In-Situ Observation of Lüders Band Formation in Hot-Rolled Steel via Digital Image Correlation

Hai Qiu,Tadanobu Inoue,Rintaro Ueji

doi:10.3390/met10040530

Abstract

Although the Lüders yield phenomenon has been investigated for more than 150 years, some understanding of Lüders band formation lack substantial support from experimental evidence. In-situ observation of Lüders band formation in hot-rolled steel experimentally clarified the following facts: (i) When stress reaches the true upper yield stress, the Lüders band begins to nucleate. True upper yield stress is greater than nominal upper yield stress. (ii) Gross stress concentration promotes the Lüders band formation, and the size of the gross stress concentration region determines the initial width of the Lüders band. (iii) The Lüders band nucleates far ahead of the gross yield point.

Highlights

The transition from elastic to plastic deformation in low carbon steels and mild steel is characterized by a material instability known as the Lüders deformation phenomenon whose macroscopic deformation is inhomogeneous
Because the initiation site of Lüders band was beyond the observed area, two tests failed to capture the initiation of Lüders band
We briefly summarize previous studies on Lüders band formation as follows

Summary

Introduction

The transition from elastic to plastic deformation in low carbon steels and mild steel is characterized by a material instability known as the Lüders deformation phenomenon whose macroscopic deformation is inhomogeneous. In a uniaxial tension test, this instability shows a typical stress-strain curve as illustrated in Figure 1 (black line). It is usually recognized that localized plastic deformation in the form of a band, denoted as a Lüders band, starts with a sudden stress drop. The Lüders band propagates through the whole gauge length of the specimen, while the global stress remains essentially constant. The stress plateau in the stress-strain curve reflects the propagation process. The initial stress peak and the level of the stress plateau are, respectively, the upper yield stress (σup.ys.ob ) and lower yield stress (σL.ys.ob )

Methods

Results

Conclusion