Workability Limit Diagram at Plane Stress Condition

Abstract

Numerous experimental studies of workability limit diagrams in the domain of bulk deformation have been performed on specimens where failure occurs at the free surface, i.e., under plane stress conditions. Previous investigations of workability diagrams using compression tests on axially symmetric specimens have yielded negative values of the stress triaxiality ratio (β < –1), while positive values have predominantly been obtained from tensile tests, often exceeding β > +3.

The objective of the present study is to explore the applicability of additional deformation models under plane stress conditions that could extend the workability diagram into regions corresponding to negative stress triaxiality ratio values. Additionally, the study aims to determine the limiting values of the stress triaxiality ratio under such stress conditions. For cold bulk forming processes, the region of the workability diagram associated with negative stress triaxiality ratio values (β < –1) is of particular technological importance.

The analysis of various formability tests under plane stress conditions was conducted using idealized deformation models, in which the deformation path was assumed to be linear.