On background Cells during the Analysis of Bulk Forming Processes by the Reproducing Kernel Particle Method

The reproducing kernel particle method based on the irreducible flow formulation is utilised to perform the numerical simulation of bulk metal forming processes. Emphasis is given on analysing the influence of employing triangular or quadrilateral background cells on the predictions of material flow, forming load and distribution of strain. A new proposal to smooth the distribution of average stresses during stress computations in the background cells is also included. The effectiveness of the proposed method is discussed by comparing its numerical predictions with a benchmark test case, finite element calculations and experimental data. The benchmark test case is included with the objective of illustrating the influence of several theoretical and numerical subjects such as; order of the basis correction functions, dimension of the compact support and computation of the volume associated to each nodal point. Experimental data was acquired from metal forming controlled laboratory-based tests that were designed so that the proposed method could be tested on its ability to efficiently handle large plastic deformations. It is shown that adaptive arbitrary triangular background cells are capable of efficiently handling large plastic deformations without remeshing.     

A NURBS-based Error Reproducing Kernel Method with Applications in Solid Mechanics

A novel method for derivation of mesh-free shape functions is proposed. The first step in the method is to approximate a function and its derivatives through non-uniform-rational-B-spline (NURBS) basis functions. However since NURBS functions neither reproduce polynomials of degree higher than one nor interpolate the control points (also referred to as grid or nodal points), the approximated function leads to uncontrolled errors over the domain including the nodal points. Accordingly the error function in the NURBS approximation and its derivatives are reproduced via a family of non-NURBS basis functions. The non-NURBS basis functions are constructed using a polynomial reproduction condition and added to the NURBS approximation of the function obtained in the first step. Since any desired order of continuity in the approximation can be achieved through NURBS, the proposed error reproducing kernel method (ERKM) can even approximate functions with discontinuous derivatives. Moreover, thanks to the variation diminishing property of NURBS, it has advantages in representing sharp layers without the so-called Gibbs‘ or Runge’s phenomena. Since derivatives are reproduced within polynomial spaces of appropriately reduced dimensions, differentiability requirements of the kernel functions are avoided. Any compactly supported continuous function, monotonically decreasing on either side of its maximum, may be used as the weight function (unlike other mesh free approximations). As it turns out, a target function is mainly approximated via NURBS and error functions are just supposed to add corrections, whose magnitudes are typically an order less than those of the NURBS components. The proposed method is observed to be nearly insensitive to the support size of the weight function. The proposed method is next applied to some linear and nonlinear boundary value problems of typical interest in solid mechanics. Some of these results are compared with those obtained via the standard form of RKPM. In the process, the relative numerical advantages and accuracy of the new method are brought out to an extent.     

采用比较法研制二级气体标准物质

以氮中二氧化碳二级气体标准物质的研制为例,探讨采用比较法研制二级气体标准物质及其不确定度的分析计算,其中标准物质的制备采用称量法配制,并对所研制的样品进行了均匀性、稳定性试验,结果表明,所研制的氮中二氧化碳气体的标准物质在一年的考察期内,其均匀性、稳定性、量值不确定度均达到国家二级标准物质要求,符合申报条件。     

Application of Reproducing Kernel Hilbert Spaces to a Minimization Problem with Prescribed Nodes

The theory of reproducing kernel Hilbert spaces is applied to a minimization problem with prescribed nodes. We re-prove and generalize some results previously obtained by Gunawan et al. [2,3], and also discuss the Hölder continuity of the solution to the problem.     

Particle size induced heterogeneity in compacted powders: Effect of large particles

We investigated the effect of particle size distribution on heterogeneity of compacted powders. We used experiments and discrete particle based simulations to compact powders, test the mechanical strength of the compact, and study the microstructure of the compact. A metallic powder which has a wide particle size distribution was used in the experiments. We found that the compaction profile is not reproducible when particles larger than 1/6 of the die diameter are present in the powder sample. The presence of these large particles generate a highly heterogeneous inter-particle contact and bonding forces. The discrete particle simulations showed that for these heterogeneous compacts the tensile strength exhibits high variability, even for one compact if the diametrical compression force is applied along different axes. Based on these results, it is recommend that the largest particle in a powder compact should not exceed one sixth of the die diameter, which is the same as the recommendation of ASTM International D4767 - 11 for compression test of cohesive soils.     

溶胶凝胶法制备二氧化钛微粉体

对二氧化钛微粉体的溶胶 凝胶法最佳制备工艺条件进行了探讨,其中溶液温度和ｐＨ 值对二氧化钛水溶胶的形成和稳定性具有较大影响,研究了二氧化钛微粉体的表面性质,ＳＥＭ 分析和孔径分布测定表明,本方法制备的二氧化钛微粉体粒子外观呈球形,其粒径以７０ ～９０Ａ 为主     

氦中氪氙气体标准物质研制

论述了静态体积法制备氦中氪、氙气体标准物质的方法、稳定性参考值,不确定度计算方法。该研制方法可行,数值准确可靠。     

标准气体中组分绝对含量推算方法的探讨

探讨了标准气体中组分绝对含量定值的一种数学方法,该方法能推算出组分绝对含量且不受分析仪器采用载气纯度和色谱标样的影响.     

应对欧V排放检测标准相关气体标准物质的研制

主要叙述了为应对欧V排放检测标准所使用的氮中一氧化碳、氮中一氧化氮和氮中丙烷气体标准物质的研制方法,同时描述了用气相色谱仪和氮氧化物分析仪对配制的氮中一氧化碳、丙烷、一氧化氮三种标准物质进行浓度检测的过程,并介绍了进行均匀性、稳定性考察的方法,保证测定数据准确可靠。配制的氮中一氧化碳、氮中丙烷气体标准物质浓度分别为1．00μmol／mol,不确定度3％。氮中一氧化氮浓度为（1．00—25．0）μmol／mol,不确定度6％。     

水热法在无机粉体材料制备中的研究进展

综述了水热反应机理、影响水热反应的主要因素及水热法制备无机粉体材料的研究新进展，并对水热法在无机粉体材料制备中的发展前景进行了展望。     

甲烷中微量气体标准物质分析方法研究及量值的比对

建立了甲烷中微量气体标准物质的分析方法和实验条件;考察了该分析方法的不确定度;得出甲烷中微量气体标准物质浓度在(1 ～50)×10-6(mol/mol)范围内,方法不确定度小于1％的实验结果.实验过程对重量法制备的系列气体标准物质量值进行了分析方法的比对,一致性验证结果在1％内吻合.该项研究成果代表国家最高实验室参与了...     

基于模型定义技术的工序模型建模方法研究与实现

为了准确、关联、快速、可控地创建出模型定义技术环境下的零件三维工序模型,采用零件设计模型到毛坯模型的倒推法.首先以不同的加工表面有序地规划成品到毛坯的逆过程;然后创建毛坯模型,并衍生出工序模型,输出关联工序模型的工艺卡片;最后以某一主轴盖为例验证此方法的有效性.     

有限元仿真在压电陶瓷粉末模压成型中的应用

介绍了压电陶瓷粉末模压成型的研究现状,以及粉末材料有限元仿真所用的Drucker-Prager-Cap连续模型和屈服准则。基于有限元仿真法,论述了模压过程中摩擦行为、加载行为等工艺参数对成型坯体内部密度、应力分布的影响,并介绍了有限元法在模压改进工艺中的研究进展。     

粉末高温合金中夹杂物特性及与不同成型工艺的关系

全面研究了FGH95粉末高温合金原始粉末和粉末处理过程中夹杂物的性质(成分、分类和形貌),分析了其数量和来源,研究了夹杂物在不同成型工艺下的变形特征,讨论了解决夹杂物问题的方法.     

Lanxide技术合成含烧结助剂的复合AIN粉体

高纯度的氮气中,以Al-Mg-Y合金为母合金,利用Lanxide技术合成了含烧结助剂Y_2O_3的复合AIN粉体.通过扫描电镜、X射线衍射、粒径分析及化学成分分析等检测手段对氮化产物进行表征.实验结果表明,合金氮化反应完全,氮化产物疏松易于粉化.粉化后获得的复合AIN粉体具有纯度高,氧杂质含量低,粒度细小等优点.     

Sintering Aids in the Consolidation of Boron Carbide (B4C) by the Plasma Pressure Compaction (P2C) Method

Boron carbide (B₄C) powder has been densified by a novel method of powder consolidation known as Plasma Pressure Compaction (P²C). The P²C technique allows for rapid consolidation of powder by Joule heating of the powder bed. Powder is placed in graphite dies, and uniaxial pressure and low-voltage, high-amperage (10 V, 5000 amps maximum) direct current are applied to achieve densification. Pure B₄C powder was consolidated at lower temperature and hold time to densities equal to those achieved by conventional hot pressing. With the addition of a small amount of alumina (Al₂O₃) as a sintering aid, densities as high as 97% theoretical were attained.     

板料成形数值模拟有限元求解算法

正确选用有限元求解算法是成形模拟成功的关键技术之一。阐述了板料成形数值模拟的4种有限元求解算法,即静力隐式算法、动力显式算法、静力显式算法和一步成形法,并对这4种算法进行了论述和比较,介绍了其在实际中的应用,探讨了在板料成形模拟中如何选择有限元算法进行可靠、高效的有限元分析。     

熔盐法在无机材料粉体制备中的应用

介绍了一种新的无机材料粉体的制备方法熔盐法,以及该方法的部分应用.以该方法制备无机材料粉体操作简便,合成温度较其它合成方法低,合成的产物纯度高,各组分配比准确,无偏析,且通过调整原料与盐的比例、熔盐的种类以及合成温度还可以控制粉体颗粒的形貌与尺寸.认为该方法具有很广阔的应用前景.     

电爆炸法制备纳米粉体材料的研究进展

电爆炸方法是制备高纯度纳米粉体材料的新技术,具有能量转化率高、工艺参数调整方便、通用性强的特征。本文分析了电爆炸制备纳米粉体材料的机制,并对近年来国内外在电爆炸法制备纳米粉体材料技术方面的研究进行了评述。在制备非金属纳米材料方面重点阐述了电爆炸法在制备碳纳米材料方面的研究进展,提出了进一步研究的建议。