Ductile fracture under non-proportional loading with anisotropic hardening modelling

Researcher: Kang Wu

Aim:

This research aims to properly model the plastic behaviours and to predict ductile fracture under nonlinear non-proportional loading cases.

Background:

With the increasing demands for high fuel efficiency with good strength in automobile and aerospace industries, the lightweight materials including advanced high strength steels (AHSS), high performance aluminium and magnesium alloys are wildly introduced. AHSSs usually have multi-phases for the balance between the strength and ductility. These advanced metals fail without obvious necking compared with conventional “soft” materials. Due to an extensive use of ductile materials, fracture prediction through finite element analysis (FEA) incorporated in the constitutive models has become an important issue in the design and forming process, especially when these parts are subjected to extreme loading cases.

 

Methodology:

1. Considering the capability of homogeneous anisotropic hardening (HAH) model to capture both Bauschinger effect under reverse loading and overshooting effect under cross loading, it can be a potential constitutive model to predict mechanical responses subjected to non-proportional loading.
2. To conduct the non-proportional loading, two-step uniaxial tension tests were conducted. Sheet metals were pre-strained by uniaxial tension on oversize specimens, then subsize uniaxial tension specimens were cut from the oversize specimens.
3. A modified integration method was proposed to consider both pre-strain level effect and anisotropic hardening behaviours on ductile fracture during non-proportional loading.

Key Findings to date:

Figure 1

Figure 1 directly shows that for sheet metals, the ductility may increase with prestrain levels.

Figure 2

The above figure shows both Bauschinger effect and overshooting effect may increase the remaining ductility.

 

Future Work:

• Verify proposed fracture model under other bilinear loading cases
• Simulate two-step loading cases on ABAQUS.

 

Contact:

Kang Wu

Institute for Frontier Materials (IFM)

Deakin University, Geelong

Email: [email protected]