Search results

The purpose of this paper is to analyze a new, whole‐spacecraft isolator and its performance of vibration isolation, which has been designed to ensure spacecraft safety at the launching stage.

The design is based on the analysis of fractional derivative stress‐strain constitutive relationship of viscoelastic materials. First, the authors study the constitutive relationships for viscoelastic solid of the damping materials, then the authors introduce the results obtained to the equations of motion for the damped isolator.

By performing a series of transformation, the authors obtain the analytical solution of the equations. It is shown that the results compare favourably to the numerical simulations and experiments. In addition, a saturation phenomenon for the first order damping ratio is also discussed.

It is found that the constitutive relationships written in terms of the fractional calculus can be applied in the system function of the whole‐spacecraft vibration isolator. Such relationships, developed previously from a model analysis base, have been shown to be useful tools for engineering analyses.

Some suggestions are given to improve the design of viscoelastic whole‐spacecraft isolators. The establishment of a theoretical basis for the new fractional differential dynamical system enhances their value, as they may now be used with increased reliability of satellite.

A fiber Bragg grating (FBG) sensor was designed to measure the door gap of automobile bodies.

The gap sensor was designed through a combination of the sliding wedge and cantilever beam, involving a magnetic force installation and arc structure of the force transmission point. Moreover, the sliding block adopted an anti-magnetic and wear-resistant material and the temperature compensation of the two FBGs was conducted. The magnetic force and contact stress of the sensor were examined to ensure that the sensor exhibited a certain magnetic attraction force and fatigue life. The performance of the gap sensor was examined experimentally.

The sensor could measure gaps with dimensions of 5 mm to 11 mm, with a sensitivity and measurement accuracy of 150.9 pm/mm and 0.0063% F.S., respectively. Moreover, the sensor exhibited a small gap sensitivity, with a repeatability error of 0.15%, anti-creep properties and magnetic interference abilities.

The sensor is compact and easy to install, as well as use for multiple sensor locations, with a maximum size of 43 mm, a mass of 26 g and installation type of magnetic suction. It can be used for high-precision static and dynamic measurements of the door inner clearance with a resolution of 0.013 mm to improve the efficiency of internal clearance on-line analysis and assembly quality inspection.

With the implementation of new emission standards, the thermal–mechanical coupling load of engine pistons becomes more important. In this case, forged steel material with higher fatigue limit and impact resistance has been applied gradually in piston manufacturing. However, new failure problems emerge, and the wear of skirt under boundary lubrication conditions is an essential problem which needs to be solved urgently.

In this research, the abrasion testing machine was used to simulate the wear behavior under different conditions of normal pressure, relative velocity and surface roughness. Besides, the wear morphology was observed by scanning electron microscope. Then, the wear model was established by using test results fitting method, offering a way to conduct qualitative analysis for the wear problem under the same conditions.

The results show that mainly the wear mechanism of the piston skirt under boundary lubricated conditions is adhesive wear and abrasive wear. In addition, the coefficient and wear rate will increase with the increase in the normal load and surface roughness and decrease with the increase in the relative speed. In the wear model, the wear loss is mainly influenced by the normal load, the relative sliding speed and the wear time.

The wear degree of piston skirt was qualitatively obtained in this investigation by factors such as pressure, velocity and so on, and the wear mechanism of forged steel piston skirt under boundary lubrication conditions was also determined. These could provide theoretical support for further optimization of cylinder motion and oil supply system, reduction of friction loss and power loss.

Poly (vinyl acetate)‐based emulsion polymer/isocyanates (EPI) structural wood adhesives were prepared and their performance benchmark tested according to the specifications of the Japanese JAS‐111 standard. The changes of the glass transition temperature of the cured emulsions relative to unmodified poly(vinyl acetate) emulsion, measured using differential scanning calorimetry, indicated the chemical structure changes resulting from modification of poly(vinyl acetate) emulsion. The EPI adhesives showed excellent water resistance and near‐colourless gluelines in wood joints, ease of application and additional significant advantages over other types of wood adhesives. The performance test results are interpreted on the basis of the viscoelastic behaviour of free‐standing adhesive films. Other types of crosslinkers were used in the study to compare with the isocyanate hardeners.

Fluorinated polyurethane combines some virtues of polyurethane and fluorinated polymer, such as low water absorption, attractive surface properties, good wearability and high weatherability. Fluorocarbon chains have been incorporated into polyurethanes by fluorinated diisocyanates, chain extenders, polyether glycols, polyester glycols and end-cappers. However, the fluorinated polyurethane, which is prepared with monohydric fluorocarbon alcohol, is seldom reported. The purpose of this research is to prepare and apply the novel fluorocarbon alcohols with side chain to modify polyurethane as the blocking agent.

The novel fluorocarbon alcohol with side chain 2-methoxy-3-nonene perfluorinated oxygen propanol (MNPOP) can be prepared via alcoholysis reaction of methanol and 2,3-epoxypropyl perfluorinated nonene ether (EPPNE), which was prepared with etherification of hexafluoropropene trimer (HFPT) and 2,3-glycidol. Structures of EPPNE and MNPOP are confirmed with FTIR and NMR. The polyurethane can be modified when MNPOP is used as blocking agent.

In comparison with the conventional polyurethane, the hydrophobic property of fluorinated polyurethane is improved. However, the increase of tensile strength of modified polyurethane is not obvious because MNPOP belongs to monohydric alcohol. And the function of MNPOP in the modified polyurethane is the blocking agent. The thermal stability of conventional and modified polyurethane is almost the same because MNPOP is de-blocked and fluorocarbon chains have not been incorporated into polyurethanes when the temperature is more than 150°C.

The polyurethane is modified with the novel fluorocarbon alcohols with side chain, which functions as the blocking agent. The hydrophobic property of fluorinated polyurethane is improved.

Various modifications of polyvinyl acetate emulsion wood adhesive were made and their performance evaluated in standard tests. The results are interpreted in the context of adhesion theories and the chemical structures of the polymers and wood. The adhesion of the polymers to wood and the cohesive strength of the polymers are the two predominant factors determining the performance of the adhesives. Adhesive strength in thermosetting resins is enhanced by irreversible chemical reactions that create extensive networks within the adhesive layer and strong bonds to the wood substrate, leading to strong and durable joints that passed all of the performance evaluation tests. Most of the PVAc emulsions exhibited good adhesive performance in the dry state, but failed in water soak and boiling water immersion tests since their adhesion and cohesion are mainly based on weaker physical interactions. Emulsions with (hard) core‐(soft) shell morphology and correspondingly high glass transition temperatures gave poor performance under all conditions.

Four different approaches were taken to improve the water resistance of poly(vinyl acetate) (PVAc) emulsion adhesives. The improved wood adhesives were tested according to the ISO 9020 standard. Tensile storage modulus (E’) and glass transition temperature of the polymer films were measured using dynamic mechanical thermal analysis to quantify the influence of different approaches on those variables. Gel fraction and swelling ratio of the polymer film were measured to evaluate internal crosslink density. The experimental results showed that blending melamine/urea/formaldehyde (MUF) resin with PVAc emulsions modified the water resistance considerably and the film had a high E’ since an interpenetrating network‐type structure was formed in the polymer. The advantages and limitations of each modification were assessed on the basis of comparison of the results.

To solve problems of low intelligence and poor robustness of traditional navigation systems, the purpose of this paper is to propose a brain-inspired localization method of the unmanned aerial vehicle (UAV).

First, the yaw angle of the UAV is obtained by modeling head direction cells with one-dimension continuous attractor neural network (1 D-CANN) and then inputs into 3D grid cells. After that, the motion information of the UAV is encoded as the firing of 3 D grid cells using 3 D-CANN. Finally, the current position of the UAV can be decoded from the neuron firing through the period-adic method.

Simulation results suggest that continuous yaw and position information can be generated from the conjunctive model of head direction cells and grid cells.

The proposed period-adic cell decoding method can provide a UAV with the 3 D position, which is more intelligent and robust than traditional navigation methods.

Self-crosslinked long fluorocarbon acrylate polymer latex has good hydrophobic and oleophobicity, weather resistance, aging resistance, stability and other excellent properties, which make the polymer be widely used in coatings, dyes, adhesives and other products. The purpose of this study is to prepare self-crosslinked long fluorocarbon acrylate polymer latex via semi-continuous seeded emulsion technology and carry out comparative study on two different cross-linked monomers.

Methyl methacrylate (MMA) and butyl acrylate (BA) were used as the main monomers, dodecafluoroheptyl methacrylate (DFMA) as the fluoromonomer, hydroxypropyl methacrylate (HPMA) and N-methylol acrylamide (NMA) as cross-linked monomers, and 1-allyloxy-3–(4-nonylphenol)-2-propanol polyoxyethylene (10) ether (ANPEO10) and 1-allyloxy-3–(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate (DNS-86) as compound emulsifiers via the semicontinuous-seeded emulsion polymerization.

The properties of the polymer emulsions, which are prepared with two different cross-linked monomers, are compared and discussed, and it is concluded that HPMA is more suitable for the preparation of self-crosslinked polymer emulsions. The formula of the polymer latex is ANPEO10: DNS-86 = 1:1, and the mass ratio of the monomers used in the polymer is MMA: BA: DFMA: HPMA = 14.40:14.40:0.60:0.60.

Self-crosslinked long fluorocarbon acrylate polymer latex can be used in many fields such as coatings, dyes, adhesives and other products.

The self-crosslinked long fluorocarbon acrylate polymer latex is prepared by mixing the nonionic emulsifier ANPEO10 and the anionic emulsifier DNS-86 when potassium persulfate is used as the thermal decomposition initiator and the semicontinuous-seeded emulsion technology is adopted and the comparative study on two different cross-linked monomer is carried out, which is not reported in the open literatures.

Gas evolution within lithium-ion batteries (LIBs) gives rise to safety concerns that question their applicability. The gas evolution is not only the result but also the inducement of performance deterioration of LIBs. In this paper, the growth characteristics and dynamic behavior of gas bubble on the electrode surface are studied, and the interference mechanism of gas evolution on Li-ion diffusion or Li-ion conduction within LIBs is discussed and validated by the numerical simulations.

First, the mathematical models and simulation method are established. The growth and flow of gas bubble in the serpentine channel on electrode surface, which results from the gas-liquid flow and the effects of surface tension, is modeled by using the multi-phase Navier-Stokes and the volume of fluid method. Integrating Butler–Volmer and Fick’s law, the mathematical model of ions transport in the electrochemical cell is set-up. Second, the motion of gas bubble is tracked, and the variations of bubble shape and characteristic parameters with time are obtained by the computed fluid dynamics (CFD) method.

Based on the CFD results, the battery models and electrochemical simulations are carried out to analyze the ionic transport characteristics. The results show that the microstructural morphology such as the serpentine channel shape and size on electrode surface are important aspects for the gas bubble growth and the local ionic transport. Li ions significantly accumulate at one side of the gas obstacle, hindering the ionic diffusion normally. When the gas bubble blocks the electrolyte, the passage of ions from the positive to the negative is interrupted, and the open circuit zone of the electrochemical cell is formed.

The gas evolution within LIBs is not only a result but also an inducement of its performance deterioration. The primary issues in this study are the growth characteristics and dynamic behavior of gas bubble on the electrode surface, providing the knowledge for the interference mechanism of gas evolution on ionic transport and ultimately leads to significant increase of battery resistance.