Interferometer for cold neutrons

Design and setup of an interferometer for cold and ultracold neutrons are described. As neutron optical components three holographically produced gratings are arranged in triple Laue geometry. The gratings are adjusted during their recording process in photosensitized polymer slabs once for ever. Employing this device we measured the coherence function of a cold neutron beam by means of interferometry.     

Identification of ductile damage and fracture parameters from the small punch test using neural networks

This paper presents a method for the identification of deformation, damage and fracture properties of ductile materials. The small punch test is used to obtain the material response under loading. The resulting load displacement curve contains information about the deformation and failure behavior of the tested material. The finite element method is used to compute the load displacement curve depending on the parameters of the Gurson-Tvergaard-Needleman damage law. Via a systematic variation of the material parameters a data base is built up, which is used to train neural networks. This neural network can be used to predict the load displacement curve of the SPT for a given material parameter set. The identification of the material parameters is done by using a conjugate directions algorithm, which minimizes the error between an experimental load displacement curve and one predicted by the network function. The identified material parameters are validated by independent tests on notched tensile specimens. Furthermore, these parameters can be used to compute the crack growth in fracture specimens, which finally leads to a prediction of classical fracture toughness parameters.     

稀土元素对掺杂钨粉还原过程及性能的影响

利用中止还原的方法,研究了稀土元素对掺杂钨粉还原过程及其性能的影响。结果表明,在同样的还原工艺条件下,稀土元素能使掺杂钨粉的还原速率减小,分裂时间更晚,但最终的钨粉粒度更细小,可获得几百纳米的超细钨粉。还原后,粉末的形貌由准球形转变为规则的立方体形。稀土元素还促进钨粉中钾含量的提高。     

烧结NdFeB磁体强度和韧性研究现状

烧结NdFeB永磁材料具有磁性能高、价格低、生产工艺简单等突出优点，因而自其开发以来，生产和应用取得了快速发展，并且其市场还将不断扩大。但是，这种材料强度和韧性差，机械加工困难，应用过程中容易开裂。因此，改善烧结NdFeB永磁材料的力学性能已成为一个迫切的需要。综述了该种材料的断裂机制及在改善材料强度和韧性等方面所做的研究工作，认为通过添加合金元素，韧化晶界，细化主相晶粒，是一种有效的方法。研究表明，材料的断裂方式主要为沿晶断裂，晶界上的薄片富Nd相是引起沿晶断裂的主要原因，通过微量添加合金元素能有效改善磁体力学特性。     

Yielding of Microstructured Geomaterial by Distinct Element Method Analysis

The purpose of this paper is to present macro- and micro-study on the yielding of microstructured geomaterials by numerical experiments. This target is achieved by carrying out 63 one-dimensional and biaxial compressions tests on an idealized bonded geomaterial with an extension of distinct element method, into which bond contact models proposed were implemented. Numerical results indicate that: (a) preconsolidated pressure appears to attribute to bond and looseness in the geomaterials, and an increase in void ratio leads to a decrease in yielding stress in one-dimensional tests; (b) an increase in bonding strength at interparticle contacts results in an increase in yielding stress and cohesion, and an internal friction angle that is smaller than the critical state value; (c) the observed first-yielding (initiation of bond breakage) is stress path dependent, and gross-yield (defined with respect to volumetric strain) of microstructured geomaterials is evidently related to bond breakage.     

Dynamic Spar Elements and Discrete Element Methods in Two Dimensions for the Modeling of Soil-Inclusion Problems

Discrete element methods (DEMs) provide new numerical means to study the behavior of soil-inclusion systems. In some cases, however, the classic DEM fails to model specific aspects of the inclusions. That is why a model based on spar elements is introduced, designed specifically for inclusions. In this model, the movement of the inclusion is considered as a dynamic process and is computed step by step in the same way as in the DEM. The model can be coupled with a DEM code, thus enabling one to simulate the interaction between an inclusion and a disk assembly. Contact laws at the contacts between disks and spar elements describe the interface constitutive behavior. Finally, the results obtained by simulating a geosynthetic anchorage in two different ways are reported. In the first case the inclusion is represented by disks, while in the last case it is represented by spar elements. The comparison shows that spar elements are much more versatile and can simplify the calibration of the discrete models used to simulate soil-inclusion systems.     

Influence of Mesh Geometry on Three-Dimensional Finite-Element Analysis of Tunnel Excavation

Finite element (FE) analysis has become an important tool for predicting building response to tunnel-induced ground movement. Because tunnel construction is a three-dimensional (3D) process, the trend is to apply 3D FE analysis to tunnel-soil-building interaction problems instead of applying the plane-strain models that are commonly used in engineering practice. Since 3D FE analyses require large amounts of computational resources, the geometric dimensions of the 3D models are often kept to a minimum to reduce calculation time. There is, however, a lack of published information concerning appropriate mesh dimensions. This paper investigates the influence of the geometry and the dimension of a 3D FE model on tunnel-induced surface settlement predictions. The paper shows how the vertical boundaries can influence the results. It demonstrates that reasonable results can be obtained by increasing the length of incremental tunnel excavation and by scaling back the settlement values to give a required tunnel volume loss. This study therefore not only highlights the limitations of 3D modeling but also shows its potential for engineering practice.     

包钢CSP生产线HP295焊接气瓶用热轧钢带研制和开发

通过合理的化学成分设计和控制轧制、控制冷却技术的应用,包钢钢联公司薄板坯连铸连轧厂成功地开发和研制出了HP295焊接气瓶用热轧钢带,并对批量试生产产品的性能和金相组织进行了分析。     

奥氏体不锈钢中稀土的作用研究及应用前景

就稀土在奥氏体不锈钢的应用研究作简要综合评述。作为稀土资源的大国,开发具有我国资源特色新型高品质稀土不锈钢,具有十分重要的战略意义和很好的应用前景。     

Active control of forced vibrations in adaptive structures using a higher order model

This paper deals with a finite element formulation for active control of forced vibrations, including resonance, of thin plate/shell laminated structures with integrated piezoelectric layers, acting as sensors and actuators, based on third-order shear deformation theory. The finite element model is a single layer triangular nonconforming plate/shell element with 24 degrees of freedom for the generalized displacements, and one electrical potential degree of freedom for each piezoelectric element layer, which are surface bonded or embedded in the laminate.

The Newmark method is considered to calculate the dynamic response of the laminated structures, forced to vibrate in the first natural frequency. To achieve a mechanism of active control of the structure dynamic response, a feedback control algorithm is used, coupling the sensor and active piezoelectric layers. The model is applied in the solution of illustrative cases, and the results are presented and discussed.