Micro-mechanical modelling of interlaminar crack propagation

Research output: Other contribution

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Abstract

Composite materials are replacing standard engineering metals and alloys for many applications. Fiber-reinforced polymers, for their inherent ability to be custom tailored for any application, are a very viable material option. Their superior specific strength, stiffness and thermal characteristics have made them very competitive in the aerospace industry. While properties in the plane of the fibrous reinforcements are strong, stiff, and tailorable, the interlaminar region is relatively weak and compliant, leading to failure due to delamination and other damage modes, thus being the interlaminar fracture toughness the primary limitation of fiber reinforced composites. Delamination failures are common due to the nature of composite construction. A variety of manufacturing techniques are available to make composites. Generally, all these methods employ a layered stacking of fiber-reinforced polymers in a primary plane. The interface between these layers is typically not reinforced with fibers and is the source of delamination or interlaminar fracture. Porosity and other manufacturing related defects also introduce nucleation sites for delamination. This thesis aims to increase the understanding of the interlaminar failure of uni- and multi-directional composites in single- and mixed-mode delamination. To achieve this goal several models with increasing complexity have been developed and implemented. A three-dimensional computational micro -mechanics framework, with a special focus on the elastic-plastic and damage constitutive behaviors of the matrix and on the response of the fiber-matrix interface, is used in the present analysis.Since the objective is to model interlaminar fracture mechanisms, the fibrous reinforcements are assumed to be linear-elastic and a thermo-visco-plastic model is implemented to simulate the mechanical behavior of the matrix, based on experimental evidence. Failure of the matrix is modeled using a damage evolution law developed in the framework of thermodynamics of admissible processes.Representative volume elements (RVEs) with random fiber distributions were created by an algorithm developed to study the sequence of mechanisms leading to interlaminar failure in composite materials and to validate the implemented models. These RVEs are representative of the reinforcements and of the matrix at the micro-scale of the composite, capable of modeling laminates with different stacking orientations. This model was combined with homogenized meso-scale parts, forming a hybrid model that represents different experimental tests, such as the double cantilever beam, end notched flexure and mixed mode bending.The models were implemented in a commercial finite element software. In order to validate the models, an Explicit analysis was performed to observe the propagation of damage along the matrix in the RVE.


Supervisors:

Nuno Correia
Antonio Torres Marques
Original languageEnglish
TypeMasters Thesis from University of Porto
Publication statusPublished - 18 Jul 2016
Externally publishedYes

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Crack propagation
Delamination
Composite materials
Fibers
Reinforcement
Plastics
Micromechanics
Aerospace industry
Supervisory personnel
Cantilever beams
Polymers
Laminates
Fracture toughness
Nucleation
Porosity
Stiffness
Thermodynamics
Defects
Metals

Cite this

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title = "Micro-mechanical modelling of interlaminar crack propagation",
abstract = "Composite materials are replacing standard engineering metals and alloys for many applications. Fiber-reinforced polymers, for their inherent ability to be custom tailored for any application, are a very viable material option. Their superior specific strength, stiffness and thermal characteristics have made them very competitive in the aerospace industry. While properties in the plane of the fibrous reinforcements are strong, stiff, and tailorable, the interlaminar region is relatively weak and compliant, leading to failure due to delamination and other damage modes, thus being the interlaminar fracture toughness the primary limitation of fiber reinforced composites. Delamination failures are common due to the nature of composite construction. A variety of manufacturing techniques are available to make composites. Generally, all these methods employ a layered stacking of fiber-reinforced polymers in a primary plane. The interface between these layers is typically not reinforced with fibers and is the source of delamination or interlaminar fracture. Porosity and other manufacturing related defects also introduce nucleation sites for delamination. This thesis aims to increase the understanding of the interlaminar failure of uni- and multi-directional composites in single- and mixed-mode delamination. To achieve this goal several models with increasing complexity have been developed and implemented. A three-dimensional computational micro -mechanics framework, with a special focus on the elastic-plastic and damage constitutive behaviors of the matrix and on the response of the fiber-matrix interface, is used in the present analysis.Since the objective is to model interlaminar fracture mechanisms, the fibrous reinforcements are assumed to be linear-elastic and a thermo-visco-plastic model is implemented to simulate the mechanical behavior of the matrix, based on experimental evidence. Failure of the matrix is modeled using a damage evolution law developed in the framework of thermodynamics of admissible processes.Representative volume elements (RVEs) with random fiber distributions were created by an algorithm developed to study the sequence of mechanisms leading to interlaminar failure in composite materials and to validate the implemented models. These RVEs are representative of the reinforcements and of the matrix at the micro-scale of the composite, capable of modeling laminates with different stacking orientations. This model was combined with homogenized meso-scale parts, forming a hybrid model that represents different experimental tests, such as the double cantilever beam, end notched flexure and mixed mode bending.The models were implemented in a commercial finite element software. In order to validate the models, an Explicit analysis was performed to observe the propagation of damage along the matrix in the RVE.Supervisors:Nuno CorreiaAntonio Torres Marques",
author = "Luis Varandas",
year = "2016",
month = "7",
day = "18",
language = "English",
type = "Other",

}

Micro-mechanical modelling of interlaminar crack propagation. / Varandas, Luis.

2016, Masters Thesis from University of Porto.

Research output: Other contribution

TY - GEN

T1 - Micro-mechanical modelling of interlaminar crack propagation

AU - Varandas, Luis

PY - 2016/7/18

Y1 - 2016/7/18

N2 - Composite materials are replacing standard engineering metals and alloys for many applications. Fiber-reinforced polymers, for their inherent ability to be custom tailored for any application, are a very viable material option. Their superior specific strength, stiffness and thermal characteristics have made them very competitive in the aerospace industry. While properties in the plane of the fibrous reinforcements are strong, stiff, and tailorable, the interlaminar region is relatively weak and compliant, leading to failure due to delamination and other damage modes, thus being the interlaminar fracture toughness the primary limitation of fiber reinforced composites. Delamination failures are common due to the nature of composite construction. A variety of manufacturing techniques are available to make composites. Generally, all these methods employ a layered stacking of fiber-reinforced polymers in a primary plane. The interface between these layers is typically not reinforced with fibers and is the source of delamination or interlaminar fracture. Porosity and other manufacturing related defects also introduce nucleation sites for delamination. This thesis aims to increase the understanding of the interlaminar failure of uni- and multi-directional composites in single- and mixed-mode delamination. To achieve this goal several models with increasing complexity have been developed and implemented. A three-dimensional computational micro -mechanics framework, with a special focus on the elastic-plastic and damage constitutive behaviors of the matrix and on the response of the fiber-matrix interface, is used in the present analysis.Since the objective is to model interlaminar fracture mechanisms, the fibrous reinforcements are assumed to be linear-elastic and a thermo-visco-plastic model is implemented to simulate the mechanical behavior of the matrix, based on experimental evidence. Failure of the matrix is modeled using a damage evolution law developed in the framework of thermodynamics of admissible processes.Representative volume elements (RVEs) with random fiber distributions were created by an algorithm developed to study the sequence of mechanisms leading to interlaminar failure in composite materials and to validate the implemented models. These RVEs are representative of the reinforcements and of the matrix at the micro-scale of the composite, capable of modeling laminates with different stacking orientations. This model was combined with homogenized meso-scale parts, forming a hybrid model that represents different experimental tests, such as the double cantilever beam, end notched flexure and mixed mode bending.The models were implemented in a commercial finite element software. In order to validate the models, an Explicit analysis was performed to observe the propagation of damage along the matrix in the RVE.Supervisors:Nuno CorreiaAntonio Torres Marques

AB - Composite materials are replacing standard engineering metals and alloys for many applications. Fiber-reinforced polymers, for their inherent ability to be custom tailored for any application, are a very viable material option. Their superior specific strength, stiffness and thermal characteristics have made them very competitive in the aerospace industry. While properties in the plane of the fibrous reinforcements are strong, stiff, and tailorable, the interlaminar region is relatively weak and compliant, leading to failure due to delamination and other damage modes, thus being the interlaminar fracture toughness the primary limitation of fiber reinforced composites. Delamination failures are common due to the nature of composite construction. A variety of manufacturing techniques are available to make composites. Generally, all these methods employ a layered stacking of fiber-reinforced polymers in a primary plane. The interface between these layers is typically not reinforced with fibers and is the source of delamination or interlaminar fracture. Porosity and other manufacturing related defects also introduce nucleation sites for delamination. This thesis aims to increase the understanding of the interlaminar failure of uni- and multi-directional composites in single- and mixed-mode delamination. To achieve this goal several models with increasing complexity have been developed and implemented. A three-dimensional computational micro -mechanics framework, with a special focus on the elastic-plastic and damage constitutive behaviors of the matrix and on the response of the fiber-matrix interface, is used in the present analysis.Since the objective is to model interlaminar fracture mechanisms, the fibrous reinforcements are assumed to be linear-elastic and a thermo-visco-plastic model is implemented to simulate the mechanical behavior of the matrix, based on experimental evidence. Failure of the matrix is modeled using a damage evolution law developed in the framework of thermodynamics of admissible processes.Representative volume elements (RVEs) with random fiber distributions were created by an algorithm developed to study the sequence of mechanisms leading to interlaminar failure in composite materials and to validate the implemented models. These RVEs are representative of the reinforcements and of the matrix at the micro-scale of the composite, capable of modeling laminates with different stacking orientations. This model was combined with homogenized meso-scale parts, forming a hybrid model that represents different experimental tests, such as the double cantilever beam, end notched flexure and mixed mode bending.The models were implemented in a commercial finite element software. In order to validate the models, an Explicit analysis was performed to observe the propagation of damage along the matrix in the RVE.Supervisors:Nuno CorreiaAntonio Torres Marques

M3 - Other contribution

ER -