Stable Cyclic Behavior Research Articles

Size and Composition Effects in Sb-Carbon Nanocomposites for Sodium-Ion Batteries.

Sodium-ion batteries are in the spotlight as viable alternatives to lithium-ion batteries in stationary storage and power grid applications. Among possible anode materials, Sb is one of the interesting candidates due to a combination of battery-type potential plateaus in the charge-discharge profiles, high capacity (theoretical capacity of 660 mAh g-1), and demonstrated good cyclic stability. The influence of Sb particle size (particularly at the nanoscale range) and the composition of Sb-carbon composites on the electrode performance, stability, and charge storage mechanism is systematically evaluated here for the first time. A range of Sb-carbon nanocomposites with varied Sb particle size (between 50 and ∼1 nm) are studied. The control of the particle size is achieved via varying the carbon and Sb weight ratio in the precursors. The shape of charge-discharge profiles, hysteresis, and the difference in cyclic stabilities and rate performance are analyzed. The nanocomposite with the smallest particle size (∼1 nm) and the largest carbon content provides the most stable cyclic behavior and a better rate capability but suffers from an increased hysteresis between charge and discharge curves. In situ synchrotron X-ray diffraction experiments indicate that the storage mechanism in the Sb-carbon nanocomposites containing Sb nanoparticles is different from the electrodes with bulkier, micron-sized Sb particles, and the electrochemical reaction proceeds through a number of crystalline intermediates.

Connection Design Recommendations for Improved BRBF Performance

Numerous component tests on buckling-restrained braces (BRBs) have demonstrated their approximately symmetric tension and compressive capacities, stable cyclic behavior and large (component) ductility prior to core fracture. These properties make them suitable ductile fuses for seismic design. Experiments on buckling-restrained braced frame (BRBF) systems show that the inelastic axial deformation capacity of BRBs may be compromised by system performance demands. Damage including significant yielding, local buckling, twisting and fracture of the beams and columns, tearing of the gusset plate welds to framing members, and out-of-plane movement of the BRB have been observed in BRBF tests. Prior test results are reviewed, and an analytical study using high-resolution models, which were validated with prior test results, is used to develop mitigation strategies for the damage. Design recommendations to mitigate damage and improve system performance are developed. The study reveals that damage to the beams and columns at a corner gusset-plate connection is related to the ratio of the component web thickness to the gusset plate thickness, suggesting a modest design change that will significantly improve BRBF performance.

Behaviour of ODS Steels in Cyclic Loading

The low cycle fatigue behaviour of several high chromium oxide dispersion strengthened (ODS) steels prepared by powder metallurgy was studied in a detailed way. Studied ODS steels were divided into two groups, ultrafine grained (UFG—grain size under 1 μm) and coarse grained (CG—grain size of 200 μm). Microstructure of as received state of individual steels was observed by means of SEM and TEM. Cyclic hardening/softening curves were measured at room temperature and at 650 °C. It is shown that 0.3 wt% of oxide nanoparticles strengthen the materials substantially and reduces the cyclic softening compared to non-ODS steels. Cyclic softening was measured in CG steel and in UFG ODS ferritic/martensitic steel at room temperature, but stable cyclic behaviour was observed at 650 °C. UFG ODS ferritic steels exhibited stable cyclic behaviour at both testing temperatures. Derived Wohler and Coffin-Manson curves were measured and substantial differences in fatigue life were revealed. Crack initiation mechanisms and fatigue crack growth rate were analysed. The crack initiation mechanism differs for studied steels, as well as fatigue crack growth rate. The relative length of nucleation and propagation stages of the fatigue life is discussed for individual materials. TEM observations revealed differences in microstructure evolution during fatigue loading in particular steels. All results are thoroughly discussed to explain differences in fatigue life of studied steels.

Dual Effect of Anionic Surfactants in the Electrodeposited MnO2 Trafficking Redox Ions for Energy Storage

The dual effect of in-situ addition of anionic surfactants, sodium octyl sulfate (SOS), sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS) on the microstructure and electrochemical properties of electrolytic manganese dioxide (EMD) produced from waste low grade manganese residue is discussed. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), BET-surface area studies, thermogravimetry-differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structure and chemistry of the EMD. All EMD samples were found to contain predominantly γ-phase MnO2, which is electrochemically active for energy storage applications. FESEM images showed that needle, rod and flower shaped nano-particles with a porous surface and platy nano-particles were obtained in the case of EMD deposited with and without surfactant respectively. Thermal studies showed loss of structural water and formation of lower manganese oxides indicating high stability of the EMD samples. The cyclic voltammetry and charge – discharge characteristics implied the presence of surfactants enhances the energy storage within the MnO2 structure. Addition of the surfactant at its optimum concentration greatly increased the EMD surface area, which in turn improved the cycle life of the EMD cathode. EMD obtained in the presence of 25, 50, 25 ppm of SOS, SDS, and STS respectively showed an improved cycle life relative to the EMD obtained in the absence of surfactant. EMD obtained without surfactant showed a capacity fade of 20 mAh g−1 within 15 discharge-charge cycles, while surfactant modified samples showed stable cyclic behavior of capacity 95 mAh g−1 even after 15 cycles.

Local buckling behavior of steel angle core members in buckling-restrained braces: Cyclic tests, theoretical analysis, and design recommendations

The local stability of buckling-restrained braces (BRBs) is one of the most concerned issues. However, few discussions were conducted on the BRBs using section steel or welded cruciform core members, and the currently proposed methods concentrated on the design of casing only. In this study, incremental cyclic tests were conducted on eight BRB specimens using steel angle core members. Key parameters included the core width-to-thickness (b/t) ratio and the gap between the core and the casing. The test results show that two types of local buckling modes of the core were observed, while no local failure of the casing induced by local buckling was found. Significant local buckling and cyclic deterioration behavior were observed for the specimens with the b/t ratio of around 8.5 when the axial core strain reached 1.4%, causing 13% reduction in energy dissipation. Local buckling waves tended to concentrate near the core ends with enlarged buckling amplitudes due to the friction and uneven gap. The ratio between buckling amplitude and buckling half-wave length is found to be a governing parameter for BRB seismic performance. This ratio is recommended to be smaller than 0.04 to ensure stable cyclic behavior. The analytical model for the local stability of steel angle core members is proposed and the inelastic local buckling critical load is obtained. The analytical results show good agreement with experiment. Three re-defined general requirements for BRB local stability design are proposed, and the design recommendations for the steel angle core members are provided. Several implications of this study to other BRB configurations are presented finally.

Experimental evaluation of dual frame structures with thin-walled steel panels

Steel plate shear walls (SPSW) are efficient structural systems for resisting lateral loads owing to their high initial stiffness and stable cyclic behavior in the plastic range. The seismic response may be improved by connecting plate walls through link beams. Beam-to-column connections may range from simple connections to full rigid moment resisting connections. Given that initial stiffness is provided mainly by the plates' rigidity, simple connections between horizontal and vertical boundary elements can be employed. Rigid, but expensive, connections may prove more beneficial than simple ones by increasing the frame capacity and also reducing residual drift after an earthquake. The more cost-effective semi-rigid connections between these members are also expected to increase capacity and reduce residual drift in comparison to simple connections. This study investigates the behavior of dual steel frames with thin walled steel shear walls and link beams. Four half-scale specimens were tested under monotonic and cyclic loading for characterizing energy dissipation and evaluating seismic behavior factors. The specimens exhibited good, stable behavior. The rigid beam-to-column connections, when compared to the semi-rigid ones, improved the ultimate capacity and dissipated energy. The experimental program provides a basis for validating a numerical model of slender SPSW.

Microstructure degradation in high temperature fatigue of TiAl alloy

Low cycle fatigue properties of lamellar TiAl with 8at.% Nb were studied at four temperatures: room temperature, 700, 750 and 800°C. Up to 750°C, stable cyclic behaviour is observed while cyclic softening is characteristic for 800°C. The strength of the alloy is still high even at 800°C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling at RT. At 750°C, the lamellar structure was in some places destroyed by cyclic plastic straining and pure γ-phase islands with high density of dislocation debris were formed. At 800°C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure and possible annealing of dislocation debris is the reason for marked cyclic softening at 800°C.

Experimental investigation on cyclic behavior of perforated steel plate shear walls

In recent decades, steel plate shear walls have come to be considered as a convenient system for resisting lateral loads due to earthquakes and wind, especially in tall buildings, because of their ductile and energy absorption behaviors. The existence of openings affects the seismic behavior and performance of steel plate shear walls. In the present research, the effects of opening dimensions as well as slenderness factors of plates on the seismic behavior of steel plate shear walls are studied experimentally. Eight 1:6 scaled test specimens, with two plate thicknesses and four different circular opening ratios at the center of the panel, have been manufactured and were tested under the effects of cyclic hysteresis loading at the thin-walled structures research laboratory of Urmia University, Urmia, Iran. The hole was put in the center of the panel because this is the most detrimental location in view of the panel tension field action. The obtained results signify a stable and desired behavior of steel plate shear walls for large displacements of up to 6% drift. The creation of openings decreases the initial stiffness and strength of the system, and increasing the opening diameter will intensify this matter. The obtained ductility of specimens shows the stable functioning of a system in the nonlinear range. Although the stable cyclic behavior of specimens in the nonlinear range causes mostly a dissipation of energy during the loading of samples, but existence of an opening at the center of the panel causes a noticeable decrease in energy absorption of the system.

A novel type of angle steel buckling‐restrained brace: Cyclic behavior and failure mechanism

AbstractA novel type of angle steel buckling‐restrained brace (ABRB) has been developed for easier control on initial geometric imperfection in the core, more design flexibility in the buckling restraining mechanism and easier assembly work. The steel core is composed of four angle steels to form a non‐welded cruciform shape restrained by two external angle steels, which are welded longitudinally to form an external tube. Component test was conducted on seven ABRB specimens under uniaxial quasi‐static cyclic loading. The test results reveal that the consistency between the actual and design behavior of ABRB can be well achieved without the effect of weld in the core. The ABRBs with proper details exhibited stable cyclic behavior and satisfactory cumulative plastic ductility capacity, so that they can serve as effective hysteretic dampers. However, compression–flexure failure at the steel core projection was found to be the primary failure mode for the ABRBs with hinge connections even though the cross‐section of the core projection was reinforced two times that of the yielding segment. The failure mechanism is further discussed by investigating the Nu– Mu correlation curve. It is found that the bending moment response developed in the core projection induced by end rotation was the main cause for such a failure mode, and it is suggested that core projection should be kept within elastic stage under the possible maximum axial load and bending moment response. Copyright © 2010 John Wiley & Sons, Ltd.

709 Ti-Nb系合金の超弾性特性に及ぼす繰返し変形の影響(OS5-(1) インプラントおよび生体材料,オーガナイズドセッション)

The effect of cyclic deformation on superelastic behavior was investigated in Ti-26Nb and Ti-23Nb-1.0N (at.%) alloys. Cyclic loading-unloading tensile tests with a constant maximum applied strain of 2.5% were carried out until the 500th cycle. With increasing number of cycles, the critical stress for inducing the martensitic transformation decreased and the residual strain increased. In the Ti-26Nb alloy, it was confirmed that the increase of the residual strain during the cyclic deformation was due primarily to the increase in the residual martensites. More stable cyclic deformation behavior was confirmed in the Ti-23Nb-1.0N alloy compared with the Ti-26Nb alloy owing to the higher critical stress for slip.

다양한 배근상세를 갖는 짧은 연결보의 주기거동 특성과 에너지소산능력의 평가

The cyclic behavior and energy dissipation mechanism of short coupling beams with various reinforcement layouts were studied. For numerical analysis of coupling beams, nonlinear truss model was used. The results of numerical analysis showed that the coupling beams with conventional reinforcement layout showed pinched cyclic behavior without significant energy dissipation, whereas the coupling beams with diagonal reinforcement exhibited stable cyclic behavior without pinching. The energy dissipation of the coupling beams was developed mainly by diagonal reinforcing bars developing large plastic strains rather than concrete which is a brittle material Based on this result, simplified equations for evaluating the energy dissipation of coupling beams were developed. For verification, the predicted energy dissipation was compared with the test results. The results showed that the simplified equations can predict the energy dissipation of short coupling beams with shear span-to-depth ratio less than 1.25 with reasonable precision, addressing various design parameters such as reinforcement layout, shear span-to-depth ratio, and the magnitude of inelastic displacement. The proposed energy equations can be easily applied to performance-based seismic evaluation and design of reinforced concrete structures and members.

Ductile Web Fracture Initiation in Steel Shear Links

Tests conducted in the 1980s showed that well-detailed short shear links can exhibit stable and ductile cyclic behavior. Recent tests of prevailing A992 rolled shapes revealed that shear links designed according to current seismic specifications can fail by ductile fracture in the link web, a mode of failure that was not observed in earlier tests. This paper investigates the observed ductile fractures through computational structural simulation. An existing criterion for judging the propensity for ductile fracture initiation in steel is modified based on published tests results for notched bars to better pinpoint the location of ductile fracture initiation. Validated finite- element analyses of previously tested shear links are conducted and the results postprocessed to evaluate the potential for ductile fracture of specimens with several different types of details. Reasons for the occurrence of web fractures in new A992 steel beams as opposed to older links are discussed. An alternative stiffener configuration that mitigates ductile fracture and is at the same time practical to construct is proposed.

On the temperature dependence of the fatigue and damage behaviour of a particulate-reinforced metal-matrix composite

The fatigue and damage behaviour of the particulate-reinforced aluminum-matrix composite AA6061-Al 2O 3-20p was investigated at temperatures between T=−100 and 300 °C. Experiments performed at the highest temperature are characterized by pronounced cyclic softening which can clearly be explained by overaging (coarsening) of the precipitate structure in the matrix. A completely different behaviour was found at low and ambient temperature, where, at larger strain amplitudes, initial hardening was observed, followed by cyclic softening until fracture. At small strain amplitudes, a more stable cyclic behaviour was obtained. Damage was characterized by particle fracture at low and intermediate temperatures and debonding at high temperature, respectively. A procedure is proposed to determine the evolution of damage during the fatigue tests on the basis of the decrease of the stiffness determined from the tensile and compressive unloading branches of the stress–strain hysteresis loops. From the separate evaluation of these two branches, the internal damage (fracture of particles) can be distinguished from the growth of the final fatigue crack. This procedure was applied successfully in low and ambient temperature fatigue tests.

Using thresholding at varying intervals to obtain different temporal patterns.

We show how stroboscopic threshold mechanisms can be effectively employed to obtain a wide range of stable cyclic behavior from chaotic systems, by simply varying the frequency of control. We demonstrate the success of the scheme in a prototypical one-dimensional map, as well as in a three-dimensional system modeling lasers where the threshold action is implemented on any one of the variables. It is evident that thresholding is capable of yielding exact limit cycles of varying periods and geometries when implemented at different intervals (even when very infrequent). This suggests a simple and potent mechanism for selecting different regular temporal patterns from chaotic dynamics.

Cyclic Deformation and Fatigue Properties of Ultrafine Grain Size Materials: Current Status and Some Criteria for Improvement of the Fatigue Resistance

ABSTRACTIn this review, some general conclusions based on studies performed to date on fatigued materials of ultrafine grain (UFG) size produced by equal channel angular pressing (ECAP) are drawn, and open issues of current interest are defined. Important aspects addressed include the apparent discrepancy between improved fatigue strengths in Wöhler (S-N) plots as opposed to inferior fatigue strengths in Manson-Coffin plots, the clarification of the microstructural mechanisms of severe cyclic softening in conjunction with dynamic (local) grain/subgrain coarsening and damaging large-scale catastrophic shear banding. The important roles of the cyclic slip mode, the friction stress, the crystal structure and the temperature of cyclic deformation with respect to stable cyclic deformation behaviour are emphasized. Based on such considerations, criteria are formulated that must be observed, when designing ECAP-processed UFG-materials of superior fatigue strength.

Effect of Severe Corrosion on Cyclic Ductility of Steel

Although some past experimental studies indicate that the monotonic structural ductility of steel is not detrimentally affected by severe corrosion, no study has investigated whether such severely rusted members can reliably exhibit the stable cyclic ductile behavior necessary for seismic survival. To generate preliminary data, a few rusted pieces taken from an existing steel bridge have been subjected to numerous cycles of alternating plasticity in flexure. Specimens had up to a 60% loss of cross-sectional area because of corrosion. This limited test program revealed that, although stable hysteretic behavior comparable with that of an unrusted specimen is possible, premature failure under alternating plasticity can typically develop (in spite of satisfactory ductile behavior under monotonic loading). Irregularities along the severely rusted surface apparently act as crack initiators and precipitate crack propagation throughout the section.

Classification of cyclic initial states and geometric phase for the spin-j system

Quantum states which evolve cyclically in their projective Hilbert space give rise to a geometric (or Aharonov-Anandan) phase. An aspect of primary interest is stable cyclic behaviour as realized under a periodic Hamiltonian. The problem has been handled by use of time-dependent transformations treated along the lines of Floquet's theory as well as in terms of exponential operators with a goal to examine the variety of initial states exhibiting cyclic behaviour. A particular case of special cyclic initial states is described which is shown to be important for nuclear magnetic resonance experiments aimed at the study of the effects of the geometric phase. An example of arbitrary spin j in a precessing magnetic field and spin j=1 subject to both axially symmetric quadrupolar interaction and a precessing magnetic field are presented. The invariant (Kobe's) geometric phase is calculated for special cyclic states.

Deformation substructure in the nickel-base alloy In738LC under superimposed creep-fatigue loading

The nickel-base superalloy IN738LC containing a unimodal distribution of [gamma]' precipitates was deformed under superimposed creep-fatigue loading at elevated temperatures. The alloy shows a stable cyclic deformation behaviour under LCF portion of the loading and at the same time a cyclic softening effect in the periods of creep deformation. Transmission electron microscopic examination reveals different mechanisms of dislocation- [gamma]' precipitate interaction under various loading conditions. At high hold stress levels and strain amplitudes stacking faults were frequently observed, indicating shearing of [gamma]' precipitates by dislocations. At low hold stress levels and strain amplitudes the observed absence of dislocations in [gamma]' precipitates suggests that they are bypassed by dislocations. Dislocation networks at [gamma]/[gamma]' interfaces were found in most of the specimens. A directional coalescence of the [gamma]' precipitates was observed under certain testing conditions. The development of both these features with deformation could be followed. The softening effect is accompanied by both processes. (orig.)

Deformation Substructure in the Nickel-Base Alloy IN738LC Under Superimposed Creep-Fatigue Loading

The nickel-base superalloy IN738LC containing a unimodal distribution of [gamma]' precipitates was deformed under superimposed creep-fatigue loading at elevated temperatures. The alloy shows a stable cyclic deformation behaviour under LCF portion of the loading and at the same time a cyclic softening effect in the periods of creep deformation. Transmission electron microscopic examination reveals different mechanisms of dislocation- [gamma]' precipitate interaction under various loading conditions. At high hold stress levels and strain amplitudes stacking faults were frequently observed, indicating shearing of [gamma]' precipitates by dislocations. At low hold stress levels and strain amplitudes the observed absence of dislocations in [gamma]' precipitates suggests that they are bypassed by dislocations. Dislocation networks at [gamma]/[gamma]' interfaces were found in most of the specimens. A directional coalescence of the [gamma]' precipitates was observed under certain testing conditions. The development of both these features with deformation could be followed. The softening effect is accompanied by both processes. (orig.)

Chaotic seismic faulting with a mass-spring model and velocity-weakening friction

We present a systematic analysis of the dynamical behavior introduced by fault zone heterogeneities, using a simple mass-spring model with velocity-weakening friction. The model consists of two sliding blocks coupled to each other and to a constant velocity driver by elastic springs. The state of this system can be characterized by the positions of the two blocks relative to the driver. Symmetry stabilizes the system and generates only cyclic behavior. For an asymmetric system where the frictional forces for the two blocks are not equal, the solutions exhibit chaotic behavior. The transition from stable cyclic behavior to chaos is characterized by the period-doubling route to chaos. Lyapunov exponents are computed to quantify the deterministic chaos and to locate the onset of the chaotic evolution in parameter space. In many examples of deterministic chaos, chaotic behavior of a low-order system implies chaos in similar higher order systems. Thus, our results provide substantial evidence that crustal deformation is an example of deterministic chaos.