利用模态声发射技术监测飞机主结构件的日历损伤

研究了腐蚀特别是点腐蚀过程产生声发射(AE)的源机制及AE信号特点,推导了AE信号幅度与腐蚀深度及频率的关系,并说明该关系对利用AE技术监测腐蚀损伤的意义。论述了利用模态声发射(MAE)技术识别腐蚀AE信号的理论根据,介绍了利用MAE技术对飞机主结构件日历损伤进行评估的方法。基于试验获得的航空用铝合金材料在加速腐蚀过程中的声发射信号与腐蚀损伤的关系对研究材料损伤程度与声发射强度之间的内在联系有重要意义。试验表明,腐蚀能远在被肉眼发现之前即可很方便地用AE仪器检测,利用AE技术探测早期腐蚀、研究腐蚀发展规律、监测和评估腐蚀损伤具有极其良好的应用前景。

碳纤维复合材料主传力典型结构试验件模压模具设计

为了实现直升机全尺寸机匣的碳纤维复合材料轻量化研发设计,典型结构试验件的试制是不可缺少的环节。分析了主传力典型结构试验件的特点,实现了主传力典型结构试验件层压模具的设计制作与主传力典型结构试验件的制作。为全尺寸机匣的碳纤维复合材料轻量化制造提供参考。

VIBRATION CONTROL OF A SPACE TRUSS STRUCTURE WITH A PIEZOELECTRIC ACTIVE MEMBER

Active vibration control is an effective way of increasing robustness of the design to meet the stringent accuracy requirements for space structures. This paper presents the results of active damping realized by a piezoelectric active member to control the vibration of a four-bay four-longern aluminum truss structure with cantilever boundary. The active member, which utilizes a piezoelectric actuating unit and an integrated load cell, is designed for vibration control of the space truss structures. Active damping control is realized using direct velocity feedback around the active member. The placement of the active member as one of the most important factor of affecting the control system performance, is also investigated by modal dissipation energy ratio as indicator. The active damping effectiveness is evaluated by comparing the closed-loop response with the open loop response.

SYSTEM IDENTIFICATION OF ADAPTIVE TRUSS STRUCTURES USING PIEZOELECTRIC ACTIVE MEMBERS

Adaptive truss structures are a new kind of structures with integrated active members,whose dynamic characteristies can be beneficially modified to meet mission requirements.Active members containing actuating and sensing units are the major components of adaptive truss structures.Modeling of adaptive truss structures is a key step to analyze the structural dynamic characteristics.A new experimental modal analysis approach,in which active members are used as excitatiDn sources for modal test,has been proposed in this paper.The excitation forces generated by the active members, which are different from the excitation forces exerted on structures in the conventional modal test,are internal forces for the truss structures.The relation between internal excitation forces and external forces is revealed such that the traditional identification method can be adopted to obtain modal parameters of adaptive structures.Placement problem of the active member in adaptive truss structures is also discussed in this work. Modal test and analysis are conducted with a planar adaptive truss structure by using piezoelectric active members in order to verify the feasibility and effectiveness of the proposed method.

Influence of expanded polystyrene size on deformation characteristics of light weight soil

Deformation characteristics of light weight soil with different EPS (expanded polystyrene) sizes were investigated by consolidation tests.The results show that the confined stress-strain relation curve is in S shape,which has a good homologous relation with e-p curve and e-lgp curve,and three types of curves reflect obvious structural characteristics of light weight soil.When cement mixed ratio and EPS volume ratio are the same for different specimens,structural strength decreases with the increase of EPS size,but compressibility indexes basically keep unchanged within the structural strength.The settlement of light weight soil can be divided into instantaneous settlement and primary consolidation settlement.It has no obvious rheology property,and 90% of total consolidation deformation can be finished in 1 min.Settlement-time relation of light weight soil can be predicted by the hyperbolic model.S-lgt curve of light weight soil is not in anti-S shape.It is proved that there is no secondary consolidation section,so consolidation coefficient cannot be obtained by time logarithm method.Structural strength and unit price decrease with the increase of EPS size,but the reducing rate of the structural strength is lower than that of the unit price,so the cost of mixed soil can be reduced by increasing the EPS size.The EPS beads with 3-5 mm in diameter are suggested to be used in the construction process,and the prescription of mixed soil can be optimized.

Investigation on color variation of Morpho butterfly wings hierarchical structure based on PCA

Morpho butterfly wings show brilliant blue color,which has a close relationship with the hierarchical micro/nano structures on the surface of scales.When liquids such as methanol,ethanol and isopropanol with different refractive indexes drop onto the scales,the reflectance of wings would decrease.The main peaks of reflectance shift to the right and the scales turn to yel-low-green.After the liquids volatilizes completely,the scales revert to the original blue color.The typical micro/nano struc-tures of Morpho butterfly wing scales are modeled,and the reflectance variation in the course of dropping liquids is simulated.Furthermore,the principal component analysis(PCA) method is employed to analyze the experimental and simulation reflec-tance data,extract principal components and reduce dimensions.As a result,the curves mapping the reflectance variation are clearly shown in the coordinate system consisting of three principal components.The typical color variation of scales during the dropping process could be monitored,and different kinds of liquids could be obviously distinguished according to the dis-tributed regions of mapping points.This study provides guidance to environmental media detecting as well as data processing,and enhances the fabrication and application of the mimic Morpho butterfly wings micro/nano structures.