基于五参数统一强度理论的刚构桥地震损伤分析

混凝土五参数统一强度理论在主应力空间偏平面上的边界线为十二边形,可通过调整中间主应力的影响系数消除角点的奇异性,以单位体积材料当前塑性耗能及其断裂能的比值定义损伤变量,根据相关流动准则推导混凝土的弹塑性损伤本构关系。该模型可同时考虑混凝土材料中间主应力的影响、高应力状态下的静水应力效应、拉压异性和随动强化效应等,不考虑循环荷载下的刚度折减。由图形回归法给出应力更新的数值方法,编写了相应的Fortran语言程序,并将其用于大跨度连续刚构桥地震损伤的模拟,计算结果验证了所用模型的预测能力。     

Structural recovery (physical ageing) of the friction coefficient of polymers

Most of the mechanical properties of the polymers are subject to structural recovery (physical ageing). The aim of this work was, therefore, to evaluate the sensitivity of the friction coefficient to physical ageing. The apparent friction coefficient is the ratio of the tangential force to the normal load applied to a moving tip in contact with the surface of a material. This coefficient includes a “true friction” at the interface and a “geometrical friction,” which is the lowing and bulk dissipative effect. In the case of solid polymers, the material underneath the moving tip may display various types of behavior: elastic, viscoelastic, elastoplastic (elastic and plastic strains are present in the contact area), or fully plastic. Scratching and sliding experiments were performed on PMMA to determine the true friction coefficient over a wide range of contact deformations. An analysis of the true friction coefficient as a function of the physical ageing (structural recovery) showed that the friction decreases with increasing structural recovery of the polymer in the case of sliding. Whatever the level of physical ageing, at a high contact strain (fully plastic contact), the true friction coefficient tended to a unique and high value independent of the thermal history of the polymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1337–1347, 2008     

An analysis of the modeling of stress and strain fields in a real microstructure using a hybrid method

The distribution of stress and strain fields in a micro-structural area of a particle reinforced composite is studied by a combination of experimental and numerical method (hybrid method). With the experimental values of displacements in a micro-region as the boundary loading condition, strain and stress fields inside the micro-region are calculated by the finite element method under two different kinds of modeling, namely, as plane stress and plane strain condition. The differences between the two kinds of modeling conditions as applied to micro-structural areas are discussed. Project Supported by the National Natural Science Foundation of China (19972046) and National Overseas Study Foundation.     

Physical aging and deformation kinetics of polycarbonate

Considering the current view that physical aging of glasses results in an increase of activation barriers to plastic deformation, it is surprising that, until now, no influence of physical aging was observed experimentally on the temperature dependence of plastic deformation in polymeric glasses. This study evaluates why such an influence has not been found, and it is shown that detailed analysis of a set of uniaxial compression data on polycarbonate (PC) at different strain rates and temperatures leads to the conclusion that a significant influence indeed exists. As a consequence, the Eyring activation energy depends on the aging history of the material. These experimental observations are rationalized in terms of a simple physical interpretation of the aging phenomenon. The article also contains a discussion of the apparent deaging of amorphous polymers induced by large‐strain plastic deformation. This discussion is of key importance here, because this study compares yield stresses of aged PC with those of mechanically deaged, or rejuvenated, PC. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

TOUGHENING OF POLYCARBONATE WITH PBA-PMMA CORE-SHELL PARTICLES

The miscibility, mechanical properties, morphology and toughening mechanism of PC/PBA-PMMA blends were investigated. The dynamic mechanical results show that PC/PBA-PMMA blend has good miscibility and strong interfacial adhesion. The Izod impact strength of blend PC/PBA-PMMA with 4% (volume fraction) PBA-PMMA core-shell modifier is 16 times higher than that of pure PC. The core-shell volume fraction and thickness of the PMMA shell have effect on the toughness of PC/PBA-PMMA blends. As PMMA volume fraction increases, the toughness of PC/PBA-PMMA blend increases, and reaches a maximum value at 30% volume fraction of PMMA or so. The tensile properties of PC/PBA-PMMA blend with a minimum amount of PBA-PMMA modifier show that brittle-tough transition has no significant variance in comparison with that of pure PC. The scanning electron microscopic (SEM) observation indicates that the toughening mechanism of the blend with the pseudo-ductile matrix modified by small core-shell latex polymer particles is the synergetic effect of cavitation and shear yielding of the matrix.     

二次积分迭代法的钢筋混凝土框架非线性全过程分析

在分析了钢筋混凝土框架受弯构件，压弯构件显示非线性特征的主要原因的基础上，提出了对钢筋混凝土框架进行非线性全过程分析的二只分迭代法，此法充分考虑了钢筋混凝土材料的非线性特征，通过构件截面的应力应变关系，力和力矩的平衡，推导出一系列的迭代公式，迭代整体可以模拟裂缝开展，钢筋屈服，混凝土压碎，塑性铰产生，内力重分布等全部过程，将模拟模型引入框架的非线性分析的单元劲度矩阵，编写了框架非线性全过程的分析程序，对两层两跨受集中荷载的框架进行计算比较，所得结果与实测吻合较好。     

Al-Cu多晶锯齿形屈服现象中的尺度效应

对Al-Cu多晶合金锯齿形屈服现象中各特征物理量(应力跌幅、跌落时间和再加载时间)随应变演化的规律进行了系统研究，讨论了不同厚度试件演化结果的区别.同时，这种尺度效应还表现为相同加载条件下1，2mm厚度试件与3mm厚度试件的Portevin-Le Chrtelier (PLC)类型的差异.利用非线性时间序列分析的方法对前者在相空间中吸引子的几何特性进行了描述，并通过主分量分析的方法初步判定其中存在着混沌行为.后者演化过程中应力跌落事件按跌落幅度统计分布符合幂律规律，具有自组织临界性特征.最后，借助自组织 关键词： 锯齿形屈服 尺度效应 Al-Cu合金     

A study of tensile yielding of isotactic polypropylene

The yielding behavior of isotactic polypropylene (iPP) sheets prepared by hot pressing was studied by tensile testing. The corresponding microstructural changes in the specimens after testing were investigated by image analysis, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The yielding of iPP was found to follow a two-process Eyring yielding model. In the necked regions, stress-whitening occurred only in specimens tested over a certain range of strain rates and temperatures. The occurrence of the stress-whitening was correlated well with the activation of Process II in the two-process Eyring model. SEM revealed that the stress-whitening in the necked regions was associated with the formation of craze-like structures that were parallel to the loading direction. Furthermore, DSC analysis showed that the necked regions of the unwhitened tensile specimens had an additional low-temperature melting peak. However, no additional melting peaks were found in the stress-whitened specimens. © 1994 John Wiley & Sons, Inc.     

莜麦结实器官分化的研究

本文以青海省优质莜麦品种L94为材料,研究了高寒地区夏莜麦结实器官的分化与外部形态的相关性以及裁培措施对莜麦产量因素的影响。在此基础上,确定了夺取莜麦丰产的“最佳”播种、施肥和灌水时间。     

锅炉用钢材强化规律的实验研究

通过对六种锅炉用钢材的实验研究,得到了材料屈服的一些特点,给出了在沿一定加载路径的拉压循环载荷作用下材料的强化规律,以及在拉伸和压缩时材料所表现出的不同性质。