Principles of the EURACHEM/CITAC guide “Use of uncertainty information in compliance assessment”

Many, possibly most, analytical measurements are carried out to assess compliance with a specification or a regulation, for example in the control contaminants in food or the detection of performance enhancing substances in sport. When making an assessment of compliance the presence of unavoidable measurement uncertainty introduces the risk of making incorrect decisions, that is of accepting a batch of material which is outside the specification or rejecting one that is within. This often leads to controversy over whether or not the compliance decision is correct. How to make reliable assessment decisions is described in the EURACHEM/CITAC Guide “Use of uncertainty information in compliance assessment”. The key is the use of decision rules that lead to an unambiguous interpretation of the measurement result and its uncertainty. These decision rules need to be designed to ensure that requirements of the specification or regulation are met and that the risk of making an incorrect decision is acceptable. Ideally they should form part of the specification or regulation. Presented at the Measurement Uncertainty Symposium, April 2008, Berlin, Germany.     

可塌陷气管的p—V关系和极限流量

通过对正常大鼠气管在不同轴向伸长比条件下作液体灌注实验,并对所得压力-容积数据进行最小二乘拟合,得到包含在拟合函数关系式中的大鼠气管材料常数,文章详细分析这些材料常数的力学含义,并对可塌陷气管的顺应性和极限流量进行讨论,文章结果为分析气管在特定力学环境中的适应性生长和塌陷特性提供重要的信息。     

Some correlations involving the shear viscosity of polystyrene melts

Based upon a compilation of steady-shear and dynamic-shear viscosity data from the literature for polystyrene melts, an assessment has been made concerning the relative merits of the Cross and Carreau models in describing the shear-rate dependence of such viscosities. It is shown that the Cross model is decidedly more appropriate for PS of BMWD. Based upon master plots, it is demonstrated that the Cox-Merz relation applies to PS of both BMWD and NMWD. It is also shown that the Cox-Merz relation applies even into the second-Newtonian regime, with being independent ofM _w and MWD. In addition, the applicability of the Prest-Porter-O'Reilly relationship between shear viscosity and recoverable shear compliance is corroborated in the case of PS of NMWD.     

A mixed variational formulation of a contact problem with adhesion

A mathematical model describing the contact between a viscoplastic body and a deformable foundation is analyzed under small deformation hypotheses. The process is quasistatic and in normal direction the contact is with adhesion, normal compliance, memory effects and unilateral constraint. We derive a mixed-variational formulation of the problem using Lagrange multipliers. Finally, we prove the unique weak solvability of the contact problem.     

Truss topology optimization under uncertain nodal locations with proportional topology optimization method

This paper presents an approach to solving truss topology optimization problem with small uncertainty in the locations of the structural nodes. The nodal locations in the truss are assumed to be random, and the probabilistic method is used here to deal with the uncertainty. The objective of the optimization problem is to minimize the mean compliance of the truss structure under nodal location uncertainty. It is a well-acknowledged barrier to compute the inverse of the structural stiffness matrix which involves variations in the optimization problem. In this paper, based on Neumann series expansion, this optimization problem can be recast into a simpler deterministic structural optimization problem. In order to avoid the sensitivity calculations for the objective function, the proportional topology optimization method which shows comparable e?ciency and accuracy with gradient-based method is used. The numerical examples demonstrate the effectiveness and high e?ciency of the proposed approach, and further illustrate that the optimal truss topology can be dramatically impacted by nodal location uncertainties.     

质量符合性评价体系的本体化建模及评价支持实证研究

本文面向质量管理评价领域对精细化和科学性的需求,研究质量符合性评价体系所蕴涵的知识共性,提出了一种构建符合性评价知识系统的多层本体化模型框架,设计了涵盖两种不同粒度水平的评价知识构成元模型,以此获取质量符合性评价在语义层次上的支持。最后,以信息安全产品防火墙质量评价为例实证了一类质量符合性评价体系知识本体的构建,以及基于规则推理的自动评价决策支持应用。     

柔度法研究镍铬合金焊材的高温疲劳裂纹扩展行为

金属材料的高温疲劳裂纹扩展速率试验,关键问题在于高温环境下精确测量试样的裂纹长度.基于柔度测试技术,通过改进现有高温应变引伸计实现了FFCT试样的高温疲劳裂纹扩展速率测试.利用有限元方法对具有分层构形CT试样的柔度方法进行了研究,获得了分层结构CT试样的等效弹性模量表达式,通过迭代方法对实时裂纹长度进行修正,获得了良好的预测精度.完成了镍铬合金焊带、焊条和焊丝三种焊材常温和350℃下的疲劳裂纹扩展速率试验,获得了相应的疲劳裂纹扩展规律.     

广黏弹组合模型的等效性及其基本性质

对广义黏弹组合模型的等效性及其基本性质进行了研究,结果表明：广义Maxwell 模型由于并联结构,其蠕变柔量很难得到. 但提出了求解广义Maxwell模型蠕变柔量的 方法,给出了其具体表达式,且在此基础上证明了广义Maxwell模型与Kelvin链的等效性, 建立了这两个模型物理参数间的转换关系式. 证明了广义黏弹组合模型的一个基本性质：当 将模型的松弛时间谱和延迟时间谱由大到小顺序排列时,松弛时间与延迟时间互不相等,且 相互交织,两相邻松弛时间中间有且仅有一个延迟时间,同时,两相邻延迟时间中间有且仅有一个松 弛时间;当两者同阶相比时,延迟时间总是大于松弛时间. 这一基本性质明确了使用广义黏 弹组合模型来描述现实中某种特定材料的黏弹性行为时,该材料必须具备的基本条件,因此, 它可作为这类流变模型在工程应用中的一个实用判据. Wiechert模型和广义中村模型、广义 Jeffreys模型和广义N-K模型、Maxwell链和广义Kelvin模型之间的等效性可作为特例. 最后,实例验证了所提出的求解广义黏弹组合模型蠕变柔量方法及其基本性质.     

锻压操作机夹持长棒料随动过程动态受力分析

研究了锻压操作机夹持长棒料锻件锻压随动过程中夹钳的受力状态。利用拉格朗日方程及有限元方法建立了包含操作机及其锻件的总体动力学方程。操作机系统建立为端部悬挂质量弹簧的Euler-Bernoulli梁模型,随动过程中因为梁上节点位移激励引起操作机系统的瞬态振动。计算结果与LS-DYNA显式有限元模型结果进行了比对,吻合良好。结果表明,对于长棒料锻件,液压机锻压的位置对操作机的动态受力有着十分显著的影响。     

物理老化对玻璃态高聚物非线性蠕变行为的影响

在不同应力水平下对经历不同老化时间的有机玻璃(PMMA)进行常温蠕变测试,分析物理老化和应力对材料蠕变柔量函数的影响.分析表明,老化时间对PMMA蠕变行为的影响满足流变简单性规律,即不同老化时间的蠕变柔量曲线可以沿对数时间轴平移而叠加到参考曲线上.取最长的老化时间为参考状态,依时间-老化时间等效原理,得到了各应力水平下的蠕变柔量主曲线.老化移位因子与老化时间在双对数坐标图上呈现线性关系,其负斜率就是老化移位率.结果表明,老化移位率随应力的增高而减小.