Local Contact Research Articles

Tribological analysis of rotor system startup considering deformations of high elastic rubber bushings and grease lubricated plastic bearings

To achieve a compact design, reduced noise, and extended operational lifespan of the air conditioner indoor unit, a novel motor rotor system was implemented. This system utilizes three engineering plastic bearings, encased in high-elasticity rubber bushings and lubricated with grease. Yet, the absence of a simulation model that accurately represents the structural and material properties of this bearing-rotor assembly hampers the precise evaluation of how design parameters influence system performance. As such, in the present study, an innovative tribo-dynamics model was established using a coupling approach that integrates dynamics and tribology. This model encompasses a 4-degree-of-freedom rotor dynamics framework and a grease elastohydrodynamic model, which accounts for the deformation of both rubber bushings and plastic bearings. Utilizing this tribo-dynamics model, the effects of the elastic modulus of the bushing on the tribological properties of the system were explored. The results show that a small elastic modulus of the bushing effectively reduced the local high contact pressure between the journal and the bearing during startup. However, the elastic modulus cannot be excessively low, as it would adversely affect the range of journal motion and the film thickness under rated operating conditions.

Analysis of the tooth-root stress of external spur gears with high effective contact ratio

For spur gears with contact ratio close to 2, the extension of the contact interval resulting from loaded tooth deflections and local contact deformations may result in an effective contact ratio above 2. In these cases, the load is transmitted by at least two tooth-pairs, the maximum load and tooth-root stress decrease, and therefore the calculation methods of the gear rating Standards ISO and AGMA provide very conservative results. In this work, two models are applied to the calculation of the tooth-root stress of load-induced high contact ratio external gears: (i) an analytic model of load sharing, based on the minimum energy method, and (ii) a finite element model, which validates the results obtained from the previous model. Obtained values of the stress are compared with those provided by ISO and AGMA rating methods, which do not account for the stress reduction due to the higher contact ratio. A new modification coefficient is proposed to correct these conservative values, which allows the AGMA and ISO geometry factors to remain as no load-dependent factors and keep their actual calculation methods and significance.

Smokeless tobacco- and quid-associated localized lesions of the oral cavity: A cross-sectional study from a dental institute.

There is a well-established link between the use of smokeless tobacco (ST) and the development of oral cancer. This study was conducted to evaluate the impact of tobacco use, quid use, and other adverse habits related to smoking and alcohol consumption on ST-induced localized lesions. The aim of the study was to examine the demographic data, frequency and contact duration of ST on the lesion, as well as to conduct a clinical evaluation of these parameters. A total of 13,442 patients who had been experiencing oral and dental symptoms for a period of at least 6 months were screened. Of these, 334 patients were diagnosed with STor quid-induced localized lesions and had a positive history of ST or quid use. A structured questionnaire was employed to conduct interviews with participants regarding their use of ST and other adverse habits, including smoking and alcohol consumption. Other information related to the use of ST or quid and clinical findings were also recorded, along with the patients' demographic details. A statistical analysis was carried out using the χ2 test and the regression analysis. The overall prevalence of ST-induced localized lesions was found to be 2.48%. In the study population, the majority of participants (58.7%) reported a habit of using khaini, while 26.8% reported using gutkha. The study found significant differences in the severity of ST-induced localized lesions and contact duration, frequency of the habit, and the presence of additional habits such as smoking and/or alcohol consumption. Based on this study, we proposed a modified Greer and Poulson's classification of ST-induced lesions, dividing them into 4 clinical types. Smokeless tobacco-induced localized lesions frequently remain asymptomatic, with patients unaware of their presence. Other adverse habits, including smoking and alcohol consumption, as well as increased ST contact duration were associated with the development of more severe ST-induced localized lesions.

Insight into the fretting corrosion behavior of 316L steel in liquid lead-bismuth eutectic at 500°C

Due to flow induced vibration caused by coolant circulation, fretting corrosion inevitably occurs between fuel cladding, heat exchanger tubes and their holders in Gen IV lead-bismuth eutectic (LBE) cooled nuclear reactors. In the current work, fretting corrosion behavior of 316 L steel in oxygen-saturated LBE at 500 °C has been investigated. It is shown that within the gross slip regime, the microstructure under fretting interface presents a stratified structure, composed of third body layer, oxide scales and plastic deformation layer. At the early stage of fretting corrosion, the dominant damage mechanism is fretting wear, showing that the thickness of third body layer is much larger than that of oxide scale. As fretting time increases, the dominant damage mechanism is gradually changed to LBE corrosion and fretting wear together, as the visible oxide scale is formed next to the third body layer. Moreover, the growth rate of oxide scales under fretting interface is accelerated by over an order of magnitude compared to that when 316 L steel exposed to LBE directly. In particular, after 60 h exposure, the thicknesses of oxide scale related to the worn and unworn regions are ∼4.5 μm and ∼0.2 μm, respectively. The occurrence of such phenomenon is thought to be ascribed to the severe plastic deformation under fretting contact interface, since the crystal defects served as perfectional nano-channels can promote the diffusivity of oxygen atoms. In addition, the acceleration diffusivities of oxygen atoms caused by the local high contact stress may also be responsible for this matter.

Design of Gearings from Involute-Bevel Gears

The article presents formulas for determining the dimensions of involute-bevel gears and the gearings composed of them. It examines the most general cases of gearings formation, consisting of two involute-bevel gears with crossing axes (hyperboloid gearings), with intersecting axes (bevel gearings), and with parallel axes (cylindrical gearings). Gearings composed of involute-bevel gears have design, technological, and operational advantages compared to gearings composed of conventional cylindrical and bevel gears. The use of involute-bevel gearings with crossing axes allows for achieving the required contact character of the teeth from localized contact to linear contact, reducing sensitivity to manufacturing and assembly errors, and increasing the load capacity of the gearing compared to helical gearings from cylindrical gears. Bevel gearings with involute-bevel gears allow for the creation of gearings with any desired small shaft angles, which is difficult to achieve with conventional bevel gears. The use of internal meshing bevel gearings with modified tooth profiles in planetary reducers allows for gearings comparable to harmonic drives in terms of power and kinematic characteristics, but with a higher operational life. The use of involute-bevel gears in cylindrical gearings improves the smoothness of the mechanism and allows for adjusting the center distance and backlash in the meshing, making them suitable for backlash-free drives. By combining the taper angles of the gears and the inclination of the teeth, it is possible to create a one-way rotation mechanism - a freewheel mechanism. Modern CAD systems do not take into account the geometry features of gearings composed of involute-bevel gears, which limits their application in technology. The article proposes an algorithm for calculating the main geometric parameters of gearings composed of involute-bevel gears with arbitrary axis placement in space. Examples of geometric calculations of various types of gearings based on the proposed algorithm are provided.

Adjacent Neuronal Fascicle Guides Motoneuron 24 Dendritic Branching and Axonal Routing Decisions through Dscam1 Signaling.

The formation and precise positioning of axons and dendrites are crucial for the development of neural circuits. Although juxtracrine signaling via cell-cell contact is known to influence these processes, the specific structures and mechanisms regulating neuronal process positioning within the central nervous system (CNS) remain to be fully identified. Our study investigates motoneuron 24 (MN24) in the Drosophila embryonic CNS, which is characterized by a complex yet stereotyped axon projection pattern, known as 'axonal routing.' In this motoneuron, the primary dendritic branches project laterally toward the midline, specifically emerging at the sites where axons turn. We observed that Scp2-positive neurons contribute to the lateral fascicle structure in the ventral nerve cord (VNC) near MN24 dendrites. Notably, the knockout of the Down syndrome cell adhesion molecule (Dscam1) results in the loss of dendrites and disruption of proper axonal routing in MN24, while not affecting the formation of the fascicle structure. Through cell-type specific knockdown and rescue experiments of Dscam1, we have determined that the interaction between MN24 and Scp2-positive fascicle, mediated by Dscam1, promotes the development of both dendrites and axonal routing. Our findings demonstrate that the holistic configuration of neuronal structures, such as axons and dendrites, within single motoneurons can be governed by local contact with the adjacent neuron fascicle, a novel reference structure for neural circuitry wiring.Significance Summary We uncover a key neuronal structure serving as a guiding reference for neural circuitry within the Drosophila embryonic CNS, highlighting the essential role of an adjacent axonal fascicle in precisely coordinating axon and dendrite positioning in motoneuron 24 (MN24). Our investigation of cell-cell interactions between motoneurons and adjacent axonal fascicles-crucial for initiating dendrite formation, soma mislocation, and axonal pathfinding in MN24-emphasizes the neuronal fascicle's significance in neural circuit formation through Dscam1-mediated inter-neuronal communication. This enhances our understanding of the molecular underpinnings of motoneuron morphogenesis in Drosophila Given the occurrence of analogous axon fascicle formations within the vertebrate spinal cord, such structures may play a conserved role in the morphogenesis of motoneurons via Dscam1 across phyla.

Optimizing strategy of bifacial TOPCon solar cells with front-side local passivation contact realized by numerical simulation

The tunnelling oxide passivation contact (TOPCon) solar cells have been impressive in the global photovoltaic (PV) market originating from their high efficiency and stability. However, it exhibits significant recombination losses due to its boron diffusion, laser damage and metal-semiconductor contact on front side. The bifacial TOPCon structure demonstrates massive potential in the improvement of passivation and contact performance with the premise that it can solve the parasitic absorption of polycrystalline silicon (poly-Si). In this study, the localized poly finger structure with excellent optics and passivation performance is designed in the front side of bifacial solar cells to compare with traditional TOPCon and full-area poly passivation devices. The theoretical efficiency and detailed power loss analysis in our simulation reveal that suppressing the recombination of FSF (front surface field) and the contact area is the crucial strategy to improve device performance, with optimized efficiency of 26.62 % and FF of 85.16 %. These results indicate that the route of BJ (back junction) structure containing localized selective contact and full coverage high-quality passivation holds potential in realizing both high Jsc and Voc for FBC (front and back contact) solar cells, featuring great instructive significance for future industrialization of PV production.

Hyperspectral Imaging Database of Human Facial Skin.

The perceived color of human skin is the result of the interaction of environmental lighting with the skin. Only by resorting to human skin spectral reflectance, it is possible to obtain physical outcomes of this interaction. The purpose of this work was to provide a cured and validated database of hyperspectral images of human faces, useful for several applications, such as psychophysics-based research, object recognition, and material modeling. The hyperspectral imaging data from 29 human faces with different skin tones and sexes, under constant lighting and controlled movements, were described and characterized. Each hyperspectral image, which comprised spectral reflectance of the whole face from 400 to 720 nm in 10 nm steps at each pixel, was analyzed between and within nine facial positions located at different areas of the face. Simultaneously, spectral measurements at the same nine facial positions using conventional local point and/or contact devices were used to ascertain the data. It was found that the spectral reflectance profile changed between skin tones, subjects, and facial locations. Important local variations of the spectral reflectance profile showed that extra care is needed when considering average values from conventional devices at the same area of measurement.

Mechanochromic Suction Cups for Local Stress Detection in Soft Robotics

Advancements in smart soft materials are enhancing the capabilities of robotic manipulators in object interactions and complex tasks. Mechanochromic materials, acting as lightweight sensors, offer easily interpretable visual feedback for localized stress detection, structural health monitoring, and energy‐efficient robotic skins. Herein, an innovative mechanochromic soft end‐effector capable of discerning local contact stresses during mechanical interactions with objects is presented and their relative position is ascertained. This system utilizes a reversible force‐induced color switch in a thin layer of spiropyran‐functionalized polydimethylsiloxane, which coats a silicone‐made suction cup. The mechanochromic suction cup is integrated with a 3D‐printed compact load‐transferring system and electronic color‐changing detection elements. The assembly may serve as a synthetic receptor for robotic actuators, discerning localized interaction forces down to 3 N. The system's resilience to varying environmental factors, including illumination, tilting, and interaction with objects of various shapes is verified. The results indicate potential for exteroceptive solutions in reconfigurable manipulation tasks without compromising the overall softness of the manipulator.

Oil Distribution around Ball–Raceway Local Contact Region in Under-Race Lubrication of Ball Bearing

The distribution of oil and gas phases around ball–raceway local regions is an important basis and foundation for determining whether a bearing is sufficiently lubricated. To obtain the oil phase distribution law in the inner raceway–ball contact local region (IBCR) and outer raceway–ball contact local region (OBCR) of the ball bearing with under-race lubrication, the numerical simulation method is used. The effects of bearing rotation speed, oil flow rate, oil viscosity, and oil density on these two regions are studied. The results indicate that the oil phase exhibited significant periodic changes in both time and space. Compared with that in the IBCR, the oil phase distribution in the OBCR is more uniform. Increasing the bearing rotation speed and reducing the oil flow rate made the IBCR and OBCR more uniform. Changing the oil viscosity only alters the distribution pattern of the OBCR. The oil density may not affect the fluid flow state or the oil phase distribution in the bearing.

Interactions of contact force, impedance, and power during repeated atrial arrhythmia ablation after previous atrial fibrillation ablation

BackgroundAcutely effective repeated radiofrequency catheter ablation (RFCA) after previous atrial fibrillation ablation depends on several parameters including local impedance (LI), contact force (CF), and power. ObjectiveWe aimed to investigate the relationship of LI, CF, and power to the LI drop in a repeated atrial RFCA environment. MethodsConsecutive patients undergoing repeated atrial RFCA were studied. High-quality local electrograms were analyzed for morphology changes indicating effective RFCA and associated LI dynamics. The influence of baseline LI, mean CF, and power on the LI drop was analyzed. Investigated power levels included ≤25 W, 30 W, and ≥40 W. ResultsA total of 1390 RFCA points from 48 patients (48% female; median age, 70 years) were analyzed. Of 309 analyzed electrograms, 40.5% showed effective RFCA morphology changes with an elevated median LI drop (effective, 19.7 Ω; partially effective, 14.1 Ω; P < .001). CF showed the highest correlation to the LI drop within high baseline LI and when applying ≥40 W (low baseline LI, R = 0.39; intermediate, R = 0.66; high, R = 0.72). Within low baseline LI regions, CF levels showed a lower correlation to the LI drop (≤25 W, R = 0.30; 30 W, R = 0.35; ≥40 W, R = 0.39). A mean CF ≥10 g resulted in elevated LI drops with higher power compared with lower power within all baseline LI tertiles (P < .001 each). ConclusionWithin high baseline LI regions, CF plays a greater role for the maximum LI drop when higher power is chosen. A mean CF ≥10 g ensures elevated LI drops with increasing power levels.

Lubrication Characteristics of Dry-Gas Seals with Spiral Grooves

To obtain an optimal range of structural parameters for dry-gas seals with good performance, this study employed advanced sensing technology to monitor and analyze the internal flow characteristics of dry-gas seals in real time. Additionally, the validity of the calculation program was verified through experimentation. Using steady-state performance parameters as evaluation indices, a calculation model with lubrication characteristics was developed. The results indicate that when there are 12 grooves, the gas film pressure distribution is uniform and has a high value. At pressures greater than 2 MPa, the opening force, leakage, and gas film stiffness change significantly due to enhanced dynamic pressure effects with high-pressure differences, which reduces the local contact forces and frictional forces. At a constant speed, decreasing the gas film thickness increases the pressure difference while increasing both the opening force and film stiffness; however, at higher rotational speeds where the gas flow becomes non-uniform, the stability of the gas film is affected, leading to increased frictional forces. When there are between 10 and 16 grooves with depths ranging from 5.0 to 6.0 μm, dynamic pressure effects caused by pressure gradients become apparent, resulting in good dry-gas sealing performance being achieved. This research provides a theoretical reference for optimizing the design of dry-gas seals, as well as their steady-state seal performance.

Atomistic understanding of ductile-to-brittle transition in single crystal Si and GaAs under nanoscratch

Ensuring ductile removal in a grinding process is crucial for achieving the desired finish on a hard and brittle single crystal. This study provides new insights into the material removal processes in Si and GaAs single crystals, exploring their deformation behaviour using Berkovich and Conical tips to replicate contact from a fixed abrasive grit. Experimental observations are compared with Molecular Dynamic (MD) simulations to uncover the atomistic deformation mechanisms during the ductile-to-brittle transition (DBT). Notable plastic deformation and minimal cracking were consistently observed in Si, irrespective of the tips used. MD simulations supported this observation, revealing pronounced chip formation indicative of ductile material removal. The resistance to cracking in Si was attributed to amorphization induced by localized high contact stresses. In contrast, GaAs showed a propensity for cracking, with MD simulations revealing dislocation and slip band formation, and cracks emerging in the areas of substantial plastic deformation. These findings address phenomena not previously discernible in experimental studies due to the challenge of real-time observation. Moreover, the tip geometry was shown to significantly influence stress distribution, impacting deformation and crack formation in GaAs. This study also reveals limitations in predicting the critical depth for DBT in both Si and GaAs throught the amended Bifano, Dow, and Scattergood (aBDS) models and MD simulation, offering nuanced insights into these challenges that have not been extensively explored. It was found that the experimental results exceeded predictions by an order of magnitude. These discrepancies underscore the aBDS model's disregard for essential material properties and tip geometry, while the disparities between MD simulation and experiment are primarily attributed to the inherent limitations in the simulated length scales and challenges in detecting initial subsurface cracks.

Evaluation of the New York City COVID-19 case investigation and contact tracing program: a cascade of care analysis

BackgroundNew York City (NYC) was the first COVID-19 epicenter in the United States and home to one of the country’s largest contact tracing programs, NYC Test & Trace (T2). Understanding points of attrition along the stages of program implementation and follow-up can inform contact tracing efforts for future epidemics or pandemics. The objective of this study was to evaluate the completeness and timeliness of T2 case and contact notification and monitoring using a “cascade of care” approach.MethodsThis cross-sectional study included all SARS-CoV-2 cases and contacts reported to T2 from May 31, 2020 to January 1, 2022. Attrition along the “cascade of care” was defined as: (1) attempted, (2) reached, (3) completed intake (main outcome), (4) eligible for monitoring, and (5) successfully monitored. Timeliness was assessed: (1) by median days from a case’s date of testing until their positive result was reported to T2, (2) from result until the case was notified by T2, and (3) from a case report of a contact until notification of the contact.ResultsA total of 1.45 million cases and 1.38 million contacts were reported to T2 during this period. For cases, attrition occurred evenly across the first three cascade steps (~-12%) and did not change substantially until the Omicron wave in December 2021. During the Omicron wave, the proportion of cases attempted dropped precipitously. For contacts, the largest attrition occurred between attempting and reaching (-27%), and attrition rose with each COVID-19 wave as contact volumes increased. Attempts to reach contacts discontinued entirely during the Omicron wave. Overall, 67% of cases and 49% of contacts completed intake interviews (79% and 57% prior to Omicron). T2 was timely, with a median of 1 day to receive lab results, 2 days to notify cases, and < 1 day to notify contacts.ConclusionsT2 provided a large volume of NYC residents with timely notification and monitoring. Engagement in the program was lower for contacts than cases, with the largest gap coming from inability to reach individuals during call attempts. To strengthen future test-and-trace efforts, strategies are needed to encourage acceptance of local contact tracer outreach attempts.

Tribological properties of ductile cast iron with in-situ textures created through abrasive grinding and laser surface ablation

This paper discusses the proposed abrasive grinding (AG) and laser surface ablation (LSA) method for creating in-situ textures on ductile cast iron (DCI) surfaces. LSA method removes spherical graphite of DCI’s surface, forming martensite and high residual stress on the matrix, thus increasing hardness. AG method uses Al2O3 abrasives to disrupt spherical graphite and form grinding-layer. Compared to LSA, AG method avoids residual stress and burrs, simplifies the processing technology. Tribological tests show that LSA-treated samples have a lower coefficient of friction (COF) and specific wear rate, especially under dry friction conditions, due to increased surface hardness. AG-treated samples have a more stable COF because the oxide layer reduces adhesive wear, grinding-layer provides solid lubrication and reduces localized contact stress.

Mitochondrial, nuclear and morphological differentiation in the swimming crab Liocarcinus depurator along the Atlantic-Mediterranean transition

Environmental gradients in the sea may coincide with phenotypic or genetic gradients resulting from an evolutionary balance between selection and dispersal. The population differentiation of the swimming crab, Liocarcinus depurator, an important by-catch species in the Mediterranean Sea and North-East Atlantic, was assessed using both genetic and morphometric approaches. A total of 472 specimens were collected along its distribution area, and 17 morphometric landmarks, one mitochondrial gene (COI) and 11 polymorphic microsatellite markers were scored in 350, 287 and 280 individuals, respectively. Morphometric data lacked significant differences, but genetic analyses showed significant genetic differentiation between Atlantic and Mediterranean populations, with a steeper gradient in COI compared to microsatellite markers. Interestingly, nuclear differentiation was due to an outlier locus with a gradient in the Atlantic-Mediterranean transition area overlapping with the mtDNA gradient. Such overlapping clines are likely to be maintained by natural selection. Our results suggest a scenario of past isolation with local adaptation and secondary contact between the two basins. Local adaptation during the process of vicariance may reinforce genetic differentiation at loci maintained by environmental selection even after secondary contact.

Highly efficient wide-bandgap perovskite solar cells prepared by fixing charge passivation in the interface layer

The severe stress on the surface of the wide-bandgap perovskite film will extend to the carrier transport layer (CTL)/metal electrode interface, leading to increased roughness of the CTL surface. This, in turn, adversely affects carrier transfer at the interface and compromises device stability. To address this issue, we devised a localized contact structure wherein molybdenum oxide (MoOx) interlayers of specific thickness were vacuum-deposited at the CTL/metal electrode interface to change the path of carrier transfer. Characterizations of the MoOx localized contact structure were done by Kelvin probe force microscopy, capacitance–voltage (C–V), electrochemical impedance spectroscopy, and x-ray photoelectron spectroscopy. It was observed that MoOx interlayer can generate negative fixed charges at hole transport layer/Ag interface, which changes the carrier concentration distribution, enhances the built-in voltage, and promotes the transfer of carriers near the interface. Compared to wide-bandgap perovskite solar cells (WB-PSCs, Eg = 1.65 eV) lacking the MoOx localized contact structure, the efficiency of the optimized device increased to 20.5%, accompanied by enhancements in overall performance parameters. Notably, the thermal and light stability of the unpackaged devices have been significantly improved.

Zoonotic Bridge: Unraveling the Role of Wild Birds in Spreading the Bacterial Pathogenic Diseases

While wild birds contribute significantly to our ecosystem, they also act as carriers for various zoonotic diseases affecting humans. These diseases are often transmitted through international and local migrations, direct contact, and water sources, as well as through droppings and the excretion of spores in their feces. Over time, they present significant risks to the health of humans and animals by serving as carriers and hosts for new strains of pathogens. This review emphasizes the significant zoonotic diseases caused by birds, which include bacterial infections. These pose substantial health risks to both humans and animals. The review delves into their epidemiology and clinical manifestations. Of utmost significance, it underscores the pivotal function of birds as both distributors and reservoirs of potentially significant zoonotic diseases.

Microstructural Analysis of Deposited Alkali Metal in “Anode-Free” Solid-State Batteries

Lithium metal as an anode material can greatly boost energy and power density in solid-state batteries.[1] However, challenges like local contact loss and dendrite growth limit the applicable current density. It was shown previously that the lithium microstructure can greatly influence the electrochemical performance of lithium, e.g. the stripping capacity until pore formation occurs.[2]Solid-state-batteries (SSBs) manufactured without the use of an alkali metal reservoir are under intense investigation, as they may enable unmatched energy densities without the need to handle reactive and inherently unsafe alkali metal foils. In these reservoir-free cells (RFCs) the alkali metal is usually stored in the discharged cathode active material upon assembly and thus only deposited at the anode current collector within the first charging step. However, despite its expected influence on the electrochemical performance, the microstructure of freshly deposited lithium has yet to be analyzed. Up to now, the lack of a combination of suitable preparation and analyses tools restrict any study of the microstructure of thin alkali metal films.Within this study, we designed a workflow to reliably analyze the microstructure of thermally processed lithium and sodium films. Using a combination of cryogenic focused ion beam (FIB) preparation and electron back-scatter diffraction (EBSD), we were able to exclude any recrystallization during room temperature storage or FIB preparation. Therefore, this newly developed workflow was further used to study the microstructure of otherwise buried alkali metal films, which were deposited in so called “anode-free” or reservoir free cell designs.Our analyses show that the grain size of plated alkali metal films is independent on the microstructure of used current collector and generally consists of very large grains, albeit not as large as as-bought foil. Even more interesting, every single deposited film consists solely of columnar grains with grain boundaries oriented perpendicular to the solid electrolyte interface, marking a clear difference to using an alkali metal foil as the anode. Our results are confirmed at two different RFCs, namely Cu|LLZO|Li and Steel|LPSCl|Li. Generally, we believe our research on metal anodes will open up the possibility of tackling more advanced scientific questions previously impossible to answer.(1) Krauskopf, T., Richter, F. H., Zeier, W. G. & Janek, J. Physicochemical Concepts of the Lithium Metal Anode in Solid-State Batteries. Chem. Rev. 120, 7745–7794 (2020).(2) Singh, D. K., Fuchs, T. et al. Origin of the lithium metal anode instability in solid-state batteries during discharge. Matter 6, 1463–1483 (2023).

The stick-slip bending behavior of the multilevel helical structures: A 3D thin rod model with frictional contact

The multilevel helical structures in various engineering and natural fields offer excellent deformation flexibility and load bearing capabilities. Understanding the interplay between the local frictional contact and the geometric characteristics of the helical structure under complex external loads has attracted considerable interest. In this work, the effect of local frictional contact behaviors on the bending in multilevel helical structures is investigated by using a combination of theoretical modeling, finite element (FE) simulations, and experiments. In the case of pure bending, the kinematic parameters of the bent multi-stage helix are derived concisely by the idea of the kinematic analogy. The bending stiffness of the multi-stage helix is further obtained. In the case of the combined tension/torsion and bending, the 3D thin rod model incorporating Coulomb’s friction is established to describe the mechanical responses. It is found that the relationship between equivalent bending stiffness and the laying angle exhibits nonlinearity. A comparison with the classical Papailiou model reveals that, for helical structures at large laying angles, the influence of friction is primarily determined by the internal force in the tangential direction, which is the core assumption of the Papailiou model. However, in the case of small laying angles, the helical twisting characteristics and the contribution of the internal forces and moments in the other two directions (normal and binormal directions) to the friction cannot be ignored. Subsequently, a multilevel frictional contact transmission formulation is proposed according to the force action–reaction principle. Based on the above formulation, the non-simplified thin rod equations with Coulomb’s friction are extended to describe the multilevel stick-slip bending behaviors of the second stage cable (3*3). The dissipation capacity of helical structures is evaluated quantitatively under the hysteretic bending. Finally, the theoretical model is verified by FE simulations and experimental results. This work provides insights for unveiling the intrinsic relationship between the nonlinear bending and local frictional contact behaviors in the multilevel helical structures.