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991.
992.
采用高温拉伸试验,研究了Ti-0.2Pd在600~800°C,应变速率10-4~10-1s-1的高温流变行为。获得了流变应力与应变速率和变形温度的依存关系以及变形激活能Q为100.9kJ.mol-1,应力指数n为4.8。建立了Ti-0.2Pd合金热变形的理论基础。 相似文献
993.
在进厂大修过程中,发现多架某型飞机液压油箱内部的隔板出现变形和疑似裂纹的质量问题。通过分析该故障的发生机理,复查修理过程,最终确定故障原因是该型飞机液压油箱增压系统存在设计缺陷。 相似文献
994.
超薄零件车削加工后存在较大的变形,严重制约了该类关键器件的广泛应用。为实现超薄零件加工变形的预测与分析,基于力学分析,建立了加工仿真系统并进行超薄零件精加工过程模拟研究。实际加工验证了所建立模型的准确性,同时基于该系统对超薄零件加工后变形进行分析,其结果对改进加工工艺和减小工件变形具有指导意义。 相似文献
995.
《中国航空学报》2020,33(6):1589-1601
In this paper, numerical investigation of hypersonic gas flow over two typical gap-cavity structures is carried out using all-speed preconditioned density-based solver. Such structures filled with porous seal in the gap are often present at the joint locations of control surfaces of the hypersonic vehicles. Single-domain approach is adopted to integrate the governing equations for both porous and fluid regions. The basic thermal invasion characteristic is first illustrated using the maze gap-cavity structure without sealing. Then, the influence of seal filling depth on the thermal invasion characteristic is investigated for the structure with sealing. Finally, a comparison of thermal invasion characteristics between maze and straight gap-cavity structures is performed to examine the influence of gap bending. Results show that the main source of hot airflow invading into the gap is from the millimeter scale gas layer within the boundary layer. And the invasion characteristic presents approximate stationary behavior. A primary vortex occurs in the gap adjacent to the leeward wall, which is ascribed to the impinging effect between the separate boundary flow and the windward wall. This effect is also the main driving force of thermal invasion. A treatment of filling the seal in certain depth inside the gap can significantly reduce the thermal load of seal and maintain an acceptable level of the invading mass flow rate. Additionally, it is found that the gap bending exerts a limited block effect on the thermal invasion without sealing, and this effect can be ignored with sealing. These results can provide a reference for optimizing the seal gap-cavity structure configuration. 相似文献
996.
997.
Marcelo Curtarelli Enner Alcântara Camilo Rennó José Stech 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
In this work we investigate the cold front passage effects on sensible and latent heat flux in a tropical hydroelectric reservoir. The study area, Itumbiara reservoir (Goiás State/Brazil) at the beginning of the austral winter, is characterized by the presence of a weak thermal stratification and the passage of several cold fronts from higher latitudes of South America. Sensible and latent heat fluxes were estimated considering the atmospheric boundary layer stability. In situ and MODIS water surface temperature data were used to adjust the coefficients for momentum and heat exchanges between water and atmosphere and spatialize the sensible and latent heat fluxes. The results showed that during a cold front event the sensible heat flux can be up to five times greater than the flux observed before. The latent heat flux tends to decrease during the cold front but increase again after the passage. The highest values of heat loss were observed at littoral zone and some Reservoir’s embayment. The heat loss intensification can be separated in two moments: first, during the cold front passage, when the wind speed increases and the air temperature decreases; second, after the cold front passage, with air humidity decreasing. This can be considered a key process to understanding the heat loss in the Itumbiara reservoir. 相似文献
998.
999.
《中国航空学报》2020,33(4):1338-1348
The microstructural evolution mechanism and constitutive behavior of 2297 Al-Li alloy were studied via thermal compression test with the constant strain rates of 0.001–1 s−1 and the deformation temperatures ranging from 623 to 773 K. To verify the predictable ability of diverse constitutive models under different stress states, the hot compression experiments with stress triaxiality varying from −0.33 to 0.46 were conducted. The microstructures of the deformed specimens under diverse deformation conditions are probed to reveal the mechanism of hot deformation behavior. The experimental results indicate that the work-hardening and dynamic softening are competitive during the hot compression process, and the dynamic softening is more obvious under low deformation temperature and high strain rate. The microstructural analysis manifests that the dynamic recovery gets predominant at high deformation temperature to produce fine grains. Meanwhile, the dynamic recrystallization becomes more dominant as the strain rate decreases, which is sensitive to the stress triaxiality. In addition, both the modified Johnson-Cook model and strain-compensated Arrhenius-type function are suitable for describing the flow behavior of 2297 alloy, while the latter reveals a more accurate prediction. However, the predictability of the two kinds of models is worsened with the transformation of stress triaxiality, and the validity of the Arrhenius-type model is restricted by high stress triaxiality. 相似文献
1000.