Study of low cycle fatigue in plain carbon steel pressurized cylinders under simulated seismic loading by Chaboche hardening model

Mostafaei, Hamed (2018) Study of low cycle fatigue in plain carbon steel pressurized cylinders under simulated seismic loading by Chaboche hardening model. Masters thesis, University of Mohaghegh Ardabili.

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Text (بررسی پدیده خستگی کم چرخه در لوله¬های مستقیم تحت فشار کربنی ساده در اثر بارهای مشابه با اثرات زلزله بر اساس مدل سختی چابوشی) Hamed Mostafaei.pdf Download (1MB) | Preview

Abstract

The phenomenon of ratchetting is one of the reasons for the failure of fatigue in the pipes. In order to predict the fatigue life of the pipes, it is necessary to accurately calculate this phenomenon and the factors affecting its amount during cyclic loading. Accordingly, in this research, the behavior of the ratchetting in straight pipes made of mild steel under internal pressure conditions and in the presence of similar periodic moments with earthquake effects has been investigated. Numerical analysis has been done based on the non-linear hardening Chaboche model using Abaqus finite element software. The constant material parameters are determined and the numerical results of the ratchetting are compared with the experimental results as well as with the results obtained from the combined hardening model (Armstrong and Frederick + isotropic rule). The results of both experimental and numerical studies indicate that the rate of ratchetting increases with increasing loading rates. The ratchetting appears in the Hoop direction and in the out side diameter of the pipe. At initial the rate of ratchetting is large, and it decreases with the increases of cycles and then reaches a constant value. It is also observed that the onset of the ratchetting in accordance with the experimental results in two specimens (MS1, MS2) are equal to the results of the numerical method. But for other specimens, the onset of the ratchetting by the experimental results occur earlier than the finite element method based on the Chaboche and the combined (Armstrong and Frederick + isotropic rule) hardening models. The results show that there is low difference between ratchetting results from the Chaboche hardening model and the combined hardening model (Armstrong and Frederick + isotropic rule). In comparison with the results obtained from the experimental method, especially in the high dynamic moments , the FE models are over-estimated. However, the ratchetting rate from the FE methods in the range of low dynamic moments is close to the experimental results.

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