Abstract
The study is devoted to mathematical modeling of the shape of the roll contact curves in two-roll modules. A two-roll module is considered, in which the rolls are positioned relative to the ...vertical with a tilt to the right, have unequal diameters and elastic coatings from the materials of different stiffness and friction coefficients, the material layer is fed with a tilt downward relative to the center line. The equations of the curves of roll contact in the considered two-roll module are derived. It is revealed that the obtained models are general in the sense that they are applicable for particular cases of interaction in a two-roll module.
Learning dexterous in-hand manipulation Andrychowicz, OpenAI: Marcin; Baker, Bowen; Chociej, Maciek ...
The International journal of robotics research,
01/2020, Letnik:
39, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We use reinforcement learning (RL) to learn dexterous in-hand manipulation policies that can perform vision-based object reorientation on a physical Shadow Dexterous Hand. The training is performed ...in a simulated environment in which we randomize many of the physical properties of the system such as friction coefficients and an object’s appearance. Our policies transfer to the physical robot despite being trained entirely in simulation. Our method does not rely on any human demonstrations, but many behaviors found in human manipulation emerge naturally, including finger gaiting, multi-finger coordination, and the controlled use of gravity. Our results were obtained using the same distributed RL system that was used to train OpenAI Five. We also include a video of our results: https://youtu.be/jwSbzNHGflM.
In this study, friction and wear of a body-centered cubic equiatomic TiZrHfNb high-entropy (HE) alloy were investigated using a nanoscratch method. Scratch tests, under both ramping and constant load ...modes, were conducted to evaluate the coefficient of friction (COF) and wear rate of the alloy. The effects of scratch rate on the friction and wear were also studied. The morphology such as the surface profile and depth of scratched tracks was examined using scanning electron microscopy (SEM) and scanning probe microscopy (SPM). It was found that, whilst wear behavior, including wear rate and wear resistance, could be described by Archard equation, friction of the alloy appeared to be more complicated. Experimental results revealed that the friction of the alloy could be divided into two distinct regimes - elastic and plastic. The COF decreased rapidly with increasing normal load in the elastic regime, but became essentially constant in the plastic regime, indicating a transition of friction mechanism. In this study, scratch tests were also performed on pure Nb and a solid-solution strengthened Nb-based C103 alloy to make a direct comparison. The TiZrHfNb HE alloy apparently exhibited an improved wear resistance and lower COF as compared to its traditional alloy counterparts. The better wear resistance and lower COF were discussed in lights of the acting plowing and adhesion mechanisms during wear.
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Abstract
The rapid development of Internet of Things and artificial intelligence brings increasing attention on the harvesting of distributed energy by using triboelectric nanogenerator (TENG), ...especially the direct current TENG (DC-TENG). It is essential to select appropriate triboelectric materials for obtaining a high performance TENG. In this work, we provide a set of rules for selecting the triboelectric materials for DC-TENG based on several basic parameters, including surface charge density, friction coefficient, polarization, utilization rate of charges, and stability. On the basis of the selection rules, polyvinyl chloride, used widely in industry rather than in TENG, is selected as the triboelectric layer. Its effective charge density can reach up to ~8.80 mC m
−2
in a microstructure-designed DC-TENG, which is a new record for all kinds of TENGs. This work can offer a basic guideline for the triboelectric materials selection and promote the practical applications of DC-TENG.
A nanofluid minimum quantity lubrication with addition of one kind of nanoparticle has several limitations, such as grinding of difficult-to-cutting materials. Hybrid nanoparticles integrate the ...properties of two or more kinds of nanoparticles, thus having better lubrication and heat transfer performances than single nanoparticle additives. However, the use of hybrid nanoparticles in nanofluid minimum quantity lubrication grinding has not been reported. This study aims to determine whether hybrid nanoparticles have better lubrication performance than pure nanoparticle. A hybrid nanofluid consisting of MoS2 nanoparticles with good lubrication effect and CNTs with high heat conductivity coefficient is investigated. The effects of the hybrid nanofluid on grinding force, coefficient of friction, and workpiece surface quality for Ni-based alloy grinding are analyzed. Results show that the MoS2/CNT hybrid nanoparticles achieve better lubrication effect than single nanoparticles. The optimal MoS2/CNT mixing ratio and nanofluid concentration are 2:1 and 6wt%, respectively.
•MoS2/CNTs nanofluids jet MQL grinding with Ni-based alloy was experimented.•MoS2/CNTs nanofluids contribute better lubrication effect compared to pure nanoparticle.•Hybrid nanoparticles have better lubrication effect caused by “physical synergistic effect”.•Experiment indicates that 2:1 is the optimum MoS2/CNTs mixing ratio.•6% is the optimal addition mass fraction of MoS2/CNTs(2:1) nanopaticles in nanofluids.
CNTs are commonly used nanoparticles in NMQL for their excellent heat transfer enhancement performance. However, winding and conglobation are constraints against their tribological performance, these ...constraints can be solved by surfactants. However, the influences of surfactant type and dispersing mechanism on the dispersion effect of CNTs have not been studied systemically. Consequently, this study analyzed the dispersing mechanism of different surfactants and evaluated the dispersion stability and tribological performances of PPO-based CNT nanofluids. Results showed that nanofluids with APE-10 obtain the highest viscosity, lowest friction coefficient, minimum roughness value and favorable surface morphology, thus indicating their excellent dispersion stability and tribological performance. Further, different experimental evaluations confirm that APE-10 is the optimal dispersant of CNT nanofluids.
•The dispersing mechanism of different surfactants was analyzed.•Dispersivity and viscosity of CNTs nanofluids with diverse surfactants was discussed.•Tribological properties of CNTs nanofluids with diverse surfactants was evaluated.•Nanofluids with APE-10 obtained the optimal dispersivity and tribological properties.•The “synergism” of mixed surfactant brings excellent dispersion effect.
Surface texturing is one of the most efficient surface modification approaches for improving the tribological performance of engineering materials. Several surface texturing techniques have been ...developed in recent years. Among these methods, laser surface texturing (LST) has gained considerable interests due to its high flexibility, superior texturing accuracy, and good controllability. This paper reviews the recent advances and developments of LST for enhanced tribological properties of engineering materials. The process designs of LST by means of direct laser ablation, laser interference, and laser shock processing are discussed. The effects of laser parameters on the texture features are highlighted. The enhanced tribological properties of LST-processed materials and their applications on various fields are reviewed. The current challenges and future directions of LST techniques are discussed.
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