随机载荷下大型构件疲劳裂纹扩展寿命的预测

本文从影响疲劳裂纹扩展随机性的外因（载荷条件）和内因（材质的分布规律）着手,探讨它们的交互作用对随机载荷作用下构件疲劳裂纹扩展的影响,采用数值模拟的方法,对桥梁、船舶、飞机、特殊容器等大型构件所承受的实际载荷谱以及材料对裂纹扩展的阻力系数等进行模拟,并进而对疲劳裂纹的随机扩展过程进行模拟,提出随机载荷作用下大型构件疲劳裂纹扩展寿命的预测及其可靠性分析方法．     

基于边界元法的疲劳裂纹扩展模拟

用数值方法模拟疲劳裂纹扩展对预测构件残余寿命具有重要意义。该文以基于子域法边界元分析的一点面力法解决了裂纹扩展全过程的应力强度因子精度问题．用坐标变换法导出了Ⅰ－Ⅱ型复合裂纹最大周向应力准则的扩展偏角和有效应力强度因子；建立了复合型裂纹疲劳扩展数值模拟算法，并在ＳＧＩ工作站上研制了具有裂纹构形自动更新和动态图形显示功能的模拟演示软件，该软件对试件裂纹扩展模拟的结果与试验结果一致，说明该文方法具有高     

基于损伤力学的疲劳全寿命数值预估方法

疲劳失效是影响结构件使用安全的主要问题,对疲劳寿命进行准确预测具有重要的工程意义。基于采用平均应力修正的损伤力学演化模型,结合有限元法建立了同时考虑裂纹萌生与扩展的疲劳全寿命数值预估方法。为了验证该方法,开展了不同应力水平下铝合金开孔板试样疲劳试验与疲劳数值模拟。结果表明,基于所建立的疲劳数值分析方法能够有效预测开孔板裂纹扩展过程及疲劳全寿命,预测寿命误差带在两倍以内。     

概率断裂力学在寿命估计中的应用

根据Ｐａｒｉｓ－Ｅｒｄｏｇａｎ提出的疲劳裂纹扩展速率ｄａ／ｄＮ＝ｃ（△Ｋ）公式，基于Ｃ、Ａ（或ａ）、△σ看成是独立的随机变量，并假定Ｃ、Ａ和△σ服从对数正态分布，应用概率断裂力学方法，导出发电机转子轴的疲劳剩余寿命Ｎ，的估算公式Ｎ＝１０。通过一个算例阐明概率断裂力学在疲劳寿命的可靠性估计中的应用及其工程意义。     

简谐激励下声学黑洞梁的疲劳裂纹扩展分析

针对含有裂纹的声学黑洞(ABH)梁,基于假设振型法建立振动力学方程,采用包含裂纹位置及深度信息的等效弯曲刚度模型描述裂纹对ABH梁振型的影响.利用Paris公式模拟疲劳裂纹的扩展速率,提出ABH梁的振动疲劳寿命预测流程图. MATLAB数值模拟与COMSOL有限元分析结果表明,基于等效弯曲刚度模型的数值模型与有限元仿真结果吻合.裂纹扩展分析表明, ABH梁特征频率的阶数与疲劳寿命没有内在关系.振动疲劳模拟表明ABH结构的特征参数会影响疲劳寿命分布.     

疲劳裂纹扩展速率与随机载荷的疲劳寿命程序模拟

本文主要探讨了恒幅和变幅载荷作用下疲劳裂纹扩展规律及随机载荷作用下疲劳寿命的模拟方法。通过对１６Ｍｎ钢的疲劳裂纹扩展试验、分析和数据处理估算出材料的疲劳寿命，说明考虑了载荷实际变动能更接近准确地估算疲劳寿命，为生产设计提供了依据。 对随机载荷的统计分析建立概率模型，并用数值计算方法——蒙特卡罗法产生随枫序列，由计算机程序模拟计算出疲劳寿命．它和变幅试验结果基本符合．说明此法应用于断裂力学中是可行的．它是对传统疲劳试验和分析方法的改进和发展．     

基于损伤力学与安全衰减路径的含裂纹缺陷压力容器扩展寿命分析

针对含裂纹缺陷压力容器的疲劳裂纹扩展寿命问题,在裂纹缺陷的安全衰减路径仿真基础上,提出了一种预测裂纹缺陷疲劳扩展寿命的计算方法。首先根据裂纹长度和深度的几何关联变化模型,基于该关联模型与失效评定图（FAD）仿真裂纹缺陷的安全衰减路径轨迹,然后采用数学积分方法求解安全衰减路径的长度和剩余轨迹线段长度,以此为度量建立裂纹缺陷安全裕度及损伤程度的计算模型,结合低周疲劳试验数据,在Lemaitre能量损伤理论上建立一种裂纹疲劳扩展寿命预测模型。此外,本文对某压力容器进行了算例分析,并运用本文提出的模型计算结果与Paris公式的计算结果及扩展有限元仿真的结果进行对比,结果表明,该方法对压力容器含裂纹缺陷的疲劳寿命评估有一定的实用价值。     

板、轴类构件中表面裂纹弯曲疲劳扩展规律

本文从断裂力学基本理论出发,引入“相当能量率”概念,给出一种表面裂纹疲劳扩展的速率分析模型及一系列计算公式,在探讨板、轴件中表面裂纹弯曲疲劳扩展规律的基础上,得到一种“用贯穿裂纹试件的实验结果预测表面裂纹构件疲劳寿命”的特性线法,提出三种方法预测“含横向表面裂纹园轴件”的疲劳寿命,并为园轴中横向表面裂纹的确定提供了一种途径。文中还给出了P105钻杆钢表面裂纹试件在弯曲疲劳时扩展特性的初步研究。     

腐蚀疲劳裂纹扩展的马尔可夫链模型及实验验证

在腐蚀环境下对LY12CZ铝合金试验件进行疲劳裂纹扩展实验,通过高倍显微镜观测并记录裂纹长度及相应的循环数。基于腐蚀条件下疲劳裂纹扩展数据的分散性及统计特性,提出用马尔可夫链模型模拟腐蚀疲劳裂纹的扩展,建立腐蚀疲劳裂纹扩展规律的概率模型,得到给定疲劳寿命时的裂纹超出数概率分布和给定裂纹长度时的疲劳寿命累积概率分布。将模拟结果与实验结果进行比较表明:马尔可夫链模型能够相当好地描述腐蚀疲劳裂纹扩展规律,为飞机结构的寿命预测提供参考。     

齿根初始裂纹倾角对圆柱齿轮疲劳寿命的影响

用有限元方法模拟圆柱齿轮齿根处疲劳裂纹的扩展过程.分析齿轮中疲劳裂纹的扩展路径和扩展形貌,依此设定合适的寿命积分路径,对齿轮的疲劳寿命进行预测,分析初始裂纹倾角对齿轮中疲劳裂纹的扩展形貌以及齿轮疲劳寿命的影响.结果表明:萌生于齿根处的疲劳裂纹,在齿廓面上朝着齿顶方向倾斜扩展,在齿端面上,从一侧齿根以圆弧状的扩展路径朝着对侧齿根扩展;对于相同的初始裂纹深度,初始裂纹的倾角较大,齿轮易发生轮缘断裂,其疲劳寿命相对较长,相反,初始裂纹的倾角较小,齿轮易发生齿根断裂,其疲劳寿命相对较短.     

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.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

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.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the