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Elastic cushion plays an important role in alleviating the dynamic interaction between train and its running foundation. The ratio of static stiffness to dynamic stiffness is the key parameter to determine the alleviation performance of elastic cushion. Aiming at a new type of honeycomb mesh-type elastic cushion plate structure,a three-dimensional finite element model was established,and the mechanical properties of rubber material were simulated by super-elastic and viscoelastic constitutive models. Under the condition that the material parameters of elastic cushion plate were unchanged,the effects of the change of key parameters such as mesh thickness and aperture on the dynamic and static stiffness of mesh-type elastic cushion plate were studied,and the traditional groove elastic cushion plate was compared. The results show that: under the condition of constant mesh aperture,with the increase of mesh wall thickness,the static stiffness of elastic cushion plate increases and the ratio of dynamic stiffness to static stiffness decreases; under the condition of constant mesh wall thickness,with the increase of mesh aperture,the static stiffness of elastic cushion plate decreases and the ratio of dynamic stiffness to static stiffness increases;compare with the traditional grooved elastic cushion plate with similar static stiffness,the meshed elastic cushion plate has the characteristics of lower dynamic and static stiffness,smaller maximum stress value and more uniform stress distribution.Therefore,reasonable adjustment of mesh wall thickness and aperture size can make mesh elastic cushion plate suitable for track structures with different stiffness requirements,and the application of mesh structure to under rail elastic cushion plate can enhance the force transmission characteristics of cushion plate and prolong the service life of cushion plate.

The loss of water resources caused by mining fissures is a key factor restricting the green development of coal resources in western mining areas. in order to analyze the influence of mining thickness and face width on the development height of water diversion fracture zone, based on the characteristics of overburden in Xinzhuang Coal Mine, the finite difference software FLAC3D is used to simulate and analyze the size effect of water diversion fracture zone height. The simulation results show that the height of the water diversion fracture zone is positively correlated with the increase of mining thickness and working face width. When the mining thickness is 9m and the width of the working face is 240m, the height of the water diversion fracture zone is 115m, and the average distance between the coal layer 8 of Xinzhuang Coal Mine and the bottom of the Cretaceous aquifer is 106.9m, which may cause water inrush in the mine. Therefore, according to the simulation results and referring to the mining size of part of the mine face in the attached Binchang mining area, it is suggested that the mining thickness of Xinzhuang Coal Mine is about 10m and the width of the working face is not more than 200m.

The warpage of brominated flame-retardant PA66 composites was investigated in terms of the compositions without glass fiber and with the circular and flat glass fibers. The warpage of the composites was analyzed on the basis of their mechanical properties, crystallization properties, shrinkage rate and transverse/longitudinal shrinkage ratio. The results indicated that the composites without glass fiber had the highest crystallinity, transverse shrinkage and longitudinal shrinkage, but the lowest transverse/longitudinal shrinkage ratio and warpage. At the same content of glass fibers, the warpage of the composites with the flat glass fiber was obviously better than that of the composite with the circular glass fiber due to a lower ratio of transverse/longitudinal shrinkage. In the case of mechanical properties, the tensile strength and bending strength of the composites with flat glass fibers were lower than that of the composites with the circular glass fiber. The different types of glass fibers had little effect on the crystallization of the composites, and their crystallinity and crystallization peak temperature were very close to each other. At the same content of flame retardant, both the transverse shrinkage and the longitudinal shrinkage of the composites decreased with an increase in the content of the flat glass fiber. However, their transverse/longitudinal shrinkage ratio increased, leading to an increase in the warpage of the composites. [ABSTRACT FROM AUTHOR]

Two diblock copolymers of poly(methyl methacrylate)-block-poly(styrene) with chlorine as terminal group (PMMA-b-PS-Cl) were synthesized via two-step atom transfer radical polymerization. The structures of the block copolymers were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and gel permeation chromatography. Thermal properties including glass transition temperature (Tg) and thermal stability were studied by differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. The block copolymers of PMMA-b-PS-Cl exhibited two glass transitions, which were attributed to the Tgs of PMMA and PS segments, respectively. According to TGA, thermal decompositions of PMMA macro-initiator and PMMA-b-PS-Cl block copolymers had two stages. The weight loss ratio in the second stage was more significant than that in the first stage, which may be attributed to the separation of the halogen atom from the terminal group and the formation of a double bond. The breaking down of the backbone dominates in the second stage in which the weight loss ratio was more than 70%, represented the main stage of pyrolysis. It was found that the introduction of the PS chain remarkably enhanced the thermal stability of the copolymer, thus endowing the block copolymers high activation energy for thermal decomposition. On the other hand, the remaining two pyrolysis procedures further indicated that thermodynamic mechanism didn’t change due to the introduction of PS segments. [ABSTRACT FROM AUTHOR]