Parametric study on design of composite–foam–resin concrete sandwich structures for precision machine tool structures

In this paper, sandwich structures for micro-EDM machines are optimized by using parametric study varying composite geometries and parameters like stacking sequence, thickness and rib geometry. The structures are composed of fibre reinforced composites for skin material and resin concrete and PVC foam (Closed cell, Divinycell) for core materials. Column structure was designed by a beam with cruciform rib and performance indices such as static bending stiffness (EI) and specific bending stiffness (EI/ρ) for dynamic stability are examined by controlling the thickness and stacking sequence of composites. For the machine tool bed, which usually has a plate shape, was designed to have high stiffness in two directions at the same time controlling stacking sequence and rib geometry; that is, rib thickness and number of ribs. The sensitivity of design parameters like rib thickness and composite skin thickness was examined and the optimal condition for high stiffness structure was suggested. Finite element analysis was also performed to verify the static and dynamic robustness of the machine structure. L-shaped joint for combining bed and column of the micro-EDM machine was proposed and fabricated using adhesive bonding. The dynamic performance such as damping characteristics was investigated by vibration tests. From the results optimal configuration and materials for high precision micro-EDM machines are proposed.     

In-plane directional mechanical properties of carbon fabric skins in sandwich structures after thermoforming

In this paper, a representative unit volume finite element (RUV FE) model was employed to simulate thermoforming process of carbon fabric-polymeric foam sandwich structures. Thermoforming simulations, which capture crimp angles and amplitude changes of carbon fabric with respect to different operational pressure, were conducted with the help of RUV FE model. Micro-deformation of tow structures after thermoforming was rigorously reflected in the second stage FE model to determine the in-plane directional stiffness of skin parts. Tensile tests were carried out to investigate mechanical properties of skin parts in sandwich structures for the potential usage of automotives, electronic housings or the satellite structure design.     

中国环流器HL和欧洲联合环JET的检漏技术进展

对HL环流器系列装置,开发了蒽-丙酮荧光液渗透检漏用于真空内衬的零部件检漏,灵敏度可以达到10-9Pa.m 3.s-1,示漏位置分辨小于0.5mm;对大容器真空检漏,采用四极质谱计和氦质谱检漏仪相配合的检漏法;对压力容器检漏,开发了真空罩吸枪-氦质谱检漏系统,还研制了适于抽除大量水汽的检漏真空机组。对氘氚放电的JET,使用普通的氦质谱检漏仪(扇形磁体型)受到真空室壁释放所吸留的氢同位素的、尤其是氘的严重干扰,因为示漏气体氦(4H e,4.0026u)与氘(D2,4.0282u)的质量数十分相近。在氦质谱检漏仪入口处串接选择性抽气泵——用液氮冷阱来抽除可凝气体、用分子筛泵或10K低温泵来抑制氢同位素本底,并前置一个涡轮分子泵来压缩加强采样气流等。这种加强组合能使原先的氦质谱检漏系统灵敏度提高3个量级以上。     

金属氚化物中3He的热解吸方法

在自行设计的全金属高真空热解吸系统上,以ELITE SPE-50型四极质谱计(QMS)为分析器,建立了金属氚化物中3He的热解吸和数据处理方法.解吸过程中,金属系统处于真空密闭状态,薄膜压力计直接测量解吸出的气体压力,质谱计则通过微量渗漏阀在线取样测量,所采集的数据均为积分形式.研究结果表明四极质谱计标定解吸系统内4He的分压＜350 Pa时,其相关系数R＞0.99,且记忆效应的贡献极弱;离子态氚T+对m/e=3组分分压的贡献可按IT+≈0.01 IT2+确定,不干扰3He的测定;将气体解吸所得的积分数据经平滑并微分处理后可准确得到气体释放速率与退火温度的关系,即热解吸谱.     

全氘甲烷大气示踪剂测量技术

文章通过系统研究甲烷中痕量全氘甲烷的分析方法、分析条件和检测能力等,证明了脉冲进样四极质谱(QMS)法用于大气扩散实验中全氘甲烷的浓度测量是可行的。同时研究建立了痕量全氘甲烷脉冲进样QMS测量技术。在50 mL/min He流洗、分流比1∶100、电子倍增器检测、慢扫描和SIM模式测量条件下,对甲烷中CD4的最小检测量(体积分数)为5.1×10-9。结合天然甲烷与全氘甲烷同位素分离技术,对甲烷中CD4的最小检测量可达到5×10-10,对空气中CD4的探测下限约为8.5×10-15。研究表明:气相色谱-四极质谱(GC-QMS)法对CD4的探测下限约是脉冲进样QMS法的40倍。     

Low velocity impact of combination Kevlar/carbon fiber sandwich composites

Impact, compression after impact, and tensile stiffness properties of carbon fiber and Kevlar combination sandwich composites were investigated in this study. The different samples consisted of impact-side facesheets having different combinations of carbon fiber/Kevlar and carbon fiber/hybrid. The bottom facesheets remained entirely carbon fiber to maintain the high overall flexural stiffness of the sandwich composite. The focus of this research was to determine if any improvement in impact properties existed as a result of replacing the impact-side facesheet layers of carbon fiber with Kevlar or hybrid. Impact tests were conducted on different sample types to obtain information about absorbed energy and maximum impact force. Also, compression after impact tests were conducted to determine the reduction in compressive strength when comparing impacted to non-impacted samples. The elastic moduli of carbon fiber, Kevlar, and hybrid were determined from tensile testing. This data was used to characterize the reduction in stiffness from replacing carbon fiber layers with the Kevlar or hybrid layers. The experimental data in its entirety helps define the benefits and disadvantages of replacing carbon fiber layers with Kevlar or hybrid.     

Thermal buckling of cross-ply laminated composite and sandwich plates according to a global higher-order deformation theory

A two-dimensional global higher-order deformation theory is presented for thermal buckling of cross-ply laminated composite and sandwich plates. By using the method of power series expansion of continuous displacement components, a set of fundamental governing equations which can take into account the effects of both transverse shear and normal stresses is derived through the principle of virtual work. Several sets of truncated Mth-order approximate theories are applied to solve the eigenvalue problems of a simply supported multilayered plate. Modal transverse shear and normal stresses can be calculated by integrating the three-dimensional equations of equilibrium in the thickness direction, and satisfying the continuity conditions at the interface between layers and stress boundary conditions at the external surfaces. Numerical results are compared with those of the published three-dimensional layerwise theory in which both in-plane and normal displacements are assumed to be C⁰ continuous in the continuity conditions at the interface between layers. Effects of the difference of displacement continuity conditions between the three-dimensional layerwise theory and the global higher-order theory are clarified in thermal buckling problems of multilayered composite plates.     

基于屏栅电离室的双参数谱仪研制及其应用

以屏栅电离室为基础，同时引出其阳级和阴极信号，研制了1台能够同时记录两路信号的双参数谱仪，在DEC－3000工作站上编制程序，实现了双维谱数据的获取、显示和存储。利用所建立的谱仪，测量了α放射源的双维谱，计算了α粒子的角分布，并讨论了如何利用角分布来校正活度测量中自吸收和反散射的影响以及改善电离室阳极能谱的能量分辨率。     

TOF电子能谱仪抛物面电子反射镜参数计算

针对TOF电子能谱仪抛物面电子反射镜的参数问题，依据电磁理论和Reflect-Grid模型，通过合理的近似和简化，对抛物面电子反射镜的电场分布和电子收集效率进行了理论计算，对电子在其中的飞行轨迹进行了模拟。结果表明，抛物网有无置电压对电子的收集效率有很大影响，当偏置电压为700V时，电子收集效率比无偏置电压时高60-80倍，理论计算为100倍，二者基本相符，为装置的改造和使用提供了理论指导。     

A note on finding all homogeneous set sandwiches

A module is a set of vertices H of a graph G=(V,E) such that each vertex of V?H is either adjacent to all vertices of H or to none of them. A homogeneous set is a nontrivial module. A graph G_s=(V,E_s) is a sandwich for a pair of graphs G_t=(V,E_t) and G=(V,E) if E_t⊆E_s⊆E. In a recent paper, Tang et al. [Inform. Process. Lett. 77 (2001) 17-22] described an O(Δn²) algorithm for testing the existence of a homogeneous set in sandwich graphs of G_t=(V,E_t) and G=(V,E) and then extended it to an enumerative algorithm computing all these possible homogeneous sets. In this paper, we invalidate this latter algorithm by proving there are possibly exponentially many such sets, even if we restrict our attention to strong modules. We then give a correct characterization of a homogeneous set of a sandwich graph.