Material modifications induced by swift heavy ions in NbTi superconducting wires

The Facility for Antiproton and Ion Research (FAIR) to be built at GSI in Darmstadt will be equipped with superconducting magnets. Due to the high ion beam intensities and related beam losses, radiation damage of the Cu/NbTi superconducting wires used in the magnet coils has to be considered. Here we report first experimental results on NbTi multifilament wires exposed to 2.6 GeV U ions at room temperature. Radiation-induced effects were examined using X-ray diffraction and transmission electron microscopy. With increasing ion fluence the amount of the α-Ti phase decreases. This is crucial because α-Ti precipitates are the main flux-pinning centres in the Nb–Ti superconducting alloy. The equilibrium hcp α-Ti transforms into the hexagonal ω-Ti phase.     

TEA-CO2激光辐照HgCdTe图像传感器的实验研究

利用TEA-CO₂激光对碲铬汞(HgCdTe)图像传感器的干扰和损伤现象进行了实验研究,分析了干扰和损伤机理。探测器上激光能量密度小于255 mJ/cm2时,饱和像素仅出现在光斑区域,激光能量密度为425.8 mJ/cm2时,像素被损伤,观察到了弥散斑和暗环等现象。建立了探测器的激光辐照模型,计算了探测器的温升,讨论了温升与载流子浓度、迁移率的关系。分析认为,弥散斑的出现是探测器升温产生的热激发载流子浓度扩散所致,暗环的出现是迁移率与载流子浓度扩散共同作用的结果,像素的损伤则是因为温升导致汞的析出。     

Fatigue behavior of cross-ply glass-fiber epoxy composites including the effect of fiber-matrix interphase

The effect of glass-fiber epoxy interface in cross-ply reinforced composites on the fatigue behavior is studied throughout this paper. The sensitivity of the interphase on fatigue life of cross-ply laminates is shown by a shift of the S-N curve to approx. 30% higher applied maximum loads for the composites with well-bonded fibers. Further, the damage as measured by stiffness reduction is more significant for the composites with poor bonded and commercial sized fibers than was found for EP sized ones. The loss energy is shown to be a sensitive tool to characterize the nature of fiber-matrix adhesion. The loss energy for composites with poor adhesion between fiber and matrix results in significantly higher amounts of consumed energy during a single stress-strain than those composites containing well-bonded fibers.     

赫兹型微裂纹光场调制增强作用的系统研究

通过改变裂纹的倾角、宽度和深度参数,模拟了赫兹型裂纹在不同参数下对光场调制能力的不同. 模拟发现,倾斜角度为20.9°到45°之间的裂纹危害最大,倾角大于45°小于48.2°的裂纹危害也十分大,而倾斜角度为45°时的裂纹危害最小. 对于30°倾角的赫兹型裂纹,一定范围内,赫兹型裂纹深度的增加会导致其光场调制增强能力呈二次方关系增加,但宽度的增加不会使其光场调制增强作用增加. 裂纹深度和宽度的增加可以用来近似裂纹的演化过程,所以裂纹的扩展导致了其光场调制能力的增加,进而导致损伤增长速率的加快,这和e指数损伤增长规律相符. 关键词： 损伤增长 亚表面缺陷 赫兹型裂纹 光场增强     

Microstructural modeling of asphalt concrete using a coupled moisture–mechanical constitutive relationship

The coupled effect of moisture diffusion and mechanical loading on the microstructure of asphalt concrete is studied. The traditional Continuum Damage Mechanics (CDM) framework is modified to model detrimental effects of moisture and mechanical loading. Adhesive/cohesive moisture-induced damage constitutive relationships are proposed to describe the time-dependent degradation of material properties due to moisture. X-ray two-dimensional (2D) computed tomography-imaging technique is used to construct finite element (FE) microstructural representation of a typical dense-graded asphalt concrete. After being calibrated against pull-off experiments, the proposed moisture-induced damage constitutive relationship, which is coupled to thermo-viscoelastic–viscoplastic–viscodamage mechanisms, is used to simulate the microstructure of asphalt concrete. Simulation results demonstrate that the generated 2D FE microstructural representation along with the coupled moisture–mechanical constitutive relationship can be effectively used to model the overall thermo-hygro-mechanical response of asphalt concrete.     

Multiscale modeling of irradiated polycrystalline FCC metals

We propose a set of models for the post-irradiation deformation response of polycrystalline FCC metals. First, a defect- and dislocation-density based evolution model is developed to capture the features of irradiation-induced hardening as well as intra-granular softening. The proposed hardening model is incorporated within a rate-independent single crystal plasticity model. The result is a non-homogeneous deformation model that accounts for defect absorption on the active slip planes during plastic loading. The macroscopic non-linear constitutive response of the polycrystalline aggregate of the single crystal grains is then obtained using a micro–macro transition scheme, which is realized within a Jacobian-free multiscale method (JFMM). The Jacobian-free approach circumvents explicit computation of the tangent matrix at the macroscale by using a Newton–Krylov process. This has a major advantage in terms of storage requirements and computational cost over existing approaches based on homogenized material coefficients in which explicit Jacobian computation is required at every Newton step. The mechanical response of neutron-irradiated single and polycrystalline OFHC copper is studied and it is shown to capture experimentally observed grain-level phenomena.     

THE FATIGUE CONSTITUTIVE MODEL OF CONCRETE BASED ON MICRO-MESO MECHANICS

该文致力于混凝土疲劳损伤发展机理的微细观解释. 以速率过程理论为基础,通过考虑裂纹断裂过程区中的水分子动力作用,在细观尺度上建立了具有物理机理的疲劳损伤能量耗散表达式. 结合细观随机断裂模型,以宏观损伤力学为框架,建立了疲劳损伤演化方程. 通过数值模拟,计算了单轴受拉时的疲劳损伤演化以及不同加载幅度下的疲劳寿命. 与相关试验结果的对比显示出该文模型能够很好地表现混凝土材料的疲劳损伤演化过程.     

HIFU治疗中换能器驱动电功率变化机制及规律*

高强度聚焦超声(HIFU)治疗中的驱动电功率对治疗效率起着非常关键的作用,驱动电功率控制的精准性势必会影响治疗的效率和安全性。前期研究表明：HIFU治疗过程中焦域瞬态物理特性的变化会导致换能器的负载阻抗发生变化,进而影响HIFU驱动电功率,但驱动电功率与焦域瞬态物理特性之间的影响关系及规律尚不明确。该文基于电压、电流传感器、空化检测探头和温度传感器等器件,构建了一种HIFU治疗中驱动电功率实时监测及焦域声空化、温度检测系统。基于该实验研究系统,以离体牛心组织作为HIFU辐照对象,分别研究了HIFU焦域温度变化、声空化及组织损伤与驱动电功率之间的变化关系及规律。研究结果表明：当焦域温度升高时,驱动电功率缓慢上升,驱动电功率与温度变化有良好的相关性;当空化产生时,驱动电功率出现明显的波动;当组织出现损伤时,驱动电功率呈陡然下降的变化。三种情景下,驱动电功率变化有明显区别,这有望为区分HIFU治疗过程中焦域处发生损伤和空化以及实时监测靶组织损伤程度提供一种新的解决方案。     

ON THE MANAGEMENT OF INTERCONNECTED WILDLIFE POPULATIONS

Abstract Economic interdependency of wildlife or fish stocks is usually attributed to ecological interdependency, such as predator–prey and competitive relationships, or to density‐dependent migration of species between different areas. This paper provides another channel for economic interdependency of wildlife where density‐independent migration and market price interaction affect the management strategies among different landowners. Management is studied under three market conditions for selling hunting licenses: price taking behavior, monopoly market, and duopoly market. Harvesting of the Scandinavian moose is used as an example. The paper provides several results on how economic interdependency works through the migration pattern. When a duopoly market is introduced, hunting license price interaction among the landowners plays an additional role in determining the optimal harvesting strategy.     

循环爆炸作用下地下洞室的动态响应及损伤累积

为研究循环爆炸对地下洞室的影响,基于相似模型试验,采用通用有限元软件ABAQUS对比研究了洞室拱顶高水平单次爆炸和低水平10次循环爆炸作用下地下洞室围岩的应力波衰减规律、损伤累积规律及洞壁位移和环向应变分布特征。结果表明:循环爆炸中,洞室围岩的应力波衰减速度随着爆炸次数的增加先减小后增大。单次爆炸中,洞壁环向峰值应变从拱顶至直墙脚由拉应变转为压应变;循环爆炸中,随着爆炸次数的增加,拱顶环向峰值应变由压应变转为拉应变。爆炸荷载总水平相同时,低水平循环爆炸中洞室围岩的损伤面积和程度比高水平单次爆炸大。循环爆炸中,围岩的损伤累积呈现不可逆的逐级增加趋势,且累积损伤和爆炸次数之间呈明显的非线性关系。