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1.
《中国航空学报》2020,33(3):1074-1084
Marciniack–Kuczinski (M–K) model is widely used to predict material’s forming limit curve (FLC). The prediction of FLC traditionally neglected through-thickness normal stress. However, it cannot be neglected in some forming processes. Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress. In addition, based on Nakazima test process, the ratio of through-thickness normal stress and maximum principal stress has been derived, which was a function of instantaneous thickness and loading path. Here, initial groove angle in M–K model was not considered. In this paper, uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy. Based on Hill 48 yield criterion and M–K model, the prediction model of FLC was established. The increase of thickness can enhance FLC. Meanwhile, it is necessary to consider through-thickness normal stress and initial groove angle in prediction model. On the left side of FLC, the effect of initial groove angle on FLC is weakened by increasing sheet thickness. On the right side of FLC, the effect of initial groove angle on FLC is strengthened by increasing sheet thickness. On the right side of FLC, the relation between limit strain points with different thicknesses is linear under one certain loading path. Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition. 相似文献
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本文从动力学角度出发,建立微机器人轮式驱动器的运动方程,并分析微驱动器运动稳定性的各种影响因素,得出造成微驱动器运动产生振动主要是存在动载荷。通过使用一相对运动弹性杆组成的模拟传动机构在微小传动力实验台进行传动力试验,试验结果表明弹性杆在啮合过程中产生了不稳定的变传动力,这种变传动力正是影响微驱动器运动产生振动的重要因素。 相似文献
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介绍了基于微机电一体化系统(MEMS)的微槽冷却系统的研究成果。分析了将微槽冷却系统用于微纳卫星热控设计时的特殊要求。讨论了表征微槽冷却系统性能的水力学系统和传热性能。理论分析和数值模拟结果表明,微槽冷却系统可使大热流密度的热源芯片温度维持在较低的范围内,能满足微纳卫星热控的要求。研究认为,压降和热阻均较小的深槽可在小泵功率时提供较优的传热性能。 相似文献
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支持MEMS的CAD/CAE系统结构研究 总被引:5,自引:0,他引:5
康建初 《北京航空航天大学学报》1998,24(4):475-478
CAD/CAE技术在MEMS(Micro Electro Mechanical Systems)研究过程中具有非常重要的作用.本文首先介绍了用于MEMS的CAD/CAE技术特点,然后研究了MEMS CAD/CAE系统结构,给出了软件支持工具结构框图,指明了解决其中关键技术的途径.CAD/CAE技术的应用,将提高微型机电系统的设计质量,缩短研制周期,使之及早走向工业化. 相似文献
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《中国航空学报》2020,33(6):1799-1811
The bent double-ridged rectangular tube (DRRT) with high forming quality is helpful to improve the microwave transmission accuracy. For reducing the cross-sectional deformation in the H-typed bending process, in addition to using rigid mandrel to support the inside of tube, ridge groove fillers are also added to restrict the deformation of ridge grooves. Because of the change of stress and strain state of bent tube in bending, rigid mandrel retracting and specially twice-springback stages, and the springback of fillers, the cross-sectional deformation of tube in each stage may be different. Therefore, based on the ABAQUS platform, the finite element models (FEM) for H-typed bending, mandrel retracting and twice-springback stages of H96 DRRT with fillers were established and validated. It is found that, for the height and width deformation of tube and spacing deformation of ridge grooves, retraction of mandrel can make the distribution of these deformations more uniform along the bending direction. The first springback can reduce these deformations significantly, which should be emphasized. But the second springback only increases them by less amount, which can be ignored. The smaller height deformation of ridge groove and filler can be neglected. 相似文献
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为了研究螺旋槽端面气膜密封结构在高温下的密封性能,建立了高温密封分析数学模型,研究了螺旋槽气膜密封的气膜温度、压力以及端面变形分布规律,在此基础上探讨了螺旋槽气膜密封的热变形机理,并进一步分析了不同密封压力、转速、环境温度下热效应对开启力和泄漏率的影响。结果表明:在高压、高速条件下,热效应使端面形成发散间隙,导致开启力减小,泄漏率增加;在低压、高速条件下,热效应使端面形成收敛间隙,导致开启力及泄漏率增大。对于螺旋槽端面气膜密封结构,环境温度的升高对端面变形的影响不明显,且环境温度从300 K升至550 K时,考虑端面热效应的开启力减小4%,泄漏率减少36%。 相似文献
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