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2 2021

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Structure and Properties of Chain Branched Nitrocellulose

Liu Yanhua, Shao Ziqiang, Yuan Jingjing, Jia Shuai, Wang Feijun, Li Yonghong, Guo Bingyi, Yang Zhonglin, Zuo Yingying

Central European Journal of Energetic Materials

2021

Vol. 18, no. 4

448--476

Nitrocellulose (NC) with a semi-rigid polymer chain is one of the typical traditional cellulose derivatives. Optimization of its mechanical properties is of great significance for improving the performance of NC-based propellants. The nitrate glycerol ether cellulose (NGEC) was prepared by introducing glycerol onto the unreacted, free hydroxyl groups on NC through a three-step process (alkalization, etherification, and nitration). The effects of both the nitration process and the degree of etherification on the NGEC nitrogen content were qualitatively explored. By adding NGEC into modified double-base propellant, a standard engine grain with a diameter of 50 mm was produced by adsorption, granulation, and screw extrusion. The heat of explosion, and other physical properties of NGEC were characterized and the variation in mechanical properties and performance after storage for 6 years was investigated. The results indicated that the sensitivity was improved, and the stability was slightly decreased on increasing the nitrogen content of NGEC. Compared with NC containing similar nitrogen levels, NGEC exhibited a slightly higher heat of explosion, similar compatibility, and lower sensitivity. Additionally, the solubility of NGEC in ethanol/ether exceeded 99.7%. Through branched-chain chemical modification, the glycerol ether played a significant role in achieving internal plasticization among the cellulose chains.

Joint Formation and Mechanical Properties of 2060 Aluminum Alloy Refill Friction Stir Spot Welding Joint

Shang Zhen, Zuo Yingying, Ji Shude, Wang Yue, Chai Peng

Archives of Metallurgy and Materials

2021

Vol. 66, iss. 1

153--161

Refill friction stir spot welding (RFSSW) was used to weld the 2060 aluminum alloy with 2 mm thickness. Joint formation, defect characteristics and mechanical properties were investigated. Results show that stir zone (SZ) is clarified into dynamic recrystallization zone (DRZ) and heat extruded zone (HEZ) due to different microstructural features. The size of void near the hook tip decreases with the increase of the plunge depth. Different hook morphologies are obtained under different plunge depths. The tensile-shear load of joint with the void defect initially decreases and then increases with increasing plunge depth. The mean loads of joints under different plunge depths are in the range of 5.1-5.8 kN. The void separates the hook from lap interface, so the cracks initiating from the hook propagate along the sleeve retreating path. The hook has a larger influence on the tensile-shear load of joint than void. All the tensile specimens present a shear-plug fracture mode.