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Although fundamental models have been developed for time extrapolation of creep rupture data, empirical methods are still dominating. One limitation with the empirical methods is that no systematic way of estimating the error in the results has been available. To remove this limitation, formulae for error estimates are developed in the present paper. Error estimates are first established for single creep rupture curves. Then error estimates are formulated for creep data at several test temperatures assessed with Time-Temperature Parameters (TTPs). A new requirement is introduced in the optimization, namely that the first and second derivatives of the rupture curve should be negative, referred to as constrained. The constrained optimization significantly reduces the error in the extrapolated values. The constrained procedure is applied to the austenitic steel Sanicro 25. The procedure gives quite a stable result, and the post-assessment tests developed by ECCC are satisfied automatically for five common TTPs tested. [ABSTRACT FROM AUTHOR]

In this work, the glass transitions of poly(methyl methacrylate) and polystyrene in compressed gaseous acetone/carbon dioxide were measured by an in situ creep compliance method at pressures lower than 7.0 MPa and at 318−338 K. When a small amount of acetone (x= 0.01−0.02) was added to a polymer-compressed carbon dioxide system, the glass transition pressure of polymer was further depressed by 1.0−4.0 MPa. The observed glass transition pressure depression increased with the acetone concentration in carbon dioxide and decreased with the temperature rise. A simple model was used to estimate the glass transition temperature depressions for the polymers in compressed gaseous acetone/carbon dioxide solution. The calculated results were in good agreement with the determined ones, except for the retrograde vitrification region. [ABSTRACT FROM AUTHOR]

A novel Mo–Si–B double-layer coating was prepared for the carbon/carbon (C/C) composites by pack cementation in an argon atmosphere. The structures of the double-layer coatings were characterized by XRD and SEM. The as-received coating shows an excellent oxidation resistance at high and intermediate temperature. It could effectively protect C/C composites from oxidation for 30 h with a weight loss of 0.9% in air at 1873 K, and for 25 h with a weight loss of l.7% at 1173 K. The oxidation protective coating was principally due to producing eutectic glass film for decreasing oxygen diffusing through the penetrable cracks in the coating. [ABSTRACT FROM AUTHOR]

The tri-axial creep tests of frozen sand with different dry densities and grain size distributions were performed at 0.1 MPa confining pressure at different temperatures. The results show that the rheological properties of frozen sand are significantly affected by the temperature, the creep deformation of the frozen sand is obvious even under a small load when the temperature is higher than - 1.5 °C. Firstly, based on the Nishihara model, the elastic modulus of viscoelastic elements is modified to be a function of stress, the coefficient of viscosity in viscoelastic part is modified considering the effect of time and stress, and the viscoplastic element is improved by introducing the damage variable. Then a new non-linear creep constitutive model for frozen sand is proposed, and the new model is verified based on test results. It can be found that the predicted results agree well with the corresponding experimental results from low stress to high stress, and the proposed model can describe the whole creep process of frozen sand with different dry densities and grain size distributions accurately under different shear stress levels and temperatures. Besides, the function relationship between the model parameters and the shear stress under different temperatures is obtained through the regression analysis. Finally, the influences of the temperature and shear stress on the parameters are analyzed as well. This study is important to further study the stability of permafrost subgrade, and can accumulate experimental data for the study of creep theory. • The tri-axial creep tests of frozen sand with different dry densities and grain size distributions were performed at 0.1 MPa confining pressure at different temperatures. • The effect of particle content ranging from 0.075 to 1 mm on creep properties of sand has been discussed in this paper. • A new non-linear creep constitutive model for frozen sand was proposed and verified based on the test results. [ABSTRACT FROM AUTHOR]