Specific heat of the antiferro/ferro-magnet NpGa3

The specific heat of NpGa₃ has been measured for the first time. The magnetic transitions and more generally the full magnetic phase diagram have been re-established precisely. The Sommerfeld coefficient and the magnetic entropy point to a rather localized system, in agreement with previous studies, in particular high pressure Mössbauer and resistivity. The comparison with other NpX₃ suggests that NpGa₃ is the most localized member of the series.     

On the proper characterization of tooling motions and initial conditions in powder die compaction modeling

The present paper is concerned with the finite element modeling of Powder Metallurgy (P/M) cold die compaction process. Rather than on material constitutive theories or on numerical algorithmic issues, attention is confined exclusively on an scarcely addressed issue in the P/M modeling literature: the proper characterization of the boundary (tooling motions) and initial conditions of the problem. A case study of the compaction of an axially symmetric multilevel adapter in an advanced CNC press machine is used to convey the relevance of the accurate representation of these input data in the quality of model predictions. It is shown that unawareness or deliberate simplification of apparently insignificant details in this respect may cause errors far overshadowing those introduced by deficiencies in either the constitutive model or in the corresponding algorithmic solution procedure. The discussion of this case study serves also to provide useful modeling guidelines; illustrate frequent difficulties, as the unavailability of some information when guessing starting conditions; and reveal subtle, yet relevant for modeling purposes, technical details of advanced CNC press machines.     

The orthogonal meshless finite volume method for solving Euler–Bernoulli beam and thin plate problems

In this paper a new method untitled “orthogonal meshless finite volume method” (OMFVM) is developed for solving elastostatic problems in Euler–Bernoulli beam and thin plate. In this method, the weak formulation of a conservation law is discretized by restricting it to a discrete set of test functions. In contrast to the usual finite volume approach, the test functions are not taken as characteristic functions of the control volumes in a spatial grid, but are chosen from a Heaviside step function. The present approach eliminates the expensive process of directly differentiating the OMLS interpolations in the entire domain. This method was evaluated by applying the formulation to a variety of patch test and thin beam problems. The formulation successfully reproduced exact solutions. Numerical examples demonstrate the advantages of the present methods: (i) lower-order polynomial basis can be used in the OMLS interpolations; (ii) smaller support sizes can be used in the OMFVM approach; and (iii) higher accuracies and computational efficiencies are obtained.     

Bending of Delaminated Composite Conoidal Shells under Uniformly Distributed Load

Conoidal shells are very popular roofing units owing to their aesthetic elegance and stiffness. Many parts of the globe, which were earlier assumed to be seismologically stable, are now being considered as earthquake prone. Hence the necessity to build light structures using composites has become very important. In this paper an eight-noded isoparametric shell element is applied for analyzing the bending behavior of delaminated composite conoidal shells under a uniformly distributed load with different practical boundary conditions. To ensure compatibility of deformation and equilibrium of forces and moments at the delamination crack front, a multipoint constraint algorithm is incorporated, which leads to an unsymmetrical stiffness matrix. This formulation is validated through the solution of benchmark problems. Lamination, curvature, and extent of delamination area are varied to compare the performances of delaminated conoidal shells against those with no damage. The results are carefully observed, and a set of conclusions is presented at the end of the paper.     

A 3D multilevel model of damage and strength of wood: Analysis of microstructural effects

A 3D hierarchical computational model of damage and strength of wood is developed. The model takes into account the four scale microstructures of wood, including the microfibril reinforced structure at nanoscale, multilayered cell walls at microscale, hexagon-shape-tube cellular structure at mesoscale and annual rings at the macroscale. With the use of the developed hierarchical model, the influence of the microstructure, including microfibril angle (MFA), the cell shape and the wood density (annual ring structure), differences between earlywood and latewood as well as microstructural arrangements and cellulose strength distributions on the tensile strength of wood is studied numerically. Good agreement of the theoretical results with experimental data has been obtained.     

On the mechanical characterization of materials by Arcan-type specimens

The simple circular notched specimen was originally proposed by Arcan to characterize the elastic properties of fibre-reinforced composites. Unfortunately, its optimized geometry does not allow to measure with reasonable accuracy both the material shear strength and the conditions of failure under a generic biaxial stress state, since the effects of stress concentration on the fillets of the two V-grooves and on the inner circular edges are responsible of premature fractures due to the uniaxial stress states of the notch edges.In a previous numerical study carried out by a parametric two-dimensional finite element model, some of the Authors of this paper found a new optimal geometry of the Arcan specimen able to minimize the notch effect and achieve a uniform pure shear stress field in the gauge cross-section. In the present paper, starting from such a geometry, a new type of Arcan specimen is proposed, having not uniform thickness. An extensive three-dimensional parametric finite element analysis has been done to define its optimal shape. The numerical results show that the new specimen is able to achieve, with a higher probability, material fracture in the minimum cross-section under a pure shear stress distribution which is more uniform than those acting in the Arcan specimen typologies until now proposed.     

A practical procedure to assess critical defects in pressure vessels subjected to fatigue loads

PSA pressure vessels are equipments used in refining industries for cleaning the hydrogen upcoming from the reforming or hydrogen generation unities. In one regular inspection, some embedded cracks were found in the entrance nozzle-head weld. Then, instead of advance its decommissioning and waste much time until the refinery purchase a new vessel, a structural stress analysis using the finite element method was performed in order to obtain the stress field at the site of the crack, considering the real loading cycle. Despite the acting load is only the internal pressure, the nozzle-head weld is a region where a complex stress state is present (bending and axial stresses). ASME VIII Division 2, Appendix 5 addresses this issue by applying a rule for multiaxial fatigue life estimation for non-proportional loading. With ASME estimated fatigue life results, it was applied the British Standard 7910 procedure to decide if the equipment can operate safely. The calculation also assesses the crack growing by using a modified bi-linear Paris law. Finally, it was computed how long the cracks would take to get to their critical size and then retire definitively the equipment.     

软模板法合成有序介孔材料的研究进展

有序介孔材料具有高度有序的孔道结构,较高的比表面积和较多活性位,已经广泛应用于气体吸附、催化剂和功能材料等领域。本文系统评述了软模板法制备有序介孔材料的合成路线及其组装机理,并对课题组采用软模板法组装介孔氧化钛粒子的机理进行了分析。     

有限元法在标准电容器电场计算中的应用

本文在分析国外标准电容器有关资料和多年来积累的研究和制造500kV及以下标准电容器经验的基础上，对高压标准电容器的绝缘结构进行了大量的研究工作，并用FORTRAN语言编制了有限元法进行标准电容器电场分析和计算的软件。该软件可用于对标准电容器电场的分析计算和优化设计。是研究开发高压标准电容器的有效工具。     

新型发射极指组合结构功率SiGe HBT热分析

提出了一种发射极指分段和非均匀发射极指长、指间距组合的新型器件结构,以改善多指功率硅锗异质结双极晶体管(SiGe HBT)的热稳定性。考虑器件具有多层热阻,发展建立了相应的热传导模型。以十指功率SiGe HBT为例,运用有限元方法对其进行热模拟,得到三维温度分布。与传统发射极结构器件相比,新结构器件最高结温从416.3 K下降到405 K,各个发射指上的高低温差从7 K～8 K下降为1.5 K～3 K,热阻值下降14.67 K/W,器件整体温度分布更加均匀。