复合材料层合板沉头多钉连接钉载分配研究

沉头螺栓连接因具有改善钉载分配不均匀性,保持结构表面光滑等优点,在飞行器复合材料表面结构连接中得到了广泛应用。但是国内外对于沉头连接钉载分配却少有研究,通过ABAQUS软件建立复合材料层合板与金属沉头螺栓多钉连接三维有限元模型,计算沉头连接的钉载分配情况。对比凸头连接的载荷分配结果发现:沉头连接对钉载分配有一定的改善作用,且金属板厚度的改变对沉头螺栓载荷分配影响很小。     

间隙补偿对单螺栓连接层合板轴向刚度的影响研究

在螺栓连接装配过程中,被连接件的轴向刚度会直接影响夹紧力的形成,以及不同工况下夹紧力的保持与衰退,对装配结构的可靠性与稳定性影响显著。由于受复合材料层合板本身的材料性质和成型工艺方法的限制,在层合板构件螺栓连接中,较小的装配间隙难以避免,飞机装配中一般采用液体垫片对层合板构件之间较小的装配间隙进行补偿。首先,以复合材料层合板单螺栓连接为研究对象,考虑强迫装配(未实施间隙补偿工艺)与采用液体垫片实施间隙补偿两种情况,利用ABAQUS建立有限元模型;其次,设计了层合板单螺栓连接结合面有效接触尺寸测量实验,有限元模型计算结果与实验测量数据的吻合度较好;最后,根据建立的模型,研究了间隙补偿及不同液体垫片参数下,层合板轴向刚度的变化。有限元分析结果表明:相对于强迫装配,随着间隙的增大,液体垫片会愈加显著地提高层合板的轴向刚度;在工艺规范的使用厚度范围内,垫片厚度的增加对层合板轴向刚度的提高具有更加明显的促进作用,同时,使用高弹性模量的液体垫片更有益于提高层合板的轴向刚度;建议0.05 mm及以上的装配间隙必须实施间隙补偿工艺。     

T800碳纤维复合材料多钉连接层压板钉载分布及有限元计算

通过对T800碳纤维预浸料复合材料层压板多钉连接试验件进行轴向拉伸测试,测得了整个试验件的载荷-位移曲线和每一个钉孔附近的应变-载荷曲线。试验结果表明,首末两排钉承担载荷最大,中间排钉载荷最小;试件的破坏都是发生在第一排钉附近;破坏模式主要为钉孔挤压和层压板拉伸破坏;建立了相应的有限元模型,模拟结果和试验结果的一致说明了有限元模型的合理性。     

复合材料单搭多钉连接钉载分配研究

为了研究多钉连接载荷分配,设计了复合材料4钉单搭连接拉伸试验件,测量了试验件拉伸过程中的应变分布,并计算出各钉的承载。结果表明,单搭接连接件由于次弯曲影响很难准确测量出载荷分布;4钉承载比例不均匀,中间两钉承载较小,外侧两钉承载较大。     

T800碳纤维复合材料混合连接层合板钉载分布及有限元计算

采用自动铺带工艺制得混合连接的T800碳纤维复合材料层压板试验件,通过轴向拉伸测试,测得了整个试验件的载荷-位移曲线和每一个钉孔附近的应变-载荷曲线。试验结果表明,首末两排钉承担载荷最大,中间排钉载最小。模量相对较大的胶层阻止了钉载的有效传递,破坏模式主要为钉孔挤压和层合板拉伸破坏。建立了相应的有限元模型,模拟结果和试验结果的一致说明了有限元模型的合理性。     

柱式平板硫化机螺纹防松设计新探

针对立柱式平板硫化机立柱处连接螺母易松动、连接不可靠,经常会造成硫化机平板之间不平行,影响硫化产品质量的现象,提出了一种既能实现任意位置可靠防松,同时又具备良好可拆性能的螺纹连接方式。连接依据棘轮运动原理,在连接件螺母、垫片的结合面处设计了棘形沟槽,沟槽呈周向均布,轴向呈三角形锥体状,其组合能够保证螺纹正向旋转时连接件能相对运动从而实现连接,反向旋转时连接件能牢固自锁从而实现防松。拆卸时可通过机械翘起棘式垫片的边翼,解除垫片与被连接件的周向固定,实现可拆性要求。     

格栅剪力键的FRP板与混凝土粘结性能试验研究

针对不同界面连接形式的FRP板与混凝土进行单剪试验,重点研究破坏形式、极限承载力及破坏机理等内容,研究表明:布置单向剪力连接件时,增加连接件数量、减小连接件间距可以提高界面抗剪承载力,也可改善构件弹性阶段整体刚度;提出的双向格栅剪力连接件可明显提高界面整体抗剪承载力,并可增强弹性阶段构件整体刚度。     

附加载荷作用下螺栓法兰连接的强度和紧密性分析

运用三维有限元方法模拟了垫片的非线性特性,分析了附加载荷对螺栓法兰连接结构的强度和紧密性的影响,确定了连接系统的紧密性、附加载荷和垫片残余压紧应力三者之间的关系。分析结果表明,附加弯矩对螺栓法兰连接结构的紧密性有较大影响。     

飞机中央翼上壁板斜切单接头复合材料长桁端头压缩性能研究

为研究飞机中央翼上壁板斜切单接头复合材料长桁端头的压缩性能,制作了中央翼斜切单接头长桁端头试验件,通过对试验件进行轴向压缩测试,建立了中央翼上壁板斜切单接头复合材料长桁端头区域的有限元模型,进行了试验前有限元分析计算,通过试验测得了整个试验件的载荷-应变曲线。试验结果表明,试验件发生非线性变形,然后随着载荷的增加,连接肋缘条、蒙皮、长桁的螺栓被剪断,紧固件连接失效,试验件被破坏。长桁蒙皮区域最大的应变出现在肋缘条和蒙皮连接的第一排钉附近,同时试验测得破坏载荷与有限元计算的结果总体一致,证明了有限元模型的合理性。     

HG“钢制管法兰、垫片、紧固件”标准介绍(下)

3.9 管法兰配套垫片标准 管法兰连接的主要失效形式是泄漏。泄漏与密封结构型式、被连接件的刚性、密封件的性能、操作和安装等许多因素有关。垫片作为法兰连接的主要元件,对密封起着重要作用。所以在修订钢制管法兰标准的同时,也相应地修订了与管法兰配套的垫片标准。     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Many Drugs of Abuse May Be Acutely Transformed to Dopamine,Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.