膨胀珍珠岩衬垫静态缓冲特性和蠕变性能研究

对研发的膨胀珍珠岩缓冲衬垫进行了静态压缩和蠕变性能试验研究,并与EPE和EPS衬垫的静态缓冲特性进行了对比分析.结果表明:膨胀珍珠岩衬垫具有与EPE相同的静态缓冲规律,在一定时间内其蠕变较小.     

Effect of oxidation on the creep behaviour of copper–chromium in situ composite

The creep deformation and fracture behaviours of a Cu–Cr in situ composite were investigated in air and in vacuum over a temperature range of 400–650 °C to study the effect of environment. The similarities of the activation energy and the stress exponent in air and in vacuum strongly suggest that the oxygen and/or the oxide have no direct effect on the deformation mechanism of Cu–Cr in situ composite. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. The mechanism of damage was found to be similar for all the creep tests performed.     

The interactions between fatigue, creep and environmental damage in Ti 6246 and Udimet 720Li

The paper reports the results of a comprehensive research programme on two different compressor disc alloys: titanium alloy Ti 6246 and the nickel based superalloy Udimet 720Li. Both alloys are used for disc applications in gas turbine engines under conditions where the rims are exposed to fatigue, creep and environmental damage. The titanium alloy was investigated at temperatures of 80, 450, 500 and 550 °C, whilst the nickel at 650 and 700 °C. The paper presents the strain-life response of plain specimens and relates these data to notch fatigue behaviour. It also explores fatigue crack propagation behaviour in air and under hard vacuum (10⁻⁶ Torr), in order to characterise the creep/environment/fatigue interactions that occur at the crack tip. The growth data encompass R values of −3 to 0.5 for cyclic and dwell waveforms. The information obtained allows the effects of environment and creep at these temperatures to be partitioned. The observed R value dependence is related to both empirical models and closure measurements. The experimental data are supported by detailed metallographic and fractographic studies using optical and SEM techniques.     

Multiaxial creep–fatigue under anisothermal conditions

Because creep–fatigue is mainly studied in uniaxial tension, it is shown here how to proceed to perform both experiments and calculations under multiaxial loading and when the temperature varies both in time and space. The constitutive equations used are those of elasto‐visco‐plasticity coupled or not, to damage, with isotropic and kinematic hardening. It is shown that the unified damage law first proposed for ductile failure and then for fatigue may also be applied to multiaxial creep–fatigue interactions with a new expression for the damage threshold. The procedure for the identification of material parameters is described in detail. Finally, it is shown that the uncoupled calculation procedure, where damage is calculated as a post‐processing of an elasto‐visco‐plastic computation, gives satisfactory results in comparison to the fully coupled analysis; the latter being more accurate but very expensive in computer time.     

Mechanical Properties of DS NiAl/Cr(Mo) Alloys with Low Addition of Hf for High-temperature Applications

1.IntroductionAs a new type of structural materials based on the B2intermetallics,NiAl offers superior characteristics,suchas low density,high melting point and excellent oxida-tion resistance at high temperature[1].However,the poorfracture toughness at ambient temperature and low creepstrength at elevated temperature limit their applicationcurrently.Although the creep strength has been sig-nificantly improved by precipitation strengthening[2]orforming a particulate composite[3],and ductility…     

Long-Term Behavior of Precast Segmental Cantilever Bridges

An investigation is conducted to quantify long-term effects on a family of four precast segmental bridges. Segments are prefabricated, transported, and set into place with an appropriate lifting device and a launching gantry. Attention has been paid to the effects of long-term deformations of concrete, to avoid noticeable geometrical variations in its shape but also to account for redistribution of stresses, which creates a difficult analytical problem to solve. An attempt is made to provide a practical treatment of serviceability analyses of this type of concrete structure, having an evolutive process of erection, presenting: (1) an “exact” incremental step-by-step time approach; (2) a simplified approach for the inclusion of time dependent effects of creep and shrinkage; and (3) a comparison of both approaches, in order to treat these kinds of problems by means of a simplified approach.     

Boundary element formulation for two-dimensional creep problems using isoparametric quadratic elements

A boundary element formulation for creep and time-dependent material behaviour problems based on an initial strain approach is presented. The details of numerical algorithm are shown where isoparametric quadratic elements are used both for the boundary elements and the quadrilateral domain cells. The Euler method with automatic time-step control scheme is implemented for time integration. Two creep power laws, time-hardening and strain-hardening, are employed to analyse a number of problems, including a square plate, a plate with a circular hole and a plate with a semi-circular notch subjected to a uniaxial load. The results are compared with analytical solutions where available and the corresponding finite element solutions.     

用于城市轨道交通的直流1500V隔离开关柜的绝缘配合

本文通过对国内外相应标准的分析、研究和对比,提出了用于城市轨道交通（直流供电接触网系统）中的1500V隔离开关柜的绝缘参数参考值,其原则是既要保证非常可靠而又节约成本。该文给出了主回路带电体间以及对地的净空气距离、爬电距离、工频耐受电压和雷电冲击耐受电压等多项数据。     

CREEP-FATIGUE CRACK GROWTH BEHAVIOR IN 1Cr-1Mo-0.25V STEEL. PART II: CRACK GROWTH BEHAVIOR AND MODELS

Abstract— Creep-fatigue crack growth (CFCG) behavior of an ex-service 1Cr-1Mo-0.25V steel was investigated for hold times of 100 s, 15 min, and 8 h for a trapezoidal loading waveform at a temperature of 538°C. The correlation of the crack growth rate with ( C _t)_avg for various hold times was significantly improved when an appropriate estimation scheme, previously proposed by the authors, was used to estimate this creep fracture mechanics parameter for this material. Crack growth data under creep-fatigue conditions and analysis procedures used to reduce them are described in detail in this paper.     

蠕变对管系热应力的影响

介绍了一段转化炉下集气管的蠕变变形计算方法。分析了实际工况中下集气管的蠕变变形及其对管系热应力分布的影响。通过实验验证了计算结果