Title

METHOD FOR ASSESSING TRUE STRESS-STRAIN CURVES AFTER NECKING USING CYLINDRICAL TENSILE SPECIMENS: THEORETICAL BACKGROUND AND EXPERIMENTS

METHOD FOR ASSESSING TRUE STRESS-STRAIN CURVES AFTER NECKING USING CYLINDRICAL TENSILE SPECIMENS: THEORETICAL BACKGROUND AND EXPERIMENTS

Authorship

Ganharul, Grace Kelly Quarteiro; Donato, Gustavo Henrique Bolognesi

Ganharul, Grace Kelly Quarteiro

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Donato, Gustavo Henrique Bolognesi

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DOI

10.5151/2594-5327-23087

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Abstract

Simulations including severe plasticity have undergone significant expansion during the last years (e.g. fracture mechanics FE models including ductile tearing), which demand accurate true stress-strain data until fracture. However, the occurrence of plastic instability (necking) on tensile specimens complicates the direct assessment of σ-ε curves due to the imposition of a complex triaxial stress state. Previous results published by current authors demonstrated that even the widespread Bridgman’s correction presents limitations, which motivated the proposal of a new model to describe the geometrical evolution of necking (in which the geometrical dimensionless parameter a/R is proportional to strain ε). In this context, this work presents two contributions: i) first, experiments regarding the geometrical evolution of necking were largely extended incorporating 10 materials to corroborate the validity of the proposed model (including Carbon and stainless steels, and copper); ii) second, for the same materials, the necking region was investigated in more details to verify to which extent an osculating circle well describes the high deformation region; iii) finally, an adapted Bridgman’s model was proposed, followed by recommended practices for tensile testing. The results provide further support to σ-ε assessment until final fracture considering severe plasticity and demanding less physical measurements.

Simulations including severe plasticity have undergone significant expansion during the last years (e.g. fracture mechanics FE models including ductile tearing), which demand accurate true stress-strain data until fracture. However, the occurrence of plastic instability (necking) on tensile specimens complicates the direct assessment of σ-ε curves due to the imposition of a complex triaxial stress state. Previous results published by current authors demonstrated that even the widespread Bridgman’s correction presents limitations, which motivated the proposal of a new model to describe the geometrical evolution of necking (in which the geometrical dimensionless parameter a/R is proportional to strain ε). In this context, this work presents two contributions: i) first, experiments regarding the geometrical evolution of necking were largely extended incorporating 10 materials to corroborate the validity of the proposed model (including Carbon and stainless steels, and copper); ii) second, for the same materials, the necking region was investigated in more details to verify to which extent an osculating circle well describes the high deformation region; iii) finally, an adapted Bridgman’s model was proposed, followed by recommended practices for tensile testing. The results provide further support to σ-ε assessment until final fracture considering severe plasticity and demanding less physical measurements.

Keywords

Plastic instability; Bridgman correction; Tensile test; True stress-strain data.

Plastic instability; Bridgman correction; Tensile test; True stress-strain data.