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• A novel mathematical model of the transmission path effect is proposed. • Path effect depends only on the geometric parameters and material properties. • A phenomenological vibration model is used to simulate all vibration sources. • Vibration characteristics are analyzed and validated through experiments. Model-based vibration signal analysis to interpret and understand vibration characteristics can provide prior guidance for the condition monitoring and fault diagnosis of planetary gearboxes (PGs). Transmission path effects due to the rotational motion of planet gears with respect to the accelerometer mounted on the PG housing make understanding its real dynamic behavior challenging. To overcome this challenge, a novel mathematical model of the transmission path effect is proposed to support the construction of more realistic dynamic response of PGs. This model is derived only from the geometric parameters and material properties, and it has higher applicability than traditional models. Subsequently, a phenomenological vibration model is used to simulate all vibration sources, including sun–planet and ring–planet gear meshes. On these bases, a comprehensive vibration signal model is proposed by considering all vibration sources and the corresponding transmission path effects. Moreover, the theoretical spectral structure is deduced via Fourier series analysis. Finally, the vibration characteristics of the vibration signals obtained using the proposed mathematical model are analyzed and validated through simulations and experiments in the time and frequency domains. [ABSTRACT FROM AUTHOR]

• An improved phenomenological model of a gear pair with local fault is proposed. • Relative phases of planetary gearboxes are calculated by a modified phase model. • The local fault characteristic frequencies of gears are deduced based on models. • The conclusions are validated based on five experiments conducted on a test rig. Planetary gearboxes (PGs) are prone to gear local faults, such as cracking, pitting, and spalling, because of their difficult working environment. These faults may lead to significant capital losses and catastrophic events. Numerous phenomenological modulation models of vibration signals of PGs have been proposed for diagnosis purposes. However, local fault diagnosis remains extremely challenging due to two aspects: (1) Most vibration modulation models cannot reflect the local fault-induced pulse modulation characteristic. (2) Studies on local fault characteristic frequencies (LFCFs) of gears lack a unified mechanism explanation. To solve these problems, an improved phenomenological vibration model of a gear pair with local fault is first proposed. This model can reflect the pulse modulation characteristic. Then, relative phases between multiple gear pairs in the PG are calculated based on a modified phase model. Based on these, phenomenological vibration models of PGs with/without local faults are established, spectral structures are derived using Fourier series analysis, and LFCFs are deduced for local fault diagnosis. Simulation and experimental studies demonstrate the effectiveness of the proposed models, which exhibit higher descriptive capability than traditional models. [ABSTRACT FROM AUTHOR]

• A mathematical vibration model of multistage wind turbine gearboxes is proposed. • Modulation sidebands in the vibration spectrum are explained based on the model. • The equivalent transmission path functions in the multistage gearbox are proposed. • The conclusions are validated based on data from 2.0MW wind turbine gearboxes. The sensor-perceived vibration signals of multistage wind turbine gearboxes have more complex frequency features than that of single-stage gearboxes since there are more meshing vibration sources and more complicated transmission paths inside them, which lead to difficulties in condition monitoring and fault diagnosis. Aiming to understand the vibration frequency features of multistage wind turbine gearboxes, a mathematical vibration model of healthy wind turbine gearboxes is developed and the spectral structure of the model is deduced by adopting Fourier series analysis. In the vibration model, the time-varying transmission paths from all the meshing vibration sources to the fixed sensor are considered, and the equivalent transmission path functions of the time-varying transmission paths are proposed for the first time. The theoretical derivations are validated by both simulations and engineering tests using two cases of 2.0MW industrial wind turbine gearboxes. The findings in this work are not only applicable to the gearboxes studied in this paper, but also to other similar multistage gearboxes, which can provide a priori spectral structure for the multistage gearbox to assist its condition monitoring and fault diagnosis. [ABSTRACT FROM AUTHOR]

Unlike thermoplastic petroleum-based materials, starch-based materials rely on aqueous systems but are incapable of hot melting, resulting in low processing efficiency and limited large-scale industrial applications. In this study, the combination of α-amylase liquefaction and urea plasticization was used for the first time to obtain enzymatic thermoplastic starch (ETPS) for hot melting by changing the molecular chain of starch. ETPS showed an apparent hot melting phenomenon when heated below 200 °C. Differential scanning calorimetry revealed that heat absorption peaks were obviously reduced, and the hot melting phenomenon occurred easily depending on the combination of enzymatic hydrolysis and plasticization. Dynamic mechanical analysis indicated that the combined modification effectively increased the number of freely movable chains. The red shift of -OH stretching vibration peaks indicated the formation of strengthened hydrogen bonds in ETPS. X-ray diffraction showed that the crystallinity of ETPS was reduced to 5.68 %, effectively reducing the regenerative phenomenon. Gel permeation chromatography revealed that the molecular weight of ETPS decreased, and the entanglements between molecular chains were reduced. A tensile test showed that the elongation at break of ETPS was as high as 235.29 %, which was much higher than those of enzymatic hydrolysis starch and thermoplastic starch. [Display omitted] [ABSTRACT FROM AUTHOR]

A kind of flexible carbon nanotubes (CNTs) paper was investigated. Cellulose fibers were used as matrix and CNTs were used as conductive additive. The CNT papers were made by suction filtration method. The size and conductivity of the CNT paper can be arbitrarily tailored. The CNT papers show good electrical conductivity, electrochemical and electromagnetic interference (EMI) shielding properties. The electrical conductivity and (EMI) shielding effectiveness (SE) of CNT papers were enhanced with an addition of CNTs in the paper. The electrical conductivity increased from 9.92 S m −1 to 216.3 S m −1 and SE improved from 15 dB to 45 dB with a loading of CNTs from 10 wt% to 71 wt%. The CNT papers also show excellent applications for lithium ion battery, supercapacitors and zinc-manganese batteries. The testing results show that the capacity of supercapacitor reached 46 F/g at a scan rate of 5 mV/s. The reversible discharge capacity reached 474.0 mAh/g with the paper as anode current collector of lithium ion battery. The discharge capacity of Zn–Mn battery increased 100% when CNT paper replaced the graphite collector as current collector. [ABSTRACT FROM AUTHOR]