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"Rubbing"
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Apparitions : frottages and rubbings from 1860 to now
This fascinating publication sheds light on a medium that combines the qualities of drawing with those of sculpture, printmaking, and painting, and is the first to focus exclusively on the art technique known as frottage, derived from the French word frotter, meaning \"to rub\"; Over 100 pieces, ranging from contemporary conceptual works to rubbings recording tombs and inscriptions, are assembled and sumptuously reproduced in color. More than 50 artists--including the famous, like Max Ernst, inventor of the term \"frottage,\" and the relatively unknown--are presented. Four thematic sections explore different aspects of frottage: its roots in Surrealism and the practice of automatic drawing; the notion of trace, of either a place or an idea left behind in a rubbing; the \"apparitions\"; or ghostlike attributes that can appear on the surface of an artwork; and the associations between rubbings, death, and memory.
Book
The numerical modeling of rotor–stator rubbing in rotating machinery: a comprehensive review
The rotor–stator rubbing in rotating machinery generated as a consequence of rotor imbalance, shaft misalignment, and casing deformation is a potential threat to the machinery that seriously affects its performance. Timely prediction and correction of the rubbing are essential for the prolonged life of the machinery and its overall performance. A complete understanding of the system behavior during interaction is a great challenge for researchers working in the field of rotor dynamics. Rubbing phenomena involve complex contact nonlinearities and associated thermal effects, which makes the analysis very difficult. Research works in this field are started with the analysis of simple two degree-of-freedom models and now dealing with extensive three-dimensional finite element models. This paper provides a comprehensive review of different numerical models of rotor–stator rubbing with respect to their ability in simulating the actual response characteristics. A detailed description of contact modeling is also presented with the advantages and disadvantages of each model. Different methods for solving the numerical models are briefly explained. In addition, a commentary on different emerging techniques of rub identification is also reported. Finally, some informed recommendations on future directions are made by stating what lacks in the current research activities.
Journal Article
Highly stable flexible pressure sensors with a quasi-homogeneous composition and interlinked interfaces
Electronic skins (e-skins) are devices that can respond to mechanical stimuli and enable robots to perceive their surroundings. A great challenge for existing e-skins is that they may easily fail under extreme mechanical conditions due to their multilayered architecture with mechanical mismatch and weak adhesion between the interlayers. Here we report a flexible pressure sensor with tough interfaces enabled by two strategies: quasi-homogeneous composition that ensures mechanical match of interlayers, and interlinked microconed interface that results in a high interfacial toughness of 390 J·m
−2
. The tough interface endows the sensor with exceptional signal stability determined by performing 100,000 cycles of rubbing, and fixing the sensor on a car tread and driving 2.6 km on an asphalt road. The topological interlinks can be further extended to soft robot-sensor integration, enabling a seamless interface between the sensor and robot for highly stable sensing performance during manipulation tasks under complicated mechanical conditions.
E-skins often have poor interfaces that lead to unstable performances. Here, authors report e-skins with a quasi-homogeneous composition and bonded micro-structured interfaces, through which both the sensitivity and stability of the devices are improved.
Journal Article
Nonlinear vibration response analysis of a rotor-blade system with blade-tip rubbing
An improved rotor-blade dynamic model is developed based on our previous works (Ma et al. in J Sound Vib, 337:301–320,
2015
; J Sound Vib 357:168–194,
2015
). In the proposed model, the shaft is discretized using a finite element method and the effects of the swing of the rigid disk and stagger angles of the blades are considered. Furthermore, the mode shapes of rotor-blade systems can be obtained based on the proposed model. The proposed model is more accurate than our previous model, and it is also verified by comparing the natural frequencies obtained from the proposed model with those from the finite element model and published literature. By simplifying the casing as a two degrees of freedom model, the single- and four-blade rubbings are studied using numerical simulation and experiment. Results show that for both the single- and four-blade rubbings, amplitude amplification phenomena can be observed when the multiple frequencies of the rotational frequency
(
f
r
)
coincide with the conical and torsional natural frequencies of the rotor-blade system, natural frequencies of the casing and the bending natural frequencies of the blades. In addition, for the four-blade rubbing, the blade passing frequency (BPF,
4
f
r
)
and its multiple frequency components also have larger amplitudes, especially, when they coincide with the natural frequencies of the rotor-blade system or casing; the four-blade rubbing levels are related to the rotor whirl, and the most severe rubbing happens on the blade located at the right end of the whirl orbit.
Journal Article
Nonlinear analysis of a rotating pre-twisted composite blade reinforced with functionally graded graphene platelets under axial and transverse excitations
Due to the harsh service environment and multiple loads, studying the nonlinear vibration characteristics of rotating blades under complex loads is necessary. The new axial force model assumed as a combined force including the non-uniform aerodynamic force in the tip clearance and blade-casing local rubbing force is proposed for the first time in this paper. The nonlinear analysis of a rotating pre-twisted composite blade reinforced with functionally graded graphene platelet (FGGP) is investigated under axial and transverse excitations. The blade is treated as FGGP-reinforced rotating twisted cantilever plate. The transverse excitation caused by subsonic airflow is derived by using the vortex lattice method. The blade-casing local rubbing and non-uniform axial force dynamic change when the blade is rotating. Based on von-Karman nonlinear geometric assumptions and Lagrange equation, the governing equations of motion for the FGGP-reinforced rotating twisted plate are derived. The averaged equations under the case of primary resonance and 1:2 internal resonance are obtained by the multiple scale method. Comparisons of frequencies and modes in the present method are carried out. The results are in good agreement with other literature. The amplitude–frequency and amplitude–force curves, bifurcations, and chaotic motions of the FGGP-reinforced rotating twisted cantilever plate under axial and transverse excitations are discussed. The results show that the nonlinear vibrations are complex when 1:2 internal resonance and primary resonance of the FGGP-reinforced rotating twisted composite blade occur. The amplitude of the blade is higher with the bigger axial force. At the same time, with the increase of axial force and incoming flow speed, the motion of the blade changes from periodic to chaotic. The interesting phenomena of inverse period-doubling bifurcations are found.
Journal Article
Material aspects of triboelectric energy generation and sensors
The triboelectric nanogenerator (TENG) is a new type of energy generator first demonstrated in 2012. TENGs have shown potential as power sources for electronic devices and as sensors for detecting mechanical and chemical stimuli. To date, studies on TENGs have focused primarily on optimizing the systems and circuit designs or exploring possible applications. Even though triboelectricity is highly related to the material properties, studies on materials and material designs have been relatively less investigated. This review article introduces recent progress in TENGs, by focusing on materials and material designs to improve the electrical output and sensing performance. This article discusses the current technological issues and the future challenges in materials for TENG.Nanotechnology: Materials for harvesting energy from motionThe development of materials for a technology that uses the movement of the human body to provide power has been reviewed by scientists in South Korea. A triboelectric nanogenerator converts mechanical energy into electricity by harnessing the fact that two surfaces rubbing against one another can become electrically charged. This is known as the triboelectric effect. One exciting use for these nanogenerators is in wearable electronics, where the motion of the body provides the power. Unyong Jeong and colleagues from Pohang University of Science and Technology have reviewed recent progress in material advances in the four main elements of a triboelectric nanogenerator: the charge-generating layer, the charge-trapping layer, the charge-collecting layer, and the charge-storage layer. These improvements all aim to increase the electrical output of such devices.
Journal Article
Design and Testing of a Device to Investigate Dynamic Performance of Aero-Engine Rotor–Stator Rubbing Dynamics
To analyze the wear performance induced by rotor–stator rubbing in an aero-engine sealing structure under authentic operating conditions, a transonic rotor system with double bearing is constructed. This system incorporates the disk, shaft, blades, joint bolts, and auxiliary support structure. The system was evaluated in terms of its critical speed, vibration characteristics, component strength under operational conditions, and response characteristics in abnormal extreme scenarios. A ball screw-type feeding system is employed to achieve precise rotor–stator rubbing during rotation by controlling the coating feed. Additionally, a quartz lamp heating system is used to apply thermal loads to coating specimens, and the appropriate heat insulation and cooling measures are implemented. Furthermore, a high-frequency rubbing force test platform is developed to capture the key characteristics caused by rubbing. The test rig can conduct response tests of the system with rotor–stator rubbing and abrasion tests with tip speeds reaching 425 m/s, feed rates ranging from 2 to 2000 μm/s, and heating temperatures up to 1200 °C. Test debugging has confirmed these specifications and successfully executed rubbing tests, which demonstrate stability throughout the process and provide reliable rubbing force test results. This designed test rig and analysis methodology offers valuable insights for developing high-speed rotating machinery.
Journal Article
Durable Janus membrane with on-demand mode switching fabricated by femtosecond laser
Despite their notable unidirectional water transport capabilities, Janus membranes are commonly challenged by the fragility of their chemical coatings and the clogging of open microchannels. Here, an on-demand mode-switching strategy is presented to consider the Janus functionality and mechanical durability separately and implement them by simply stretching and releasing the membrane. The stretching Janus mode facilitates unidirectional liquid flow through the hydrophilic micropores-microgrooves channels (PG channels) fabricated by femtosecond laser. The releasing protection mode is designed for the in-situ closure of the PG channels upon encountering external abrasion and impact. The protection mode imparts the Janus membrane robustness to reserve water unidirectional penetration under harsh conditions, such as 2000 cycles mechanical abrasion, 10 days exposure in air and other rigorous tests (sandpaper abrasion, finger rubbing, sand impact and tape peeling). The underlying mechanism of gridded grooves in protecting and enhancing water flow is unveiled. The Janus membrane serves as a fog collector to demonstrate its unwavering mechanical durability in harsh real-world conditions. The presented design strategy could open up new possibilities of Janus membrane in a multitude of applications ranging from multiphase separation devices to fog harvesting and wearable health-monitoring patches.
Janus membranes are highly valued for their unique water unidirectional transportation capabilities. Here, authors report an on-demand mode-switching strategy that significantly enhances the durability of the Janus membrane.
Journal Article
A high body mass index strengthens the association between the time of eye rubbing and keratoconus in a Chinese population: a case control study
Background
Although body mass index (BMI) and eye rubbing are linked to an increased risk of keratoconus (KC), the interactive effect of eye rubbing and BMI on KC is largely unknown. This study aimed to evaluate the independent and interactive effects of BMI and eye rubbing on KC and to further explore the role of environmental factors on the occurrence of KC.
Methods
A total of 621 individuals (291 KC patients and 330 control individuals) were enrolled in this hospital‑based study on KC patients in Central China after individuals missing BMI data were excluded. BMI was calculated as weight in kilograms divided by the square of height in meters. Data on eye rubbing was recorded through face-to-face interviews. Generalized linear regression models were used to analyze associations among BMI, eye rubbing and KC. Interaction plots were used to describe the interactive effects of BMI and eye rubbing on KC.
Results
The β and 95% confidence interval (CI) were 0.923 (0.112, 1.733) (
p
= 0.026) and 3.356 (1.953, 4.759) (
p
< 0.001), respectively, for the effect of each 10 kg/m
2
increase in BMI and each 1 min increase in eye rubbing on KC. The interaction of BMI and eye rubbing were positively correlated with KC (
p
< 0.001).
Conclusion
These findings suggested that a high BMI aggravated the negative effect of eye rubbing on KC, implying that individuals with a high BMI may be more susceptible to exposure to eye rubbing, which is related to an increased risk of KC.
Journal Article
In-situ catalysis of green lubricants into graphitic carbon by iron single atoms to reduce friction and wear
Reducing friction and wear in moving mechanical systems is essential for their intended functionality. This is currently accomplished by using a large variety of anti-friction and anti-wear additives, that usually contain sulfur and phosphorous both of which cause harmful emission. Here, we introduce a series of diesters, typically dioctyl malate (DOM), as green and effective anti-friction and anti-wear additives which reduce wear by factors of 5-7 and friction by over 50% compared to base oil when tested under high pressures. Surface studies show that these impressive properties are primarily due to the formation of a 30 nm graphitic tribofilm that protects rubbing surfaces against wear and hence provides low shear stress at nanoscale. This graphitic tribofilm is prone to form from diesters derived from short-chain carboxylic acid due to their lone pair effect, which stabilizes the carbon free radicals. Furthermore, the formation of this tribofilm is catalyzed by nascent iron single atoms, which are in-situ generated due to the mechanochemical effects during sliding contact. Computational simulations provided additional insights into the steps involved in the catalytic decomposition of DOM by iron and the formation of a graphitic carbon tribofilm. Due to its anti-friction and wear properties, DOM holds promise to replace conventional additives, and thus provides a green and more effective alternative for next-generation lubricant formulations.
Reducing friction and wear in mechanical systems can lower energy consumption and material loss. Here, a green lubricant additive is introduced, free of harmful elements, that effectively minimizes friction and wear, offering a sustainable solution.
Journal Article