Vibration Evaluation of Wrinkled Membrane Inflated Beam

Inflated booms are under increasing application in various membrane spacecraft structures. A specific emphasis is often placed on determining static characteristics of inflated beams in bending. There is a lack of knowledge in dynamic conditions, especially for simple and accurate solutions for wrinkled inflated beams. This article deals with the theoretical evaluation on the natural frequencies of wrinkled inflated beams. Three factors, including the inflated pressure, the wrinkles, and the aspect ratio, are introduced into the vibration equation of the beam to predict the first-order natural frequency of the wrinkled inflated beams. The predictions on the first-order natural frequency agree well with the vibration simulations. The parametric studies on the vibration characteristics of the wrinkled inflated beam are performed in the end. Results reveal that the wrinkles decrease the first-order natural frequency of the inflated beam greatly. The first-order frequency of the wrinkled inflated beam is sensitive to the aspect ratio. The results and conclusions are good references to the design and the wrinkling control of the inflated booms.     

AZ41 镁合金管材充液压形规律探究

目的实现镁合金管材的室温成形。方法利用物理实验的方法研究AZ41镁合金薄壁管材充液压形过程中的成形规律,分析主要缺陷形式,并揭示圆角填充过程和壁厚分布规律。结果 AZ41镁合金管材充液压形易发生破裂和失稳缺陷。内压过低变形部位难以转移,导致弯曲破裂的发生;内压过高,管坯合模前膨胀,导致截面周长大于零件截面周长,进而发生起皱。结论最终在5.6 MPa的支撑内压下成功成形出了最小圆角5 mm的零件,最大减薄率小于5%。     

方盒形件混合分块压边拉深工艺研究

目的 提高盒形件拉深成形过程中的成形件质量及成形极限。方法 提出混合分块压边方法,即将法兰区的4个直边区和4个圆角区沿周向分开进行压边,并在每个圆角区分别采用径向分块压边。采用有限元方法,结合正交试验,对压边圈的分块位置及压边力的分配方案进行优化设计,并通过实验比较分别采用混合分块压边方法和整体压边方法时方盒形件拉深成形的抑制起皱效果及成形极限。结果 有限元模拟和实验结果表明,采用混合分块压边方法,成形件皱纹最大幅值及最大减薄率显著减小,板料最小厚度增加,有效降低了成形件的起皱和破裂风险。结论 新方法抑制起皱的效果显著优于普通压边方法,在合理的工艺条件下,板料的成形极限也得到明显的提高。     

考虑膜材各向异性的膜结构褶皱分析

推导了应用于向量式有限元三角形膜单元的各向异性膜材本构矩阵;进一步推导了各向异性膜材褶皱状态下的修正本构矩阵,并提出更为合理的主偏夹角计算方法。在此基础上编制了考虑膜材各向异性的膜结构荷载分析与褶皱分析程序,并进行了算例验证。算例分析表明,所编制的向量式有限元程序可以很好地完成各向异性膜结构的荷载分析与褶皱分析,验证了理论推导的正确性和分析程序的可靠性。分析结果还表明膜材的各向异性与褶皱效应会对膜结构的受力性能产生显著影响。     

The modeling and numerical analysis of wrinkled membranes

In this paper three fundamental issues regarding modeling and analysis of wrinkled membranes are addressed. First, a new membrane model with viable Young's modulus and Poisson's ratio is proposed, which physically characterizes stress relaxation phenomena in membrane wrinkling, and expresses taut, wrinkled and slack states of a membrane in a systematic manner. Second, a parametric variational principle is developed for the new membrane model. Third, by the variational principle, the original membrane problem is converted to a non‐linear complementarity problem in mathematical programming. A parametric finite element discretization and a smoothing Newton method are then used for numerical solution. The proposed membrane model and numerical method are capable of delivering convergent results for membranes with a mixture of wrinkled and slack regions, without iteration of membrane stresses. Three numerical examples are provided. Copyright © 2003 John Wiley & Sons, Ltd.