A contribution to the study of crack initiation in metal plates

Details

Supervisors

Pardoen, Thomas

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

The fracture toughness of a material is a critical factor in the material selection process to ensure safe and reliable designs. This Master’s thesis aims to explore two key aspects of fracture toughness: the influence of strain hardening and the impact of material thickness. Specifically, the study focuses on plane strain and plane stress conditions. To achieve these objectives, 2D finite element simulations under plane strain conditions and 3D finite element simulations under plane stress conditions were conducted using SSY conditions and the J integral approach. The numerical investigations were complemented by an experimental study on Crack Tip Opening Displacement (CTOD) of Al2050 T8 samples with thicknesses of 1mm and 10mm. For the 2D simulations, the effect of the hardening exponent, as described by the Swift strain hardening law, on the stress and strain fields ahead of the crack tip and on CTOD was thoroughly examined. Additionally, the behavior at the crak tip was analyzed using the Kocks-Mecking strain hardening law to gain a more physical understanding of how strain hardening influences fracture properties. In the 3D simulations, the evolution of stress and strain fields through the material’s thickness was investigated. The comparison between the 2D and 3D finite element simulations provided insights into the fracture toughness of the modeled material under plane strain and plane stress conditions, respectively. The experimental CTOD tests served to validate the findings from the simulations, confirming the differences in CTOD and critical J values between near plane stress and plane strain conditions. Additionally, fractography of the fractured samples offered a micro-mechanical perspective on the mechanisms of ductile fracture, enriching the overall understanding of the material’s behavior. The project’s key findings are that higher Swift’s law strain hardening exponents lead to increased stress triaxiality but enhance fracture toughness by reducing plastic strain. The Kocks-Mecking hardening law, with lower dynamic recovery rates and higher dislocation storage, similarly improves fracture toughness. The analysis also revealed that fracture toughness is greater under 3D plane stress conditions than plane strain, a result confirmed by CTOD experiments and experimental JIc values.

Citations

• APA

Javangorouh, S. (2024). A contribution to the study of crack initiation in metal plates. https://dial-mem.test.bib.ucl.ac.be/handle/2078.2/40403