TY - THES

T1 - Numerical Simulation of Crack Propagation during the Deformation of Galvanized PHS Sheets

AU - Hammer, Philipp Jörg

N1 - embargoed until null

PY - 2020

Y1 - 2020

N2 - In the automotive industry, the development of advanced steels and production techniques is driven by the desire to produce ever lighter parts while still maintaining good crashworthiness. In order to produce lightweight steel parts, their strength has to be enhanced. For the common steels used in cold forming processes, large forming forces and springback set an upper limit. The direct press-hardening process combines the forming in hot condition with a subsequent hardening step, therefore lowering forming forces and springback while still enhancing the material strength. However, for reasons of corrosion prevention, the formed blanks are usually already zinc-coated and entail the risk of cracking during deformation. Hence, this thesis aims to develop a numerical model for the investigation of crack propagation during press-hardening. A theoretical description on the production process of press-hardened car parts is followed by a specification on the used alloy and zinc-layer modifications. The theoretical chapter is closed by a summary of crack modelling techniques within the finite element program ABAQUS. Through implementation of different crack growth modelling techniques into a three point bending test model, the best approach is determined and later used to describe crack growth in a pre-existing press-hardening simulation by using the submodel technique. Finally, different positions in the press-hardening model are addressed and compared regarding their cracking behaviour, and the findings of the model development process are evaluated.

AB - In the automotive industry, the development of advanced steels and production techniques is driven by the desire to produce ever lighter parts while still maintaining good crashworthiness. In order to produce lightweight steel parts, their strength has to be enhanced. For the common steels used in cold forming processes, large forming forces and springback set an upper limit. The direct press-hardening process combines the forming in hot condition with a subsequent hardening step, therefore lowering forming forces and springback while still enhancing the material strength. However, for reasons of corrosion prevention, the formed blanks are usually already zinc-coated and entail the risk of cracking during deformation. Hence, this thesis aims to develop a numerical model for the investigation of crack propagation during press-hardening. A theoretical description on the production process of press-hardened car parts is followed by a specification on the used alloy and zinc-layer modifications. The theoretical chapter is closed by a summary of crack modelling techniques within the finite element program ABAQUS. Through implementation of different crack growth modelling techniques into a three point bending test model, the best approach is determined and later used to describe crack growth in a pre-existing press-hardening simulation by using the submodel technique. Finally, different positions in the press-hardening model are addressed and compared regarding their cracking behaviour, and the findings of the model development process are evaluated.

KW - Risswachstum

KW - Presshärten

KW - Simulation

KW - crack-growth

KW - press-hardening

KW - simulation

M3 - Master's Thesis

ER -