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。     

激光熔覆粉末粒径对熔覆层成形控制的影响

目的 揭示激光熔覆过程中TiC粉末粒径及工艺参数对复合材料熔覆形貌的影响规律,实现熔覆层成形控制。方法 采用响应面法中心复合设计模块分析扫描速度、激光功率、粉末粒径对复合材料熔覆形貌的影响,建立工艺参数及TiC粉末粒径与复合材料熔覆层面积、熔覆层高度、熔覆层宽度之间的数学模型,通过方差分析和模型检验验证模型的准确性。结果 激光功率对复合材料熔覆形貌的影响不显著,粉末粒径对熔覆面积影响最为显著,熔覆层面积随着扫描速度的减小和粉末粒径的增大而增大;粉末粒径对熔覆层高度影响最为显著,熔高随着粉末粒径的增大而增大,随着扫描速度的降低而减小;扫描速度对熔覆层宽度的影响最为显著,熔宽随着扫描速度的增大而下降,随着粉末粒径的增大而增大。结论 以熔覆面积最大及熔宽熔高最大为优化目标,对比预测值与实际值,熔覆层面积、熔覆层高度、熔覆层宽度的误差率分别为6.81%,3.9%,7.7%。该研究成果为提高复合材料熔覆形貌的预测与控制提供了理论依据。     

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.     

基于位错密度的晶体塑性有限元方法的数值模拟及参数标定

运用ABAQUS有限元分析软件对基于位错密度的晶体塑性有限元方法(CPFEM)及其晶体塑性参数进行了深入的研究。结果表明,CPFEM晶体塑性本构可以准确地体现材料的力学性能。通过讨论不同晶体塑性参数,得到各个参数可以分别控制材料的屈服强度、硬化过程、剪切应变速率、极限强度等性能。此外,为了标定材料的晶体塑性参数引入多晶的代表体积单元(RVE)模型,并讨论了晶粒数以及晶粒规整度对于RVE模型的影响。结果表明,RVE模型的晶粒数达到临界值750个时能够体现等轴晶的宏观各向同性。结合晶体塑性RVE模拟和拉伸试验结果,对Inconel 718合金的晶体塑性参数进行标定,晶体塑性有限元的模拟结果和实验结果的误差小于5%。证明经过标定的晶体塑性参数可以准确反映Inconel 718的力学性能,也使得进一步研究该合金介观晶粒尺度的力学性能成为可能。     

煅烧煤矸石粉体材料活性评价方法的研究进展

煤矸石是煤炭开采和加工过程中产生的固体废弃物,将其应用于水泥基材料是煤矸石资源化的有效途径。本文综述了国内外关于煅烧煤矸石粉体材料活性的评价方法——强度评价方法、火山灰性试验方法和现代分析测试方法(XRD、IR、NMR和ICP-AES)。针对煅烧煤矸石活性材料在水泥基材料研究和应用中存在的主要问题,分析阐明了其高效应用于实际工程中的研究重点。为加快煤矸石在水泥基材料中的资源化利用,提出了一些参考性建议。     

塑性有限元在金属体积成形过程中应用的进展

塑性有限元法已经成为研究金属体积成形的重要方法。介绍了刚塑性有限元和弹塑性有限元的原理;综述了金属体积成形过程中锻造、挤压和轧制工艺有限元模拟的国内外最新应用进展,并分析了有限元法在不同工艺中应用的未来发展方向。最后总结了塑性有限元法在金属体积成形领域未来发展的难点和趋势。     

基于修正Drucker-Prager Cap模型的金属粉末成形本构模型参数确定方法

针对修正Drucker-Prager Cap模型参数复杂且难准确获取的问题,提出一种采用相对简单实验操作结合联合仿真反演优化确定模型参数的方法,用于金属粉末成形的数值模拟。首先通过实验分析与理论推导,确定重点反演优化参数,即偏心距参数R;采用联合仿真反演优化方法,借助ABAQUS有限元及二次开发平台与MATLAB优化算法,对参数R进行反演计算,进而完成相关硬化参数的确定;以金属粉末Distaloy AE为例,讨论参数R不同函数表达形式的反演结果对粉末压制成形过程数值模拟的影响。研究结果表明,偏心距参数R2及其关联的硬化参数比R1在压制力、脱模力、相对密度和残余应力数值模拟方面具有更高的准确性。     

难变形金属小模数齿形件电流辅助分形旋压成形工艺优化

目的 针对30CrMnSiA合金结构钢小模数齿形件电流辅助分形旋压成形工艺,探究工艺参数对小模数齿形件成形质量的影响规律,分析工艺参数间的相关性,获得优化后的工艺参数组合。方法 选取小模数齿形件齿廓偏差、齿距偏差、轮齿饱和度为成形质量响应指标,以电流密度、占空比以及旋轮进给速度为影响因素,设计响应面试验方案;根据有限元模拟结果建立成形质量回归预测模型,分析电流密度、占空比以及旋轮进给速度对小模数齿形件成形质量的影响规律,计算获得最优的参数组合并进行试验验证。结果 电流密度、脉冲占空比、旋轮进给速度对小模数齿形件成形质量有显著影响,成形质量随着电流密度与占空比的升高而升高,随旋轮进给速度的升高而先升高后降低;且电流密度与旋轮进给速度、脉冲占空比与旋轮进给速度在对轮齿饱和度的影响上有一定的交互性;通过建立的回归模型预测得到的优化工艺参数如下:电流密度为17.5 A/mm²、脉冲占空比为40%、旋轮进给速度为0.6 mm/min。结论 回归模型预测值与试验值的相对误差小于8%,说明所构建的成形质量回归预测模型是准确的,利用优化后的参数可制备出成形质量良好的小模数齿形件。     

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。     

光子相关法测量空气声场中的粒子振速

声场中的粒子振速是评价空气声场特性的一个重要参量。在平面波声场中,通过获取激光多普勒测速仪对不同声压级声场中散射粒子产生的光电信号,采用光子自相关法对原始多普勒信号进行处理,粒子的速度量值根据相关函数的时间特征值得出,并与传声器测量声压值计算的粒子振速值进行比较。在原有自相关算法的基础上,利用样条插值法来估计相关周期,减小原有信号频偏与多普勒频率之比并非整数倍的引入的差异。实验结果表明,光子相关法能够获得声场中的粒子振速,与传声器测量值吻合较好,当振速较大时,插值法有利于减小测量偏差。在96~110 dB的声压量值范围内,光子相关法与传声器测量值之间的振速偏差优于0.7 dB。     

响应面法优化稻草模塑材料热压工艺参数

目的 探讨热压过程中压力、温度和湿纸胚含水率等因素对稻草秸秆纤维模塑包装材料主要力学性能的影响,确定各因素的权重及最佳工艺参数。方法 采用单因素试验法和响应曲面法,以裂断长和弯曲强度为评价指标,确定最佳工艺条件。结果 最佳热压工艺条件,热压温度为175 ℃,热压压力为6.9 MPa,湿纸胚含水率为70%,此时得到的平均裂断长为7697.93 m,弯曲强度为72.36 MPa,与理论裂断长7712.62 m、弯曲强度71.44 MPa接近,优化结果可信。热压过程中各因素对模塑包装材料裂断长和弯曲强度影响的大小为湿纸胚含水率＞热压压力＞热压温度。结论 过高的温度会造成半纤维素的热解,过高的压力会导致纤维的压溃,过高的含水率产生的能耗过高。适当的热压工艺参数能够降低能耗,保证模塑包装材料的品质及性能。     

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...