Logarithmic Spiral Movable Tooth Drive (LSMTD) is a novel type of precision heavy-duty transmission that possesses a wide array of potential applications in the field of robotic joints. Due to the unique transmission principle, the influence of design parameters on tooth profile curvature is significant. Inappropriate design parameters can lead to curvature interference, resulting in tooth profile top cutting and subsequent transmission failure. However, the lack of research on the curvature interference characteristics of LSMTD seriously restricts the development of forward design methods. To solve this problem, this study proposes a design method to avoid curvature interference. First, a curvature interference analysis model for LSMTD is established based on coordinate transformation and the meshing principle. This model is used to analyze the relationship between top cutting and curvature interference. On this basis, the influence of design parameters on tooth profile curvature is quantitatively analyzed through orthogonal experiments. A curvature interference boundary equation is established. With the validity of the equation verified, the distribution of curvature interference boundary lines is analyzed. Finally, the effectiveness of the proposed design method is validated through a design example, and a robotic joint component is manufactured. This study holds significant implications for the forward design of LSMTD.

Aluminum foams have attracted considerable attention from both industry and academia due to their distinctive mechanical and structural properties, which arise from their complex cellular architecture. A thorough understanding of the microstructural transformations during foam production is essential for optimizing such materials’ performance and expanding their industrial applications. In this study, molecular dynamics (MD) simulations employing the angular-dependent potential were performed to extract critical input parameters for developing a phase-field (PF) modeling framework of the aluminum–silicon (Al-Si) system. These parameters include the diffusion coefficient, specific heat capacity, gradient energy coefficient, and grain boundary mobility. The extracted values enable PF models to more accurately predict the microstructural evolution of the Al-Si systems during their foaming process. Alongside MD simulations, a suite of numerical methods including the mean-squared displacement method, energy fluctuation analysis, the capillary fluctuation method, and the random walk method were employed to obtain key thermophysical and kinetic parameters of the Al-Si system, which are difficult to measure experimentally. The established computational framework will ultimately be extended into a multiscale approach to advance the understanding of process–structure–property–performance relationships in metal foams and to enhance the predictive capabilities of multiscale material models for the design and optimization of metal foams.

As a critical component of the pantograph-catenary system, the surface physical characteristics of the carbon strip directly affect the wear mechanism of the friction pair and the current-carrying stability. In this study, a ring-on-block high-speed current-carrying tester was employed to investigate the correlation between the surface physical characteristics of the carbon strip (surface roughness) and its wear mechanisms under a sliding speed of 300 km/h, a current of 300 A, different normal loads, and varying test durations. The evolution of surface roughness was analyzed using white light interferometry (WLI). The results indicate that the surface roughness of carbon strips varies with both increasing normal load and prolonged test duration. Furthermore, the surface roughness of the carbon strips shows a negative correlation with current-carrying efficiency and a positive correlation with the wear-rate. Scanning electron microscopy (SEM) analysis reveals that the wear mechanism of the carbon strip varies under different loads. Notably, nodular protrusions appear on the surface of the carbon strip under low normal loads, which are formed by material transfer from the contact wire. Due to their high hardness, they significantly increase the friction coefficient and surface roughness of the carbon strip. The suppression of arc erosion pits and nodular protrusions can effectively improve the contact state of the friction pair, thereby enhancing the current-carrying efficiency of the pantograph-catenary system and the operational stability of the train.

Zinc oxide (ZnO) is widely used in high-performance semiconductor and optoelectronic devices. Nevertheless, ZnO is a hard-brittle solid, becoming a difficult-to-process material, and strong acids and alkalis are usually employed in the slurry. Moreover, the surface roughness (Sa) is normally more than 0.6 nm, and the material removal rate (MRR) in chemical mechanical polishing (CMP) is generally lower than 78.8 nm min-1. To solve this challenge, a novel, environmentally friendly CMP technique was developed, and the new slurry contains silica and ceria mixed abrasives, sodium carbonate, hydrogen peroxide, and disodium ethylenediaminetetraacetate (EDTA). After CMP, a surface roughness (Sa) of 0.514 nm is acquired, and the MRR is 137.182 nm min-1. To the best of our knowledge, both the Sa and MRR are the best for CMP on ZnO, compared with those reported hitherto. X-ray photoelectron spectroscopy (XPS) reveals that the peaks at 284.8 and 286.3 eV after CMP on ZnO are assigned to C-C or C-H bonds of the carbon backbone and C-O bonds of carboxylate of EDTA, respectively, according to the C 1s fine spectra. These peaks indicate the occurrence of complexation between Zn2+ and EDTA. Fourier transform infrared (FTIR) spectroscopy shows that a peak appears at 3415 cm-1, corresponding to the O-H stretching vibration originating from Zn-OH of Zn(OH)2. The peak at 1414 cm-1 is derived from the symmetric stretching vibration of COO- in EDTA. The emergence and shift of this peak from the free state in general at 1400 cm-1 verify the formation of a Zn-EDTA complex. The CMP mechanism is elucidated by XPS and FTIR. Firstly, ZnO was hydrated, forming Zn(OH)2. Then, ZnO and Zn(OH)2 were dissolved in an alkaline environment, and Zn2+ ions were released. The released Zn2+ ions were complexed by EDTA, generating a water-soluble complex and inhibiting the redeposition on the surface of ZnO. Mixed silica and ceria removed the softened ZnO and Zn(OH)2, and a fresh surface of ZnO was exposed. This cycle continues, and microscopic protrusions are preferentially removed. Finally, an ultrasmooth surface is obtained. Our outcomes pave a new way for achieving an ultrasmooth surface on hard-brittle ZnO with relatively high MRR using environmentally friendly CMP in an alkaline environment.

The logarithmic spiral movable tooth driver (LSMTD) is a new type of precision heavy-duty transmission, which is expected to solve the coexistence of high precision, strong overload and high-power density in traditional gear transmission. However, due to the special transmission principle, the tooth profile modification method of LSMTD and the influence of design parameters on meshing characteristics are still unclear, which seriously restricts its development. To solve this problem, this study proposes a systematic LSMTD tooth profile modification method and establishes the corresponding key meshing characteristic calculation model. First, according to the transmission defects of the basic tooth profile of LSMTD, a modification method and corresponding tooth profile equation are established; on this basis, the calculation model of key meshing characteristics such as entrainment speed, induced normal curvature, pressure angle of LSMTD is constructed, and the influence of design parameters on the meshing characteristics of LSMTD is analyzed; finally, the correctness of the LSMTD tooth profile modification method proposed in this paper is verified by comparing the finite element method with the experimental prototype, and the realization mechanism of high load-bearing capacity of LSMTD is further discussed. This research proposes the tooth profile modification method and key meshing characteristic calculation model of LSMTD, which is of great significance for the structural optimization design of LSMTD.

Titanium (Ti) alloys have low thermal conductivity, suffer from tool wear and deformation of workpieces and are difficult-to-machine metals. This contributes to surface roughness, Sa > 240 nm of Ti alloys after mechanical polishing with a low material removal rate (MRR). With the addition of assisting energy fields, the MRR is usually lower than 7 μm h-1. Nevertheless, there is a high demand to achieve Sa < 50 nm on a free surface blade to save energy and reduce the resistance of fluids. To address this challenge, novel photocatalytic shear-thickening chemical mechanical polishing (PSTCMP) was developed using a custom-made polisher. The new PSTCMP slurry contained ceria, corn starch, sodium bicarbonate and deionized water. After PSTCMP, the Sa and thickness of the damaged layer of a free surface blade of a Ti alloy decreased from 501.71 to 38.46 nm and from 634.79 to 7.83 nm, respectively, representing reductions of 92% and 99%. The MRR is 12.52 μm h-1. To the best of our knowledge, both the Sa and MRR are the best published to date for a Ti alloy blade with a free surface. PSTCMP mechanisms were interpreted using first-principles molecular dynamics, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Hydroxyl radicals were generated under ultraviolet irradiation on ceria with a size of 4.2 nm, oxidizing the surface of the Ti alloy and forming Ti-OH and Ti-O groups. A Ce-O-Ti interface bridge was produced between Ti-OH and Ce-OH, induced by the hydrolysis of ceria. Our findings provide a new way to fabricate nanometer-scale surface roughness on a free surface blade of a Ti alloy with a high MRR.

High-speed trains operate in low-temperature regions, where the low-temperature environment significantly alters the current-carrying performance and wear mechanisms of the friction pair materials in the pantograph-catenary system. To elucidate the frictional and current-carrying performance and wear mechanisms of the friction pair in a pantograph-catenary under extremely low-temperature conditions, especially the third-body effect induced by ice crystals and the role of layered brittle spalling, sliding wear experiments were conducted at 300 km/h, 150 A, 80 N, and ambient temperatures from −40 °C to 20 °C. The experimental results indicate that both the coefficient of friction and wear rate of the carbon strip increase with decreasing ambient temperature and exhibit a pronounced rise below 0 °C. Meanwhile, contact resistance fluctuations intensify and cumulative arc energy continuously increases, deteriorating current-carrying efficiency and stability. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses reveal that, with decreasing temperature, the interfacial oxide film is progressively reduced, while ice crystals and wear debris jointly form a third-body layer. Accordingly, the wear mechanism gradually evolves from predominantly adhesive wear at room temperature to abrasive wear at low temperatures, and further transforms into a mode dominated by lamellar brittle spalling at −30 °C to −40 °C. Especially, low-temperature-induced material embrittlement, oxide film failure, and third-body wear are the primary factors responsible for the degradation of current-carrying stability and the occurrence of abnormal wear in the pantograph-catenary friction pair. This study provides experimental evidence and theoretical guidance for material selection, design, and maintenance of pantograph-catenary systems in cold and alpine regions.

The tooth surface contact stress in the zero-backlash roller enveloping precision reducer (ZREPR) is a critical factor governing its transmission accuracy, efficiency, service life and structural strength. However, due to the complex thermal-structural interaction arising from rolling friction between the worm and the rollers, accurately predicting the frictional heat generated during meshing and the consequent thermal deformation remains challenging, resulting in imprecise characterization of thermal stress distribution and hindering effective design optimization. Here, this study calculates the frictional heat power generated at the interface between the outer and internal ring of the roller and the worm tooth surface, as well as the convective heat transfer coefficients based on the rolling contact characteristics. Taking these parameters as the thermal boundary conditions, a thermal-structural coupling model is established for the ZREPR, which enables the accurate analysis of the tooth surface stress to be realized under the temperature-rising conditions. This study shows that the rolling friction between the outer ring of the roller and the gear tooth surface is the main source of thermal power; the temperature of the worm wheel increases with the increase of the worm rotational speed and the worm wheel load; furthermore, the temperature rise of the worm tooth surface significantly affects the magnitude and distribution of the contact stress, which underscores the necessity of considering thermal effects in the design process. This study provides a valuable theoretical foundation for optimizing the performance and durability of the ZREPR.

As a critical component for transmitting electrical energy in pantograph-catenary systems of high-speed railways, carbon strips operate under high-speed and heavy-current conditions, where elevated surface temperature directly governs the wear mechanisms and operational safety of carbon strips. Therefore, investigating the surface temperature and wear mechanisms of carbon strips in the pantograph-catenary system is critical. This study quantitatively investigates the effects of loading current (70-150 A), normal load (90-110 N), and sliding speed (200-300 km/h) on the surface temperature, wear-rate, and friction coefficient of carbon strips sliding against copper contact wires, using a ring-block type high-speed wear tester. Surface morphology and elemental composition are characterized by scanning electron microscopy and energy-dispersive spectroscopy. Results indicate that the sliding speed has the most pronounced effect on surface temperature. A fundamental transition in the wear mechanism is identified at a critical threshold of 521 degrees C. Beyond this point, a severe molten-material ejection phenomenon occurs due to the abrupt change in arc force on the contact surface of the carbon strip. This phenomenon leads to splattering of surface material accompanied by direct material loss. It generates a substantial amount of cupric oxide particulate matter, markedly diminishing the carbon content on the strip surface while inducing a sharp nonlinear increase in the wear-rate. Therefore, controlling the interfacial temperature to suppress molten-material ejection is crucial for mitigating severe wear and ensuring the operational reliability of the carbon strip under extreme conditions.

Material removal mechanisms in whole frequency range of polishing are elusive, rising a challenge to control precisely on the accuracy and efficiency for form, waviness and surface roughness. To solve this challenge, novel generalized frequency range material removal models are proposed, based on the dynamic interaction between abrasives and polishing pads. The models were built using Preston equation with constrained modes of abrasives in various polishing pads according to structural features, utilizing Sigmoid function, Euler-Bernoulli beam theory, Green's function and Gaussian distribution. Single-point polishing and polishing experiments were performed on a developed five-axis polisher using 4 wt% ceria slurry at a pressure of 20 kPa and rotational speed of 200 rpm on a polishing pad. Material removal functions calculated by models are in good agreement with those of single-point polishing experiments. After polishing for 40 min on a fused silica specimen, peak-to-valley (PV) decreased from 391.908 to 113.166 nm conducted by a pitch pad. Non-woven fabric pad showed that rootmean-square (RMS) and surface roughness Sa reduced from 16.985 to 6.959 nm, and from 2.145 to 0.657 nm, respectively, and an average convergence efficiency of mid-frequency error enhanced 55%. Polished surface topography characterized by scanning electron microscopy reveals continuous and smooth, orange peel, and discrete characteristics for pitch, polyurethane and non-woven fabric pads, respectively, which is consistent with those predicted by the models. Our proposed models offer new insights to control precisely on the accuracy and efficiency for overall frequency range of a polished surface.

The effect of polishing pads is generally incorporated as a coefficient in the conventional Preston equation and its modified forms during the past century, and macroscopic stress distribution and microscopic motion states are discussed separately. To solve this challenge, we propose a novel cross-scale model using a unified physical framework integrating the macroscopic and microscopic states. The proposed model decomposes the effect of polishing pads into stress transfer and abrasive constraint factors. It connects microstructure, stress transfer, abrasive constraint and material removal in sequence and establishes a relationship between the microstructure of pads and the evolution of a polished surface. Finite element simulations show that the maxima of von Mises stresses on fused silica are 0.171, 0.749 and 0.446 MPa for non-woven, polyurethane, and asphalt pads, respectively, corresponding to the support of discrete fibers, local stress concentration and continuous transfer of stress. Furthermore, single-abrasive scratching confirms that the maxima of equivalent stress exerted by the associated three pads are 2.059, 4.701 and 7.771 MPa, respectively, relevant to weak, unstable and strong constraints of abrasives. Polishing experiments were performed on fused silica with ceria slurry. They demonstrate that the peak-to-valley value obtained using an asphalt pad decreases from 385.976 to 115.237 nm and the attenuation of power spectral density is 88%. The surface roughness Sa achieved using a non-woven pad is reduced from 2.145 to 0.721 nm. The predictions of the proposed model are in good agreement with the simulation and experimental results. Our outcomes provide new insights into achieving error convergence of full bands on polished surfaces using different polishing pads.

The non-uniform wear of the carbon strip decreases the performance of the carbon strip and the shortens the service life of the carbon strip. Especially at speeds above 300 km/h, the non-uniform wear of the carbon strip is more obvious and has an impact on the physical and chemical properties of the wear surface of the carbon strip. However, the behavior and mechanism of non-uniform wear of carbon strip and their effect on current-carrying properties of the carbon strip are not clear. In this work, the metal-impregnated carbon /copper alloy is used as the friction pairs to study the non-uniform wear of the carbon strip, under the test condition of speed (100 km/h-350km/h), current-carrying of 250 A and normal load of 140 N. The friction behavior of the contact pairs is detected, and the micro-morphology of wear surface of carbon sliding plate was observed by the scanning electron microscope (SEM) to reveal the non-uniform wear mechanism of the strips. The experimental results show that the non-uniform wear of the carbon strip becomes more and more obvious with the increase of sliding speed. The obvious non-uniform wear and metal condensate were observed on the surface of the carbon strip when the sliding speed exceeds 300 km/h. The wear mechanism of different areas on the worn surface is different, and the wear gradually increases along the sliding direction. Delamination wear and metal condensate reduce the hardness of the carbon strip, increase the wear depth, and decrease the electrical conductivity (increase the resistivity). The composition of metal condensate was analyzed by energy dispersive spectrometer (EDS), and it was found that the main components of the metal condensate were copper and its oxides. The metal condensate aggravates the non-uniform wear and the uneven electrical conductivity of the strip. Through this study, it indicates the current-carrying performance and wear stability of carbon strips can be significantly improved by reducing the metal condensate.

A novel near-neutral green CMP slurry was developed, achieving a close atomic surface on aluminum alloy. The surface roughness (Sa) was 0.231 nm, and the material removal rate was 12.56 μm h −1 .

It is extremely difficult to garner atomic surface of fused silica with surface roughness less than 0.1 nm, due to its hard and brittle nature. For achieving such atomic surface, material removal rate (MRR) is usually sacrificed greatly. In this regard, surface roughness and MRR are a pare of contradiction eternally in manufacturing field. To solve this challenge, novel green chemical mechanical polishing (CMP) was developed, and the slurry consisted of ceria, erbia, sodium tripolyphosphate, choline chloride (CC) and deionized water. After CMP, atomic surface is acquired on fused silica with surface roughness Sa of 0.07 nm at a measurement area of 20 x 20 mu m2, and MRR is 37.53 mu m/h. To the best of our knowledge, both the Sa and MRR are the best, compared with those published previously, breaking the contradiction between surface roughness and MRR. Transmission electron microscopy confirmed that the thickness of damaged layer is 3.25 nm. X-ray photoelectron spectroscopy (XPS) reveals that the concentration of Ce3+ increases from 24.17 % to 35.81 % and 41.54 % with addition of erbia and CC, respectively. Through incorporating CC, polydispersity index, zeta potential and contact angle varied from 0.213 to 0.168, -34.38 mV to -44.11 mV, and 51.996 degrees to 34.757 degrees, correspondingly, indicating the improvement of dispersity, stability and wettability, respectively. Fourier transform infrared spectroscopy and XPS demonstrate that hydroxylation happened on the surface of ceria and fused silica, forming Ce-OH and Si-OH bonds respectively, and generating Si-O-Ce bonds between them after dehydration condensation reaction. Our developed novel CMP on fused silica provides new insights to gain atomic surface with high MRR for a hard and brittle solid, which is beneficial for the potential application in high-performance devices.

The Dujiangyan–Siguniangshan mountain rack railway project is China’s first mountain rail transit. Most of its lines are located in mountainous areas and close to natural ecological protection areas, which have strict restrictions on the vibration and noise of train operation. At the same time, the vibration of mountain rack railway trains is also an important factor affecting the safety and riding comfort of trains. However, due to the multi-source vibration of gear teeth, wheels, rails, and suspensions, it is difficult to clearly define the vibration characteristics and vibration transmission path of the train, which has a serious impact on its vibration noise suppression and optimization. To this end, this study proposed a set of evaluation methods for the vibration characteristics and transfer paths of mountain rack trains based on a combination of dynamics and operational transfer path analysis (OTPA). Considering the interaction between the dynamic behaviors of the primary and secondary suspensions, the gear tooth contact behavior, the wheel–rail contact behavior and the dynamic behaviors of the track system, a dynamic model of a mountain rack train based on the finite element method was established, and the effectiveness of the model was verified through field experiments. On this basis, the OTPA method was used to establish a vibration transfer path model between the secondary suspension and the center of mass of the car body, and it was used to analyze the vibration mechanism and transfer path of the train body at the rated speed (20 km/h) and the limited speed (30 km/h). This study is of great significance for suppressing the vibration noise of mountain rack trains, reducing the impact on the ecological environment and improving ride comfort.

Tooth profile modification (TPM) is an essential process in the design of open gear rack, which plays an important role in improving the meshing performance and reducing the tooth surface wear. However, TPM and tooth surface wear cause significant alterations to the tooth profile, which in turn affects the contact characteristics on the tooth surface. This poses a significant challenge for predicting the dynamic wear evolution of modified gear rack. In this paper, a dynamic wear evolution model of modified gear rack considering the real-time variation of contact characteristics is proposed. Firstly, a wear model of gear rack under mixed elastohydrodynamic lubrication (EHL) is established, considering the lubrication state of the tooth surface. By incorporating the effects of TPM and tooth surface wear, a modified time-varying meshing stiffness (TVMS) model and a contact load distribution model are proposed. Based on the proposed model, the dynamic wear evolution of modified gear rack under mixed EHL is accurately predicted, by employing a cyclic iterative method to determining the real-time contact characteristics under the wear degradation of the tooth profile. After validating the effectiveness of the model, the dynamic wear evolution of the gear rack driving mechanism of a rack rail train is investigated, and a quantitative analysis of the effect of TPM parameters on wear depth is conducted. This study holds significant implications for unveiling the wear failure mechanism of modified gear rack and optimizing the design of TPM parameters.

As the current-carrying equipment for the high-speed railway, the pantograph-catenary system works under the condition of high speed and current density, which easy results in the non-uniform wear of the carbon strip in the pantograph-catenary system and affects the physical and chemical properties of the carbon strip. Especially, the heat-dissipation performance of carbon strips is deeply affected by non-uniform wear. The friction and non-uniform wear behavior of the carbon strip were studied under different working conditions (v = 350 km/h, Fn = 40-80N, I = 200-300A), using a ring-on-block friction and wear tester with a designed speed of 400 km/h. The temperature field, heat dissipation performance and their relationship with the wear characteristics of the carbon strip are also analyzed. The experimental results show that the temperature has a significant impact on the friction and wear behavior of the strip. The distribution law of the surface temperature of the carbon ribbon has a significant impact on its wear mechanism, that is: the areas with high surface temperature of the strip have severe wear, while the areas with low temperature show slight wear. In addition, the heat dissipation experiment results show that the heat flux density of thermal conduction in the slight wear area is nearly 40 times higher than that in the severe wear area. There is a clear coupling relationship between heat dissipation and wear of the carbon strip. Reducing delamination wear is one of the important ways to decrease the non-uniform wear of the carbon strip.

Graphene structural defects, including vacancies and line defects, are ubiquitous in assembled anti-wear coatings. The most typical line defects, such as atomic step edges and in-plane defects, are particularly susceptible to severe mechanical deformation and stress during tribological tests, which significantly declines load-bearing capacity and durability of graphene coatings. Herein, we utilized chemically inert diamond probes to systematically investigate the wear behavior of graphene step edges and in-plane defects under high contact stress. The experimental results show that at a critical contact stress (-6.7 GPa), the graphene defects undergo significant mechanical degradation, characterized by pronounced tearing and folding along a direction oriented approximately 60 degrees relative to the step edges or in-plane defects. Interfacial adhesion and friction measurements revealed that the observed purely mechanical wear behavior is governed primarily by the weakened chemical interactions at the contact interface under high mechanical stress. Furthermore, lattice characterization of the fractured edges using conductive atomic force microscopy (CAFM) shows that the torn graphene edges predominantly exhibit a zigzag (ZZ) crystallographic orientation, suggesting that a preferential tearing direction along the ZZ orientation. Further molecular dynamics (MD) simulations confirmed an intrinsic preference for ZZ-direction tearing, irrespective of stretching orientations or defect presence. This study provides insights into the failure mechanisms of graphene coatings subjected to high mechanical stress.

Daily inspection as a top priority to ensure the safe production of intelligent workshops, can directly respond to the degree of intelligence of the factory workshop, which often needs robots to inspect multiple target devices. To enhance the inspection quality of intelligent workshop inspection robots, this thesis is based on the InformedRapidly Exploring Random Tree (RRT) algorithm and introduces the concept of simultaneous expansion of multiple trees. This paper proposes a strategy involving random tree connectivity to the Multi-Informed-RRT* (MI-RRT*) global path planning algorithm, which is suitable for multi-objective point planning. It is verified through simulation that in solving the same planning problem for eight objective points, compared with the basic Informed-RRT* algorithm, the MI-RRT* algorithm's running time is reduced by 79.56 %, and the final generated path length is reduced by 25.26 %; compared with the Multi-RRT* algorithm, which is also used for solving the multi-objective point planning problem, the running time of the algorithm is reduced by 48.48 % and the final generated path length is reduced by 7.45 %. In conclusion, this study proposes a multi-objective point path planning algorithm tailored for the dynamic environment of intelligent workshops, achieved through the integration of MI-RRT* and an enhanced Dynamic Window Approach (DWA) algorithm. Experimental evidence substantiates that the path generated by the MI-RRT* algorithm, as presented in this paper, is superior, resulting in shorter robot running times and a substantial enhancement in inspection efficiency within the workshop. Simultaneously, it mitigates the issue of traditional inspection equipment leakage, thereby possessing tangible practical value.