不同应力路径循环加卸载下大理岩变形特性试验研究

对粉色大理岩进行常规三轴加载试验和循环三轴加卸载试验,分析了不同应力路径下岩石破坏应力-应变关系,研究了循环加卸载条件下大理岩动弹性模量演化规律。研究表明：不同应力路径下塑性屈服段应力-应变曲线差异较大,围压越大差异越明显;循环加卸载路径下的峰值强度较常规三轴路径下峰值强度减小,滞回环面积与形状随围压增加而增大;循环加卸载下动弹性模量波动式缓慢增长,恒围压路径下的动弹性模量较卸围压路径下的大。     

粘性土应力路径试验

利用GDS多功能三轴仪,对南京河西地区原状粘性土进行了常规三轴压缩、减压三轴压缩和等p应力路径的固结不排水三轴试验,探讨不同应力路径下粘性土的变形和强度特性。实验表明:不同应力路径下土的应力应变关系都呈曲线形态相似的非线性应变硬化型,而土的峰值强度和土中孔隙水压力差异明显;相同应力路径试验得到的有效应力路径形态一致,常规三轴压缩试验中有效应力路径呈S形。     

加卸载应力路径对砂岩能量演化机制的影响

为了明确应力路径对砂岩能量演化的影响,采用RMT岩石力学试验系统开展了砂岩三轴和不同卸围压速率试验,详细分析了不同应力路径下砂岩破坏过程中吸收总能量、弹性应变能和耗散能的演化规律.结果 表明,加载和卸围压应力路径下,砂岩屈服前吸收的总能量基本都以弹性应变能的形式存储,弹性应变能的增速与吸收总能量的增速保持一致,并逐渐增大.弹性应变能在单轴时经历较短的慢速增加阶段;三轴时随着围压的增大,慢速增加阶段越加显著,且在后期其增速很小;卸围压阶段弹性应变能基本保持不变.砂岩单轴耗散能出现较早表明内部损伤发展较早;三轴屈服阶段后期耗散能增速加快表明该阶段内部损伤发展加快;卸围压阶段耗散能线性增大表明内部损伤稳步发展.砂岩峰值处弹性应变能与吸收总能量的比值在单轴时最大,随着围压或初始围压的增大逐渐减小并趋于稳定;在相同围压下,卸围压应力路径下弹性应变能与总能量的比值小于三轴加载应力路径下的比值.在0.01 MPa/s卸围压速率下,弹性应变能与吸收总能量的比值受初始围压影响大,而1 MPa/s卸围压速率下,受初始围压影响小.砂岩弹性储能极限随着破坏时围压的增大按线性规律增大,加载应力路径相对卸围压应力路径能够提高砂岩的弹性储能极限.以上成果从能量演化角度分析了地下工程稳定性,具有一定的指导意义.     

活性粉末混凝土单轴循环压缩试验条件下力学特性研究

通过对3种钢纤维体积含量(0％、2％、4％)活性粉末混凝土在较长龄期(3年)进行单轴循环及常规单轴压缩试验,得到其在对应加载制度下轴向及径向应力应变全曲线数据.比较分析了3种钢纤维体积含量活性粉末混凝土在两种加载制度下峰值强度、轴向峰值应变、弹性模量、泊松比、破坏模式及轴应力体应变曲线的异同,并对RPC基本力学性能随钢纤维体积含量增加的变化规律进行了定量分析.结果 显示:峰值强度、轴向峰值应变、弹性模量、泊松比、破坏模式只与钢纤维体积含量有关,与加载制度无关;活性粉末混凝土峰值强度、轴向峰值应变、泊松比随钢纤维体积含量的增加而增大;对3种钢纤维体积含量活性粉末混凝土在单轴循环压缩试验条件下的滞回性能也进行了详细分析.     

碳纤维再生混凝土循环受压性能及本构关系研究

为了研究循环荷载下碳纤维再生混凝土(CFRAC)的受压性能,以再生粗骨料取代率、碳纤维体积掺量和加载速率作为变化参数,设计并制作了40个圆柱体试件进行循环受压加载试验。试验观察了试件的破坏形态,获取了应力-应变曲线,分析了不同变化参数对峰值应力、峰值应变、塑性应变、刚度退化和应力退化等性能的影响规律。结果表明：碳纤维再生混凝土试件在循环荷载作用下主要发生脆性破坏;碳纤维改善了再生混凝土的循环受压性能,与未掺碳纤维混凝土相比,当碳纤维体积掺量为0.3%时,峰值应力和峰值应变分别提高了11.33%和12.22%;刚度退化与应力退化程度得到降低;当再生粗骨料取代率为100%时,峰值应力和峰值应变分别提高了10.16%和14.29%;最后,提出了碳纤维再生混凝土在循环受压下应力-应变本构方程。     

湿筛混凝土动态受压力学性能及破坏形态细观数值模拟

湿筛混凝土通常用来代替由于骨料粒径较大而不便开展物理试验的水工全级配混凝土。为了研究加载速率对湿筛混凝土力学性能及破坏形态的影响,从细观角度出发,运用颗粒流离散元软件PFC^2D建立湿筛二级配混凝土细观数值试件,根据拟静态单轴压缩(应变速率10^-5 s^-1)试验数据标定出数值试件中砂浆颗粒之间、粗骨料颗粒之间及砂浆颗粒与粗骨料颗粒接触面之间的细观参数,进而开展应变速率为10^-4 s^-1、10^-3 s^-1、10^-2s^-1的动态加载并进行动态力学性能及破坏形态的数值模拟和机理分析。结果表明,不同应变速率下试件的应力-应变曲线形状相近,峰值应力随着应变速率的增加而增大,增长率为7.3%～37.9%,峰值应力处应变增大幅度不大。试件破坏形态与物理试验现象吻合较好,随着应变速率的增加,裂缝数量不断增加,裂缝分布趋于均匀,裂缝数量增长率平均为峰值应力增长率的4.2倍。此外,随着应变速率的增加,数值试件内部...     

不同应变速率下橡胶混凝土损伤本构模型

为获得低应变速率下橡胶混凝土的力学性能,本文进行了不同应变速率下橡胶混凝土的轴压试验,分析了混凝土细骨料的橡胶颗粒体积替换率和应变速率对橡胶混凝土力学性能的影响规律。结果表明,随着应变速率的增加,橡胶混凝土的应力-应变关系曲线和抗压强度均呈现增大的趋势,橡胶混凝土初始损伤值呈现递减的趋势,但应变速率对橡胶混凝土的弹性模量影响不显著。当应变速率从3.3×10^-5/s增加至3.3×10^-3/s时,橡胶体积替换率为0%、20%和30%的橡胶混凝土抗压强度分别增加了31%、24%、10%。当橡胶体积替换率率从0%变化到30%时,承受应变速率为3.3×10^-5/s、3.3×10^-4/s和3.3×10^-3/s的橡胶混凝土抗压强度分别减少了17%、15%、30%;橡胶混凝土的耗能随着加载速率的增加,整体呈现增大的趋势。最后基于试验数据建立了不同应变率下橡胶混凝土的损伤本构关系模型,并采用试验数据验证了新建立模型的准确性。     

高压水直接作用下井壁混凝土真实强度特性研究

为研究井壁混凝土在高地下水压作用下强度发展趋势,配制了C60、C70、C80三种高强度等级井壁混凝土,根据养护条件不同将每种强度等级混凝土均分为常规状态试件和密封状态试件,分别在4 MPa、6 MPa、8 MPa、10 MPa水压作用下进行常规三轴加载试验.结果表明:Bresler三参数正八面体强度破坏准则更能准确反映井壁混凝土峰值强度与围压的非线性关系,随着围压的增加井壁混凝土峰值强度具有明显的增强效应,随着混凝土强度等级提高围压敏感性降低;常规状态下并壁混凝土峰值强度随围压增长速率较慢,且比同等级密封状态下井壁混凝土峰值强度大约降低6.3％.     

基于最小耗能理论的混凝土力学本构模型研究

为了准确描述复杂应力下混凝土应力应变关系,通过对混凝土进行不同围压作用下三轴压缩试验,考虑轴、径向应力和球应力对轴向应变的影响,结合最小能耗原理建立一种混凝土损伤本构模型,得出:该模型对混凝土峰前应力应变变化趋势预测基本一致,而对于峰后变形虽有出入,但是总体上较好地描述混凝土峰后应力应变关系.最后,试验曲线与拟合曲线也具有较高的拟合度,说明了模型的正确性与合理性,也对实际工程具有指导意义.     

循环荷载下煤的变形及渗透率演化规律研究

掌握多孔煤介质的渗透率及其演化规律对井下瓦斯抽采防治工作具有重要意义。然而现有实验研究大都忽视了不可逆变形对煤体渗透特性的影响,并且针对轴压循环加-卸载路径下的研究工作较少。本文采用三轴试验装置,开展了不同轴压峰值条件下的循环荷载试验,运用现有经验公式对煤体应力与渗透率关系进行非线性回归拟合。结果表明：循环荷载应力下煤的应变具有良好的记忆性,其应力峰值相对常规加载实验较低;渗透率变化曲线与体积应变变化曲线呈明显的对称关系。渗透率呈负幂指函数变化。     

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。