蚀变岩的蠕变特性研究

以某水电站工程项目为依托,利用自行研制的试验仪器对大量的蚀变岩做了单轴压缩流变试验。通过对试验数据的处理和分析,得到了该种岩石的流变,并对蚀变岩的蠕变特性进行了分析总结,为工程设计提供了试验依据。     

Effects of entanglement concentration on Tg and local segmental motions

The process of spin-coating to fabricate thin polymer films with high molecular weight can produce samples with entanglement concentrations that are far below the equilibrium value. It is not clear whether or not such low entanglement concentrations are responsible for the depression of the glass temperature in thin polymer films. In this work, we measure the calorimetric glass temperature and viscoelastic response of polystyrenes with molecular weights ranging from 3×10³ to 43.7×10⁶ g/mol, for both bulk material and for samples freeze-dried from dilute solution. We conclude that the reduction of the glass temperature observed in thin polymer films cannot be due to the reduced entanglement concentration in the samples. Received 15 August 2001 and Received in final form 2 March 2002     

The influence of imperfections on the creep behavior of woven polymer composites at elevated temperatures

The dynamic behavior of compression molded polymer/woven graphite fiber composites at elevated temperatures is investigated analytically. This is performed with the objective of predicting the initiation of catastrophic failure that may occur after prolonged usage of the material at these temperatures. Special attention is paid to the behavior of the voids present in them where the failure may occur. The polymer matrix is modeled as a 4-parameter model (Maxwell-Voigt combination) (Govindarajan et al., in: Advances in Computer-Aided Engineering, ASME, 1994) while the composite structure is modeled using the fiber undulation model (Ishikawa and Chou, J. Mater. Sci. 17, pp. 3211–3220, 1982). The relation between the polymer properties and the ambient temperature is modeled after Arhenius' relation (Govindarajan et al., 1994; Ferry, Viscoelastic Properties of Polymers, Wiley, New York, 1961). The multiple phases in the matrix are taken into account through Eshelby's theory (Proc. Royal Soc. London A 241, pp. 376–396, 1957) and its extension for multiple occurrences of the same phase (Tanden and Weng, Polymer Composites 5, pp. 327–333, 1984; Weng, Internat. J. Eng. Sci. 22 (7), pp. 845–856, 1984) which assumes an ellipsoidal shape for inclusions. The resulting elastic equations are transformed into the time domain using Laplace transformation and the correspondence principle (Govindarajan et al., 1994; Wang and Weng, ASME J. Appl. Mech, 1992). All the voids are considered to be prolate ellipsoids with the 1-axis being the axis of symmetry. The distribution of voids is assumed to be of a Gaussian form with respect to the aspect ratio. The response of the composite under creep condition (constant load) has been simulated. Relations between the applied stress and the stresses in the matrix/void phase are also supplied, so that the influence of the voids may be characterized. The model is then applied to simulate the behavior of an epoxy/woven graphite composite to obtain the numerical results.     

Long-term non-linear behaviour and buckling of shallow concrete-filled steel tubular arches

This paper presents a theoretical analysis for the long-term non-linear elastic in-plane behaviour and buckling of shallow concrete-filled steel tubular (CFST) arches. It is known that an elastic shallow arch does not buckle under a load that is lower than the critical loads for its bifurcation or limit point buckling because its buckling equilibrium configuration cannot be achieved, and the arch is in a stable equilibrium state although its structural response may be quite non-linear under the load. However, for a CFST arch under a sustained load, the visco-elastic effects of creep and shrinkage of the concrete core produce significant long-term increases in the deformations and bending moments and subsequently lead to a time-dependent change of its equilibrium configuration. Accordingly, the bifurcation point and limit point of the time-dependent equilibrium path and the corresponding buckling loads of CFST arches also change with time. When the changing time-dependent bifurcation or limit point buckling load of a CFST arch becomes equal to the sustained load, the arch may buckle in a bifurcation mode or in a limit point mode in the time domain. A virtual work method is used in the paper to investigate bifurcation and limit point buckling of shallow circular CFST arches that are subjected to a sustained uniform radial load. The algebraically tractable age-adjusted effective modulus method is used to model the time-dependent behaviour of the concrete core, based on which solutions for the prebuckling structural life time corresponding to non-linear bifurcation and limit point buckling are derived.     

Cross-linking kinetics study and high temperature mechanical properties of ethylene–octene copolymer (EOC)/dicumylperoxide(DCP) system

Ethylene–octene copolymer (EOC) was cross-linked by dicumyl peroxide (DCP) at various temperatures (150–200 °C). Six concentrations of DCP in range 0.2–0.7 wt.% were investigated. Cross-linking was studied by rubber process analyzer (RPA). From RPA data analysis real part modulus s′, tan(delta) and reaction rate constant K were investigated as a function of peroxide content and temperature. The highest s′_max and the lowest tan(delta) were found for 0.7% of DCP at 150 °C. The quantitative analysis confirmed that the DCP–EOC cross-linking was occurring as first order reaction. The highest cross-linking kinetics constant K was found for 0.6% of peroxide at 200 °C. The activation energy of cross-linking E_A obtained by Arrhenius plot had maximum at 0.5–0.6% of peroxide. While at 190–200 °C temperature range there was no detectable degradation for 0.2% of peroxide, for 0.4–0.7% of peroxide there was increasing level of degradation with increasing peroxide content. Generally, at low temperatures (150–180 °C) the increasing peroxide content caused increase in cross-linking kinetics. However at higher temperatures (190–200 °C) increase in kinetics (for 0.2–0.5% of peroxide) was followed by decrease. Especially in 0.6–0.7% peroxide level range the cross-linking is in competition with degradation which lowers the overall cross-linking kinetics. Gel content of the cross-linked EOC samples was found to be increasing with increase in peroxide content, which is caused by the increased cross-link network. Cross-linked samples were subjected to creep studies at elevated temperature (150 °C) and the result was found in agreement with the gel content and RPA results. Storage modulus and tan(delta) values obtained by Dynamic Mechanical Analysis (DMA) also support the RPA results.     

Evaluation of the Surface Referencing Technique in Depth‐Sensing Indentation of Soft Materials

Abstract

Thermal drift is an important consideration for reliable nanoindentation measurements. The surface‐referencing technique for eliminating thermal drift effects is critically assessed in this work. When applied to soft materials such as polymers and low‐melting metals, the surface‐referencing technique is found to cause a serious and problematic artificial drift due to the creep of the sample under the pressure exerted by the reference ring. A possible solution is proposed here to overcome this problem.     

三峡永久船闸衬砌墙分水平缝对结构及结构锚杆受力影响研究

采用考虑三维接触非线性的结构温度徐变仿真计算方法, 针对三峡永久船闸 (全衬式和混合式)闸室墙整体和分缝两种结构形式进行了计算分析, 研究表明:闸室墙分水平缝可以有效地降低全衬式和混合式结构混凝土铅直向拉应力, 但使最大锚杆拉应力值和平均锚杆拉应力值增加, 分布的离散性增大, 在横缝和纵缝交点附近出现锚杆拉应力集中现象。