Nonlinear vibration of hypoid gear with backlash

Due to the machining errors, alignment error, wear, tear and time varying stiffness of hypoid teeth, the vibration of hypoid gears is inevitably produced in the course of working, and its vibration and noise is the main sources of vibration and noise in the automobile transmission. Study on nonlinear vibration and noise of the hypoid gear pair, and investigating on reducing its vibration and noise are of great significance. Firstly, a simplified nonlinear vibration model of the hypoid gears of main reducer, with considering the time-varying teeth stiffness and teeth surface friction damping, was established. Then, a numerical simulation method was employed to simulate different gear backlash effects on the hypoid gear vibration behaviors caused by the gear worn, and effects on the gear non-linear vibration from different work speeds of gear and different loading torques were investigated. In order to help to explain the non-linear vibration phenomenon of the hypoid gears, the 2-D phase plane diagram and the 3-D trajectory were employed. Lastly, the bench test was carried out to verify the simulation results on vibration of hypoid gears with backlash

Janus Monolayer Transition Metal Dichalcogenides

A novel crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe2 the top layer of selenium atoms are substituted by sulfur atoms while the bottom selenium layer remains intact. The peculiar structure of this new material is systematically investigated by Raman, photoluminescence and X-ray photoelectron spectroscopy and confirmed by transmission-electron microscopy and time-of-flight secondary ion mass spectrometry. Density-functional theory calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction (HER) activity is discovered for the Janus monolayer and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.Comment: 22 pages, 12 figure

Nonlinear vibration of hypoid gear with backlash

Due to the machining errors, alignment error, wear, tear and time varying stiffness of hypoid teeth, the vibration of hypoid gears is inevitably produced in the course of working, and its vibration and noise is the main sources of vibration and noise in the automobile transmission. Study on nonlinear vibration and noise of the hypoid gear pair, and investigating on reducing its vibration and noise are of great significance. Firstly, a simplified nonlinear vibration model of the hypoid gears of main reducer, with considering the time-varying teeth stiffness and teeth surface friction damping, was established. Then, a numerical simulation method was employed to simulate different gear backlash effects on the hypoid gear vibration behaviors caused by the gear worn, and effects on the gear non-linear vibration from different work speeds of gear and different loading torques were investigated. In order to help to explain the non-linear vibration phenomenon of the hypoid gears, the 2-D phase plane diagram and the 3-D trajectory were employed. Lastly, the bench test was carried out to verify the simulation results on vibration of hypoid gears with backlash

Nonlinear vibration of hypoid gear with backlash

Due to the machining errors, alignment error, wear, tear and time varying stiffness of hypoid teeth, the vibration of hypoid gears is inevitably produced in the course of working, and its vibration and noise is the main sources of vibration and noise in the automobile transmission. Study on nonlinear vibration and noise of the hypoid gear pair, and investigating on reducing its vibration and noise are of great significance. Firstly, a simplified nonlinear vibration model of the hypoid gears of main reducer, with considering the time-varying teeth stiffness and teeth surface friction damping, was established. Then, a numerical simulation method was employed to simulate different gear backlash effects on the hypoid gear vibration behaviors caused by the gear worn, and effects on the gear non-linear vibration from different work speeds of gear and different loading torques were investigated. In order to help to explain the non-linear vibration phenomenon of the hypoid gears, the 2-D phase plane diagram and the 3-D trajectory were employed. Lastly, the bench test was carried out to verify the simulation results on vibration of hypoid gears with backlash

Note on a conjecture for the sum of signless Laplacian eigenvalues

summary:For a simple graph $G$ on $n$ vertices and an integer $k$ with $1\leq k\leq n$, denote by $\mathcal {S}_k^+(G)$ the sum of $k$ largest signless Laplacian eigenvalues of $G$. It was conjectured that $\mathcal {S}_k^+(G)\leq e(G)+{k+1 \choose 2}$, where $e(G)$ is the number of edges of $G$. This conjecture has been proved to be true for all graphs when $k\in \{1,2,n-1,n\}$, and for trees, unicyclic graphs, bicyclic graphs and regular graphs (for all $k$). In this note, this conjecture is proved to be true for all graphs when $k=n-2$, and for some new classes of graphs

A NOVEL CHARCTERIZATION METHOD ON MECHANICAL BEHAVIOR OF UNLOADING CURVES BY USING BEERKOVICH TIP

Unloading curve analysis is a popular method in nan-indentation testing process,while the physical signification of the power-law exponent is obscure. Based on the Sneedon’s solution to elastic indentation of plane half infinite space,a new model was presented to characterize the plastic unloading behavior of Berkovich tip. The residual stress among elastic-plastic stain regions was taken into accounted. The plastic unloading behavior of Berkovich tip was characterized approximately using parabolic tip and conical tip. Experimental results indicated that parabolic tip can characterize the plastic unloading behavior more accurate and the rationality of the new model was validated

Poly(neopentyl glycol 2,5-furandicarboxylate): A Promising Hard Segment for the Development of Bio-based Thermoplastic Poly(ether-ester) Elastomer with High Performance

With a high melting temperature and good crystallization ability, poly(neopentyl glycol 2,5-furandicarboxylate) (PNF), a polyester derived from bio-based 2,5-furandicarboxylic acid and neopentyl glycol, has been proposed and proved to be a promising hard segment for the development of novel bio-based thermoplastic poly(ether-ester) elastomer (TPEE). The resulting TPEE, namely PNF-PTMG, has high performance comparable to the petroleum-based counterpart PBT-PTMG (i.e., Hytrel, Dupont). Among all of the existing polyesters derived from bio-based 2,5-furandicarboxylic acid (FDCA), PNF has perfectly balanced properties, namely, a high melting temperature of 200 degrees C and a good crystallization ability to easily grow medium to large-size crystalline spherulites. Characterizations based on dynamic mechanical analysis and small-angle X-ray scattering suggest that there are two domains in PNF-PTMG, the crystalline PNF and a mixture of amorphous PNF and PTMG. These two domains form microphase separation induced mainly by the crystallization of PNF. By adjusting the PTMG soft segment from 30 to 60 wt%, PNF-PTMG shows a melting temperature, tensile modulus (E), and elongation at the break (epsilon(b)) ranging from 180 to 134 degrees C, 738 to 56 MPa, and 38 to 1089%, respectively. More importantly, the shape recovery ratios increase from 57 to 90% at 200% strain when the amount of PTMG increases from 50 to 70 wt%, indicating excellent elastic property. These results indicate that PNF is an excellent hard segment to serve as a strong physical cross-link so that PNF-PTMG is able to display high performance comparable to extensively commercialized PBT-PTMG