This study investigates the ablation resistance of C/C-SiC composites using the ground simulation internal flow-field supersonic oxygen-rich ablation test technology. The microstructure evolution and ablation mechanism of the composites in a supersonic oxygen-rich environment were explored by examining the macroscopic and microscopic ablation morphologies of the composites before and after the test. The results demonstrate that C/C-SiC composites exhibit excellent ablation resistance, with mass and linear ablation rates of .46 x 10-2 g/s and .42 x 10-2 mm/s, respectively, after 120 s of ablation in a low gas temperature and high oxygen-rich ablation thermal environment. As the gas temperature increases, the mass and linear ablation rates of C/C-SiC composites gradually increase, even though the oxygen enrichment within the gas components decreases. When the gas temperature reaches 2178-2491 K, the mass and linear ablation rates increase to 1.31 x 10-2 g/s and .84 x 10-2 mm/s, respectively. Furthermore, at high temperatures above 2650 K, the mass and linear ablation rates of the composites exhibit a geometric multiple increase, reaching 4.73 x 10-2 g/s and 1.89 x 10-2 mm/s, respectively. These findings indicate that the ablation resistance of C/C-SiC composites in the supersonic oxygen-rich ablation environment is more sensitive to gas temperature than oxygen enrichment. The main factors contributing to the increased ablation rate of C/C-SiC composites in the supersonic oxygen-rich ablation process include the formation of a glass SiO2 oxide film, transition to molten SiO2, erosion of molten SiO2, and high-temperature sublimation of the SiC matrix. The graphical abstract image briefly introduced the system composition of the ground simulation supersonic internal flow-field ablation environment. Then, the ablation thermal environment during the supersonic oxygen-enriched ablation test was analyzed. And further analysis was conducted on the evolution of microstructure and ablation mechanism of C/C-SiC composites under different supersonic oxygen-enriched ablation environment. image
根据柔性接头弹性件的实际工况,采用有限元方法模拟哑铃试样和四重片试样的循环受载情况,预估不同应变条件下试样的疲劳寿命.分析仿真结果发现,四重片试样在结构及受力状态等方面更符合柔性接头摆动疲劳测试工况.选取四重片为柔性接头寿命表征件,并对其开展剪切疲劳寿命试验,发现随着应变增加橡胶的疲劳寿命减小.对比有限元预估试样件寿命与试验结果,循环次数相差 13%以内,验证了该有限元寿命预估方法的正确性.文中所提出的有限元预估寿命方法可进一步应用于多种载荷情况下柔性接头的寿命预估,可节省试验成本,为柔性接头摆动寿命测试提供参考.
裂纹扩展特性是含缺陷发动机药柱结构完整性分析的前提.利用非固有内聚力模型,在有限元方法的基础上结合网格拓扑操作,发展了裂纹扩展仿真方法.以圆管发动机为例,研究了指数型点火压力作用下裂纹扩展的规律.研究结果表明,裂纹张开位移、裂尖横向位置在加载初期增速较大,加载末期增速较缓;随着压力因子绝对值、初始裂纹深度的增加,以及内表面均布裂纹数量的减少,裂纹张开位移会增大;压力因子绝对值越大,点火压力越大,裂纹也越容易提前扩展.初始裂纹深度的增加会在加载初期提前导致裂纹的扩展,在加载的后期,初始裂纹深度的增加反而会延迟裂纹扩展的时间.在加载的后期,尽管裂纹累计扩展次数一致,但裂纹数的增加会导致裂纹张开位移的减小,进而延迟裂纹扩展的时间.
采用热重-差示扫描量热法(TG-DSC)、热重-红外光谱实验(TF-IR)研究 1,1-二氨基-2,2-二硝基乙烯(FOX-7)的热分解过程、热分解产物以及金属氧化物V2O5 对FOX-7热分解过程、热分解产物的影响,并通过Gaussian 09 进行量子化学计算,得出一条FOX-7热分解途径.实验研究表明,FOX-7热分解分为两个阶段,产物有NO2、HNCO、CO2 和少量的NO,其中首先生成产物是NO2,含量最高是HNCO;V2O5 催化剂能使FOX-7 热分解峰温提前,添加催化剂后,FOX-7 热分解第二阶段放热量增加,放热量超过第一阶段并且FOX-7热分解产物中不再有HCN和N2O,说明V2O5 能够影响FOX-7 热分解.计算结果表明,FOX-7热分解首先生成NO2,并且1 mol FOX-7生成2 mol HNCO和1 mol NO2,实验结果和理论计算结果一致.
对于上支撑式导轨发射装置,由于火箭质心超出前滑块之外,起竖后需要发射电气分离机构具有较大的补偿量,而带有套接结构缓冲插头的脱落电连接器要求机构赋予其较大的插拔力和较短的分离时间.因此,结合近年来发射系统和火箭发展状态,介绍了一种新型电气分离机构基本构成和工作程序,以及关键技术参数的计算与仿真分析.通过自适应偏差补偿设计机理和四连杆运动情况动力学仿真计算,完成机构主要参数和结构优化设计,并经过地面试验和飞行试验验证.测试结果表明,该机构选择合理的机构尺寸和运动参数,采用弹簧浮板结构对箭上脱落插座位置进行补偿调整方案合理可行,解决了特种电连接器分离问题;连杆和拨动杆组合实现总分离时间 0.11 s,避免出现火箭较大直径的助推段和机构碰撞干涉.对该电气分离机构的技术优点进行了综合评析,对于同类产品的设计和应用有一定借鉴作用.
