Prediction of yield and long‐term failure of oriented polypropylene: Kinetics and anisotropy

The time‐dependent yield and failure behavior of off‐axis loaded uniaxially oriented polypropylene tape is investigated. The yield and failure behavior is described with an anisotropic viscoplastic model. A viscoplastic flow rule is used with an equivalent stress, based on Hill's anisotropic yield criterion, and the Eyring flow theory combined with a critical equivalent strain definition. This model is based on factorization of the rate and draw ratio dependence and is capable of quantitatively predicting the rate, angle and draw ratio dependence of the yield stress as well as time‐to‐failure in various off‐axis tensile loading conditions characterized solely from the transverse direction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2026–2035, 2009     

Toughening effect of ethylene‐vinyl acetate rubber on nylon 1010 compatibilized by maleated ethylene‐vinyl acetate copolymers

The toughening effect of ethylene‐vinyl acetate rubbers (EVM) with maleated ethylene‐vinyl acetate copolymers (EVA‐g‐MAH) on the nylon 1010 was investigated. The addition of 5 phr (per hundred nylon 1010) EVM increased the elongation at break of nylon 1010 to a great extent. The notched Izod impact strength of nylon/EVM blends increased with increasing EVM content. Scanning electron microscope showed that the EVM particle size was around 0.5 μm when the EVM content was 5 phr and increased with increasing EVM content. After the addition of EVA‐g‐MAH to nylon/EVM (100/20) blend, the average diameter of EVM particles decreased from more than 1 μm to 0.5–0.6 μm. EVA‐g‐MAH could improve the adhesion between nylon 1010 and EVM. A sharp brittle‐ductile transition (BDT) was observed when the interparticle distance was about 0.2 μm, independent of the addition of EVA‐g‐MAH. The notched Izod impact strength of nylon/EVM blends at low temperatures was measured and the BDT shifted toward low temperatures with increasing EVM or EVA‐g‐MAH content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 434–444, 2009     

“无中生有”计的一个博弈模型

“无中生有”计系《三十六计》中的第七计，本首先给出此计的一个博弈模型，然后由此研究破此计的一个算法。     

高阶奇异项及J积分表达式

从４种典型裂纹情况的特征展开式出发，运用其微分性质和伪正交性质得到了含有高阶奇异项的Ｊ积分表达式．它们是通用的显函数表征的．本研究支持了Ｈｕｉ和Ｒｕｉｎａ的杰出研究和重要观点，即高阶奇异项和非奇异项一样在小范围屈服描述中扮演着重要角色．研究表明，常规柔度方法确定的Ｊ积分已隐含了高阶奇异项的贡献．断裂准则有可能由含高阶奇异项和非奇异项的Ｊ积分的临界值来描述     

考虑中间主应力效应的损伤钢管混凝土构件承载力分析

混凝土三参数统一强度理论在Haigh-Westgaard空间的偏平面上的边界线为十二边形,通过调整中间主应力的影响系数消除角点的奇异性,根据相关流动准则推导基于标量损伤的弹塑性本构方程,考虑了混凝土材料的随动强化效应,结合塑性损伤理论给出了应力计算的数值方法,编制了相应的Fortran语言程序,并将其用于钢管混凝土构件承载能力的计算,计算结果验证了所用模型的预测能力。     

颗粒型砂介质的受压力学特征及屈服滑动

提出颗粒型砂介质在压实过程中的两种特征：孔隙填充状态和颗粒滑动状态；针对孔隙填充状态的力学行为特征，提出相对体积改变量(压实量)作为表征此状态的特征参量，研究了瞬时压缩模量与压实量的函数关系；针对型砂的颗粒滑动状态，提出具有强化效应的Mohr-Coulomb屈服条件，推导描述颗粒屈服滑动状态的增量本构方程、以及三轴压实过程条件下的状态本构方程，最后，就不同侧向压力下的三轴压缩试验、带模样的型砂压实试验的大量试验数据进行处理和验证。     

A single-surface yield function for geomaterials

Summary The article outlines a seven-parametric yield function for geomaterials such as soils and rocks. Proceeding from a geometric representation in the principal stress space, the yield surface exhibits a closed shape, thus reflecting the sensitivity of the plastic response of this type of media to hydrostatic stresses. The yield function is able to describe the effects of primary yielding, as well as of isotropic and kinematic hardening. In addition the failure envelope contains an open cone when the number of material parameters is reduced from seven to five.Dedicated to F. G. Kollmann on the occasion of his 60th birthday     

沉淀对A1-Cu—Mg合金中锯齿形屈服现象影响及其微观实验研究

经固溶处理的A1-Cu—Mg合金在常应变率拉伸实验中具有显著的锯齿形屈服现象，且屈服行为随固溶处理温度的改变而呈现不同的特征。塑性变形特性与合金材料的微细观结构，尤其是位错运动的演化密切相关。本文运用透射电子显微镜，研究在不同温度下固溶处理的Al—Cu—Mg合金的微观结构，尤其是析出颗粒的大小和含量。并结合宏观的拉伸实验结果，分析Al—Cu—Mg合金动态应变时效的机制。     

Molecular dynamics studies on the dislocation gliding near a tilt boundary

The gliding behavior of edge dislocation near a grain boundary (GB) in copper under pure shear stresses is simulated by using molecular dynamics(MD) method. Many-body potential incorporating the embedded atom method (EAM) is used. The critical shear stresses for a single disocation to pass across GB surface are obtained at values of σ _c =23MPa ∼ 68 MPa and 137MPa∼274 MPa for Ω=165 small angle tilt GB at 300K and 20K, respectively. The first result agrees with the experimental yield stress σ _y (=42MPa) quite well. It suggests that there might be one of the reasons of initial plastic yielding caused by single dislocation gliding across GB. In addition, there might be possibility to obtain yield strength from microscopic analysis. Moreover, the experimental value of σ _y at low temperature is generally higher than that at room temperature. So, these results are in conformity qualitatively with experimental fact. On the other hand, the Ω=25 GB is too strong an obstacle to the dislocation. In this case, a dislocation is able to pass across GB under relatively low stress only when it is driven by other dislocations. This is taken to mean that dislocation pile-up must be built up in front of this kind of GB, if this GB may take effect on the process of plastic deformation. The project supported by KM85-33 of Academia Sinica and the National Natural Science Foundation of China