疲劳荷载与环境因素耦合作用下混凝土损伤劣化研究进展

建筑物真实的服役状态是承受的荷载与环境的同时作用.概述了目前关于混凝土在疲劳荷载与环境因素耦合作用下的损伤劣化规律的研究.从材料、结构角度对疲劳荷载和腐蚀介质的耦合作用进行了总结与分析.重点论述了严寒地区桥梁、高速铁路等在疲劳荷载和冻融循环耦合作用下的损伤劣化特征.阐述了目前广泛采用的间接耦合作用方式--交替作用存在的问题,并提出从与材料细观结构密切相关的内应力角度,同时结合疲劳效应解决这一问题的可能办法.     

受疲劳荷载作用后的预应力混凝土构件冻融循环试验与损伤模型

对8根预应力混凝土梁进行受不同疲劳荷载后的冻融循环试验,研究疲劳荷载作用后预应力混凝土结构的冻融损伤特性。试验结果表明:荷载循环对预应力混凝土冻融损伤的发展有明显影响。运用损伤理论,对混凝土冻融损伤的疲劳效应问题进行了分析,并结合Aas-Jakobsen的混凝土材料疲劳寿命公式,引入疲劳效应影响因子(f(m)),建立了基于相对动弹模量的冻融损伤演化模型。结果表明:该损伤模型具有较高的精度,与试验结果吻合较好,适合工程应用。     

循环荷载对煤矸石混凝土损伤试验研究

为了研究煤矸石混凝土在疲劳荷载作用下的损伤特性,制作了煤矸石质量取代率分别为0、20％、40％、60％、80％、100％的混凝土试件,循环荷载取0.3fc0和0.5fc0,分别在循环加载2500次、5000次、7500次、10000次后测试其抗压强度和相对动弹性模量.结果表明:不同质量取代率的煤矸石混凝土在循环加载次数较少时,可致密内部结构,抗压强度不但无损而且性能还有所提升,煤矸石的质量取代率越高,混凝土抗压强度越小,达到最大值所需的循环次数越少,循环10000次煤矸石质量取代率40％的混凝土抗压强度开始出现损伤,且疲劳荷载越大,损伤越大;不同质量取代率的煤矸石混凝土在循环加载初期相对动弹性模量下降较快,后期逐渐趋于稳定,疲劳荷载越大,煤矸石质量取代率越高,损伤越严重,加速了结构内部微裂隙的扩展以及新孔隙的产生.     

碱溶液疲劳耦合作用下BFRP布加固损伤钢筋混凝土梁抗弯试验研究

基于桥梁结构所处环境的复杂性及所承受荷载的特殊性,试图探索碱溶液环境和疲劳荷载耦合作用下BFRP布加固既有损伤混凝土性能,开展了粘贴二层玄武岩纤维布加固,pH值分别为7、9、10的溶液环境和等幅疲劳耦合作用下损伤RC梁的抗弯试验研究。试验结果表明,即使在碱溶液环境和疲劳荷载耦合作用下,BFRP布仍能提高损伤RC梁极限承载力和抗弯刚度;相同疲劳次数下,在pH=9的溶液环境中,作用90d的加固梁比作用60d的加固梁挠度增加了23.13%;其他参数相同情况下,pH=7、pH=10的试验梁较未经环境作用试验梁抗弯强度分别降低10.06%、21.15%,可见,随着碱溶液浓度的增加、作用时间的延长,RC梁极限承载力、抗弯刚度、抗疲劳等性能显著下降;最后以试验梁挠度变化作为疲劳损伤指标,拟合出了考虑pH值、疲劳次数混凝土加固梁变形模量表达式。     

拉压循环荷载作用下预裂纹混凝土疲劳性能研究

利用电液伺服材料试验机,对带有预裂纹的粗骨料混凝土进行疲劳试验,分析混凝土在拉压循环试验荷载作用下的疲劳寿命、疲劳强度以及预裂纹对混凝土拉压疲劳性能的影响。根据试验数据,进行回归处理,得出混凝土的疲劳寿命S-N曲线以及S-lgN曲线,并利用有限元仿真技术,对混凝土在疲劳荷载作用下的疲劳寿命的结果做详细的研究。结果表明,带预裂纹的混凝土疲劳极限值远低于无损伤的混凝土的疲劳极限值,预裂纹使混凝土的疲劳寿命大大地降低,使其疲劳寿命缩短了75%~80%左右。     

基于混凝土基体和界面过渡区性质的疲劳方程

根据混凝土材料在静态荷载与疲劳荷载作用下破坏的相似性,结合其在静态荷载作用下的破坏分析了疲劳破坏过程,通过引入基体和界面过渡区对疲劳性能的影响因子f1,f2,定义基体性质特征参数I和界面过渡区性质特征参数M,应用数学模型描述f1,f2随疲劳寿命对数值lgN的变化趋势,建立混凝土材料基体、界面过渡区性质与疲劳性能之间的定量关系,并得到基于基体与界面过渡区性质的疲劳方程.测试了水胶比为0.35,不同矿物掺合料掺量混凝土在不同应力水平下的疲劳寿命.应用所建立的疲劳方程能较好地拟合S-N关系,尤其是大矿物掺合料掺量的情况下,反映了低周疲劳向高周疲劳过渡的非线性变化.     

单轴荷载作用下钢纤维混凝土疲劳性能研究

利用多轴子结构万能疲劳试验机,进行钢纤维混凝土的疲劳试验研究,得到钢纤维混凝土在拉压循环试验荷载作用下的受力状况、破坏形式以及变形等力学性能参数。依据设计试验得到的数据,拟合作出试验试件的疲劳寿命曲线,以及钢纤维混凝土在疲劳荷载作用下,变形随加载周期的变化规律。结果表明,钢纤维混凝土的疲劳性能明显高于普通混凝土,其疲劳强度较普通混凝土提高40%左右。     

长期持续荷载下废弃纤维再生混凝土徐变破坏规律研究

采用NM-4A非金属超声检测仪测定技术研究了不同设计变量下废弃纤维再生混凝土在长期荷载下的徐变损伤规律.通过测定穿过混凝土的超声波速,计算出损伤变量,从而求出弹性模量,直观对比出不同设计变量下废弃纤维再生混凝土在长期高荷载作用下的损伤情况.结果表明:在长期持续荷载作用下,损伤变量会随着再生骨料取代率的增大而增大,添加废弃纤维可以增强混凝土承受损伤的能力.     

动态疲劳荷载下玄武岩纤维混凝土抗渗性衰减及机理研究

为了探究动态疲劳荷载作用下玄武岩纤维混凝土抗渗性衰减规律及机理,基于抗渗性优选了玄武岩纤维最佳参数;利用自主研发的加载装置设计了疲劳试验,分析疲劳荷载下电通量的变化规律;研究了荷载作用下微观结构的演化以揭示玄武岩纤维混凝土抗渗性衰减机理。结果表明:混凝土抗渗性随玄武岩纤维长度和掺量增加呈现先增强后减弱的变化规律,基于抗渗性推荐玄武岩纤维的最佳长度为12 mm,掺量为0.08%(质量分数);随疲劳作用次数和应力比增加,玄武岩纤维混凝土电通量增加幅度低于基准混凝土,其更适合在重载、重交通地区应用;玄武岩纤维细化了混凝土孔结构,无害孔比例增加18.51%,疲劳荷载下混凝土孔径呈扩张趋势,孔分布呈粗化状态;疲劳加载前期混凝土微裂缝主要沿长度方向延伸,而加载后期以宽度扩展为主;玄武岩纤维延缓了混凝土孔结构劣化和微裂缝扩展,从而降低了抗渗性衰减幅度。     

疲劳荷载与氯盐耦合作用下氯离子在砂浆中的传输模型

从实验和理论角度系统研究了在动态荷载作用下,氯离子在砂浆中的传输性能.通过疲劳荷载与氯离子传输的同步实验,并采用已有损伤传输模型对实验数据进行分析.结果表明:已有的含损伤的传输模型中损伤为“静态”而非“动态”,已不再适用目前的实验工况;给出了适合于研究疲劳与氯离子传输同步进行的传输模型,此模型的预测结果与实验结果吻合很好.     

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.     

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。     

Inorganic/organic nanocomposite coatings: The next step in coating performance

Inorganic/organic hybrid materials have considerable promise and are beginning to become a major area of research for many coating usages, including abrasion and corrosion resistance. Our primary approach is to prepare the inorganic phase in situ within the film formation process of the organic phase. The inorganic phase is introduced via sol-gel chemistry into a thermosetting organic phase. By this method, the size, periodicity, spatial positioning, and density of the inorganic phase can be controlled. An important aspect of the inorganic/organic hybrid materials is the coupling agent. The initial task of the coupling agent is to provide uniform mixing of the oligomeric organic phase with the sol-gel precursors, which are otherwise immiscible. UV-curable inorganic/organic hybrid systems have the advantages of a rapid cure and the ability to be used on heat sensitive substrates such as molded plastics. Also, it is possible to have better control of the growth of the inorganic phase using UV curing. It is our ultimate goal to completely separate the curing of inorganic and organic phases to gain complete control over the morphology, and hence optimization of “all” the coating properties. Thus far, it has been found that concomitant UV curing of the inorganic and organic phases using titanium sol-gel precursors afforded nanocomposite coatings which completely block the substrate from UV light while maintaining a transparent to visible light. Also, it has been found that the morphology of the inorganic phase is highly dependent on the concentration and reactivity of the coupling agent. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.