Abstract9,10‐dihydro‐9‐oxo‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and special tetra functional epoxy resin (EP) AG‐601 were combined to synthesize a reactive flame retardant (FREP) and then incorporated into EP, obtaining the flame retardant material EP/FREP. To achieve EPs with higher flame retardancy and mechanical properties, a new intrinsically flame retardant EP system named EP/FRDM was produced by modifying EP/FREP with high thermal resistance bismaleimide (BDM). In the presence of a distinct FRDM structure comprising phosphaphenanthrene/nitrogen, the EP possessed superior flame retardancy and impact toughness. The curing process of EP/FRDM was investigated using Real‐Time Fourier‐transform Infrared. In terms of fire performance, the limiting oxygen index of the EP/FRDM‐3 was raised from 31.4% to 38.2%, and the vertical burning rating was improved after BDM was added to the EP/FREP system. It was discovered that EP/FRDM exhibited a classic two‐phase flame retardant influence by analyzing the residual carbon morphology and pyrolysis behavior. Simultaneously, the glass transition temperature (Tg) of EP/FRDM remained essentially stable, and the char residue yield rose markedly, which indicated that the system had outstanding thermal stability, according to the results of the dynamic mechanical analysis and thermogravimetric analysis tests. Notably, the EP/FRDM experienced an internal chain expansion reaction when BDM was added, giving flame retardant materials excellent flexural and impact strengths and promising future application opportunities.
Flywheel, as a kinetic energy storage and conversion device, has promising applications due to its high efficiency, no pollution and long lifetime. In particular, with a three-layer structure packed with heavy metal alloy middle layer, a flywheel can achieve both a large rotational inertia and a high energy density. To guarantee structural strength safety of this type of multi-ring packed flywheel operating at high temperature, structural and thermal stress analysis for a flywheel with a tungsten alloy layer sandwiched between two stainless steel layers is carried out using finite element method (FEM). Based on plane stress assumption, flywheel stress characteristic along radius under assembly force, centrifugal force and thermal loading is demonstrated. The results show that, the rise of temperature causes inconsistent thermal expansion between neighbouring layers and results in a large thermal stress. Particularly, a high circumferential tensile stress occurs in the middle layer. It is also found that, the segments of the middle tungsten alloy layer can efficiently relieve the inconsistent thermal expansion and lower the thermal stress. Moreover, the number of segments significantly influences the efficiency of thermal stress releasing and the reserved gap between adjacent segments significantly improves the contact pressure between inner hub and tungsten alloy layer. This work may provide reference for structural design of the multi-ring packed flywheels under thermal loading.
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