Diffusional creep induced stress relaxation in thin Cu films on silicon

The results of stress measurements during annealing of thin copper films deposited on 100 μm Si substrates are presented. The stress in thin films was determined by using an optical system for curvature measurements. The annealing experiments were done during thermal cycles of heating and cooling procedures from room temperature up to 400 °C with a rate 10 °C/min. The total thickness of thin films was between 20 and 100 nm. The obtained results showed that the difference between the end and the initial values of the ratio of force to width increases with the thickness of the samples. The initial linear shape of the temperature-stress plots reaches higher temperature values with an increase in film thickness. In order to explain the observations, the dependence of stress on temperature was calculated using the rate of Coble creep. It was found that the theoretical curves reveal the same features as the experimental data. It was concluded that diffusional creep mechanism dominates for thin film of thickness below 100 nm.     

On the influence of preloading in the nonlinear viscoelastic–viscoplastic response of carbon–epoxy composites

On an ongoing research for the nonlinear viscoelastic response of composites and polymers, a study of the influence of preloading applied to composite laminates subjected to creep–recovery loading is performed. In cases where high stress levels are applied, this response becomes highly nonlinear and has to be taken into account when designing composite parts. A major problem encountered in the experimental investigation of the nonlinear viscoelastic behaviour is the mode of the initial applied loading and its effect in the overall viscoelastic response of the test sample. The damage that occurs due to the instantaneous application of the load leads to an additional viscoelastic/viscoplastic strain component. In order to investigate this effect as well as to compare different preloading modes, as far as viscoelastic/viscoplastic response is concerned, a test program was initiated and the experimental data were investigated in the current study. A preloading mode is applied in each specimen prior to the creep–recovery testing at different applied stress levels. Useful results concerning the effect of preloading in the time dependent response of the material are concluded. Variation of the values of viscoplastic strain in respect to the preloading mode is also of great concern.     

掺合料和粗骨料对C60高性能混凝土徐变性能的影响

通过混凝土徐变试验研究了C60高性能混凝土的徐变性能.试验结果表明,随着龄期增长,徐变系数增大,收缩变形增加,徐变速率降低.同龄期时,双掺23％粉煤灰和10％矿粉降低了混凝土的徐变系数和收缩应变;持荷180d,纯水泥混凝土的徐变系数为1.304,而双掺混凝土徐变系数较纯水泥混凝土下降了10.4％.小石率60％的双掺混凝...     

预应力混凝土楼盖结构长期水平方向的变形

本文提供了混合配筋预应力混凝土框架扁梁楼盖结构在施工和长期使用荷载下两端水平变位的计算方法。通过两批１／３缩尺模型的结构长期试验观测与检验结果，证明了该计算方法可供设计计算和施工期间控制变形与裂缝时参考。     

考虑软弱夹层蠕变特性的某矿山边坡稳定性研究

为研究软弱夹层的存在状态对岩土体强度变形特性的影响,选用PFC3D离散元软件进行不同条件下的复合岩样标准三轴试验模拟,深入分析其强度变化规律及变形破坏特征;借助FLAC3D软件建立了依托实际工程的三维模型,选用考虑蠕变特性的Burgers模型,对露天矿山边坡的稳定状态进行深入分析,得到如下结论:（1）软弱夹层的倾角、厚度、层数等参数均对复合岩样的强度有显著影响;（2）随着夹层倾角增大,三轴试样产生大量剪切裂缝;随着夹层厚度增大,三轴试样由剪切破坏向张拉破坏转变;随着夹层层数增加,三轴试样呈现中间部位的张拉破坏;（3）当考虑露天矿山软弱夹层的蠕变特性时,其强度折减系数为1.16,比不考虑蠕变特性降低了约10%,可为实际工程提供更高的安全存储。     

A comparison of the mechanical properties of fire-resistant and S275 structural steels

The mechanical properties of two fire-resistant (FR) structural steels and an S275 steel have been investigated from room temperature up to 700°C, with the aim of assessing the viability of FR steels. The major focus has been on the tensile and creep properties of the steels at high temperature and the effect of these properties on the fire resistance of model steel beams. It has been found that the FR steels performed significantly better than the S275 at high temperature, retaining 50% of their room temperature strength at a temperature of approximately 650°C. The S275 steel retained 50% strength to a temperature of 550°C, this being consistent with literature values. In creep tests carried out at 600°C, the FR steels also exhibited lower maximum strains and strain rates than the S275. The improved strength reduction factors led to a significant increase in fire resistance for a model steel beam with various floor slab configurations, showing that FR steels can become a practical alternative to conventional structural steels.     

露天矿顺层蠕动边坡稳定性动态分析探讨

进行了阜新海州露天矿北帮东部一号断层区顺层蠕动边坡变形、失稳机理分析讨论。根据老化理论提出了软弱夹层的一般流变方程τ =Ao( 1 δ·tα) ·γm ( 1 σmH) ,确定由等速蠕变向加速蠕变过渡的临界应变量作为破坏时刻的破坏应变量γs,从而建立长期抗剪强度与应力作用时间变化的关系τ =Ao·γs( 1 δ·tα) Ao·γsH ( 1 δ·tα) ·σm=c σm·tgφ ,对于非稳定蠕动变形 ,等速蠕变阶段的应变速率与剪应力超过长期极限强度的程度有关 ,在此基础上探讨并建立顺层蠕动边坡的流变稳定性分析方法 ,评价蠕动边坡变形、失稳的动态演化     

Effects of geometry and combined loading on steady-state creep stresses in welded branches

In our previous paper, it was found that the mis-match effect in creep on steady-state stresses within the weld metal for a large bore branch junction could be uniquely quantified by the mis-match factor defined as a function of the creep stress exponent and the ratio of creep constants for the base and weld materials. Furthermore ratios of section-averaged (effective and maximum principal) stresses for the mis-matched case to those for the even-matched case were linearly dependent on the mis-match factor. Above results were obtained for a specific branch geometry under single loading. This paper extends our previous analysis to other branch geometries and to combined loading. It is found that above conclusions can be applied to general branch components under combined loading.     

The prediction of creep rupture of pressurized tubes using a model for void growth and coalescence

A phenomenological formulation based on a theory of plasticity for voided solids, and power-law creep, to estimate the rupture times and strains for pressurized tubes is presented. Realistic values of the damage parameters involved are selected by satisfying the creep rupture uniaxial data for the same materials. Void growth and coalescence and hence the loss of load-carrying capacity of the tube is taken as a failure criterion. Computed values of rupture times for thin- and thick-walled tubes are shown to be mostly in close agreement with the experimental data found in the literature. Only fair agreement among predicted and experimental fracture strains is observed.     

加热炉炉管材质损伤机理及其金相检测

石化系统加热炉炉管常见的材质损伤机理,包括珠光体球化、石墨化、蠕变、σ相脆化、渗碳、脱碳、晶间腐蚀、渗氮和裂纹等,总结了上述损伤机理可能发生的条件及其危害,介绍了金相检测等技术在炉管材质损伤检测方面的应用。基于对加热炉炉管的现场金相检测经验,给出了五种典型炉管材质损伤的实际案例,并简要介绍了其应对措施。