XML在机械CAD系统中的应用

分析了Internet上最新的XML技术的特点，通过实例用XML技术对机械CAD产生的各种文档信息进行了描述，并且构造了基于XML文档交换的分布式支持环境的体系结构。     

Geometry-Dependent R-Curve for Quasi-Brittle Materials

Fracture of quasi-brittle materials such as ceramics and cement-based materials can be described by an R -curve, defined as fracture resistance. The R -curve can be constructed as the envelope of the strain energy release rates ( G ). In this study, R -curve is defined as an envelope of G -curves obtained by varying the dimensions of identical specimens, while keeping the geometry and the initial flaw size constant. By approximating the G -curve with a second-order function of the crack length, a simple formulation of the R -curve is derived by solving a differential equation. Three parameters are needed for the proposed R -curve. These parameters can be obtained by testing a notched-beam specimen and using linear elastic fracture mechanics. The proposed R -curve simulates well the geometry dependency as well as other characteristics of the fracture response of quasi-brittle materials.     

Effects of mastication on the distribution of molecular weights and on the mechanical properties of native and commercial dental gutta percha (trans-polyisoprene)

Mastication of gutta percha (trans-polyisoprene) resulted in the selective scission of molecules, producing a narrower distribution of lower molecular weights. The mechanical properties of the samples also underwent a significant change due to mastication. The greater the content of incompatible substances (salts and oxides) in commercial gutta percha. the more substantial were these effects. The atmosphere (air, N₂, O₂) in which the experiments were conducted yielded significantly different results. The decrease in molecular weight was far greater in an O₂ atmosphere than under a current of nitrogen or air, owing to the combination of double bonds with O₂.     

求解机械装配规划的新方法

本文提出一个求解机械装配规划的算法,其计算量～O(sN~2),其中s是零件所有可能装配方向的个数,N是工件的零件数(一般s～O(N)).而现行的求机械装配规划的算法,其计算量均随N的增加按指数律增加.     

A time series approach to fatigue crack propagation

The inherently nonlinear phenomenon of fatigue crack propagation is modeled as a linear random process. To a first approximation, simple, nonstationary time series models are introduced and standard techniques for determining the parameters of autoregressive integrated moving-average processes are applied. Multiplicative time series models are next utilised for the representation of a group of crack history curves. Implementation of the models on the Virkler experimental data set yields satisfactory results. Reliable Gaussian approximations to the distribution of the time required by a crack to reach a specified critical length are obtained, and the usefulness of the approach is demonstrated when updating lifetime predictions after periodic inspections.     

由三面投影图生成三维立体图的方法研究

针对创新设计中零部件的三维虚拟造型问题，提出了一种由二维投影图生成三维立体图的计算机化辨识方法。通过辨识简单三维立体的形状和空间位置，克服了二维图形中面的积聚性和零件之间不规则相贯和截交曲线的识别问题，进而实现了复杂组合形体的计算机化设计与造型。最后，以箱体类零件为例，在AutoCAD环境下利用VC 和ObiectARX开发工具编程验证了该方法的有效性。