新型轻木GFRP夹芯板拉挤成型工艺及其界面性能

选用无碱玻璃纤维束、短切纤维毡、不饱和树脂与泡桐木芯材,制备了轻木-玻璃纤维增强塑料(GFRP)夹芯板,对其拉挤工艺进行了研究.研究表明:设定模具加热温度(凝胶区)为160 ℃、选取的拉挤速率为10 cm/min时,可制造得到表观性能良好的泡桐木-GFRP夹芯板.通过双悬臂梁(DCB)试验,在芯材表面开槽和不开槽2种情况下,研究了泡桐木与GFRP面层之间的界面黏结性能,并与真空导入工艺制作的夹芯板的界面黏结性能进行了对比.结果表明:拉挤工艺生产的泡桐木-GFRP夹芯板的界面黏结性能已达到甚至优于真空导入工艺生产的.芯材表面开槽可以有效提高试件的界面能量释放率,且对真空导入工艺制作的试件效果更为明显.在拉挤工艺中,树脂难以有效填充齿槽形成"树脂钉",故不能明显提高界面黏结力.在对界面性能要求不严格时,拉挤工艺中芯材表面可不开槽,以减少生产工序、降低生产难度.     

夹层结构复合材料低速冲击试验与分析

设计了聚甲基丙烯酰亚胺(PMI)泡沫、 交联聚氯乙烯(X-PVC)泡沫、 NOMEX蜂窝、 缝合PMI以及开槽PMI泡沫等形式的玻璃布面板夹层结构复合材料, 研究了芯材种类和厚度、 面板玻璃布层数以及缝合和开槽等因素对夹层结构低速冲击性能的影响。结果表明, PMI泡沫芯较X-PVC泡沫芯和NOMEX蜂窝芯具有更高的冲击破坏载荷和吸收能量。随着泡沫密度及面板厚度的增加, 夹层结构复合材料的冲击破坏载荷和破坏吸收能量增大。合理的缝合和开槽, 能够增加PMI泡沫夹层结构的强度、 刚度及界面性能, 提高冲击承载能力。     

格构增强木芯复材板的弯曲性能试验及其理论分析

设计一种新型格构增强木芯复材板,通过四点弯试验研究其抗弯性能.该复材板的面层及腹板为复合材料(FRP),芯材分为泡桐木和南方松两种.保持复材板截面尺寸不变,分别将1、2、3、4块木芯利用真空辅助树脂传递模塑工艺一次成型,从而改变格构腹板数目.此外,以纯木板作为对照试验标的物.结果表明:木芯种类会影响木芯复材板的抗弯性能;不同芯材的最佳格构数目也不同;格构数目增加不会导致复材板刚度产生线性增加.     

新型折叠夹芯结构材料研究进展

折叠夹芯结构是一种具有轻质、高比强、高比刚度以及多功能潜力的新型三维结构材料,近几年受到国内外学者的极大关注.它将成为新一代结构功能一体化的理想结构材料.主要概述了折叠夹芯结构的发展历程,包括折叠芯材的拓扑构型设计、制备工艺研究以及折叠夹芯结构力学性能、失效方式、数值模拟和隔音、热力学等方面的工作.同时结合折叠夹芯结构的性能和优势,对其可能应用的领域进行预测,并对其未来研究方向进行了展望.     

复合芯材夹芯结构成型工艺研究

为了改善复合材料夹芯结构中芯材与面板界面结合强度,研制了一种新型夹芯结构,即复合材料柱/泡沫塑料复合芯材夹芯结构.该结构中用过渡层取代胶结层,使芯材和面板为一体,芯材由泡沫塑料和柱结构组成,其中柱结构是与面板同材质的纤维增强复合材料.通过该夹芯结构的芯材结构设计、加工工具的设计、加工工艺设计,使增强材料在法向上植入芯材中,并与上下面板的增强材料连通.由于在同一个工艺过程中固化成型,构成一个整体,没有界面,从根本上改善了面板与芯材之间粘接性能薄弱问题.试验结果表明,该结构具有较高的抗层间剪切、抗平压、抗剥离及抗疲劳性能.     

装配式冷藏库生产中的若干问题

本文讨论了装配式冷藏库生产过程中有关库板结构、尺寸、及玻璃钢面板、硬质聚氨酯泡沫塑料芯材的质量要求， 模具及生产技术。     

面板材料对泡沫铝夹芯梁抗冲击性能的影响

为考查泡沫铝夹芯梁面板材料对其抗冲击性能的影响,运用数值模拟方法计算了相同重量下面板材料分别为304#不锈钢、工业纯铝和HRB335级钢三种泡沫铝夹芯梁在不同冲量作用下的动力响应;分析了面板材料对泡沫铝夹芯梁跨中变形及芯材压缩应变的影响。结果显示,在冲量相同的情况下,面板材料对泡沫铝夹芯梁的抗冲击性能有一定的影响;爆炸荷载冲量越大,芯材的压缩应变越大,而且面板材料对压缩应变的这种影响也相应地增大。在较大的冲量作用下,HRB335级钢面板泡沫铝夹芯梁的跨中位移及芯材压缩应变都是三者中最小的。     

面板材料对泡沫铝夹芯梁抗冲击性能的影响

为考查泡沫铝夹芯梁面板材料对其抗冲击性能的影响,运用数值模拟方法计算了相同重量下面板材料分别为304#不锈钢、工业纯铝和HRB335级钢三种泡沫铝夹芯梁在不同冲量作用下的动力响应;分析了面板材料对泡沫铝夹芯梁跨中变形及芯材压缩应变的影响.结果显示,在冲量相同的情况下,面板材料对泡沫铝夹芯梁的抗冲击性能有一定的影响;爆炸...     

具有开槽结构的大尺寸立方形超声塑料焊接焊头的设计

提出一种具有开槽结构的大尺寸立方形超声塑料焊接焊头的设计方法,并对其进行了实验验证.首先通过合理开槽将大尺寸立方形焊头划分为若干单元,然后将各焊头单元和立方形半波振子比较,利用等效机械阻抗的概念得出焊头单元的频率方程,其间考虑了耦合振动的影响.最后利用该方程研究了开槽数、槽宽度以及槽长度等因素对焊头振动特性的影响.按此方法设计加工了几组具有开槽结构的大尺寸立方形焊头,结果表明焊头谐振频率的实测值和理论值吻合得很好.     

圆形金属蜂窝芯材冲击性能的有限元分析

利用ANSYS/LS-DYNA有限元软件,对12×8圆形金属蜂窝芯材的共面冲击过程进行模拟,得出了圆形金属蜂窝芯材不同冲击速度下的多种变形模式及其动态峰应力的值.从结果可以看出:在共面冲击下,其动态峰应力和冲击速度之间是二次线性关系.这与试验的结果是相一致的.     

Numerical and experimental evaluation of performance of centrifugal seals

‘Centrifugal seals’ or ‘Slinger seals’ offer an attractive choice as non-contact-type sealing in fluid machinery. These seals utilize the radial pressure gradient caused by centrifugal forces in a rotating fluid ring, to create a sealing of the working fluid. Basic construction of a typical seal consists of a rotating disc inside a stationary casing; one side of the disc (sealing side) is provided with a set of slots (Type-1) or vanes (Type-2) to enhance the tangential velocity of the fluid. The other side of the disk (back side) in both the configurations is exposed to high pressure liquid being sealed. Both numerical and experimental investigations of the performance of Type-1 seal (with slots) have been carried out so as to optimize the seal configuration to achieve maximum sealing capacity, with minimum power consumption. A comparison of the performance of Type-1 seal has been made with that of conventional one (Type-2) in view of economy of construction and better sealing with minimal expense of power consumption. A test rig that allows for varying the major geometrical and operating parameters was designed and tests were conducted with water as the medium. Influence of major geometric parameters like dimensions and number of slots, axial/radial clearances and major operating parameters like rotational speed, inlet pressure and sealing fluid bypass flow rate has been investigated. Apart from various pressure, temperature, flow and torque measurements, the interface between the sealing and working fluid for the experiments was captured and recorded using a high speed camera at ~26,000 frames per second. Geometrical configuration for the slots that maximizes the sealing capacity is arrived through 3D numerical simulations using commercial CFD solver ANSYS Fluent^®. A good agreement is obtained with respect to experimental results. In view of economy of construction and better sealing with minimal expense of operating power, a modified version of Type-1 seal termed as Type-3 seal is investigated. A simple 1D model for prediction of the interface radius during the seal operation, which could be used as a quick design guide, is also presented.     

Experimental investigation into the thermoelastic spring-in of curved sandwich panels

An investigation into the thermoelastic spring-in of curved sandwich panels has been conducted. Sandwich panels incorporating solid foam cores and biaxial glass–epoxy skins were manufactured and spring-in measured. The major contributors to spring-in were found to be the thermal expansion and Poisson’s ratio of the foam which were subsequently characterised. Also important was the development of resin rich regions on the surface of the panel. Experimental findings were implemented into a finite element (FE) model developed using 3-dimensional elements in ANSYS. The investigation was extended to panels including a core with machined slots. A refined FE model highlighted the influence of in-plane restraint reduction within the core, as well as the effect of a much thicker resin rich region caused by core segmentation. Results showed good agreement with experiment and provided a good basis for shape prediction of sandwich panels.     

A novel synchronous permanent magnet planar motor and its model for control applications

A novel synchronous permanent magnet planar motor (SPMPM) with iron core is proposed. It has higher continuous force compared to the coreless SPMPM. In the novel SPMPM, two sets of windings for generating x-direction thrust and y-direction thrust are perpendicularly fixed in the x-direction slots and y-direction slots of a mover core, respectively. For control system development applications, an electromagnetic model is derived and the analytical method for calculating the model parameters is also reported. The model describes an important characteristic of the novel SPMPM that the x-direction thrust and y-direction thrust are independent of each other. To verify the model and the parameter calculation method, the finite element method (FEM) is used for calculating the phase inductances and electromagnetic forces of an example SPMPM. The results from FEM are in good agreement with the results from the analytical equations. It demonstrates the feasibility and credibility of the proposed model and parameter calculation method to a certain extent.     

A Dynamic Multi-ary Query Tree Protocol for Passive RFID Anti-collision

In this paper, a dynamic multi-ary query tree (DMQT) anti-collision protocol for Radio Frequency Identification (RFID) systems is proposed for large scale passive RFID tag identification. The proposed DMQT protocol is based on an iterative process between the reader and tags which identifies the position of collision bits through map commands and dynamically encodes them to optimize slots allocation through query commands. In this way, the DMQT completely eliminates empty slots and greatly reduces collision slots, which in turn reduces the identification time and energy costs. In addition and differently to other known protocols, the DMQT does not need to estimate the number of tags, reducing the protocol implementation complexity and eliminating the uncertainty caused by the estimation algorithm. A numerical analysis shows that DMQT has better performance than other algorithms for a number of tags larger than 300. Meanwhile, when the number of tags is 2000 and the tag identity (ID) length is 128 bits, the total identification time is 2.58 s and the average energy cost for a tag identification is 1.2 mJ, which are 16.9% and 10.4% less than those of state-of-the-art algorithms, respectively. In addition, a DMQT extension based on ACK command has also been presented to deal with capture effect and avoid missing identification.

     

Improving Internationally Core Competences Based on the Capabilities of Precise and Accurate Project Management

Modern international project management has entered the phase of precise and accurate project management after the global financial crisis broke out at the beginning of the 21^st century. However, its development has faced new challenges since there has been lack of explicitly unanimous definition for the capability dimensions of precise and accurate project management, as well as the models and their process control parameters. The required core capabilities based on the precise and accurate project management for various rings are involved in the project life cycle, namely, the required internationally core competences and their components for the phases of project strategic planning and decision making in the early project phase, as well as the value engineering, and the project supervision and controls during the execution phase. Through studying the effects of the internationally core competences based on precise and accurate project management capabilities for the success and excellence of projects and configuring such models, the goal is to help the main contractors continuously obtain project success and excellence, thus improve its internationally core competences with continuous project success and excellence.     

带弧形槽成形件冲压工艺分析及模具设计

在分析了某汽车上带R24弧形槽成形件结构和工艺特点的基础上,利用Dynaform软件进行CAE模拟分析,确定了成形工艺。介绍了带R24弧形槽成形件冲压工艺方案的选择、排样设计和模具设计要点。     

Crack detection in conducting materials using SQUID magnetometry

A highly sensitive multichannel SQUID gradiometer, optimized uniquely for spatial resolution, was used to map in two dimensions the magnetic field perturbations from circular holes and thin slots in conducting plates and strips, respectively. Holes as small as 0.75 mm radius in electrically conducting plates were measured directly using a single channel. Edge slots as short as 0.5 mm long in conducting strips were detected, using a multiple-channel measurement method which eliminated the effects from the edge of the strip and the current leads. Clear magnetic signatures from these simulated cracks were measured using low current densities. Numerical computations of the theoretical field distributions are presented which confirm the experimental results. Calculations indicate that much smaller defects should be detectable with an optimization of test parameters.     

Nondestructive Measurement of Materials Using a Waveguide-Fed Series Slot Array

The reflection from an array of narrow series slots on the broad face of a rectangular waveguide is used to determine the permittivity of lossy materials. The theoretical study of the electromagnetic field in the vicinity of the slots yields a system of integral equations which takes into account the internal and external coupling between slots. The numerical solution is discussed and an optimization procedure for the array is presented, which provides a simple relationship linking the reflection coefficient to the complex permittivity over a specified range. Computed results are compared to experimental values for air and a lossy dielectric at 10 GHz, showing good agreement. Interpolation from computed data is provided by a polynomial expansion: this allows one to determine the complex permittivity once the reflection factor has been measured.     

Advanced reflector characterization with ultrasonic phased arrays in NDE applications

Ultrasonic arrays are increasingly widely used in nondestructive evaluation (NDE) due to their greater flexibility and potentially superior performance compared to conventional monolithic probes. The characterization of small defects remains a challenge for NDE and is of great importance for determining the impact of a defect on the integrity of a structure. In this paper, a technique for characterizing reflectors with subwavelength dimensions is described. This is achieved by post-processing the complete data set of time traces obtained from an ultrasonic array using two algorithms. The first algorithm is used to obtain information about reflector orientation and the second algorithm is used to distinguish between point-like reflectors that reflect uniformly in all directions and specular reflectors that have distinct orientations. Experimental results are presented using a commercial 64-element, 5-MHZ array on two aluminum test specimens that contain a number of machined slots and side-drilled holes. The results show that the orientation of 1-mm-long slots can be determined to within a few degrees and that the signals from 1-mm-long slots can be distinguished from that from a 1-mm-diameter circular hole. Techniques for quantifying both the orientation and the specularity of measured signals are presented and the effect of processing parameters on the accuracy of results is discussed.     

Estimating building dimensions from synthetic aperture radar image sequences

The problem of automatically extracting building dimensions from synthetic aperture radar (SAR) image sequences of urban scenes is considered. An algorithm based on the delineation of shadows using active contours constrained by a simple wire-frame building model has been developed and demonstrated using SAR imagery of a village on Salisbury plain. The core of the algorithm is a novel technique for target delineation involving multiple active contours evolving simultaneously. In particular, a technique referred to as multiple hypothesis delineation, in which contours can be in several states simultaneously, is developed and shown to lead to considerable improvement in convergence time and delineation accuracy when used to delineate multiple targets in close proximity. The technique is applied to the automatic estimation of building dimensions by delineation of shadows in a sequence of SAR images of an urban scene. The estimation of building dimensions is automatic; user interaction is limited identifying a building of interest and a region of background clutter close to the building. Results are presented for six different buildings, in each case two SAR images were used in the estimation process separated in illumination angle by either 28deg or 90deg. The estimates of building dimensions are compared with the actual building dimensions obtained from architectural drawings. The algorithm was found to perform robustly and provide reasonably accurate estimates of the building dimensions, typically within ~10% of the true values.