The effect of the yield to tensile strength ratio on the stress field in stress/strain concentrations around holes in steel structures

The effect of the yield to tensile strength ratio on the stress field in stress/strain concentrations around holes in steel structures

Obers, Siemen (TU Delft Mechanical, Maritime and Materials Engineering)

Walters, C.L. (mentor)
Jiang, X. (graduation committee)
Wong, W.J. (graduation committee)
Overal, Jaap (mentor)
Romeijn, Eric (mentor)

Delft University of Technology

2021-07-30

The aim of this thesis is to determine the influence of the Y/T, yield to tensile strength, ratio on the stress fields of high strength steels. This is relevant to the offshore industry as regulations restrict the use of steels with a high yield to tensile strength ratio, which is a characteristic of high­-strength and
ultra high­-strength steels. Identifying the influence of these parameters on behavior could lead to a scientific underpinning and review of the rules. The focus of this thesis is on stress concentrations at circular cutouts under uniform tension. The local stress and strain was found, which could be used to
assess the risk of strain localization and fracture.
Analytical models of Stowell, Neuber and Irwin are used to establish new relationships between the Y/T ratio and the stress field. The analytical methods of Stowell and Neuber were able to account for strain hardening, while the Irwin analytical relationship only provides a elastic-­perfectly plastic solution. Besides the stress field, an analytical formulation for the local strain based on Stowell’s theory is also established.
Numerical simulations were carried out for S690, S960, and S1100 materials. The numerical material models are later used in the research to validate analytical approaches. Also, an infinite plate approach is applied to the specimens by scaling the ligaments of the specimens by a factor of 6.
A parametric study has been carried out to gain insights into the influence of the governing parameters in relation to local strain. The parameters studied are the Y/T, yield strength, strain hardening exponent, and strength coefficient. Each parameter is varied separately.
The main conclusions are that a high Y/T ratio causes a slight decrease in plastic stress concentration factor, resulting in a slight increase in local strain. The strain hardening exponent shows the same trend, but the changes are even less significant. The yield strength and strength coefficient have no effect on the stress concentration factor or local strain. None of the parameters show any influence on the extent of the plastic zone of the material.

SCF
Elasto-plastic
Strain
Stress
Y/T

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Student theses

master thesis

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