# Effect of Strain Rate on the Formability Prediction of Cold-Rolled DX56D+Z100-M-C-O Steel Sheets

## TL;DR

This study examines how strain rate affects the formability of cold-rolled steel sheets used in deep drawing operations.

## Contribution

The novel contribution is the detailed analysis of formability changes in DX56D+Z100-M-C-O steel sheets across varying strain rates.

## Key findings

- Increasing strain rate improves strength but reduces plastic properties of the steel sheets.
- Formability, as measured by forming limit curves, decreases at higher strain rates.
- Safety margins in hemispherical punch stretching tests decrease with increased strain rate.

## Abstract

Formability testing is a fundamental method for determining sheet metal’s susceptibility to deep drawing operations. This article presents the results of formability analysis of several batches of 0.7 mm thick cold-rolled DX56D+Z100-M-C-O steel sheets. As part of the preliminary tests, mechanical properties of the tested steel sheets were determined. The ARAMIS digital image correlation system was used to determine the formability of sheet metal during the hemispherical punch stretching test. The stretching tests were conducted over a wide range of strain rate variations between 2 mm/min and 17 mm/min. A total of 540 individual geometry measurements were taken to analyze the test material’s formability. It was observed that with increasing strain rate, the strength properties increased, while the plastic properties decreased. From the perspective of formability, the margin of plasticity (the ratio of yield strength to tensile strength) deteriorated with increasing strain rate in tensile tests. Forming limit curves revealed that at higher strain rates, the metal sheet’s formability decreased. A reduction in the safety margins with an increasing hemispherical punch stretching test speed was also observed.