فهرست مطالب محمد حمیصی

The basic idea of this study is based on the relationship between the vibrational andmechanical properties of matter and its structural changes due to operation at hightemperatures. In this regard, samples of DIN X12CrNi2525 steel were aged at three differentworking temperatures for a full three days and nights, which led to the formation ofprecipitation and increased sigma phase. By comparing the results of experimental tests, wesee a very strong relationship between the properties of matter. By comparing the results ofexperimental tests, we see as the temperature of aging rises, the natural frequency of the firstfive modes and the damping coefficients increase. Also, the tensile modulus and the hardnessof the Vickers increase, as the temperature of aging rises. This study examines the feasibilityof developing a new and non-destructive method for estimating residual life using dampingcoefficients in the conditions of super-heating of power plant parts.

In long-terms of overheating conditions, structural changes are the most important cause of mechanical deterioration and reduce the life of hot components. Given the difficulty or costliness of tests needed to assess the remaining life, searching for a non-destructive, simpler and more accurate way to estimate the remaining life of hot components and assess their remaining life is essential and have many economic benefits. The purpose of this study is to investigate the effect of structural changes on natural frequencies and damping coefficients of samples of carbon steel SA516-Grade55 so that, if there are significant effects, this method will be developed for other metals, in particular hot power plant parts. In this research, severe structural changes were observed on the samples by performing heat treatment of aging. As perlite decompose into ferrite and spheroidal carbides in the boundaries. With increasing structural changes, it was found that the natural frequencies of the first to sixth modes and the elastic modulus are decreased and the coefficients of damping and logarithmic decrease are increased significantly. These promising results are the elaboration of a non-destructive new method for estimating the remaining life for components of different types under long-term overheated operation conditions.