Session: 03-02-01 Fatigue Performance and Testing

Paper Number: 128187

128187 - An Engineering Approach for Capturing Flat-to-Shear Fracture Transition in High-Strength Pipeline Steel Under Quasi-Static and Dynamic Conditions 

Ductile fracture initiation and propagation in metallic materials are complex phenomena involving irreversible damage and the creation of fracture surfaces at the mesoscale. The mechanism that controls ductile failure is typically associated with the nucleation, growth, and coalescence of voids generated from second-phase particles and inclusions. Although this process commonly occurs at the mesoscale (microns), it has profound implications for the material's mechanical response at the macroscopic (global) level, especially in the post-localization response, which includes damage accumulation, crack initiation and growth, and fracture modes.

The primary objective of this study is to provide an efficient post-failure softening evolution rule for uncoupled damage models to simulate ductile fracture in metals more realistically to capture different fracture features. To achieve this goal, we first introduce a cubic unit cell containing a spherical void. The cell model is subjected to proportional loading and periodic boundary conditions to investigate the micromechanics of ductile failure, especially the post-localization behavior under varying stress states (stress triaxiality and Lode angle). The onset of void coalescence is defined as the point at which inhomogeneous yielding begins, and this is detected by monitoring the elastically unloaded zones. The effect of initial void volume fraction and strain hardening is also investigated. Subsequently, based on the analysis of the unit cell simulation, we incorporate the post-localization behavior into the Modified Mohr-Coulomb fracture model using a novel dual-surface method, which also accounts for the influence of stress state on the softening evolution. VUMAT user subroutines are coded for numerical simulations employing ABAQUS. Furthermore, we utilize several experimental results involving X70 and X65 Q&T steels including notched round bars, SENT specimens and drop weight tear tests (DWTT) to investigate the occurrence of flat-to-slant fracture. This enhancement not only preserves the model's ability to accurately predict strain-to-fracture but also enhances its capacity to capture various fracture modes, such as the 'cup-cone' pattern observed in round bar specimens and the slant fracture pattern seen in plain strain specimens.

Presenting Author: Marcelo Paredes Texas A&M University

Presenting Author Biography: Marcelo Paredes is an assistant professor in the Department of Ocean Engineering at Texas A&M University, Galveston campus. His research interests lie in the fields of solid and structural mechanics of ocean engineering structures including fracture and fatigue; material modeling and finite element analysis; material testing and specimen design; and monitoring and sensing technologies.

Authors:

Yuhao Li Texas A&M University
R. Vigneshwaran Texas A&M University
Amine A. Benzerga Texas A&M University
Marcelo Paredes Texas A&M University