فهرست مطالب seyed ebrahim moussavi torshizi

Shot-peening is a mechanical surface treatment used extensively in the industry to enhance the performance of metal parts against fatigue. Thus, it is important to determine main parameters of shot-peening in order to obtain its optimal values. The purpose of this study is to achieve a statistical model to determine the important parameters of the shot-peening process by considering the effect of sample thickness on the responses and achieving the multi-objective optimal parameters. To do this, response surface methodology are used to determine the governing models between the response variable and the input parameters. Shot velocity, shot diameter, coverage percentage and sample thickness are selected as shot-peeningparameters. Residual compressive stress, its depth and roughness are considered as the response variable. Using finite element analysis, shot-peening process are simulated. The desirability function approach is used for multi-objective optimization so that the optimal shot-peeningparameters, which simultaneously provide two response variables in optimal mode, are obtained. The results show that surface stress and maximum residual stress are independent of shot velocity, whereas, the depth of the compressible stress and roughness are directly related to shot velocity. In addition, thickness modifies surface stress and the depth of the compressible stress. The optimal conditions for surface stress, maximum compressive stress, and roughness simultaneously with high-coverage and low-velocity can be achieved as well.

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.