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为研究某型高能固体发动机的热安全性,建立了发动机在火烧环境下的有限元计算模型,数值模拟了发动机及装药在不同烤燃工况下的温度分布和爆炸延迟期。研究表明,大型发动机烤燃特性与小型发动机呈现相同规律,热扩散速率在快速烤燃工况下较大,温度梯度在慢速烤燃工况下较大,烤燃速率对推进剂起始反应位置有一定影响。发动机尺寸和快烤环境温度对其热安全性影响较大,发动机尺寸减小和温度升高均导致推进剂点火延迟时间明显降低。 相似文献
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对真空自耗电极电弧熔炼制备的传感器用Ti-6Ni-3Mo-1Sn合金进行热处理,先经过不同温度的固溶处理在经过500℃时效处理4 h,通过实验测试手段研究固溶温度对固溶态和时效态合金组织和力学性能的影响。研究结果表明:固溶温度700℃时,在固溶态合金晶粒中产生了大量初生α相。随着固溶温度增加,形成了更大的β晶粒。以更高温度处理后固溶态合金获得更大拉伸强度以及屈服强度,而伸长率表现为先升高再减小。经过时效处理的时效态合金晶粒中产生了许多弥散态的细小α相。以700℃固溶处理后,形成了初生α相,在残余β相内产生更多β稳定元素。随着固溶温度增加,时效态Ti-6Ni-3Mo-1Sn合金的拉伸强度,屈服强度及伸长率均表现出先增加后减小,最大值发生在固溶温度700℃时,分别为1268,1192 MPa, 5.62%。在低于700℃固溶时效处理后的试样断口区域形成许多尺寸差异较大微孔,呈现脆性断裂特点。 相似文献
97.
Anupam Ojha Barun Das Shyamal Kumar Mondal Manoranjan Maiti 《Applied Soft Computing》2013,13(8):3703-3712
This paper presents the recently introduced modified subgradient method for optimization and its effectiveness in a fuzzy transportation model. Here a multi-item balanced transportation problem (MIBTP) is formulated where unit transportation costs are imprecise. Also available spaces and budgets at destinations are limited but imprecise. The objective is to find a shipment schedule for the items that minimizes the total cost subjected to imprecise warehouse and budget constraints at destinations. The proposed model is reduced to a multi-objective optimization problem using tolerances, then to a crisp single-objective one using fuzzy non-linear programming (FNLP) technique and Zimmermann's method. The above fuzzy MIBTP is also reduced to another form of deterministic one using modified sub-gradient method (MSM). These two crisp optimization problems are solved by Genetic Algorithm (GA). As an extension, fuzzy multi-item balanced solid transportation problems (STPs) with and without restrictions on some routes and items are formulated and reduced to deterministic ones following FNLP and Zimmermann's methods. These models are also solved by GA. Models are illustrated numerically, optimum results of fuzzy MIBTP from two deductions are compared. Results are also presented for different GA parameters. 相似文献
98.
《粉末冶金学》2013,56(5):397-404
AbstractSilver based composites with varying concentration of graphite and/or MoS2 were prepared by powder metallurgy method. Impacts of composition on the tribological performance of the composites in ambient air and vacuum were investigated. The lowest friction in air was achieved by Ag–20G (vol.-%) composite, while Ag–20MoS2 exhibited the best lubricity in vacuum. XPS evaluation revealed the oxidation of MoS2 in air and a decrease concentration of graphite on the surface of the wear tracks under vacuum. As the proportion of graphite to MoS2 increased, the friction coefficient and the wear rates ascended gradually in air while decreased sharply under vacuum. As compared with other compositions, Ag–15MoS2–5G exhibited a comparable stable and good tribological performance as the environmental condition changed for its friction coefficient and wear rate remained around 0·14 and 5×10?6 mm3 N?1 m?1. 相似文献
99.
Crystallization and infrared radiation properties of iron ion doped cordierite glass-ceramics 总被引:1,自引:0,他引:1
Shu-Ming Wang Feng-Hua KuangQing-Zhi Yan Chang-Chun GeLong-Hao Qi 《Journal of Alloys and Compounds》2011,509(6):2819-2823
Heterogeneous ion solution is an important method to improve the wanted property of polycrystalline materials. In this paper, for the purpose of infrared radiation property modification, different contents Fe2O3 were doped in MgO-Al2O3-SiO2 system glasses. The effects of Fe2O3 doping on nucleation mechanism, crystallization behaviors and especially infrared radiation properties of this cordierite-crystalline based glass-ceramics were systematically investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results show that, the doping of iron ion can promote the phase separation of this magnesium aluminosilicate glass, and therefore change the crystallization mechanism of this glass from surface crystallization to bulk crystallization. The iron ion incorporates into the crystal structure of cordierite by mean of substituting Mg2+ in M site. The substitution of Fe3+ to Mg2+ can form the vacant site of Mg2+ cations. For the effects of lattice distortion, impurity and vacancy defects which caused by the incorporation of iron ion, the infrared radiation performance of cordierite based glass-ceramics can be improved effectively. 相似文献
100.
The synthesis, structural, magnetic and dielectric properties of a new type of high permittivity materials La2−xCaxNiO4+δ (x = 0, 0.1, 0.2, 0.3) (abbreviated as LCNs) were reported. The samples were prepared through conventional solid state reaction route. Detailed structural information was retrieved by Rietveld refinement; normalized bond length and bond valence was calculated to investigate the compression/dilation effect of bonds and atoms in unit cell. It can be found all samples belong to K2NiF4 structure with space group I4/mmm. Doping of Ca in La2NiO4+δ shrinks the unit cell and makes the structure tend to become instable. Three types of (La, Ca)-O bonds, and two kinds of Ni-O bonds exist in LCNs. Along c axis there are alternately compressed (La,Ca)O9 dodecahedra and lengthened NiO6 octahedra. Room temperature magnetic measurements show that the materials are paramagnetic and Ca doping can improve the spontaneous magnetization. Furthermore, all samples have colossal values of the dielectric constant (?) at frequencies lower than 1 kHz. Interestingly, La1.8Ca0.2NiO4+δ maintains its high permittivity at frequencies up to 1 MHz while La1.7Ca0.3NiO4+δ has the lowest dielectric loss (tan δ). Calcium doping can effectively enhance ? and inhibit tan δ. The distortion of (La,Ca)O9 dodecahedra can well explain their dielectric properties. 相似文献