built material. Further research is underway to explore the low cycle fatigue performance of this additively manufactured metal.

Influence of hydrogen on the low cycle fatigue performance of P91 steel

The present work aims to assess the influence of hydrogen on strain controlled low cycle fatigue (LCF) properties of P91 steel. Specimens were electrochemically charged using H2SO4 solution, subsequently uniaxial tensile and LCF tests were performed at ambient temperature. An increase in strength and reduction in elongation are noticed for hydrogen charged samples relative to as received or uncharged specimens. Hydrogenated specimens depict drastic reduction in fatigue life as compared to the uncharged specimens. Irrespective of imposed strain amplitude, P91 steel show cyclic softening nature throughout its life. The peak stress amplitude and rate of cyclic softening for hydrogenated specimens are found to be more than the as received specimens at all strain amplitudes. The magnitude of proportional limit from master curve depicts that as received specimen exhibit near Masing behavior whereas hydrogenated specimens reveal non-Masing behavior. Local misorientation analyses carried out by electron back scattered diffraction technique are correlated with the evolution of local plastic strain and substructural development. The fracture morphology of tensile test transformed from dimple failure for uncharged specimen to quasi cleavage fracture for hydrogenated specimens. Finite element simulation considering Chaboche kinematic hardening rule is utilized to simulate the cyclic stress-strain behavior of as received and hydrogenated specimens.