Low Cycle Fatigue Performance Research Articles

Experimental study on low-cycle fatigue performance of high-strength bolted shear connections

In strong earthquakes, low-cycle fatigue fractures may occur in the bolted connections of steel braced frames. Ensuring a high low-cycle fatigue life for high-strength bolted connections is of paramount significance in enhancing the overall safety and collapse resistance of steel structures. Despite substantial research on plate fatigue failure within bolted connections, there remains a research gap regarding low-cycle fatigue failure of high-strength bolts in these connections. This study aims to address the aforementioned shortcomings by conducting 34 sets of low-cycle fatigue tests on high-strength bolted connections. The test specimens all experienced low-cycle shear fatigue fracture at the threaded or unthreaded portion of the bolt shank as the dominant failure mode. Residual deformations were observed in the holes of connection plates. Based on the test data, ultimate shear capacity of a single shear connection is around 0.61Fy (tensile yield bearing capacity of bolt) when the shear force passes through the unthreaded portion and drops to 0.54Fy for the shear force at the thread. The untreated Q355 (minimum yield strength of 355 MPa) steel surface has an average anti-slip coefficient of around 0.37, while milling reduces it to approximately 0.30. The influence patterns of loading amplitude, bolt material, minimum plate thickness, bolt diameter, shear force position and connection type on low-cycle fatigue life are given by range analysis. Among them, variance analysis shows that loading amplitude and bolt material are the primary influencing factors. The correlation coefficient between loading amplitude and low-cycle fatigue life is −0.92, indicating a strong negative correlation. The degradation amount and rate of anti-slip capacity and shear capacity of bolted connections are also investigated. To propose reliable life prediction method, three models were used to establish the relationship between dimensionless shear deformation and low-cycle fatigue life of 10.9-grade high-strength bolted connections. It is not appropriate to use the fatigue categories defined in current standards to predict the low-cycle shear fatigue life of high-strength bolted connections.

Effects of yttrium on microstructure and low cycle fatigue properties of superalloy IN713C at high temperature

In order to improve the high temperature and low cycle fatigue performance of the IN713C alloy, trace amounts of yttrium (Y) element were added to such an alloy. The effect of Y on the microstructure and fatigue performance under push-pull loading condition of the IN713C alloy at 650 °C was investigated, and the fracture mechanisms of the IN713C alloy with different Y additions at strain amplitudes of 0.3%, 0.4% and 0.5% were also investigated. The results showed that addition of Y significantly increased the fatigue life of the IN713C alloy under different strain amplitude values. Compared with the traditional IN713C, the fatigue life of the alloy with 300 ppm Y was increased by 44.4%, 213.3%, and 61.4%, and that of the alloy with 500 ppm Y was increased by 184.6%, 66.1%, and 172.1%, respectively, at the strain amplitudes of 0.3%, 0.4%, and 0.5%. Shrinkage pores were found to be the main crack source at low strain amplitude (0.3%), while carbides and other interdendritic precipitates were the source of cracks at high strain amplitude (0.4% and 0.5%). The addition of Y increased the fatigue life of the IN713C alloy by reducing shrinkage and refining carbides and grain size.

Low-Cycle Fatigue Properties of Bimetallic Steel Bar with Buckling: Energy-Based Numerical and Experimental Investigations.

A bimetallic steel bar (BSB) consisting of stainless-steel cladding and carbon steel substrate exhibits excellent corrosion resistance and good mechanical properties. The bimetallic structure of BSBs may affect their low-cycle fatigue performance, and current investigations on the above issue are limited. In this study, the low-cycle fatigue properties of bimetallic steel bars (BSBs) with inelastic buckling were investigated. Experiments and numerical studies were conducted to investigate the low-cycle fatigue capacity for BSBs, considering buckling. The buckling mode of BSBs is discussed. The hysteretic loops and energy properties of BSBs with various slenderness ratios (L/D) and fatigue strain amplitudes (εa) are investigated. With increases in the L/D and εa, the original symmetry for hysteresis loops disappears gradually, which is caused by the buckling. A predictive equation revealing the relation between the εa and fatigue life is suggested, which considers the effects of the L/D. A numerical modelling method is suggested to predict the hysteretic curves of BSBs. The effect of buckling on the stress and energy properties of BSBs is discussed through the numerical analysis of 44 models including the effects of the L/D, εa, and cladding ratios. The numerical analysis results illustrate that the hysteresis loops of BSBs with various εa values exhibit similar shapes. The increase in the cladding ratio reduces the peak stress and the dissipated energy properties of BSBs. The hysteresis loop energy density decreases by about 3% with an increase of 0.1 in the cladding ratio. It is recommended that the proportion of stainless steel inBSBs should be minimized once the corrosion resistance requirements are met.

Low-cycle fatigue behavior and microstructure evolution of ODS steel pipes at high temperatures

Oxide-dispersion-strengthened (ODS) steels are candidate materials for application in advanced nuclear reactors. In this study, the low-cycle fatigue performances of 13Cr-ODS ferritic steel pipes were investigated at 600, 700, and 800 °C. Cyclic softening was observed at high strain amplitudes with an increase in the number of fatigue cycles. However, cyclic hardening appeared first, and then cyclic softening occurred at a low strain amplitude with the increase in the number of fatigue cycles. By comparing the cyclic stress–strain curves and the monotonic stress–strain curves, it was found that cyclic softening occurred regardless of the strain amplitude. The Coffin–Manson and Basquin equations were used to predict the fatigue of the pipes. Microstructure analysis indicated that cyclic softening was induced by the dynamic recovery and recrystallization, which reduced the number of low-angle grain boundaries in the deformed grains by promoting dislocation annihilation and reorganization. A complex multi-layer core–shell structure with a large size (∼500 nm) was observed.

Hysteretic behavior optimization of hollow laminated viscoelastomer-filled steel tube damper

This study proposes a shape optimization approach for designing hollow laminated viscoelastomer-filled steel tube dampers (HLVSTDs), aiming to reduce stress concentration, enhance energy dissipation capacity, and improve low-cycle fatigue performance. The shape optimization curve is obtained based on the definition of stress contours for HLVSTD bending moments and shear forces, with the assumption that points on the same contour yield simultaneously. Cyclic loading experiments were conducted on four HLVSTDs. Numerical models were established and validated to further investigate the mechanical properties, energy dissipation capacity, and seismic performance of the shape-optimized HLVSTDs. The results demonstrate that the shape-optimized HLVSTDs specimen exhibits excellent energy dissipation capacity and improved low-cycle fatigue performance. The calculated initial stiffness and yield force closely align with experimental values. Compared to non-optimized HLVSTDs, the shape-optimized HLVSTDs exhibit more uniform stress and equivalent plastic strain distributions, effectively reducing the concentration of plastic strains. Additionally, structures equipped with shape-optimized HLVSTDs demonstrate superior seismic performance.

Post-fire mechanical behavior of iron-based shape memory alloy used for structural damping

This study sheds light on the post-fire mechanical behavior of Fe-SMA by conducting a series of tests at material level, with a particular focus on the low-cycle fatigue (LCF) performance. Three temperatures (500 °C, 750 °C, 1000 °C) and three cooling methods (air cooling, water spray quenching, water quenching) are considered to simulate different fire-cooling scenarios. After the heating-cooling cycle, 10 monotonic tensile specimens and 20 LCF specimens are tested. Essential material parameters for Manson-Coffin model and combined hardening model are also calibrated based on the experimental data. The failure mechanism and possible factors affecting the post-fire LCF performance of Fe-SMA are further explored by scanning electron microscope (SEM), metallographic observation (MO), electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) analysis. Results show that Fe-SMA could exhibit even better LCF resistance after undergoing the considered fire-cooling procedure, especially those heated up to 750 °C and 1000 °C. Even under rapid cooling, no signs of brittle fracture are observed, which is superior to traditional structural steels. Different heating temperatures and cooling methods affect the grain sizes and microstructure of Fe-SMA, leading to variations in its post-fire LCF behavior.

High Temperature Fatigue of Additively Manufactured Inconel 718: A Short Review

Abstract With the increasing interest in adopting additively manufactured (AM) IN718 for high-temperature applications, driven by the design and manufacturing flexibility offered by AM technologies, understanding its fatigue performance is crucial before full-scale adoption. This paper reviews the recent literature on the high-temperature fatigue behavior of AM IN718. The review focuses on two primary stages of fatigue damage: fatigue crack initiation and fatigue crack growth. Notably, most existing studies have concentrated on fatigue crack initiation, and thus, this review emphasizes this aspect. In the fatigue crack initiation stage, discrepancies in low cycle fatigue (LCF) and high cycle fatigue (HCF) life performances are observed in the literature. Some studies have shown that the average room temperature (RT) fatigue life of AM IN718 is superior or comparable to that at high temperatures in the LCF regime. Conversely, in the HCF regime, high-temperature fatigue life is sometimes found to be superior to that at room temperature. However, other studies indicate no clear trend regarding the effect of temperature on HCF life. Although various mechanisms have been proposed to either improve or degrade fatigue performance across the LCF, HCF, and very high cycle fatigue (VHCF) regimes, the underlying reasons for the distinct behaviors in these regimes remain unclear. Competing mechanisms, such as surface oxide formation and thermally driven dislocations glide, can potentially enhance or reduce fatigue life. However, the interaction and control of these mechanisms over the fatigue strength of AM IN718 are not yet fully understood. Systematic studies are required to elucidate their roles in high-temperature fatigue. Microstructural investigations have suggested that controlling the formation and precipitation of deleterious secondary phases is crucial for tailoring the high-temperature fatigue strength of AM IN718. Therefore, it is imperative to design heat treatment protocols informed by a comprehensive understanding of phase formation kinetics to improve the high-temperature fatigue performance of AM IN718 compared to their traditionally manufactured (TM) counterparts. This is particularly important for IN718 parts manufactured using directed energy deposition technology, which currently lacks standardized heat treatment procedures. The review also identifies open research areas and provides recommendations for future work to address these gaps.

Effect of Thermal Shock Conditions on the Low-Cycle Fatigue Performance of 3D-Printed Materials: Acrylonitrile Butadiene Styrene, Acrylonitrile-Styrene-Acrylate, High-Impact Polystyrene, and Poly(lactic acid).

3D printing technology is becoming a widely adopted alternative to traditional polymer manufacturing methods. The most important advantage of 3D printing over traditional manufacturing methods, such as injection molding or extrusion, is the short time from the creation of a new design to the finished product. Nevertheless, 3D-printed parts generally have lower strength and lower durability compared to the same parts manufactured using traditional methods. Resistance to the environmental conditions in which a 3D-printed part operates is important to its durability. One of the most important factors that reduces durability and degrades the mechanical properties of 3D-printed parts is temperature, especially rapid temperature changes. In the case of inhomogeneous internal geometry and heterogeneous material properties, rapid temperature changes can have a significant impact on the degradation of 3D-printed parts. This degradation is more severe in high-humidity environments. Under these complex service conditions, information on the strength and fatigue behavior of 3D-printed polymers is limited. In this study, we evaluated the effects of high humidity and temperature changes on the durability and strength properties of 3D-printed parts. Samples made of commonly available materials such as ABS (Acrylonitrile Butadiene Styrene), ASA (Acrylonitrile-Styrene-Acrylate), HIPS (High-Impact Polystyrene), and PLA (Poly(lactic acid)) were subjected to temperature cycling, from an ambient temperature to -20 °C, and then were heated to 70 °C. After thermal treatment, the samples were subjected to cyclic loading to determine changes in their fatigue life relative to non-thermally treated reference samples. The results of cyclic testing showed a decrease in durability for samples made of ASA and HIPS. The ABS material proved to be resistant to the environmental effects of shocks, while the PLA material exhibited an increase in durability. Changes in the internal structure and porosity of the specimens under temperature changes were also evaluated using microcomputed tomography (microCT). Temperature changes also affected the porosity of the samples, which varied depending on the material used.

Inelastic Cyclic Tests of Grade 80 (550 MPa) Bars with Mechanical Splices

This study addresses low-cycle fatigue performance of high-strength steel reinforcement bars (HSRB) when used with mechanical couplers due to the growing demand for higher-strength steel reinforcement bars in both seismic and non-seismic applications, driven by the need to reduce bar congestion, lower material quantities, and consider economic and environmental factors. Low-cycle fatigue involves material failure owing to a finite number of load or deformation cycles, generally occurring under substantial strain rates that surpasses the yielding limit. The experimental program assesses the fatigue behavior of HSRB produced using microalloying, quenching, and tempering techniques, coupled with mechanical couplers (eleven different types) from five companies in the United Stated of America. The study highlights significant differences in fatigue endurance based on the type and make of couplers and suggests potential improvements in manufacturing processes to enhance fatigue resistance. It is found that the mechanical couplers sustain a loading protocol of (-1% to 3%) when there is a clear distance of 2 times the diameter of the bar between the coupler and the gripping machine from top to bottom. The coupled bars sustained a minimum of 6 half cycles and a maximum of 38 half cycles.

Seismic performance of shuttle-shaped double-restrained buckling-restrained brace: Experimental investigation and numerical analysis

To solve the problems of excessive cross-section size and self-weight and buckling instability of super-long buckling-restrained brace, a new lightweight shuttle-shaped double-restrained BRB (SDR-BRB) is proposed in this study. Firstly, cyclic loading experiments are conducted on three SDR-BRB specimens to investigate their failure mode and seismic performance. Then, a finite element model considering geometric, material, and contact nonlinearity is established and verified by experimental results. Finally, the effect of the restraining ratio on the hysteretic performance of SDR-BRB is studied by parameter analysis, and the restraining ratio requirement of the energy-dissipation type of SDR-BRB that meets the ductility requirements is obtained. The results show that SDR-BRB has stable and plump hysteretic curves, excellent energy-dissipation capacity, and low cycle fatigue performance, exhibiting obvious strain-strengthening characteristics. The restraining ratio is an important factor affecting the overall stability and failure mode of SDR-BRB, and it is recommended that the restraining ratio requirements of the SDR-BRB should be 2.25. The above research can provide a design reference for the practical engineering application of SDR-BRB.

Experimental investigation into corrosion effect on buckling and low-cycle fatigue performance of high-strength steel bars

The reinforcement in marine RC structures will inevitably be corroded under long-time erosion of chloride ions, which will weaken steel mechanical properties and then structural seismic resistance. The new metallurgical technology is adopted for manufacturing high-strength steel bars (HSSB), but that may affect the corrosion resistance of steel bars at the same time. This paper experimentally investigates the effects of corrosion on monotonic and low-cycle fatigue properties of HSSB HTRB600 and normal strength steel bars (NSB) HRB400E. The HRB400E and HTRB600 steel bars were corroded to different corrosion rates by electrochemical accelerated corrosion technique. The monotonic tensile and compressive, as well as low-cycle fatigue tests of corroded steel bars were conducted to investigate the effects of corrosion on steel mechanical properties, of which corrosion levels (0–20% target corrosion mass loss), slenderness ratios (L/D=6, 8, 10, 12) and strain amplitudes (2%, 4%) are considered. Test results show that, the corrosion morphology of steel bars under electrochemical accelerated corrosion is basically consistent with that observed under natural corrosion. Compared with uncorroded HRB400E and HTRB600 steel bars, 20% corrosion mass loss leads to 38% and 35% decrease in tensile strength, as well as 33% and 28% reduction in buckling stress, respectively. The HTRB600 steel bars present slightly superior monotonic tensile and compressive corrosion resistance than HRB400E steel bars. Corrosion obviously decreases the low-cycle fatigue (LCF) life of steel bars, resulting in reductions of 44% and 36% in LCF life at 20% corrosion mass loss for HTRB600 and HRB400E steel with a L/D of 6, respectively. Moreover, the HTRB600 steel bars present more significant corrosion degradation in total hysteretic dissipated energy, compared with HRB400E steel bars. The combined effect of corrosion and inelastic buckling further exacerbates the deterioration of LCF performance of steel bars. The corresponding deterioration models are proposed to determine the LCF life and energy dissipation capacity of corroded steel bars.

Effect of aging state on low cycle fatigue performance of AA 2099 alloy

The evaluation of the fatigue performance is a crucial subject in the research of structural materials utilized in the field of aerospace engineering. In order to examine the influence of aging state on fatigue performance, low cycle fatigue (LCF) experiments were conducted on specimens made from AA2099 alloy in the under-aged (UA), peak-aged (PA), and over-aged (OA) states, with varying strain amplitudes (Δεt/2=0.3 %-0.5 %). In the UA and PA states, the grain boundary precipitates exhibit a small size, thereby prompting the crack to propagate through the grains. Certain grains in this region exhibit a crystallographic feature of crack propagation along the (111) slip plane, which is associated with the formation of the precipitation free bands (T1-PFB) within the grains. In contrast, in the OA state, the size of the grain boundary precipitates increases significantly, accompanied by a minimum precipitation free zones (PFZs) width increase to 75 nm, exacerbating the stress concentration at grain boundaries, with cracks primarily extending along the grain boundaries. Furthermore, the presence of coarse grain boundary precipitates and the widened PFZs promote the initiation and propagation of fatigue cracks, leading to a pronounced reduction in fatigue life.

Effect of Force and Heat Coupling on Machined Surface Integrity and Fatigue Performance of Superalloy GH4169 Specimens

GH4169 is one of the key materials used to manufacture high-temperature load-bearing parts for aero-engines, and the surface integrity of these parts in service conditions significantly affects their high-temperature fatigue performance. Under a coupling effect of high temperature and alternating load, the evolution process of the machined surface integrity index of superalloy GH4169 specimens was studied, and fatigue performance tests at 20 °C, 450 °C, and 650 °C were carried out to analyze the primary factors affecting the high-temperature fatigue performance of specimens. The results indicated that the surface roughness of specimens remained essentially unchanged. However, the value of surface residual stress decreased significantly, with a release of more than 60% at the highest temperature. At 650 °C, the surface microhardness increased, while the degree of surface plastic deformation decreased under alternating loads. Simultaneously, when the surface roughness was less than Ra 0.4 μm, surface microhardness was the main factor affecting the high-temperature fatigue performance of specimens. The influence of surface microhardness on low-cycle fatigue performance was not consistent with that on high-cycle fatigue performance. The latter increased monotonically, whereas the former initially increased and then decreased with increasing surface microhardness.

The effect of powder recycling on the mechanical performance of laser powder bed fused stainless steel 316L

Powder recycling refers to the reuse of unused powder feedstock in the laser powder bed fusion (PBF-LB/M) process. This approach is crucial for the economic viability and sustainability of PBF-LB/M, as powder accounts for a large proportion of the total production cost. However, through powder recycling, the physical and chemical properties of powder are liable to change. This variation in powder properties can subsequently lead to knock-on effects on the mechanical properties of a fully built component.This research has investigated the changes that occur to stainless steel 316L (SS316L) powder as a result of recycling. This includes changes to powder size distribution (PSD), flowability, chemistry and phase composition. Likewise, the impact that these changes have will also be assessed in PBF-LB/M SS316L components manufactured from powders after different levels of recycling and subjected to alternative post processing routes such as hot isostatic pressing (HIP). This comprehensive investigation involves a thorough examination of both macro- and microstructures, encompassing detailed analyses of chemical composition, microstructural features, and defects. The study aims to elucidate differences in mechanical behaviour through a series of experiments, including uniaxial tensile tests, Charpy impact assessments, and low cycle fatigue (LCF) experiments. Additionally, the investigation will be complemented by pitting potential tests, providing a holistic understanding of the material's performance and characteristics.Although moderate changes to powder were observed for both PSD and chemistry, this was found to be negligible and not enough to result in any adverse changes to part performance. In addition, the microstructure of SS316L remained stable across differing levels of powder recycling. Whereas the porosity content increased marginally as the fine particle content of powder was reduced, this was not found to be sufficient to affect the LCF performance of the material. After powder recycling, increases in ductility and Young’s modulus were attributed to a reduction in oxides present in the microstructure, which were sources of localised damage and deformation.

Microstructure degradation and residual low cycle fatigue life of a serviced turbine blade

AbstractThis paper was attempted to investigate the microstructure degradation and low cycle fatigue (LCF) performance of a serviced K465 Ni‐based superalloy turbine blade. LCF tests were carried out with small‐scale plate specimens sampled from the blades. Relationship between residual LCF life and microstructure state was estimated. The results indicate that the coarsening of γ/γ′ phases was the most significant microstructure degradation mode for the serviced blades. Both the γ matrix width and the γ′ precipitate diameter increased with the increase of service duration, while the γ′ precipitate volume fraction slightly decreased. The most severe microstructure degradation occurred at the leading edge along the chord direction, particularly at 50–70 % airfoil spans. The residual LCF life exhibited an accelerated decrease characteristic as increases of microstructure degradation degree. The coarsened microstructure diminished shear resistance of the superalloy, which resulted in additional accumulated inelastic deformation and a corresponding reduction in LCF life.

Effect of surface modification on the high temperature low cycle fatigue performance of LPBF 316L austenitic steel

In this study, high temperature low cycle fatigue (LCF) tests at 550 °C were conducted on LPBF (Laser powder bed fusion) 316L with three different surface states, including the As-built surface (AB), fill contour (FC) manufacturing surface, and the surface combining FC and electropolishing (FC + EP). The effect of surface treatment on the high temperature LCF performance of LPBF 316L was investigated. Experimental results showed that the FC + EP surface treatment had the most significant effect on enhancing life. The difference in enhancing the fatigue life behavior was mainly attributed to the various crack initiation mechanisms with different surface states. The cracks on the surfaces of AB and FC mostly originate from the powder adhesion areas and the boundaries of the melt pool, while FC + EP surface treatment weaken the damage induced by powder adhesion. Furthermore, a parameter representing the fatigue crack propagation driving force that considers the surface condition has been defined, and a proposed life prediction model can provide guidance for surface modification and post-treatment of additive manufacturing materials as well as other metal materials.

Effect of production angle on low cycle fatigue performance of 3D printed auxetic Re-entrant sandwich panels

This study explores the static and fatigue behavior of re-entrant sandwich structures fabricated via 3D printing to assess their energy dissipation capability and durability. Various core structures of sandwich panels with different angles are considered for analysis. The shells, cores, and the entire sandwich structures are manufactured using polylactic acid (PLA) material. A combination of numerical simulations and experimental tests were employed to evaluate the energy absorption capacity and stiffness of re-entrant sandwich structures. Initial mechanical properties of the core structures were obtained through static tensile testing and the experimental fatigue analysis was carried out by using an Instron 8871 servo hydraulic test device, following the principles of the three-point bending test. The results of both static and fatigue analyses evaluated and the energy absorption capacity of the structures increases with increase in production angles. FEM and experimental results are compared and both results are in good agreement with eachother. Additionally, affect of changes in the geometry of re-entrant sandwich panels evaluated in terms of Young's Modulus and Poisson's ratio. The improved structures characterized by a negative Poisson's ratio hold significant innovation potential, especially in the defense and automotive industries, through the integration of various topological research findings.

Matching relationship of low-cycle fatigue life and fatigue design method of concentrically braced frames with H-section steel

Simulations on 192 concentrically braced frames with H-section steel (Q355B) are carried out to investigate their low-cycle fatigue performance. The fatigue life of a steel-braced frame is predicted using a multiaxial fatigue damage parametric model. To depict the fatigue failure sequence and the matching relationship of the fatigue life between the two components in the braced frame, the fatigue life ratio (β) is introduced. This ratio represents the gusset plate's fatigue life to the brace's fatigue life. Simulated results are analyzed, and β is found to be positively correlated with four influencing factors, the width-to-thickness ratio of the brace flange, connection coefficient, ratio of the column length to beam length, and slenderness ratio of the gusset plate. Also, β is found to be negatively correlated with the slenderness ratio of the brace. Based on the Bayesian updating method, a probabilistic model is formulated to predict β of a steel-braced frame. Accordingly, a fatigue design method is proposed, which contributes to avoiding the in-coordination of seismic capacity caused by the significant difference between the brace’s and gusset plate’s fatigue life within the steel braced frame. The proposed fatigue design method has the potential to serve as a reference for improving design specifications.

Study on the Effect of Solid Solution Treatment on the Bending Fatigue Property of Fe-Mn-Si Shape Memory Alloys

Fe-Mn-Si shape memory alloys have excellent low-cycle fatigue performance and broad application prospects in the field of civil engineering and construction. It is necessary to conduct comprehensive and in-depth research on the mechanical properties of Fe-Mn-Si shape memory alloys. This study takes the Fe17Mn5Si10Cr5Ni shape memory alloy as the research object. After solid solution treatment at different temperatures and times, the effect of solid solution treatment on the bending fatigue performance of Fe-Mn-Si shape memory alloys was studied using bending cycle tests. The phase composition and fracture morphology of the sample were analyzed. The results showed that solid solution treatment can significantly improve the bending fatigue performance of Fe-Mn-Si shape memory alloys, reaching the optimal value at 850 °C for 1 h. The number of bending cycles until fracture increased by 131% compared to untreated specimens. Stress induction γ → ε martensitic transformation occurred in Fe-Mn-Si shape memory alloy specimens during bending cyclic testing, which is reversible. The fracture area of Fe-Mn-Si shape memory alloy specimens is mainly characterized by ductile fracture, with some areas exhibiting quasi-quasi-cleavage fracture characteristics.

Cyclic behavior of carbon steel and austenitic stainless steel hollow laminated viscoelastomer-filled steel tube damper under unidirectional and bidirectional loadings

The hollow laminated viscoelastomer-filled steel tube damper (HLVSTD) is a metallic damper with stable working performance and excellent energy dissipation capability. It can exhibit equal mechanical performance in any single horizontal direction based on the geometric features of the circular shape. However, the impact of carbon steel tube material, stainless steel tube material and bidirectional loading on the mechanical behavior of HLVSTD remains unclear. The objective of this study is to analyze the mechanical performance of HLVSTD under bidirectional loading conditions using carbon steel tubes and austenitic stainless steel tubes, which are commonly utilized in China. Experimental tests were conducted using both unidirectional loading and bidirectional loading to comprehensively assess the performance. The results indicate that, under unidirectional and bidirectional loading, HLVSTDs made from both carbon steel and austenitic stainless steel tubes exhibit stable hysteresis curves. In comparison to the carbon steel tube HLVSTD, the counterpart with an austenitic stainless steel tube demonstrates higher equivalent stiffness, ultimate force, energy dissipation and low-cycle fatigue performance. Moreover, HLVSTDs under bidirectional loading exhibit a similar trend in mechanical performance compared to those under unidirectional loading. Regardless of whether the tube material is carbon steel or austenitic stainless steel, the cumulative displacement and cumulative energy under bidirectional loading were found to be twice as much as those observed under unidirectional loading, which demonstrates the excellent mechanical performance of HLVSTD under bidirectional loading.