Date of Award

2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Nader Zamani

Second Advisor

Sreekanta Das

Keywords

Applied sciences, Empirical formula, Fatigue, Low temperature, Mechanical behavior, Structural steels, Cyclic loading

Rights

CC BY-NC-ND 4.0

Abstract

It was found that the cyclic loading has a considerable effect on the mechanical behaviour of materials. This effect may lead to an early failure which results in human and economical losses. This study was developed to investigate changes in mechanical behaviour of structural steels. Two steels were considered and these are: G40.21 350WT which is used in ship hull structures and AISI 1022 HR which is used in general structural applications. The study was carried out in three parts: experimental, statistical, and numerical. The experimental tests were conducted using strain-controlled axial loading in room, zero, and sub-zero temperatures. In the statistical part, empirical formulae were derived to predict changes in mechanical properties as well as assessment of the experimental strain-life relationship. In the numerical part, a numerical model was developed to determine the strain-life relationship. The experimental results exhibited an increase in tensile, yield, and fracture strengths. However, reduction in ductility and toughness was observed. The strain-life plots showed higher fatigue life for AISI 1022 HR steel in the high strain region if compared with G40.21 350WT steel. However, the fatigue strain limit was similar in both steels. The fatigue life of G40.21 350WT steel increased significantly at zero and sub-zero temperatures. The numerical model is able to accurately determine the strain-life plot.

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