Deformation and damage models of high strength steels for automotive applications

The objective of this thesis project is to determine, analyse, and implement the different estimating models commonly used in the automotive field to predict the material behaviour in the post-necking region. An additional objective of this project is to comprehend which are the principal damage models used to predict the fracture initiating point on the material, and how these models are implemented concretely. The automotive world is constantly evolving, not only in the technology sector, but also in the material sector. Particularly, the regulations shifted to an always more increased safety in vehicles components and, most importantly, in the passenger cabin. For this reason, improved Advanced High Strength Steels (AHSS), Dual Phase steels (DP), Quenching and Partitioning steels (QP) and others are emerging on the market. Being stronger and lighter, the modern steels allow to reach an improved passengers safety, while guaranteeing low pollutant emissions and low fuel consumption. Chapter 1 briefly analyse this current situation, putting in evidence the automotive world requests and the solutions adopted in vehicles. The chapter is principally focused on the structural part, and so different microstructures are described, together with the technological processes used to achieve them, in order to understand how the increased strength of these steels has been possible to obtain. Chapter 2 describes the plastic behaviour implemented for the analysis and fitting of the engineering curve, and necessary to build the true curve which will be used as input for FEM simulations, and the most known damage behaviour models used to study and predict the fracture process of the material under test. Chapter 3 is focused on the results obtained on all the steels used in this project.