铝合金梁受低速撞击动态响应的试验研究

梁受横向撞击时,其撞击力、局部变形和整体变形等动态响应受到撞击体质量、撞击速度、撞击位置以及梁刚度特性等因素的影响,研究这些参数对动力响应以及对撞击局部效应和整体效应的影响规律,是合理提出抗撞击防护手段的基础。该文利用低速落锤冲击试验装置进行了铝合金梁横向撞击试验,着重研究不同撞击速度、撞击位置和试件刚度等因素对铝合金梁所受撞击力、整体与局部变形、应变与能量等的影响规律。实验结果表明:随着撞击速度的增加,试件吸收能量的速率增大,撞击力幅值不断增加,撞击荷载主峰值段的持续时间减小;试件的整体变形和局部变形都明显增大,但局部效应相对增加更为显著;随着试件刚度（厚度）的增加,试件受相同速度撞击的吸收能量速率增大,撞击力荷载峰值显著增加;试件整体变形减小,而局部变形增加,说明试件刚度越大,其撞击整体效应减弱,而局部效应增强;试件受撞击后整体变形与撞击力相比明显具有滞后性,表明整体效应滞后于局部效应。     

Molecular mechanics studies on MFI-typezeolites: Part 3. The monoclinicorthorhombic phase transition

The transition of the all-silica MFI structure from monoclinic toward orthorhombic symmetry isexamined with our molecular mechanics force field for all-silica zeolites. From experimental measurements, it is known that the symmetry of the framework changes from monoclinic (space group P2₁/n.1.1.) toward orthorhombic (space group Pnma) by increasing the temperature above 340 K. The experimentally observed change in the geometry of the zeolite is compared with that calculated by molecular mechanics. The phase transition is accompanied by a shift of (100) pentasil layers.     

基于柔度法梁模型的盾构隧道衬砌结构纵向变形计算方法

由于纵向力及螺栓屈服等因素的影响,盾构隧道衬砌结构的纵向抗弯刚度沿隧道轴线分布并不均匀。针对该问题,引入隧道在附加沉降变形条件下的典型内力分布模式构造内力形函数,建立基于柔度法的盾构隧道衬砌结构纵向梁模型,并通过在轴向和环缝两个层次引入数值积分方法进行求解;基于该模型,得到了在柔性边界和刚性边界两种典型边界下沿隧道轴线的环缝变形分布,并讨论了数值积分策略对于计算结果的影响。研究结果表明:纵向力和螺栓屈服的影响在结构纵向变形计算中不可忽略,而考虑以上两点因素后,结构由于受局部集中变形的影响,位移模式将非常复杂,所提出的柔度法模型则能够避免传统刚度法模型在处理该问题上的局限性,从而用很小的计算代价获得较为精确的隧道结构纵向变形。     

AZ31 镁合金压痕-压平复合形变数值模拟

目的研究AZ31镁合金压痕-压平复合形变过程中工艺参数对形变区温度场、应力场、应变场、塑性变形力的影响规律。方法采用有限元模拟软件,对复合形变过程进行数值模拟研究,获得不同工艺参数条件下,温度场、应力场、应变场、塑性变形力的变化规律。结果在压痕形变过程中,随着形变温度的增大,形变区温度场的最高温度随之增大,最大塑性变形力的随之减小。在压痕形变过程中,随着模具温度的增大,形变区温度场的最高温度随之增大,最大塑性变形力随之减小。结论实验结果与数值模拟结果相吻合,说明数值模拟过程中的几何模型及相关参数设定是合理的。     

NaA分子筛改性聚砜超滤膜的通量及截留性能

利用溶液相转化法,在铸膜液中加入分子筛NaA和PEG来协同提高聚砜超滤膜的水通量和截留率,研究了分子筛的含量对聚砜超滤膜的形貌结构,表面粗糙度,水通量,蛋白质截留率和亲水性的影响。利用场发射扫描电镜、扫描探针原子力显微镜、膜评价仪和接触角仪分别对该膜的形貌、水通量、蛋白质截留率和亲水性进行表征。结果表明分子筛含量从0g增加到3.0g,聚砜超滤膜的水通量从140L/(m2·h)提高到500L/(m2·h),对胃蛋白酶的截留率从78.8%提高到92.7%,对牛血清蛋白的截留率从97.6%增加到99.0%以上。分子筛NaA可以协同提高聚砜超滤膜的水通量和蛋白质截留率。     

150MD24Z7.5高速电主轴多场耦合模型与动态性能预测

电主轴是机电一体化产品,充分考虑并预测其动态特性是机床主轴系统优化设计的前提。本文基于电主轴内部磁场、电场、温度场、结构场间的耦合关系,建立了150MD24Z7.5高速电主轴多场耦合有限元模型,通过电主轴电机电磁损耗及轴承摩擦生热计算,仿真电主轴温度场及结构场变化,讨论电主轴热态特性与振动特性之间耦合关系,分析电主轴温升热膨胀后气隙变化对振动特性的影响并通过实验加以验证。研究结果表明,电主轴温升形变对振动幅值影响较大,其中由气隙变化引起的电磁力幅值增加12.1%。利用该多场耦合模型可预测电主轴振动幅值,预测误差为10.2%。     

特长公路隧道取消变形缝试验研究

结合包家山隧道的施工情况,利用数值模拟和现场试验两种方法,对设置变形缝和不设置变形缝两种工况下衬砌结构的受力、变形及安全性进行了对比分析.研究认为:a.无论设置变形缝与否,隧道纵向的安全性要求均能满足.b.对于隧道结构的横向安全性,不设置变形缝时,Ⅴ级围岩端的安全系数增加,Ⅳ级围岩端的安全系数减小,此时需要进行配筋;设置变形缝时,Ⅳ级和Ⅴ级围岩处的拱顶安全系数均较小,不能满足安全要求,此时需要进行配筋.     

Localized indentation of sandwich panels with metallic foam core: Analytical models for two types of indenters

Sandwich structures with metallic foam core are sensitive to local indentation because of the low strength of the core and low bending stiffness of the thin face sheets. In this paper, local indentation response of sandwich panels with metallic foam core under a flat/spherical indenter was analyzed. The composite sandwich is modeled as an infinite, isotropic, plastic membrane on a rigid-plastic foundation. For simplicity, a quadratic polynomial displacement field was employed to describe the deformation of the upper face sheet. By using the principle of minimum work, explicit solutions for the indentation force and the sizes of the deformation regions were derived. The analytical results were verified by those from simulation by using the ABAQUS code, and they are in close agreement. Distribution of radial tensile strain of the upper face sheet and the ratio of energy dissipation of foam core to that of the upper face sheet were analyzed.     

沸石分子筛膜研究新进展

介绍了6种沸石分子筛膜及其结构，评论了沸石膜的合成方法，综述了沸石膜的发展和应用，展望了沸石膜的发展前景．     

Substrate and Fe-doping effects on the hydrophilic properties of TiO2 thin films

Titanium dioxide films are known for their hydrophilic and photocatalytic characteristics. Increasing specific surface area and doping can enhance their photocatalytic activity and hydrophilicity. We report here results regarding the enhancement of the photocatalytic properties of titania by both controlling surface morphology and the anatase/rutile ratio. The samples were deposited on glass, indium tin oxide covered glass, and SrTiO₃ by sputtering and laser ablation techniques. Film structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy. Film hydrophilicity was assessed from contact angle measurements during- and post-irradiation with UV light. The contact angle data are discussed in terms of the synergic effects of surface morphology, structure and composition of the films.     

形变诱发纳米晶局域固态非晶化的研究进展

形变诱发纳米晶金属材料局域固态非晶化转变是近年来提出的获得局域固态非晶化组织的一种新途径,这种转变机制使得以位错、变形孪晶、晶界滑动和晶粒转动为主要变形机制的纳米晶材料中可能存在一种全新的塑性变形机制,并且,局域固态非晶化的临界转变条件和转变机制可为材料的结构优化设计提供依据。概括了国内外实验及数值模拟手段关于形变诱发局域固态非晶化转变的研究,例如采用机械球磨、高压扭转变形、经典力场和分子动力学等方法,证明了形变诱发局域固态非晶化转变的存在。此外,还分析了发生局域固态非晶化转变的内在机制。基于晶体相场模型的优势,提出用该方法模拟局域固态非晶化转变的突出之处,表明了晶体相场法能够有效研究局域固态非晶化转变过程。     

基于磁场变换器的双向加载式管件电磁翻边成形效果研究

目的 针对传统管件电磁翻边时,仅采用径向电磁力加载,翻边效果不够理想的问题,提出基于磁场变换器的双向加载式管件电磁翻边技术.方法 使用COMSOL软件构造二维轴对称分析模型,分析线圈参数的改变对径向、轴向电磁力和管件翻边效果的影响.在此基础上,进一步在电磁力、变形速率、管件变形轮廓3个方面将新型加载方式与传统管件电磁翻...     

凸模结构对大截面带筋方筒件挤压力的影响研究

目的 解决大截面铝合金带筋方筒构件在反挤压过程中成形力大的难题,实现在3 000 t压力机下成功制备内孔为665 mm×665 mm的大截面带筋方筒形构件。方法 提出了一种使用新型棱台凸模结构代替平凸模结构的方法,用主应力法得出了棱台凸模结构与平凸模结构的挤压力计算公式,对比分析了2种凸模结构反挤压成形力的大小,并用DEFORM有限元软件模拟分析了不同结构参数下的棱台凸模反挤压过程,最终进行工程试制,验证了反挤压工艺的可行性。结果 通过主应力法得出了方筒形件的变形力计算公式,得出棱台凸模结构反挤压成形力小于平凸模结构反挤压成形力,经模拟分析得出在反挤压过程中棱台凸模结构的最优结构参数为棱台斜角15°、棱台高度40 mm,并在3 000 t压力机上成功制得内孔为665 mm×665 mm的大截面带筋方筒形构件。结论 通过数值模拟分析可知,与采用平凸模结构相比,采用棱台凸模结构时的反挤压成形力降低了约13%,同时减少了挤压变形过程中的金属流动“死区”。经实验验证,在3 000 t压力机上成形了内孔为665 mm×665 mm的大截面带筋方筒形构件,实现了省力挤压。     

外伸悬挑组合式锅炉大板梁的静力试验及有限元模拟分析

为揭示外伸悬挑组合式锅炉大板梁的受力机理和破坏模式,并验证某工程大板梁的设计可靠性,通过对外伸悬挑组合式大板梁缩尺模型的静力试验和考虑各种非线性的ABAQUS有限元数值模拟分析,研究了大板梁简支段和悬挑段在各加载阶段的承载力、局部应力、整体变形和局部屈曲等关键响应,对试验中的破坏现象给出了合理解释,并重点研究了悬挑段与简支段拼接端板与拼接螺栓的受力和变形特点。试验与模拟结果均表明大板梁在设计荷载作用下处于线弹性阶段,并具有足够的安全储备;支座附近腹板局部屈曲和悬挑段端板拼接螺栓断裂是大板梁的主要破坏模式,决定了梁的整体承载力;按拼接螺栓群的受力模式,悬挑梁端的弯矩和剪力分别由翼缘附近螺栓的抗拉连接和腹板附近螺栓的摩擦连接来承担。各阶段试验现象和数值模拟结果吻合较好,也验证了数值模拟方法的可靠性。     

Force criterion for delayed failure of metastable austenitic steel

The phenomenon of delayed failure detected in metastable austenitic steels is connected with martensite formation during plastic deformation of austenite. In these steels a zone with a martensitic structure exhibiting a high level of residual internal microstresses develops ahead of a stress concentrator. In model representations a scheme has been suggested for distribution of deformation zones and stresses ahead of a stress concentrator. It is proposed that during delayed fracture a crack generates close to the boundary of plastically and elastically deformed martensite. A force criterion has been established for crack generation during delayed failure of metastable austenitic steel, i.e., the maximum local tensile stress (MLTS). The threshold value of the maximum local tensile stress does not depend on stress concentrator geometry and it is characterized by the tendency of metastable austenitic steel towards delayed failure.Central Scientific-Research Institute of Ferrous Metallurgy, Moscow. Translated from Problemy Prochnosti, No. 11, pp. 69–72, November, 1989.     

Creating Local Reinforcement of a Channel in a Composite Casting Using Electromagnetic Separation

This article presents a new method to obtain local reinforcement in near-surface layers of channels in castings made of a particle-reinforced metal matrix composite in the alternating electromagnetic field generated by an inductor placed inside the channel. In centrifugal casting, the centrifugal force on the particles leads to the formation of composite structures, while in the proposed method, the electromagnetic force field on the particles results in the designed structure of the composite casting. The article reports the experimental verification of this method using an aluminium sleeve reinforced locally with Si C particles at the inner wall.     

砰击荷载下金字塔点阵夹层板动力响应分析与估算

该文以轻质金字塔点阵夹层平板结构为对象,对其在不同撞水速度下(1m/s~6m/s)的流-固耦合动力学行为进行数值和理论计算分析。首先建立了气-液-固三相数值模型,通过详细计算获得了砰击压力的分布特征与结构砰击变形特征,分析表明当砰击压力脉宽和结构自振周期(湿模态)之比大于4时流-固耦合效应不显著。与同等质量实体板相比,轻质金字塔点阵夹层平板平均流-固砰击压力与结构最大变形均显著降低,而且存在#x0201c;局部气垫#x0201d;现象(在实体平板撞水的过程中未发现该效应)。提出一种将砰击变形位移场分解为总体变形和局部变形,然后进行叠加的计算模型,该种工程近似计算方法获得的变形估算值与数值计算结果吻合较好。     

Transport Phenomena in Zeolites in View of Graph Theory and Pseudo‐Phase Transition

Transport phenomena play an essential role in catalysis. While zeolite catalysis is widely applied in industrial chemical processes, its efficiency is often limited by the transport rate in the micropores of the zeolite. Experimental and theoretical methods are useful for understanding the transport phenomena on multiscale levels. Traditional diffusion models usually use a linear driving force and an isotropic continuum medium, such that transport in a hierarchical catalyst structure and the occurrence of nonlinear deactivation cannot be well understood. Due to the presence of spatial confinement and an ordered structure, some aspects of the transport in a zeolite cannot be regarded as continuum phenomena and discrete models are being developed to explain these. Graph theory and small‐world networks are powerful tools that have allowed pseudo‐phase transition phenomena and other nontrivial relationships to be clearly revealed. Discrete models that include graph theory can build a bridge between microscopic quantum physics and macroscopic catalyst engineering in both the space and time scales. For a fuller understanding of transport phenomena in diverse fields, several theoretical methods need to be combined for a comprehensive multiscale analysis.     

Micromechanical modeling of local field distribution for a planar composite under plastic deformation

Summary Due to statistical distribution of local material property, local stress and strain fields in a composite are random in nature. Classical micromechanical methods can only predict the average value of these local fields in different phases. An analytical method, which combines the maximum entropy theory and secant moduli method, is proposed in this paper. The distribution of the local field for a planar composite with plastic deformation is examined by the proposed method. The results show that with increase of plastic deformation the stress field in the matrix becomes more and more inhomogeneous. The predicted results on the stress distribution are in reasonable agreement with finite element simulation. Some salient features near the elastic and plastic deformation transition revealed by finite element simulation are also discussed.     

Phase field simulation of domain structures in cracked ferroelectrics

The fracture of ferroelectrics is a complex process which is influenced by various factors, among which are the domain switching near the crack tip, the crack face boundary conditions and the applied electric field. Domain switching near crack tips induces major local nonlinearity, while the crack face boundary conditions vary considerably due to different working conditions. In this work, a phase field model and a generalization of the configurational force theory into this model are used to investigate the microstructure around the crack tip and to quantitatively study the influence of the applied electric field and the crack face boundary conditions (permeable, impermeable, semi-permeable and energetically consistent). Evaluation of the fracture properties is done by the nodal configurational force at the crack tip based on the generalized configurational force theory. Results show that the induced domain structure relies significantly on the loading and on the surface boundary conditions. Among the four different conditions considered, the energetically consistent conditions lead to the smallest crack driving force, and the permeable conditions lead to the largest crack driving force. Calculations also show that positive electric fields tend to inhibit fracture, whereas negative electric fields tend to promote fracture.