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461.
Jagadish Singh Aishetu Umar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
We have studied the positions and stability of the collinear equilibrium points, L1,2,3 of an infinitesimal body in the elliptic restricted three-body problem (ER3BP) when both primaries of the system are luminous and oblate spheroids moving in elliptic orbits around their common center of mass. We observe that their positions are affected by the radiation pressure forces, oblateness and the eccentricity of the orbits, but the stability character remains unchanged and are unstable. The effects of the parameters involved on the collinear points, in particular for the binary systems Achird, Luyten 726-8, Kruger 60, Alpha Centauri AB and Xi Bootis, and their stability in general have been investigated numerically using the analytical results obtained. 相似文献
462.
在飞机结构的设计定型阶段,要综合考虑载荷谱和结构特性的分散评估机群的可靠寿命。为此,进行了某型飞机结构细节的TA15M钛合金模拟试件在3个单机谱下的耐久性试验,断口判读得到主裂纹扩展(a,t)数据,反推得到了当量初始缺陷尺寸(EIFS)。对比分析表明,载荷谱分散对EIFS分布参数无影响,估计得到了通用EIFS分布参数。建立了考虑载荷谱分散的裂纹扩展对数正态随机变量模型及参数估计方法,由此确定裂纹超越概率并进行损伤度评估,建立了综合考虑载荷谱和结构特性分散的概率断裂力学方法(PFMA)。 相似文献
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467.
复合材料混合模式分层断裂的实验表征 总被引:1,自引:0,他引:1
介绍了一种碳纤维增强复合材料混合模式层间断裂试验方法,它采用改进的混合模式弯曲试验构型,可对Ⅰ型对Ⅱ型断裂按比例加载,且使用对开裂的梁形试件。 相似文献
468.
《中国航空学报》2023,36(4):299-314
A multi-objective optimization method was proposed for different dome reinforcement methods of a filament-wound solid rocket motor composite case based on a Radial Basis Function (RBF) model. Progressive damage of the composite case was considered in a simulation based on Hashin failure criteria, and simulation results were validated by hydraulic burst tests to precisely predict the failure mode, failure position, and burst pressure. An RBF surrogate model was established and evaluated by Relative Average Absolute Error (RAAE), Relative Maximum Absolute Error (RMAE), Root Mean Squared Error (RMSE), and R2 methods to improve the optimization efficient of dome reinforcement. In addition, the Non-dominated Sorting Genetic Algorithm (NSGA-II) was employed to establish multi-objective optimization models of variable-angle and variable-polar-radius dome reinforcements to investigate the coupling effect of the reinforcement angle, reinforcement layers, and reinforcement range on the case performance. Optimal reinforcement parameters were obtained and used to establish a progressive damage model of the composite case with dome reinforcement. In accordance with progressive damage analysis, the burst pressure and performance factor were obtained. Results illustrated that variable-angle dome reinforcement was the optimal reinforcement method compared with variable-polar-radius dome reinforcement as it could not only ensure the reinforcement angle’s continuous changing but also decrease the mass of composite materials. Compared with the unreinforced case, the reinforced case exhibited an increase in the burst pressure and performance factor of 36.1% and 23.5%, respectively. 相似文献
469.
《中国航空学报》2023,36(4):556-564
Poor fracture toughness leads to premature failure of La2(Zr0.75Ce0.25)2O7 (LCZ) thermal barrier coatings in an elevated temperature service environment. A novel coating material, namely (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2(Zr0.75Ce0.25)2O7 (LNSGY) based on the high-entropy concept, was successfully fabricated by solid-state sintering. The microstructure of LCZ and LNSGY was investigated by X-Ray Diffraction (XRD), Raman Spectrometer (RS), Transmission Electronic Microscopy (TEM) and Scanning Electron Microscopy (SEM). The fracture toughness of the LCZ and LNSGY ceramics was evaluated. The LNSGY has excellent high-temperature phase stability, and the grain size of LNSGY ceramic is smaller than that of LCZ ceramic at an elevated temperature due to the sluggish diffusion effect. Compared with LCZ (fracture toughness is (1.4 ± 0.1) MPa∙m1/2), the fracture toughness of LNSGY is significantly enhanced (fracture toughness is (2.0 ± 0.3) MPa∙m1/2). Therefore, the LNSGY can be a promising advanced thermal barrier coating material in the future. 相似文献
470.
网球初学者正手击球技术难点分析 总被引:1,自引:0,他引:1
汪军锋 《西安航空技术高等专科学校学报》2010,28(1)
网球的技术性很强,正手击球是其中最为基本的一项技术。从网球技术动作的生物力学原理以及身体姿势、动作轨迹、动作时间、动作速度、动作速率、动作力量几项动作要素分析了网球正手击球技术动作,帮助网球初学者解析拍面角度的控制、击球点的掌握以及挥拍的轨迹等技术难点,从而建立了清晰的动作概念,促进了正手击球技术的快速掌握。 相似文献