含分层损伤的复合材料层压板后屈曲及低周疲劳分层扩展有限元模拟研究

基于Abaqus软件建立3D层压板有限元模型,采用虚拟裂纹扩展技术(Virtual Crack Closure Technology,简称"VCCT")模拟分层界面。为接近真实物理模型,引入几何扰动。以含圆形分层区的层压板为研究对象,进行非线性后屈曲分层模拟。根据后屈曲分层扩展分析结果,以Paris模拟疲劳分层的萌生及扩展,研究复合材料低周疲劳特性。     

埋置元件复合材料层合板的分层损伤

通过对含与不含薄膜埋置元件复合材料层合板的拉伸和层间韧性的力学性能表征,探讨影响埋置元件结构完整性的一些关键因素。利用ABAQUS有限元软件,基于断裂力学用以研究裂纹扩展问题的虚拟裂纹闭合技术(VCCT),建立了在拉伸荷载作用下层合板分层起裂和扩展过程的数值模拟方法。在模拟分析中,考虑了裂纹萌生位置对分层扩展规律及结构强度的影响,并与实验结果比较,验证了本方法的合理性和有效性。     

交变载荷作用下纤维增强密封复合材料界面脱黏研究

界面脱黏是纤维增强密封复合材料界面破坏的主要表现形式,其可视为一种特殊的裂纹扩展。本文基于剪滞模型研究了纤维增强密封复合材料中纤维和基体界面在交变载荷作用下的裂纹扩展规律。在考虑疲劳加载引起的脱黏界面损伤和损伤分布不均匀性以及材料泊松比影响的基础上,建立了等效Paris公式,得到了疲劳裂纹扩展长度、扩展速率、界面上摩擦系数和加载次数之间的关系。     

ABS/GF疲劳裂纹扩展的研究

通过对(丙烯腈/丁二烯/苯乙烯)共聚物(ABS)/玻璃纤维(GF)复合材料疲劳裂纹扩展速度研究,得到ABS/GF复合材料在不同应力和振动频率下疲劳性能随GF填充量变化的趋势.结果表明,高频(0.85 Hz)低应力(0.8 kN)条件下,GF对裂纹的扩展具有阻滞作用,其中GF质量分数为20%时ABS/GF复合材料疲劳性能最好;低频(0.25 Hz)高应力(1.6 kN)条件下,试样疲劳性能最差,疲劳周次均在2000次以下,加入GF有利于裂纹的扩展.     

应力氧化环境中3D C_f/SiC复合材料损伤演变

以裂纹的产生和扩展为线索,通过扫描电镜研究了疲劳氧化环境中3DCf/SiC复合材料损伤演变特征。结果表明:应力氧化环境中3DCf/SiC复合材料的损伤形式主要为:基体开裂,界面相脱粘和氧化以及纤维的氧化与断裂。基体开裂为氧化性气体与复合材料内部的界面相和纤维反应提供通道。界面相脱粘和氧化导致纤维伸长量增加,促使裂纹扩展。纤维氧化断裂和裂纹张开扩展相互促进,形成了裂纹扩展的动力。     

复合材料Ⅱ型分层损伤演化声发射监测

通过风电叶片复合材料Ⅱ型分层扩展力学性能实验,并借助声发射技术手段,研究复合材料[0/0]、[0/45]和[+45/-45]层间界面损伤演化特性。复合材料试件弯曲加载时,采用声发射实时监测整个分层损伤过程。结果表明,[0/0]复合材料分层试件裂纹扩展快、分层面积大、前沿平齐,不稳定扩展对应较多高幅值、长持续时间的声发射信号;受±45°方向纤维作用,[0/45]和[+45/-45]复合材料试件不稳定分层扩展前声发射撞击累积数较高,裂纹扩展相对缓慢,分层面积小,前沿不齐。复合材料分层损伤演化可分为预分层裂纹尖端区域微损伤累积和分层不稳定扩展两个基本的过程。     

2.25Cr-1Mo复杂应力状态下低周疲劳寿命预测

通过对无预裂纹圆柱形缺口试件的常温、高温低周疲劳总寿命试验以及对带有预裂纹圆柱形缺口试件的常温、高温裂纹扩展寿命试验,并利用ＮＨＲＤＳ有限元程序进行了缺口附近轴对称问题的循环应力和应变计算,研究了非均匀分布复杂应力状态下低周疲劳寿命。结果表明,２ ．２５Ｃｒ １Ｍｏ 材料复杂应力状态下低周疲劳总寿命和裂纹扩展寿命可采用当量形式的Ｍａｎｓｏｎ Ｃｏｆｆｉｎ 公式进行表征。     

B_4C/2009Al复合材料的高周疲劳性能研究

本研究采用体积分数为17%的碳化硼颗粒(B_4C)增强2009Al复合材料,然后进行热挤压加工(挤压比为90∶1)。对复合材料室温下高周疲劳性能进行了测试,同时通过分析疲劳断口、观察微观结构深入研究其失效机理。在拉-压循环载荷条件下测试了B_4C/2009 Al复合材料的高周疲劳性能。B_4C/2009 Al复合材料的疲劳破坏机制为:微裂纹主要萌生于试样表面划痕和B_4C与Al之间界面的脱粘;微裂纹萌生后首先在基体中扩展,当微裂纹遇到B_4C颗粒时,裂纹发生偏折或者停止;随着微裂纹继续扩展,裂纹尖端塑性区变大,B_4C颗粒断裂和B_4C与基体界面的脱粘增多;最后,微裂纹不断扩展聚集造成了B_4C/2009 Al复合材料最终断裂。     

复合材料气瓶漏点定位分析研究

某复合材料气瓶在疲劳试验中远低于平均疲劳寿命时即发生漏水,通过对复合材料气瓶整体损伤研究、异常区泄漏判定研究及微观分析,定位了漏水部位并对低疲劳寿命原因进行了分析.结果表明:内衬在制造过程中产生的微小凹坑缺陷是导致复合材料气瓶低疲劳寿命的原因,在疲劳试验中,凹坑缺陷作为疲劳裂纹源,产生应力集中,引发裂纹扩展,最终形成穿透性裂纹,导致复合材料气瓶提前泄漏.     

含裂纹金属板复合材料胶接修补结构残余热应力分析

残余热应力会增大裂纹尖端的应力强度因子SIF,加快疲劳裂纹扩展速率,缩短修补结构的疲劳寿命。利用三维有限元方法,对含裂纹金属板复合材料胶接修补结构中的残余热应力进行了分析,利用虚拟裂纹闭合技术(VCCT)计算了修复结构裂纹尖端的SIF。并以SIF为判据,讨论了补片铺层方向、固化温度、胶层的材料参数对修复结构残余热应力的影响。结果表明,[0°/45°/-45°/90°]s的铺层方式可有效降低残余热应力引起的SIF;残余热应力引起的SIF随着固化温度的升高而线性增加;胶层的材料参数及胶层厚度对残余热应力引起的SIF影响不显著。     

Sapindaceae,cyanolipids, and bugs

Scentless plant bugs (Heteroptera: Rhopalidae) are so named because adults of the Serinethinae have vestigial metathoracic scent glands. Serinethines are seed predators of Sapindales, especially Sapindaceae that produce toxic cyanolipids. In two serinethine species whose ranges extend into the southern United States,Jadera haematoloma andJ. sanguinolenta, sequestration of host cyanolipids as glucosides renders these gregarious, aposematic insects unpalatable to a variety of predators. The blood glucoside profile and cyanogenesis ofJadera varies depending on the cyanolipid chemistry of hosts, and adults and larvae fed golden rain tree seeds (Koelreuteria paniculata) excrete the volatile lactone, 4-methyl-2(5H)-furanone, to which they are attracted.Jadera fed balloon vine seeds (Cardiospermum spp.) do not excrete the attractive lactone. Loss of the usual heteropteran defensive glands in serinethines may have coevolved with host specificity on toxic plants, and the orientation ofJadera to a volatile excretory product could be an adaptive response to save time.Mention of a commercial product does not consititute an endorsement by the USDA.     

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.     

2008～2009年世界塑料工业进展

收集了2008年7月～2009年6月世界塑料工业的相关资料,介绍了2008～2009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、环氧树脂、不饱和聚酯树脂)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。     

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.