Creep-rupture reliability analysis

A probabilistic approach to the correlation and extrapolation of creep-rupture data is presented. Time temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson-Miller and on the Manson-Haferd parameters, but it can be applied to any of the TTP's. A method is developed for evaluating material dependent constants for TTP's. It is shown that optimized constants can provide a significant improvement in the correlation of the data, thereby reducing modelling error. Attempts were made to quantify the performance of the proposed method in predicting long term behavior. Uncertainty in predicting long term behavior from short term tests was derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state of the art reliability methods to the design of components under creep

Experimental study of the compaction dynamics for 2D anisotropic granular materials

We present an experimental study of the compaction dynamics for two-dimensional anisotropic granular systems. Compaction dynamics is measured at three different scales : (i) the macroscopic scale through the packing fraction $\rho$, (ii) the mesoscopic scale through both fractions of aligned grains $\phi_{a}$ and ideally ordered grains $\phi_{io}$, and (iii) the microscopic scale through both rotational and translational grain mobilities $\mu_{r,t}$. The effect of the grain rotations on the compaction dynamics has been measured. At the macroscopic scale, we have observed a discontinuity in the late stages of the compaction curve. At the mesoscopic scale, we have observed the formation and the growth of domains made of aligned grains. From a microscopic point of view, measurements reveal that the beginning of the compaction process is essentially related to translational motion of the grains. The grains rotations drive mainly the process during the latest stages of compaction.Comment: 8pages, 11 figure