NiTiNb形状记忆合金的应力松驰研究

为了解NiTiNb形状记忆合金的高温松驰性能，进行了高温下的松驰试验，由应力松驰与蠕变的关系。推导得到松驰曲线表达式，通过实验数据回归，发现松驰曲线表达式与实验结果吻合良好，并得到了表征材料抗松驰性能的材料松驰特征系数和剩余应力比，结果表明，温度越高，初始应力越大，应力松驰越明显：当温度在300－400℃，初始应力在260－360MPa时，NiTiNb的应力松驰很小，在高温下NiTiNb的抗松驰性能优于NiTiFe，更适合于高温下使用。     

40CrNi2MoV钢应力松弛特性研究

为获得４０ＣｒＮｉ２ＭｏＶ钢的高温松弛性能,对该材料进行了松弛试验研究。试验数据经回归和高通量得到了所有用于表征材料抗松弛性能的材料常数,并得到与试验结果吻合良好,可反映松弛全过程的松弛曲线表达式。试验结果表明,该材料具有良好的抗松弛性能。还对工程应用中的不同初应力,松弛应变速率和试验结果外推等问题进行了讨论,认为当材料的松弛极限较高时,在强度允许的条件下,有可能通过加大初应力来延长服役周期或减小     

螺栓材料1Cr10NiMoW2VNbN的应力松弛行为及预测模型

为了研究和预测国产螺栓材料1Cr10NiMoW2VNbN的长时应力松弛性能,对该材料进行了应力松弛试验.研究了环境温度、初应力对松弛行为的影响;分析了利用Hook-Norton模型、广义Maxwell模型、Logistic模型以及多项式模型进行长时数据外推的可行性.结果表明:温度对螺栓松弛行为影响最大,实验数据难以推断应力松弛极限存在;所建立的双对数多项式模型可以较好地外推松弛剩余应力.     

基于蠕变的高温构件应力松弛损伤模型

基于SchIottner-Seeley平均蠕变断裂速率原理和松弛方程,构建了应力松弛损伤模型;采用该模型对高温紧固材料1Cr10NilMoW2VNbN进行了损伤预测和实验验证.结果表明,该模型预测的数据与实际试验结果吻合较好.     

TMSR-LF1停堆系统高温螺栓连接结构应力松弛分析与结构安全评定

钍基熔盐液态堆(Thorium Molten Salt Reactor-Liquid Fuel 1,TMSR-LF1)停堆系统螺栓连接结构服役环境约在650°C的高温区域,连接结构包括三种材质的构件;升温过程热膨胀以及高温下寿期内的蠕变效应,对螺栓的预紧力都有很大影响。本文采用ANSYS程序,对TMSR-LF1停堆系统高温螺栓连接结构,在预紧载荷及热膨胀组合作用下的结构进行了应力分析和寿期内蠕变应力松弛分析。考虑从常温升高至工作温度的过程中,连接结构件由于使用不同材料,其热膨胀差导致预紧力发生变化的过程;着重研究分析运行寿期内螺栓结构材料的高温蠕变,所引起应力松弛的变化规律,及其对螺栓连接结构预紧力的影响;并根据ASME-III-5-HBB规范对螺栓进行力学分析和应力评定,论证该螺栓连接件全寿期内结构安全可靠。     

N18锆合金的单轴拉伸和应力松弛性能

本工作试验研究20~700℃、不同应变加载速率下N18锆合金的单轴拉伸和应力松弛性能。结果表明，N18合金的单轴拉伸应力-应变曲线出现明显的屈服拐点，且温度低于500℃时呈现后继屈服强化，高于500℃后又呈后继屈服软化。除横向试样的断面收缩率高于轧向试样外，试样取向对N18合金的单轴性能影响不大。温度低于300℃时，N18合金的应变速率敏感性受温度的影响不大；350℃时，N18合金的敏感系数达到最小值，其后，对应变速率的敏感性随着温度的升高逐渐增强。N18合金在不同温度和应变水平下均产生明显的应力松弛。在300℃以内，最大应力松弛程度受温度影响较小，且随应变水平的增大明显降低；在350~550℃范围内，应变水平越高，对应的最大应力松弛程度越大；N18合金的最大松弛程度在350℃附近出现最小值。在350~450℃范围内，N18合金表现出明显的动态应变时效特性。     

7AXX铝合金在热压缩状态下的流变行为

研究7AXX铝合金在热变形过程中的流变行为对于提高专用设备锻件综合性能、避免材料热开裂有重要意义。本文利用Gleeble-3500热模拟试验机在变形温度360～460 ℃、应变速率0.001～1 s^-1的条件下，对7AXX铝合金铸锭进行高温压缩实验，研究了热压缩状态下温度和应变速率对该合金流变行为的影响程度，拟合得到了含Zener-Hollomon参数的7AXX铝合金流变应力表达式，建立了基于双曲正弦关系的合金热变形本构方程及热加工图。结果显示，变形温度及应变速率对7AXX铝合金的流变行为有显著影响。合金的流变应力随温度的升高而降低，随应变速率的增加而增加。合金在热压缩过程中的应力指数为3.21，热激活能为137.31 kJ/mol。变形温度385～450 ℃、应变速率0.01～0.1 s^-1是适用于7AXX铝合金的热加工条件范围。     

6XN不锈钢与825合金的高周疲劳行为研究

采用旋转弯曲疲劳方法完成了6XN不锈钢与825合金在室温和550℃空气中的高周疲劳试验。结果表明:室温时,6XN不锈钢的耐久极限应力大于825合金的耐久极限应力,与静强度顺序一致;550℃高温时,试样氧化速率增加,材料疲劳寿命降低,6XN不锈钢的疲劳寿命下降趋势较大,耐久极限应力接近825合金的耐久极限应力;6XN不锈钢对温度更敏感,而825合金对应力循环次数更敏感;与经验公式比较,2种材料具有较好的抗高周疲劳性能;疲劳过程为裂纹源产生、扩展和断裂,最后断裂区具有韧窝特征。     

氩气保护条件下微小试样的高温蠕变行为研究

高温蠕变性能是反应堆材料性能评价的一个重要指标,为降低试验成本、辐射剂量及加强辐照试验的穿透度,用非常规微小试样已成为试验研究的趋势。用微小片状试样进行高温蠕变试验。为避免高温氧化对材料性能数据的影响,用自主设计改进的带氩气保护装置的高温蠕变机,研究超临界水堆包壳候选材料镍基合金C276在氩气保护条件下的高温蠕变行为。根据实验数据得到不同应力水平下的高温蠕变曲线,分析蠕变机理,评价材料的蠕变性能。     

镍基合金825在超临界水中的腐蚀性能研究

研究了镍基合金825在550 ℃/25 MPa、600 ℃/25 MPa和650 ℃/25 MPa超临界水（SCW）中的应力腐蚀开裂敏感性,以及在超临界650 ℃/25 MPa、次临界290 ℃/15.2 MPa水中的均匀腐蚀性能。通过慢应变速率拉伸实验得到了相应的应力-应变曲线,结果表明,随温度的升高,825的机械强度和塑性逐渐下降;实验后试样的SEM图像表明,825在3种工况下的应力腐蚀开裂倾向大小关系为600 ℃＞550 ℃＞650 ℃。825在SCW条件下的腐蚀实验表明,其腐蚀增重大致符合幂函数生长规律;而其在次临界条件下的腐蚀增重变化却呈现出先减后增的特征。     

Evaluation of dielectric relaxation parameters from TSDC analysis of pristine and ion irradiated kapton-H polyimide

The TSD currents of pristine and 75 MeV oxygen ion irradiated kapton-H polyimide were obtained in the temperature region 20-250 °C. The samples were polarized under different temperature windows (temperature regions in the absence of electric field) termed as window-I (75-55 °C) and window-II (90-75 and 55-20 °C). The TSDC characteristics consist of two current maxima termed as β′-peak and β-peak around 30 and 120 °C, respectively. The peak magnitude significantly depends on temperature windows. The strength of the β′-peak and β-peak is being affected in opposite modes in the pristine and ion irradiated samples, as pristine samples show an enhancement in the β′-peak while there appears a suppression in the β′-peak in case of ion irradiated samples. The precise determination of the dielectric relaxation parameters has been made by elementary Debye processes.     

钛酸钡中极化团簇的特征弛豫时间随温度的变化规律

BaTiO3中存在极化团簇已经被大量实验所证明,并且极化团簇的空间、时间信息以及随温度的演化信息对介电性质有着重要影响。因此探测BaTiO3中极化团簇的相关信息对于理解其功能和揭示相变机理具有重要意义。本实验利用光子相关谱方法,在精确温控的条件下,观测到BaTiO3中300nm周期长程极化团簇微秒量级的特征弛豫时间τc,并揭示了该时间在TC附近4K温度范围内变化的细节特征。实验表明光子关联谱是研究铁电动力学的有效方法。     

Relaxation of surface tracks on polycarbonate thin films induced by MeV heavy-ion impacts

In the present work, the relaxation behavior of nanometer-sized deformations produced by single ion impacts on the surface of monodisperse (M_w = 60,000 u) polycarbonate thin films was investigated at temperatures close to and below the glass transition. The relaxation functions for the length, height and width of the deformations were well described by a stretched exponential law, with characteristic relaxation times τ strongly dependent on temperature. For T > 100 °C, the temperature dependence of τ obeys a Vogel-Fulcher law, but for lower temperatures it becomes less steep and tends to an Arrhenius-type behavior.     

New Evidence of Relaxation in High-β Plasmas Driven by Rotating Magnetic Fields

New evidence of relaxation in high-β plasmas has appeared in the steady-state field reversed configuration sustained by rotating magnetic fields, as signified by the self-generation of a significant toroidal field, with spontaneous transition to a higher confinement state. Detailed internal magnetic measurements reveal that the transition occurs at the onset of low-frequency drift modes. The final relaxed state exhibits the following key properties: (1) a near-force-free state in the core region, (2) a large q ∼ 1 along with significant magnetic shear near the magnetic axis, and (3) significantly improved confinement.     

μSR技术与穆斯堡尔谱学

本文对近年来发展起来的μSR技术(μ子自旋转动)进行了介绍,并与穆斯堡尔谱学进行了比较,最后讨论了μSR技术在磁学中关于内磁场的测量和自旋动力学方面的研究应用。     

Density functional theory study of H,C and O chemisorption on UN(001) and(111) surfaces

We performed density functional theory calculations of H, C, and O chemisorption on the UN(001) and(111) surfaces using the generalized gradient approximation(GGA) and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof(RPBE) exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN(001) and UN(111) surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06,25.50 and 27.34 kJ/mol for UN(001) surface, respectively. From the point of adsorbent(UN(001) and UN(111)surfaces in this paper), interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN(001) surface, U-N bond lengths change relatively little( 9%) as a result of H chemisorption, however C and O chemisorptions result in remarkable changes for U-N bond lengths in interlayer( 10%). Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C,and O atoms are all Bridge(or Hollow) position for the UN(111) surface. Calculated electronic density of states(DOSs) demonstrate electronic charge transfer between s, p orbitals in chemisorbed atoms and U 6d, 5f orbitals.     

Density functional theory study of H,C and 0 chemisorption on UN（O01） and （111） surfaces

We performed density functional theory calculations of H, C, and O chemisorption on the UN（001） and （111） surfaces using the generalized gradient approximation （GGA） and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof （RPBE） exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN（001） and UN（111） surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06, 25.50 and 27.34 kJ/mol for UN（001 ） surface, respectively. From the point of adsorbent （UN（001） and UN（111） surfaces in this paper）, interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN（001） surface, U-N bond lengths change relatively little （〈 9%） as a result of H chemisorption, however C and O chemisorptions result in remarkable changes for U-N bond lengths in interlayer （〉 10%）. Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C, and O atoms are all Bridge （or Hollow） position for the UN（1 11） surface. Calculated electronic density of states （DOSs） demonstrate electronic charge transfer between .9, p orbitals in chemisorbed atoms and U 6d, 5f orbitals.     

Shear viscosity of nuclear matter

This paper reports my recent studyIll on the shear viscosity of neutron-rich nuclear matter from a relaxation time approach. An isospin- and momentum-dependent interaction is used in the study. Dependence of density, temperature, and isospin asymmetry of nuclear matter on its shear viscosity have been discussed. Similar to the symmetry energy, the symmetry shear viscosity is defined and its density and temperature dependence are studied.     

两相自然循环非线性特征及实验研究

采用均相模型,基于分岔理论预测了两相自然循环系统的流量漂移(静态分岔)相关特性,并对其进行了实验验证.同时,对系统的动态参数时序进行了时域和频域分析,研究了特定工况下沸腾喷发弛张动态不稳定性机理.通过对系统相关时序的相空间重构与分维分析,探讨了系统随加热功率变化的非线性演化规律.