Abstract

At certain temperatures, strain rates and slender geometries, low carbon steels, as well as some aluminum, magnesium and nickel-based alloys, exhibit plastic flow instability at the onset of their respective yield points, known as the Lüders phenomena. Such phenomenon is recognized by a distinct yield point and subsequent plateau on the stress-strain curve. This thesis aims to investigate the effect of the sample’s thickness on the Lüders phenomena in AISI 1524 hot-rolled steel alloy. Sixteen samples were machined from hot-rolled plates and uniaxial testing in conjunction with digital image correlation were performed to gain insight and quantify the Lüders band’s characteristics during the extent of the plateau. The thicknesses investigated were 1 mm, 2 mm, 3 mm, and 4 mm, all of which tested under identical conditions, most notably strain rate, in order to isolate and understand the effect of material’s thickness on the Lüders phenomena. Results revealed that an increase in specimen thickness resulted in an increase in Lüders band width as well as an increase in Lüders band velocity in 1524 steel alloy. Results also showed that a dual band formation took place in all samples regardless of thickness. Moreover, the angle at which the Lüders band appeared on the front surface of the specimen increased with increasing structure thickness. The obtained results and observations suggested a 3D nature of the band’s formation in AISI 1524; whereby nucleation takes place at the core of the material before propagating in the thickness direction towards the structure’s surface. Moreover, it was concluded that the Lüders band initiated ahead of the upper yield stress point.

Library of Congress Subject Headings

Steel alloys; Thickness measurement; Strains and stresses; Lüders bands

Publication Date

10-2022

Document Type

Thesis

Student Type

Graduate

Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)

Advisor

Wael A. Samad

Campus

RIT Dubai

Plan Codes

MECE-MS

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