Cyclic Mechanism Research Articles

Cyclic response and shear mechanisms of RC short walls strengthened with engineered cementitious composites thin layers

Cyclic response and shear mechanisms of RC short walls strengthened with engineered cementitious composites thin layers

Cyclic deformation mechanism and fracture behaviour of 316L stainless steel under thermomechanical fatigue loading

Thermomechanical fatigue (TMF) behaviour of 316L is investigated based on the internal stress and microstructural characterization at various cyclic stages. Results reveal that the cyclic stress response shows initial hardening followed by cyclic softening at a high strain amplitude, while presenting continuous cyclic hardening as the strain amplitude decreases. Among these, Out-of-phase TMF always shows cyclic softening irrespective of strain amplitude. It is important to note that the hardening of back stress and friction stress contribute to the initial and subsequent cyclic hardening. In contrast, the subsequent cyclic softening is mainly dominated by the reduced friction stress. It is observed that the proliferation of dislocations at grain boundaries and the enhanced dislocation interactions within the grains are primarily responsible for the hardening of back stress and friction stress, respectively. Specifically, the cyclic softening of friction stress is attributed to the annihilated dislocations as a result of cross-slip. It is also found from the hysteresis curves that the intensity of dynamic strain ageing is related to strain amplitude, loading history and phase angle, which correlates to the occurrence of cross-slip, the diffusion rate of the solute atom, the density of point defect and the mobility of vacancies. Finally, the effect of loading conditions on fracture behaviour is demonstrated from the point view of crack sources, secondary cracks, creep cavities and oxidation damage.

Molecular dynamics simulation of thermomechanical fatigue properties of Ni-based single crystal superalloys

In this paper, the thermomechanical fatigue (TMF) properties of Ni-based single crystal superalloys are studied by molecular dynamics simulations. Two different cyclic deformation mechanisms of superalloys are found under TMF loadings. The sample has a higher cyclic stress range, plastic strain energy density and a shorter fatigue life under Out-of-phase TMF loading than those under In-phase TMF loading. Moreover, the low-temperature tension half-cycle is more favorable for dislocations and stacking faults to cut into the γʹ precipitate phase, causing an earlier failure of superalloys under Out-of-phase TMF loading, which attracts more attention in actual operation.

Reaction mechanisms of alkyloxiranes for combustion modeling

Cyclic ethers are intermediates formed from unimolecular reaction of carbon-centered hydroperoxy-substituted radicals (̇QOOH), which are central to low-temperature chain-branching. Because cyclic ethers are isomer-specific proxies for ̇QOOH, detailed prescription of chemical reactions describing the consumption mechanisms is required for accurate combustion modeling. However, the most common approach in the development of chemical kinetics mechanisms is to use a simplified set of elementary steps that neglect the formation and subsequent reaction of cyclic ether radicals, which creates a source of mechanism truncation error. As a consequence, quantitative discrepancies between model predictions and experimental species profiles of cyclic ethers are ubiquitous and span a range of hydrocarbons such as n-butane, n-pentane, n-hexane, cyclohexane, hexene isomers, and hexanal. Moreover, uncertainties in species profile predictions of cyclic ethers translate directly to uncertainty in ignition predictions.For the explicit purpose of determining the extent to which cyclic ether consumption mechanisms affect combustion modeling, the present work examines the chemical kinetics underpinning such discrepancies using, as a representative case, a subset of cyclic ethers produced from n-butane oxidation. Detailed sub-mechanisms are developed using Reaction Mechanism Generator (RMG) for ethyloxirane and 2,3-dimethyloxirane, which form from unimolecular decomposition of β-̇QOOH radicals during n-butane combustion. The sub-mechanisms prescribe consumption reactions for both cyclic ethers, including ̇OH-initiated H-abstraction, O2-addition, RȮO isomerization, among other reactions, and were integrated with the NUIGMech1.1 mechanism to examine model predictions of species profiles and ignition delay times.Inclusion of the sub-mechanisms led to closer consistency between model predictions and experimental species profiles and also affected ignition predictions. Sensitivity analysis shows that rates of ̇OH-initiated H-abstraction are critical for determining temperature dependence of species profiles of cyclic ethers, which may serve as an indicator for the importance of branching fractions in the initiation step ̇OH + n-butane → H2O + 1‑butyl/2‑butyl. Moreover, flux towards ketohydroperoxide formation from n-butane increased upon addition of the sub-mechanisms, as determined by rate-of-production analyses conducted on ̇OH and related impact on ignition delay time simulations.The results herein demonstrate that detailed sub-mechanisms and accurate H-abstraction rates from cyclic ethers are necessary for high-fidelity predictions of chemical kinetics for combustion modeling. Continued refinement of detailed reaction mechanisms is required in order to produce accurate models for combustion that serve as a starting point for mechanism reduction techniques applied either to detailed mechanisms or to sub-mechanisms for consequent integration. Such techniques are required to enable modeling of reactive flows that incorporate computational fluid dynamics at practical conditions.

Perylene derivative and persulfate as highly efficient electrochemical system for constructing sensitive amperometric aptasensor

To design highly efficient electrochemistry system was important for construct simple and sensitive biosensors, which was crucial in clinical diagnosis and therapy. In this work, a novel electrochemistry probe N,N′-di (1-hydroxyethyl dimethylaminoethyl) perylene diimide (HDPDI) with positive charges was reported to show two-electron redox behavior in neutral phosphate buffer solution between 0 and -1.0 V. And K2S2O8 in solution could significantly increase the reduction current of HDPDI at −0.29 V, which was interpreted with cyclic catalysis mechanism of K2S2O8. Moreover, HDPDI as electrochemical probe and K2S2O8 as signal enhancer was used to design aptasensors for protein detection. Thrombin was used as target model protein. Thiolate ssDNA with thrombin-binding sequence was immobilized on gold electrode to selectively capture thrombin and adsorb HDPDI. The thiolate ssDNA without binding with thrombin was with random coil structure and could adsorb HDPDI through electrostatic attraction interaction. However, the thiolate ssDNA binding with thrombin became G-quadruplex structure and hardly adsorbed HDPDI. Thus, with increasing the concentration of thrombin, the current signal stepwisely decreased and was taken as detection signal. Compared with other aptasensors based on electrochemistry molecules without signal enhancer, the proposed aptasensors exhibited wider linear response for thrombin between 1 pg mL−1 and 100 ng mL−1 with lower detection limit 0.13 pg mL−1. In addition, the proposed aptasensor showed good feasibility in human serum samples.

Highly efficient LaMO3 (M = Co, Fe) perovskites catalyzed Fenton's reaction for degradation of direct blue 86

Perovskite-structured catalysts LaMO3 (M = Co, Fe) were successfully synthesized and attempted to catalyze hydrogen peroxide (H2O2) for the degradation of Direct Blue 86 (DB86), a carcinogenic phthalocyanine dye. The heterogeneous Fenton-like reaction revealed that the oxidative power of the LaCoO3-catalyzed H2O2 (LaCoO3/H2O2) process was higher than that of LaFeO3/H2O2. When LaCoO3 was calcined at 750 °C for 5 h, 100 mg/L of DB86 could be completely degraded within 5 min via LaCoO3/H2O2 system under H2O2 0.0979 mol/L, initial pH 3.0, LaCoO3 0.4 g/L, and 25 °C. The oxidative LaCoO3/H2O2 system has a low activation energy (14.68 kJ/mol) for DB86 degradation, indicating that it is a fast reaction process with highly favorable at high reaction temperatures. For the first time, a cyclic reaction mechanism of catalytic LaCoO3/H2O2 system was proposed based on the evidence of coexisting CoII and CoIII on the LaCoO3 surface and the presence of HO• radicals (major), O2•- radicals (minor), and 1O2 (minor). LaCoO3 perovskite catalyst was reusable and still maintained reactive with a satisfactory degradation efficiency within 5 min even after five consecutive uses. This study shows that the as-prepared LaCoO3 is a highly efficient catalyst for phthalocyanine dye degradation.

Short-range ordering plays a determining role in the low-cycle fatigue life improvement of fcc metals: A conclusive study on low solid-solution hardening Ni-Cr alloys

The effect of short-range ordering (SRO) on the low-cycle fatigue (LCF) behavior of low solid-solution hardening Ni-Cr alloys with high stacking fault energies (SFEs) was systematically studied under cycling at constant total strain amplitude (Δεt/2) in the range of 0.1%–0.7%. The results show that an inducement of SRO structures can notably improve the fatigue life of the alloy regardless of Δεt/2, and several unique fatigue characteristics have been detected, including the transition of fatigue cracking mode from intergranular cracking to slip band cracking, the non-negligible evolution from non-Masing behavior in pure Ni to Masing behavior in the Ni-40Cr alloy, and the secondary cyclic hardening behavior in the Ni-10Cr and Ni-20Cr alloys. All these experimental phenomena are tightly associated with the transformation in cyclic deformation mechanisms that is induced by SRO based on the “glide plane softening” effect. Furthermore, a comprehensive fatigue life prediction model based on total hysteresis energy has been reasonably proposed, focusing on the analyses of the macroscopic model parameters (namely the fatigue cracking resistance exponent β and the crack propagation resistance parameter W0) and microscopic damage mechanisms. In brief, on the premise that the effects of SFE and friction stress can be nearly ignored, as in the case of the present low solid-solution hardening Ni-Cr alloys with high SFEs, an enhancement of SRO in face-centered cubic metals has been convincingly confirmed to be an effective strategy to improve their LCF performance.

Deformation responses and strength criteria of different shotcrete-rock composites under triaxial cyclic compression

Understanding the mechanical performance of shotcrete-rock composites under cyclic loading is important for deep-buried underground projects. In this study, triaxial cyclic compressive tests were conducted on the shotcrete-rock composites (SC-G with granite and SC-S with sandstone) to investigate their cyclic failure mechanisms. The results showed that the confining pressure and rock type both had significant effects on the failure modes of the composite materials. Under triaxial cyclic loading, the failure process of the composites can be divided into five stages. Both the axial and lateral deformations of SC-S were larger than that of SC-G, but the elastic modulus of SC-S was smaller than that of SC-G. Besides, the volumetric deformations of the composites included both contraction and dilation stages, and the plasticity parameter was introduced to establish the dilatancy angle models for shotcrete-rock composites. In addition, considering the damage accumulation during triaxial cyclic loading, a yield surface model was proposed based on the M−C failure criterion to characterize the correlation of post-peak stress state, plasticity parameter, and strength parameters of the composite. The research findings can provide a great theoretical significance and engineering value for the safe design and construction of deep-buried tunnels.

Cyclic Liquid Nitrogen Fracturing Performance on Coal with Various Coal Ranks: Laboratory Investigation and Mechanism Analysis

Summary Hydraulic fracturing is one of the important stimulation methods to enhance the productivity of coalbed methane (CBM) wells. However, the commonly used water-based fracturing fluids can bring some bottlenecks such as large amount of water consumption, clay-mineral swelling, and poor fracturing performance on ductile coals. Cyclic liquid nitrogen (LN2) fracturing, as a novel nonaqueous stimulation method, has the potential to solve the above problems. In cyclic LN2 fracturing, supercooling LN2 is injected in a cyclic manner [i.e., alternating high injection rate (or pressure) and low injection rate (or pressure)]. Coals will be subjected to cyclic freeze-thaw, stress oscillation, and fatigue damage, which is expected to improve the stimulated reservoir volume. First, laboratory cyclic LN2 fracturing tests were conducted on coal samples with various coal ranks to investigate the fracture initiation/propagation behavior and fracture network patterns. Cyclic water fracturing tests were also conducted as comparisons. Then, computed tomography (CT) scanning and geomechanical/petrophysical properties tests before and after LN2 fracturing were performed to assist in understanding the cyclic LN2 fracturing mechanisms and implications. Finally, to solve the field application concerns, we investigated the possible fracture geometries at the field scale, temperature distribution of LN2 along the wellbore during injection, and the economic feasibility. The key factors affecting the temperature distribution during LN2 transportation along the wellbore were clarified for the first time. The results indicate that cyclic LN2 fracturing shows the potential to decrease the breakdown pressure and produce complex fracture networks. Different coal ranks have different responses to cyclic LN2 fracturing attributed to the variances in natural fracture development and geomechanical/petrophysical properties. Besides, increasing the cycle number is effective in enhancing the cyclic LN2 fracturing performance on coals with relatively higher geomechanical strengths and tighter rock mass. The suggested cycle numbers from low to high for different coal ranks are listed here: low-rank coal < high-rank coal < middle-rank coal. In field applications, gaseous nitrogen (N2) can be used as the annulus fluid to provide an effective insulation for heat transfer between the low-temperature LN2 and the surrounding environment. In addition, the net present value (NPV) analysis indicates that LN2 fracturing is an economically feasible stimulation method, which can exceed slickwater fracturing in some cases. The key findings are expected to provide preliminary insights into the potential field applications of cyclic LN2 fracturing in CBM or other unconventional oil/gas exploitation.

Cyclic bond deterioration of deformed steel bar in well-confined concrete

The cyclic bond deterioration mechanism of deformed steel bars embedded in concrete is critical for establishing the hysteretic bond stress-slip relationship. For a deformed steel bar, well-confined in concrete, the bond failure model under monotonic loading is governed by pullout, the bond deterioration trend under cyclic loading is remains unclear, especially in the case of applied lateral pressure. In this paper, the effect of uniaxial lateral pressure on the bond performance under different loading histories was studied. The test results indicate that the variation in bond parameters under varied lateral pressure is negligible. Therefore, the monotonic and reversed bond stress-slip constitutive relationship of a deformed bar failed by pullout, without lateral pressure confinement, can be used for simulating the bond response under different uniaxial lateral pressures. Cubic concrete specimens with small openings were used to quantitatively analyze the failure process under reversed loading through digital imaging correlation (DIC). The bond stress was observed to be nearly uniformly distributed along the interface at the initial loading stage. After increasing the pull-out or push-in loading to 75 %–85 % of the peak bond strength, we observed minute shear cracks between the interfaces. Subsequently, the length and width of the cracks were then gradually developed with the controlling slip and number of cycles, leading to reduced mechanical interaction and friction between the shear cracks.

Cyclic plasticity and deformation mechanism of AlCrCuFeNi high entropy alloy

High entropy alloys (HEAs) are newer siblings of multi-component metallic compound alloys with high tensile strength and ductility. The impact of temperature and strain rates under cyclic plasticity of AlCrCuFeNi HEA are investigated using molecular dynamics (MD) simulations. The modeling results show that interactions between partial dislocations in AlCrCuFeNi HEA during cycle deformation cause various lattice disorders. The impact of Bauschinger in the HEA is minimized by lattice disorder, which prevents dislocations from moving in reverse. Temperature, strain rates, and the twin boundary significantly impact Bauschinger's effect, which influences the plasticity cycle of AlCrCuFeNi. Furthermore, the effect of temperature, strain rates, and grain boundaries on lattice disorder is disclosed. The current study provides new insights into the mechanical property of AlCrCuFeNi HEA subjected to cyclic plasticity and deformation mechanism with atomic size.

Cyclic failure mechanisms of saturated marine coral sand under various consolidations

The undrained cyclic response of coral sand in earthquake is an important issue that must be considered in ocean engineering. A series of undrained cyclic triaxial tests was conducted on saturated coral sand using GDS dynamic triaxial apparatus. This study discusses the influence of consolidation ratio (kc), cyclic stress ratio (CSR), and relative density (Dr) on the undrained cyclic response of saturated coral sand. The characteristics of excess pore water pressure (EPWP), axial strain (εa), effective stress path, and undrained cyclic resistance of saturated coral sand are analyzed. The test results show that two axial strain generation modes exist in saturated coral sand: cyclic mobility and plastic strain accumulation. The EPWP (ue) generation modes are quite different subjected to various CSRs under isotropic consolidation, while that is consistent under anisotropic consolidation. Suitable models are selected to describe various EPWP generation patterns. Consolidation condition can significantly affect the development of effective stress path. The residual effective stress becomes large with the increase of kc. A new index called stress parameter (λ) is introduced to consider the effect of kc and CSR on undrained cyclic resistance comprehensively. The critical line to distinguish the failure point from non-failure point of coral sand specimens can be clearly found in the correlation between λ and the relative density after consolidation (Drc). The existence of the critical line in the relationship between stress parameter and relative density is also verified by using the literature data.

Graphical and Analytical Approaches for Analyzing Collective Behavior of Dynamic Multi-Agent Systems Governed by Generalized Cyclic Pursuit Mechanism

Graphical and Analytical Approaches for Analyzing Collective Behavior of Dynamic Multi-Agent Systems Governed by Generalized Cyclic Pursuit Mechanism

Cyclic Differentiable Architecture Search.

Differentiable ARchiTecture Search, i.e., DARTS, has drawn great attention in neural architecture search. It tries to find the optimal architecture in a shallow search network and then measures its performance in a deep evaluation network. The independent optimization of the search and evaluation networks, however, leaves a room for potential improvement by allowing interaction between the two networks. To address the problematic optimization issue, we propose new joint optimization objectives and a novel Cyclic Differentiable ARchiTecture Search framework, dubbed CDARTS. Considering the structure difference, CDARTS builds a cyclic feedback mechanism between the search and evaluation networks with introspective distillation. First, the search network generates an initial architecture for evaluation, and the weights of the evaluation network are optimized. Second, the architecture weights in the search network are further optimized by the label supervision in classification, as well as the regularization from the evaluation network through feature distillation. Repeating the above cycle results in a joint optimization of the search and evaluation networks and thus enables the evolution of the architecture to fit the final evaluation network. The experiments and analysis on CIFAR, ImageNet and NATS-Bench [95] demonstrate the effectiveness of the proposed approach over the state-of-the-art ones. Specifically, in the DARTS search space, we achieve 97.52% top-1 accuracy on CIFAR10 and 76.3% top-1 accuracy on ImageNet. In the chain-structured search space, we achieve 78.2% top-1 accuracy on ImageNet, which is 1.1% higher than EfficientNet-B0. Our code and models are publicly available at https://github.com/microsoft/Cream.

Recent advances of structural/interfacial engineering for Na metal anode protection in liquid/solid-state electrolytes.

Na metal anode is one of most promising anode materials for next-generation secondary batteries. However, the practical application of Na anode is limited by dendritic growth, rapid volume change, and serious interface problems in the process of Na electroplating/stripping, resulting in low coulombic efficiency, short life, and safety issues of sodium metal batteries (SMBs). Herein, the cyclic instability mechanisms of the Na anode and the corresponding advanced protection strategies including in situ solid-electrolyte-interphase (SEI), artificial SEI, and three-dimensional conductive frame, are systematically reviewed. Notably, this review summarizes the latest research progress on interface modification and electrode modification of all-solid-state SMBs. Finally, the outlooks of anode interphase in SMBs are summarized and prospected, providing a promising way for high-energy and safe SMBs.

Theoretical mechanistic insights into the electrophilic addition of hydrogen halides to alkynes.

The electrophilic addition of hydrogen halides to alkynes, also called polar hydrohalogenation of alkynes, is one of the most classical and important organic reactions. Mechanistic and stereoselective insights into the hydrohalogenation of various structurally different distinct alkynes, including both alkyl and aryl substituted acetylenes, in acetic acid were investigated theoretically via density functional theory (DFT) calculations. The results indicate that π-complexes between hydrogen halides and alkynes are first formed, and then all alkynes can undergo a competitive bimolecular intimate ion-pair syn-addition process and a pentamolecular concerted anti-addition process through the cyclic proton transfer mechanism for proton transfer in the absence of tetraalkylammonium halides or a termolecular electrophilic addition (AdE3) process in the presence of tetraalkylammonium halides. All aliphatic alkynes undergo slightly to obviously predominant anti-addition in hydrohalogenations both in the absence and presence of tetraalkylammonium halides. Aromatic 1-arylalk-1-ynes favour syn-additions through bimolecular intimate ion-pair processes with asynchronous concerted characteristics in the absence of tetraalkylammonium halides, while most of them generally prefer anti-addition in the presence of tetraalkylammonium halides. The stereoselectivity is significantly affected by both the electronic and steric effects of 1-arylalk-1-ynes and halides in the reaction mixture. Strongly electron-rich and bulky 1-arylalk-1-ynes generally favour syn-addition in the presence of tetraalkylammonium halides, especially arylethynes in hydrochlorination. Anti-Markovnikov hydrohalogenations of 1-arylalk-1-ynes also prefer anti-addition both in the absence and presence of tetraalkylammonium halides even in small amounts due to high activation energies. The current investigation provides deep insights into the mechanism and stereoselectivity in polar hydrohalogenations of alkynes.

A coupled XFEM fatigue modelling of crack growth, delamination and bridging in FRP strengthened metallic plates

This paper proposes an extended finite element method (XFEM) modelling approach coupled with cyclic damage mechanics criteria to simulate the fatigue crack growth (FCG), progressive delamination, and bridging in metal-fibre reinforced polymer (FRP) composites. The FCG in the metal is described using linear elastic fracture mechanics. The cycle-by-cycle degradation of the adhesive layer, progressive damage in the FRP layers, and metal-FRP interface delamination are modelled using the damage mechanics criteria. The proposed XFEM model successfully simulates the fatigue behaviour of FRP-strengthened metallic plates. The FCG rates, crack trajectories, fatigue lives, and failure modes satisfactorily agree with the corresponding experimental data.

Cyclic deformation response and strain-induced martensitic transformation of β single phase Ti-35421 alloy

Compared with bimodal microstructure, the low-cycle fatigue (LCF) behavior and cyclic deformation mechanism of a near β Ti-3Al-5Mo-4Cr-2Zr-1Fe (Ti-35421) alloy with single β were systematically investigated. Lower strength, but higher ductility and longer LCF life were found for Single β. The nanoscale α'' martensite was detected in Single β by selected area electron diffraction pattern. Besides, slips and strain induced martensitic transformation played the major deformation mechanisms in Single β. Moreover, the existence of α'' contributed to the limit of microcracks nucleation in Single β, which resulted in a better fatigue life.

Unusual phototransduction via cross-motif signaling from Gq to adenylyl cyclase in intrinsically photosensitive retinalganglion cells

Nonimage-forming vision in mammals is mediated primarily by melanopsin (OPN4)-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs). In mouse M1-ipRGCs, melanopsin predominantly activates, via Gαq,11,14, phospholipase C-β4 to open transient receptor 6 (TRPC6) and TRPC7 channels. In M2- and M4-ipRGCs, however, a prominent phototransduction mechanism involves the opening of hyperpolarization- and cyclic nucleotide-gated channels via cyclic nucleotide, although the upstream steps remain uncertain. We report here experiments, primarily on M4-ipRGCs, with photo-uncaging of cyclic nucleotides and virally expressed CNGA2 channels to conclude that the second messenger is cyclic adenosine monophosphate (cAMP) - very surprising considering that cyclic guanosine monophosphate (cGMP) is used in almost all cyclic nucleotide-mediated phototransduction mechanisms across the animal kingdom. We further found that the upstream G protein is likewise Gq, which via its Gβγ subunits directly activates adenylyl cyclase (AC). Our findings are a demonstration in a native cell of a cross-motif GPCR signaling pathway from Gq directly to AC with a specific function.

Hydrogenated Si-doped g-C3N4: Promising electrocatalyst for CO2 capture and conversion

Electrochemically converting CO2 into value-added carbonaceous chemicals offers an effective route to alleviate anthropogenic climate change as well as achieve a carbon–neutral life for society. Herein, a metal-free electrocatalyst of hydrogenated Si-doped C3N4 (HSi1@C3N4) was proposed via the first-principles calculations for carbon dioxide reduction reaction (CO2RR). It was found that the hydrogenation strategy on Si-doped C3N4 remarkably modulated the electronic properties of the Si atom, which accounted for initial CO2 adsorption. In addition, the results demonstrated that the appropriate applied potentials could also boost CO2 activation. Through comprehensive simulations of the reductive reactions under various voltages which have always been studied in experiments, we unravel a cyclic reaction mechanism on –OH terminated HSi1@C3N4 (HSi1@C3N4-OH) for efficient and selective conversion of CO2 into CH4. The effect of Si concentration on CO2 reduction was also studied. The present work predicts the HSi1@C3N4 as high activity and selectivity electrocatalyst towards CO2RR, and highlights the important roles of hydrogenation strategy and applied potentials on CO2 activation, which may provide useful guidance for the design of high-performance and eco-friendly CO2RR electrocatalysts.