流变岩体中椭圆洞室断面开挖过程的力学分析

给出了黏弹性流变岩体中深埋椭圆隧洞断面开挖过程中力学响应的解析解答。通过设定长短半轴随时间变化的函数可模拟施工过程。首先,结合变边界黏弹性问题对应关系和平面弹性复变方法,求得岩体应力及开挖引起位移的统一表达。在推导中,通过建立逆映射函数,分离出参与Laplace变换的时间。然后,对模拟为Boltzmann黏弹模型的岩石材料,给出了积分形式的位移表达式。最后,针对不同类型岩石进行不同开挖方式和速度下无量纲位移及应力的参数分析。分析表明,施工方式对位移与应力有明显影响。给出的解析解答可用于地下椭圆孔型隧道在开挖过程中的力学分析,并可作为实际工程初步设计的手段。     

硫酸钠溶液和硫酸钠盐渍土的冻结温度及盐晶析出试验研究

为了探索硫酸钠盐渍土的盐胀与冻胀机理,对硫酸钠溶液分别在环境温度-20℃和变环境温度-5℃～-10℃下进行降温试验;并对硫酸钠盐渍土在环境温度-20℃下进行降温试验,通过试验研究了硫酸钠溶液和硫酸钠盐渍土中芒硝的析出规律及各自的冻结温度。试验表明：在相同外界环境温度下,浓度大的溶液,芒硝更容易析出;具备一定浓度的溶液,在环境温度变化缓慢条件下更容易析出但溶液的冻结温度的趋势一致;相同浓度硫酸钠盐渍土的冻结温度均低于硫酸钠溶液的冻结温度,随着含盐量增加,其冻结温度降低;在相同外界环境温度下,盐晶在土体中更容易析出。     

单点和多点荷载输入的虚拟激励法实用求解模式

在实际工程中采用虚拟激励法（pseudo excitation method,PEM）往往需要编写复杂计算程序,为方便工程应用,建立了一种对应单点和多点荷载输入的虚拟激励法实用求解模式。考虑地震作用、风荷载等多种随机荷载,提取单点和多点荷载输入下计算结构虚拟响应的实用求解模式,并利用常规有限元分析软件的谐振稳态分析完成PEM核心计算,最后通过线性组合重新构建结构虚拟响应和功率谱密度函数的求解公式,从而在常规有限元分析软件中实现了PEM算法。由于采用建议方法可将PEM算法的核心计算交由有限元分析软件完成,在保持PEM高效准确计算优势的前提下显著提高了工作效率,避免了编写复杂计算程序,方便实际工程应用。通过两个典型数值算例验证了建议方法的正确性与有效性,并且指出其对于多种荷载工况的计算效率具有一定优势。     

非静水压力场中考虑应力释放的圆形隧道黏弹性解

在非静水压力场中考虑应力释放的圆形隧道弹性解基础上,先利用对应性原理求解应力释放率λ为常数时隧道的黏弹性解。然后考虑到施工过程中应力逐步释放,隧道内壁(r=R0)处边界条件随开挖面和研究断面之间距离x变化,距离x取决于掘进速度v和时间t,从而边界条件可以表示为时间t的函数。采用斯蒂尔杰斯积分法将常应力释放率时黏弹性解中的λFi(t)(i=1～11)转换为Fi(t)对应力释放率导数dλ(t)的积分形式,可得非静水压力场中考虑应力释放的圆形隧道黏弹性解。该解在侧压系数k0=1时,可转化为静水压力场中考虑应力释放的黏弹性解;在λ=1时,可以转化为非静水压力场中不考虑应力释放的黏弹性解,所以后2种解均为非静水压力场中考虑引起释放圆形隧道黏弹性解的特例。考虑非静水压力场,求解边界条件能较好地反应工程实际中原岩应力分布;考虑应力释放能够反应隧道掘进过程中围岩应力及变形分布情况。故所提出的黏弹性解能够为隧道设计、施工阶段及长期变形及稳定性预测提供理论依据。     

An inverse solution of the lifetime-oriented design problem

This paper presents a new solution of the lifetime-oriented design problem. This solution is based on a point-to-point allocation between the space of the design parameters and the space of structural responses. Each point in the space of the design parameters defines a feasible or non-feasible design, and all feasible designs guarantee compliance with a predetermined lifetime. From the set of feasible designs, one or more designs may be selected with the aid of technical or economic criteria. The presented solution permits the consideration of non-statistical data uncertainty, thereby leading to an uncertain lifetime. Because of the unavoidable information deficit, for example incomplete data in practical problems, the application of non-statistical data uncertainty is more realistic than the application of stochastic data models. The selection of feasible design variants is based on methods of explorative data analysis.     

高分子链结构对聚酰胺酰亚胺溶液流变行为的影响

以高分子主链分别含3个和10个亚甲基结构的脂肪族–芳香族聚酰胺酰亚胺(PAI)为模型聚合物,采用旋转流变仪研究了高分子链结构对PAI溶液流变行为的影响。研究结果表明,含10个亚甲基结构的PAI在较宽的剪切速率范围内表观黏度变化不大,但含3个亚甲基结构的PAI溶液在一定的剪切速率区间发生了剪切增稠现象,并且随着温度的升高,剪切增稠现象逐渐减弱,同时剪切增稠所对应的剪切速率向高剪切速率方向移动。     

硫酸亚铁铵容量法测定高锰酸钾含量

建立了硫酸亚铁铵容量法测定氧化物处理槽液中高锰酸钾含量的分析方法,进行了指示剂选择、精密度和加标回收率等条件实验。实验结果表明,相对标准偏差均小1.0%(n=7),加标回收率为99.49%~100.61%。此方法的精密度好、准确度高。     

铬酸改性超高相对分子质量聚乙烯纤维的研究

研究了铬酸对超高相对分子质量聚乙烯(UHMWPE)纤维的作用机制,用扫描电镜和傅里叶红外光谱仪分析了铬酸改性前后UHMWPE纤维的结构变化,用单因素分析法分析铬酸处理条件对纤维拉伸强度、静摩擦因数以及与基体黏接强度的影响,从而得到铬酸改性UHMWPE纤维的较优工艺条件:处理液m(K_2Cr_2O_7)∶m(H_2O)∶m(H_2SO_4)为7∶12∶(78~82);处理温度为60~66℃;处理时间为6~10 min。     

Advances in Epoxy/Graphene Nanoplatelet Composite with Enhanced Physical Properties: A Review

In this review, development from graphene nanoplatelet, that is, comprised of short bulk of single layer graphene, into modified-polymer/graphene nanoplatelet composite is presented. Preparation methods of graphite, graphene, and graphene nanoplatelets have also been discussed. Graphene nanoplatelet and modified graphene nanoplatelet commend unique properties to composites such as excellent thermal and electrical conductivity as well as mechanical and barrier properties. Graphene nanoplatelet fabrication techniques by solution mixing, melt blending, and in situ polymerization are also discussed. Excellent dispersion of nanoplatelets in polymer/graphene nanoplatelet depends upon the selection of suitable fabrication technique. Moreover, the corresponding significance, exploitation, challenges, and future aspect of polymer/graphene nanoplatelet-based material is overviewed.     

Solution combustion of spinel CuMn2O4 ceramic pigments for thickness sensitive spectrally selective (TSSS) paint coatings

A series of spinel-type CuMn₂O₄ ceramic pigments were prepared by a facile and low-cost sol-gel solution combustion method and used as cost-effective materials to fabricate thickness sensitive spectrally selective (TSSS) paint coatings by a convenient spray-coating technique. The chemical component, crystalline morphology, and optical property of the copper manganese oxide ceramic pigment could be accurately controlled by altering the annealing temperature. X-ray diffraction (XRD) analysis confirmed that the ceramic pigments annealed at 500 °C for 1 h coincided well with the XRD patterns of crystalline CuMn₂O₄ in the JCPDS database, and there were segregated phases of CuO and Mn₂O₃. Furthermore, the pure spinel CuMn₂O₄ phase could be achieved at 900 °C for 1 h. The copper manganese oxide ceramic pigments could serve as an effective pigment for fabricating the TSSS paint coating, and the TSSS paint coatings based on ceramic pigments calcined at 900 °C showed solar absorptance of 0.895–0.905 and thermal emittance of 0.186–0.310. In addition, the accelerated thermal stability test revealed that the TSSS paint coating exhibited good thermal stability when it was exposed to air at a temperature of 300 °C for 300 h. Hence, the fabricated TSSS paint coating could be used as a solar absorber coating in the low-to-mid temperature domain.