含中心裂纹铝合金厚板复合材料补片胶接结构应力强度因子有限元分析

含裂纹铝合金板经复合材料补片胶接修复后,裂纹尖端的应力强度因子(Stress Intensity Factor,简称SIF)是关注的重点。基于有限元软件ABAQUS,建立了含中心裂纹铝合金厚板复合材料补片胶接修复件的分析模型。计算了裂纹尖端的SIF,与Rose解析模型进行了对比验证,得到裂纹尖端SIF在板厚方向上的变化,以及补片在厚度方向上修补效果的变化,对比了不同修复方式的修复效果。结果表明,裂纹尖端SIF的有限元解偏保守,被修补板厚较大时,裂纹尖端SIF值在板厚方向上的差异更加显著,双面修复方式的修复效果明显优于单面修复方式。     

残余热应力对复合材料修理金属裂纹板影响分析

本文建立了复合材料胶接修理金属裂纹板的三板有限元模型;采用分析金属裂纹板裂纹尖端应力强度因子的方法,分析了残余热应力对复合材料修理金属裂纹板修理效果的影响。结果表明,残余热应力对单面修理结构的影响小于双面修理结构。残余热应力对单面修理结构的影响由于裂纹板宽度比值不同而不同。补片与母板的热膨胀系数相差越大,残余热应力对修补效果影响越大。     

复合材料补片胶接修复钢板影响参数仿真分析

在对钢结构进行胶接修复时,不同的胶接方案对修复结果有显著影响。为更好制定胶接修复方案,在ABAQUS中建立有限元模型,侧重探究补片尺寸和胶层参数对应力强度因子(SIF)和胶层应力的综合影响。分析表明,增加补片厚度和胶层剪切刚度都可以有效降低裂纹尖端应力强度因子,同时会增大胶层端部应力。增加补片厚度比增加胶层剪切刚度能得到更好的修复效果。补片厚度选在1.5 mm左右最佳,胶层剪切刚度选在5 GPa左右最佳。补片等宽修复对钢板有更好的补强效果,不建议对较厚的结构进行胶接修复。     

双向受载裂纹板的复合材料补片胶接修补

建立和验证了碳纤维/环氧复合材料补片单面胶接修补双向受载的裂纹板的3D有限元模型,探讨了补片材料、铺层顺序、补片长度及双向载荷比等对裂纹应力集中强度因子的影响规律.结果表明,单面贴补的复合材料补片能有效地降低裂纹铝板的裂纹尖端的应力强度因子,同时胶接的复合材料补片使裂纹铝板的垂直裂纹方向的载荷和平行裂纹板方向的载荷发生偶合作用,应根据裂纹铝板的不同载荷情况,选择不同的补片进行修补.     

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。     

玻纤铺层方向对玻纤/EVE复合材料性能的影响

以0°,90°,0°/90°,0°/45°/-45°/90°分别作为玻璃纤维(GF)单向铺层方式,研究了不同的铺层方式对GF/EVE(环氧乙烯基酯树脂)复合材料力学性能的影响。结果表明,0°铺层方向的复合材料在单一方向的力学性能最好,0°/45°/-45°/90°铺层方向的复合材料可以看作各向同性材料,应用范围更加广泛。     

不同对流换热条件下复合材料层合板固化温度场与热应力分析

采用有限元方法,构建了3234/T300B复合材料层合板固化过程的物理模型以及数学模型。对不同对流换热条件下层合板固化时的温度场及热应力场进行了数值模拟。分析了不同对流换热系数对层合板固化阶段的热应力以及固化后残余热应力的影响。结果表明:上表面施加的对流换热系数越大,固化过程升温阶段层合板内部的热应力越小,固化残余热应力显著减小。当施加的对流换热系数由5 W/(m~2·K)增大到10 W/(m~2·K)时,温度和热应力的下降幅度最大。研究表明通过引入对流换热条件来减小固化过程升温阶段层合板热应力以及固化残余应力是可行的,也为优化热风枪固化方法提供了参数依据。     

升降桅杆用CFRP管件铺层设计及弯曲性能研究

根据选定的升降桅杆管体结构形式、尺寸参数和材料,设计了升降桅杆用CFRP管铺层,用静力学和有限元计算相结合的方法分析了其弯曲性能;优化并确定了升降桅杆用CFRP管的铺层方案。结果表明:CFRP管的弯曲承载能力比铝合金管提高了2~4倍;通过对CFRP管材不同铺层的分析,结果显示0°/90°/±45°铺层的等价弯曲模量和最大弯曲载荷比0°/90°铺层提高约5%。     

挖补角度对复合材料修补片固化过程温度和热应力的影响

利用有限元方法,数值模拟了不同挖补角度的树脂基复合材料修补片热固化过程中的温度场和热应力场,并分析了挖补角度对修补片的温度、固化度和热应力的影响。仿真计算结果表明:挖补角度越小,修补片中心点处的温度峰值越大,固化速率越快,热应力越大;挖补角度越小,修补片非中心点处的固化速率越快,热应力越小,且挖补角度对非中心点处的热应力影响较大。综合分析后可知,在一定挖补角度范围内,合理选择挖补角度,可控制修补材料内部热应力,并获得较好的复合材料修补质量。研究结果为实际修理提供了良好的数值依据。     

铺层结构对复合材料层合板弯曲强度及失效行为的影响

通过改变偏轴角为45°和90°的[45°/–45°],[0°/90°]正交铺层组的质量分数,设计了6种复合材料层合板铺层结构。研究了两种偏轴角正交铺层组共同存在的铺层结构对真空辅助树脂传递模塑工艺复合材料层合板弯曲强度及失效行为的影响。通过弯曲实验获得6种复合材料层合板的弯曲强度、损伤特征以及应力–应变曲线。结果表明,随偏轴角为90°的[0°/90°]铺层组质量分数的增加,复合材料层合板的弯曲强度逐渐增大;两种偏轴角正交铺层组共同存在的铺层结构可引起复合材料层合板在弯曲载荷作用下的损伤模式多元化。     

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。