Ductile fracture of metallic materials through micromechanics based cohesive zone elements

Tandoğan, İzzet Tarık
Gaining popularity after its coupling with the finite element method, cohesive zone modelling has been used extensively to model fracture, especially in delamination problems. Its constitutive relations, i.e. traction-separation laws, are mostly derived phenomenologically without considering the physical mechanisms of crack initiation and propagation. The approach could also be used for ductile fracture where the micromechanics of the phenomenon is explained by nucleation, growth and coalescence of pores. In this context, the objective of the current thesis is to develop and implement a cohesive zone modelling framework for ductile fracture in metallic materials. In order to accomplish this, a micromechanics based traction-separation relation which considers the growth of a physical pore is developed based on the previous works in [1–3]. Tractions are directly represented as a function of pore fraction, and its evolution is driven by separations. The model is implemented as an intrinsic cohesive zone model in a two-dimensional (2D) setting. Implementation steps and methodology including the finite element framework are presented in detail for mode-I, mode-II and mixed-mode fracture cases. The derivation of the mixed-mode case leads to a yield function representation of tractions and separations, instead of an explicit expression. Hence, an incremental implicit elasto-plastic numerical integration scheme is developed to solve mixed-mode system of equations. Implementation is validated by running tests with a single cohesive element. In addition, the framework is implemented as a user element subroutine in Abaqus (UEL) and the numerical simulations are conducted with compact tension (CT) and single edge notch (SEN) specimens to show the capability of the model and the influence of the micromechanical parameters such as pore size and shape on the ductile crack initiation and propagation. The work is concluded by presenting an outlook for the usage of the model in micron sized specimens where the developed micromechanical model presents a great potential in explaining certain deformation mechanisms in high strength aerospace alloys.


Development of a Micromechanics Based Cohesive Zone Model and Application for Ductile Fracture
Yalçınkaya, Tuncay; Tandoğan, İzzet Tarık (2019-01-01)
In this paper, derivation and implementation of a micromechanically motivated traction separation law for cohesive zone modeling of ductile fracture is discussed. The formulation of the framework is based on the growth of pores in an array of representative volume elements where pores are idealized as cylinders. Two relations are derived under normal and shear loading for mode-I and mixed-mode respectively, based on the upper bound for a perfectly plastic material (Yalcinkaya and Cocks (2015), Yalcinkaya an...
Physics Based Formulation of a Cohesive Zone Model for Ductile Fracture
Yalçınkaya, Tuncay (2015-07-01)
This paper addresses a physics based derivation of mode-I and mode-II traction separation relations in the context of cohesive zone modeling of ductile fracture of metallic materials. The formulation is based on the growth of an array of pores idealized as cylinders which are considered as therepresentative volume elements. An upper bound solution is applied for the deformation of the representative volume element and different traction-separation relations are obtained through different assumptions.
3D Simulation of Dynamic Delamination in Curved Composite Laminates
Ata, Tamer Tahir; Çöker, Demirkan (Elsevier BV; 2019-01-01)
In this study, dynamic fracture of curved carbon fiber reinforced plastic (CFRP) laminates under quasi-static loading is investigated using explicit three dimensional (3D) finite element method in conjunction with Cohesive Zone Modelling (CZM). The simulations are based on the experimental studies conducted by Tasdemir (2018). Three dimensional finite element models of two different ply architectures (unidirectional and fabric laminate) are generated corresponding to the experimental configurations. The com...
Delamination Analysis of Tapered Composite Laminates using Cohesive Elements
Dashatan, Saeid; Parnas, Kemal Levend; Çöker, Demirkan; Poorzeinolabedin, Mohsen (null; 2018-12-01)
In this study, the initiation and propagation of delamination in tapered composite laminates are investigated using a finite element modelling with cohesive zone. The structural model with several drop-offs is assumed to be under tension. For this purpose, UD plies of 0-degree orientations are used for each sub-laminate. For a single step drop off, the results show that the delamination failure starts at the interface between ply drop-off and resin pocket. The next delamination generally starts either from ...
Formulation and Implementation of a New Porous Plasticity Model
Yalçınkaya, Tuncay; Erdoğan, Can; Tandoğan, İzzet Tarık (Elsevier BV; 2019-01-01)
A new rate independent porous plasticity model is proposed for the modeling of ductile damage initiation due to void growth in metallic materials. The model is based on a simple yield description which includes two porosity functions that affect both deviatoric and hydrostatic stress evolution. The current version of the model predicts damage solely due to void growth and it should be extended to include the void initiation and coalescence criteria. The numerical examples study the performance of the develo...
Citation Formats
İ. T. Tandoğan, “Ductile fracture of metallic materials through micromechanics based cohesive zone elements,” M.S. - Master of Science, Middle East Technical University, 2020.