随机缺陷下结构疲劳寿命及其尺寸效应的概率建模与评估

通常球墨铸铁和铝合金制成的工程部件的疲劳寿命由制造过程中产生的制造缺陷所决定。因此,本文基于制造缺陷的尺寸和位置,提出了考虑制造缺陷对疲劳寿命影响的概率模型。具体而言,就是将CT扫描获得的缺陷近似作为圆形裂纹进行裂纹扩展分析,并结合威布尔分布对试件的疲劳寿命建模。基于此,提出一个基于表面初始裂纹损伤机理的表面缺陷修正系数,并利用三组铸铁和铝合金的实验数据对模型进行验证和比较。此外,还探讨了等幅载荷作用下统计尺寸效应对疲劳寿命分布的影响。最后,分别对三种不同尺寸材料的疲劳寿命进行预测,预测的P-S-N图表明所提出模型进行预测的结果与概率分散带吻合一致,具有较好的预测效果

Cyclic plastic zone-based notch analysis and damage evolution model for fatigue life prediction of metals

Fatigue strength analysis of critical components plays a vital role for ensuring structural integrity and operational reliability of major equipment. In notched components, the concept of cyclic plastic zone (CPZ) is commonly utilized for fatigue cracking analysis, in which the CPZ size normally relates to the material strength. In particular, materials with higher yield stress have shown smaller CPZ size and vice versa. According to this, a new approach for determining closed-form stress at the notch tip is proposed by considering the size of cyclic plastic zone, which can be used for the notch tip stress evaluation along the load direction under cyclic loadings. By implementing FE analysis, experimental data of 304 stainless steel, 40Cr steel and Ti-6Al-4V alloy are utilized for model validation and comparison. Results show that the scope of damaged CPZ alters the notch tip stress under fatigue loadings, and the proposed model yields better correlation of fatigue life predictions with experimental results of the three materials than other two models. (C) 2020 The Authors. Published by Elsevier Ltd

Structural and electronic properties of hydrogenated bilayer boron nitride

采用第一性原理方法研究了表面氢化的双层氮化硼的结构和电子性质.考虑了表面氢化的双层bn可能存在的六种主要构型,计算结果表明:Ab-bn和AA-bn两种构型最为稳定.进一步分析了氢化后的双层bn最稳定构型的能带和电子性质.Ab-bn和AA-bn两种构型的原子薄片均为直接带隙半导体,ggA计算的带隙值分别为1.47 EV和1.32 EV.因为ggA通常严重低估带隙值,采用HybrId泛函计算得到带隙值分别为2.52EV和2.34 EV.在最稳定的Ab-bn和AA-bn两种构型中,b-n键呈现共价键,而b-H和n-H则具有明显的离子键的特点.在双轴应变下氢化双层bn原子薄片可以被连续地调节带隙,当晶格常数被压缩约8%时,原子薄片由半导体性转变为金属性.The structural and electronic properties of hydrogenated bilayer boron nitride(BN) were studied by employing the frst-principles calculations.Six major polymorphic structures of hydrogenated bilayer BN are considered.Calculated results show that,among them,the AB-BN and AA-BN structures are the most stable ones.The analysis on the energy bands and electronic properties of the two most stable structures are then performed.Structures of AB-BN and AA-BN are both semiconducting with direct band gaps,and the gaps are 1.47 eV and 1.32 eV,respectively,calculated using the GGA method.Since GGA usually severely underestimates the band gap,the hybrid density functional calculations are then conducted,which suggests that the band gaps are 2.52 eV and 2.34 eV for AB-BN and AA-BN structures,respectively.In the most stable structures of AB-BN and AA-BN,B-N bonds show mainly covalent characters,while B-H and N-H bonds exhibit clear ionic characteristics.Moreover,the band gap of hydrogenated bilayer BN atomic sheet can be continuously modulated by biaxial strains.When the lattice constant is compressed by around 8%,the electronic character of the atomic sheet changes from semiconducting into metallic.国家自然科学基金(批准号:11004165;21233004); 福建省教育厅科技项目(批准号:JK2013054)资助的课题~

Probabilistic framework for fatigue life assessment of notched components under size effects

Structural integrity assessments with discontinuities are critical for ensuring operational life and reliability of engineering components. In this work, through combining with the generalized local model, a probabilistic framework is proposed for fatigue life assessment of notched components under size effects, in which the Smith-Watson-Topper damage parameter is utilized to characterize the multiaxial stress state at the notch tip. In particular, an effective stress concept is introduced to characterize the inhomogeneous stress distribution within the notch region. Finally, experimental data of TA19 notched specimens with different scales are utilized for model validation and comparison, results show that the proposed framework yields acceptable correlations of predicted fatigue lives with experimental ones

First-principles Calculations on the Optical Properties of Monolayer MoS_2

采用基于密度泛函理论的第一性原理方法计算了单层和体材料二硫化钼(MOS2)的电子能带结构及光学性质.在能带结构计算的基础上,计算了单层和体材料MOS2的介电函数虚部及实部,并导出了单层MOS2的能量损失谱、吸收系数、反射率、折射率和消光系数等.同时给出了体材料及单层MOS2介电函数图像中各峰值与对应的能带带间跃迁之间的关系.所得结果与实验结果及现有的理论结果相符合.The first-principles method based on the density functional theory has been used to calculate the electronic band structures and the optical properties of monolayer and bulk MoS2.Based on calculated band structures,imaginary and real parts of the dielectric functions are determined.The energy loss spectrum,the absorption coefficient,the reflectivity,the refractive and the extinction coefficient are then calculated on the basis of complex dielectric functions.The relationship between peaks in the dielectric function pictures and the inter-bands transitions in the calculated band structures are pointed out,for both the monolayer and bulk MoS2.Our calculation results are in good agreements with available experimental data and previous theoretic results.国家自然科学基金(10774124;10702056

巴夫杜氏藻15二磷酸核酮糖羧化酶加氧酶小亚基基因的克隆和分析

1,5-二磷酸核酮糖羧化酶/加氧酶（Rubisco）是光合作用中的一个关键酶,其小亚基rbcS具有调控羧化反应催化效率和影响该酶对二氧化碳/氧气底物特异性的功能。从巴夫杜氏藻中克隆rbcS基因及其5′-上游序列,并对基因及5′-上游序列进行了分析。根据已知rbcS基因保守核苷酸序列设计引物,分别克隆到1 841 bp的DNA和380 bp的cDNA序列。以此为基础,使用染色体步移（Genome walking）和cDNA末端快速扩增（RACE）技术,获得了799bp的5′端DNA序列和500 bp的3′端cDNA序列。序列分析发现,巴夫杜氏藻rbcS DNA全长为2 031 bp（不包括476 bp 5′-上游序列）,cDNA全长包括570 bp开放读码框（GenBank登录号：HQ315783）和294 bp 3′端非翻译区。5′-上游序列区域存在一系列预测的顺式作用元件。该研究旨在为后继的rbcS基因的功能和表达研究、Rubisco的遗传改造奠定基础。同时,rbcS启动子因其可驱动基因高效表达而引起广泛关注,因此获得的rbcS 5′-上游序列经验证和优化后,可用于在嗜盐微藻中驱动转基因的高效表达以及完善微藻转化系统

Structural and electronic properties of Al-doped spinel LiMn_2O_4

采用基于密度泛函理论的第一性原理方法,在广义梯度近似(ggA)和ggA+u方法下对尖晶石型lIMn_2O_4及其Al掺杂的尖晶石型lIAl_(0.125)Mn_(1.875)O_4晶体的结构和电子性质进行了计算.结果表明:采用ggA方法得到尖晶石型lIMn_2O_4是立方晶系结构,其中的Mn离子为+3.5价,无法解释它的JAHn-TEllEr畸变.给出的lIMn_O_4能带结构特征也与实验结果不符.而采用ggA+u方法得到在低温下的lIMn_2O_4和其掺杂体系lIAl_(0.125)Mn_(1.875)O_4的晶体都是正交结构,与实验一致.也能明确地确定Mn的两种价态Mn--3+/Mn--(4+)的分布并且能够说明Mn--3+O_6的z方向有明显的JAHn-TEllEr畸变,而Mn--(4+)O_6则没有畸变.lIMn_2O_4的能带结构与实验比较也能够符合.采用ggA+u方法对Al掺杂体系的lIAl_(0.125)Mn_(1.875)O_4的研究表明,用Al替换一个Mn不会明显地改变晶体的电子性质,但可以有效地消除Al--3+O_6八面体的JAHn-TEllEr畸变,从而改善正极材料lIMn_2O_4的性能,这与电化学实验的观察结果相一致.The structural and electronic properties of spinel LiMn_2O_4 and its Al doping system LiAl_(0.125)Mn_(1.875)O_4 are investigated within the density functional theory in both the generalized gradient approximation(GGA) and the GGA with Hubbard U correction (GGA+U).The results from the GGA method suggest that LiMn_2O_4 has a cubic structure and the valences of Mn ions are all +3.5,which is unable to explain the Jahn-Teller distortions in the material.The band structure of LiMn_2O_4 predicted by the GGA method is also inconsistent with experimental result.With the GGA+U method,the low temperature structures of LiMn_2O_4 and its Al doping system LiAl_(0.125)Mn_(1.875)O_4 are shown to be orthogonal,the two different valence states of Mn,i.e.,Mn--(3+)/Mn--(4+) ions,are then determined,which is then able to explain the Jahn-Teller distortion in octahedron Mn--(3+)O_6 and the non-existence of distortion in octahedron Mn--(4+)O_6.These results are in good accordance with experimental data.Their band structures by GGA+U calculations are also consistent with experimental results.The GGA+U calculations on the LiAl_(0.125)Mn_(1.875)O_4 indicate that with the replacement of an Mn by Al,the crystal structure and electronic properties are not significantly changed,but the Jahn-Teller distortion in octahedron Al--(3+)O_6 can be effectively eliminated,which could improve the performance of the anode materials based on LiMn_2O_4.The phenomenon is in consistent with the electrochemical experiments.国家重点基础研究发展计划(批准号:2011CB935903);福建省自然科学基金(批准号:2008J04018)资助的课题---

皮状丝孢酵母脂肪酸CoA 连接酶(Facl)基因的克隆与分析

从皮状丝孢酵母（Trichosporon cutaneum）中克隆了Facl基因及其5 ＇-上游序列,并对Facl基因及其5＇-上游序列进行了分析.根据前期的基因组文库测序结果,获得了898 bp DNA序列.以此为基础,2次使用染色体步移（Genome walking）方法,分别获得了854 bp和1 236 bp 5＇-DNA序列.根据获得的5和3端序列,合成引物用于扩增Facl基因的全长DNA和cDNA序列.分析发现,皮状丝孢酵母Facl基因cDNA包含一个1 662 bp的开放读码框,DNA不含内含子序列.同时获得了482 bp的5＇-上游序列.在5＇-上游序列区域存在一系列预测的顺式作用元件.相似性分析的结果表明T.cutaneum和Rhodococcus erythropolis的Facl氨基酸序列相似性最高.该研究旨在为后继的Facl基因的功能和表达的研究、油脂代谢的遗传改造奠定基础

Cloning and Characterization of a Gene Encoding Fatty Acid CoA Ligase （Facl） from Trichosporon Cutaneum

The Facl gene and its 5 ＇-flanking sequence has cloned from Trichosporon cutaneum and amalysis.Based on the former result of genome library sequencing, 898 bp DNA DNA sequence, the 5＇ genomic DNA was cloned by genome walking m were amplified respectivel