循环荷载作用下聚丙烯纤维再生混凝土受压性能试验研究

为研究循环荷载作用下聚丙烯纤维再生混凝土(PFRAC)的力学性能,以粗骨料取代率、纤维掺量、加载速率为变化参数,设计了78个圆柱体试件进行单轴循环受压试验。通过试验观察PFRAC的破坏形态,获取了应力-应变曲线、峰值应力、峰值应变、刚度退化等重要指标,研究了不同变化参数对其力学性能指标的影响规律,得到了循环荷载作用下聚丙烯纤维对再生混凝土的阻裂机理。结果表明：循环荷载作用下PFRAC主要发生斜向劈裂破坏;随着聚丙烯纤维掺量的增加,试件表面主裂缝宽度减小;循环荷载下PFRAC试件受压应力-应变曲线包络线与单调受压应力-应变曲线相似;聚丙烯纤维的加入可显著改善PFRAC循环荷载下的力学性能,随着纤维掺量的增加,峰值应力、弹性刚度比先增大后减小;纤维掺量为0.9%时的纤维改性效果最优,峰值应力和峰值刚度比分别提高了4.4%和7.4%。     

Nanostructural modifications of polyamide/MMT hybrids under isothermal and nonisothermal elongational flow

The aim of this work is to investigate the effects of elongational flow on the nanoscale arrangement of the silicate inside polyamide‐based nanocomposites. Hybrids, at different loadings of a commercial organoclay, were produced by melt compounding using two polyamide matrices, a nylon‐6, and a copolyamide with similar molecular weight and rheological properties. The elongational flow characterization was performed under both isothermal and nonisothermal conditions by using, respectively, an elongational rheometer (SER) and a fiber‐spinning technique. The extensional rheological response of melt‐compounded nanocomposites, correlated to TEM and X‐ray analyses, was used to probe the nanostructural modifications developed during the uniaxial stretching. The results demonstrated that isothermal and nonisothermal elongational flow can modify the nanomorphology of the nanocomposite hybrids affecting the degree of silicate exfoliation as well as the extent of silicate orientation upon the stretching direction. The entity of structural modifications induced by the stretching were highly dependent on the initial nanomorphological state and on the polymer‐clay affinity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 981–993, 2009     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

在制备出Gd₃(Fe_1-xCo_x)_29-yCr_{y化合物基础上，成功制备出Sm3(Fe1-xCox)29 -yCry化合物，通过x射线衍射和热磁分析对R3(Fe1-x< /sub>Co x)29-yCry 关键词： 3(Fe1-xCox)29-yCry化合物')" href="#">R3(Fe1-xCox)29-yCry化合物 相结构 单轴磁晶各向异性}     

碳纳米管增强氟橡胶高温力学行为及本构关系研究

改性氟橡胶因其优异的耐油耐高温及良好的物理性能,广泛应用于汽车、航空航天和国防等领域。本文通过对不同温度(120 ℃~220 ℃)下碳纳米管增强氟橡胶的单轴拉伸试验结果进行分析,得到改性氟橡胶力学行为随温度变化的特点。通过本构模型评估和材料参数拟合,推导出适用于改性氟橡胶的温度相关修正本构方程。最终对比了特定温度下单轴拉伸的试验结果与模型预测结果,证明了温度相关的修正Yeoh模型可以较好地描述试验温度内碳纳米管增强氟橡胶的力学性能,为高温下改性氟橡胶的工程应用提供理论基础。     

基于WOA-XGBoost模型的胶结充填体强度预测

单轴抗压强度作为胶结充填体重要的力学性能指标,通常使用传统的力学试验来确定。使用鲸鱼优化算法（whale optimization algorithm,WOA）对极限梯度提升模型（XGBoost）进行优化,建立了WOA-XGBoost混合模型。以某铅锌矿充填料浆配比试验得到的80组数据作为数据库,选取固体质量分数、水泥占比、尾砂占比及养护天数作为输入参数,充填体试块抗压强度作为输出参数。为了与WOA-XGBoost模型进行比较,还构建了XGBoost、RF和WOA-RF模型。结果表明：WOA-XGBoost模型的决定系数为0.965 0,均方根误差为0.207 4,平均绝对误差为0.170 3;XGBoost模型的决定系数、均方根误差、平均绝对误差分别为0.897 1、0.408 4和0.246 7。可见,鲸鱼优化算法能够显著提高XGBoost模型的预测能力。相比XGBoost、RF和WOA-RF模型,WOA-XGBoost混合模型具有更高的预测精度。研究结果对于胶结充填材料的设计和配比优化具有重要意义。

     

水饱和度对再生混凝土力学性能的影响及微观机理分析

为探究再生混凝土在水工建筑物中应用的可行性,提升资源利用效率,对4种骨料取代率下不同水饱和度的再生混凝土进行力学性能试验研究,并结合核磁共振和电镜扫描试验对再生混凝土进行微观机理分析。结果表明：随着骨料取代率和水饱和度的增加,混凝土弹性模量逐渐增大,而抗压强度、峰值应变和劈裂抗拉强度逐渐减小;对试件横向弛豫时间(T₂谱)曲线进行分析发现,骨料取代率为0%、30%、50%和70%试件内的小孔隙数量占比分别为83%、77%、82%、84%;通过扫描电镜观察发现,混凝土基质密实度随再生骨料取代率增加而下降,易被自由水渗透,对再生混凝土的力学性能产生不利影响。本文研究成果可为再生混凝土在水工结构上的应用提供参考。     

Leakage of light in liquid crystal displays and birefringent thin film compensators

This paper elucidates the physical origin of leakage of light in the dark state of liquid crystal displays (LCDs) and describes birefringent thin film compensators to mitigate the problems. There are two fundamental sources of leakage of light in LCDs. They are the leakage of light through a pair of ideal crossed polarizers, and the leakage of light due to elliptical state of polarization after transmitting through the liquid crystal (LC) cell. The leakage of light in the dark state leads to poor contrast ratios and color instability, particularly at large viewing angles. The paper then describes the employment of sixth-wave (λ/6) plates as well as various wave plates that function as birefringent compensators for eliminating the leakage of light in LCDs.     

Features of the E 2 g phonon mode in MgB2

A model estimate of the energy eigenvalues of the E _2g phonon mode of the ion vibrations in the plane of boron atoms is obtained. It is shown that the anharmonic contribution to the energy of E _2g monotonously increases with the increase in z = A ₄/A ₂², where A ₄ is the fourth-order anharmonic coefficient and A ₂ is the harmonic constant. The results agree with the estimate in the Hartree-Fock approach. However, the discrepancy between these results and Raman spectroscopy data indicates the necessity to account for the influence of the electron-phonon interaction on the energy of E _2g in more detail. Original Russian Text ? V.V. Rzhevskii, 2009, published in Vestnik Moskovskogo Universiteta. Fizika, 2009, No. 1, pp. 93–94.