Powder metallurgy (PM) technology is extensively employed in the manufacturing sector, yet its processing presents numerous challenges. To alleviate these difficulties, green machining of PM green ...compacts has emerged as an effective approach. The aim of this research is to explore the deformation features of green compacts and assess the impact of various machining parameters on the force of cutting. The cutting variables for compacts of PM green were modeled, and the cutting process was analyzed using Abaqus (2022) software. Subsequently, the orthogonal test ANOVA method was utilized to evaluate the significance of each parameter for the cutting force. Optimization of the machining parameters was then achieved through a genetic algorithm for neural network optimization. The investigation revealed that PM green compacts, which are brittle, undergo a plastic deformation stage during cutting and deviate from the traditional model for brittle materials. The findings indicate that cutting thickness exerts the most substantial influence on the cutting force, whereas the speed of cutting, the tool rake angle, and the radius of the rounded edge exert minimal influence. The optimal parameter combination for the cutting of PM green compacts was determined via a genetic algorithm for neural network optimization, yielding a cutting force of 174.998 N at a cutting thickness of 0.15 mm, a cutting speed of 20 m/min, a tool rake angle of 10°, and a radius of the rounded edge of 25 μm, with a discrepancy of 4.05% from the actual measurement.
The seismic performance of prefabricated reinforced concrete shear walls is a key point in the safety of the whole assembly structure under earthquake actions. In this study, six specimens of ...reinforced concrete shear walls were assembled with a cast-in-place vertical joint with a straight, L, or convex shape. The specimens were tested using a low cyclic loading test under an axial compression ratio of 0.2 or 0.3. The stress process, failure pattern, and hysteretic curve of each specimen were measured. Combined with a numerical analysis using the finite element method, the variations in the bearing capacity, stiffness degradation, ductility, and energy dissipation capacity of the tested specimens were analyzed. Results showed that all specimens failed in a shear pattern without an obvious failure phenomenon along the vertical joint. The hysteresis curves exhibited an obvious pinch phenomenon and good deformation ability. The seismic behavior decreased in sequence for the shear walls assembled with a cast-in-place vertical joint with a straight, L, or convex shape, while a higher axial compression ratio improved the bearing capacity of the shear walls. The shear wall with an L-shaped vertical joint had similar seismic behavior to that with a straight vertical joint, but the shear wall with a convex vertical joint exhibited a decrease of 8.5% and 10.9% in bearing capacity, 18.2% and 1.2% in ductility, and 13.1% and 20.6% in energy dissipation, respectively, under an axial compression ratio of 0.2 and 0.3. The bearing mechanisms of shear walls with different vertical joints are explained with the numerical analysis of the stress vector maps of concrete and the stress cloud maps of reinforcements at different stress levels.
In order to solve the problem of high fuel consumption and poor emission performance in high horsepower tractors, a parallel hybrid tractor system was designed using a dual power source of an engine ...and motor matched with a hydro-mechanical continuously variable transmission (HMCVT). An equivalent fuel consumption minimization strategy (ECMS) was used for power distribution of this hybrid system. To address the problem of poor adaptability of the equivalence factor to different working cycles in the conventional ECMS, a fuzzy adaptive equivalent fuel consumption minimization strategy (FA-ECMS) was proposed. A fuzzy PI controller based on battery SOC (State of Charge) feedback was designed to adjust the equivalence factor in real time, so as to achieve adaptive control of the equivalence factor. The physical model of the system was built by SimulationX, and the model of the control strategy was built using Matlab/Simulink. Two typical cycles of tractor plowing and road transportation were simulated. Under ECMS, the fuel consumption of the hybrid agricultural tractor was 14.3 L and 1.19 L in one plowing cycle and one transport cycle, respectively, with final battery SOC values of 60.75% and 60.32%, respectively. Under FA-ECMS, the hybrid farm tractor consumed 13.34 L and 1.13 L in one plowing cycle and one transport cycle, respectively, with final battery SOC values of 60.27% and 60.17%, respectively. The results showed that, with the introduction of a fuzzy PI controller to dynamically adjust the equivalence factor, the overall fuel consumption was reduced by 6.71% and 5.04%, respectively, and the battery power maintenance performance was improved. The designed control strategy could achieve a more reasonable power distribution between the engine and motor while maintaining the balance of the battery SOC.
•A new approach to make drift-hardening concrete walls by utilizing PC strands was proposed.•Four concrete walls were tested under reversed cyclic lateral loading.•The walls utilizing PC strands ...exhibited good drift-hardening capability up to 2.5% drift.•The PC strands were effective in reducing the residual deformation and crack width.•The flexural capacities calculated by ACI code show good agreement with test results.
A simple reinforcing method is proposed to make drift-hardening concrete walls with reduced residual deformation and crack width. In this method, high strength PC strands are utilized as the longitudinal reinforcing bars placed in the edge zones of wall panel in lieu of general normal-strength deformed rebars. To verify effectiveness of the proposed method, four concrete walls were fabricated and tested under reversed cyclic lateral loading while subjected to constant axial compression with an axial load ratio of 0.13. Two walls were reinforced by PC strands to represent the proposed drift-hardening walls, and the others utilized normal-strength deformed rebars, representing the code-based ductile walls. The code-based walls performed in a ductile manner until 2.5% drift before significant strength degradation occurred. The wall utilizing PC strands and properly confined by transverse reinforcement in the wall panel exhibited significant drift-hardening capability up to about 2.5% drift. The residual drift and crack width of this wall measured after unloading from the 2.0% drift were 0.41% and 0.16 mm, while those of the ductile walls were 1.06% and 0.8 mm, respectively. Comparisons with the test results have indicated that the calculated flexural capacities by AIJ code provisions agree fairly well with the test results and that utilizing ACI code provisions and AIJ code equation can give a reasonable evaluation of the failure mode of concrete walls, drift-hardening and ductile.
The complex physical properties of recycled fine aggregate affect the rheological and mechanical properties of mortar, thereby limiting its application in cement-based materials. This paper evaluated ...the geometric shape and pore structure of natural fine aggregate (NFA), recycled fine aggregate (RFA), and recycled fine aggregate modified by water glass (MRFA), and studied its water absorption and bulk density. The influence of complex physical properties of RFA before and after modification on the rheological behavior, strength development, and microscopic properties of mortar was analyzed. The rheological tests were carried out on the fresh mortar with 7 mixes, and the compressive strength and flexural strength of hardened mortar after curing for 3, 7 and 28 days were tested. The results shown that the modification of water glass has improved the water absorption and geometric shape of RFA to some extent, resulting in a small increase in the apparent viscosity and yield stress of recycled mortar compared to NFA mortar. When the replacement level of RFA was less than 30 %, the compressive strength of recycled mortar was 13 % higher than that of NFA mortar. As the replacement level increased to 40 %, the incorporation of water glass also helped to improve the mortar strength. The irregular geometric shape and high water absorption of RFA were conducive to achieving dense mechanical bonding and reducing the Ca/Si ratio in the interface transition zone.
•The geometric shape and pore structure of NFA, RFA and MRFA were evaluated.•Modification of water glass improved the water absorption and geometric shape of RFA.•The irregular geometric shape and high water absorption of RFA improved the ITZ.
Powder metallurgy (PM) is a manufacturing technique that employs metal powder as the raw material, which is then molded and sintered to produce various products. PM green compacts are inherently ...weak, rendering them prone to damage during machining due to cutting forces, which also affect the quality of the machined surface. To study the impact of different machining variables on cutting force, a finite element simulation (FEM) was employed, focusing on cutting thickness, cutting speed, tool rake angle, and rounded edge radius. The results indicated that cutting thickness had a highly significant impact on cutting force, while the rounded-edge radius and cutting speed were also significant factors. The tool rake angle was found to have minimal effects. The optimal parameters for minimizing cutting force were identified: a cutting thickness of 0.20 mm, a cutting speed of 120 m/min, a tool rake angle of 0°, and a rounded-edge radius of 40 μm, which reduced the cutting force to 887.95 N.
Graphite is extensively used in the engineering field due to its unique properties, and the study of its cutting mechanism has become particularly important. However, the brittle fracture mechanism ...of graphite makes it rather easy for cracks with a unique pattern of initiation and growth to develop when processing. Herein, the ABAQUS was selected to establish a finite element model (FEM) of the graphite cutting process. The internal crystal structure of graphite was modelled by a Voronoi structure, and a cohesion unit was globally embedded into the solid unit to simulate crack initiation and growth. In addition, the complete process of chip formation and removal was demonstrated. The analysis of the simulation results showed that the graphite material underwent three periodic cycles of material removal during the cutting process, i.e., large, tiny, and small removal stages. Meanwhile, the simulation results indicated that when ac was large enough, the crack gradually grew inside the graphite and then turned to the upper surface of the graphite. However, when ac was tiny enough, the cracks hardly expanded towards the inside of the graphite but grew upwards for a short period. Then, orthogonal cutting experiments of graphite were conducted, and the FEM was verified based on the experimental chip morphology, machined surface morphology, and current geometric model of the graphite cutting process. The simulation and experimental results were consistent. The hereby-presented FEM was a complement to simulations of the processing of brittle materials.
Numerous studies of changes in the climate, vegetation and landscape responses of the Tibetan Plateau (TP) during the Holocene have been published in recent decades. However, several conflicting ...interpretations are evident within these studies and a comprehensive review of the topic is needed to reconcile them, and thus to provide an improved understanding of the history and forcing mechanisms of Holocene environmental changes within the region. Here we review the evidence for changes in climate (temperature, precipitation/moisture), vegetation and landscape attributes (glacier and eolian activity) on the TP during the Holocene. Our main conclusions are as follows. 1) The patterns of Holocene mean annual temperature change on the TP remain controversial; however, an early to middle Holocene summer temperature maximum is evident, which coincided with high summer insolation and a strengthening of the Indian summer monsoon (ISM). This suggests that the summer land-sea thermal gradient, impacted by the temperature of the TP, may be an important factor driving orbital-scale ISM changes. 2) Lake-level records indicate an optimum in moisture conditions on the southwestern (SW) TP in the early Holocene, while on the northeastern (NE) TP the optimum occurred in the middle to late Holocene. This out-of-phase or anti-phased relationship may be linked to the role of the ISM in dominating precipitation on the SW TP, while the westerlies and East Asian summer monsoon dominated the precipitation on the NE TP. 3) Most of the lake-sediment-based stable isotope records (δ18O and leaf wax δD) exhibit a pattern similar to that of stalagmite δ18O records from monsoonal Asia, reflecting the dominance of large-scale patterns of atmospheric circulation, rather than localized moisture changes reflected by lake level records. 4) A synthesis of pollen records reveals that the extent of forest was maximal in the mid-Holocene, while from the early Holocene onwards alpine steppe shrunk and alpine meadow and desert gradually expanded. 5) Evidence of glacier advance increased slightly during the early Holocene, decreased during the mid-Holocene, and then increased substantially after 3 ka BP. 6) The integrated ages of eolian sand and loess from the NE TP reveal that eolian activity intensified during the early and late Holocene. Site inter-comparisons reveal that regional climate change played a major role in modulating changes in vegetation and other landscape attributes. Overall, producing Holocene climate reconstructions for the entire TP remains a major challenge even though much progress has been made. Further improvements in terms of the spatial coverage of high-resolution paleoclimatic records with robust chronological control, and a deeper understanding of the specific climatic significance of several climatic proxies, will facilitate an improved understanding of how the monsoon and the westerlies interacted and their impacts on vegetation and landscape changes on the TP.
•First comprehensive review of Holocene climatic and environmental changes for TP.•Early to middle Holocene summer temperature maximum on TP, driving a strong ISM.•Divergent patterns of changes in moisture conditions between the northern and southern TP.•Regional climate change modulating changes in vegetation and other landscape attributes.
It has been reported that several immune cells can release chromatin and granular proteins into extracellular space in response to the stimulation, forming extracellular traps (ETs). The cells ...involved in the extracellular trap formation are recognized including neutropils, macrophages, basophils, eosinophils, and mast cells. With the development of research related to central nervous system, the role of ETs has been valued in neuroinflammation, blood-brain barrier, and other fields. Meanwhile, it has been found that microglial cells as the resident immune cells of the central nervous system can also release ETs, updating the original understanding. This review aims to clarify the role of the ETs in the central nervous system, especially in neuroinflammation and blood-brain barrier.
Highlights
MnO rich in oxygen vacancies has been synthesized.
The synthesized MnO demonstrates excellent oxygen reduction reaction performance and high output power in Zn–air battery.
The high ...catalytic activity is attributed to the synergetic catalytic effect between oxygen vacancies and in situ generated Mn
3+
/Mn
4+
.
Among various earth-abundant and noble metal-free catalysts for oxygen reduction reaction (ORR), manganese-based oxides are promising candidates owing to the rich variety of manganese valence. Herein, an extremely facile method for the synthesis of cubic and orthorhombic phase coexisting Mn(II)O electrocatalyst as an efficient ORR catalyst was explored. The obtained MnO electrocatalyst with oxygen vacancies shows a significantly elevated ORR catalytic activity with a half-wave potential (
E
1/2
) of as high as 0.895 V, in comparison with that of commercial Pt/C (
E
1/2
= 0.877 V). More impressively, the MnO electrocatalyst exhibits a marked activity enhancement after test under a constant applied potential for 1000 s thanks to the in situ generation and stable presence of high-valence manganese species (Mn
3+
and Mn
4+
) during the electrochemical process, initiating a synergetic catalytic effect with oxygen vacancies, which is proved to largely accelerate the adsorption and reduction of O
2
molecules favoring the ORR activity elevation. Such an excellent ORR catalytic performance of this MnO electrocatalyst is applied in Zn–air battery, which shows an extra-high peak power density of 63.2 mW cm
−2
in comparison with that (47.4 mW cm
−2
) of commercial Pt/C under identical test conditions.
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