高温环境下薄壁结构声疲劳失效验证技术研究

目的针对高温环境下薄壁结构声疲劳失效问题,研究分析薄壁结构在高温环境下的声疲劳失效特征,验证薄壁结构热声响应计算方法与疲劳寿命预估模型的有效性。方法较系统地阐述高温环境下薄壁结构声疲劳失效试验验证技术,重点总结热声疲劳试验环境建立与加载、高温环境下噪声测试、高温环境下动态响应测试和疲劳破坏寿命测试方法,并通过具体案例说明工程中试验验证方法的有效性。结果试验件在仿真计算与试验中的破坏位置一致,响应频率吻合较好,应力水平一致,疲劳寿命量级相当。结论薄壁结构热声响应计算方法与疲劳寿命预估模型的有效性高。     

基于疲劳累积损伤等效理论的PCB板振动加速试验研究

目的建立小样本情况下,通过试验及仿真结合求解PCB板在随机振动激励下的振动加速因子的方法。方法以疲劳累计损伤等效为研究基础,以PCB板为研究对象,通过实验室的动力学环境模拟试验,在施加相同谱型不同量级的随机激励载荷下的振动加速因子,并通过采用试验数据对仿真局部模型修正的方法得出PCB板在随机振动激励载荷下的振动加速因子。结果通过试验数据与仿真计算结果的对比,两种方法得出的振动加速因子的误差在5%以内,满足工程实践精度要求。且进一步的证实了该方法的可行性。结论对于不同种类的PCB板在进行小样本摸底试验及随机振动仿真计算的前提下,确定电路板产品的薄弱位置,之后通过疲劳仿真计算局部的疲劳寿命便可以求得一定精度要求下的振动加速因子。     

热声复合环境下薄壁锥壳结构响应计算与疲劳寿命预估

目的研究热声复合环境下薄壁锥壳结构的动力学响应与疲劳寿命。方法采用耦合的有限元/边界元法,完成不同热声载荷下的振动应力计算。基于改进的雨流计数法,对不同热声载荷下危险点位置及典型位置的疲劳寿命进行预估。结果屈曲前随温度的增加,薄壁锥壳结构的基频降低,屈曲后在一定温度范围内时,基频增加。薄壁锥壳结构的应力集中主要出现在孔边位置,基频在热声激励响应中起主导作用。低阶固有频率处存在较大峰值,高阶频带范围内的峰值较小,模态密度较高。结论在800～1000℃的温度载荷与强声载荷下,薄壁锥壳结构的疲劳寿命只能维持几个小时,所以在抗声疲劳结构设计中要考虑响应谱的频率结构,及注重结构孔边位置的结构设计。     

结构振动疲劳加速试验技术研究

目的提出一种用于评估随机振动环境下工程结构长期耐久性和疲劳可靠性的加速试验技术。方法通过开展一系列高斯和非高斯振动疲劳对比试验,系统研究影响结构振动疲劳寿命的各种因素,包括随机振动激励的均方根值、功率谱密度、带宽和峭度值等。结果非高斯随机振动激励的带宽和峭度值对结构振动疲劳寿命也有明显影响。结论当结构振动激励呈现明显的非高斯特征时,设计随机振动疲劳加速试验方案必须综合考虑振动激励的带宽和峭度值。     

疲劳损伤等效在随机振动试验中的应用

以疲劳损伤等价为基础的随机振动试验是评价结构振动环境适应性能力的重要手段.将基于位移模态和应变模态的模态叠加方法分别应用于结构振动位移响应和应力响应的分析中,建立了随机振动试验不同激励条件下,结构振动响应的关系;将结构随机振动应力响应的峰值概率分布通用关系应用于疲劳损伤评估,导出了振动疲劳损伤等效关系.以一个试验为例介绍了疲劳损伤等效原则在随机振动试验中的应用.     

某车载油箱在随机振动环境下的疲劳寿命研究

目的 针对某车载油箱高周疲劳寿命难以预测问题,研究该设备在随机载荷环境下的疲劳寿命。方法 首先通过模态试验得到油箱固有频率及振型,然后利用Solidworks建立该车载油箱的仿真模型,在ANSYS Workbench软件中进行模态分析、随机振动分析、谐响应分析。最后利用ANSYS Workbench软件中的nCode SN Vibration (DesignLife)模块,在随机振动疲劳寿命频域分析法基础上,通过nCode模块中的Narrowband法进行油箱在多个加速度功率谱密度下的疲劳寿命研究。结果 该油箱在约束模态试验和仿真分析下所表现的动力学特性基本相同,油箱纵向为振动严酷方向。在已知加速度功率谱密度下,油箱疲劳寿命随低阶固有频率处功率谱密度幅值的增加而降低,但油箱薄弱部位始终保持不变。结论 建立的仿真模型准确,可为油箱优化设计及后续油箱疲劳试验提供参考。     

基于临界面的多轴振动疲劳寿命预测

目的提出一种新的基于临界面正应力的高周多轴疲劳寿命预测方法。方法通过对主应力进行投影,得到各时刻下临界平面内的应力大小,利用雨流法计算不同临界面下的疲劳损伤,并通过权函数,得到主应力的角度期望值,进而预测结构的疲劳寿命。结果通过试验件进行仿真模拟,对底端作用两个方向PSD频率范围为8～200 Hz,大小为0.006、0.003、0.008 g~2/Hz的强制加速度激励得到多轴应力响应,以此计算4种工况下的随机加速度振动疲劳试验预测寿命,对比试验寿命误差基本处于2倍界以内。结论新的基于临界面正应力的疲劳寿命预测方法能有效预测多轴振动疲劳寿命。     

某梁结构静动联合加载疲劳研究试验件设计与分析

目的解决工程结构在交变静载荷和动载荷联合作用下的疲劳寿命预估难题。方法拟设计一梁结构试验件,方便施加静力与动载荷,并具有合适的疲劳寿命,用于静动联合加载下疲劳寿命预估研究。并采用名义应力法计算出静载荷作用下结构的寿命,采用频域法计算动载荷单独作用下结构的寿命,再以线性损伤累积理论为基础,以载荷块为单位来计算静动载荷联合加载下的寿命。结果初步给出试验载荷,得到静动载荷联合加载下危险点的寿命为1225 s。试件在1 h之内失效,满足设计要求。结论通过该方法,可以用来校核试件的实际寿命,以设计试件。     

一种连接器振动故障分析

目的 分析得出轴向弹性触碰式连接器内导体失效的主要原因。方法 以某机载电子模块的连接器在功能振动试验后出现的故障为研究对象,对其进行目测检查、随机振动仿真分析和受力分析,定位故障原因,随后结合应力应变关系公式、高斯区间法和Miner累积损伤定律,推导内导体的疲劳寿命计算公式。结果计算得到内导体自身的振动响应应力仅为0.26 MPa,不足以产生疲劳破坏,但在振动激励下,连接器随模块的振动位移较大,超出了连接器的间隙容差范围,致使受压的内导体端面出现较大的往复动摩擦力,而摩擦力引起内导体根部的应力（250.13 MPa）超过了材料的疲劳极限,内导体有疲劳断裂的风险。进一步计算出内导体的振动疲劳寿命为0.67 h,小于功能振动试验时间,证实是振动位移引起的摩擦导致了内导体的疲劳断裂。结论 轴向弹性触碰式连接器必须要重视摩擦力的危害,提高模块的安装刚度,可以有效地提高连接器的可靠性。     

有限元仿真在振动结构疲劳分析中的应用

为了对某机载产品进行结构疲劳分析,采用有限元分析软件ANSYS对产品结构进行了模态分析和随机振动分析,结合模态试验修正了有限元模型。由随机振动分析得到应力响应功率谱,最后利用频域方法计算结构的疲劳损伤。仿真结果基本吻合强化试验结果,并给出了产品结构设计改进方案。     

Effects of two sludge application on fractionation and phytotoxicity of zinc and copper in the soil

The potential harm of heavy metals is a primary concern in application of sludge to the agricultural land. A pot experiment was conducted to evaluate the effect of two sludges on fractionation of Zn and Cu in soil and their phytotoxicity to pakchoi. The loamy soil was mixed with 0%, 20%, 40%, 60% and 80% (by weight) of digested sewage sludge (SS) and composted sludge (SC). The additions of both sludges caused a significant raise in all fractions, resulting in that exchangeable (EXCH) and organic bound (OM) became predominance of Zn and organic bound Cu occupied the largest portion. There was more available amount of Zn and Cu in SS treatments than SC treatments. During the pot experiment, the concentration of Zn in EXCH, carbonate (CAR) and OM and Cu in EXCH and OM fractions decreased in all treatments, so their bioavailability reduced. Germination rate and plant biomass decreased when the addition rate was high and the best yield appeared in 20% mixtures at the harvest of pakchoi. The two sludges increased tissue contents of Zn and Cu especially in the SS treatments. Zn in pakchoi was not only in relationship to ΔEXCH and ΔCAR forms but also in ΔOM forms in the sludge-soil mixtures. Tissue content of Cu in pakchoi grown on SC-soils could not be predicted by ΔEXCH. These correlation rates between Zn and Cu accumulation in pakchoi and variation of different fractions increased with time, which might indicate that sludges represented stronger impacts on the plant in long-term land application.     

Intraspecific differences in effects of co-contamination of cadmium and

A hydroponic experiment was carried out to study intraspecific differences in the effects of different concentrations of cadmium (Cd)(0-10 mg/L) and arsenate (As(V)) (0-8 mg/L) on the growth parameters and accumulation of Cd and As in six wheat varieties Jing-9428, Duokang-1, Jingdong-11, Jing-411, Jingdong-8 and Zhongmai-8. The endpoints of wheat seedlings, including seed germination,biomass, root length and shoot height, decreased with increasing the Cd and As concentrations. Significant differences in seed germination, biomass, root length, shoot height and the accumulation of Cd and As were observed between the treatments and among the varieties (p ＜ 0.05). The lethal dosage 50% were about 20, 80, 60, 60, 80 and 20 mg As/L for Jing-9428, Duokang-1, Jingdong-11,Jing-411, Jingdong-8 and Zhongmai-8, respectively, and the corresponding values for Cd were about 30, 80, 20, 40, 60 and 10 mg Cd/L, respectively. Among the six varieties, Duokang-1 was found to be the most resistant to Cd and As toxicity, and Zhongmai-8 was the most sensitive to Cd and As co-contamination. The resistance of the six varieties was found dependant on the seedling uptake of Cd and As. Duokang-1 was the most suitable for cultivation in Cd and As co-contaminated soils.     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils.Bidens maximowicziana is a new Pb hyperaccumulator,which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb.The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues.The Pb distribution order in the B. maximowicziana was:leaf>stem>root.The effect of amendments on phytoremediation was also studied.The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application.Compared with CK(control check),EDTA application promoted translocation of Pb to overground parts of the plant.The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg.This research demonstrated that B.maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil,especially,combination with EDTA.     

Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day, Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury （HgT）, combinative mercury （Hgc） and gaseous mercury （HgG）, and content of total organic carbon （TOC）, but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average Hgv of profiles 1992, 1996, and 2000 was similar, but their average HgG was quite different. HgT was significantly correlated with Hgc in profile 1992 and 2000, and Hgv was significantly correlated with Hg6 in profile 1996. HgG/Hgv ratio in profile samples decreased in the order of （HgG,/HgT）1992〉（HgG/HgT）1996〉〉（HgG/HgT）2000. A simple outline of Hg release in landfill could be drawn： with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf〉root〉stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants （e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum） are capable of enriching more Hg than herbaceous plants.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Enzymatic oxidation of aqueous pentachlorophenol

The influence of the nonionic surfactant Tween 80 on pentachlorophenol （PCP） oxidation catalyzed by horseradish peroxidase was studied. The surfactant was tested at concentrations below and above its critical micelle concentration （CMC）. Enhancement of PCP removal was observed at sub-CMCs. The presence of Tween 80 in the reaction mixture reduced enzyme inactivation which occurred through a combination of free radical attack and sorption by precipitated products. A simple first-order model was able to simulate time profiles for enzyme inactivation in the presence or absence of Tween 80. At supra-CMCs, the surfactant caused noticeable reductions in PCP removal, presumably through micelle partitioning of PCP which precluded the hydrophobic PCP molecule from interacting with the enzyme.     

Decomposition of alachlor by ozonation and its mechanism

Decomposition and corresponding mechanism of alachlor, an endocrine disruptor in water by ozonation were investigated. Results showed that alachlor could not be completely mineralized by ozone alone. Many intermediates and final products were formed during the process, including aromatic compounds, aliphatic carboxylic acids, and inorganic ions. In evoluting these products, some of them with weak polarity were qualitatively identified by GC-MS. The information of inorganic ions suggested that the dechlorination was the first and the fastest step in the ozonation of alachlor.     

基于综合水质标识指数和对应分析法的校园河道水质评价

以三峡大学的校园河道求索溪为研究对象,利用综合水质标识指数法确定求索溪水质类别,分析其水质时空变化规律,并利用对应分析法得出求索溪中不同监测点的主要污染因子.研究结果表明:求索溪整体的综合水质标识指数为7.423,整体水质为劣V类(地表水环境质量标准GB 3838-2002)且黑臭.从时间变化来看,求索溪4月份的水质最差,5月份次之,4、5月份所有监测点的水质都劣于V类且黑臭;8月份水质最好,水质为Ⅳ类;从空间分布来看,8个监测点综合水质标识指数均超过6.0,水质为劣V类,其中6号监测点的水质相对最好,监测点3号的水质相对最差;对应分析法得出求索溪的整体水体污染程度受总氮因子的影响最大,其次为总磷.该研究拟为求索溪及类似校园河道的水环境治理研究提供基础依据和参考.     

Potential of plant polyphenol oxidases in the decolorization and removal of textile and non-textile dyes

In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.