Experimental study of the stress state and strain rate dependent mechanical behaviour of TRIP-assisted steels

A Pontillo,C Lonardi,S Chandran,P Verleysen,F Vercruysse,L Corallo

doi:10.1051/epjconf/202125005003

Abstract

This paper presents an investigation into the effect of different stress states and strain rates on the austenite-to-martensite transformation during plastic straining of a Q&P steel. Different stress states are imposed to the steel using purposed-designed samples. The sample geometries, including in-plane shear, dogbone and plane strain samples, are optimised by finite element modelling. Tensile tests are performed at different strain rates of 0.001 s-1, 10 s-1 and 500 s-1. Digital image correlation is used to capture the strain fields during the entire deformation process. The mechanical results indicate a positive strain rate sensitivity for both the shear and plane strain specimens and a negative strain rate sensitivity for the dogbone sample. In addition, the influence of the strain rate on the strain level is more pronounced for the shear than for the plane strain specimens and for the dogbone samples.

Highlights

The trends in advanced high strength steel (AHSS) development for the automotive industry are driven by ever more stringent rules for both safety, fuel consumption and CO2-emissions
This paper presents an investigation into the effect of different stress states and strain rates on the austenite-to-martensite transformation during plastic straining of a quenched and partitioned (Q&P) steel
Regarding the effect of the strain rate on the mechanical stability, it is known from literature [9] that,for Q&P steel, the stability increases with the strain rate at lower strain rate levels (1 s-1), the stability decreases with the strain rate

Summary

Introduction

The trends in advanced high strength steel (AHSS) development for the automotive industry are driven by ever more stringent rules for both safety, fuel consumption and CO2-emissions. The mechanical stability of RA is determined by material intrinsic parameters, such as chemical composition, grain size and morphology, though by loading conditions such as stress state, strain rate and deformation temperature [3],[4]. Present work aims to investigate the effect of strain rate and stress state, stress triaxiality, on the martensite formation and mechanical properties of third generation TRIP-assisted steels. For this purpose, static, intermediate and dynamic tensile tests are performed on a Q&P steel using three different sample geometries. In order to capture the highly heterogeneous strain fields during testing, static and high-speed camera recordings of a speckle pattern applied on the sample surfaces are processed by Digital Image Correlation (DIC)

Methods

Results

Discussion

Conclusion