高速扩展裂纹尖端的理想弹塑性场

在理想弹塑性材料中,高速扩展裂纹尖端的应力分量都只是θ的函数.利用这个条件以及定常运动方程、应力应变关系与屈服条件,我们得到反平面应变和平面应变两者的一般解.将这两个一般解分别用于扩展Ⅲ型裂纹和Ⅰ型裂纹,我们就求出了Ⅲ型裂纹和Ⅰ型裂纹的高速扩展尖端的理想弹塑性场和理想塑性场.     

平面应变Ⅰ型裂纹弹塑性分析的一种方案

本文给出了一种求解平面应变Ⅰ型裂纹弹塑性近似解析解的一种方法.     

裂纹尖端场弹塑性分析的加权残数法及塑性应力强度因子的计算

本文以幂强化材料,平面应变情形为例,系统地提出了裂纹尖端场弹塑性分析的加权残数法,并根据此法,得出了裂纹尖端场的解析式弹塑性近似解.在此基础上.对整个裂纹区域,构造了弹塑性解叠加非线性有限元计算塑性应力强度因子的方法,从而为裂纹尖端场和整个裂纹体的分析和计算,提供了一个方法.     

高速扩展裂纹尖端的各向异性塑性应力场

在理想弹塑性材料中,高速扩展裂纹尖端的应力分量都只是θ的函数.利用这个条件以及定常运动方程、应力应变关系与Hill各向异性屈服条件,我们得到反平面应变和平面应变两者的一般解.将这两个一般解分别用于扩展Ⅲ型裂纹和Ⅰ型裂纹,我们就求出了Ⅱ型裂纹和Ⅰ型裂纹的高速扩展尖端的各向异性塑性应力场.     

引用复变量伪应力函数来解幂硬化材料平面应力问题

本文引用复变量伪应力函数将幂硬化材料平面应力问题的协调方程化为双调和方程,从而使此类有强化材料的弹塑性平面应力问题能像线弹性力学平面问题那样采用复变函数法进行求解.本文推导出了幂硬化材料平面应力问题的应力、应变及位移分量的复变函数表达式,可推广应用于满足全量理论的一股弹塑性平面应力问题.作为算例,文中给出了含圆孔幂硬化材料无限大板单向受拉问题的解答,并和有关文献用摄动法获得的同一问题的渐近解进行了比较.     

理想弹塑性Ⅲ型扩展裂纹的全新和精确分析

本文采用线场分析方法对理想弹塑性Ⅲ型准静态扩展裂纹进行了分析.本文的意义在于突破了小范围屈服理论的限制.通过求得裂纹线附近塑性区应力和位移率的通解,并将此通解(而不是过去一直采用的特解)与弹性场的精确解(而不是线弹性奇异K场)在裂纹线附近的弹塑性边界上匹配,本文得出了裂纹线附近塑性区的应力变形场、塑性区的长度及弹塑性边界的单位法向量的全新和精确解答.本文的分析放弃了小范屈服理论的所有近似假定并且不再附加任何其它的近似假定,本文的结果在裂纹线附近是足够精确的.本文的结果表明:对理想弹塑性Ⅲ型准静态扩展裂纹,不存在“定常扩展状态”,且裂纹线附近塑性应变不存在奇异性.本文还对裂纹稳定扩展过程讨论了两种重要情形.     

弹塑性状态下Ⅰ型裂纹前缘应力应变场的奇异性分析

本文从弹塑性力学的三维基本方程出发,分析了幂硬化材料Ⅰ型裂纹前缘应力、应变场的奇异性,发现,裂尖附近诸应力、应变分量的奇异性沿厚度不变;六个应力分量的奇异性不完全相同,六个应变分量的奇异性也不完全相同.     

折线强化弹塑性应力分析的有限元法

本文对材料的应力应变曲线用三段直线的折线拟合,按照弹塑性的简单加载理论,对以增量理论得出的完整应力应变关系进行简化,导出按位移求解的有限元的增量方程.其中弹塑性刚度矩阵可以从弹性刚度矩阵补充后得出,从而节省计算时间.根据von Mises屈服准则确定各次荷载的增量,引入迭代法进行求解,省去对弹塑性刚度矩阵的重复地三角分解,进一步减少计算时间.本文对于应用高次单元、偏离简单加载的荷载、卸载计算、曲线拟合以及荷载的估算问题,均作了说明.     

有限变形下的等效应力和等效应变问题

重点讨论了在有限变形条件下，弹塑性理论中的等效应力、等效应变是否仍然成立．选择了平面应力和平面应变下的单向压缩应力状态，对这一问题进行了探讨．在这两种应力状态下，在众多的应力应变描述中，对数应变与旋转Kirchhoff应力得到的应力应变曲线与实验数据符合良好．     

应变空间中的岩土屈服准则与本构关系

本文从Илъюшин公设出发评述了在应变空间中研究岩土弹塑性问题的必要性和特点.建立了应力不变量与弹性应变不变量之间的关系式,实现了应力屈服面到应变屈服面的转换,导出和讨论了十二个以应力表达的屈服准则的应变表达式.应用正交法则导出了十二个与上述应变屈服准则相联系的理想塑性材料的本构关系.本文工作的结果可供实际应用,并有助于应变空间塑性理论的进一步研究.     

Detection of multivariate outliers with location slippage or scale inflation in left orthogonally invariant or elliptically contoured distributions

This paper is concerned with two kinds of multiple outlier problems in multivariate regression. One is a multiple location-slippage problem and the other is a multiple scale-inflation problem. A multi-decision rule is proposed. Its optimality is shown for the first problem in a class of left orthogonally invariant distributions and is also shown for the second problem in a class of elliptically contoured distributions. Thus the decision rule is robust against departures from normality. Further the null robustness of the decision statistic which the rule is based on is pointed out in each problem.     

View factor for inclined plane with Gaussian source

The view factor (angle factor) for a differential inclined plane in the case of a radiating source of radially Gaussian intensity is considered. This information is useful for modelling of solar radiation in certain applications. The view factor is expressed in terms of two integrals, one of which is obtained in closed form in terms of special functions, and the other is approximated. A compact estimate for the view factor is presented which is suitable for machine computation. While the relative error associated with the final estimate is typically less than 0.01%, and in all cases, less than 0.2%, the method is easily extended to yield even greater accuracy.     

Generalising a characterisation of Hermitian curves

This article proves a characterisation of the classical unital that is a generalisation of a characterisation proved in 1982 by Lefèvre-Percsy. It is shown that if is a Buekenhout-Metz unital with respect to a line in such that a line of not through meets in a Baer subline, then is classical. An immediate corollary is that if is a unital in PG such that is Buekenhout-Metz with respect to two distinct lines, then is classical. Received 5 August 1999; revised 15 February 2000.     

Monomorphism categories associated with symmetric groups and parity in finite groups

Monomorphism categories of the symmetric and alternating groups are studied via Cayley’s Em-bedding Theorem. It is shown that the parity is well defined in such categories. As an application, the parity in a finite group G is classified. It is proved that any element in a group of odd order is always even and such a group can be embedded into some alternating group instead of some symmetric group in the Cayley’s theorem. It is also proved that the parity in an abelian group of even order is always balanced and the parity in an nonabelian group is independent of its order.     

Polynomial-time algorithms for regular set-covering and threshold synthesis

A set-covering problem is called regular if a cover always remains a cover when any column in it is replaced by an earlier column. From the input of the problem - the coefficient matrix of the set-covering inequalities - it is possible to check in polynomial time whether the problem is regular or can be made regular by permuting the columns. If it is, then all the minimal covers are generated in polynomial time, and one of them is an optimal solution. The algorithm also yields an explicit bound for the number of minimal covers. These results can be used to check in polynomial time whether a given set-covering problem is equivalent to some knapsack problem without additional variables, or equivalently to recognize positive threshold functions in polynomial time. However, the problem of recognizing when an arbitrary Boolean function is threshold is NP-complete. It is also shown that the list of maximal non-covers is essentially the most compact input possible, even if it is known in advance that the problem is regular.     

3-连通3-正则图中的可序子集

图G的k元点集X={x1,x2,…,xk}被称为G的k-可序子集,如果X的任意排列都按序排在G的某个圈上.称G是k-可序图,如果G的每一个k元子集都是G的k-可序子集.称G为k-可序Hamilton图,如果X的任意排列都位于G的Hamilton圈上.研究了3-连通3-正则图的可序子集的存在性问题.     

A Generalized Machine-Scheduling Algorithm

It is proposed to treat a general machine-job-scheduling problem using a branch-and-bound method. Here the general problem is that in which the routing of any job through the machines is specified in advance but is independent of the routing of any other job. In addition there is no requirement for the job to visit all machines. Since any two operations to be performed on the same machine cannot be performed simultaneously, the set of all schedules can be divided into two subsets-one in which the pair of operations is performed in one order and the second in which the order is reversed. This division corresponds to branching in the method. For each of the new subsets formed by branching a lower bound on the duration of all schedules in the subset is calculated and the schedule with minimum duration is found by successive subdivision. An illustrative example is solved and the method is compared to other published general methods.     

煤业集团供应商选择的可拓方法

结合煤业集团的实际，提出了供应商选择的指标体系。应用可拓学的理论与方法，结合熵理论，建立了基于熵权的可拓综合评价模型。由于在该模型中采用了熵权，从而避免了低层次多因素权重确定的主观性；该模型以综合关联度作为评价准则，避免了评价中的主观性。通过将该模型在平顶山煤业集团供应商选择中进行应用，得出了其最佳的供应商。而且评价过程表明，该方法易于操作和使用。     

Complexity and approximation results for the connected vertex cover problem in graphs and hypergraphs

We study a variation of the vertex cover problem where it is required that the graph induced by the vertex cover is connected. We prove that this problem is polynomial in chordal graphs, has a PTAS in planar graphs, is APX-hard in bipartite graphs and is 5/3-approximable in any class of graphs where the vertex cover problem is polynomial (in particular in bipartite graphs). Finally, dealing with hypergraphs, we study the complexity and the approximability of two natural generalizations.     

树状网络上的Web代理服务器最优放置问题

一般网络上Web代理服务器(Web proxy)最优放置问题是一个NP困难问题.此文讨论树状网络上的最优放置问题,改进了已有结果,得到了一个时间复杂度为O(nhk)的多项式时间算法,这里n为网络结点数,h为树的高度,而k为要放置的代理服务器个数.