A Diffusive crack model for fiber reinforced polymer composites

Download
2020
Aksu Denli, Funda
Recently, classical fracture mechanics approaches based on Griffith type sharp crack topologies have left the stage to diffusive crack approaches or the so called phase field models. Crack initiation and propagation is based on the variational principles for energy minimization leading to symmetric set of algebraic equations. In this thesis, which is the first attempt to model failure of engineered composites using an anisotropic crack phase–field approach, Fiber Reinforced Polymer (FRP) specific anisotropic phase field model is developed in the light of the previous studies on isotropic brittle materials and anisotropic materials like biological tissues. It started with the continuous formulation of the variational principle for the multi-field problem manifested through the deformation map and the crack phase-field at finite strains which leads to the Euler–Lagrange equations of the coupled problem. In particular, the coupled balance equations derived render the evolution of the anisotropic crack phase-field and the balance of linear momentum. In addition, a novel energy-based anisotropic failure criterion is proposed which regulates the evolution of the crack phase-field. Distinct failure processes for the ground matrix and the fibers are modelled by additively decomposing the energetic force, driving force for the damage, into isotropic and anisotropic parts. Distinct fracture energies were introduced for isotropic and anisotropic parts and anisotropic damage field interpretation is used for the dispersed damage field. In addition, an anisotropic geometric resistance expression has been added to the theory, which regulates the crack length scale distribution in different directions, to ensure that geometric constraints are taken into account in the direction of crack propagation. The coupled problem is solved using a one-pass operator-splitting algorithm composed of a mechanical predictor step that updates the displacement field and a crack evolution step that updates the damage field. Representative numerical examples are devised for crack initiation and propagation in Carbon-Fiber-Reinforced Polymeric (CFRP) composites. Model parameters are obtained by fitting the set of experimental data reported in the literature to the predicted model response; the finite element results capture the effect of anisotropy in stiffness and strength both qualitatively and quantitatively. The proposed approach and its algorithmic implementation validated by Mixed Mode Bending (MMB) test results of APC2-prepreg unidirectional (UD) laminate. The success of the model in capturing different modes of failure and the ability to simulate interface effects have been demonstrated for double fix–end supported CFRP composite beam subjected to transverse load.

Suggestions

A computer simulation of void dynamics under the action of electromigration and capillary forces in narrow thin interconnects
Ogurtani, TO; Oren, EE (2000-10-25)
In these studies a comprehensive picture of void dynamics in connection with the critical morphological evaluation has been thoroughly anticipated in order to understand main reasons as well as the conditions under which premature failure of metallic thin interconnects occur. Our mathematical model on diffusion and mass accumulation on void surfaces, under the action of applied electrostatic potential and capillary effects, follows a novel irreversible but discrete thermodynamic formulation of interphases a...
A PHASE FIELD APPROACH TO MODEL FRACTURE OF ARTERIAL WALLS
GÜLTEKİN, Osman; Dal, Hüsnü; HOLZAPFEL, Gerhard A (2016-06-10)
This study uses a recently developed phase-field approach to model fracture of arterial walls with an emphasis on aortic tissues. We start by deriving the regularized crack surface to overcome complexities inherent in sharp crack discontinuities, thereby relaxing the acute crack surface topology into a diffusive one. In fact, the regularized crack surface possesses the property of Gamma-Convergence, i.e. the sharp crack topology is restored with a vanishing length-scale parameter. Next, we deal with the con...
A finite elements based approach for fracture analysis of welded joints in construction machinery
Karagöz, Taner; Dağ, Serkan; Department of Mechanical Engineering (2007)
This study aims to develop a computer program to perform finite elements based fracture mechanics analyses of three dimensional surface cracks in T-welded joints of construction machinery. The geometrical complexity of the finite elements models and the requirement of large computer resources for the analyses necessitate the use of shell elements for general stress distribution optimization. A sub-modeling technique, together with a shell to solid conversion method, enables the user to model a local region ...
A Numerical Approach to Simulating Oxidation in Thermal Barrier Coatings
Saeidi, Farid; Gürses, Ercan; Aslan, Özgür (Elsevier, Elsevier, 2020-01-01)
Computational analysis and simulation of multi-physics phenomena taking place in coating systems is still a challenging task. Specifically, for ceramic coatings used as a system of protection for base materials against elevated temperatures, known as thermal barrier coating (TBC) systems, construction of continuum level models which can express coupled nonlinear phenomena has attracted great attention. Thermal stresses, oxidation, creep and numerous other mechanisms and phenomena makes it even harder to mod...
A drift capacity prediction model for retrofitted reinforced concrete columns
ÖZCAN, OKAN; Binici, Barış (2022-03-01)
Seismic assessment of reinforced concrete (RC) buildings heavily relies on the deformation capacity predictions of members. Similarly, the prediction of the deformation capacity of retrofitted RC columns has the utmost importance for seismic retrofit design. In this paper, a new unified drift model is proposed in order to estimate the rotation capacity of RC columns retrofitted with concrete jacketing, steel jacketing and fibre-reinforced polymer (FRP) wrapping. In order to generate the model, an extensive ...
Citation Formats
F. Aksu Denli, “A Diffusive crack model for fiber reinforced polymer composites,” Thesis (Ph.D.) -- Graduate School of Natural and Applied Sciences. Mechanical Engineering., Middle East Technical University, 2020.