Date of Award

Winter 2024

Project Type

Thesis

Program or Major

Mechanical Engineering

Degree Name

Master of Science

First Advisor

Jinjin Ha

Second Advisor

Mrityunjay Kothari

Third Advisor

Brad Kinsey

Abstract

In the field of sheet metal forming, it is important to accurately model the plastic stress-strain behavior of materials for use in simulations. Various tests are performed to characterize the plastic behavior, such as plastic anisotropy and strain hardening, which is used to identify material parameters of constitutive models. Shear testing in particular is an area of increasing interest in metal forming applications due to significantly larger strain level compared to uniaxial tension. This thesis aims to design a torsional in-plane shear testing fixture, to characterize the strain hardening and plastic anisotropy in shear for DDQ and DP980 steel sheets, and to model the hardening law and yield function using the experiment results. A custom testing fixture and two types of disc-shaped specimens are designed to facilitate stress and strain measurements. A grooved specimen to concentrate stress is used in monotonic and cyclic testing. The monotonic testing produces stress-strain curves to 2.5 times greater strains than possible in uniaxial tension testing for DP980, and at least 8 times greater for DDQ. Cyclic testing enables the characterization of anisotropic hardening behaviors, including the Bauschinger effect, transient behavior, hardening rate stagnation, and permanent softening, at high strains. A specimen with bridges in a direction of interest is used to characterize the shear anisotropy at various orientations with respect to the rolling direction. The experimental data of shear anisotropy is used to model the non-quadratic anisotropic yield function, Yld2004-18p, along with data from uniaxial and biaxial tension. Validations are performed for DDQ by drawing a cup from a circular blank and comparing the earring profile with a simulation. Results show minimal differences between yield functions with and without shear anisotropy in this application but demonstrate how the addition of shear stress state data could improve results.

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