吸胶膜对复合材料构件固化过程中树脂流动行为的影响

热固性树脂基复合材料构件成型过程中的树脂流动行为决定了其最终成型后的纤维体积分布情况,严重影响构件的最终成型质量。而吸胶膜作为预浸料中的多余树脂流出构件后的吸收载体,其材料特性对树脂的流动过程起主导作用。以吸胶膜为关注重点,基于AS4/3501-6复合材料体系,建立了厚截面复合材料构件在热压罐中固化压实的仿真模型,模型包括了固化反应、热传导和紧密压实三个模块。模型与实验中构件的压实情况对比,验证模型的可行性。通过模型计算结果研究了吸胶膜的孔隙率、渗透率及厚度等关键参数在压力、温度等工艺条件的协同作用下对树脂流动行为的影响规律。结果表明:吸胶膜的孔隙率和厚度作为吸收树脂载体的空间度量,对构件的最终压实厚度起主要作用;吸胶膜的渗透率通过树脂流动速度影响固化压实过程,渗透率过小时,构件的压实厚度明显减小。     

基于材料物性参数时变特性的复合材料层合板固化残余应变应力数值模拟

热固性树脂基复合材料层合板成型过程形成的残余应力是影响材料质量的重要因素。针对复合材料固化过程建立了基于复合材料物性参数时变特性的复合材料固化过程的三维多场耦合计算模型。该模型包含经典的热-化学模型、树脂固化动力学模型、残余应力模型;在此基础上将材料物性参数时变特性引入多场耦合计算模型中,模型计算结果通过与文献中实验结果比较,验证所建立的固化模型的可靠性;在此基础上,对AS4/3501-6复合材料层合板的固化残余应变应力进行数值模拟,研究了固化过程中残余应变/应力的变化规律,分析工艺参数对应力应变的影响。通过与光纤光栅应变试验比较,验证其正确性。研究结果表明:模型可以很好地仿真复合材料固化过程;温度、树脂体积分数、铺层角度对层合板应力/应变都有较为显著的影响,为正相关关系,其中树脂的体积分数影响最为显著。     

VARI成型V型构件固化变形和影响因素分析

复合材料在成型过程中会伴随着复杂的热化学和物理变化,此现象会导致复合材料内部的残余应力积累并进一步使复合材料在脱模后产生固化变形。采用顺序耦合热应力的方法建立了预测复合材料固化变形的三维有限元模型,对真空辅助成型(VARI)的复合材料V型构件的固化变形进行了数值模拟和试验验证,并进一步分析了固化温度、对流换热系数、构件厚度等因素对复合材料V型构件的影响。模拟结果表明,复合材料V型构件的回弹角会随着固化温度和对流换热系数的升高而增大,随着构件的厚度增加而减小。固化温度从150℃升高至190℃,回弹角增加了72%;对流换热系数从1 W/(m2 K)升高至100 W/(m2 K),回弹角增加了15%;构件厚度从2.4 mm增加至4.8 mm,回弹角减小了43%。     

纤维增强热固性复合材料构件的固化变形研究进展

热固性复合材料的固化是一个热性能、化学性能和力学性能同时发生变化的复杂过程,也是固化变形和残余应力产生的过程。引起复合材料变形的因素主要包括构件的结构形式、树脂含量、铺层方式、基体树脂的特性、固化工艺参数及模具因素等。其中,复合材料固化过程中树脂的热收缩、化学收缩以及模具材料与复合材料间热膨胀系数的差异是引起复合材料发生固化变形的根本原因。     

热塑性复合材料制件热残余应力产生原因及测试方法分析

纤维增强热塑性复合材料以其优异的综合性能被广泛用于大型民用飞机结构,但在复合材料成型过程中基体材料需要经历较高的工艺温度和降温速率;增强纤维和聚合物基体之间因热膨胀系数不匹配、铺层间各向异性和温度的梯度分布等因素将导致在基体中形成热残余应力,这将对所得热塑性复合材料构件的力学性能产生影响,需要在复合材料结构的设计和分析中加以考虑。为有效控制和降低复合材料制件中热残余应力,需要对其产生来源及发展机理进行分析。对热塑性复合材料中热残余应力的形成原因从三个不同层次进行讨论,并分析热塑性复合材料在成型过程中残余应力水平的控制方法,最后对热残余应力的测试方法进行研究,评价了各测试方法的优缺点。     

模具构件相互作用对复合材料固化应变的影响分析

复合材料热压罐固化工艺中,构件的脱模变形是影响成型质量的重要原因。通过热电偶和光纤光栅传感器相结合的方法对复合材料构件在热压罐成型工艺过程中的温度和应变进行了在线监测,研究了模具构件的相互作用导致的应变发展,并分析了树脂固化对模具构件相互作用的影响。结果表明:固化过程初期,应变主要来自构件压实和树脂的流动、凝胶,而后模具构件的相互作用会随树脂固化度的增大而增大,模具与构件之间转变为粘接状态,降温时模具构件的相互作用会使二者发生分离导致构件发生应力释放,并且应力释放会使模具构件的相互作用减弱。     

复合材料挖补修理固化过程残余应力的三维数值模拟

基于热化学和残余应力理论,采用顺序热-力耦合方法建立了复合材料固化过程的三维有限元模型,通过与文献中C形构件计算结果的对比,验证了该仿真模型具有较高的精度。采用该模型计算了AS4/3501复合材料层合板挖补修理固化过程中模量和残余应力的变化历程。结果表明,凝胶点之前,树脂模量和复合材料横向模量很小,而平行于纤维方向存在残余压应力;凝胶点之后,模量均随时间快速增大到一定值,残余应力先逐渐增大到一定值,再随降温过程快速增大。     

复合材料整体化构件的装配破坏仿真研究

复合材料在固化过程中,由于材料各向异性、铺层非对称不均衡、构件布置不对称,温度改变和固化度的分布不均匀,导致不同程度的固化收缩,使复合材料结构件发生与预期形状不一样的固化变形。复合材料层合构件发生固化变形后,在装配过程中须进行校正。对固化变形的校正会增大整个构件的应力水平。特别在装配点附近的构件连接处,会产生较大的装配应力,对整体构件产生很不利的影响。本文研究固化变形校正装配的过程,并建立一套考虑固化变形校正装配破坏的分析方法。研究了复合材料固化变形的机理,并介绍了复合材料分层仿真的界面元方法。基于以上研究,在复合材料层合结构分析软件ADGS中,建立了一套较完整的复合材料整体化构件的装配破坏仿真分析模型。     

树脂基碳纤维卷铺管件热残余应力分析

对树脂基碳纤维卷铺管在高温固化后冷却至室温过程中进行了热应变实验,基于实体单元的分层属性建立了多种铺层复合材料管件的热残余应力数值模型,数值计算结果与实验结果吻合较好。在该数值模型基础上,从纤维方向应力的角度分析了铺层角度、环向层纤维含量、环向层铺设位置以及径厚比对卷铺管件热残余应力的影响。结果表明,上述诸因素均对残余应力有较大的影响,(±φ)_n铺层和90°/0°正交组合铺层中的0°纤维在纤维方向上残余应力均为轴向受压、环向受拉,该应力状态可能导致管件出现微裂缝等初始缺陷。     

不同降温速率条件下复合材料修补片固化温度场和热应力分析

通过采用有限元分析方法,构建了复合材料修补片热固化过程的数学模型和物理模型,数值模拟了树脂基复合材料修补片相同挖补修理方式不同降温速率下的固化温度场和热应力场,并分析了降温速率对修补片固化温度和固化残余热应力的影响。仿真计算结果表明:降温速率越快,修补片内的温度梯度越大,固化残余热应力越大。从中获取了一些减小固化残余热应力优化复合材料固化成型工艺的有帮助的结果。     

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.     

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.     

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.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.     

2007～2008年世界塑料工业进展

收集了2007年7月～2008年6月世界塑料工业的相关资料,介绍了2007～2008年国外塑料工业的发展情况,提供了世界塑料产量、消费量及全球各类树脂的需求量及产能情况.按通用热塑性树脂(聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂)、工程塑料(尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚)、特种工程塑料(聚苯·硫醚、液晶聚合物、聚醚醚酮)、通用热固性树脂(酚醛、聚氨酯、不饱和聚酯树脂、环氧树脂)不同品种的顺序,对树脂的产量、消费量、供需状况及合成工艺、产品应用开发、树脂品种的延伸及应用的进一步扩展等技术作了详细介绍.     

2005～2006年国外塑料工业进展

收集了2005年7月～2006年6月国外塑料工业的相关资料,介绍了2005—2006年国外塑料工业的发展情况。提供了世界塑料产量、消费量及全球各类树脂生产量以及各国塑料制品的进出口情况。作为对比,介绍了中国塑料的生产情况。按通用热塑性树脂（聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂）、工程塑料（聚酰胺、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚）、通用热固性树脂（酚醛、聚氨酯、不饱和树脂、环氧树脂）、特种工程塑料（聚苯硫醚、液晶聚合物、聚醚醚酮）的品种顺序,对树脂的产量、消费量、供需状况及合成工艺、产品开发、树脂品种的延伸及应用的扩展作了详细的介绍。