The effect of serrated yielding on the determination of r-values in aluminium alloys and yield locus calibration

W Kilpatrick, D Brown, R McMurray, AG Leacock

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

This study investigates the effect serrated yielding (Portevin-Le Châtelier effect) has on the determination of the plastic strain ratio (r-value) for the 2024 aluminium alloy. The aluminium alloy specimens were initially in the fully annealed O-condition. The specimens experienced a softening mechanism through a solution heat treatment (SHT) process, followed by an oil quench. The specimens were permitted to recover for periods ranging between 0.5 and 12 h by room temperature (RT) natural ageing before undergoing a uniaxial tensile test along the longitudinal axis to determine the r-value as a function of natural ageing time. The current study reveals the irregular variation in the transverse strain affects the gradient of the longitudinal–transverse strain plot and consequently the r-value. It is demonstrated that the serrated yielding directly influences the Hill 1948 yield locus when calibrated using two r-values and one yield strength for the 2024 aluminium alloy. Serrated yielding results in an underestimation of the plane stress (rolling) of 0.5 ≤ plane stress rolling (MPa) ≤ 5.6, plane stress (transverse) of 1.0 ≤ plane stress transverse (MPa) ≤ 9.2, and biaxial stress of 1.4 ≤ biaxial stress (MPa) ≤ 7.4. It is also shown that serrated yielding occurs after a critical strain of 0.07 ≤ plastic strain ≤ 0.13 and is reduced by natural age hardening.
LanguageEnglish
Pages7557-7564
JournalMaterials Science and Engineering: A
Volume527
Issue number29-30
DOIs
Publication statusPublished - 2010

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plane stress
loci
aluminum alloys
Aluminum alloys
Calibration
plastics
Portevin-le Chatelier effect
precipitation hardening
Plastic deformation
yield strength
tensile tests
Aging of materials
softening
heat treatment
Age hardening
oils
plots
gradients
Yield stress
Oils

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Kilpatrick, W ; Brown, D ; McMurray, R ; Leacock, AG. / The effect of serrated yielding on the determination of r-values in aluminium alloys and yield locus calibration. 2010 ; Vol. 527, No. 29-30. pp. 7557-7564.
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The effect of serrated yielding on the determination of r-values in aluminium alloys and yield locus calibration. / Kilpatrick, W; Brown, D; McMurray, R; Leacock, AG.

Vol. 527, No. 29-30, 2010, p. 7557-7564.

Research output: Contribution to journalArticle

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AU - Brown, D

AU - McMurray, R

AU - Leacock, AG

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N2 - This study investigates the effect serrated yielding (Portevin-Le Châtelier effect) has on the determination of the plastic strain ratio (r-value) for the 2024 aluminium alloy. The aluminium alloy specimens were initially in the fully annealed O-condition. The specimens experienced a softening mechanism through a solution heat treatment (SHT) process, followed by an oil quench. The specimens were permitted to recover for periods ranging between 0.5 and 12 h by room temperature (RT) natural ageing before undergoing a uniaxial tensile test along the longitudinal axis to determine the r-value as a function of natural ageing time. The current study reveals the irregular variation in the transverse strain affects the gradient of the longitudinal–transverse strain plot and consequently the r-value. It is demonstrated that the serrated yielding directly influences the Hill 1948 yield locus when calibrated using two r-values and one yield strength for the 2024 aluminium alloy. Serrated yielding results in an underestimation of the plane stress (rolling) of 0.5 ≤ plane stress rolling (MPa) ≤ 5.6, plane stress (transverse) of 1.0 ≤ plane stress transverse (MPa) ≤ 9.2, and biaxial stress of 1.4 ≤ biaxial stress (MPa) ≤ 7.4. It is also shown that serrated yielding occurs after a critical strain of 0.07 ≤ plastic strain ≤ 0.13 and is reduced by natural age hardening.

AB - This study investigates the effect serrated yielding (Portevin-Le Châtelier effect) has on the determination of the plastic strain ratio (r-value) for the 2024 aluminium alloy. The aluminium alloy specimens were initially in the fully annealed O-condition. The specimens experienced a softening mechanism through a solution heat treatment (SHT) process, followed by an oil quench. The specimens were permitted to recover for periods ranging between 0.5 and 12 h by room temperature (RT) natural ageing before undergoing a uniaxial tensile test along the longitudinal axis to determine the r-value as a function of natural ageing time. The current study reveals the irregular variation in the transverse strain affects the gradient of the longitudinal–transverse strain plot and consequently the r-value. It is demonstrated that the serrated yielding directly influences the Hill 1948 yield locus when calibrated using two r-values and one yield strength for the 2024 aluminium alloy. Serrated yielding results in an underestimation of the plane stress (rolling) of 0.5 ≤ plane stress rolling (MPa) ≤ 5.6, plane stress (transverse) of 1.0 ≤ plane stress transverse (MPa) ≤ 9.2, and biaxial stress of 1.4 ≤ biaxial stress (MPa) ≤ 7.4. It is also shown that serrated yielding occurs after a critical strain of 0.07 ≤ plastic strain ≤ 0.13 and is reduced by natural age hardening.

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