不同应力下7B04铝合金的疲劳断口

采用金相、电镜扫描显微技术对不同应力下铝合金的疲劳断口显微组织进行分析和对比研究,揭示该合金疲劳裂纹萌生与扩展的微观特征。研究结果表明:疲劳裂纹一般在材料表面或近表面处萌生,与表面的距离随加载应力升高而减小,在应力为285MPa时裂纹于距表面约250μm处萌生,而在430MPa时裂纹萌生于材料表面;在裂纹源附近观察不到疲劳辉纹,且加载应力越高,这个区域的面积就越小,而裂纹扩展区的疲劳辉纹间距随应力的增大而增大;裂纹形成后,微裂纹沿着与应力轴呈45°角的最大切应力方向向纵深扩展,然后转向与拉应力轴正交的方向扩展,最后瞬断,且随着应力的增大,断口上疲劳裂纹扩展区的面积减小,瞬断区的面积增大。     

高温环境2A12–T4铝合金多轴疲劳失效规律研究

许多工程结构在服役过程中往往承受着复杂的多轴疲劳载荷和热力耦合作用,仅靠常温情况下的单周载荷来简化复杂多轴载荷状态的失效预测方法将不再适用。为研究2A12–T4铝合金的高温多轴疲劳失效规律,本实验在175℃环境温度下,选取等效Von-Mise应力幅值,通过间断式加载记录不同拉扭加载循环下的裂纹萌生与扩展情况,研究特定加载路径对裂纹萌生与扩展的影响。实验结果表明,相位差为0时,裂纹萌生方向沿MSSA平面;在相位差为45°时,裂纹萌生传播方向与最大切应力平面方向相近,最大切应力在裂纹萌生过程中起到主要作用;在λ=0.5、φ=0和λ=1.0、φ=0两种情况下,裂纹萌生初期沿着最大切应力平面方向传播,传播过程中存在第I阶段向第II阶段转变的过程;在λ=0.5、φ=45°和λ=1.0、φ=45°两种情况下,不存在明显的第I阶段向第II阶段转变的过程;对比4种加载方式下的疲劳裂纹萌生期与疲劳寿命比,发现切应力比重的增大加速裂纹的萌生过程,相位差的存在阻碍了裂纹的萌生过程。     

Inconel 718合金短管高温低周疲劳行为

基于位移循环加载试验,对反应堆压力容器密封元件Inconel 718合金O形环短管试样变形幅控制下进行了常温和300℃高温低周疲劳试验研究.结果表明,在循环加载中试样发生接触力松弛,当位移压缩比峰值不低于8%且压缩比幅值超过0.6%时试样会产生低循环疲劳失效.采用弹塑性接触有限元方法对引发疲劳裂纹的试样危险局部的应力应变进行了分析,给出了位移压缩比幅值与危险局部应变幅值的短管疲劳寿命估算式.疲劳试样断口微观分析表明,在初始大变形引起的裂纹萌生区,断口微观形貌表现为晶体滑移与解理撕裂,而在裂纹扩展区表现为解理撕裂与疲劳辉纹共生的混合型裂纹扩展.     

10CrNiMo高强钢的低周疲劳特性

采用圆形横截面光滑试样,通过轴向不同应变幅控制的低周疲劳试验,研究了10CrNiMo高强钢的低周疲劳特性,包括循环应力-应变行为、应变-寿命特点、循环应力响应及其力学滞后现象,给出了相应的疲劳参数、循环软硬化特性及应变滞后规律.对裂纹扩展方向及试样疲劳断口的观察表明:裂纹扩展面与轴向力呈现多角度关系,裂纹萌生于试样表面,沿断口周边分布,且具有多源性;疲劳裂纹主要以锐化--钝化机制扩展.     

GH4169合金高温疲劳裂纹扩展的微观损伤机制

空气环境对高温合金在高温下的损伤行为有显著影响.为了研究标准热处理态GH4169合金在高温疲劳裂纹扩展过程中的微观损伤机制,在空气环境中进行650℃、初始应力强度因子幅ΔK=30MPa·m1/2和应力比R=0.05的低周疲劳裂纹扩展试验.使用扫描电镜(SEM)及能谱(EDS)对试样的断口、外表面和剖面进行观察和分析.实验结果表明:疲劳主裂纹以沿晶方式萌生并扩展,随后沿晶二次裂纹出现,并且其数量和长度沿主裂纹方向逐渐增加,进入快速扩展阶段后,断口呈现韧窝组织形貌;在裂纹扩展过程中,δ相与基体的界面发生氧化,使得沿晶二次裂纹沿界面扩展并产生偏折,从而起到阻碍二次裂纹扩展的作用;试样外表面的主裂纹周围出现晶界氧化损伤区,其尺寸和晶界开裂程度沿主裂纹扩展方向逐渐增大.     

XCQ16和20Mn2车轴用钢疲劳失效的微观机理

利用扫描电镜(SEM)对XCQ16和20Mn2两种车轴用钢疲劳断口和裂纹扩展断口进行分析,研究疲劳失效过程中的裂纹萌生及扩展机理.结果表明:裂纹均是从试样表面萌生,非金属夹杂和位错是主要的萌生机制;XCQ16钢在疲劳断口中部区的裂纹闭合效应大于20Mn2钢,裂纹扩展较慢;两者在裂纹扩展区的扩展机理不同,XCQ16钢属于塑性断裂,20Mn2钢属于解理断裂;在非金属夹杂上,XCQ16钢多含氧化物和硫化物的混合夹杂,20Mn2钢主要是氧化物夹杂,混合夹杂对材料的疲劳性能影响较小.     

固溶温度和稳定化工艺对GH864合金疲劳裂纹扩展特征的影响

研究了不同固溶温度和稳定化处理工艺后GH864合金的裂纹扩展情况.通过分析合金的微观组织,断口形貌以及lga--lgNi/Nf、da/dN--a及da/dN--N曲线特征,定量计算了裂纹萌生期、稳态扩展期及失稳瞬断期在整个疲劳断裂过程中所占比例,并进一步分析影响各自比例的微观组织因素.结果表明:随着固溶温度的升高,晶粒尺寸增加,合金的裂纹扩展速率降低,同时裂纹的萌生期的比例降低,而裂纹的扩展期比例则会增加;随稳定化时间的延长和温度的升高,晶界碳化物析出量增加,降低了合金的裂纹扩展速率,但是裂纹萌生期的比例在逐渐增加.     

考虑应力梯度及附加强化的多轴疲劳寿命预测

以多轴缺口件为研究对象,考虑应力梯度和非比例附加强化对疲劳寿命的影响,建立一种适用于多轴缺口件的疲劳寿命预估模型.首先,以最大剪切应变幅作为损伤参量,借助坐标变换原理确定临界面位置,研究了裂纹萌生和扩展的物理机制;其次,利用有限元方法获得临界面上非均匀应力场,提取特定路径上的应力分布并进行归一化处理,给出多轴加载时的等效应力梯度因子;最后,考虑相位差的影响提出一种新的非比例附加强化因子,基于Manson-Coffin方程提出了一种多轴疲劳寿命预测方法.将本文模型、Smith-Watson-Toper(SWT)模型和Manson-Coffin方程的计算结果与实验寿命进行对比,结果表明本文方法的预测精度高于SWT模型和MansonCoffin方程.     

45#钢中Ⅰ +Ⅲ复合型疲劳裂纹的转型扩展及断口分析

以带有不同角度侧斜裂纹的紧凑拉伸试件研究了Ⅰ+Ⅲ复合型裂纹在单向拉伸疲劳载荷作用下的转型情况,着重研究转型过程中应力强度因子(ΔK)和断口形态的变化.有限元计算表明,Ⅰ+Ⅲ复合型裂纹是向Ⅰ型裂纹转化,侧斜角越大,Ⅲ型应力强度因子变化幅(ΔKⅢ)越大,裂纹转型越快;断口分析表明试件疲劳断口的疲劳源呈多源性,裂纹萌生于紧凑拉伸试件线切割缺口处的微裂纹;在转型过程中,带侧斜角试件断裂面较为粗糙,断面上存在较为粗大的撕裂棱和二次裂纹;疲劳辉纹更加不连续,不均匀;完全转型后断裂面较为平坦,撕裂棱和二次裂纹尺寸减小.即转型是通过在疲劳源形成与原裂纹面成一定角度的台阶,在裂纹的随后扩展中通过不同台阶与台阶的连接而转向,最后转到Ⅰ型扩展方向.     

TC17合金电子束焊接接头高周疲劳失效行为研究

电子束焊接构件广泛应用于航空发动机关键部位,其需要满足长寿命与高可靠性的设计要求.针对TC17合金电子束焊接接头,采用旋转弯曲疲劳试验方法,获得焊接接头的高周疲劳性能,同时利用电子扫描电镜对疲劳断口进行微观观察,探明焊接接头的高周疲劳裂纹萌生和扩展机理.结果表明,TC17合金电子束焊接接头在10~7周次的疲劳强度为450 MPa,约为母材强度的81%,试样失效位置均位于焊缝区;试样表面最大应力与内部气孔缺陷处应力集中形成竞争机制,在10~5～10~7周次内,裂纹萌生于内部气孔,在10~7周次后,裂纹萌生于试件表面;试样断口显示出明显的穿晶断裂区和沿晶断裂区,疲劳寿命随沿晶断裂区的应力强度因子下降而增加;气孔面积及真实应力为影响疲劳寿命的主要因素,气孔处应力强度因子与疲劳寿命呈线性下降关系.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

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Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with